JP2015094785A - Optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemically strengthened optical element, the optical element preventing the occurrence of color unevenness, intensity unevenness, and a reduction in color balance to an image of an optical instrument using the optical element.SOLUTION: There is provided an optical element composed of chemically-strengthened glass having, on the surface, a compressive stress layer formed by chemical strengthening processing, and having a birefringence amount with respect to normal incident light of 20 nm/cm or less, a birefringence amount with respect to 20° incident light of 20 nm/cm or less, and a birefringence amount with respect to 40° incident light of 20 nm/cm or less.

Description

  The present invention relates to a lens used in various optical devices and an optical element such as a cover glass for protecting the lens.

  In optical devices such as digital still cameras and digital video cameras, many optical elements made of glass or plastic, such as lenses and filters, or protective covers for protecting these lenses, are used. In recent years, optical devices have been improved in functionality, accuracy, strength, size and weight, and accordingly, optical elements have been required to be reduced in weight along with improvements in function and accuracy. In particular, since glass is heavier than plastic, it is strongly required to reduce its weight.

  Thus, it has been studied to reduce the thickness of the glass by reducing the thickness. However, since the mechanical strength and impact resistance are reduced when the thickness is reduced, it is necessary to strengthen the glass by chemical treatment, for example. Strengthening by chemical treatment is generally referred to as chemical strengthening. Usually, alkali metal ions are exchanged on the surface of glass, and a strong compressive stress layer is formed on the surface, whereby mechanical strength is improved.

  However, such chemically tempered glass exhibits birefringence due to the formation of a compressive stress layer, and in optical equipment using this, color unevenness and intensity unevenness appear in the image, and color balance is also observed. May decrease. Such a phenomenon is particularly remarkable when polarized light such as light reflected from the water surface is incident.

JP 2000-226227 A

  An object of the present invention is to provide an optical element that is a chemically strengthened optical element and does not cause color unevenness, intensity unevenness, color balance deterioration, or the like in an image of an optical apparatus using the optical element.

An optical element according to one embodiment of the present invention is an optical element made of chemically strengthened glass having a compressive stress layer formed on the surface by a chemical strengthening treatment, and has an amount of birefringence of 20 nm / cm or less, 20 nm / cm or less, 20 The birefringence amount with respect to incident light is 20 nm / cm or less, and the birefringence amount with respect to 40 ° incident light is 20 nm / cm or less.
Here, the “birefringence amount” refers to a value obtained by measuring the birefringence value of the optical element and dividing the value by the thickness (unit: cm) of the optical element.

  ADVANTAGE OF THE INVENTION According to this invention, it is an optical element strengthened chemically, Comprising: It can provide the optical element which does not generate | occur | produce a color nonuniformity, intensity | strength nonuniformity, a color balance fall, etc. to the image of the optical apparatus using this.

Embodiments of the present invention will be described below.
The optical element of the present invention is an optical element made of chemically strengthened glass having a compressive stress layer formed on the surface by a chemical strengthening treatment, and has an amount of birefringence of 20 nm / cm or less with respect to normal incident light and with respect to 20 ° incident light. The birefringence amount is 20 nm / cm or less, and the birefringence amount with respect to 40 ° incident light is 20 nm / cm or less.

[Glass composition]
First, the composition of the glass used in the present invention, that is, the glass used for the chemical strengthening treatment will be described. For example, the composition shown below is mentioned. Here, the description of the glass composition is performed using the mass% display content unless otherwise specified.

This glass composition, the _{SiO 2 30~80%, B 2 O} 3 0 to 15% of _{Al 2 O 3 0~25%, 5~20} % of Na ₂ O, _{K 2} O and 0 to 15% MgO contains 0 to 10%, CaO contains 0 to 10%, BaO contains 0 to 10%, ZrO ₂ contains 0 to 7%, and TiO ₂ contains 0 to 30%.

SiO ₂ is a component constituting the skeleton of glass and essential. If it is less than 30%, the stability or weather resistance as glass is lowered. Preferably it is 40% or more, More preferably, it is 55% or more. On the other hand, if the SiO ₂ content exceeds 80%, the viscosity of the glass increases and the meltability decreases significantly. Preferably it is 75% or less, More preferably, it is 70% or less.

B ₂ O ₃ is a component that improves the weather resistance of the glass, and is not essential, but can be contained as necessary. When B ₂ O ₃ is contained, if it is less than 4%, a significant effect may not be obtained for improving weather resistance. Preferably it is 5% or more, More preferably, it is 6% or more. On the other hand, if B ₂ O ₃ exceeds 15%, striae due to volatilization occur and the yield may be reduced. Preferably it is 11% or less, More preferably, it is 10% or less.

Al ₂ O ₃ is a component that improves the weather resistance and chemical strengthening properties of the glass, and is not essential, but can be contained as necessary. When Al ₂ O ₃ is contained, if it is less than 4%, a significant effect may not be obtained for improving weather resistance and chemical strengthening characteristics. Preferably it is 3% or more, More preferably, it is 4% or more. On the other hand, if Al ₂ O ₃ exceeds 25%, the viscosity of the glass becomes high and uniform melting becomes difficult. Preferably it is 20% or less, more preferably 16% or less.

Na ₂ O is a component that improves the meltability of the glass, and is essential because a surface compressive stress layer is formed by ion exchange. If it is less than 5%, the meltability is poor, and a desired surface compressive stress layer cannot be formed by ion exchange. Preferably it is 7% or more, More preferably, it is 8% or more. On the other hand, if Na ₂ O exceeds 20%, the weather resistance is lowered. Preferably it is 18% or less, More preferably, it is 15% or less.

K ₂ O is a component that improves the meltability of the glass, and has the effect of increasing the ion exchange rate in chemical strengthening, but is not essential, but is a preferable component. When it contains K ₂ O, if it is less than 0.01%, there is a possibility that a significant effect cannot be obtained for improving the melting property, or a significant effect cannot be obtained for improving the ion exchange rate. Preferably it is 0.3% or more. On the other hand, if K ₂ O exceeds 15%, the weather resistance decreases. Preferably it is 12% or less, More preferably, it is 8% or less.

  MgO is a component that improves the meltability of the glass, and is not essential, but can be contained as necessary. When it contains MgO, if it is less than 2%, there is a possibility that a significant effect cannot be obtained for improving the meltability. Preferably it is 4% or more. On the other hand, if MgO exceeds 10%, the weather resistance is lowered. Preferably it is 8% or less, More preferably, it is 6% or less.

  CaO is a component that improves the meltability of the glass, and can be contained as necessary. When CaO is contained, if it is less than 0.01%, a significant effect for improving the meltability cannot be obtained. Preferably it is 0.1% or more. On the other hand, if CaO exceeds 10%, the chemical strengthening properties are lowered. Preferably it is 8% or less, More preferably, it is 5% or less.

  BaO is a component that improves the meltability of the glass, and can be contained as necessary. When BaO is contained, if it is less than 0.01%, a significant effect cannot be obtained for improving the meltability. Preferably it is 0.1% or more. On the other hand, when BaO exceeds 10%, the chemical strengthening characteristics are lowered. Preferably it is 8% or less, More preferably, it is 5% or less.

ZrO ₂ is a component that increases the ion exchange rate, and is not essential, but can be contained as required. When ZrO ₂ is contained, if it is less than 1%, there is a possibility that a significant effect for improving the meltability cannot be obtained. Preferably it is 2% or more. On the other hand, if MgO exceeds 7%, the weather resistance decreases. Preferably it is 6% or less, More preferably, it is 5% or less.

TiO ₂ is a component that improves weather resistance, and is not essential, but can be contained as necessary. When TiO ₂ is contained, if it is less than 1%, a significant effect may not be obtained with respect to improvement in meltability. Preferably it is 2% or more. On the other hand, if TiO ₂ exceeds 30%, the glass becomes unstable and devitrification may occur. Preferably it is 25% or less, more preferably 20% or less.

If necessary, the present glass contains components other than the above components, such as Li ₂ O, SrO, SnO ₂ , Sb ₂ O ₃ , ZnO, Nb ₂ O ₅ , Fe ₂ O _3, RbO _{2, and the} like. be able to. Further, SO ₃ , Cl and the like can be contained as necessary.

Table 1 describes specific examples of the glass suitable for the present invention together with its physical properties (glass transition point Tg, glass strain point StP, glass annealing point AP, glass softening point SP, specific gravity, refractive index n _d ). A method for measuring physical properties is described below. In addition, the measurement sample was prepared by preparing commonly used glass starting materials such as oxides, carbonates, nitrates and the like so as to have a target composition, and putting the prepared raw materials in a platinum crucible, about 1350 After being melted, clarified and stirred at 1500 ° C. for 3 hours, it was cast into a mold preheated to about 320 to 370 ° C. and then slowly cooled at about 0.5 ° C./min. In Table 1, “−” is described for data not measured.

Refractive index _{n d} is a side 20 mm, using a sample thickness was processed into a rectangular parallelepiped of 10 mm, refractive index meter (manufactured by Shimadzu Corporation, Model: KPR-2000) was measured in. Refractive index values are rounded to the third decimal place by rounding off to the fourth decimal place.

  The glass transition point Tg of thermal characteristics is 4 ° C. by a thermal expansion method using a thermomechanical analyzer (model name: TMA4000SA) manufactured from a sample processed into a cylindrical shape having a diameter of 4 mm and a length of 50 mm. Measured at a rate of temperature increase per minute. Glass strain point StP and glass annealing point AP were measured using the fiber elongation method defined in JIS-R3103 and ASTM-C336. The glass softening point SP was measured using a fiber elongation method defined in JIS-R3104 and ASTM-C338.

  Specific gravity is JIS standard Z8807 (1976, measuring method which measures the ratio of the mass of a sample and the mass of 4 degreeC pure water of the same volume under the pressure of 101.325 kPa (standard pressure) in a liquid. ).

[Optical element]
The optical element of the present invention can be obtained by molding glass comprising the above glass composition, or cutting the molded product into a desired size, grinding and polishing as necessary, and then applying chemical strengthening treatment. it can. Alternatively, it can be obtained by obtaining a preform having the above glass composition by a conventional method, further forming the preform into a required shape, and then applying a chemical strengthening treatment.

The method of chemical strengthening treatment is not particularly limited as long as it is a method capable of ion exchange between Na ₂ O of the glass surface layer and K ₂ O in the molten salt. For example, the heated potassium nitrate (KNO ₃ ) molten salt is used. The method of immersing glass is mentioned. However, the chemical strengthening has a birefringence amount of 20 nm / cm or less for normal incident light, a birefringence amount of 20 nm / cm or less for 20 ° incident light, and a birefringence amount of 20 nm / cm or less for 40 ° incident light. In order to obtain glass, the processing conditions (temperature, immersion time) are important. The treatment conditions vary depending on the composition and thickness of the glass, the type of treatment solution, etc., but when KNO ₃ molten salt is used, the glass is immersed in KNO ₃ molten salt at 350 to 500 ° C. for 2 to 20 hours. It is typical. The KNO ₃ molten salt may contain, for example, NaNO ₃ in an amount of about 5% by mass or less in addition to KNO ₃ .

  The optical element of the present invention has a birefringence amount of 5 nm / cm or less in terms of birefringence for normal incident light and 5 nm / cm in terms of birefringence for 20 ° incident light in order to obtain good optical characteristics. It is preferably made of glass having a birefringence amount of 6 nm / cm or less with respect to 40 ° incident light. The birefringence amount is 2 nm / cm or less as a birefringence amount with respect to normal incident light, 2 nm / cm or less as a birefringence amount against 20 ° incident light, and 4 nm / cm or less as a birefringence amount against 40 ° incident light. preferable.

  The optical element of the present invention is preferably made of glass having a depth of a surface compressive stress layer formed by chemical strengthening treatment of 5 to 35 μm from the viewpoint of mechanical strength, and glass having a thickness of 10 to 25 μm. More preferably, it consists of. If the depth of the surface compressive stress layer is less than 5 μm, sufficient strength cannot be obtained, and if it exceeds 35 μm, the amount of birefringence increases, which is not preferable.

  Further, in the glass, the surface compressive stress of the surface compressive stress layer formed by the chemical strengthening treatment is preferably 500 MPa or more, and more preferably 600 MPa or more. If the surface compressive stress is less than 500 MPa, sufficient strength cannot be obtained. The surface compressive stress is preferably 800 MPa or less, and more preferably 700 MPa or less. When the surface compressive stress exceeds 800 MPa, the stress becomes too strong and the glass is deformed, and there is a possibility that performance as an optical element, for example, a transmitted wavefront cannot be maintained.

  The present invention is particularly effective when applied to an optical element made of chemically strengthened glass having a thickness of 1 to 6 mm. If the thickness of the optical element is less than 1 mm, it becomes extremely difficult to produce an optical element before chemical strengthening treatment. Further, the optical element may be deformed and the performance as the optical element may not be maintained. When the thickness of the optical element exceeds 6 mm, sufficient mechanical strength can be obtained without chemical strengthening treatment.

  It goes without saying that the present invention is not limited to the description of the embodiment described above, and can be appropriately changed without departing from the gist of the present invention.

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples at all. Examples 1-6, 2-5, 3-6, and 4-5 are comparative examples, and other examples are examples.

(Example 1-1)
In Table 1, a glass material having the composition shown in K was melted and refined at 1400 ° C. in a glass melting furnace, homogenized at 1280 ° C., and introduced into the outflow pipe. The molten glass introduced into the outflow pipe was caused to flow out of the nozzle and supplied onto a mold for forming the glass into a plate shape, thereby obtaining a plate-like glass material. The obtained plate material was gradually cooled at about 0.5 ° C./min.
By applying commonly used processing techniques such as cutting, reheat pressing, grinding, and polishing to the plate material, a meniscus lens having a diameter of 100 mm, a thickness of 3 mm, and a curvature radius of both main surfaces of 1200 mm was manufactured.

  In addition, in the production of glass material, first, the starting materials of commonly used glass, such as oxides, carbonates, nitrates, etc., are prepared so as to have a target composition, the prepared raw materials are put into a platinum crucible, After melting at about 1350-1500 ° C. for 3 hours, it was cast into a water tank to form a granulated cullet, which was used as a glass material.

Next, chemical strengthening treatment was performed on the meniscus lens. That is, the meniscus lens was washed and dried, and then immersed in 400 ° C. KNO ₃ molten salt (100%) for 2 hours.

(Examples 1-2 to 1-6, Examples 2-1 to 2-5)
A meniscus lens was obtained in the same manner as in Example 1-1 except that the glass material and / or the chemical strengthening treatment conditions were changed as shown in Table 2, and each of the obtained meniscus lenses was chemically strengthened. Examples 1-6 and 2-5 are examples in which no chemical strengthening treatment was performed on the meniscus lens.

(Examples 3-1 to 3-6, Examples 4-1 to 4-5)
Meniscus lenses were obtained in the same manner as in Examples 1-1 to 1-6 and Examples 2-1 to 2-5, except that the thickness of the meniscus lenses was changed from 3 mm to 1 mm. Reinforcement treatment was performed. In addition, Example 3-6 and Example 4-5 are examples in which the chemical strengthening treatment was not performed on the meniscus lens.

  Each meniscus lens after chemical strengthening treatment thus obtained (Examples 1-6, 2-5, Example 3-6 and Example 4-5 are meniscus lenses without chemical strengthening treatment) is shown below. By the method, the depth, surface compressive stress, and birefringence value of the compressive stress layer formed on the surface were measured. The results are shown in Tables 2 and 3.

[Depth of compressive stress layer]
About each glass after a chemical strengthening process, the depth of the compressive-stress layer formed in both front and back using the refractometer surface stress meter (Orihara Seisakusho model name: FSM-6000-V) based on JISR32226.4. The average value was calculated.
[Surface compressive stress]
About each glass after a chemical strengthening process, it measured using the refractometer surface stress meter (Orihara Seisakusho make type name: FSM-6000-V) based on JISR32226.4.
[Birefringence value and birefringence value]
Using an automatic birefringence measuring apparatus (model name: ABR-10A-40A manufactured by UNIOPTO), birefringence values were measured at incident angles of 0 °, 20 ° and 40 °. Further, the birefringence value was calculated by dividing the measured birefringence value by the thickness of the meniscus lens.

  As is apparent from Tables 2 and 3, the glass after the chemical strengthening treatment of Examples 1-1 to 1-5 and 3-1 to 3-5 has a thickness that guarantees mechanical strength sufficient for use as an optical element. The compressive stress layer is formed, and the birefringence amount is reduced to 20 nm / cm or less with respect to light having an incident angle of 0 ° (vertical), 20 °, and 40 °. On the other hand, in Examples 2-1 to 2-4 and 4-1 to 4-4, the surface compressive stress and the thickness of the compressive stress layer were out of the preferable ranges, but the birefringence amount was 0 ° (vertical). The incident angle was reduced to 20 nm / cm or less with respect to light having an incident angle of 20 ° or 40 °, and could be used sufficiently depending on the use of the optical element.

  In the optical element of the present invention, the birefringence amount is reduced to 20 nm / cm or less with respect to light having an incident angle of 0 ° (vertical), 20 °, and 40 °. Therefore, the present invention is useful for optical devices that are required to be reduced in size and weight, such as digital still cameras, digital video cameras, mobile phones, notebook personal computers, and PDAs.

Claims (6)

An optical element made of chemically strengthened glass having a compressive stress layer formed on the surface by chemical strengthening treatment,
An optical element having a birefringence amount of 20 nm / cm or less for normal incident light, a birefringence amount of 20 nm / cm or less for 20 ° incident light, and a birefringence amount of 20 nm / cm or less for 40 ° incident light.   2. The optical element according to claim 1, wherein the birefringence amount for normal incident light is 5 nm / cm or less, the birefringence amount for 20 ° incident light is 5 nm / cm or less, and the birefringence amount for 40 ° incident light is 6 nm / cm or less.   2. The optical element according to claim 1, wherein the birefringence amount for normal incident light is 2 nm / cm or less, the birefringence amount for 20 ° incident light is 2 nm / cm or less, and the birefringence amount for 40 ° incident light is 4 nm / cm or less.   The optical element according to claim 1, wherein the compressive stress layer has a depth of 5 to 35 μm.   The optical element according to any one of claims 1 to 4, wherein the compressive stress of the compressive stress layer is 500 MPa or more and 800 MPa or less.   The optical element according to claim 1, wherein the chemically strengthened glass has a thickness of 1 to 6 mm.