JP2022066785A - Optical element with compressive stress layer - Google Patents

Abstract

To provide an optical element excellent in press moldability, having a desired compressive stress and a desired compressive stress layer depth, and excellent in heat shock resistance.SOLUTION: An optical element has a compressive stress layer on the surface. The compressive stress in the compressive stress layer is 100-1000 MPa, the compressive stress layer depth is 10-100 μm, and the temperature with logη=8.5 (viscosity) is lower than 700°C.SELECTED DRAWING: None

Description

The present invention relates to an optical element having a compressive stress layer.

In recent years, there has been an increase in demand for projection optical equipment such as projectors and imaging optical equipment such as in-vehicle cameras and surveillance cameras, and the optical elements used inside the optical system are assumed to be in various environments. It is becoming necessary to take measures.

In projection optical system equipment, a light source using a high-output semiconductor light-emitting element is required in order to magnify and project an image onto a screen more clearly, and high-pressure discharge or the like has been used in the past, but there is a demand for compactness. Since then, LDs and LED light sources have come to be used.

Since heat is also emitted from the LD or LED light source of the projection optical system device together with the light, the optical element inside the projection optical system device may be exposed to a high temperature. In particular, the use of high-power light sources has led to exposure to large temperature changes. The temperature change is large, and the temperature of the optical element may be about 200 ° C. or higher, and there is a problem that the optical element is cracked when the temperature is lowered from the high temperature state to room temperature.
Therefore, optical elements used in projection optical systems are required to have high transmission and high homogeneity as well as thermal shock resistance.

Further, for the optical element inside the projection optical system device, it is necessary to manufacture an aspherical lens having a complicated shape such that the vertical and horizontal arrangements are arranged in a matrix, and higher press formability than the conventional optical element is required. ..

In particular, it is expensive and low efficiency to manufacture an aspherical lens by grinding or polishing, so as a method for manufacturing an aspherical lens, a preform material obtained by cutting and polishing a gob or a glass block is heated and softened. By precision mold molding, in which this is pressure-molded with a molding mold having a high-precision surface, it is possible to omit the grinding and polishing steps, and low cost and mass production are realized.

On the other hand, in an imaging optical system device, there is a problem that the optical element and the entire optical device are rapidly heated by direct sunlight, and after being heated, the optical element is rapidly cooled by rain or water at the time of car wash and the optical element is cracked. ..

The invention described in Patent Document 1 is disclosed as a glass having good press formability.

Japanese Unexamined Patent Publication No. 2019-006643

However, in the invention disclosed in Patent Document 1, although a glass having good press formability is obtained by lowering the transition point, a complicated aspherical lens is manufactured because the temperature at logη = 8.5 is high. It is not possible, and it is difficult to stabilize the thermal shock resistance.

The present invention has been made in view of the above problems, and an object thereof is excellent in press moldability, having a desired compressive stress and a depth of a compressive stress layer, and having thermal shock resistance. The purpose is to obtain an excellent optical element.

As a result of intensive test and research to solve the above problems, the present inventor has improved the press formability by setting the temperature at which logη = 8.5 (viscosity) is less than 700 ° C. The present invention has excellent thermal shock resistance by having a compressive stress of 1000 MPa and a depth of a compressive stress layer of 10 to 100 μm and setting the ratio of compressive stress to thermal stress (compressive stress / thermal stress) to 1.00 or more. It came to be completed.

(1) An optical element having a compressive stress layer on its surface.
The compressive stress of the compressive stress layer is 100 to 1000 MPa, and the depth of the compressive stress layer is 10 to 100 μm.
An optical element having a temperature of less than 700 ° C. at logη = 8.5 (viscosity).

(2) The optical element according to (1), wherein the refractive index (nd) is 1.45,000 or more and 1.70000 or less, and the Abbe number (νd) is 45.00 or more and 70.00 or less.

(3) The optical element according to (1) or (2), wherein the ratio of compressive stress to thermal stress (compressive stress / thermal stress) is 1.00 or more.

(4) The optical element according to any one of (1) to (3) used in a projection optical system device.

(5) The optical element according to any one of (1) to (3) used in an imaging optical system device.

The optical element of the present invention has a compressive stress layer on its surface. There are a physical strengthening method and a chemical strengthening method as a method of forming a compressive stress layer on the surface, and the optical element of the present invention is formed by the chemical strengthening method.
Further, in the present invention, the mold press formability is described as press formability.

In the optical element of the present invention, the lower limit of the compressive stress of the compressive stress layer is preferably 100 MPa or more, more preferably 200 MPa or more, further preferably 280 MPa or more, and most preferably 340 MPa or more. The greater the compressive stress, the higher the mechanical strength of the tempered glass.
On the other hand, when an extremely large compressive stress is formed on the surface, the tensile stress CT inherent in the tempered glass becomes high, and there is a risk of self-destruction. Therefore, the compressive stress of the compressive stress layer is more preferably 1000 MPa or less, more preferably 800 MPa or less, further preferably 650 MPa or less, and most preferably 600 MPa or less.

As for the depth of the compressive stress layer, the larger the depth of the compressive stress layer, the more difficult it is for scratches formed on the surface to penetrate the compressive stress layer, so that the crack resistance is improved. Therefore, the lower limit is preferably 10 μm or more, more preferably 15 μm or more, and most preferably 20 μm or more. On the other hand, the deeper the compressive stress layer, the higher the tensile stress CT inherent in the tempered glass, which may cause self-destruction, which further affects the refractive index and Abbe number, making it difficult to use as an optical element. .. Therefore, the depth of the compressive stress layer is preferably 100 μm or less, more preferably 70 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, and most preferably 33 μm or less.

The ratio of compressive stress to thermal stress (compressive stress / thermal stress) is preferably 1.00 or more. As a result, the thermal shock resistance is increased, and the optical element is less likely to crack even if a large temperature difference occurs. Therefore, the lower limit is preferably 1.00 or more, more preferably 1.60 or more, more preferably 2.00 or more, still more preferably 2.20 or more, and most preferably 2.40 or more.

The thermal stress here represents the thermal stress using the temperature difference when the temperature drops from 300 ° C to 100 ° C.
Thermal stress (MPa) = Young's modulus (10 ⁸ Pa) x average linear thermal expansion coefficient α ( ^10-7 / ° C) x 200 (° C) x ^10-6

The optical element of the present invention can suppress the occurrence of thermal cracking due to the small thermal stress. Therefore, the thermal stress may be preferably 330 (MPa) or less, more preferably 230 (MPa) or less, and further preferably 180 (MPa) or less as the upper limit.

The optical element of the present invention may have a small Young's modulus. In particular, the Young's modulus of the optical element of the present invention may be preferably 1100 (108 Pa) or less, more preferably 1000 ( ^{10 8} Pa) or less, and further preferably 950 ( ¹⁰⁸ Pa) or less.

In the optical element of the present invention, the average linear thermal expansion coefficient α at 100 to 300 ° C. is preferably in the range of 40 to 150 (× ^10-7 / ° C.). Since the optical glass of the present invention has α in the above range, the expansion matching with the mold at the time of precision press molding is good without impairing the heat impact resistance. This α is more preferably 40 to 150 (× 10 ^-7 / ° C.), still more preferably 50 to 135 (× 10 ^-7 / ° C.), and even more preferably 60 to 115 (× 10 ^-7 / ° C.). ), Particularly preferably 65 to 105 (× 10 ^-7 / ° C.).

The optical element of the present invention preferably has a temperature at which logη = 8.5 (viscosity) is less than 700 ° C. As a result, the glass softens at a lower temperature, so that the glass can be easily press-molded at a lower temperature, and an aspherical lens having a more complicated shape can be press-molded. It is also possible to reduce the oxidation of the die used for press molding to extend the life of the die. Therefore, it is preferably less than 700 ° C., more preferably 650 ° C. or lower, still more preferably 620 ° C. or lower, still more preferably 610 ° C. or lower.

The optical element of the present invention has a predetermined refractive index and a predetermined Abbe number in a predetermined range.
The lower limit of the refractive index (nd) of the optical element of the present invention is preferably 1.45,000 or more, more preferably 1.48,000 or more. The upper limit of the refractive index is preferably 1.70000 or less, more preferably 1.65000 or less, more preferably 1.60000 or less, and further preferably 1.55000.
The Abbe number (νd) of the optical element of the present invention is preferably 45.00 or more, more preferably 47.00 or more, and further preferably 50.00 or more as the lower limit. The upper limit of the Abbe number is preferably 70.00 or less, more preferably 67.00 or less.
The optical element of the present invention having such a refractive index and Abbe number is useful in optical design, and the optical system can be miniaturized while achieving particularly high imaging characteristics, so that the optical design is free. You can increase the degree.

Hereinafter, the glass constituting the optical element of the present invention will be described.
[Glass component]
In the present specification, the content of each component shall be indicated by cation% or anion% based on the molar ratio, unless otherwise specified. First, the constituent components of glass are divided into a cation component and an anion component. The "cation%" is a unit in which the content of each cation component is expressed as a percentage when the total content of all cation components contained in the glass is 100 mol%. The "anion%" is a unit in which the content of each anion component is expressed as a percentage when the total content of all anion components contained in the glass is 100 mol%.

<About essential ingredients and optional ingredients>
Si ⁴⁺ is a component capable of promoting stable glass formation, lowering the liquidus temperature, and reducing devitrification (generation of crystals).
In particular, by setting the Si ⁴⁺ content to 37.0% or more, vitrification becomes easier, the coefficient of thermal expansion can be lowered, thermal impact resistance is improved, and glass with excellent devitrification resistance can be obtained. Not only can it be obtained, but the ion exchange performance tends to improve and the compressive stress tends to increase. Therefore, the lower limit of the Si ⁴⁺ content is preferably 37.0% or more, more preferably 41.0%, more preferably 44.0% or more, still more preferably 45.5% or more.
On the other hand, by setting the Si ⁴⁺ content to 75.0% or less, the meltability and moldability are likely to decrease, and the coefficient of thermal expansion can be prevented from becoming too low. Therefore, the content of Si ⁴⁺ is preferably 75.0% or less, more preferably 70.0% or less, still more preferably 67.5% or less.
As the Si ⁴⁺ , SiO ₂ , K ₂ SiF ₆ , Na ₂ SiF ₆ , and the like can be used as raw materials.

Li ⁺ is an ion exchange component, a component that lowers high-temperature viscosity, enhances meltability and moldability, and is an optional component that enhances Young's modulus. Therefore, the lower limit of the Li ⁺ content is preferably 0% or more, more preferably more than 0%, more preferably 5.0% or more, more preferably 10.0% or more, and most preferably 12.0% or more. And.
On the other hand, when the Li ⁺ content is extremely high, the compressive stress tends to decrease. Low temperature viscosity may decrease, stress relaxation may occur more easily, and compressive stress may decrease. The coefficient of thermal expansion becomes too high, the thermal impact resistance decreases, and it becomes difficult to match the coefficient of thermal expansion of the peripheral materials.
Therefore, the Li ⁺ content is preferably 30.0% or less, more preferably 26.0% or less, still more preferably 24.0% or less.
As Li ⁺ , Li ₂ CO ₃ , LiNO ₃ , LiF or the like can be used as a raw material.

Na ⁺ is an ion exchange component, and is an optional component that increases compressive stress, reduces high-temperature viscosity, enhances meltability and moldability, and increases the coefficient of thermal expansion. Therefore, the lower limit of the Na ⁺ content is preferably 0% or more, more preferably 0.1% or more, still more preferably 0.2% or more.
On the other hand, by setting the Na ⁺ content to 25.0% or less, devitrification due to excessive content can be reduced.
Therefore, the Na ⁺ content is preferably 25.0% or less, more preferably 12.5% or less, still more preferably 10.0% or less.
As Na ⁺ , Na ₂ CO ₃ , NaNO ₃ , NaF, Na ₂ SiF ₆ and the like can be used as raw materials.

K ⁺ is a component that promotes ion exchange, and is an optional component that easily increases the depth of the compressive stress layer among alkali metal oxides. It is also a component that lowers high-temperature viscosity, enhances meltability and moldability, and improves devitrification resistance. Therefore, the lower limit of the K ⁺ content is preferably 0% or more, more preferably more than 0%, more preferably 1.0% or more, and most preferably 3.0% or more.
On the other hand, if the content of K ⁺ is too high, the coefficient of thermal expansion becomes too high and the thermal shock resistance deteriorates. Therefore, the content of K ⁺ is preferably 18.0% or less, more preferably 15.0% or less, still more preferably 13.0% or less.
For K ⁺ , K ₂ CO ₃ , KNO ₃ , KF, KHF ₂ , K ₂ SiF ₆ , or the like can be used as a raw material.

When B ³⁺ is contained in an amount of more than 0%, stable glass formation can be promoted and the liquidus temperature can be lowered, so that the devitrification resistance is enhanced, the meltability of the glass raw material is enhanced, and the glass is made of glass. It is an optional component that improves mechanical properties such as strength and crack resistance. Therefore, the content of B ³⁺ is preferably 0% or more, more preferably more than 0%, more preferably 5.0% or more, still more preferably 10.0% or more, still more preferably 13.0% or more, most preferably. The lower limit is preferably 15.0% or more.
On the other hand, if the amount of B ³⁺ increases, the chemical durability deteriorates and phase separation occurs. Therefore, the content of B ³⁺ is preferably 35.0% or less, more preferably 30.0% or less, still more preferably 27.0% or less, and most preferably 25.0% or less.
As the B ³⁺ , H ₃ BO ₃ , Na ₂ B ₄ O ₇ , Na ₂ B ₄ O ₇・ 10H ₂ O, BPO ₄ and the like can be used as raw materials.

Zn ²⁺ is an optional component capable of reducing high temperature viscosity. However, if the content of Zn ²⁺ is too large, the glass is phase-separated, the devitrification resistance is lowered, the depth of the compressive stress layer is reduced, stress relaxation is more likely to occur, and the compressive stress is rather increased. May decrease. Therefore, the lower limit of the Zn ²⁺ content is preferably 0% or more, more preferably more than 0%, more preferably 0.1% or more, still more preferably 0.2% or more.
On the other hand, by setting the Zn ²⁺ content to 2.0% or less, it is possible to suppress the phase separation of the glass and the decrease in devitrification resistance, and it is possible to prevent the decrease in compressive stress due to stress relaxation. .. Therefore, the content of Zn ²⁺ is preferably 2.0% or less, more preferably 1.5% or less, more preferably 1.0% or less, and most preferably 0.8% or less.

Rare earth oxides such as Nb ⁵⁺ and La ³⁺ , Gd ³⁺ , Y ³⁺ , and Yb ³⁺ are optional components that increase rigidity. However, the cost of the raw material itself is high, and if a large amount is added, the devitrification resistance tends to decrease. Therefore, the content of the rare earth oxide is preferably 3% or less, preferably 2% or less, preferably 1% or less, preferably 0.5% or less, and particularly preferably 0.1% or less.
Nb ^5+, La ³⁺ , Gd ³⁺ , Y ³⁺ and Yb ³⁺ are raw materials such as Nb ₂ O _5, La ₂ O ₃ , La (NO ₃ ) ₃ · XH ₂ O (X is an arbitrary integer), Y ₂ O ₃ , YF ₃ , Gd ₂ O ₃ , GdF ₃ , Yb ₂ O ₃ , and the like can be used.

Ti ⁴⁺ is a component that enhances ion exchange performance and is an optional component that lowers high-temperature viscosity. Therefore, the lower limit of the Ti ⁴⁺ content is preferably more than 0%, more preferably 0.02% or more, and most preferably 0.03% or more.
On the other hand, by setting Ti ⁴⁺ to 10.0% or less, the coloring of the glass can be reduced and the internal transmittance can be increased. Therefore, the content of Ti ⁴⁺ is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 1.0% or less.
For Ti ⁴⁺ , TIO ₂ or the like can be used as a raw material.

Al ³⁺ is an optional component that enhances ion exchange performance. If the amount of Al ³⁺ is too small, the ion exchange performance cannot be fully exhibited. Therefore, the lower limit of the content of Al ³⁺ is preferably more than 0%, more preferably 1.0% or more, further preferably 1.5% or more, and most preferably 2.0% or more.
On the other hand, by reducing the content of Al ³⁺ to 10.0% or less, devitrification due to excessive content of Al ³⁺ can be reduced. Therefore, the content of Al ³⁺ is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 3.0% or less.
As the Al ³⁺ , Al ₂ O ₃ , Al (OH) ₃ , Al F ₃ and the like can be used as raw materials.

Mg ²⁺ is an optional component that can lower the melting temperature of glass, lower the high temperature viscosity, increase the meltability, and increase Young's modulus.
On the other hand, by setting the content of Mg ²⁺ to 10.0% or less, devitrification can be reduced while suppressing a decrease in the refractive index. Therefore, the content of Mg ²⁺ is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 1.0% or less.
As the Mg ²⁺ , MgO, MgCO ₃ , MgF ₂ , or the like can be used as a raw material.

Ca ²⁺ is an optional component capable of lowering high-temperature viscosity, increasing meltability, and increasing Young's modulus without reducing devitrification resistance. However, if the content of Ca ²⁺ is too large, the density and the coefficient of thermal expansion become high, and the component balance of the glass composition is lost, so that the glass tends to be devitrified, the ion exchange performance deteriorates, and ions. It tends to deteriorate the exchange solution. Therefore, the Ca ²⁺ content is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less, and most preferably 1.0 or less.
For Ca ²⁺ , CaCO ₃ , CaF ₂ , or the like can be used as a raw material.

Sr ²⁺ is an optional component that can lower the melting temperature of glass, lower the high-temperature viscosity, increase the meltability, and increase Young's modulus.
On the other hand, by setting the content of Sr ²⁺ to 10.0% or less, the glass is stabilized and the devitrification of the glass can be suppressed. Therefore, the content of Sr ²⁺ is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 1.0% or less.
For Sr ²⁺ , Sr (NO ₃ ) ₂ , SrF ₂ , or the like can be used as a raw material.

Ba ²⁺ is an optional component capable of lowering high-temperature viscosity and improving meltability and moldability when it is contained in an amount of more than 0%.
On the other hand, by setting the Ba ²⁺ content to 20.0% or less, devitrification during reheat pressing can be reduced, and the ion exchange reaction is less likely to be inhibited. Therefore, the content of Ba ²⁺ is preferably 20.0% or less, more preferably 15.0% or less, still more preferably 12.0% or less.
For Ba ²⁺ , BaCO ₃ , Ba (NO ₃ ) ₂ , and the like can be used as raw materials.

The sum of the contents (mass sum) of Rn ⁺ (in the formula, Rn ⁺ is one or more selected from the group consisting of Li ⁺ , Na ⁺ , and K ⁺ ) is melted when it is contained in an amount of 5.0% or more. It is an optional component that can enhance the properties and moldability. Therefore, the lower limit of the sum of Rn ⁺ is preferably 5.0% or more, more preferably 15.0% or more, and more preferably 20.0% or more.
On the other hand, when the sum of the contents of Rn ⁺ (sum of mass) is 35.0% or less, the decrease in the refractive index can be suppressed and the devitrification due to the excessive content can be reduced. Therefore, the upper limit is preferably 35.0% or less, more preferably 32.0% or less, and further preferably 30.0% or less.

Zr ⁴⁺ is an optional component that can increase the refractive index and Abbe number of glass when it is contained in excess of 0%.
On the other hand, by setting the content of Zr ⁴⁺ to 10.0% or less, devitrification can be reduced and more homogeneous glass can be easily obtained. Therefore, the content of Zr ⁴⁺ is preferably 10.0% or less, more preferably 5.0% or less, and more preferably 1.0% or less.
For Zr ⁴⁺ , ZrO ₂ , ZrF ₄ , or the like can be used as a raw material.

Ta ⁵⁺ is an optional component that can increase the refractive index and the Abbe number when it is contained in excess of 0%.
On the other hand, by setting the Ta ⁵⁺ content to 10.0% or less, the devitrification of the glass due to the excessive Ta ⁵⁺ content can be reduced. Therefore, the content of Ta ⁵⁺ is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less, still more preferably 1.0% or less.
For Ta ⁵⁺ , Ta ₂ O ₅ or the like can be used as a raw material.

W ⁶⁺ is an optional component that, when it is contained in excess of 0%, can increase the refractive index, reduce the Abbe number, and enhance the meltability of the glass raw material.
On the other hand, by setting the W ⁶⁺ content to 10.0% or less, the coloring of the glass can be reduced and the devitrification of the glass can be suppressed. Therefore, the content of W ⁶⁺ is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less, still more preferably 1.0% or less.
For W ⁶⁺ , WO ₃ or the like can be used as a raw material.

P ⁵⁺ is an optional component capable of enhancing the stability of the glass, enhancing the ion exchange performance, and increasing the depth of the compressive stress layer when the content exceeds 0%.
On the other hand, by reducing the content of P ⁵⁺ to 10.0% or less, devitrification due to excessive content of P ⁵⁺ can be reduced, phase separation of glass can be prevented, and deterioration of water resistance can be suppressed. .. Therefore, the content of P ⁵⁺ is preferably 10.0% or less, more preferably 5.0% or less, and further preferably 3.0% or less.
For P ⁵⁺ , Al (PO ₃ ) ₃ , Ca (PO ₃ ) ₂ , Ba (PO ₃ ) ₂ , BPO ₄ , H ₃ PO ₄ , and the like can be used as raw materials.

Ge ⁴⁺ is an optional component capable of increasing the refractive index when it is contained in excess of 0%.
On the other hand, devitrification can be suppressed by setting the content of Ge ⁴⁺ to 10.0% or less. Therefore, the content of Ge ⁴⁺ is preferably 10.0% or less, more preferably 5.0% or less, still more preferably 3.0% or less.
For Ge ⁴⁺ , GeO ₂ or the like can be used as a raw material.

Sn ⁴⁺ is an optional component capable of clarifying (defoaming) the melted glass and enhancing the ion exchange performance when the content exceeds 0%.
On the other hand, by setting the Sn ⁴⁺ content to 1.0% or less, it is possible to prevent the glass from being colored or devitrified by the reduction of the molten glass. Further, since the alloying of Sn ⁴⁺ and the melting equipment (particularly noble metal such as Pt) is reduced, the life of the melting equipment can be extended. Therefore, the Sn ⁴⁺ content is preferably 1.0% or less, more preferably 0.5% or less, still more preferably 0.1% or less.
For Sn ⁴⁺ , SnO, SnO ₂ , SnF ₂ , SnF ₄ , and the like can be used as raw materials.

Sb ³⁺ is a component that promotes defoaming of glass and clears glass when it is contained in excess of 0%, and is an optional component in the optical glass of the present invention. By setting the content of Sb ³⁺ to 1.0% or less of the total mass of the glass, it is possible to prevent excessive foaming during glass melting, and Sb ³⁺ is an alloy with melting equipment (particularly precious metals such as Pt). It can be difficult to change. Therefore, the content of Sb ³⁺ is preferably 1.0% or less, more preferably 0.8% or less, and further preferably 0.6% or less.
As the Sb ³⁺ , Sb ₂ O ₃ , Sb ₂ O ₅ , Na ₂ H _{2 Sb 2} O _7.5 H ₂ O and the like can be used as raw materials.

The component that clarifies and defoams the glass is not limited to the above Sb ³⁺ , and a clarifying agent, a defoaming agent, or a combination thereof known in the field of glass production can be used.

F ⁻ has a property of making it difficult for the glass to be devitrified when it is contained in excess of 0%.
On the other hand, when the content of F ⁻ is high, the Abbe number of the glass is excessively increased, the refractive index is lowered, and the liquidus temperature is lowered. Therefore, the content of F ⁻ is preferably 10.0% or less, more preferably 7.0% or less, still more preferably 5.0% or less.
F ⁻ can be contained in glass by using fluoride of various cationic components such as AlF ₃ , MgF ₂ , and BaF ₂ as a raw material.

<Ingredients that should not be included>
Next, components that should not be contained in the optical glass of the present invention and components that are not preferable to be contained will be described.

Other components can be added as needed within a range that does not impair the characteristics of the glass of the present invention. However, each transition metal component such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Mo, excluding Ti, Zr, Nb, W, La, Gd, Y, Yb and Lu, is used alone. Alternatively, even if the glass is compounded and contained in a small amount, the glass is colored and has a property of causing absorption at a specific wavelength in the visible region. ..

Further, since lead compounds such as Pb ²⁺ and arsenic compounds such as As ³⁺ are components having a high environmental load, it is desirable that they are not substantially contained, that is, they are not contained at all except for unavoidable contamination.

Furthermore, each component of Th, Cd, Tl, Os, Be, and Se has tended to refrain from being used as a harmful chemical substance in recent years, and is used not only in the glass manufacturing process but also in the processing process and disposal after commercialization. Environmental measures are required up to this point. Therefore, when the environmental impact is emphasized, it is preferable that these are not substantially contained.

[Production method]
The optical glass used in the present invention is produced, for example, as follows. That is, the above raw materials are uniformly mixed so that each component is within a predetermined content range, and the prepared mixture is put into a platinum crucible, a quartz crucible or an alumina crucible and roughly melted, and then a gold crucible and a platinum crucible. , Platinum alloy crucible or iridium crucible, melted in a temperature range of 1000 to 1400 ° C for 3 to 5 hours, stirred and homogenized to break bubbles, etc., then lowered to a temperature of 950 to 1250 ° C and then finished stirring. It is produced by removing the crucible, casting it in a mold, and slowly cooling it.

[Optical element]
A glass optical element can be manufactured from the manufactured optical glass by using, for example, mold press molding means. That is, a preform for mold press molding is produced from optical glass, and the preform is molded by mold press molding to produce a glass molded body, or, for example, a preform produced by polishing is molded. A glass optical element can be manufactured by press molding. The means for producing the glass molded body is not limited to these means.

The optical element thus produced is particularly preferably used for applications such as lenses and prisms. As a result, color bleeding due to chromatic aberration in the transmitted light of the optical system provided with the optical element is reduced. Therefore, when this optical element is used in a camera, an object to be photographed can be expressed more accurately, and when this optical element is used in a projector, a desired image can be projected with higher definition.

The chemical strengthening method of the optical element of the present invention is a method of introducing alkaline ions having a large ionic radius into the surface of glass by ion exchange treatment at a temperature equal to or lower than the strain point of the glass. If the compressive stress layer is formed by the chemical strengthening method, the compressive stress layer can be formed properly even if the glass plate thickness is small, and even if the tempered glass is cut after the compressive stress layer is formed, it is air-cooled. Unlike the physical strengthening method such as the strengthening method, the tempered glass is not easily broken.

The chemical fortification method can be carried out, for example, in the following steps. The crystallized glass base material is contacted or immersed in a salt containing potassium or sodium, such as potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ) or a mixed salt thereof or a molten salt of a composite salt. The treatment of contacting or immersing the molten salt (chemical strengthening treatment) may be performed in one step or in two steps.

For example, in the case of a one-step chemical strengthening treatment, the salt containing potassium or sodium heated at 350 ° C. to 550 ° C., or a mixed salt thereof, is contacted or immersed for 30 minutes to 24 hours. In the case of the two-step chemical strengthening treatment, first, it is contacted or immersed in a sodium salt heated at 350 ° C. to 550 ° C. or a mixed salt of potassium and sodium for 30 minutes to 24 hours. Subsequently, it is contacted or immersed in a potassium salt heated at 350 ° C. to 550 ° C. or a mixed salt of potassium and sodium for 30 minutes to 24 hours.

Table 1 is a composition example (ac) of the glass used in this example and the comparative example. The following examples are for illustrative purposes only, and are not limited to these examples.

For the glass in Table 1, high-purity raw materials used for ordinary optical glass such as oxides, hydroxides, carbonates, nitrates, fluorides, and metaphosphate compounds corresponding to each component are selected as raw materials. Then, after weighing and mixing uniformly so as to have the composition ratio shown in Table 1, the glass is put into a stone crucible (a platinum crucible or an alumina crucible may be used depending on the meltability of the glass) and glass. Depending on the difficulty of melting the composition, it is melted in an electric furnace in a temperature range of 1100 to 1400 ° C. for 0.5 to 5 hours, then transferred to a platinum crucible, stirred and homogenized to break bubbles, and then 1000 to 1200 ° C. After lowering the temperature to homogenize by stirring, the glass was cast into a mold and slowly cooled to prepare glass.

The refractive index (nd) and Abbe number (νd) of the glass in Table 2 were measured according to the V-block method specified in JIS B 7071-2: 2018.

The method for measuring the photoelastic constant in Table 2 is that the sample shape is face-to-face polished to form a disk with a diameter of 25 mm and a thickness of 8 mm, and the compressive load is 0 to about 100 in the lateral direction. kgf was added, and the optical path difference at a wavelength of 546.1 nm generated in the center of the glass was measured and determined by the relational expression of δ = β · d · F. In the above formula, the optical path difference is expressed as δ (nm), the glass thickness is expressed as d (cm), and the stress is expressed as F (MPa).

The photoelastic constant is used to measure the compressive stress of the surface compressive stress layer and the depth of the compressive stress layer.

The average coefficient of linear thermal expansion α (100-300 ° C.) of glass in Table 2 measures the relationship between temperature and sample elongation in accordance with the Japan Optical Glass Industry Association standard JOBIS08-2003 “Method for measuring thermal expansion of optical glass”. It was obtained from the thermal expansion curve obtained by doing so.

The Young's modulus in Table 2 was measured according to the elastic modulus test method for fine ceramics specified in JIS R 1602: 1995.

The temperature at which logη = 8.5 (viscosity) in Table 2 is such that the sample shape is about φ7 × 7 mmt, the glass sample is processed so that the planes are parallel, and the glass parallel plate viscosity measuring device (model number: PPVM-1100). The measurement was carried out using.

Each sample (ac) was cut and ground, and double-sided parallel polishing was performed so that the thickness was about 1.0 mm to prepare a glass plate.

Next, the prepared glass plate was chemically strengthened under the conditions shown in Tables 3 to 5. The compressive stress of the surface compressive stress layer and the depth of the compressive stress layer were calculated from the number of interference fringes observed using a surface stress meter (FSM-6000LE manufactured by Orihara Seisakusho) and their intervals. In the calculation, the measured values of the refractive index (nd) and the optical elastic constant (β) of each sample were used.

Table 3 shows an example and a comparative example of the sample a subjected to the chemical strengthening treatment.

Table 4 shows an example and a comparative example of the sample b subjected to the chemical strengthening treatment.

Table 5 shows an example of the sample c that has been chemically strengthened.

As shown in Table 2, the temperature at which logη = 8.5 (viscosity) of the sample (ac) used in this example and comparative example was less than 700 ° C. Therefore, it was clarified that the samples (ac) used in this example and the comparative example were excellent in press formability.

Further, the samples (ac) had a refractive index (nd) of 1.45,000 or more and 1.70000 or less, and an Abbe number (νd) of 45.00 or more and 70.00 or less, which were within the desired ranges. ..

The compressive stress of the examples represented by Tables 3 to 5 was 100 to 1000 Mpa, and the depth of the compressive stress layer was 10 to 100 μm, which were within the desired range. In Comparative Example b-1 represented by Table 4, the depth of the compressive stress layer was only 9.7 μm, which was out of the desired range.

As shown in Tables 3 to 5, the compressive stress / thermal stress of the examples was 1.00 or more. Therefore, the examples shown in Tables 3 to 5 had good thermal impact resistance.

Although the present invention has been described in detail above for the purpose of illustration, the present embodiment is merely for the purpose of illustration, and many modifications can be made by those skilled in the art without departing from the idea and scope of the present invention. Will be understood.

Claims (5)

An optical element having a compressive stress layer on its surface.
The compressive stress of the compressive stress layer is 100 to 1000 MPa, and the depth of the compressive stress layer is 10 to 100 μm.
An optical element having a temperature of less than 700 ° C. at logη = 8.5 (viscosity). The optical element according to claim 1, wherein the refractive index (nd) is 1.45,000 or more and 1.70000 or less, and the Abbe number (νd) is 45.00 or more and 70.00 or less. The optical element according to claim 1 or 2, wherein the ratio of compressive stress to thermal stress (compressive stress / thermal stress) is 1.00 or more. The optical element according to any one of claims 1 to 3, which is used in a projection optical system device. The optical element according to any one of claims 1 to 3, which is used in an imaging optical system device.