CN111801557B - Evaluation apparatus of tempered glass, evaluation method of tempered glass, manufacturing method of tempered glass, and tempered glass - Google Patents

Abstract

The evaluation apparatus for this tempered glass includes: a polarization retardation variable member that changes the polarization retardation of laser light by one wavelength or more with respect to the wavelength of the laser light; and an imaging element that captures scattered light a plurality of times at predetermined time intervals to obtain a plurality of images, wherein the scattered light is scattered light emitted when the laser light whose polarization phase difference is changed is incident on the tempered glass; and a calculation unit that measures the periodicity of the scattered light using the plurality of images The brightness change of the glass is calculated, the phase change of the brightness change is calculated, the stress distribution in the depth direction from the surface of the tempered glass is calculated based on the phase change, and the plurality of images are used to measure the relationship between the tempered glass and the tempered glass. strength-related physical quantity.

Description

Apparatus for evaluating tempered glass, method for producing tempered glass, and tempered glass

Technical Field

The present invention relates to a device for evaluating a tempered glass, a method for producing a tempered glass, and a tempered glass.

Background

In electronic devices such as mobile phones and smart phones, glass is often used for a display portion and a housing main body. With the recent reduction in thickness and weight of electronic devices, there is a demand for reduction in thickness of glass used for electronic devices. When the thickness of the glass is reduced, the strength is lowered. Therefore, in order to improve the strength of glass, it is common to use so-called chemically strengthened glass having improved strength by forming a surface layer (ion exchange layer) by ion exchange on the glass surface, measure the stress value of the surface by an optical method, confirm whether or not the glass is correctly strengthened, and deliver the glass to the market.

As a technique for measuring the stress of the surface layer of the tempered glass, for example, a technique for nondestructively measuring the compressive stress of the surface layer by utilizing the optical waveguide effect and the photoelastic effect when the refractive index of the surface layer of the tempered glass is higher than the refractive index of the inside (hereinafter, referred to as a nondestructive measurement technique) can be cited. In this nondestructive measurement technique, monochromatic light is made incident on the surface layer of the tempered glass to generate a plurality of modes by the optical waveguide effect, and light determined by the ray trajectory in each mode is extracted and imaged as a bright line corresponding to each mode by a convex lens. Note that the number of bright line presence patterns to be imaged is.

In this nondestructive measurement technique, light extracted from the surface layer is observed as bright lines of two light components, i.e., horizontal and vertical, in the light vibration direction with respect to the emission surface. Further, the refractive index of each light component is calculated from the position of the bright line corresponding to mode 1 of the two light components by utilizing the property that the light of mode 1 having the lowest order passes through the surface layer on the side closest to the surface, and the stress in the vicinity of the surface of the tempered glass is obtained from the difference between the two refractive indices and the photoelastic constant of the glass (for example, see patent document 1).

On the other hand, based on the principle of the nondestructive measurement technique described above, a method has been proposed in which the stress (hereinafter referred to as a surface stress value) of the outermost surface of the glass is obtained by extrapolation from the positions of the bright lines corresponding to the modes 1 and 2, and the depth of the compressive stress layer is obtained from the total number of bright lines on the assumption that the refractive index distribution of the surface layer changes linearly (see, for example, patent document 3 and non-patent document 1).

Further, a method has been proposed in which the tensile stress CT inside the glass is defined based on the surface stress value and the depth of the compressive stress layer measured by the above-described surface waveguide light measurement technique, and the strength of the tempered glass is controlled by the CT value (see, for example, patent document 2). In this method, the tensile stress CT is calculated using "CT ═ CS × DOL)/(t × 1000-2 × DOL) (expression 0). Here, CS is a surface stress value (MPa), DOL is a depth (unit: μm) of the compressive stress layer, and t is a sheet thickness (unit: mm).

Generally, if no external force is applied, the sum of the stresses is 0. Therefore, the tensile stress is generated substantially uniformly so that the value obtained by integrating the stress formed by the chemical strengthening in the depth direction is balanced in the central portion that is not chemically strengthened.

Further, a method has been proposed in which the stress distribution on the glass surface layer side from the glass depth (DOL _ TP) at the position where the stress distribution is bent is measured, and the stress distribution on the glass depth side from DOL _ TP is predicted based on the measurement result (measurement image) of the stress distribution on the glass surface layer side (for example, see patent document 4). However, this method has a problem that measurement reproducibility is poor because the stress distribution on the deep glass layer side of DOL _ TP is not measured.

However, chemically strengthened glass is also diversified due to the improvement in strength and performance, and conventional stress measurement methods cannot be sufficiently evaluated.

For example, there are tempered glass in which a stress distribution is controlled by ion-exchanging lithium-containing glass with two types of ions, i.e., potassium and sodium, and chemically tempered glass in which ion-exchanging is performed with transparent crystallized glass.

In the case of a conventional optical surface stress measuring device for chemically strengthened glass containing lithium glass, although the stress layer in the vicinity of the surface in which lithium is replaced with potassium can be evaluated, the stress layer in the interior in which lithium is replaced with sodium cannot be evaluated, and therefore the stress depth cannot be measured.

Among crystallized glasses, it is necessary to be transparent in order to be used particularly in a display portion, and therefore crystallized glass used here is crystallized glass having crystal grains much smaller than the wavelength of visible light, and is transparent in the visible region. Therefore, the stress of the surface formed by the chemical strengthening step can be measured by a conventional optical surface stress measuring apparatus.

However, the strength of the crystallized glass depends not only on the stress in the vicinity of the surface to be chemically strengthened, but also greatly on the crystal grain size, crystal grain density, crystal grain type, and the like generated by recrystallization, and the influence on the chemical strengthening step after recrystallization is also large. In addition, the crystal generated in the recrystallization step may be changed in the chemical strengthening step.

Therefore, in order to maintain the quality of diversified chemically strengthened glass, it is necessary to measure the distribution of stress managed to the deep part, the crystalline state of crystallized glass, and the like.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 53-136886

Patent document 2: japanese patent publication No. 2011-530470

Patent document 3: japanese patent laid-open publication No. 2016-142600

Patent document 4: U.S. patent publication 2016/0356760

Non-patent document

Non-patent document 1: Yogyo-Kyokai-Shi (journal of kiln Association) 87{3}1979

Non-patent document 2: Yogyo-Kyokai-Shi (journal of kiln Association) 80{4}1972

Disclosure of Invention

Problems to be solved by the invention

In recent years, lithium-aluminosilicate glasses have attracted attention as glasses which are easy to ion exchange, have a short time, have a high surface stress value, and can have a deep stress layer in a chemical strengthening step.

The glass was immersed in a high-temperature molten salt of a mixture of sodium nitrate and potassium nitrate to perform chemical strengthening treatment. Since both sodium ions and potassium ions are present in a high concentration in the molten salt, the sodium ions are ion-exchanged with lithium ions in the glass, but the sodium ions are more easily diffused into the glass, and therefore, the lithium ions in the glass are first ion-exchanged with the sodium ions in the molten salt.

Here, when sodium ions are ion-exchanged with lithium ions, the refractive index of the glass decreases, and when potassium ions are ion-exchanged with lithium ions or sodium ions, the refractive index of the glass increases. That is, the potassium ion concentration in the region ion-exchanged near the glass surface is higher than that in the portion not ion-exchanged in the glass, and the sodium ion concentration is higher when the region ion-exchanged is deeper. Therefore, the following features are provided: the refractive index decreases with depth in the vicinity of the outermost surface of the ion-exchanged glass, but increases with depth from a certain depth to a region where the ion-exchange is not performed.

Therefore, in the stress measuring device using the waveguide light on the surface described in the background art, the stress distribution in the deep portion cannot be measured only by the stress value or the stress distribution on the outermost surface, and the depth of the stress layer, the CT value, and the stress distribution as a whole cannot be known. As a result, development for finding appropriate chemical strengthening conditions cannot be achieved, and quality control of production cannot be performed.

In addition, when chemical strengthening is performed after air-cooling strengthening of aluminosilicate glass or soda glass, the stress distribution or the stress value can be measured by the stress measuring device using surface waveguide light described in the background art in the chemically strengthened portion. However, the change in refractive index of a portion that has not been chemically strengthened but has been air-cooled strengthened is small, and cannot be measured by the stress measuring apparatus using waveguide light on the surface described in the background art. As a result, the depth of the stress layer, the CT value, and the overall stress distribution cannot be known. As a result, development for finding appropriate chemical strengthening conditions cannot be achieved, and quality control of production cannot be performed.

On the other hand, the crystallized glass has higher strength than general glass. Therefore, the chemically strengthened crystallized glass can obtain higher strength than the ordinary strengthened glass. However, in the crystallized glass, physical properties such as strength are greatly affected by a crystalline state (particle diameter, crystal grain density, crystal type) and the like. Therefore, in the crystallized glass, it is necessary to measure physical quantities related to the strength of the crystallized glass together with the stress distribution by the chemical strengthening.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an apparatus for evaluating a tempered glass, which can measure a stress distribution of the tempered glass and can measure a physical quantity related to the strength of the tempered glass.

Means for solving the problems

The essential elements of the evaluation device for tempered glass are that the device comprises: a polarization phase difference varying member that varies a polarization phase difference of the laser light by one wavelength or more with respect to a wavelength of the laser light; an imaging element that captures a plurality of images at predetermined time intervals, and acquires a plurality of images, the scattered light being scattered light emitted by the laser light of which the polarization phase difference has been changed being incident on a tempered glass; and a calculation unit that measures a periodic luminance change of the scattered light using the plurality of images, calculates a phase change of the luminance change, calculates a stress distribution in a depth direction from a surface of the tempered glass based on the phase change, and measures a physical quantity related to a strength of the tempered glass using the plurality of images.

Effects of the invention

According to the disclosed technology, it is possible to provide an apparatus for evaluating a tempered glass, which can measure the stress distribution of the tempered glass and can measure a physical quantity related to the strength of the tempered glass.

Drawings

Fig. 1 is a diagram illustrating an evaluation apparatus according to a first embodiment.

Fig. 2 is a view of the evaluation apparatus of the first embodiment as viewed from the direction H of fig. 1.

Fig. 3 is a diagram illustrating a relationship between an applied voltage of the liquid crystal element and a phase difference of polarized light.

Fig. 4 is a diagram illustrating a circuit for generating a drive voltage by which the polarization phase difference of the liquid crystal element changes linearly in time.

Fig. 5 is a diagram illustrating a scattered light image at a certain moment of the laser light L imaged by the imaging element.

Fig. 6 is a graph illustrating temporal changes in scattered light luminance at points B and C of fig. 5.

Fig. 7 is a graph illustrating the phase of the change in scattered light according to the glass depth.

Fig. 8 is a diagram illustrating a stress distribution obtained by equation 1 based on phase data of a change in scattered light in fig. 7.

Fig. 9 is a diagram illustrating actual scattered light images at different times t1 and t 2.

Fig. 10 is a diagram showing an unfavorable design example of the incident surface of the laser light L in the tempered glass.

Fig. 11 is a diagram showing a preferred design example of the incident surface of the laser light L in the tempered glass.

Fig. 12 is a diagram illustrating functional blocks of the arithmetic unit 70 of the evaluation device 1.

Fig. 13 is a flowchart (1 thereof) illustrating an evaluation method using the evaluation apparatus 1.

Fig. 14 is a flowchart (2 thereof) illustrating an evaluation method using the evaluation apparatus 1.

Fig. 15 is an image of scattered light at a certain time obtained by the imaging element 60.

Fig. 16 is a graph showing temporal changes in average scattered light luminance in the region E in fig. 15 (a).

Fig. 17 is a graph illustrating a relationship between the scattering light luminance amplitude value As and the depth of the glass.

Fig. 18 is a diagram illustrating an evaluation apparatus according to modification 1 of the first embodiment.

Fig. 19 is a diagram illustrating an evaluation apparatus according to modification 2 of the first embodiment.

Fig. 20 is a diagram illustrating an evaluation apparatus according to modification 3 of the first embodiment.

Fig. 21 is a diagram illustrating an evaluation apparatus according to modification 4 of the first embodiment.

Fig. 22 is an explanatory diagram of a polarization phase difference variable member utilizing the photoelastic effect.

Fig. 23 is a diagram illustrating an evaluation apparatus according to a second embodiment.

Fig. 24 is a graph in which the stress distributions measured by the evaluation devices 1 and 2 are shown in the same graph.

Fig. 25 is a flowchart illustrating an evaluation method using the evaluation apparatus 2.

Fig. 26 is a diagram illustrating functional blocks of the arithmetic unit 75 of the evaluation device 2.

Fig. 27 is a diagram illustrating a stress distribution in the depth direction of the tempered glass.

Fig. 28 is a flowchart (1 thereof) of deriving a characteristic value based on a stress distribution.

Fig. 29 is a diagram showing an example in which each characteristic value is derived from the measured stress distribution.

Fig. 30 is a flowchart (2 thereof) of deriving a characteristic value based on a stress distribution.

Fig. 31 is a diagram (1) showing another example in which each characteristic value is derived from the measured stress distribution.

Fig. 32 is a flowchart (3 thereof) of deriving a characteristic value based on the stress distribution.

Fig. 33 is a view (fig. 2) showing another example in which each characteristic value is derived from the measured stress distribution.

Fig. 34 is a diagram showing an example of a flowchart for quality determination using characteristic values obtained by measurement of stress distribution.

Fig. 35 is a diagram showing another example of a flowchart for quality determination using each characteristic value obtained by measurement of the stress distribution.

Fig. 36 is an example of a flowchart (1) of quality determination when lithium-containing glass is strengthened two or more times.

Fig. 37 is an example of a flowchart (2) of quality determination when lithium-containing glass is strengthened two or more times.

Fig. 38 shows an example of a synthesis result of a stress distribution on the glass surface layer side and a stress distribution on the glass deep layer side.

FIG. 39 shows stress distributions obtained in comparative example 1 and examples 1 to 3.

Fig. 40 is a diagram illustrating an evaluation apparatus according to a third embodiment.

Fig. 41 is a view illustrating a scattered light image of the laser light L advancing at the interface between the light supplying member and the tempered glass.

Fig. 42 is a view illustrating a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 43 is a diagram showing a second example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 44 is a diagram showing a third example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 45 is a diagram showing a fourth example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 46 is a diagram showing a fifth example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 47 is a diagram showing a sixth example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 48 is a diagram showing a seventh example of a structural portion for sandwiching a liquid between a light supply member and tempered glass.

Fig. 49 is a diagram illustrating a case where the laser light L is incident into the tempered glass.

Fig. 50 is a diagram illustrating an image of a laser trace captured from the position of the imaging element of fig. 49.

Fig. 51 is a diagram illustrating definitions of angles and lengths of laser beams in the light supplying member or the tempered glass of fig. 49.

Fig. 52 is a plan view, a front view, and a side view of fig. 51.

Fig. 53 is a conceptual diagram of the laser light advancing through the light supplying member and the tempered glass.

Fig. 54 is a conceptual diagram of a laser beam advancing through a tempered glass.

Fig. 55 is an example of a flowchart for determining the complementary angle of incidence Ψ.

Fig. 56 is an example of a flowchart for determining the refractive index ng of the tempered glass.

Fig. 57 is another example of a flowchart for determining the complementary angle of incidence Ψ.

Fig. 58 is an example of a flowchart for determining θ L that does not change between the surface through which the laser light passes and the observation surface.

Fig. 59 is a diagram illustrating a stress distribution in the depth direction of the tempered glass.

Fig. 60 is a view illustrating an evaluation apparatus provided with a glass thickness measurement device.

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and overlapping description may be omitted.

< first embodiment >

Fig. 1 is a diagram illustrating an evaluation apparatus according to a first embodiment. As shown in fig. 1, the evaluation apparatus 1 includes a laser light source 10, a polarizing member 20, a polarization phase difference varying member 30, a light supplying member 40, a light converting member 50, an imaging device 60, a calculating unit 70, and a light wavelength selecting member 80.

Reference numeral 200 denotes a tempered glass to be measured. The tempered glass 200 is glass strengthened by a chemical strengthening method, an air-cooling strengthening method, or the like, for example. The tempered glass as referred to herein also includes crystallized glass subjected to tempering treatment. Here, the crystallized glass is a glass produced through a crystallization step, in other words, a glass having crystals intentionally precipitated. In the present application, the crystallized glass subjected to the strengthening treatment may be referred to as a strengthened crystallized glass, if necessary.

The laser light source 10 is disposed so that the laser light L is incident from the light supply member 40 to the surface layer of the tempered glass 200, and the polarization phase difference variable member 30 is interposed between the laser light source 10 and the light supply member 40.

As the laser light source 10, for example, a semiconductor laser, a helium neon laser, or an argon laser can be used. Semiconductor lasers generally have polarized light, and semiconductor lasers having wavelengths of 405nm, 520nm, 630nm, 850nm, and the like are being put to practical use. As the wavelength of the laser light is shorter, the beam diameter is reduced, and the spatial resolution can be improved. Further, the shorter the wavelength of the laser light, the smaller the noise tends to be, and therefore, this is preferable. The laser light needs to transmit through the measurement object.

In order to improve the resolution in the depth direction of the tempered glass 200, it is preferable that the position of the minimum beam diameter of the laser is in the ion exchange layer of the tempered glass 200, and the minimum beam diameter is 20 μm or less. The position of the minimum beam diameter of the laser light is more preferably set to the surface 210 of the tempered glass 200. Since the beam diameter of the laser beam has a resolution in the depth direction, the beam diameter needs to be equal to or smaller than the required resolution in the depth direction. Here, the beam diameter is 1/e of the maximum brightness at the center of the beam²(about 13.5%) and the beam diameter means the minimum width in the case where the beam shape is an elliptical shape or a sheet shape. However, in this case, the minimum width of the beam diameter needs to be oriented in the glass depth direction.

Since the cross-sectional shape of the beam emitted from the semiconductor laser is generally an ellipse, the beam is shaped into a circle by the beam shaping member, thereby improving the spatial resolution and the measurement accuracy. Further, although the output distribution of the beam emitted from the semiconductor laser is gaussian in the beam shape, the measurement accuracy can be improved even if the output distribution shaping means shapes the beam into a constant distribution in the beam shape such as a top hat distribution.

The beam shaping member and the output distribution shaping member are interposed between the laser light source 10 and the polarized light phase difference variable member 30, for example. Examples of the beam shaping member include a cylindrical lens, an anamorphic prism, and a diaphragm. Examples of the output distribution shaping member include an aspherical lens and a DOE (Diffractive Optical Element).

The polarization member 20 is interposed between the laser light source 10 and the polarization phase difference varying member 30 as necessary. Specifically, when the laser light L emitted from the laser light source 10 is not polarized light, the polarization member 20 is inserted between the laser light source 10 and the polarization phase difference varying member 30. When the laser light L emitted from the laser light source 10 is polarized light, the polarizing member 20 may be inserted or may not be inserted. The laser light source 10 and the polarizing member 20 are disposed so that the polarization plane of the laser light L is 45 ° with respect to the surface 210 of the tempered glass 200. As the polarizing member 20, for example, a polarizing plate or the like disposed in a rotatable state may be used, but other members having similar functions may be used.

The light supplying member 40 is placed in optical contact with the front surface 210 of the tempered glass 200 as a measurement object. The light supply member 40 has a function of allowing light from the laser light source 10 to enter the tempered glass 200. As the light supplying member 40, for example, a prism made of optical glass can be used. In this case, in order for light to be optically incident on the surface 210 of the tempered glass 200 through the prism, the refractive index of the prism needs to be substantially the same as the refractive index of the tempered glass 200 (± 0.2 or less).

A liquid having a refractive index substantially equal to that of the tempered glass 200 may be interposed between the light supplying member 40 and the tempered glass 200. This enables the laser light L to be efficiently incident into the tempered glass 200. Here, the third embodiment will be described in detail.

The laser light L passing through the tempered glass 200 generates a slight amount of scattered light L_S. Scattered light L_SThe brightness of (b) is changed by the polarization phase difference of the portion scattered by the laser light L. Then, the polarization direction of the laser beam L is set to θ in FIG. 2 with respect to the surface 210 of the tempered glass 200_s2The laser light source 10 is disposed so as to be 45 ° (± 5 °). Accordingly, birefringence occurs due to the photoelastic effect of stress acting in the in-plane direction of the tempered glass 200, the polarization phase difference changes as the laser light L advances through the tempered glass, and the scattered light L is scattered along with the change_SThe brightness of (a) also changes. The polarization phase difference is a phase difference (retardation) generated by birefringence.

The laser light L is emitted in a direction of θ with respect to the surface 210 of the tempered glass_s1The angle is set to 10 DEG to 30 deg. This is because, when the angle is less than 10 °, the laser light propagates on the glass surface due to the optical waveguide effect, and information in the glass cannot be obtained. On the other hand, if it exceeds 30 °, the depth resolution of the inside of the glass with respect to the optical path length of the laser beam is lowered, and this is not preferable as a measuring method. Thus, it is preferable to set θ_s1＝15°±5°。

Next, the imaging element 60 will be described with reference to fig. 2. Fig. 2 is a view of the evaluation apparatus of the first embodiment as viewed from the direction H of fig. 1, and is a view showing a positional relationship of the imaging element 60. The polarized light of the laser light L is incident at an angle of 45 ° with respect to the surface 210 of the tempered glass 200, and thus the scattered light L_SAnd also radiates at a 45 angle relative to the surface 210 of the strengthened glass 200. Therefore, in order to capture the scattered light L emitted at 45 DEG with respect to the surface of the tempered glass_SThe photographing element 60 is disposed at an orientation of 45 ° with respect to the surface 210 of the tempered glass 200 in fig. 2. That is, in FIG. 2, θ_s2＝45°。

Between the imaging element 60 and the laser beam L, scattered light L is emitted from the laser beam L_SThe image of (2) is imaged on the imaging element 60 and the light conversion member 50 is inserted. As the light conversion member 50, for example, a convex lens made of glass or a lens in which a plurality of convex lenses and concave lenses are combined can be used. In this case, it is preferable that the number of openings (n.a.) of the lens is large because noise is reduced.

Further, regarding the lens in which a plurality of lenses are combined, by providing a telecentric lens in which the principal ray is parallel to the optical axis, only light mainly scattered in the 45 ° direction (imaging element direction) with respect to the glass surface of the tempered glass 200 can be used to form an image of scattered light scattered in all directions from the laser light L. As a result, unnecessary light such as diffuse reflection on the glass surface can be reduced.

Further, a light wavelength selection member 80 for removing unnecessary light for stress measurement is inserted between the laser light L and the imaging element 60. The optical wavelength selection member 80 does not transmit 50% or more, preferably 90% or more of light having a wavelength other than the wavelength of the laser light L. The wavelength width of the light transmitting wavelength selection member 80 is preferably about 10nm or less. By inserting the optical wavelength selection member 80, only the scattered light L necessary for measuring the stress can be removed by removing the raman scattered light, the fluorescence light, and the extraneous light which are unnecessary for measuring the stress by the laser light L_SToward the photographing element 60. As the optical wavelength selection member 80, for example, a bandpass filter or a short-pass filter in which a dielectric film is a multilayer can be used.

As the imaging element 60, for example, a CCD (Charge Coupled Device) element or a CMOS (Complementary Metal Oxide Semiconductor) sensor element can be used. Although not shown in fig. 1 and 2, the CCD element and the CMOS sensor element are connected to a control circuit that controls the elements and takes out an electric signal of an image from the elements, a digital image data generating circuit that converts the electric signal into digital image data, and a digital recording device that records a plurality of pieces of digital image data. The digital image data generation circuit and the digital recording device are connected to the arithmetic section 70.

The arithmetic unit 70 has a function of acquiring image data from the image pickup device 60 or a digital image data generating circuit or a digital recording device connected to the image pickup device 60, and performing image processing or numerical calculation. The calculation unit 70 may have other functions (for example, a function of controlling the light amount and the exposure time of the laser light source 10). The operation unit 70 includes, for example, a cpu (central Processing unit), a rom (read Only memory), a ram (random Access memory), and a main memory.

In this case, various functions of the arithmetic unit 70 can be realized by reading a program recorded in the ROM or the like into the main memory and executing the program by the CPU. The CPU of the arithmetic unit 70 can read and store data from the RAM as necessary. However, a part or all of the arithmetic unit 70 may be realized by hardware only. The arithmetic unit 70 may also physically include a plurality of devices. As the arithmetic unit 70, for example, a personal computer can be used. The arithmetic unit 70 may also function as a digital image data generating circuit or a digital recording device.

The polarization phase difference varying member 30 temporally varies the polarization phase difference when entering the tempered glass 200. The changed polarization phase difference is 1 time or more of the wavelength λ of the laser light. The phase difference of the polarized light must be uniform with respect to the wave surface of the laser light L. For example, in a crystal wedge, the wave surface of the laser light is not uniform because the polarization phase difference is not uniform in the direction of the inclined surface of the wedge. Therefore, it is not preferable to use a crystal wedge as the polarization phase difference variable member 30.

The polarization phase difference varying member 30 that can electrically and uniformly change the polarization phase difference by 1 λ or more on the wave surface of the laser beam is, for example, a liquid crystal element. The liquid crystal element can change the polarization phase difference by the voltage applied to the element, and for example, when the wavelength of the laser light is 630nm, the wavelength can be changed by 3 to 6 wavelengths. In the liquid crystal element, the maximum value of the polarization phase difference that can be changed by an applied voltage is determined by the size of the cell gap.

Since a cell gap of a typical liquid crystal cell is several μm, a maximum polarization phase difference is about 1/2 λ (several hundred nm). Further, in a display using a liquid crystal, etc., no change more than that is required. In contrast, when the wavelength of the laser beam is 630nm, for example, the liquid crystal device used in the present embodiment needs to change the polarization phase difference of about 2000nm, which is about 3 times as large as 630nm, and needs a cell gap of 20 to 50 μm.

The voltage applied to the liquid crystal element is not proportional to the phase difference of the polarized light. For example, fig. 3 shows the relationship between the applied voltage and the polarization phase difference of a liquid crystal element having a cell gap of 30 μm. In fig. 3, the vertical axis represents the polarization phase difference (the number of wavelengths of 630 nm), and the horizontal axis represents the voltage applied to the liquid crystal element (plotted logarithmically).

The voltage applied to the liquid crystal element is 0V to 10V, and the phase difference of the polarized light of about 8 λ (5000nm) can be changed. However, the liquid crystal element generally has unstable alignment of liquid crystal at a low voltage of 0V to 1V, and the polarization phase difference fluctuates due to temperature change or the like. When the voltage applied to the liquid crystal element is 5V or more, the change in the polarization phase difference with respect to the change in the voltage is small. In the case of this liquid crystal element, the polarization phase difference of 4 λ to 1 λ, that is, about 3 λ can be stably changed by using the liquid crystal element under an applied voltage of 1.5V to 5V.

When a liquid crystal device is used as the polarization phase difference variable member 30, the polarization phase difference variable member 30 is connected to a liquid crystal control circuit that controls liquid crystal, and is controlled in synchronization with the imaging device 60. In this case, it is necessary to linearly change the polarization phase difference in time in synchronization with the timing of imaging by the imaging element 60.

Fig. 3 is a diagram illustrating a relationship between an applied voltage of the liquid crystal element and a phase difference of polarized light. As shown in fig. 3, the applied voltage of the liquid crystal element and the phase difference of the polarized light do not change linearly. Therefore, it is necessary to generate a signal in which the polarization phase difference linearly changes within a certain time and apply the signal as a driving voltage to the liquid crystal element.

Fig. 4 is a diagram illustrating a circuit for generating a drive voltage by which the polarization phase difference of the liquid crystal element changes linearly in time.

In fig. 4, the digital data storage circuit 301 records, as digital data, the voltage value corresponding to the polarization phase difference for changing the polarization phase difference at constant intervals in the range of the required change in the polarization phase difference, in the order of addresses, based on the data obtained by measuring the applied voltage of the liquid crystal element used and the polarization phase difference in advance. Table 1 illustrates a part of digital data recorded in the digital data storage circuit 301. The voltage column in table 1 is digital data recorded, and is a voltage value of 10nm per change in the phase difference of polarized light.

[ TABLE 1 ]

The clock signal generation circuit 302 generates a clock signal having a constant frequency using a crystal oscillator or the like. The clock signal generated by the clock signal generation circuit 302 is input to the digital data storage circuit 301 and the DA converter 303.

The DA converter 303 is a circuit that converts digital data from the digital data storage circuit 301 into an analog signal. The digital data of the stored voltage values are sequentially read from the digital data storage circuit 301 in accordance with the clock signal generated by the clock signal generation circuit 302, and transferred to the DA converter 303.

In the DA converter 303, digital data of voltage values read out at constant time intervals is converted into an analog voltage. The analog voltage output from the DA converter 303 is applied to the liquid crystal element used as the polarization phase difference variable member 30 through the voltage amplifier circuit 304.

Although not shown in fig. 4, the driving circuit of the liquid crystal element is synchronized with the circuit for controlling the image pickup element 60 in fig. 2, and image pickup is started by the image pickup element 60 in time series with the start of application of the driving voltage to the liquid crystal element.

Fig. 5 is a diagram illustrating a scattered light image at a certain moment of the laser light L imaged on the imaging element. In fig. 5, the depth from the surface 210 of the strengthened glass 200 is deeper the further upward the travel. In fig. 5, point a is the surface 210 of the tempered glass 200, and the scattered light image spreads in an elliptical shape due to the intensity of the scattered light at the surface 210 of the tempered glass 200.

Since a strong compressive stress acts on the surface portion of the tempered glass 200, the polarization phase difference of the laser light L changes together with the depth due to birefringence caused by photoelastic effect. Therefore, the scattering luminance of the laser light L also changes along with the depth. The principle of the change in the brightness of the laser light scattered according to the internal stress of the tempered glass is described in, for example, Yogyo-Kyokai-Shi (journal of the kiln society) 80{4} 1972.

The polarization phase difference varying member 30 can change the polarization phase difference of the laser light L before entering the tempered glass 200 continuously in time. Accordingly, at each point of the scattered light image in fig. 5, the brightness of the scattered light changes according to the polarization phase difference that has changed by the polarization phase difference changing member 30.

Fig. 6 is a graph illustrating a temporal change in the brightness (scattered light brightness) of scattered light at points B and C in fig. 5. The temporal change in the intensity of the scattered light periodically changes with the period of the wavelength λ of the laser light in accordance with the changed polarization phase difference of the polarization phase difference varying member 30. For example, in fig. 6, at points B and C, the periods of changes in the intensity of scattered light are the same, but the phases are different. This is because the polarization phase difference further changes due to birefringence caused by stress in the tempered glass 200 when the laser light L advances from the point B to the point C. When a value expressed by a line difference of a polarization phase difference that changes when the laser light L advances from the point B to the point C is q and a wavelength of the laser light is λ, a phase difference δ between the point B and the point C becomes δ equal to q/λ.

When considered locally, the phase F of the periodic change in the scattered light luminance associated with the change in the temporal polarization phase difference of the polarization phase difference varying member 30 at an arbitrary point S on the laser light L is a birefringence amount generated by the in-plane stress of the tempered glass 200 as a differential value dF/ds with respect to S by a function F (S) expressed by a position S along the laser light L. From the photoelastic constants C and dF/ds of the tempered glass 200, the stress σ in the in-plane direction of the tempered glass 200 at the point S can be calculated by the following formula 1 (formula 1).

In the present specification, since the laser light L is incident obliquely to the glass, when obtaining a stress distribution with respect to the depth in the vertical direction from the glass surface, conversion from the point s to the depth direction is necessary, as shown in formula 8 (formula 8) described later.

[ mathematical formula 1 ]

On the other hand, the polarization phase difference changing member 30 changes the polarization phase difference by 1 wavelength or more continuously in time within a certain time. During this time, a plurality of scattered light images of the laser light L that are continuous in time are recorded by the imaging device 60. Then, the temporal change in luminance at each point of the scattered light image obtained by the continuous imaging is measured.

The variation of the scattered light at each point of the scattered light image is periodic, and the period is constant regardless of the position. Therefore, the period T is determined from the change in the intensity of the scattered light at a certain point. Alternatively, the period T may be an average of periods at a plurality of points.

Since the polarization phase difference is changed by 1 wavelength or more (1 cycle or more) in the polarization phase difference changing member 30, the scattered light brightness is also changed by 1 cycle or more. Therefore, the period T can be measured from the difference between a plurality of peaks or valleys, the difference between timings at which the peaks or valleys pass through the midpoint of the amplitude, or the like. Note that, in the data of 1 cycle or less, it is impossible to know 1 cycle in principle.

In the data of the periodic change of the scattered light at a certain point, the phase F at the certain point can be accurately obtained by the least squares method or fourier integration of the trigonometric function based on the determined period T.

In the least squares method or fourier integration of the trigonometric function at a previously known period T, only the phase component at the known period T is extracted, and the noise at other periods can be removed. The longer the temporal change of data is, the higher the removal capability is. In general, since the scattered light brightness is weak and the actually changing phase amount is small, measurement based on variable data of the polarization phase difference of several λ is necessary.

When the time-based change data of the scattered light at each point along the scattered light image of the laser light L on the image captured by the imaging device 60 is measured and the phase F is obtained for each data by the same method as described above, the phase F along the intensity of the scattered light of the laser light L can be obtained. Fig. 7 shows an example of the phase of the scattered light change according to the glass depth.

In the phase F along the scattered light intensity of the laser light L, the differential value at the coordinate on the laser light L is calculated, and the stress value at the coordinate s on the laser light L can be obtained by equation 1. Further, if the coordinate s is converted into a distance from the surface of the glass, a stress value with respect to a depth from the surface of the strengthened glass can be calculated. Fig. 8 is phase data based on changes in scattered light in fig. 7, and an example of a stress distribution is obtained by equation 1.

Fig. 9 shows an example of an actual scattered light image at different times t1 and t2, and point a in fig. 9 shows the surface of the tempered glass, and the surface scattered light is reflected by the roughness of the surface of the tempered glass. The center of the surface scattered light image corresponds to the surface of the tempered glass.

In fig. 9, it is understood that the scattered light image of the laser light has different brightness at each point, and that the brightness distribution at time t2 is different from the brightness distribution at time t1 even at the same point. This is due to the phase shift of the periodic scattered light brightness change.

In the evaluation apparatus 1, the incidence plane of the laser light L is preferably inclined at 45 ° to the surface 210 of the tempered glass 200. This will be described with reference to fig. 10 and 11.

Fig. 10 is a diagram showing an unfavorable design example of the incident surface of the laser light L in the tempered glass. In fig. 10, the incidence plane 250 of the laser light L in the tempered glass 200 is perpendicular to the surface 210 of the tempered glass.

Fig. 10(b) is a view seen from the direction H of fig. 10 (a). As shown in fig. 10(b), the imaging element 60 is disposed at an inclination of 45 ° with respect to the surface 210 of the tempered glass 200, and the laser light L is observed from the inclination of 45 °. In the case of fig. 10, distances from two different points on the laser beam L, that is, the point a and the point B to the imaging element 60 are different when the distances are the distance a and the distance B. That is, it is not possible to simultaneously focus the points a and B, and it is not possible to obtain a satisfactory image of the scattered light image of the laser light L in a desired region.

Fig. 11 is a diagram showing a preferred design example of the incident surface of the laser light L in the tempered glass. In fig. 11, the incidence plane 250 of the laser light L in the tempered glass 200 is inclined by 45 ° with respect to the surface 210 of the tempered glass 200.

Fig. 11(b) is a view seen from the direction H of fig. 11 (a). As shown in fig. 11(b), the imaging element 60 is disposed inclined at 45 ° with respect to the surface 210 of the tempered glass 200, but the incident surface 250, which is a surface through which the laser light L passes, is also inclined at 45 ° similarly. Therefore, the scattered light image of the laser light L in a desired region can be obtained as a good image regardless of the distance (distance a and distance B) to the imaging element 60 at which point on the laser light L is the same.

In particular, when a laser beam having a minimum beam diameter of 20 μm or less is used, the focal depth is shallow, and is at most about several tens of μm. Therefore, it is very important to obtain a good image if the incident surface 250 of the laser beam L in the tempered glass 200 is inclined 45 ° with respect to the surface 210 of the tempered glass 200 and the distance to the imaging device 60 is the same at any point on the laser beam L.

Fig. 12 is a diagram illustrating functional blocks of the arithmetic unit 70 of the evaluation device 1. As shown in fig. 12, the arithmetic unit 70 includes a luminance change measurement means 701, a phase change calculation means 702, a stress distribution calculation means 703, and a physical quantity measurement means 704.

The evaluation apparatus 1 can measure the stress distribution of the tempered glass by the luminance change measuring means 701, the phase change calculating means 702, and the stress distribution calculating means 703 of the computing unit 70. The physical quantity measuring means 704 is a portion having a function of measuring a physical quantity related to the strength of the tempered glass, and when only the stress distribution of the tempered glass is measured, the physical quantity measuring means 704 may not be used.

(measurement flow 1: measurement of stress distribution of tempered glass)

Fig. 13 is a flowchart (1) illustrating an evaluation method using the evaluation apparatus 1, and is a flowchart illustrating a method of measuring a stress distribution of the tempered glass in the evaluation apparatus 1. The flow of the measurement of the stress distribution of the tempered glass in the evaluation apparatus 1 will be described with reference to fig. 12 and 13.

The measurement shown in fig. 13 may be performed, for example, after the step of producing tempered glass by subjecting the original plate to a tempering treatment. The measurement shown in fig. 13 is performed after the step of producing crystallized glass by subjecting the original plate to crystallization treatment, and further producing reinforced crystallized glass by subjecting the produced crystallized glass to reinforcing treatment.

First, in step S401, the polarization phase difference of the laser light from the laser light source 10 having polarization or the laser light source 10 to which polarization is applied is changed by 1 wavelength or more continuously in time with respect to the wavelength of the laser light by the polarization phase difference changing member 30 (polarization phase difference changing step).

Next, in step S402, the laser light whose polarization phase difference is changed is made to enter the tempered glass 200 as the measurement object obliquely with respect to the front surface 210 via the light supplying member 40 (light supplying step).

Next, in step S403, the image pickup device 60 picks up a plurality of images of scattered light generated by the laser beam having a variable polarization phase difference traveling through the tempered glass 200 at predetermined time intervals, and acquires a plurality of images (image pickup step).

Next, in step S404, the luminance change measurement means 701 of the calculation unit 70 measures a periodic luminance change of the scattered light associated with a temporal change in the polarization phase difference that is changed in the polarization phase difference changing step, using a plurality of images of the scattered light obtained in the imaging step at time intervals (luminance change measurement step).

Next, in step S405, the phase change calculation means 702 of the calculation unit 70 calculates a phase change along a periodic luminance change of the scattered light of the laser light incident on the tempered glass 200 (phase change calculation step).

Next, in step S406, the stress distribution calculating means 703 of the computing unit 70 calculates the stress distribution in the depth direction from the surface 210 of the tempered glass 200 based on the phase change along the periodic luminance change of the scattered light of the laser light incident on the tempered glass 200 (stress distribution calculating step). The calculated stress distribution may be displayed on a display device (a liquid crystal display or the like).

(measurement flow 2: measurement of stress distribution of tempered glass and measurement of physical quantity relating to Strength)

The evaluation device 1 can measure the stress distribution of the tempered glass by the luminance change measuring means 701, the phase change calculating means 702, the stress distribution calculating means 703, and the physical quantity measuring means 704 of the computing unit 70, and measure the physical quantity related to the strength of the tempered glass.

Fig. 14 is a flowchart (2) illustrating an evaluation method using the evaluation apparatus 1, and is a flowchart illustrating a method of measuring a stress distribution of the tempered glass and a method of measuring a physical quantity related to the strength of the tempered glass in the evaluation apparatus 1. With reference to fig. 12 and 14, the flow of measurement of the stress distribution of the tempered glass and measurement of the physical quantity related to the strength of the tempered glass in the evaluation apparatus 1 will be described.

The measurement shown in fig. 14 may be performed, for example, after the step of producing crystallized glass by subjecting the original plate to crystallization treatment, and further producing strengthened crystallized glass by subjecting the produced crystallized glass to strengthening treatment.

First, steps S401 to S403 are executed as in the case of fig. 13. Then, step S414 is executed in parallel with steps S404 to S406. In step S414, the physical quantity measuring means 704 of the computing unit 70 measures a physical quantity related to the strength of the tempered glass using a plurality of images of the scattered light obtained in the imaging step of step S403 at time intervals (physical quantity measuring step). Step S414 may be performed substantially simultaneously with steps S404 to S406. The measured physical quantity may be displayed on a display device (a liquid crystal display or the like).

Here, the "physical quantity related to the strength of the strengthened glass" includes physical quantities such as a refractive index, a crystallization ratio, a crystal grain diameter, a crystal grain density, a haze, and an amount of defects or impurities in the glass, and parameters (a scattering light intensity amplitude value, an average scattering light intensity, a scattering light intensity variance value, and the like) necessary for obtaining these physical quantities. That is, the physical quantity measuring means 704 may measure only the amplitude value of the scattered light intensity or the average scattered light intensity without directly measuring the physical quantity such as the crystallization ratio. In this case, the strength of the tempered glass can also be estimated from the measurement result of the physical quantity measuring means 704.

The measurement of the physical quantity related to the strength of the tempered glass will be described in more detail below.

(measurement example 1 of physical quantity relating to Strength of tempered glass)

Fig. 15(a) is an image of scattered light at a certain time obtained by the imaging element 60, and fig. 15(b) is an enlarged view of the region E in fig. 15 (a). Fig. 16 is a graph showing a temporal change in average scattered light luminance in the region E in fig. 15 (a). When the phase difference of the laser light L incident on the polarization phase difference varying member 30 varies, the scattered light brightness also varies in accordance with the variation. Therefore, in the graph of temporal change in the scattered light luminance shown in fig. 16, the scattered light luminance changes periodically with a change in the phase difference of the laser beam. The amplitude value of the variation in the scattered light luminance Is referred to As a scattered light luminance amplitude value As, and the average value of the variation in the scattered light luminance Is referred to As an average scattered light luminance Is.

Typically, the scattered light comprises scattered light produced by several scattering mechanisms. Scattered light having the same wavelength as that of incident light differs in scattering property due to the relationship between the size and wavelength of the scattered particles. When the wavelength λ of the incident light is constant, the scattering particles are scattered by the scattering mechanism under rayleigh scattering when the size of the scattering particles is sufficiently small, and the scattering mechanism under mie scattering starts from position D ═ λ × 1/10, and becomes completely mie scattering at D ≧ λ.

The haze of the crystallized glass is determined by the crystal grain size, the crystal grain density, and the difference in refractive index between the crystal and the glass phase. Although haze is reduced as the refractive index difference between the crystal and the glass phase is smaller, it is difficult to completely match the refractive index between the crystal and the glass phase, and there is generally a refractive index difference of about 0.05 to 0.50. For example, when the difference in refractive index between the crystal and the glass phase is about 0.1, the crystal grain size (diameter of crystal grain) of the reinforced crystallized glass is transparent under visible light, and therefore, the crystal grain size of the reinforced crystallized glass is controlled to be sufficiently smaller than the wavelength of visible light by about 600nm and controlled to be 10nm to 100 nm. Therefore, although the rayleigh scattering mechanism is dominant in most cases, the influence of the mie scattering mechanism appears also at 100nm where the crystal grain size is the largest. The brightness of scattered light, whether rayleigh scattering or mie scattering, is in high order proportion to the diameter of the scattering particles and in proportion to the density of the scattering particles. In rayleigh scattering, the scattering particle diameter is proportional to the 6 th power, and in mie scattering, the scattering particle diameter is proportional to the 2 nd power, and this period can be considered in a region where the rayleigh scattering changes to the mie scattering mechanism. That is, in rayleigh scattering and mie scattering, which do not change in wavelength from incident light, the higher the scattering particle diameter, the higher the density, and the higher the scattering light intensity.

Further, there are fluorescence scattering and raman scattering as scattering in which the wavelength of scattered light is different from the wavelength of incident light. In general, fluorescence scattering occurs due to impurities or defects in the glass, and raman scattering occurs due to the composition or bonding state.

Among the scattering mechanisms described above, in rayleigh scattering, the brightness of scattered light differs depending on the polarization state of incident light. In the measurement of the stress, birefringence is generated due to the photoelastic effect of the internal stress, the laser light L advances in the glass, and the state of the polarized light changes, with which the scattered light brightness changes. This is used in the principle of the evaluation device 1. On the other hand, in mie scattering, fluorescence scattering, and raman scattering, which are other scattering mechanisms, the scattered light brightness is generally independent of the polarization state of incident light. Therefore, mie scattering, fluorescence scattering, and raman scattering are not used in the principle of the evaluation apparatus 1.

In the evaluation apparatus 1, a light wavelength selection member 80 that transmits only the vicinity of the wavelength of the laser light is provided between the light supply member 40 and the imaging element 60. Since the width of the wavelength transmitted through the optical wavelength selection member 80 is very narrow, about 10nm or less, the imaging element 60 can image only scattered light having a wavelength substantially equal to the wavelength of the laser light. For example, the scattered light does not include fluorescence scattering and raman scattering components having different wavelengths. Therefore, the scattered light luminance amplitude value As Is a value based on rayleigh scattering, and the average scattered light luminance Is a value based on mie scattering.

The scattering light intensity amplitude value As Is determined by the size of the crystal grains of the reinforced crystallized glass, which are scattering particles, and the crystal grain density, and the ratio of the average scattering light intensity Is to the scattering light intensity amplitude value As Is determined by the ratio of the rayleigh scattering component to the mie scattering component, and thus Is determined by the size of the crystal grains, which are scattering particles.

From the two measured values of the scattered light luminance amplitude value As and the average scattered light luminance Is, the absolute values of the direct scattered particle diameter and the scattered particle density cannot be calculated. However, in the strengthened crystallized glass having different scattering particle diameters, scattering particle densities, that Is, crystal particle diameters, and crystal particle densities, the values of the scattering luminance amplitude value As and the average scattering luminance value Is are different, and the differences can be observed independently from each other. That Is, although the absolute values of the scattering particle diameter and the scattering particle density cannot be directly calculated, by measuring the scattered light luminance amplitude value As or the average scattered light luminance Is, it Is possible to know the variation in the scattering particle diameter and the scattering particle density.

Further, the crystal grain size or the crystal grain density can be estimated by measuring the scattering grain size and the scattering grain density by another method and experimentally obtaining the relationship between the scattering brightness amplitude value As and the average scattering brightness Is and the crystal grain size or the crystal grain density.

For example, the relationship between the scattering light intensity amplitude value As and the average scattering light intensity Is and the crystal grain size or the crystal grain density Is experimentally obtained and stored in advance As a table or a function in the memory in the arithmetic unit 70. The physical quantity measuring means 704 of the computing unit 70 measures the scattered-light intensity amplitude value As and the average scattered-light intensity Is using the image obtained in the imaging step of step S403, and can estimate the crystal grain size or the crystal grain density from the measured values of the scattered-light intensity amplitude value As and the average scattered-light intensity Is using a table or a function.

The measured values of the amplitude value As of the scattered-light intensity and the average scattered-light intensity Is, which reflect the particle diameter and the particle density of the scattered particles, are values in the region E in fig. 15 (a). However, if the measurement region is moved from the glass surface of the laser image to each depth in the depth direction and measured, the scattering particle diameter and the scattering particle density in the depth direction of the reinforced crystallized glass can be known. This confirmed that the crystallized state was uniform in the depth direction from the surface.

(measurement example 2 of physical quantity relating to Strength of tempered glass)

As shown in fig. 15(b), the scattered light image is not uniform and is in a particle shape. This is because the incident light is laser light, and unevenness due to speckle is called a speckle pattern. The speckle pattern is determined by the size, density, and optics of the scattering particles.

The degree of unevenness in luminance of the speckle pattern, for example, the variance value of the luminance of the region E is calculated and set to be Ss. The variance value Ss reflects the scattering particle density. When the crystal grain size is small, the mie scattering component is small, and the intensity of the mie scattering component cannot be measured, the crystal grain size and the crystal grain density can be estimated from the variance value Ss of the luminance of the speckle pattern and the scattered light luminance amplitude value As.

That is, even if the absolute value of the scattering particle diameter or the scattering particle density is not directly calculated, the dispersion of the scattering particle diameter or the scattering particle density can be known by measuring the variance value Ss or the scattered light luminance amplitude value As. Similarly to the case of the scattered light intensity amplitude value As and the average scattered light intensity Is, the crystal grain diameter or the crystal grain density can be estimated by measuring the scattered particle diameter and the scattered particle density, experimentally obtaining the relationship between the variance value Ss and the scattered light intensity amplitude value As and the crystal grain diameter or the crystal grain density, and storing the relationship in advance As a table or a function in the memory in the arithmetic unit 70.

(measurement example 3 of physical quantity relating to Strength of tempered glass)

In fig. 15(a), θ is an angle along the beam of the laser light of the scattered light image. The angle θ is determined by the refractive index of the glass to be measured, and will be described later.

The refractive index of the light-supplying member 40 is desirably exactly the same as that of the tempered glass 200. However, since it is not realistic to replace the light supply member 40 with a tempered glass of a different type, a material having a refractive index close to that of the tempered glass 200 is generally used as the light supply member 40. That is, the refractive index of the tempered glass 200 and the refractive index of the light supplying member 40 are slightly different. Further, the refractive index of the tempered glass also varies. When the refractive indexes of the light supplying member 40 and the tempered glass 200 are different, the incident angle θ of the laser light L into the tempered glass 200_s1Angle of refraction theta with respect to the incident light into the tempered glass_s1' different. Since this angle is determined by the position and angle of the laser light source 10, the angle and refractive index of each surface of the light supplying member 40, the position and angle of the imaging element, and the refractive index of the tempered glass, if the refractive index of the tempered glass is known in addition to the refractive index, the angle θ of the beam along the laser light L in the scattered light image can be measured, and the refractive index of the tempered glass can be calculated.

On the other hand, in many cases, the refractive index of the glass itself is different from that of the precipitated crystal in the strengthened crystallized glass. For example, in a strengthened crystallized glass using a lithium aluminosilicate base material, the refractive index of the glass of the base material is 1.52, and the refractive index of the precipitated β spodumene is 1.66. The volume ratio of the precipitated crystal to the matrix is about 10 to 50%, and the refractive index of the whole crystal changes according to the volume ratio of the crystal. That is, the volume fraction of crystallization can be calculated by measuring the refractive index of the reinforced crystallized glass.

(measurement example 4 of physical quantity relating to Strength of tempered glass)

Fig. 17 illustrates the relationship between the amplitude value As of the scattered light luminance and the depth of the glass. The external haze value of the glass surface layer can be estimated from the amplitude value of the glass surface. Further, the internal haze value can be estimated from the attenuation curve of the amplitude value of the inside of the glass. The transmittance can be estimated by using the external haze value and the internal haze value. When one of the haze values is small, the estimation may be performed using only the other haze value. Further, the chromaticity of the tempered glass may be estimated by estimating the transmittance at each wavelength by using a plurality of laser beams. Further, the surface of the glass may be determined by measuring both surfaces of the glass and examining the difference between the surface layers of the glass based on the difference in the amplitude value of the scattered light brightness or the difference in transmittance. Specifically, an antiglare surface, an antifingerprint surface, an AR coating surface, an antibacterial surface, an ITO surface, a floating transfer surface (tin surface), and the like can be considered.

The measured values of the amplitude value As of the scattered-light brightness, the average scattered-light brightness Is, the dispersion value Ss, and the refractive index of the glass shown in the above measurement examples 1 to 4 are not limited to the reinforced crystallized glass, but are also useful As numerical values indicating the quality such As defects, composition, unevenness, transparency, and the like of the glass, such As impurities or abnormal crystallization, in the non-crystallized reinforced glass. That is, the measurement shown in fig. 14 may be performed after the step of producing a strengthened glass (not a strengthened crystallized glass) by subjecting the original plate to a strengthening treatment. Further, physical quantities other than those shown in measurement examples 1 to 4 described above may be measured.

As described above, in the evaluation apparatus 1, unlike a stress measurement apparatus using waveguide light on the surface, measurement by scattered light is performed without performing stress measurement depending on the refractive index distribution of the tempered glass. Therefore, regardless of the refractive index distribution of the tempered glass (regardless of the refractive index distribution of the tempered glass), the stress distribution of the tempered glass can be measured from the outermost surface of the tempered glass to a deeper portion than before. For example, stress measurement can be performed also for a lithium aluminosilicate-based tempered glass having a characteristic that the refractive index increases from a certain depth together with the depth.

The polarization phase difference of the laser beam is changed by 1 wavelength or more continuously in time with respect to the wavelength of the laser beam by the polarization phase difference changing member 30. Therefore, the phase of the periodic luminance change of the scattered light can be obtained by the least squares method or fourier integration of the trigonometric function. In the least squares method or fourier integration of the trigonometric function, unlike the conventional method of detecting a phase from a change in the position of a peak or a trough of a wave, all data of the wave is processed and the noise of other periods can be removed because the period is known in advance. As a result, the phase of the periodic luminance change of the scattered light can be easily and accurately obtained.

In the evaluation apparatus 1, the same image as the image captured for measuring the stress distribution can be used to measure the physical quantity related to the strength of the tempered glass. This enables efficient measurement of physical quantities related to strength and enables wide-range evaluation of tempered glass.

< modification 1 of the first embodiment >

In modification 1 of the first embodiment, an example of an evaluation apparatus having a different configuration from that of the first embodiment is shown. In modification 1 of the first embodiment, description of the same components as those of the already described embodiment may be omitted.

Fig. 18 is a diagram illustrating an evaluation apparatus according to modification 1 of the first embodiment. As shown in fig. 18, the evaluation apparatus 1A is different from the evaluation apparatus 1 (see fig. 1) in that the optical wavelength selection means 80 is replaced with optical wavelength selection means 81 and 82. In fig. 18, the arithmetic unit is not shown.

The optical wavelength selection members 81 and 82 are, for example, two types of band pass filters having different wavelength bands and capable of being switched manually or automatically.

The optical wavelength selection member 81 is configured to make light having a wavelength other than the wavelength of the laser light L opaque by 50% or more, preferably 90% or more, as in the optical wavelength selection member 80 of the first embodiment. The width of the wavelength transmitted through the optical wavelength selection member 81 is preferably about 10nm or less.

The optical wavelength selection member 82 is a band-pass filter that transmits light having a wavelength different from the wavelength of the laser light L, and the center wavelength can match the wavelength of raman scattering or the wavelength of fluorescence scattering peculiar to the tempered glass to be measured, for example. The width of the wavelength of light transmitted through the optical wavelength selection member 82 may not necessarily be as narrow as the optical wavelength selection member 81.

In the evaluation apparatus 1A, first, the light wavelength selection member 81 is used to measure the intensity of the scattered light together with the stress measurement. Next, the light wavelength selection member 81 is switched to the light wavelength selection member 82, and the scattered light brightness is measured. Then, the ratio of the scattered light luminance when the optical wavelength selection member 81 is used to the scattered light luminance when the optical wavelength selection member 82 is used is calculated. This makes it possible to know information on crystals precipitated in the tempered glass, the amount of specific impurities, and the like.

The optical wavelength selection members are not limited to two types, and three or more types may be arranged so as to be switchable.

< modification 2 of the first embodiment >

In modification 2 of the first embodiment, another example of an evaluation apparatus having a different configuration from that of the first embodiment is shown. In modification 2 of the first embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 19 is a diagram illustrating an evaluation apparatus according to modification 2 of the first embodiment. As shown in fig. 19, the evaluation apparatus 1B is different from the evaluation apparatus 1 (see fig. 1) in that the laser light source 10 is replaced with the laser light sources 11 and 12, and the light wavelength selection member 80 is replaced with the light wavelength selection members 81 and 82. In fig. 19, the arithmetic unit is not shown.

The laser light sources 11 and 12 are two types of laser light having different oscillation wavelengths. The optical wavelength selection members 81 and 82 are, for example, two types of band pass filters having different wavelength bands. The switching can be made manually or automatically in such a manner that the light wavelength selection member 81 is selected in the case of the laser light source 11 and the light wavelength selection member 82 is selected in the case of the laser light source 12.

The wavelengths of the laser light sources 11 and 12 can be selected from 405nm, 520nm, 640nm, 850nm, and the like. The optical wavelength selection members 81 and 82 may be appropriately selected from band pass filters that transmit only around the wavelength of the selected laser light sources 11 and 12.

In the evaluation apparatus 1B, the laser light sources 11 and 12 and the optical wavelength selection means 81 and 82 having different wavelengths are used, and the scattered light intensity amplitude value As, the average scattered light intensity Is, the variance value Ss, and the like can be measured. Since the relationship between the wavelength and the particle diameter of the scattered light is sensitively influenced by the intensity or behavior of the scattered light, the crystallization state with higher reliability can be known by obtaining information from the scattered light at a plurality of wavelengths.

The laser light source and the optical wavelength selection member are not limited to two types, and three or more types may be arranged so as to be switchable.

In addition, similar effects can be obtained even when a plurality of evaluation devices 1 including laser light and light wavelength selection means having different wavelengths are used instead of the evaluation device 1B.

< modification 3 of the first embodiment >

In modification 3 of the first embodiment, another example of an evaluation apparatus having a different configuration from that of the first embodiment is shown. In modification 3 of the first embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 20 is a diagram illustrating an evaluation apparatus according to modification 3 of the first embodiment. As shown in fig. 20(a), the evaluation apparatus 1C differs from the evaluation apparatus 1 (see fig. 1) in that the light wavelength selection member 80, the light conversion member 50, and the imaging element 60 are disposed on the opposite side of the tempered glass 200 from the light supply member 41, and the light extraction member 42 is disposed in contact with the back surface 220 of the tempered glass 200. In fig. 20, the arithmetic unit is not shown.

In the evaluation apparatus 1C, the scattered light L generated on the back surface 220 side of the tempered glass 200 was caused to occur_S2The light enters the image pickup device 60 through the light extraction member 42 such as a prism, the optical wavelength selection member 80, and the light conversion member 50, and is picked up by the image pickup device 60a plurality of times at time intervals within a predetermined period of time. The other structures and operations are the same as those of the first embodiment.

Although the reflection of the laser light L on the surface 210 of the tempered glass 200 can be reduced by providing the light supply member 41, the reflection of the laser light L on the surface 210 of the tempered glass 200 may be of a level that causes no problem, and the laser light L may be directly incident on the tempered glass 200 without providing the light supply member 41.

Since the tempered glass 200 has the same stress distribution on the front and back surfaces, the scattered light Ls on the front surface 210 side (incident side of the laser light L) of the tempered glass 200 can be detected as in the first embodiment, and the scattered light L on the back surface 220 side (emission side of the laser light L) of the tempered glass 200 can be detected as in modification 1 of the first embodiment_S2。

The scattered light L on the back surface 220 side of the tempered glass 200 is detected_S2In the case of (2), the laser light in the tempered glass 200 preferably satisfies the condition of total reflection. This is because, when the laser light is totally reflected on the rear surface 220 of the tempered glass 200, the diffuse reflection on the rear surface 220 of the tempered glass 200 can be reduced, and the incidence of unnecessary light to the imaging element 60 can be prevented. By adjusting the incident angle of the laser light to the tempered glass 200, the laser light can satisfy the condition of total reflection on the rear surface 220 of the tempered glass 200.

Alternatively, as in the evaluation apparatus 1D shown in fig. 20(b), the scattered light L generated on the front surface 210 side of the tempered glass 200 and emitted to the back surface 220 side may be caused to occur_S3The light enters the image pickup device 60 through the light extraction member 42 such as a prism, the optical wavelength selection member 80, and the light conversion member 50, and is picked up by the image pickup device 60a plurality of times at time intervals within a predetermined period of time. The other structures and operations are the same as those of the first embodiment.

Although the reflection of the laser light L on the surface 210 of the tempered glass 200 can be reduced by providing the light supply member 41 as in the evaluation apparatus 1C, the reflection of the laser light L on the surface 210 of the tempered glass 200 may be of such a degree that there is no problem, and the laser light L may be directly incident on the tempered glass 200 without providing the light supply member 41.

In both of the evaluation devices 1C and 1D, as in the evaluation device 1, the stress distribution in the depth direction from the back surface 220 of the tempered glass 200 can be calculated from the phase change along the periodic luminance change of the scattered light of the laser light L incident on the tempered glass 200.

In particular, according to the evaluation apparatus 1D, the focal point of the laser light is set to the same position from the surface layer of the glass regardless of the thickness of the glass sheet. Therefore, even when the tempered glass having the same stress distribution is measured, the focal position of the laser light does not need to be adjusted or fine-tuned, and thus the effect of shortening the measurement time or further improving the repetition accuracy is obtained.

< modification 4 of the first embodiment >

In modification 4 of the first embodiment, another example of an evaluation apparatus having a different configuration from that of the first embodiment is shown. In modification 4 of the first embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 21 is a diagram illustrating an evaluation apparatus according to modification 4 of the first embodiment. As shown in fig. 21, the evaluation apparatus 1E differs from the evaluation apparatus 1 (see fig. 1) in that the light wavelength selection member 80A, the light conversion member 50A, and the imaging element 60A are disposed on the opposite side of the tempered glass 200 from the light supply member 40, and the light extraction member 42 is disposed in contact with the back surface 220 of the tempered glass 200. In fig. 21, the arithmetic unit is not shown.

In the evaluation apparatus 1E, similarly to the evaluation apparatus 1, the scattered light L emitted from the surface 210 side of the tempered glass 200 can be detected_S. In addition, in the evaluation apparatus 1E, the scattered light L emitted from the back surface 220 side of the tempered glass 200 was caused to exit_S2The light enters the image pickup device 60A through the light extraction member 42 such as a prism, the light wavelength selection member 80A, and the light conversion member 50A, and is picked up by the image pickup device 60A plurality of times at time intervals within a fixed time. The other operations are the same as those of the first embodiment.

In the evaluation apparatus 1E, with the configuration of fig. 21, the stress distribution in the depth direction from the front surface 210 of the tempered glass 200 and the stress distribution in the depth direction from the back surface 220 of the tempered glass 200 can be calculated at the same time. The present invention is effective when a tempered glass having a stress distribution different from that of the front and back surfaces is measured, or when it is desired to confirm whether the front and back surfaces have the same stress distribution in any tempered glass.

< modification 5 of the first embodiment >

In modification 5 of the first embodiment, an example of a polarization phase difference variable member having a different configuration from that of the first embodiment is shown. In modification 5 of the first embodiment, description of the same components as those of the above-described embodiment may be omitted.

The polarization phase difference varying member may be made of a transparent material and may vary the polarization phase difference by applying pressure, using the photoelastic effect of the transparent material. Fig. 22 is an explanatory diagram of a polarization phase difference variable member utilizing the photoelastic effect.

In the polarization phase difference variable member 30A shown in fig. 22, one surface of a substantially rectangular parallelepiped polarization phase difference generating material 310 is fixed by a fixing jig 311, the opposite surface of the polarization phase difference generating material 310 is in contact with one surface of a piezoelectric element 312, and the opposite surface of the piezoelectric element 312 is fixed by a fixing jig 313.

The two surfaces 310a and 310b of the polarization phase difference generating material 310 facing each other in the direction perpendicular to the surface contacting the piezoelectric element 312 are processed into mirror surfaces, and the polarized light beam Q can pass through. As the polarized light phase difference generating material 310, a material which is transparent and has a large photoelastic effect can be used, for example, quartz glass can be used for glass, and polycarbonate can be used for resin.

When a voltage is applied, the piezoelectric element 312 expands and contracts in the voltage application direction. Whether to elongate or contract is determined by the positive or negative voltage. Although not shown in fig. 22, a piezoelectric element driving voltage generation circuit that controls the voltage applied to the piezoelectric element 312 is connected to the piezoelectric element 312.

In the piezoelectric element 312, when a voltage for extending the piezoelectric element 312 is applied by the piezoelectric element driving voltage generation circuit, the length is extended in the direction of the applied voltage, but the piezoelectric element 312 is disposed so that the polarized light phase difference generating material 310 is positioned in the extended direction.

When a voltage in the direction in which the piezoelectric element 312 extends is applied by the piezoelectric element driving voltage generation circuit, the piezoelectric element 312 extends in the direction of the polarized light phase difference generating material 310. Since the polarizing phase difference generating material 310 is fixed by the fixing jigs 311 and 313, a compressive stress is generated due to shrinkage. Birefringence is generated in the direction in which the light beam Q passes due to the compressive stress of the polarization phase difference generating material 310, and a polarization phase difference is generated in the light beam Q. The amount of this polarization phase difference is proportional to the voltage applied to the piezoelectric element 312, and the polarization phase difference can be controlled by a piezoelectric element driving voltage generation circuit that applies a driving voltage to the piezoelectric element 312.

For example, 10mm cubic polycarbonate is used as the polarized light phase difference generating material 310. The photoelastic constant of the polycarbonate was about 700nm/cm/MPa, and the Young's modulus was about 2.5 GPa.

As the piezoelectric element 312, for example, a laminated piezoelectric element in which a high dielectric ceramic having a perovskite crystal structure such as lead zirconate titanate having a large piezoelectric effect and electrodes are alternately laminated can be used. For example, in the laminated piezoelectric element, an extension of 10 μm or more can be obtained at an applied voltage of 100V by setting 1 layer having a thickness of 200 μm to 100 layers and having a length of about 20 mm.

Since the young's modulus of lead zirconate titanate, which is a material of the piezoelectric element 312, is 10 times or more higher than that of polycarbonate, almost all the extension of the piezoelectric element 312 becomes the compression of polycarbonate, and when the piezoelectric element 312 is extended by 10 μm, 10mm of cubic polycarbonate is compressed by 0.1%, and the compressive stress at that time becomes 2.5 MPa. When the light beam Q passes through the 10mm polarization phase difference generation material 310, a polarization phase difference of 1750nm is generated, and if the wavelength is 630nm, a polarization phase difference of 2.8 λ can be changed.

For example, 10mm cubic quartz glass is used as the polarized light phase difference generating material 310. The photoelastic constant of the quartz glass was about 35nm/cm/MPa, and the Young's modulus was about 70 GPa. Since the young's modulus of lead zirconate titanate, which is a material of the piezoelectric element 312, is approximately the same level as that of quartz, approximately half of the elongation of the piezoelectric element 312 becomes the compression of quartz glass, and when the piezoelectric element 312 is elongated by 10 μm, 10mm cubic polycarbonate is compressed by about 0.05%, and the compressive stress at this time becomes about 35 MPa. When the light Q passes through the 10mm polarized light phase difference generating material 310, a polarized light phase difference of 1225nm is generated, and if the wavelength is 630nm, the polarized light phase difference of 1.9 λ can be changed.

When the polarizing retardation is produced by deforming the material in this way, the value obtained by multiplying the photoelastic constant by the young's modulus is important, and is 0.18 (no unit) in the case of polycarbonate and 0.26 (no unit) in the case of quartz. That is, it is important to use a transparent member having a value of 0.1 or more as the polarization phase difference generation material 310.

As described above, the polarization phase difference varying member is not limited to the liquid crystal device, and may be a mode using a piezoelectric element or any other mode as long as the polarization phase difference when entering the tempered glass 200 can be temporally changed and the changed polarization phase difference can be 1 time or more of the wavelength λ of the laser light.

< second embodiment >

In the second embodiment, an example of an evaluation apparatus used in combination with the evaluation apparatus of the first embodiment is shown. In the second embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 23 is a diagram illustrating an evaluation apparatus according to a second embodiment. For example, Yogyo-Kyokai-Shi (journal of the kiln Association) 87{3}1979 and the like. As shown in fig. 23, the evaluation device 2 includes a light source 15, a light supply member 25, a light extraction member 35, a light conversion member 45, a polarization member 55, an imaging element 65, and a calculation unit 75. The evaluation device 2 can be used in combination with the evaluation device 1 shown in fig. 1. The evaluation device 2 may be used in combination with the evaluation device 1A shown in fig. 18, the evaluation device 1B shown in fig. 19, the evaluation devices 1C and 1D shown in fig. 20, and the evaluation device 1E shown in fig. 21.

In the evaluation apparatus 2, the light source 15 is disposed so that the light La is incident on the surface layer of the tempered glass 200 from the light supplying member 25. In order to utilize interference, the wavelength of the light source 15 is preferably a single wavelength for a simple bright-dark display.

As the light source 15, for example, a Na lamp, which easily obtains light of a single wavelength, may be used, and the wavelength in this case is 589.3 nm. As the light source 15, a mercury lamp having a shorter wavelength than an Na lamp can be used, and the wavelength in this case is 365nm, which is a mercury I line, for example. However, since the mercury lamp has many bright lines, it is preferably used by passing through a band-pass filter that transmits only 365nm light.

In addition, an led (light Emitting diode) may be used as the light source 15. In recent years, many wavelength LEDs have been developed, but the spectral width of an LED is 10nm or more at half-width, the single wavelength property is poor, and the wavelength changes depending on temperature. Therefore, it is preferably used by passing through a band-pass filter.

When the light source 15 is an LED and is configured to pass through a band-pass filter, the single wavelength is not as good as that of an Na lamp or a mercury lamp, but it is preferable to use any wavelength from the ultraviolet region to the infrared region. Since the wavelength of the light source 15 does not affect the basic principle of the measurement by the evaluation device 2, a light source other than the above-described exemplary wavelengths may be used.

However, by using a light source for irradiating ultraviolet rays as the light source 15, the resolution of measurement can be improved. That is, since the surface layer of the tempered glass 200 measured by the evaluation device 2 has a thickness of about several μm, an appropriate number of interference fringes can be obtained by using a light source for irradiating ultraviolet rays as the light source 15, and the resolution is improved. On the other hand, when a light source that irradiates light having a longer wavelength than ultraviolet rays is used as the light source 15, the number of interference fringes decreases, and thus the resolution decreases.

The light supplying member 25 and the light extracting member 35 are placed in optical contact with the front surface 210 of the tempered glass 200 as the measurement object. The light supply member 25 has a function of allowing light from the light source 15 to enter the tempered glass 200. The light extraction member 35 has a function of emitting light propagating through the surface layer of the tempered glass 200 to the outside of the tempered glass 200.

As the light supplying member 25 and the light extracting member 35, for example, a prism made of optical glass can be used. In this case, in order to optically enter and exit light through these prisms in the surface 210 of the tempered glass 200, the refractive index of these prisms needs to be larger than the refractive index of the tempered glass 200. In addition, it is necessary to select a refractive index at which incident light and outgoing light pass substantially perpendicularly on the inclined surface of each prism.

For example, when the tilt angle of the prism is 60 ° and the refractive index of the tempered glass 200 is 1.52, the refractive index of the prism is, for example, 1.72. Note that, instead of the prism, another member having the same function may be used as the light supplying member 25 and the light extracting member 35. The light supply member 25 and the light extraction member 35 may be formed integrally. In order to stably perform optical contact, a liquid (may be in a gel state) having a refractive index between the refractive indices of the light supply member 25 and the light extraction member 35 and the refractive index of the tempered glass 200 may be filled between the light supply member 25 and the light extraction member 35 and the tempered glass 200.

The image pickup device 65 is disposed in the direction of the light emitted from the light extraction member 35, and the light conversion member 45 and the polarization member 55 are interposed between the light extraction member 35 and the image pickup device 65.

The light conversion member 45 has a function of converting the light emitted from the light extraction member 35 into a bright line and condensing the bright line on the image sensor 65. As the light conversion member 45, for example, a convex lens may be used, but another member having the same function may be used.

The polarizing member 55 is a light separating means having a function of selectively transmitting one of two light components vibrating parallel and perpendicular to the interface between the tempered glass 200 and the light extraction member 35. As the polarizing member 55, for example, a polarizing plate or the like disposed in a rotatable state may be used, but other members having the same function may be used. Here, the light component vibrating parallel to the interface between the tempered glass 200 and the light extraction member 35 is S-polarized light, and the light component vibrating vertically is P-polarized light.

The interface between the tempered glass 200 and the light extraction member 35 is perpendicular to the light exit surface of the light emitted to the outside of the tempered glass 200 through the light extraction member 35. Therefore, the light component that oscillates perpendicularly to the exit surface of the light emitted to the outside of the tempered glass 200 through the light extraction member 35 may be referred to as S-polarized light instead, and the light component that oscillates in parallel may be referred to as P-polarized light instead.

The image pickup device 65 has a function of converting light emitted from the light extraction member 35 and received through the light conversion member 45 and the polarization member 55 into an electric signal. As the imaging element 65, for example, the same element as the imaging element 60 can be used.

The arithmetic unit 75 has a function of acquiring image data from the imaging device 65 and performing image processing or numerical calculation. The calculation unit 75 may have other functions (for example, a function of controlling the light amount of the light source 15 or the exposure time). The operation unit 75 includes, for example, a cpu (central Processing unit), a rom (read Only memory), a ram (random Access memory), a main memory, and the like.

In this case, various functions of the arithmetic unit 75 can be realized by reading a program recorded in the ROM or the like into the main memory and executing the program by the CPU. The CPU of the arithmetic unit 75 can read and store data from the RAM as necessary. However, a part or all of the arithmetic unit 75 may be realized by hardware only. The arithmetic unit 75 may also physically include a plurality of devices. As the arithmetic unit 75, for example, a personal computer can be used.

In the evaluation apparatus 2, the light La incident from the light source 15 to the surface layer of the tempered glass 200 through the light supplying member 25 propagates in the surface layer. When the light La propagates through the surface layer, a mode is generated by the optical waveguide effect, and the light La travels through a plurality of determined paths and is extracted from the light extraction member 35 to the outside of the tempered glass 200.

Then, the light is converted into bright lines of P-polarized light and S-polarized light for each mode by the light conversion means 45 and the polarizing means 55, and the bright lines are imaged on the imaging element 65. The image data of the bright lines of P-polarized light and S-polarized light of the number of patterns generated in the image pickup device 65 is transmitted to the arithmetic unit 75. The arithmetic unit 75 calculates the positions of the bright lines of the P-polarized light and the S-polarized light on the image sensor 65 based on the image data transmitted from the image sensor 65.

With such a configuration, in the evaluation device 2, the refractive index distributions of the P-polarized light and the S-polarized light in the depth direction from the surface of the surface layer of the tempered glass 200 can be calculated based on the positions of the bright lines of the P-polarized light and the S-polarized light. Then, based on the calculated difference in refractive index distribution between the P-polarized light and the S-polarized light and the photoelastic constant of the tempered glass 200, the stress distribution in the depth direction from the surface of the surface layer of the tempered glass 200 can be calculated.

In this way, the evaluation apparatus 2 is an evaluation apparatus capable of measuring the stress distribution by the waveguide light of the surface layer of the tempered glass. Here, the waveguide light on the glass surface is generated in a layer having a lower refractive index of the tempered glass 200 as the distance from the surface is deeper. Waveguide light is not generated in the layer whose refractive index increases with the deepening. For example, in a lithium aluminosilicate glass, the refractive index decreases with depth only in the vicinity of the outermost surface of the glass, but from a certain depth, the refractive index increases with depth. In the case of such a tempered glass, waveguide light is generated only in the outermost layer where the refractive index decreases with increasing depth, and the stress distribution can be measured up to the depth at which the refractive index distribution is inverted.

On the other hand, in the scattered light image shown in fig. 9 of first embodiment 1, point a in fig. 9 is the glass surface, and the surface scattered light spreads strongly to the surroundings. The extended surface scattered light reflects the information of the surface points. Although accurate information is obtained at the surface point a, for example, the scattered light of the laser light L in a portion of the glass slightly deeper than the surface point a is in a state where the scattered light reflecting the stress at the surface point a is mixed with the scattered light originally reflecting the stress of the glass at the point, and it is difficult to accurately measure the stress at a portion where the surface scattered light overlaps.

The depth of the portion where the surface scattered light overlaps varies depending on the properties of the glass and the surface state of the glass, but is usually about 10 μm. In a tempered glass having a deep strengthened layer, a low surface stress value in which a change in stress in the depth direction is gradual, or a deep strengthened layer, in the vicinity of the outermost surface, for example, in a surface region having a depth of about 10 μm, even if the depth is within 10 μm, which cannot be accurately measured, the distribution of stress at a portion deeper than the depth can be extrapolated to the glass surface to estimate an accurate stress.

However, in the tempered glass in which the stress distribution of the tempered glass 200 is in the vicinity of the outermost surface, for example, the stress sharply increases between the surface of the tempered glass 200 and the depth of 10 μm, a large error occurs in the estimated value Hi based on the extrapolated stress value in the vicinity of the outermost surface. In particular, the error of the stress value of the outermost surface is large. However, the stress distribution can be accurately measured as an absolute value outside the region where the surface scattered light interferes.

By adding the stress value of the outermost surface, the stress value of the stress distribution in the vicinity of the outermost surface measured by the evaluation device 2, or the stress distribution to the stress distribution at a portion sufficiently deep from the outermost surface, which is not disturbed by the surface scattered light, in the stress distribution measured by the evaluation device 1, the entire stress distribution can be measured with high accuracy.

Even when a sufficiently reliable depth region of the evaluation device 1 is not continuous with a measurable depth region of the evaluation device 2, the stress of the discontinuous region can be accurately estimated by performing an approximate calculation by the least squares method using a stress distribution function that is theoretically expected in the tempered glass.

Fig. 24 is a graph showing the stress distributions measured by the evaluation devices 1 and 2 in the same graph. More specifically, a stress distribution (region a) in the vicinity of the outermost surface measured by the evaluation device 2 and a stress distribution (region C) in a sufficiently reliable region measured by the evaluation device 1 are represented in the same graph for a tempered glass having a stress distribution that is chemically strengthened in two stages, such as a region having a sharp change in the slope of stress at a depth of about 10 μm from the surface.

In the example of fig. 24, there is a region B that is not measured by either the evaluation device 1 or the evaluation device 2. Based on the stress distributions in the regions a and C, a curve obtained by the least squares method using a function of an expected stress distribution in the region B is represented by a dotted line. In this case, even if the actual data of the region including the bending point does not exist, the bending point position can be estimated from the curve obtained by the least squares method.

(procedure of measurement)

Next, the flow of measurement will be described with reference to fig. 25 and 26. Fig. 25 is a flowchart illustrating an evaluation method using the evaluation apparatus 2. Fig. 26 is a diagram illustrating functional blocks of the arithmetic unit 75 of the evaluation device 2.

First, in step S407, light from the light source 15 is made incident into the surface layer of the tempered glass 200 (light supply step). Next, in step S408, the light propagating through the surface layer of the tempered glass 200 is emitted to the outside of the tempered glass 200 (light extraction step).

Next, in step S409, the light conversion member 45 and the polarizing member 55 convert two kinds of light components (P-polarized light and S-polarized light) of the emitted light, which vibrate parallel to and perpendicular to the emission surface, into two kinds of bright line arrays each having at least two bright lines (light conversion step).

Next, in step S410, the imaging element 65 images the two kinds of bright line sequences converted by the light conversion process (an imaging process). Next, in step S411, the position measurement unit 751 of the arithmetic unit 75 measures the position of each of the two bright lines from the image obtained in the imaging step (position measurement step).

Next, in step S412, the stress distribution calculating means 752 of the calculating unit 75 calculates the refractive index distribution in the depth direction from the surface of the tempered glass 200 corresponding to the two light components, based on the positions of at least two or more bright lines in each of the two bright line rows. Then, the stress distribution in the depth direction from the surface of the tempered glass 200 is calculated based on the difference between the refractive index distributions of the two optical components and the photoelastic constant of the glass (stress distribution calculating step).

Next, in step S413, the synthesizing unit 753 of the arithmetic unit 75 synthesizes the stress distribution calculated in step S412 with the stress distribution calculated by the stress distribution calculating unit 703 of the arithmetic unit 70 of the evaluation device 1.

When the sufficiently reliable depth region of the evaluation device 1 is not continuous with the depth region that can be measured by the evaluation device 2, the synthesizing means 753 of the computing unit 75 calculates the stress distribution of the region B by the least squares method or the like based on the stress distribution of the region a calculated by the stress distribution calculating means 752 of the computing unit 75 of the evaluation device 2 and the stress distribution of the region C calculated by the stress distribution calculating means 703 of the computing unit 70 of the evaluation device 1, as shown in fig. 24, for example.

In addition to the configuration of fig. 26, the calculation unit 75 may include a CT value calculation unit that calculates a CT value, a DOL _ Zero value calculation unit that calculates a DOL _ Zero value, and the like. In this case, the CT value and DOL _ Zero value can be calculated based on the stress distribution calculated by the synthesizing unit 753.

Next, an example of deriving each characteristic value of the stress distribution will be described. Fig. 27 is a diagram illustrating a stress distribution in the depth direction of the tempered glass. In fig. 27, CS2 is the outermost stress value, CS _ TP is the stress value at the position where the stress distribution is bent, CT is the stress value at the deepest portion of the glass, DOL _ TP is the glass depth at the position where the stress distribution is bent, DOL _ zero is the glass depth at which the stress value becomes 0, and DOL _ tail is the glass depth at which the stress value becomes the same value as CT.

As shown in fig. 28, the stress distribution is measured in step S501, and the characteristic value can be derived based on the stress distribution measured in step S501 in step S502. This will be described in more detail below.

Fig. 29 shows an example in which each characteristic value is derived from the measured stress distribution. For example, in step S601 in fig. 30, the entire distribution of the stress distribution (entire solid line shown in fig. 29) is measured by the evaluation device 1. Then, each characteristic value is derived in step S604.

In step S604, each characteristic value is derived as follows, for example. That is, as shown in fig. 29, two line segments, i.e., a line segment passing through CS2 and a line segment passing through DOL _ zero, are considered. When the difference between the two line segments and the measured stress distribution becomes minimum, the intersection point of the two line segments is CS _ TP and DOL _ TP. Then, the intersection of the line segment passing through DOL _ zero and CT is DOL _ tail.

This method can be applied to, for example, a lithium aluminosilicate-based tempered glass, a tempered glass that has been chemically tempered once with a mixed salt of sodium nitrate and potassium nitrate, a tempered glass that has been chemically tempered with a molten salt containing sodium nitrate and a molten salt containing potassium nitrate each used once or more, a tempered glass that has been both air-cooled tempered and chemically tempered, and the like.

Fig. 31 shows another example in which each characteristic value is derived from the measured stress distribution. For example, in step S601 in fig. 32, the entire distribution of the stress distribution is measured by the evaluation device 1. Next, in step S602, the evaluation device 2 measures the glass surface layer side with respect to DOL _ TP. It is difficult to measure the depth side of DOL _ TP by the evaluation device 2. Step S601 is in a different order from step S602.

Next, in step S603, the portion measured in step S602 is combined with the portion measured in step S601 on the deeper side than the portion measured in step S602. This makes it possible to obtain the stress distribution shown in fig. 31. Then, for example, each characteristic value can be derived in the same manner as step S604 of fig. 30.

Alternatively, in step S602, DOL _ zero and CT are measured in step S601, as described above. Then, in step S603, as shown in fig. 33, a straight line passing through DOL _ zero obtained in step S601 may be drawn from the intersection of CS _ TP and DOL _ TP obtained in step S602, and the stress distribution may be set to CT.

The quality can be determined by using the characteristic values obtained by measuring the stress distribution. Fig. 34 is an example of a flowchart of quality determination using characteristic values obtained by measurement of stress distribution. In fig. 34, first, steps S601 to S603 are executed as in fig. 32. Next, in step S604, six characteristic values (hereinafter, may be referred to as only six measurement values) of CS2, CS _ TP, CT, DOL _ TP, DOL _ zero, and DOL _ tail are derived based on the data obtained in steps S601 and S602. Next, in step S605, it is determined whether the six characteristic values derived in step S604 fall within the allowable range determined by the prior requirement specification. In this method, two measurements in steps S601 and S602 are necessary for one quality determination.

Fig. 35 is another example of a flowchart of quality determination using characteristic values obtained by measurement of stress distribution. In fig. 35(a), first, preliminary data is acquired in step S600. Specifically, for example, for a predetermined number of batches, 6 characteristic values are derived using the evaluation devices 1 and 2. Then, an allowable range of the characteristic value is determined based on the required specification of the product and the derived characteristic value.

Next, in step S601, the evaluation apparatus 1 measures the glass depth side from DOL _ TP. Then, in step S604, six characteristic values are derived again based on the data of the evaluation device 2 in step S600 and the data of the evaluation device 1 in step S601.

Next, in step S605, it is determined whether or not the six characteristic values measured in step S604 have entered the allowable range determined in step S600. In this method, only one measurement in step S601 is required for one quality determination, in addition to the number of measurements in the preliminary step. This can simplify the quality control flow as compared with the case of fig. 34.

Note that the plate thickness is also measured in the preliminary data of fig. 35(a), and by measuring the plate thickness also in step S601, the characteristic value can be derived in step S604 including the effect of the difference in plate thickness.

Alternatively, the same may be applied as shown in fig. 35 (b). In fig. 35(b), as in fig. 35(a), first, in step S600, preliminary data is acquired, and an allowable range of the characteristic value is determined.

Next, in step S602, the evaluation device 2 measures the glass surface layer side with respect to DOL _ TP. Then, in step S604, six characteristic values are derived again based on the data of the evaluation device 1 in step S600 and the data of the evaluation device 2 in step S602.

Next, in step S605, it is determined whether or not the six characteristic values measured in step S604 have entered the allowable range determined in step S600. In this method, only one measurement in step S602 is required for one quality determination, in addition to the number of measurements in the preliminary step. In this case as well, the quality control flow can be simplified as compared with the case of fig. 34, as in fig. 35 (a).

Note that the plate thickness is also measured in the preliminary data of fig. 35(b), and by measuring the plate thickness also in step S602, the characteristic value can be derived in step S604 including the effect of the difference in plate thickness.

Fig. 36 is an example of a flowchart of quality judgment when lithium-containing glass (glass containing 2 wt% or more of lithium) such as lithium aluminosilicate-based tempered glass is tempered twice or more. In fig. 36, whether or not the strengthened glass of the strengthening process other than the final strengthening process is acceptable is determined based on the measurement result of the evaluation device 1, and whether or not the strengthened glass of the final strengthening process is acceptable is determined based on the measurement result of the evaluation device 2.

Specifically, first, the first chemical strengthening is performed in step S650. Then, in step S651, the evaluation apparatus 1 measures a stress distribution on the glass depth side of DOL _ TP (hereinafter, may be referred to as a first stress distribution). If there is a problem (in the case of a failure) in the measurement result in step S651, the tempered glass is not shipped. On the other hand, if there is no problem in the measurement result in step S651 (in the case of passing), the process proceeds to step S652, and a second chemical strengthening is performed. The determination of whether or not the test is acceptable (determination of acceptable/unacceptable) in step S651 may be performed based on all or a part of the six characteristic values (for example, CT and DOL _ zero) derived from the measurement result of the evaluation apparatus 1.

Next, in step S653, the stress distribution on the glass surface layer side of DOL _ TP (hereinafter, may be referred to as a second stress distribution) is measured by the evaluation apparatus 2. If there is a problem (in the case of failure) in the measurement result in step S653, the tempered glass is not shipped. On the other hand, if there is no problem (if it is acceptable) in the measurement result in step S653, the process proceeds to the next step in step S654. A specific method of the non-qualification determination (non-qualification determination) in step S653 will be described later.

As the next step, for example, a contact polishing step can be cited. The contact polishing step is a finish polishing step of polishing the surface of the tempered glass 200 with a relatively low surface pressure, for example. However, the contact polishing step is not necessarily provided, and step S653 may be a final step.

After step S653, chemical strengthening and a pass/fail determination may be performed for the third time. In this case, in step S653, the strengthened glass for the second strengthening is determined to be acceptable based on the measurement result of the evaluation apparatus 1 in the same manner as in step S651, and the strengthened glass for the third strengthening (final strengthening) is determined to be acceptable based on the measurement result of the evaluation apparatus 2.

Similarly, when the number of times of strengthening is further increased, whether or not the strengthened glass of strengthening other than the final strengthening is acceptable is determined based on the measurement result of the evaluation device 1, and whether or not the strengthened glass of strengthening of the final strengthening is acceptable is determined based on the measurement result of the evaluation device 2. This can shorten the evaluation time while maintaining the measurement reproducibility.

Here, a specific method of the non-qualification determination (non-qualification determination) in step S653 will be described.

(data derivation for evaluation)

First, data for evaluation is derived in advance. Specifically, as shown in fig. 37, in step S660, the first chemical strengthening is performed. Then, in step S661, the evaluation apparatus 1 measures the glass depth side from DOL _ TP (first measurement). Next, in step S662, chemical strengthening is performed for the second time. Then, in step S663, the evaluation apparatus 1 measures the glass depth side from DOL _ TP (second measurement). Then, in step S664, evaluation data (first stress distribution) is derived based on one or both of the first measurement result obtained in step S661 and the second measurement result obtained in step S663.

The evaluation data derivation is performed only by using a predetermined number for one batch. The first chemical strengthening and the second chemical strengthening in the derivation of the evaluation data are performed under the same conditions as the first chemical strengthening and the second chemical strengthening in mass production.

(method of judging acceptability in step S653)

First, based on the measurement result obtained in step S653, the sheet thickness t of the glass that is chemically strengthened, and the evaluation data obtained as shown in fig. 37, the stress distribution on the glass surface layer side from DOL _ TP (second stress distribution) and the stress distribution on the glass depth layer side from DOL _ TP (first stress distribution) are synthesized. For example, the results shown in fig. 38 were obtained.

In fig. 38, FSM indicated by a solid line indicates a stress distribution (second stress distribution) on the glass surface layer side from DOL _ TP, and SLP indicated by a broken line indicates a stress distribution (first stress distribution) on the glass deep layer side from DOL _ TP. Further, t/2 represents the center of the thickness of the glass. And, CS₀The first stress distribution (SLP) indicates a stress value of the surface when the surface side of the tempered glass is extended.

Next, each characteristic value is derived by finding CT from the synthesized stress distribution, and whether or not each characteristic value is within an allowable range is determined (shipment determination).

At this time, the second stress profile (FSM of fig. 38) may also be functionally approximated. As an example of the function approximation, a case of performing a straight line approximation by the following expression 2 (expression 2) can be cited.

[ mathematical formula 2 ]

σ_f(x)＝a·x+CS2…(2)

In equation 2, σ f (x) is the second stress distribution, a is the slope, and CS2 is the most superficial stress value.

As another example of the function approximation, a curve approximation may be performed by the following expression 3 (expression 3).

[ mathematical formula 3 ]

σ_f(x)＝CS2·erfc(a·x)…(3)

In equation 3, σ f (x) is the second stress distribution, a is the slope, CS2 is the stress value of the outermost surface, and erfc is the error function shown in equation 4 (equation 4).

[ mathematical formula 4 ]

As another example of the function approximation, polynomial approximation may be performed.

In addition, the first stress distribution (SLP of fig. 38) may be shifted in the up-down direction of fig. 38 (stress value axial direction). Specifically, for example, in the synthesized stress distribution shown in fig. 38, the first stress distribution (SLP) is moved in the stress value axial direction, and each characteristic value is derived by finding a CT in which the integral value of the synthesized stress distribution becomes 0. Then, whether or not the characteristic values are within the allowable range can be determined (shipment determination). In this case, the amount of vertical movement of the first stress distribution may be calculated by a theoretical equation based on the sheet thickness of the glass and the second stress distribution, or the amount of movement may be assumed, an integrated value of the synthesized stress distribution may be calculated, and a movement amount at which the integrated value becomes 0 may be found.

The synthesized stress distribution σ (x) is approximated by the following equation 5 (equation 5), and each characteristic value is derived by finding a CT in which the integral value (x is 0 to t/2: t is the thickness of the glass) of σ (x) becomes 0. Then, the acceptance determination (shipment determination) may be performed based on whether or not each characteristic value enters the allowable range.

[ math figure 5 ]

In formula 5, σ (x) is the stress distribution after synthesis, σ f (x) is the second stress distribution, t is the thickness of the strengthened glass, and CS is₀And c is a parameter derived based on the first stress distribution.

In formula 5, t is known. And, CS₀And c can be obtained from the measurement result of the evaluation device 1 in the derivation of the evaluation data.

CS₀And c can also be derived from simulations based on the intensification conditions.

Or, CS₀And c can also be derived from the measurement result of the evaluation device 1 for the tempered glass relating to the last strengthening in mass production₀'and c' and the following formulas 6 (formula 6) and 7 (formula 7).

[ mathematical formula 6 ]

CS₀＝A1×CS₀′…(6)

In equation 6, a1 is a proportionality constant.

[ mathematical formula 7 ]

c＝A2×c′…(7)

In equation 7, a2 is a proportionality constant.

Here, a1 and a2 may be obtained from the measurement results of the evaluation device 1 in the derivation of the evaluation data, or may be obtained by simulation.

The approximation of σ (x) is not limited to expression 5, and may be a polynomial approximation, for example.

[ examples ]

In example 1, the method described with reference to fig. 34 was used to derive CS _ tp (mpa), which is a characteristic value of stress distribution of a tempered glass that was chemically tempered twice, three times for the same sample, and the evaluation time and measurement reproducibility were examined.

In example 2, the method described with reference to fig. 36 to 38 was used to derive CS _ tp (mpa), which is a characteristic value of stress distribution of the tempered glass that was chemically tempered twice, three times for the same sample, and the evaluation time and the measurement reproducibility were examined. Specifically, based on the measurement result obtained in step S653 in fig. 36, the sheet thickness t of the glass that is chemically strengthened, and the evaluation data obtained as shown in fig. 37, when the second stress distribution (FSM) is combined with the first stress distribution (SLP), the first stress distribution (SLP) is moved in the axial direction of the stress value, and CT in which the integrated value of the combined stress distribution becomes 0 is found, and CS _ TP is derived.

In example 3, the method described with reference to fig. 36 to 38 was used to derive CS _ tp (mpa), which is a characteristic value of stress distribution of the tempered glass that was chemically tempered twice, three times for the same sample, and the evaluation time and the measurement reproducibility were examined. Specifically, when the second stress distribution (FSM) is synthesized with the first stress distribution (SLP) based on the measurement result obtained in step S653 in fig. 36, the chemically strengthened glass sheet thickness t and the evaluation data obtained as shown in fig. 37, the synthesized stress distribution σ (x) is approximated by equation 5, and CT in which the integral value (x is 0 to t/2: t is the glass sheet thickness) of σ (x) becomes 0 is found to derive CS _ TP.

As comparative example 1, the characteristic value of stress distribution of the tempered glass chemically strengthened twice, namely CS _ tp (mpa), was derived three times for the same sample by the method described in patent document 4, and the evaluation time (minutes) and the measurement reproducibility (difference between the maximum value and the minimum value) were examined.

The stress distributions obtained in comparative example 1 and examples 1 to 3 are shown in fig. 39, and the results are summarized in table 2. In fig. 39, the stress value at the position where the stress distribution is bent is CS _ TP.

[ TABLE 2 ]

According to table 2, in comparative example 1, the values of CS _ TP were derived three times for each variation of the same sample, and the reproducibility of the measurement was poor. In contrast, in examples 1 to 3, the variation in the CS _ TP value derived three times for the same sample was small, and the measurement reproducibility was greatly improved compared to comparative example 1. In particular, in examples 2 and 3, the measurement reproducibility was excellent. It was confirmed that the evaluation time in example 1 was long, but the evaluation time was short and the measurement reproducibility was excellent in examples 2 and 3 because the number of measurements by the evaluation device 1 was reduced.

< third embodiment >

In the third embodiment, an example is shown in which a liquid is interposed between the light supply member and the tempered glass. In the third embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 40 is a diagram illustrating an evaluation apparatus of a third embodiment, and shows a cross section in the vicinity of an interface between a light-emitting member and a tempered glass.

As shown in fig. 40, in the present embodiment, a liquid 90 having a refractive index substantially the same as that of the tempered glass 200 is sandwiched between the light supplying member 40 and the tempered glass 200. This is because the refractive index of the tempered glass 200 slightly differs depending on the type of tempered glass, and therefore, in order to completely match the refractive index of the light supplying member 40, the light supplying member 40 needs to be replaced according to the type of tempered glass. However, since the exchange work is not efficient, the laser light L can be efficiently incident into the tempered glass 200 by sandwiching the liquid 90 having a refractive index substantially equal to that of the tempered glass 200 between the light supplying member 40 and the tempered glass 200.

As the liquid 90, for example, a mixed liquid of 1-bromonaphthalene (n ═ 1.64) and xylene (n ═ 1.50) can be used. As the liquid 90, a mixed liquid of a plurality of silicone oils having different structures may be used. For example, dimethylsilicone oil (n ═ 1.38 to 1.41) or phenylmethylsilicone oil (n ═ 1.43 to 1.57) can adjust the refractive index by changing the chain length of the methyl group or phenyl group. A mixture of a plurality of silicone oils whose refractive indices have been adjusted in this manner may be used as the liquid 90. Since the refractive index of the liquid 90 is determined by the respective mixing ratios, the refractive index can be easily the same as that of the tempered glass 200.

In this case, the difference in refractive index between the tempered glass 200 and the liquid 90 is preferably ± 0.03 or less, more preferably ± 0.02 or less, and still more preferably ± 0.01 or less. In the absence of the liquid 90, scattered light is generated between the tempered glass 200 and the light supplying member, and data cannot be acquired within a range of about 20 μm.

When the thickness of the liquid 90 is 10 μm or more, the scattered light is suppressed to about 10 μm or less, and therefore, it is preferably 10 μm or more. In principle, the thickness of the liquid 90 may be arbitrary, but is preferably set to 500 μm or less in consideration of handling of the liquid.

Fig. 41 is a diagram illustrating a scattered light image of the laser light L advancing at the interface between the light supplying member 40 and the tempered glass 200. In fig. 41, point a is surface scattering light of the tempered glass, and point D is surface scattering light of the surface of the light supplying member 40. Between points a and D is scattered light from the liquid 90.

When the thickness of the liquid 90 is thin, the point a and the point D become substantially the same point, and surface scattering light is generated by surface scattering of the tempered glass 200 and surface scattering of the light supply member 40. When a large amount of the tempered glass 200 is measured, the light supplying member 40 causes a large amount of damage on the surface. In this case, very large surface scattered light is generated.

However, as shown in fig. 41, by securing the space between the light supply member 40 and the tempered glass 200 by sandwiching the liquid 90, it is possible to prevent the surface scattered light of the light supply member 40 from overlapping with the surface scattered light in the vicinity of the outermost layer of the tempered glass 200.

Fig. 42 is a diagram illustrating a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 42(a), a recess 40x of 10 μm or more is formed on the surface of the light supplying member 40 by polishing or etching, and the liquid 90 is filled in the recess 40x, whereby the thickness of the liquid 90 can be stably set to 10 μm or more. The depth of the recess 40x may be arbitrary in principle, but is preferably 500 μm or less in view of ease of processing.

Instead of forming the recess 40x on the surface of the light supply member 40, a pad member 100 having a thickness of 10 μm or more may be formed on the surface of the light supply member 40 by a thin film forming technique such as vacuum deposition or sputtering as shown in fig. 42(b) using a metal, an oxide, a resin, or the like, and a pad of the liquid 90 held by the pad member 100 may be formed. By holding the liquid 90 by the pad member 100, the thickness of the liquid 90 can be stably set to 10 μm or more. The thickness of the pad member 100 is arbitrary in principle, but is preferably 500 μm or less in view of ease of processing.

< modification of the third embodiment >

In a modification of the third embodiment, an example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200 is shown, which is different from fig. 42. In a modification of the third embodiment, description of the same components as those of the above-described embodiment may be omitted.

Fig. 43 is a diagram showing a second example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 43, the bottom of the recess 40x formed in the surface of the light supplying member 40 may also be uneven. The concave portion 40x is, for example, a spherical concave portion similar to the concave lens.

The depth of the recess 40x is, for example, 10 μm or more and 500 μm or less. For example, when the depth of the recess is 50 μm and the diameter around the recess is 10mm, the radius of curvature R is 200 mm.

The concave portion 40x can be easily formed as a spherical concave portion by the same manufacturing method as the concave lens. Since the liquid 90 filled in the concave 40x has the same refractive index as that of the light supply member 40, the lens effect of the liquid 90 in the spherical concave is eliminated, and the trajectory of the laser light or the image of the camera for capturing scattered light is not affected.

Fig. 44 is a diagram showing a third example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 44, a plano-concave lens 43 as a protrusion is attached to the surface of the light supply member 40 on the tempered glass 200 side. The plano-concave lens 43 is in contact with the tempered glass 200.

The plano-concave lens 43 forms a part of the optical path of the laser light entering the tempered glass 200 through the light supplying member 40. The plano-concave lens 43 has, for example, a spherical concave portion 43 x. The depth of the recess 43x is, for example, 10 μm or more and 500 μm or less.

The light supply member 40 and the plano-concave lens 43 are formed separately from each other and are bonded to each other by an optical adhesive material having substantially the same refractive index as the light supply member 40 and the plano-concave lens 43.

Since the optical adhesive material for bonding the light supply member 40 and the plano-concave lens 43 is exposed to laser light for a long time, an adhesive having high durability is preferably used.

In particular, when the wavelength of the light source is short and ultraviolet rays or near ultraviolet rays are used, for example, at a wavelength of 500nm or less, since the deterioration of the optical adhesive material is significant, it is preferable to use an inorganic adhesive or a low melting point glass as the optical adhesive material for bonding the light supply member 40 and the plano-concave lens 43. Alternatively, the light supplying member 40 and the plano-concave lens 43 are preferably bonded by optical contact or the like without using an adhesive.

In the processing of general optical elements, a prism forming process using only a flat surface is different from a lens forming process using a spherical surface, and it is difficult to form a prism having a spherical depression, and thus many processes are required, which results in poor productivity and extremely high manufacturing cost. That is, it is difficult to form the light supply member 40 as a prism and the plano-concave lens 43 as an integral structure.

However, the light supply member 40 as a prism and the plano-concave lens 43 can be easily formed by respective processing techniques. A glass plate having substantially the same refractive index as the light supplying member 40 and the plano-concave lens 43 may be inserted between the light supplying member 40 and the plano-concave lens 43. The glass plate can be used for attaching the light supply member 40 to the evaluation apparatus main body.

In this case, when the wavelength of the light source is short and ultraviolet rays or near ultraviolet rays are used as the optical adhesive material for bonding the light supply member 40 to the glass plate and the optical adhesive material for bonding the glass plate to the plano-concave lens 43, it is preferable to use an inorganic adhesive or a glass with a low melting point. Alternatively, the light supplying member 40 and the glass plate, and the glass plate and the plano-concave lens 43 are preferably bonded by optical contact or the like without using an adhesive.

Fig. 45 is a diagram showing a fourth example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 45, a flat outer edge portion 43e may be formed around the plano-concave lens 43. In the structure shown in fig. 45, since the flat outer edge portion 43e is a surface that contacts the tempered glass 200, the tempered glass 200 can be parallel to the light supply member 40 with high accuracy when being brought into contact with the light supply member, and damage to the tempered glass 200, such as damage, can be eliminated.

Fig. 46 is a diagram showing a fifth example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 46, the light supply member 40 and the plano-concave lens 43 may be fixed from the outer peripheral side surface so as to be prevented from moving by a detachable support 44, without being fixed by an optical adhesive material, with a liquid having the same refractive index as the liquid 90 interposed therebetween.

By configuring the support body 44 to be openable and closable using a spring or the like, only the plano-concave lens 43 can be easily replaced. For example, when the plano-concave lens 43 is damaged or scratched due to contact with the tempered glass 200 or the like, or when the plano-concave lens 43 having a recess is changed to another shape, a plurality of the plano-concave lenses 43 may be manufactured and replaced.

The support 44 may have any shape or structure as long as the plano-concave lens 43 can be held in a replaceable manner.

Fig. 47 is a diagram showing a sixth example of a structural portion for sandwiching the liquid 90 between the light supply member 40 and the tempered glass 200. As shown in fig. 47, a groove 43y for discharging the liquid 90 may be formed in the flat outer edge portion 43e formed around the plano-concave lens 43. The groove 43y communicates with the recess 43 x.

When the tempered glass 200 is placed by dropping the liquid 90 into the recess 43x, air bubbles may remain in the recess 43 x. By providing the groove 43y for discharging the liquid 90 around the depression 43x, when the tempered glass 200 is placed by dropping the liquid 90 into the depression 43x, bubbles are discharged from the groove 43y together with the liquid 90, and therefore, it is possible to make it difficult for bubbles to remain in the depression 43 x.

As shown in fig. 48, a groove 40y communicating with the recess 43x may be formed on the surface of the light supplying member 40 on the side contacting the tempered glass 200. Similarly to the case of fig. 47, by providing the groove 40y for discharging the liquid 90 around the depression 40x, when the liquid 90 is dropped into the depression 40x and the tempered glass 200 is placed, air bubbles are discharged from the groove 40y together with the liquid 90, and therefore, it is possible to make it difficult for air bubbles to remain in the depression 40 x.

In fig. 43 to 48, the intersecting curved lines drawn in the depressions 40x or 43x and the vertical lines drawn on the side surfaces of the plano-concave lenses 43 are lines drawn for the convenience of viewing the drawings, and do not represent lines (fine grooves, projections, and the like) that actually exist.

Although the dimples 40x and 43x have been described as spherical dimples, the dimples 40x and 43x are not limited to spherical dimples, and may be surfaces having curved portions. The depressions 40x and 43x may be aspheric depressions, for example. The shape and number of the grooves 40y or 43y can be set arbitrarily.

< fourth embodiment >

In the fourth embodiment, an example of an evaluation method considering the refractive index of the tempered glass is shown. In the fourth embodiment, description of the same components as those of the previously described embodiments may be omitted.

When the photoelastic constant of the tempered glass is C and the residual angle of incidence (refraction angle) which is the angle formed by the laser beam and the surface 210 of the tempered glass 200 is Ψ, the equation for obtaining the stress St from the polarization phase difference Rt at the depth D of the laser beam is as shown in the following equation 8 (equation 8).

[ mathematical formula 8 ]

In equation 8, the term of the last Ψ is a correction of the contribution amount of the stress to the birefringent laser light. That is, the internal stress generated by the strengthening of the strengthened glass 200 is parallel to the surface 210, and one laser beam is obliquely incident on the surface 210. Therefore, correction of the amount of contribution of stress to the birefringent laser light is required, and the term of the last Ψ of equation 8 becomes a correction amount. Although St is used in this formula, the coordinate system of the stress distribution is different from that of formula 1, and therefore, for the sake of simplicity, a separate symbol is used.

Fig. 49 is a diagram illustrating a case where the laser light L is incident into the tempered glass 200. In fig. 49, the surface of the tempered glass 200 is in contact with the upper surface of the light supplying member 40, and is located at xyz coordinates where the upper surface of the light supplying member 40 and the surface of the tempered glass 200 in contact with the upper surface of the light supplying member 40 are the XZ plane. The laser light L is incident on the incident end surface of the light supplying member 40, and passes through the boundary between the upper surface of the light supplying member 40 and the surface of the tempered glass 200 to be incident into the tempered glass 200. The imaging element 60 images the laser light trajectory (trajectory of the laser light L) from below at an inclination of 45 °.

Fig. 50 is a diagram illustrating an image of a laser trace captured from the position of the imaging element 60 in fig. 49. Let Cpass be the laser track on the image captured by the imaging element 60, Pc be the length, χ be the angle on the image of the laser track, Lx be the lateral distance on the image, and V be the longitudinal distance on the image. In the evaluation apparatus 1, the stress in the tempered glass 200 is finally measured by performing image analysis from an image of the laser light L (precisely, scattered light from the laser light L) from the imaging device 60.

However, the image taken by the imaging element 60 is an image from below at an angle of 45 °, so the length Pc of the laser trajectory Cpass on the image is not limited to be the same as the actual length of the laser light L, and the angle χ on the image is not the actual residual angle Ψ. Therefore, in order to obtain the stress from the image of the laser beam L using equation 8, it is necessary to obtain a conversion equation of the actual distance P and the residual angle of incidence Ψ of the laser beam L.

Fig. 51 is a diagram illustrating definitions of angles and lengths of laser beams in the light supplying member 40 and the tempered glass 200 of fig. 49. Here, a rectangular parallelepiped having an apex of abcdefgh can be considered. Let the length of the side bf be Lx, the length of the side ab be H, and the length of the side fg be D. D is the same as the depth of the light supplying member 40 or the tempered glass 200. In fig. 51, the laser beam L advances from the vertex c to the vertex e, and Pass represents the trajectory of the laser beam L.

Upper surface abfe is parallel to the upper surface of light supply member 40 and the surface of tempered glass 200 in fig. 49. Let P be the length ce of the trajectory Pass of the laser light, and Ψ be the complementary angle of incidence with respect to the surface of the tempered glass 200. The plane acge is equal to the incident plane of the laser beam L.

Fig. 52 is a plan view, a front view, and a side view of fig. 51. Let the trajectory viewed from the top surface of the laser beam L be Upass, the length be Pu, the trajectory viewed from the front be Fpass, the length be Pf, the trajectory viewed from the side be Lpass, and the length be Pl. The angle ω of the trajectory Lpass of the laser light L viewed from the side surface is the incident surface angle of the laser light L. Phi is the Z-axis rotation angle of the laser L and theta is the Y-axis rotation angle.

In fig. 51, when H is D, ω is 45 °, and the incident surface of the laser beam L is 45 °. When H is equal to D, it can be seen in fig. 52 that since the Z-axis rotation angle Φ of the laser light L is equal to the Y-axis rotation angle θ, the Z-axis and Y-axis rotation angles of the laser light L may be equal to each other in order to make the incident surface of the laser light L in the tempered glass 200 45 °.

The length P of the laser trace Pass is expressed by the following expression 9 (expression 9).

[ mathematical formula 9 ]

Further, when Lx is 1, for example, the length P of the laser light L and the residual angle Ψ of incidence on the surface of the tempered glass 200 can be easily determined from Φ and θ, since D, H, Pu is obtained and the residual angle Ψ of incidence on the surface of the tempered glass is an angle between Pass and upstas.

(the refractive index np of the light supplying member is equal to the refractive index ng of the tempered glass)

If the refractive index np of the light supplying member 40 is the same as the refractive index ng of the tempered glass 200, the angle of the laser beam and the relationship thereof are the same in both the light supplying member 40 and the tempered glass 200. For example, if the Y-axis rotation angle θ of the laser light in the light supply member 40 or the tempered glass 200 is 15 °, the Z-axis rotation angle Φ is 15 °, the refractive index ng of the tempered glass 200 is 1.516, and the refractive index of the light supply member 40 is also np 1.516 as in the tempered glass, the incident surface angle ω of the tempered glass 200 is 45 °, and the residual incident angle Ψ is 14.5 °.

From fig. 50, if the incident surface is 45 °, the image is viewed perpendicular to the incident surface, and the distance Pc of the trajectory Cpass of the laser light shown in fig. 50 is the same as the distance P of the actual trajectory Pass of the laser light, and the actual depth D can be obtained from the depth V on the image by the following equation 10 (equation 10).

[ MATHEMATICAL FORMULATION 10 ]

D＝V×sin45°…(10)

This makes it possible to calculate the stress of the tempered glass from the image of the laser beam pickup device 60.

(in the case where the refractive index np of the light supplying member 40 is not equal to the refractive index ng of the tempered glass 200.)

In the above description, when the light supplying member 40 and the tempered glass 200 have the same refractive index, the laser light advances at the interface between the light supplying member 40 and the tempered glass 200 without being refracted, and the laser light in the light supplying member 40 and the tempered glass 200 is parallel. However, the refractive indices of the light supplying member 40 and the tempered glass 200 are not necessarily the same in practice.

When the refractive indices of the light supplying member 40 and the tempered glass 200 are different, the Z-axis rotation angle of the laser light is not changed, and only the Y-axis rotation angle is changed. Therefore, under the condition that the refractive index of the light supply member 40 is the same as that of the tempered glass 200, even if the incident surface of the laser light in the tempered glass 200 is 45 °, if the refractive index of the tempered glass 200 is different from that of the light supply member 40, the incident surface of the laser light in the tempered glass 200 is deviated from 45 °. In this case, the distance Pc between the laser tracks Cpass shown in fig. 50 is different from the distance P between the actual laser tracks Pass (Pc ≠ P), and equation 10 also does not hold.

It is difficult to directly measure the complementary incident angle Ψ and the incident surface angle ω of the laser beam in the strengthened glass. Therefore, the trajectory of the laser light can be considered when the refractive index np of the light supplying member 40 and the refractive index ng of the tempered glass 200 are different.

In order to enter the light supplying member 40 from the air, the laser light is refracted at an angle formed by an angle between an angle of the laser light before entering the light supplying member 40 and the laser light on the incident end surface of the light supplying member 40 on which the laser light enters, and enters the light supplying member 40. Therefore, the residual angle of incidence and the incident surface angle of the laser beam in the tempered glass 200 required are also considered in consideration of the residual angle of incidence of the laser beam before the laser beam enters the light supplying member 40 and the angle of the incident end surface of the light supplying member 40.

In order to separate phi and theta in fig. 52 from the tempered glass 200, phi g and theta g are set in the tempered glass 200, phi p and theta p are set in the light supplying member 40, and phi L and theta L are set before the light is incident on the light supplying member 40. The Z-axis rotation angle of the incident end surface of the light supply member 40 on which the laser light is incident is β, and the Y-axis rotation angle is α. The refractive index of the light supplying member 40 is np, and the refractive index of the tempered glass 200 is ng.

When np is different from ng, or β, α is different from Φ L, θ L, if snell's law holds for the Z-axis rotation angles Φ L, Φ p, β and Φ p, Φ g, the Y-axis rotation angles θ L, θ p, α and θ p, θ g, respectively, and if angles Φ L, θ L before the laser beam enters the light supplying member 40, angles α, β of the incident end surface of the light supplying member 40, refractive indices ng, np are known in advance, the rotation angles Φ g, θ g, residual incident angle Ψ, and incident surface angle ω of the laser beam in the tempered glass 200, which are parameters necessary for measurement, can be easily calculated.

Here, the rotation angles Φ L, θ L before the laser beam enters the light supplying member 40, the rotation angles β, α of the incident end surface of the light supplying member 40 on which the laser beam enters, and the refractive index np of the light supplying member 40 are determined by the device design and known. The refractive index of the tempered glass 200 can be known by a general refractive index measuring apparatus.

Therefore, phi g and theta g of the laser beam in the tempered glass 200, the residual angle of incidence psi and the plane of incidence omega are obtained from the refractive index of the tempered glass 200 measured by another unit, phi L, theta L, alpha, beta and np determined by the device design, and the refractive index of the tempered glass 200, and the conversion expressions of the residual angle of incidence psi and the plane of incidence omega of the laser beam into the tempered glass 200 are obtained from Pc and chi of the image of the laser beam pickup device 60, and the stress distribution in the tempered glass can be measured from expression 8. Specific examples are shown below.

Fig. 53 is a conceptual diagram of the laser light advancing through the light supplying member and the tempered glass. Although the angle is actually a three-dimensional angle, it is shown two-dimensionally in fig. 53 for the sake of simplicity. Fig. 54 is a conceptual diagram of a laser beam advancing through the tempered glass, and 215 schematically shows an observation surface observed from the imaging device 60 in a pearskin pattern.

In fig. 53 and 54, θ L represents the incidence of the laser light from the laser light source 10 to the light supplying member 40 and the incidence of the light supplying member 40The angle (laser side) formed by the normal line of the surface 40 a. And, theta_P1Is an angle (light supply member 40 side) formed by the laser light incident from the laser light source 10 to the light supply member 40 and the normal line of the incident surface 40a of the light supply member 40, theta_P2The angle (light supply member 40 side) between the laser beam incident from the light supply member 40 to the tempered glass 200 and the normal line of the emission surface 40b of the light supply member 40 is shown. The incident surface 40a of the light supply member 40 and the exit surface 40b of the light supply member 40 are not substantially perpendicular to each other, and therefore, the angle is not limited to θ_P1+θ_P2＝90°。

Further, θ g is an angle (strengthened glass 200 side) formed by the laser light incident from the light supplying member 40 to the strengthened glass 200 and the normal line of the exit surface 40b of the light supplying member 40, and Ψ is a residual angle (90- θ g) formed by the surface 210 (evaluation surface) of the strengthened glass 200 and the laser light in the strengthened glass 200. χ is the slope of the laser light observed from the imaging element 60. It should be noted that, when θ, Ψ, or the like is considered three-dimensionally, it may be considered separately as shown in fig. 52.

The complementary angle Ψ can be obtained, for example, according to a flowchart shown in fig. 55. That is, first, in step S701, θ is derived from θ L and np_P1。θ_P1Can be found by Snell's equation from θ L and np.

Next, in step S702, according to θ_P1Deriving θ_P2。θ_P2According to theta based on the shape of the light supplying member 40_P1Can be obtained. Next, in step S703, according to θ_P2Np, ng to derive θ g. θ g according to θ_P2Np, ng can be obtained by the equation of Snell.

Next, in step S704, Ψ is derived from θ g. Ψ can be determined from θ g by geometric calculation. I.e., Ψ -90- θ g.

Although it is preferable that the refractive index np of the light supplying member 40 is the same as the refractive index ng of the tempered glass 200, there are a plurality of types of tempered glass and the refractive indices are different. However, the optical glass forming the light supplying member 40 may not necessarily be glass having the exact same refractive index as the tempered glass.

For example, the most widely used optical glass S-BSL7 (manufactured by wako corporation) is np ═ 1.516, np ═ 1.487 in S-FSL5 (manufactured by wako corporation) below, np ═ 1.5317 in S-TIL6 (manufactured by wako corporation) above, and the like.

Therefore, in the case of measuring a tempered glass having a refractive index in a certain range, it is necessary to perform the measurement using the light supplying member 40 formed of an optical glass having a refractive index close to the range. For example, when the refractive index ng of the tempered glass is 1.51, the complementary angle Ψ of the tempered glass becomes 13.7 °, and the incident surface angle ω becomes 43 °. This yields a conversion equation, and the accurate stress can be obtained by equation 8.

The refractive index ng of the tempered glass 200 can be calculated from the angle χ of the laser image of the imaging element 60. That is, the refractive index ng of the tempered glass 200 may be derived based on the image of the laser beam acquired by the imaging element 60.

Specifically, first, in step S711 of the flowchart shown in fig. 56, the relationship between the residual angle of incidence Ψ and the angle χ shown in fig. 54 is derived. The relationship between the residual angle of incidence Ψ and the angle χ can be determined by geometric calculation. Next, in step S712, the angle χ is measured by the imaging element 60 (camera).

Next, in step S713, the complementary angle Ψ is determined from the relationship derived in step S711 using the angle χ measured in step S712. Then, θ g is determined to be 90- Ψ, based on the known θ_P2Np, θ g can derive ng by the equation of Snell.

In this way, the refractive index ng of the tempered glass 200 is determined from the angle χ of the laser image of the imaging element 60, and the stress distribution of the tempered glass 200 can be measured by obtaining the conversion equation based on the refractive index ng of the tempered glass 200.

However, depending on the slope or the like when the tempered glass 200 is mounted on the light supply member 40, an error occurs in the value of the refractive index ng of the tempered glass 200 derived by the method of fig. 56. Therefore, when it is desired to stably measure the stress distribution in the tempered glass with high accuracy, it is preferable to previously measure the refractive index ng of the tempered glass 200 by another method (measurement in a refractive index measuring device, or the like).

Further, the residual angle of incidence Ψ can be corrected according to the angle χ of the laser image of the imaging element 60. For example, in step S711 of the flowchart shown in fig. 57, the relationship between the residual angle of incidence Ψ and the angle χ is derived as in the case of fig. 56, and in step S712, the angle χ is measured by the imaging element 60 as in the case of fig. 56. Then, in step S714, the complementary angle of incidence Ψ is derived from the relationship derived in step S711 using the angle χ measured in step S712. By applying the complementary angle of incidence Ψ derived in step S714 to equation 8, an accurate stress can be obtained.

In addition, when the value of the refractive index ng of the tempered glass 200 is known in advance, it is also effective to design the optimum light supplying member 40 in consideration of the value of the refractive index ng of the tempered glass 200.

The complementary angle of incidence Ψ or the face angle of incidence ω in the tempered glass 200 can be known by calculation, but as the difference between the refractive index ng of the tempered glass 200 and the refractive index np of the light supplying member 40 increases, the deviation of the face angle Ψ from 45 ° increases. Thus, if the focal depth of the lens of the imaging element 60 is exceeded, the focal point is shifted, the spatial resolution is degraded, and an accurate stress distribution cannot be measured.

For example, when the refractive index ng of the tempered glass 200 is 1.49, the residual angle Ψ of the laser beam in the tempered glass 200 becomes 10.3 °, and the incident surface angle ω becomes 35 °. In this case, although correction can be performed for the complementary incident angle Ψ by calculation, the measurement accuracy cannot be maintained only by the correction performed by calculation, in which the incident surface angle ω is 10 ° away from 45 °.

Therefore, the angle of the surface of the light supply member 40 on which the laser light is incident is preferably set so that the angle of the surface of the tempered glass 200 on which the laser light is incident is 45 ± 5 ° with respect to the surface of the tempered glass 200.

For example, when the distance of the laser beam trajectory is 300 μm, if the incident surface angle ω is deviated by 10 °, the difference between the distances of the laser beams from the image pickup device 60 to the tempered glass 200 becomes 52 μm, which exceeds the focal depth of the lens for forming an image on the image pickup device 60, and the focal points are not uniformly aligned over the entire distance of the laser beam trajectory photographed by the image pickup device 60, thereby deteriorating the measurement accuracy.

Therefore, for example, in step S721 of the flowchart shown in fig. 58, the value of the refractive index ng of the target tempered glass 200 is obtained. Next, in step S722, the refractive index ng of the tempered glass 200 and the refractive index np of the light supplying member 40 are fixed, and θ L in which the surface through which the laser light passes and the observation surface do not change is obtained.

For example, if the refractive index ng of the tempered glass 200 is 1.49, the Y rotation angle θ L of the laser light is 15 °, the Z rotation angle Φ L is 15 °, and the Z rotation angle Φ L is 15 °, the same applies, and if the rotation angle β of the incident end surface of the light supply member 40 is 15 °, and the Z rotation angle α is 24.5 °, the laser light can be at the residual incident angle of 14.4 °, the incident surface angle of 44.8 °, and the angle is almost the designed angle in the tempered glass 200. Therefore, the deterioration of the measurement accuracy is eliminated.

The light supply member 40 of this specification is manufactured, and the stress distribution of the tempered glass 200 having the refractive index ng largely different from the refractive index np of the light supply member 40 can be accurately measured only by replacing the light supply member 40 without changing the installation of the laser light source 10. In addition, in order to cancel the return light to the laser light source 10, when the tempered glass 200 and the surface on which the laser light is incident on the light supply member 40 are slightly deviated (about 0.5 to 1 °), the correction can be performed by the equation 8.

< fifth embodiment >

In the fifth embodiment, an example of an evaluation device having a function of measuring a glass thickness is shown. In the fifth embodiment, description of the same components as those of the above-described embodiment may be omitted.

In a thin plate-like tempered glass, a compressive stress is formed on the surface for tempering. In this case, tensile stress is generated inside to balance the stress as a whole.

Fig. 59 is a diagram illustrating a stress distribution in the depth direction of the tempered glass. A tensile stress is generated in the center portion with respect to the compressive stress formed on the surface, and the overall stress becomes 0 in principle. That is, the integral value (stress energy) of the stress distribution becomes 0 from the front surface to the back surface in the depth direction.

If another expression is used, the integral value of the compressive stress (compressive energy) on the surface is equal to the integral value of the tensile stress (tensile energy) in the central portion. In addition, in the chemical strengthening step, since chemical strengthening of both surfaces of the glass is generally performed under the same conditions, the stress distribution is symmetrical with respect to the center of the glass. Therefore, the integral from the surface to the midpoint of the glass in the depth direction also becomes 0.

In the evaluation device 1, the stress value is obtained from the differential value of the glass depth and the phase value of the change in the scattered light intensity (for example, fig. 7) and the photoelastic constant (see the first embodiment). Therefore, the phase of the change in the glass depth and the scattered light brightness in fig. 7 is the same as the integral value of the stress value. That is, in fig. 7, the center point of the tempered glass is the same as the phase value of the outermost surface of the tempered glass.

In the evaluation apparatus 1, when the laser light is diffusely reflected on the outermost surface of the tempered glass and the diffuse reflection light is generated, there is a disadvantage that the phase value of the change in the brightness of the scattered light on the outermost surface of the tempered glass cannot be accurately measured.

Therefore, the phase value of the center point of the tempered glass is used to correct the phase value of the brightness variation of the scattered light on the outermost surface. This makes it possible to accurately measure, for example, the stress value and the stress distribution on the outermost surface of the tempered glass and in the vicinity of the outermost surface. In addition, when the measured phase value does not reach the center of the tempered glass, the measured phase value may be extrapolated to the center of the tempered glass as the phase value of the center of the tempered glass.

In this way, when the thickness of the tempered glass is known, the amount of phase change of the outermost surface of the tempered glass, which is to achieve stress balance, is estimated based on the calculated stress distribution and the thickness of the tempered glass, and the surface stress value can be corrected.

Fig. 60 is a view illustrating an evaluation apparatus provided with a glass thickness measurement device. The evaluation apparatus 3 shown in fig. 60 is configured such that a glass thickness measuring apparatus 120 is provided in the evaluation apparatus 1.

The glass thickness measuring device 120 includes a laser light source, a light receiving unit, and a computing unit, which are not shown. The laser light Lg emitted from the laser light source of the glass thickness measuring device 120 is reflected by the front surface 210 and the back surface 220 of the tempered glass 200, and is received by the light receiving unit of the glass thickness measuring device 120. The arithmetic unit of the glass thickness measuring device 120 measures the thickness of the tempered glass 200 based on the light received by the light receiving unit. As the glass thickness measuring device 120, for example, a commercially available glass thickness meter can be used.

In the evaluation device 3, the phase value can be measured in the depth direction from the surface of the tempered glass 200 by the evaluation device 1 based on the change in the intensity of the scattered light in the tempered glass 200 by the laser light from the laser light source 10. At the same time, in the evaluation apparatus 3, the thickness of the tempered glass 200 can be measured by the glass thickness measuring apparatus 120.

The phase value of the center of the tempered glass 200 can be obtained by measurement or extrapolation from the phase values in the thickness and depth directions of the tempered glass 200 measured by the glass thickness measuring device 120. Then, based on the phase value, a phase value of the outermost surface of the tempered glass 200 is formed or corrected, and the stress distribution can be obtained from the phase value in the depth direction after the correction of the outermost surface.

In this way, in the evaluation device 3 including means for measuring the thickness of the tempered glass, the stress distribution and the thickness of the tempered glass are measured, and the amount of phase change in the outermost surface of the tempered glass can be estimated based on the measured thickness of the tempered glass.

< modification of phase value determination >

The determination of the phase value of the change in the brightness of the scattered light on the outermost surface can be modified as described below.

As described above, in the evaluation device 1, the laser light is diffusely reflected on the outermost surface of the tempered glass 200, and when the diffusely reflected light occurs, there is a disadvantage that the phase value of the change in the brightness of the scattered light on the outermost surface of the tempered glass 200 cannot be accurately measured. To compensate for this disadvantage, the following method may be used.

First, two sets of the laser light source 10, the polarization member 20, and the polarization phase difference varying member 30 may be prepared, and the laser light L and the polarization phase difference varying member 30 may be combinedL' from two different angles theta_s1And an angle of θ'_s1And (4) incidence. At this time, the scattered light from the laser light L and the scattered light from the laser light L' are measured separately. The error in the phase value of the outermost surface of the tempered glass 200 due to the influence of the diffuse reflection on the surface of the tempered glass 200 using one of the two sets of laser beams incident from a smaller angle is less, and on the other hand, the measurement to the deep part of the tempered glass 200 may not be performed. Therefore, in the measurement using the laser light incident from a smaller angle, the phase value of the outermost surface of the tempered glass 200 is determined, and the result is set as the phase value of the outermost surface of the measurement using the laser light incident from a larger angle, whereby the measurement accuracy is improved and the depth of the tempered glass 200 may be measured.

Secondly, in order to suppress the occurrence of the diffused reflection of the laser light on the outermost surface of the tempered glass 200, a step of cleaning the surface of the tempered glass 200 by a cleaning system may be provided before step S601. The cleaning system may be a cleaning operation, a wiping operation, or the like, by a wet or dry cleaning machine.

Third, when the means for calculating the value of DOL _ zero is provided, the phase of the outermost surface on the front surface 210 side of the tempered glass 200 may be estimated as follows using DOL _ zero (front surface) on the front surface 210 side and DOL _ zero (back surface) on the back surface 220 side of the tempered glass 200.

That is, the sum of DOL _ zero (front surface) and DOL _ zero (back surface) becomes the thickness of the tempered glass 200, and therefore the midpoint thereof becomes the glass midpoint. Since the integral value of the stress from the outermost surface of the tempered glass to the midpoint is 0, the central point of the tempered glass and the phase value of the outermost surface of the tempered glass are the same. Thus, the phase value of the outermost surface of the glass can be obtained without separately measuring the thickness of the glass. The position of the origin of the phase may be calculated by extrapolation so that the outermost surface of the tempered glass is a phase of the midpoint of the glass.

Note that DOL _ zero (back surface) is a length measured from the front surface 210 side of the tempered glass 200 to a point where the stress value on the back surface 220 side becomes 0. In addition, the liquid 90 may be provided on the back surface 220 side in order to measure DOL _ zero (back surface) with high accuracy. This can suppress the diffuse reflection on the surface on the rear surface 220 side. Further, in order to prevent light from the back surface side from entering, a light shielding function by a light shielding plate or the like may be provided between the glass and the camera.

Fourth, in the fifth embodiment, when the means for calculating the value of DOL _ zero is further provided, the phase of the outermost surface on the glass front surface 210 side may be estimated as follows using DOL _ zero (front surface) on the glass front surface 210 side and DOL _ zero (back surface) on the back surface 220 side. That is, since the sum of DOL _ zero (front surface) and DOL _ zero (back surface) is the glass thickness, the position of the outermost surface is determined so that the sum coincides with the value measured by the glass thickness measuring device, and thus the entire stress distribution can be obtained with high accuracy. The phase of the outermost surface is estimated by extrapolating the phase to the position of the outermost surface.

Fifth, after the phase change calculation step (S405), a step of evaluating whether or not the origin position of the calculated phase change is appropriate may be provided. In this case, the origin position of the phase change calculated in S405 may be displayed at a corresponding position in the image obtained in the imaging step (S403) using a display, and the measurer may perform visual evaluation. This makes it possible to easily perform re-measurement determination when the position of the origin of the phase change is greatly deviated due to light scattering caused by noise, debris, bubbles, disturbance light, or the like at the time of measurement. In the case where the disturbance light is a cause, the position of the laser light source may be moved.

Although the preferred embodiments have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and substitutions can be made to the above embodiments without departing from the scope of the claims.

For example, in the above-described embodiments, the evaluation devices 1 and 2 have been described with the light source as a component, but the evaluation devices 1 and 2 may be configured without the light source. The light source can be used in a suitable configuration prepared by the user of the evaluation apparatus 1 or 2.

The international application claims priority of Japanese patent application No. 2018-031579 which is filed on 26.2.2018, and the entire contents of the Japanese patent application No. 2018-031579 are cited in the international application.

Description of the reference symbols

1. 1A, 1B, 1C, 1D, 1E, 2, 3 evaluation device

10. 11, 12 laser light source

15 light source

20. 55 polarized light component

25. 40, 41 light supply member

30. Phase difference variable member for 30A polarized light

35. 42 light extraction member

40a incident surface of light supplying member

40b light emitting surface of light supplying member

40x, 43x recess

40y, 43y groove

43 plano-concave lens

43e outer edge part

44 support

45. 50, 50A light conversion member

60. 60A, 65 imaging element

70. 75 arithmetic unit

80. 80A, 81, 82 optical wavelength selection member

90 liquid

100 pad member

120 glass thickness measuring device

200 tempered glass

210 surface of tempered glass

215 observation plane

Back side of 220 tempered glass

Incident surface of 250 laser

301 digital data storage circuit

302 clock signal generating circuit

303 DA converter

304 voltage amplifying circuit

310 polarization phase difference generating material

311. 313 fixing clamp

312 piezoelectric element

701 luminance change measuring unit

702 phase change calculation unit

703 stress distribution calculating unit

704 physical quantity measuring unit

751 position measuring unit

752 stress distribution calculating unit

753 synthesis unit.

Claims (55)

1. An evaluation device for tempered glass, comprising: a polarized light phase difference variable member, which changes the polarized light phase difference of the laser light by more than one wavelength relative to the wavelength of the laser light; an imaging element that captures a plurality of images of scattered light at predetermined time intervals, the scattered light being the scattered light emitted by the incident laser light having the polarized light phase difference changed on the tempered glass; and A calculation unit measures a periodic luminance change of the scattered light using the plurality of images, calculates a phase change of the luminance change, and calculates a depth direction from the surface of the tempered glass based on the phase change stress distribution, and use the plurality of images to determine physical quantities related to the strength of the strengthened glass. 2 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 2 . The computing unit measures the brightness of the scattered light as the physical quantity. 3 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 3 . the plurality of images have speckle patterns, The computing unit measures a variance value of the luminance of the speckle pattern as the physical quantity. 4. The evaluation device for tempered glass according to claim 1, wherein The computing unit measures the refractive index of the tempered glass as the physical quantity. 5 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 6 . A first optical wavelength selective member having a relatively high transmittance of the wavelength of the laser light and a second optical wavelength selective member having a relatively low transmittance of the wavelength of the laser light are switchably inserted into the imaging element of the laser beam. on the incident light path, The computing unit measures the first luminance of the scattered light when the first optical wavelength selection member is inserted into the optical path and the scattered light when the second optical wavelength selection member is inserted into the optical path as the physical quantity, and calculate the ratio of the first brightness to the second brightness. 6 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 7 . The first optical wavelength selective member that transmits the laser light of the first wavelength band and the second optical wavelength selective member that transmits the light of the second wavelength band when the laser light of the first wavelength band is incident The method of selecting the first optical wavelength selection member and selecting the second optical wavelength selection member when the laser light in the second wavelength band is incident can be switchably inserted until the laser light is incident on the imaging element. on the light path, The computing unit measures the first luminance of the scattered light and the laser light in the second wavelength band when the laser light in the first wavelength band is incident and the first optical wavelength selection member is inserted into the optical path The second luminance of the scattered light when incident and the second light wavelength selection member is inserted into the optical path is taken as the physical quantity. 7 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 8 . The computing unit measures the physical quantity in a plurality of regions in the depth direction from the surface of the tempered glass. 8 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 9 . The polarized light retardation variable member is a liquid crystal element. 9 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 10 . The polarized light retardation variable member is a transparent member in which the value obtained by multiplying the photoelastic constant and the Young's modulus is 0.1 or more, and the polarized light retardation is generated by pressing. 10 . The evaluation apparatus for tempered glass according to claim 9 , wherein: 10 . The transparent member is quartz glass or polycarbonate. 11 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 11 . the position of the minimum beam diameter of the laser is within the ion exchange layer of the strengthened glass, The minimum beam diameter is 20 μm or less. 12 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 12 . The incident surface of the laser beam incident on the tempered glass is 45±5° with respect to the surface of the tempered glass. 13 . The evaluation apparatus for tempered glass according to claim 12 , wherein: 13 . The evaluation apparatus of the tempered glass includes a light supply member that causes the laser light having the changed polarization phase difference to be incident obliquely with respect to the glass surface into the tempered glass as the object to be measured, The angle of the surface of the light supply member on which the laser light is incident is set so that the incident surface of the laser light entering the tempered glass is 45±5° with respect to the surface of the tempered glass. 14 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 14 . The evaluation apparatus of the tempered glass includes a light supply member that causes the laser light having the changed polarization phase difference to be incident obliquely with respect to the glass surface into the tempered glass as the object to be measured, between the light supply member and the tempered glass, a liquid whose refractive index difference with the tempered glass is 0.03 or less is provided, The thickness of the liquid is 10 μm or more and 500 μm or less. 15. The evaluation apparatus for tempered glass according to claim 14, wherein: A recess having a depth of 10 μm or more and 500 μm or less is formed on the surface of the light supply member in contact with the tempered glass. The recess is filled with the liquid. 16 . The evaluation apparatus for tempered glass according to claim 14 , wherein: 16 . The surface of the light supply member is provided with a protruding portion in contact with the tempered glass, The protruding portion becomes a part of the optical path of the laser light incident into the tempered glass via the light supply member, A depression having a depth of 10 μm or more and 500 μm or less is formed on the side of the protruding portion that is in contact with the tempered glass. The recess is filled with the liquid. 17. The evaluation device for tempered glass according to claim 16, wherein The protruding portion is removably held on the surface of the light supply member. 18. The evaluation apparatus for tempered glass according to claim 16 or 17, wherein: A flat outer edge portion is formed around the depression, and the flat outer edge portion becomes a surface in contact with the tempered glass. 19 . The evaluation apparatus for tempered glass according to claim 15 , wherein: 19 . The recess is constituted by a surface having a curved portion. 20 . The evaluation apparatus for tempered glass according to claim 15 , wherein: 20 . A groove for discharging the liquid is formed around the depression. 21 . The evaluation apparatus for tempered glass according to claim 15 , wherein: 21 . When the refractive index of the light supply member is different from the refractive index of the tempered glass, to obtain the refractive index of the tempered glass, From the relationship between the trajectory of the laser light in the tempered glass obtained based on the refractive index of the tempered glass and the image of the laser light obtained by the imaging element, the case where the laser light is incident on the tempered glass is derived the incident angle, Based on the value of the incident angle, the stress distribution in the depth direction from the surface of the tempered glass is corrected. 22. The evaluation apparatus for tempered glass according to claim 21, wherein The refractive index of the tempered glass is derived based on the image of the laser light acquired by the imaging element. 23 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 23 . When the thickness of the tempered glass is known, based on the calculated stress distribution and the thickness of the tempered glass, the phase change amount of the outermost surface of the tempered glass that achieves stress balance is estimated, and the surface stress value is corrected. 24. The evaluation apparatus for tempered glass according to any one of claims 1 to 4, wherein The evaluation apparatus for the tempered glass includes means for measuring the thickness of the tempered glass, The stress distribution and the thickness of the tempered glass are measured, and the phase change amount of the outermost surface of the tempered glass is estimated based on the measured thickness of the tempered glass. 25 . The evaluation apparatus for tempered glass according to claim 1 , wherein: 25 . The laser beam in the tempered glass satisfies the condition of total reflection on the emission side of the laser beam of the tempered glass. 26. The evaluation device for tempered glass according to any one of claims 1 to 4, wherein the evaluation device for tempered glass includes: a second light supply member for making the light from the second light source incident into the surface layer of the tempered glass having the compressive stress layer; a light extraction member for emitting light propagating in the surface layer to the outside of the tempered glass; A light conversion member that converts two light components that vibrate parallel and perpendicular to the interface between the tempered glass and the light extraction member, which are included in the light emitted through the light extraction member, into two or more bright light components, respectively. Two bright line columns of lines; a second photographing element for photographing the two types of bright lines; and a position measuring unit for measuring the positions of two or more bright lines in each of the two types of bright line columns from an image obtained by the second imaging element, The computing unit compares the stress distribution of the first region in the depth direction from the surface of the tempered glass corresponding to the two light components calculated based on the measurement result of the position measuring unit with the phase change based on the stress distribution. The calculated stress distributions outside the first region are synthesized. 27. A method for evaluating tempered glass, comprising: The polarized light phase difference variable step is to change the polarized light phase difference of the laser light by more than one wavelength relative to the wavelength of the laser light; an imaging step of capturing a plurality of images of scattered light at predetermined time intervals, the scattered light being the scattered light emitted by the incident laser light having the polarized light phase difference changed on the tempered glass; and an arithmetic step of measuring a periodic luminance change of the scattered light using the plurality of images, calculating a phase change of the luminance change, and calculating a depth direction from the surface of the tempered glass based on the phase change a first stress distribution, and using the plurality of images to determine a physical quantity related to the strength of the tempered glass. 28. The method for evaluating tempered glass according to claim 27, wherein In the calculation step, the brightness of the scattered light is measured as the physical quantity. 29. The evaluation method of tempered glass according to claim 27, wherein the plurality of images have speckle patterns, In the calculation step, a variance value of the luminance of the speckle pattern is measured as the physical quantity. 30. The method for evaluating tempered glass according to claim 27, wherein In the calculation step, the refractive index of the tempered glass is measured as the physical quantity. 31. The method for evaluating tempered glass according to any one of claims 27 to 30, wherein A first optical wavelength selective member having a relatively high transmittance of the wavelength of the laser light and a second optical wavelength selective member having a relatively low transmittance of the wavelength of the laser light are switchably inserted into the laser beam to the image pickup. On the light path on which the imaging element used in the process is incident, In the calculation step, the first luminance of the scattered light when the first optical wavelength selection member is inserted into the optical path and the total brightness of the scattered light when the second optical wavelength selection member is inserted into the optical path are measured. Using the second brightness of the scattered light as the physical quantity, the ratio of the first brightness to the second brightness is calculated. 32. The method for evaluating tempered glass according to any one of claims 27 to 30, wherein The first optical wavelength selective member that transmits the laser light of the first wavelength band and the second optical wavelength selective member that transmits the light of the second wavelength band when the laser light of the first wavelength band is incident The method of selecting the first optical wavelength selection member and selecting the second optical wavelength selection member when the laser beam in the second wavelength band is incident can be switchably inserted into the laser beam direction in the imaging step. On the light path incident on the imaging element used in In the calculation step, the first luminance of the scattered light and the second wavelength band of the scattered light when the laser light in the first wavelength band is incident and the first optical wavelength selection member is inserted into the optical path are measured. The second luminance of the scattered light when the laser beam of the domain is incident and the second light wavelength selection member is inserted into the optical path is used as the physical quantity. 33. The evaluation method of tempered glass according to any one of claims 27 to 30, wherein In the said calculation process, the said physical quantity is measured in the some area|region in the depth direction from the surface of the said tempered glass. 34. The method for evaluating tempered glass according to any one of claims 27 to 30, wherein In the polarized light retardation variable step, the polarized light retardation is changed by a liquid crystal element. 35. The evaluation method of tempered glass according to any one of claims 27 to 30, wherein The evaluation method of the tempered glass includes the steps of calculating the respective refractive index distributions based on the positions of the bright lines of the P-polarized light and the S-polarized light, and based on the difference in the refractive index distribution between the P-polarized light and the S-polarized light and the photoelastic constant of the tempered glass to obtain the second stress distribution. 36. A method for evaluating tempered glass, characterized in that: The said 1st stress distribution and the said 2nd stress calculated|required by the evaluation method of the tempered glass of Claim 35 about the tempered glass of at least 1 or more among the some tempered glass manufactured by the same manufacturing process The distributions were synthesized to obtain a stress distribution, and about the remaining tempered glass, only one of the first stress distribution and the second stress distribution was measured to obtain a stress distribution. 37. A method for producing tempered glass, characterized in that: The characteristic value is obtained from the stress value obtained by the evaluation method of tempered glass including the step of changing the polarized light retardation, and making the determination of shipment after confirming whether the characteristic value is within the management value. The polarization phase difference of the laser light changes by more than one wavelength with respect to the wavelength of the laser light; in the photographing process, scattered light is photographed multiple times at a predetermined time interval, and a plurality of images are obtained, and the scattered light is obtained by changing the polarized light phase and a calculation step of measuring a periodic brightness change of the scattered light using the plurality of images, calculating a phase change of the brightness change, and calculating a phase change of the brightness change based on the The phase change calculates the first stress distribution in the depth direction from the surface of the tempered glass, and uses the plurality of images to measure a physical quantity related to the strength of the tempered glass. 38. The method for producing tempered glass according to claim 37, wherein In the polarized light retardation variable step, the polarized light retardation is changed by a liquid crystal element. 39. The method for producing tempered glass according to claim 37 or 38, wherein The method for producing the tempered glass includes the steps of: calculating the respective refractive index distributions based on the positions of the bright lines of the P-polarized light and the S-polarized light; The second stress distribution was obtained from the photoelastic constant of the tempered glass. 40. The method for producing tempered glass according to claim 39, wherein With regard to at least one tempered glass among a plurality of tempered glasses produced by the same production process, the stress distribution is obtained by combining the first stress distribution and the second stress distribution obtained by the evaluation method, Regarding the remaining tempered glass, only one of the first stress distribution and the second stress distribution was measured to obtain the stress distribution. 41. The method for producing tempered glass according to claim 37 or 38, wherein Including two or more tempering steps for producing tempered glass tempered with lithium-containing glass and for determining shipment of the tempered glass, The said each strengthening process performs the said shipment determination based on the said 1st stress distribution obtained by the said evaluation method. 42. The method for producing tempered glass according to claim 41, wherein In the final strengthening step, the evaluation method includes a step of calculating respective refractive index distributions based on positions of bright lines of P-polarized light and S-polarized light, and calculating the respective refractive index distributions based on the P-polarized light and S-polarized light. The step of obtaining the second stress distribution from the difference in the refractive index distribution of light and the photoelastic constant of the tempered glass, and based on the second stress distribution obtained by the above-mentioned evaluation method, the shipment judgment is performed. 43. The method for producing tempered glass according to claim 42, wherein In the strengthening process other than the last time, the shipping determination is performed based on the stress value of the deepest part of the glass derived from the first stress distribution and the glass depth at which the stress value becomes 0. 44. The method for producing tempered glass according to claim 42 or 43, wherein In the last strengthening step, the second stress distribution is functionally approximated, and the shipment determination is performed. 45. The method for producing tempered glass according to claim 44, wherein The function approximation is performed using the following formula (2), σ _f (x)=a·x+CS2…(2) where σf(x) is the second stress distribution, a is the slope, and CS2 is the stress value at the outermost surface. 46. The method for producing tempered glass according to claim 44, wherein The function approximation is performed using the following formula (3), σ _f (x)=CS2·erfc(a·x)…(3) where σf(x) is the second stress distribution, a is the slope, CS2 is the stress value at the outermost surface, and erfc is the error function. 47. The method for producing tempered glass according to claim 42 or 43, wherein In the strengthening process other than the last time, using the second stress distribution obtained in the strengthening process, the plate thickness t of the tempered glass, and the first stress distribution of the tempered glass measured in advance under the same conditions, the said The first stress distribution and the second stress distribution are combined, the stress value in the deepest part of the glass is found from the combined stress distribution, and the characteristic value is derived, and the shipment judgment is made according to whether the characteristic value is within the allowable range. 48. The method for producing tempered glass according to claim 42 or 43, wherein In the strengthening process other than the last time, using the second stress distribution obtained in the strengthening process, the plate thickness t of the tempered glass, and the first stress distribution of the tempered glass measured in advance under the same conditions, the said The first stress distribution and the second stress distribution are combined, the stress value of the deepest part of the glass where the integrated value of the combined stress distribution becomes 0 is found, the characteristic value is derived, and the shipment judgment is made according to whether the characteristic value is within the allowable range. . 49. The method for producing tempered glass according to claim 42 or 43, wherein In the strengthening process other than the last time, using the second stress distribution obtained in the strengthening process, the plate thickness t of the tempered glass, and the first stress distribution of the tempered glass measured in advance under the same conditions, the said The first stress distribution and the second stress distribution are combined, the combined stress distribution is approximated by the following formula (5), and the glass whose integral value (x=0 to t/2) of σ(x) becomes 0 is found. The characteristic value is derived from the stress value CT of the deepest part, and the shipment judgment is made according to whether or not the characteristic value falls within the allowable range.

Here, σ(x) is the stress distribution after synthesis, σf(x) is the second stress distribution, t is the plate thickness of the tempered glass, and CS ₀ and c are parameters derived based on the first stress distribution. 50. The method for producing tempered glass according to claim 49, wherein The CS ₀ and c are derived based on the first stress distribution of the tempered glass under the same conditions measured in advance. 51. The method for producing tempered glass according to claim 49, wherein The CS0 and c are derived based on CS0' and c' derived from the first stress distribution obtained by the last strengthening step, and the following equations (6) and (7 ₎ , CS ₀ =A1×CS ₀ ′...(6) c=A2×c′...(7) Among them, A1 and A2 are proportional constants. 52. The method for producing tempered glass according to claim 51, wherein A1 and A2 are derived based on the first stress distribution of the tempered glass under the same conditions measured in advance. 53. A tempered glass produced by the method for producing tempered glass according to any one of claims 37 to 52. 54. The tempered glass according to claim 53, wherein Chemical strengthening is performed on glasses containing 2 wt % or more of lithium. 55. The tempered glass according to claim 53, wherein The tempered glass is produced by chemically tempering after air-cooling tempering.

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