JP6696437B2 - Float glass - Google Patents

Description

  The present invention relates to float glass.

  In a flat panel display device such as a digital camera, a mobile phone or a personal digital assistant PDA (Personal Digital Assistants), a thin plate-like cover glass is formed so as to have a wider area than an image display portion in order to enhance the protection and aesthetics of the display. Is being placed in front of the display.

  With the demand for weight reduction and thickness reduction of flat panel display devices, the cover glass itself is required to be thin. Therefore, the cover glass is required to have further strength on the surface and the end face in order to satisfy the purpose.

  On the other hand, the float method is widely used as a method for manufacturing plate glass. Glass molded by the float method has lower strength because the bottom surface in contact with the molten metal during float molding is more likely to have surface scratches due to contact with the rollers in the manufacturing process, as compared to the top surface not in contact with the molten metal. There is a risk.

  It is known to perform surface etching treatment with hydrofluoric acid or the like in order to improve the strength of glass (Patent Document 1).

Japanese special table 2013-516387

However, when the glass surface has latent scratches, the etching treatment using hydrofluoric acid or the like may expand the latent scratches, resulting in defective appearance due to pits. Furthermore, hydrofluoric acid requires careful handling from the viewpoint of safety.
Further, a method of polishing or grinding the bottom surface to scrape off the surface layer is also conceivable, but there is a possibility that the glass surface is damaged by polishing or grinding and the strength is rather lowered.

  An object of the present invention is to provide a float glass in which the lowering of the strength of the bottom surface is effectively suppressed.

  The present inventors have found that the surface strength of glass is dramatically improved by setting the summit density (Sds) of the bottom surface within a specific range, and completed the present invention.

That is, the present invention is as follows.
<1>
There are no polishing scratches on the surface,
Float glass having a summit density (Sds) of 4700 or less measured under the following conditions on the bottom surface in contact with molten metal during float forming.
Summit density (Sds) measurement conditions: atomic force microscope (AFM, Atomic Force Microscope) (XE-HDM; manufactured by Park Systems), measurement mode: non-contact mode, scan size: 1 μm × 0.5 μm, number of pixels: 256 × 128, color scale: ± 0.5 nm, scan speed: 1 Hz, cantilever: Non-Contact Cantilever (Item: PPP-NCHR 10M; manufactured by Park Systems), and then attached to the AFM device. Image analysis software (XEI) is used to perform flattening processing in the X and Y directions of the shape image, and the flattened shape image is analyzed using image analysis software (SPIP 6.2.6; Image Metrology Co., Ltd.). Is used to perform L-filtering processing (ISO value 2.0 μm) of the shape image, and the summit density (Sds) is obtained by roughness analysis.
<2>
The straight line linearly approximating the hydrogen concentration Y in the region of depth X from the outermost surface of the glass satisfies the following relational expression (I) at X = 0.10 to 0.25 (μm). Float glass.
Y = aX + b (I)
[The meaning of each symbol in formula (I) is as follows.
Y: Hydrogen concentration (H ₂ O conversion, mol / L)
X: Depth from the outermost surface of the glass (μm)
a: -2.700 or more b: 0.700 or less]
<3>
The float glass according to <1> or <2>, which is compatible with a chemical strengthening treatment.
<4>
A step of contacting the glass molded by the float method with an inorganic salt,
Cleaning the glass after contact with the inorganic salt,
Comprising a step of acid-treating the glass after the cleaning, and a step of alkali-treating the glass after the acid treatment,
The inorganic salts _are selected from _{K 2 CO 3, Na 2 CO} 3, KHCO 3, NaHCO 3, K 3 PO 4, Na 3 PO 4, K 2 SO 4, Na 2 SO 4, KOH and the group consisting of NaOH At least one salt is included, and when K / Na mass ratio in the inorganic salt is A and K / Na mass ratio in the glass composition is B, A ≧ 0 and A−B = −0.30. It will be in the range of +1.00,
Float glass manufacturing method.
<5>
The method for producing a float glass according to <4>, wherein the inorganic salt further contains at least one of potassium nitrate and sodium nitrate.
<6>
A step of contacting the glass molded by the float method with an inorganic salt,
Cleaning the glass after contact with the inorganic salt,
Comprising a step of acid-treating the glass after the cleaning, and a step of alkali-treating the glass after the acid treatment,
The inorganic salt contains at least one salt selected from the group consisting of Li ₂ CO ₃ , LiHCO ₃ , Li ₃ PO ₄ , Li ₂ SO ₄ and LiOH, and the Na / Li mass ratio in the inorganic salt is C, When Na / Li mass ratio in the glass composition is D, C ≧ 0 and C−D = −0.30 to +1.00.
Float glass manufacturing method.
<7>
The method for producing a float glass according to <6>, wherein the inorganic salt further contains at least one of potassium nitrate and sodium nitrate.
<8>
A method for producing chemically strengthened glass, which comprises producing float glass by the method according to any one of <4> to <7> and subjecting the obtained float glass to chemical strengthening treatment.

  According to the float glass of the present invention, the surface strength of the bottom surface can be significantly improved by setting the summit density (Sds) of the bottom surface within a specific range.

1 (a) to 1 (c) are schematic diagrams showing a manufacturing process of the chemically strengthened glass according to the present invention. FIG. 2 is a schematic diagram for explaining a ball-on-ring test method. FIG. 3 is an explanatory diagram for deriving the relational expression (I) from the graph obtained by plotting the hydrogen concentration profile of the surface layer of the chemically strengthened glass obtained in Example 1-1. FIG. 4 is an explanatory diagram for deriving the relational expression (I) from the graph obtained by plotting the hydrogen concentration profile of the surface layer of the chemically strengthened glass obtained in Example 1-3. FIG. 5 is a graph in which the hydrogen concentration profile of the surface layer of the chemically strengthened glass obtained in Examples 1-1 to 1-3 is plotted. FIG. 6 is a graph in which the hydrogen concentration profile of the surface layer of the chemically strengthened glass obtained in Example 2-1 to Example 2-3 is plotted. FIG. 7 is a graph in which the hydrogen concentration profile of the surface layer of the chemically strengthened glass obtained in Example 3-1 to Example 3-3 is plotted. FIG. 8 is an AFM image of a glass surface having surface scratches. FIG. 9 is an AFM image of the glass surface without surface scratches.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be arbitrarily modified and carried out without departing from the scope of the present invention.
Here, in this specification, “mass%” and “weight%” have the same meaning.

<Float glass>
The float glass of the present invention is formed by the float method, and has a bottom surface that comes into contact with molten metal during forming, and a top surface that faces the bottom surface.
In the production of glass by the float method, while forming a glass ribbon by continuously supplying molten glass from the upstream side to the surface of the molten metal stored in the float bath, after forming from the downstream end of the float bath. Sheet glass is manufactured by pulling out a glass ribbon and slowly cooling with a layer.
Here, the bottom surface is likely to be scratched due to contact with the roller in the manufacturing process, which is considered to be one of the causes of the strength reduction.

(Summit density (Sds))
The float glass of the present invention has a bottom surface summit density (Sds) of 4700 or less, preferably 3500 or less. When the summit density (Sds) of the bottom surface is within such a range, it is possible to obtain a float glass in which reduction in surface strength is suppressed.
The summit density (Sds: Summit Density) represents the number of points (= the number of vertices) where the height per unit area (1 μm ² ) is maximum. That is, it can be said that the lower the Sds, the higher the flatness of the glass surface, and the smaller the number of recesses that can be the starting point of crack generation due to external pressure. Therefore, it is considered that the lower the Sds, the higher the surface strength of the glass.
In the present invention, the summit density (Sds) of the bottom surface can be obtained by image analysis software after obtaining a shape image by an atomic force microscope (AFM) as shown below.
[AFM measurement conditions and analysis procedure of image analysis software]
First, an atomic force microscope (AFM, Atomic Force Microscope) (XE-HDM; manufactured by Park Systems), measurement mode: non-contact mode, scan size: 1 μm × 0.5 μm, number of pixels: 256 × 128, color scale : ± 0.5 nm, scan speed: 1 Hz, cantilever: Non-Contact Cantilever (Item: PPP-NCHR 10M; manufactured by Park Systems) is used to obtain a shape image. After that, the image analysis software (XEI) attached to the AFM device is used to perform the flattening process in each of the X direction and the Y direction of the shape image. Further, the flattened shape image was subjected to L-filtering processing (ISO value 2.0 μm) of the shape image by using image analysis software (SPIP 6.2.6 manufactured by Image Metrology Co., Ltd.), and roughness analysis was performed. The summit density (Sds) is calculated.

(Hydrogen concentration profile)
In the float glass according to the present invention, it is preferable that the hydrogen concentration in a constant depth region from the outermost surface of the glass satisfies the relational expression (I) described later.
In the float glass of the present invention, it is preferable that the hydrogen concentration profile in the glass surface layer is within a specific range. Specifically, it is preferable that the straight line approximating the hydrogen concentration Y in the region of the depth X from the outermost surface of the glass satisfies the following relational expression (I) at X = 0.10 to 0.25 (μm). ..
Y = aX + b (I)
[The meaning of each symbol in formula (I) is as follows.
Y: Hydrogen concentration (H ₂ O conversion, mol / L)
X: Depth from the outermost surface of the glass (μm)
a: -2.700 or more b: 0.700 or less]

Regarding the strength of glass, it is known that the strength of glass decreases due to the presence of hydrogen (water) in the glass. The strength decrease on the bottom surface is considered to be mainly caused by scratches caused by contact with the roller in the manufacturing process, but in addition, it is also caused by water entering the glass from the atmosphere in the manufacturing process, The present inventors have found out.
When the hydrogen concentration in the glass is high, hydrogen enters the Si—O—Si bond network of the glass in the form of Si—OH, and the Si—O—Si bond is broken. It is considered that when the hydrogen concentration in the glass is high, the number of portions where Si—O—Si bonds are broken is increased, chemical defects are easily generated, and the strength is reduced.

  The above relational expression (I) is established in a region where the depth X from the outermost surface is X = 0.10 to 0.25 μm. At the outermost surface (X = 0 μm), the water concentration may change due to deterioration over time, so it is assumed that it holds in the near surface (X = 0.10 to 0.25 μm) region where it is considered that there is no effect. ..

In the formula (I), a is a slope that defines the degree of decrease in hydrogen concentration. The range of a is -2.700 or more, preferably -1.500 or more, and more preferably -0.180 or more.
In the formula (I), b corresponds to the hydrogen concentration on the outermost surface (X = 0 μm). The range of b is 0.700 or less, preferably 0.000 to 0.400, more preferably 0.000 to 0.120, and further preferably 0.000 to 0.100.

Generally, it is considered that the decrease in the strength of glass is caused by the extension of microcracks existing on the glass surface due to external mechanical pressure. According to the literature (Won-Taek Han et. Al., "Effect of residual water in silica glass on static fatique", Journal of Non-Crystalline Solids, 127, (1991) 97-104, structure of crack). It is considered that the cracks are more likely to spread as the state of Si is richer in Si-OH. Assuming that the tip of the crack is exposed to the atmosphere, the amount of Si-OH at the tip of the crack is estimated to have a positive correlation with the hydrogen concentration on the outermost surface of the glass. Therefore, b corresponding to the hydrogen concentration on the outermost surface is preferably in the low range as shown above.
The penetration depth of hydrogen is likely to change depending on the glass composition, float production conditions, conditions for contact with an inorganic salt described later, etc., but if it does not change, it corresponds to the hydrogen concentration on the outermost surface b And a corresponding to the slope that defines the degree of decrease in hydrogen concentration have a negative correlation. Therefore, a is preferably in the high range as shown above.

[Method of measuring hydrogen concentration profile]
Here, the hydrogen concentration profile (H ₂ O concentration, mol / L) of glass is a profile measured under the following analysis conditions.
Secondary ion mass spectrometry (Secondary Ion Mass Spectrometry: SIMS) was used for the measurement of the hydrogen concentration profile of the glass substrate. When obtaining a quantitative hydrogen concentration profile by SIMS, a standard sample with a known hydrogen concentration is required. The method for preparing the standard sample and the method for quantifying the hydrogen concentration are described below.
1) Cut out a part of the glass substrate to be measured.
2) A region of 50 μm or more from the surface of the cut glass substrate is removed by polishing or chemical etching. The removal process is performed on both sides. That is, the removal thickness on both sides is 100 μm or more. This removed glass substrate is used as a standard sample.
3) infrared spectroscopy for the standard samples (Infrared spectroscopy: implement IR), the absorbance of the peak top in the vicinity of 3550 cm ^-1 of the IR spectrum the height _{A 3550} and 4000 cm ^-1 absorbance height _{A 4000} (the baseline) Ask.
4) The plate thickness d (cm) of the standard sample is measured using a plate thickness measuring device such as a micrometer. 5) _Referring to the document A, the infrared practical absorption coefficient _εpract (L / (mol · cm)) of H ₂ O of glass is set to 75, and the hydrogen concentration of the standard sample (H ₂ O conversion, mol / L).
The hydrogen concentration of the standard sample _{= (A 3550 -A 4000) /} (ε pract · d) ··· formula II
Reference A) S. Illievski et al. , Glatech. Ber. Glass Sci. Technol. 73 (2000) 39.

A glass substrate to be measured and a standard sample with a known hydrogen concentration obtained by the above method are simultaneously transported into a SIMS device, and are sequentially measured to obtain depth profiles of ¹ H ⁻ and ³⁰ Si ⁻ intensities. To do. ^Then, 1 H ^- by dividing the ^profile, 1 ^{H -} - ³⁰ Si from the profile obtained of the intensity ratio of depth profile ^{- /} 30 Si. ¹ H reference samples ^- / ³⁰ Si ^- than depth profile of the intensity ratio, average in the region of from a depth 0.70μm to 0.85μm ¹ H ^- / ³⁰ Si ^- calculate an intensity ratio, this value and the hydrogen A calibration curve with the concentration is created so as to pass through the origin (calibration curve with one level of standard sample). Using this calibration curve, the ¹ H ⁻ / ³⁰ Si ⁻ intensity ratio on the vertical axis of the profile of the glass substrate to be measured is converted into hydrogen concentration. Thereby, the hydrogen concentration profile of the glass substrate to be measured is obtained. The SIMS and IR measurement conditions are as follows.

[SIMS measurement conditions]
Equipment: ULVAC-PHI ADEPT1010
Primary ion species: Cs ⁺
Accelerating voltage of primary ion: 5kV
Current value of primary ion: 50 nA
Incident angle of primary ion: 60 ° to the normal to the sample surface
Raster size of primary ion: 300 × 300 μm ²
Secondary ion polarity: Minus secondary ion detection area: 60 × 60 μm ² (4% of primary ion raster size)
Use of Neutralizing Gun: Yes Method of converting the horizontal axis from sputtering time to depth: The depth of the analytical crater is measured by a stylus type profilometer (Dektak150 manufactured by Veeco) to obtain the sputtering rate of primary ions. .. Using this sputtering rate, the horizontal axis is converted from the sputtering time to the depth.
¹ H ^- upon detection of Field Axis Potential: could optimum value for each device is changed. The operator carefully sets the value so that the background is sufficiently cut.

[IR measurement conditions]
Device: Nic-plan / Nicolet 6700 manufactured by Thermo Fisher Scientific
Resolution: 4 cm ^-1
Total: 16
Detector: TGS detector

The following procedure is used to derive the relational expression (I) from the hydrogen concentration profile (H ₂ O concentration, mol / L) of glass measured under the above analysis conditions. As shown in FIGS. 3 and 4, linear approximation is performed on the hydrogen concentration profile in the depth region where X is 0.10 to 0.25 μm. The expression of the obtained approximate straight line is defined as the relational expression (I).
Further, as means for controlling a and b, for example, changing the salt concentration, temperature, time, etc. at the time of contact with an inorganic salt can be mentioned.

(Surface abrasion)
The float glass according to the present invention does not have polishing scratches on the surface. Here, the polishing in the present invention means that the glass surface is smoothed by using abrasive grains. The presence or absence of polishing scratches can be determined by observing the surface with an AFM (Atomic Force Microscope), and there are two or more scratches with a length of 5 μm or more and a width of 0.1 μm or more in a 10 μm × 5 μm region. If not, it can be said that there is no polishing scratch on the surface. FIG. 8 shows a state with surface polishing scratches, and FIG. 9 shows a state without surface polishing scratches.

(Glass surface strength)
The strength (surface strength) of the float glass of the present invention can be evaluated by a ball on ring (BOR) test.

(Ball on ring test)
In the float glass of the present invention, a glass plate is placed on a ring made of stainless steel having a diameter of 30 mm and a contact portion having a radius of curvature of 2.5 mm, and a spherical body made of steel having a diameter of 10 mm is brought into contact with the glass plate. Then, the BOR surface strength F (N) measured by the BOR test in which the sphere is loaded on the center of the ring under static load conditions is evaluated.

  FIG. 2 shows a schematic diagram for explaining the BOR test used in the present invention. In the BOR test, with the glass plate 1 placed horizontally, the glass plate 1 was pressed using a pressure jig 2 made of SUS304 (hardened steel, diameter 10 mm, mirror-finished) to obtain the surface strength of the glass plate 1. To measure.

  In FIG. 2, a glass plate 1 serving as a sample is horizontally installed on a receiving jig 3 made of SUS304 (diameter 30 mm, curvature of contact part R2.5 mm, contact part is hardened steel, mirror finish). A pressure jig 2 for pressing the glass plate 1 is installed above the glass plate 1.

In the present embodiment, the central region of the glass plate 1 is pressed from above the glass plate 1 obtained after Examples and Comparative Examples. The test conditions are as follows.
Lowering speed of the pressure jig 2: 1.0 (mm / min)
At this time, the breaking load (unit N) when the glass is broken is the BOR surface strength, and the average value of 20 measurements is the BOR average surface strength. However, if the breaking starting point of the glass plate is more than 2 mm away from the ball pressing position, it is excluded from the data for calculating the average value.

<Float glass manufacturing method>
One aspect of the method for producing the float glass according to the present invention will be described below, but the present invention is not limited thereto.

  The glass used in the present invention may have various compositions. Specific examples include aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkali barium glass, aluminoborosilicate glass, and the like.

  The method for producing glass is not particularly limited as long as it is formed by the float method, and a desired glass raw material is charged into a continuous melting furnace, and the glass raw material is preferably heated and melted at 1500 to 1600 ° C. and clarified, It can be manufactured by supplying the molten glass to a float molding device, molding the molten glass into a plate shape, and then slowly cooling it.

  The thickness of the glass is not particularly limited, but when the float glass of the present invention is subjected to a chemical strengthening treatment later, it is usually preferably 5 mm or less and 3 mm or less in order to effectively perform the treatment. More preferably. Further, from the viewpoint that the effect of improving the surface strength by the acid treatment described below is particularly exhibited, the plate thickness is more preferably 1 mm or less, and particularly preferably 0.7 mm or less.

The composition of the float glass of the present invention is not particularly limited, but examples thereof include the following glass compositions.
(I) a composition that is displayed in mol%, the SiO ₂ 50 to 80%, the _{Al 2 O 3 2~25%, 0~10} % of Li ₂ O, 0 to 18% of Na _{2 O, K} 2 O Is 0 to 10%, MgO is 0 to 15%, CaO is 0 to 5%, and ZrO ₂ is 0 to 5%, and the composition is expressed as mol% of glass (ii), and SiO ₂ is 50 to 74% and Al. ₂ O ₃ 1-10%, Na ₂ O 6-14%, K ₂ O 3-11%, MgO 2-15%, CaO 0-6% and ZrO ₂ 0-5%. , The total content of SiO ₂ and Al ₂ O ₃ is 75% or less, the total content of Na ₂ O and K ₂ O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%. With a composition expressed by a certain glass (iii) mol%, SiO ₂ is 68 to 80%, Al ₂ O ₃ is 4 to 10%, Na ₂ O is 5 to 15%, K ₂ O is 0 to 1%, MgO. Of glass (iv) containing 4 to 15% of ZrO ₂ and 0 to 1% of ZrO ₂ , and 67 to 75% of SiO ₂ , 0 to 4% of Al ₂ O ₃ , and 7 of Na ₂ O. ˜15%, K ₂ O 1-9%, MgO 6-14% and ZrO ₂ 0-1.5%, the total content of SiO ₂ and Al ₂ O ₃ is 71-75%, The total content of Na ₂ O and K ₂ O is 12 to 20%, and when CaO is contained, the content is less than 1%. The composition represented by mol% of glass (v) is 56% SiO ₂ . -71%, the _{Al 2 O 3 5~15%, B} 2 O 3 0-3%, 0.1% to 10% of Li ₂ O, 0% to Na ₂ O, 0 to a _{K 2} O Glass containing 5%, MgO 0 to 13%, CaO 0 to 21%, SrO 0 to 3% and BaO 0 to 3%.

  In the production method of the present invention, a glass formed by the float method and an inorganic salt containing a specific salt described below and having a K / Na mass ratio or Na / Li mass ratio adjusted according to the glass composition used. Contact. As a method of contacting the glass with the inorganic salt, a method of applying a paste-like inorganic salt, a method of spraying an aqueous solution of the inorganic salt on the glass, a method of immersing the glass in a salt bath of a molten salt heated to a melting point or higher, etc. Although possible, among these, the method of immersing in molten salt is preferable.

  As the inorganic salt, those having a melting point below the strain point of glass (usually 500 to 600 ° C.) are preferable, and in the present invention, either or both of potassium nitrate (melting point 330 ° C.) and sodium nitrate (melting point 308 ° C.) are used. The salt contained is preferred. Containing potassium nitrate and sodium nitrate is preferable because the glass is in a molten state below the strain point of the glass and the handling is easy in the operating temperature range. The content of potassium nitrate and sodium nitrate in the inorganic salt is preferably 50% by mass or more.

If the glass comprises K, the inorganic salts may further be K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH and It is preferable to contain at least one salt selected from the group consisting of NaOH. Above all, it is more preferable to contain at least one salt selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ and NaHCO ₃ .

When the glass contains Li, the inorganic salt preferably contains at least one salt selected from the group consisting of Li ₂ CO ₃ , LiHCO ₃ , Li ₃ PO ₄ , Li ₂ SO ₄ and LiOH. Above all, it is more preferable to contain a salt of at least one of Li ₂ CO ₃ and LiHCO ₃ .

  The above-mentioned salts other than potassium nitrate and sodium nitrate (hereinafter sometimes referred to as “fluxing agent”) have the property of cutting the glass network represented by Si—O—Si bonds. By appropriately breaking the covalent bond between Si and O of the glass, the low-density treatment described below easily proceeds.

  The degree of breaking the covalent bond depends on the glass composition, the type of salt (fluxing agent) used, the temperature at which the inorganic salt is contacted, the processing conditions such as time, but among the four covalent bonds extending from Si. It is considered that it is preferable to select a condition such that one or two bonds are broken.

The amount of the flux added is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, and particularly preferably 2 mol% or more, from the viewpoint of securing the removal amount. From the viewpoint of productivity, the saturated solubility of each salt or less is preferable. In addition, excessive addition may lead to glass corrosion. For example, when K ₂ CO ₃ is used as the flux, it is preferably 24 mol% or less, more preferably 12 mol% or less, particularly preferably 8 mol% or less.

For example, when K ₂ CO ₃ is mixed and used as the flux, the content of the flux in the inorganic salt is 0.1 mol% or more, preferably 24 mol% or less, more preferably 12 mol% or less, and 8 mol% or less. Particularly preferred. Further, when the glass contact temperature is 350 to 500 ° C., the glass contact time is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, still more preferably 10 minutes to 4 hours.

For example, when Na ₂ CO ₃ is mixed and used as the flux, the content of the flux in the inorganic salt is 0.1 mol% or more, preferably 24 mol% or less, more preferably 12 mol% or less, and 8 mol% or less. Particularly preferred. Further, when the glass contact temperature is 350 to 500 ° C., the glass contact time is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, still more preferably 10 minutes to 4 hours.

  The inorganic salt may contain, in addition to the fluxing agent, other chemical species as long as the effect of the present invention is not impaired, for example, sodium chloride, potassium chloride, sodium borate, potassium borate, and other alkali hydrochlorides. And alkali borate. These may be added alone or in combination of two or more.

In the production method of the present invention, the composition of the inorganic salt is calculated by the K / Na mass ratio in the glass composition and the flux concentration necessary to secure the removal amount. The inorganic salt is prepared so that the K / Na mass ratio in the inorganic salt is approximately the same as the K / Na mass ratio in the glass composition. Moreover, the inorganic salt contains the above-mentioned flux. Here, when the K / Na mass ratio in the inorganic salt is A and the K / Na mass ratio of the glass composition is B, A ≧ 0 is satisfied and the difference between A and B (AB) is The range is −0.30 to +1.00, and the range 0.00 to +0.30 is more preferable. With an inorganic salt having a K / Na mass ratio satisfying the above, a compressive stress layer is not formed on glass even when it is brought into contact with glass. The K / Na mass ratio in the inorganic salt can be adjusted, for example, by adding NaNO ₃ , KNO ₃ , and the above-mentioned fluxing agent to the inorganic salt.

  For glass containing Li, the same effect can be obtained by adjusting the Na / Li mass ratio. That is, the inorganic salt is prepared so that the Na / Li mass ratio in the inorganic salt is about the same as the Na / Li mass ratio in the glass composition. Moreover, the inorganic salt contains the above-mentioned flux. Here, when the Na / Li mass ratio in the inorganic salt is C and the Na / Li mass ratio of the glass composition is D, C ≧ 0 is satisfied, and the difference between C and D (C−D) is The range is −0.30 to +1.00, and the range 0.00 to +0.30 is more preferable.

Hereinafter, the examples and either or both of NaNO ₃ and KNO _3, an inorganic salt in a molten state was added and Na ₂ CO ₃ as a flux, a mode of contacting with the inorganic salt by immersing the glass, the The manufacturing method of the invention will be described.

(Production of molten salt 1)
The molten salt can be produced by the steps shown below.
Step 1a: Preparation of molten salt containing one or both of sodium nitrate and potassium nitrate Step 2a: Addition of flux to molten salt containing one or both of sodium nitrate and potassium nitrate

(Step 1a-Preparation of Molten Salt Containing Either or Both of Sodium Nitrate and Potassium Nitrate-)
In step 1a, a salt containing one or both of sodium nitrate and potassium nitrate is placed in a container, and heated to a temperature equal to or higher than the melting point to melt, thereby preparing a molten salt. The melting is performed at a temperature within the range of the melting point of sodium nitrate (308 ° C.) or the melting point of potassium nitrate (330 ° C.) and the strain point of glass (500 to 600 ° C.). Particularly, it is more preferable to set the melting temperature to 350 to 500 ° C. from the viewpoint of securing the removal amount and suppressing the deformation of the glass.

  As a container for melting one or both of sodium nitrate and potassium nitrate, metal, quartz, ceramics or the like can be used. Above all, a metallic material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Step 2a-Addition of Fluxing Agent to Molten Salt Containing Either or Both of Sodium Nitrate and Potassium Nitrate-)
In step 2a, the above-mentioned flux is added to the molten salt containing either or both of sodium nitrate and potassium nitrate prepared in step 1a, and while the temperature is kept within a certain range, the whole is stirred by a stirring blade or the like. Mix to homogeneity. When a plurality of fluxes are used in combination, the order of addition is not limited and they may be added simultaneously.
The temperature is preferably the melting point of sodium nitrate or potassium nitrate, that is, 308 ° C or 330 ° C or more, and more preferably 350 to 500 ° C. The stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 2 hours.

(Production of molten salt 2)
In the above-described production 1 of molten salt, the method of adding the flux after the preparation of the molten salt of sodium nitrate is exemplified, but the molten salt can also be produced by the steps shown below.
Step 1b: Mixing one or both of sodium nitrate and potassium nitrate with a flux Step 2b: Melting a mixed salt of one or both of sodium nitrate and potassium nitrate and a flux

(Step 1b-mixing of either or both of sodium nitrate and potassium nitrate with flux)
In step 1b, one or both of sodium nitrate and potassium nitrate and the flux are put into a container and mixed with a stirring blade or the like. When a plurality of fluxes are used in combination, the order of addition is not limited and they may be added simultaneously. The same container as that used in the above step 1a can be used.

(Step 2b-Melting of mixed salt of one or both of sodium nitrate and potassium nitrate and flux-)
In step 2b, the mixed salt obtained in step 1b is heated and melted. The melting is performed at a temperature within the range of the melting point of sodium nitrate (308 ° C.), the melting point of potassium nitrate (330 ° C.) and the strain point of glass (500 to 600 ° C.). Particularly, it is more preferable to set the melting temperature to 350 to 500 ° C. from the viewpoint of securing the removal amount and suppressing the deformation of the glass. The stirring time is preferably 1 minute to 10 hours, more preferably 10 minutes to 2 hours.

  In the molten salt obtained through the above step 1a and step 2a or step 1b and step 2b, when a precipitate is generated by the addition of the flux, the precipitate is precipitated on the bottom of the container before immersing the glass. Let stand until you do. This deposit contains a flux that exceeds the saturated solubility and a salt in which the cations of the flux are exchanged in the molten salt.

Next, it is immersed in the prepared molten salt. Specifically, the following step 3 can be performed.
Step 3: Contact Treatment of Glass with Inorganic Salt By contacting glass with an inorganic salt in a molten state, the glass network represented by Si—O—Si bonds is cut on the glass surface.

(Step 3-Glass contact treatment-)
In step 3, the glass is preheated and the molten salt prepared in steps 1a and 2a or steps 1b and 2b is adjusted to a predetermined temperature. Then, the preheated glass is immersed in the molten salt for a predetermined time, and then the glass is pulled out of the molten salt and allowed to cool. Before the immersion treatment, the glass may be subjected to shape processing according to the application, for example, mechanical processing such as cutting, end face processing, and hole drilling.

  The preheating temperature of the glass depends on the temperature of immersion in the molten salt, but it is generally preferably 100 ° C. or higher.

  The immersion temperature is preferably 500 ° C. or lower from the viewpoint of suppressing deformation of the glass, and is preferably 350 ° C. or higher from the viewpoint of securing the removal amount.

  The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, still more preferably 10 minutes to 4 hours. Within this range, the glass network represented by Si-O-Si bonds is broken.

In the production method of the present invention, subsequently, the following steps are performed after the contact treatment between glass and an inorganic salt.
Step 4: Glass cleaning step 5: Acid treatment of glass after step 4 At the time point up to the above step 5, the surface layer of the glass surface has deteriorated, specifically, the intermediate layer 30 ( It has the low-density layer 10 whose density is lower than that of the bulk [FIG. 1 (a) to FIG. 1 (b)]. The low-density layer is formed when Na or K escapes (leaches) from the outermost surface of the glass and H enters (replaces) instead.
Hereinafter, step 4 and step 5 will be described in detail.

(Step 4-Washing of glass-)
In step 4, the glass is washed with industrial water, ion-exchanged water, or the like. Of these, ion-exchanged water is preferable. The washing conditions vary depending on the washing liquid used, but when ion-exchanged water is used, washing at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt.

(Step 5-acid treatment-)
In step 5, the glass cleaned in step 4 is further acid-treated.
The acid treatment of glass is performed by immersing the glass in an acidic solution, whereby Na and / or K on the glass surface can be replaced with H.
The solution is not particularly limited as long as it is acidic, and may have a pH of less than 7, and the acid used may be a weak acid or a strong acid. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid and citric acid are preferable. These acids may be used alone or in combination of two or more.

The temperature for the acid treatment varies depending on the type and concentration of the acid used and the time, but it is preferably 100 ° C. or lower.
The time for performing the acid treatment varies depending on the type and concentration of the acid used and the temperature, but is preferably 10 seconds to 5 hours from the viewpoint of productivity, and more preferably 1 minute to 2 hours.
The concentration of the solution to be acid-treated varies depending on the type of acid used, time and temperature, but is preferably such that there is little concern about container corrosion, and specifically 0.05% by weight to 20% by weight is preferable.

  Since the low-density layer is removed by the alkali treatment described later, the thicker the low-density layer, the more easily the glass surface is removed. Therefore, the thickness of the low-density layer is preferably 5 nm or more, and more preferably 20 nm or more, from the viewpoint of the amount of glass surface removed. The thickness of the low density layer can be controlled by the flux concentration, temperature, time, etc. in the contact treatment step.

  The density of the low-density layer is preferably lower than the density of the deep region (bulk) at the center of the glass from the viewpoint of glass surface removability.

The thickness of the low-density layer can be obtained from the period (Δθ) measured by the X-ray reflectance method (XRR).
The density of the low density layer can be determined by the critical angle (θc) measured by XRR.
It is also possible to confirm the formation of the low density layer and the layer thickness by simply observing the cross section of the glass with a scanning electron microscope (SEM).

In the production method of the present invention, subsequently, the following steps are performed after the acid treatment.
Step 6: Alkali treatment By the step 6, the low density layer formed up to the step 5 can be partly or wholly removed [FIG. 1 (b) to FIG. 1 (c)].
Hereinafter, step 6 will be described in detail.

(Step 6-Alkali treatment-)
In step 6, the glass treated with acid in step 5 is further subjected to alkali treatment.
The alkali treatment is carried out by immersing the glass in a basic solution, whereby a part or all of the low density layer can be removed.
The solution is not particularly limited as long as it is basic, as long as it has a pH of more than 7, and a weak base or a strong base may be used. Specifically, bases such as sodium hydroxide, potassium hydroxide, potassium carbonate and sodium carbonate are preferred. These bases may be used alone or in combination of two or more.

The temperature for performing the alkali treatment varies depending on the type and concentration of the base used and the time, but is preferably 0 to 100 ° C, more preferably 10 to 80 ° C, and particularly preferably 20 to 60 ° C. Within this temperature range, there is no risk of glass being corroded, which is preferable.
The time for performing the alkali treatment varies depending on the type and concentration of the base used and the temperature, but is preferably 10 seconds to 5 hours from the viewpoint of productivity, and more preferably 1 minute to 2 hours.
The concentration of the solution subjected to the alkali treatment varies depending on the type of the base used, time and temperature, but is preferably 0.1% by weight to 20% by weight from the viewpoint of glass surface removability.

  By the alkali treatment, part or all of the low density layer in which H has penetrated is removed, and the surface layer having a summit density (Sds) within a specific range is exposed. This makes it possible to obtain glass with improved surface strength. Furthermore, by removing the low-density layer, the scratches existing on the bottom surface of the glass are also removed at the same time, which is also considered to contribute to the improvement of strength.

  It is preferable to have a washing step similar to step 4 between the acid treatment step 5 and the alkali treatment step 6 or after the end of the alkali treatment step 6.

  According to the manufacturing method of the present invention, since the chemical solution to be handled is highly safe, no special equipment is required. Therefore, it is possible to safely and efficiently obtain the float glass having a significantly improved surface strength.

  The amount of the low density layer to be removed depends on the conditions of alkali treatment. FIG. 1C shows a mode in which the low density layer 10 is completely removed, but a part of the low density layer 10 may be removed and a part thereof may remain. From the viewpoint of improving the strength, the effect can be obtained without removing all of the low density layer, but it is preferable to remove all of the low density layer from the viewpoint of stably securing the transmittance of glass.

(Chemical strengthening)
The float glass according to the present invention can be applied to chemical strengthening treatment. After the float glass is obtained by the production method of the present invention, ordinary chemical strengthening treatment can be performed to produce the chemically strengthened glass.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

<Evaluation method>
Various evaluations in this example were performed by the following analysis methods.

(Evaluation of glass: Summit density (Sds))
The summit density (Sds) was obtained according to the method described in the above [AFM measurement conditions and analysis procedure of image analysis software].

(Glass evaluation: amount removed)
The thickness of the amount of glass removed was determined by measuring the weight before and after the chemical treatment with an analytical electronic balance (HR-202i; manufactured by AND) and converting the thickness using the following formula.
(Thickness of removed amount per one side) = ((weight before treatment)-(weight after treatment)) / (glass specific gravity) / treatment area / 2

(Evaluation of glass: surface strength)
The glass surface strength was measured according to the method described in the above [ball-on-ring test].

(Evaluation of glass: hydrogen concentration)
The hydrogen concentration profile was measured according to the method described in [Method for measuring hydrogen concentration profile] above, and the relational expression (I) was derived.

  Of the following test examples, Examples 1-1, 1-2, 2-1, 2-2, 3-1 and 3-2 are examples, and Examples 1-3, 2-3 and 3-3 are examples. This is a comparative example.

<Example 1-1>
(Process of contacting inorganic salt with glass)
Sodium nitrate (938 g), potassium nitrate (429 g) and sodium carbonate (33 g) were added to a SUS cup and heated to 430 ° C. with a mantle heater to prepare a molten salt having a K / Na mass ratio of 0.62. A glass A having a size of 50 mm × 50 mm × 0.56 mm formed by the float method was prepared, preheated to 350 ° C., immersed in a molten salt at 430 ° C. for 1 hour, and cooled to near room temperature for contact treatment. .. The obtained glass was washed with water and subjected to the next step.
Glass A composition (in mol% display): SiO ₂ 64.4%, Al ₂ O ₃ 8.0%, Na ₂ O 12.5%, K ₂ O 4.0%, MgO 10.5%, CaO 0. 1%, SrO 0.1%, BaO 0.1%, ZrO ₂ 0.5%
Glass A specific gravity (g / cm ³ ): 2.48

(Acid treatment process)
6.0 wt% nitric acid (HNO ₃ ; manufactured by Kanto Chemical Co., Inc.) was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. The glass obtained in the contact treatment step was immersed in the adjusted hydrochloric acid for 120 seconds, acid-treated, washed with pure water several times, and then dried by air blow. The glass thus obtained was subjected to the next step.

(Alkaline treatment process)
A 4.0 wt% sodium hydroxide aqueous solution was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. The glass obtained in the acid treatment step was dipped in the adjusted sodium hydroxide aqueous solution for 120 seconds, subjected to alkali treatment, then washed with pure water several times, and then dried by air blow.
From the above, the float glass of Example 1-1 was obtained.

<Example 1-2>
A float glass of Example 1-2 was obtained in the same manner as in Example 1-1, except that the molten glass at 450 ° C. was immersed in the molten salt for 2 hours in the contact treatment with the inorganic salt.

<Example 1-3>
A float glass of Example 1-3 was obtained in the same manner as in Example 1-1, except that the contact treatment with an inorganic salt, the acid treatment, and the alkali treatment were not carried out.

<Example 2-1>
To a SUS cup, 1365 g of sodium nitrate and 35 g of sodium carbonate were added, and heated to 430 ° C. with a mantle heater to prepare a molten salt having a K / Na mass ratio of 0.0. A glass B having a size of 50 mm × 50 mm × 0.56 mm formed by the float method was prepared, preheated to 350 ° C., immersed in a molten salt at 430 ° C. for 1 hour, and then cooled to around room temperature for contact treatment. .. The obtained glass was washed with water and subjected to the next step.
Glass B composition (expressed in mol%): SiO ₂ 68%, Al ₂ O ₃ 10%, Na ₂ O 14%, MgO 8%
Glass B specific gravity (g / cm ³ ): 2.41
The acid treatment and the alkali treatment were performed in the same manner as in Example 1-1 to obtain the float glass of Example 2-1.

<Example 2-2>
In the contact treatment with the inorganic salt, a float glass of Example 2-2 was obtained in the same manner as in Example 2-1, except that it was immersed in a molten salt at 450 ° C for 2 hours.

<Example 2-3>
A float glass of Example 2-3 was obtained in the same manner as in Example 2-1, except that the contact treatment with an inorganic salt, the acid treatment, and the alkali treatment were not carried out.

<Example 3-1>
5280 g of sodium nitrate, 84 g of potassium nitrate and 136 g of sodium carbonate were added to a SUS cup and heated to 430 ° C. with a mantle heater to prepare a molten salt with a K / Na mass ratio of 0.02. A glass C having a size of 50 mm × 50 mm × 0.7 mm formed by the float method was prepared, preheated to 350 ° C., immersed in a molten salt at 430 ° C. for 1 hour, and cooled to near room temperature for contact treatment. .. The obtained glass was washed with water and subjected to the next step.
Glass C composition (in mol%): SiO ₂ 68.5%, Al ₂ O ₃ 5%, Na ₂ O 14.6%, MgO 4.1%, CaO 7.3%, K ₂ O 0.2%
Glass C specific gravity (g / cm ³ ): 2.5
The acid treatment and the alkali treatment were performed in the same manner as in Example 1-1 to obtain the float glass of Example 3-1.

<Example 3-2>
In the contact treatment with the inorganic salt, a float glass of Example 3-2 was obtained in the same manner as in Example 3-1, except that the molten glass at 450 ° C was immersed for 2 hours.

<Example 3-3>
A float glass of Example 3-3 was obtained in the same manner as in Example 3-1, except that the contact treatment with an inorganic salt, the acid treatment, and the alkali treatment were not carried out.

Table 1 shows the evaluation results of each float glass obtained as described above.
Regarding the surface strength of glass, when the surface strength of Example 1-3 was set to 1 in Examples 1-1 and 1-2, the surface of Example 2-3 was set in Examples 2-1 and 2-2. When the strength is set to 1, each of Examples 3-1 and 3-2 is represented by a relative ratio when the surface strength of Example 3-3 is set to 1.
5 to 7 are graphs in which the hydrogen concentration profile of the surface layer of each float glass obtained in each example is plotted.

  Although the present invention has been described in detail and with reference to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on the Japanese patent application filed on January 20, 2015 (Japanese Patent Application No. 2015-008850), the contents of which are incorporated herein by reference.

10 Low-density layer 30 Intermediate layer

Claims (9)

There are no polishing scratches on the surface,
Float glass having a summit density (Sds) of 4700 or less measured under the following conditions on the bottom surface in contact with molten metal during float forming.
Summit density (Sds) measurement conditions: atomic force microscope (AFM, Atomic Force Microscope) (XE-HDM; manufactured by Park Systems), measurement mode: non-contact mode, scan size: 1 μm × 0.5 μm, number of pixels: 256 × 128, color scale: ± 0.5 nm, scan speed: 1 Hz, cantilever: Non-Contact Cantilever (Item: PPP-NCHR 10M; manufactured by Park Systems), and then attached to the AFM device. Image analysis software (XEI) is used to perform flattening processing in the X and Y directions of the shape image, and the flattened shape image is analyzed using image analysis software (SPIP 6.2.6; Image Metrology Co., Ltd.). Is used to perform L-filtering processing (ISO value 2.0 μm) of the shape image, and the summit density (Sds) is obtained by roughness analysis. The float according to claim 1, wherein a straight line linearly approximating the hydrogen concentration Y in the region of depth X from the outermost surface of the glass satisfies the following relational expression (I) at X = 0.10 to 0.25 (μm). Glass.
Y = aX + b (I)
[The meaning of each symbol in formula (I) is as follows.
Y: Hydrogen concentration (H ₂ O conversion, mol / L)
X: Depth from the outermost surface of the glass (μm)
a: -2.700 or more b: 0.700 or less]   The float glass according to claim 1, which does not have a compressive stress layer. The float glass according to claim 1, which is compatible with a chemical strengthening treatment. Contacting by immersing the glass molded by the float process in a molten salt of an inorganic salt,
Cleaning the glass after contact with the inorganic salt,
Comprising a step of acid-treating the glass after the cleaning, and a step of alkali-treating the glass after the acid treatment,
The inorganic salts _are selected from _{K 2 CO 3, Na 2 CO} 3, KHCO 3, NaHCO 3, K 3 PO 4, Na 3 PO 4, K 2 SO 4, Na 2 SO 4, KOH and the group consisting of NaOH When the K / Na mass ratio in the inorganic salt is A and the K / Na mass ratio in the glass composition is B, A ≧ 0 and A−B = −0.30 containing at least one flux. ~ +1.00 range,
Float glass manufacturing method. The method for producing a float glass according to claim 5 , wherein the inorganic salt further contains at least one of potassium nitrate and sodium nitrate. Contacting by immersing the glass molded by the float process in a molten salt of an inorganic salt,
Cleaning the glass after contact with the inorganic salt,
Comprising a step of acid-treating the glass after the cleaning, and a step of alkali-treating the glass after the acid treatment,
The inorganic salt contains at least one flux selected from the group consisting of Li ₂ CO ₃ , LiHCO ₃ , Li ₃ PO ₄ , Li ₂ SO ₄ and LiOH, and the Na / Li mass ratio in the inorganic salt is C. When the Na / Li mass ratio in the glass composition is D, C ≧ 0 and C−D = −0.30 to +1.00.
Float glass manufacturing method. The method for producing a float glass according to claim 7 , wherein the inorganic salt further contains at least one of potassium nitrate and sodium nitrate. A method for producing chemically strengthened glass, comprising producing float glass by the method according to claim 5 , and subjecting the obtained float glass to chemical strengthening treatment.

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