Patent Application
20240327268
This application claims priority under 35 U.S.C 119 to Japanese Patent Application No. 2023-058567 filed on Mar. 31, 2023 and Japanese Patent Application No. 2024-016057 filed on Feb. 6, 2024, which are hereby expressly incorporated by reference, in their entirety.
The present disclosure relates to an optical glass, a light guide plate, an image display device and an optical element.
For example, Japanese Patent Application Publication No. 2019-116408, which is hereby expressly incorporated by reference, in its entirety, discloses optical glass having a high refractive index.
In recent years, a light guide plate, i.e., a constituent member of an image display device, has been manufactured from optical glass. Optical glass having a high refractive index can manufacture a light guide plate having a wide viewing angle.
An aspect of the present disclosure provides for optical glass having a high refractive index and suitable for a light guide plate material.
The present inventor conducted a diligent study, and as a result, has newly found the following: a light guide plate comprised of optical glass with a wavelength λ5, which provides a spectral transmittance of 5% for a thickness of 10 mm, of more than 370 nm and less than 410 nm, a difference (λ70−λ5) between a wavelength λ70, which provide a spectral transmittance of 70% for a thickness of 10 mm, and λ5, of 70 nm or less, and a refractive index nd of 2.00000 or more can widen a range of a viewing angle, and can provide a clear image.
One aspect of the present disclosure is as follows.
In accordance with one aspect of the present disclosure, it is possible to provide optical glass having a high refractive index and suitable for a light guide plate material.
Further, in accordance with another aspect of the present disclosure, it is possible to provide a light guide plate comprised of the above optical glass and an image display device including the light guide plate.
The refractive index nd of the above optical glass is 2.00000 or more, can be 2.01000 or more, 2.02000 or more, 2.03000 or more, 2.04000 or more, 2.05000 or more, 2.06000 or more, 2.07000 or more, or 2.08000 or more from the viewpoint of widening the range of the viewing angle. The refractive index nd of the above optical glass is, for example, 2.20000 or less, 2.15000 or less, 2.14000 or less, 2.13000 or less, 2.12000 or less, 2.11000 or less, and 2.10000 or less. In the present disclosure and in the present specification, the term “refractive index” means the “refractive index nd”.
λ5,λ70−λ5
The “λ5” represents the wavelength such that a spectral transmittance (including the surface reflection loss) of glass with a thickness of 10 mm becomes 5% from the ultraviolet region to the visible region. The “λ70” represents the wavelength such that a spectral transmittance including the surface reflection loss (i.e., the external transmittance) of glass with a thickness of 10 mm becomes 70% from the ultraviolet region to the visible region. The spectral transmittance described below is also the spectral transmittance including the surface reflection loss.
The λ5 and the λ70 shown in the column of Examples described later are the values measured within the wavelength region of 250 to 700 nm. The spectral transmittance more specifically represents, for example, the spectral transmittance obtained by using a glass sample having mutually parallel planes polished to a thickness of 10.0±0.1 mm, and making a light incident upon the polished surfaces from the vertical direction, namely, the Iout/Iin where Iin represents the intensity of the light made incident upon the glass sample, and Iout represents the intensity of the light transmitted through the glass sample. When the thickness of the glass to be measured is not a thickness of 10.0±0.1 mm, the value is converted to the value in terms of the thickness of 10 mm by a known method. For example, for glass with an internal transmittance (not including the surface reflection loss) of τ (%), the external transmittance (including the surface reflection loss) for a thickness of 10 mm can be determined using the following equation:
In the equation, T1(%) represents the transmittance (including the surface reflection loss) obtained at a sample thickness d1 (mm), T2(%) represents the transmittance (including the surface reflection loss) obtained at a sample thickness d2, and Δd represents the difference (d2−d1) in sample thickness.
The optical glass with a difference (λ70−λ5) between λ70 and λ5 of 70 nm or less is optical glass exhibiting a high transmittance characteristic in a wide wavelength region. For example, a light guide plate of an image display device for AR (Augmented Reality) is required to have a high transmittance characteristic in a wide wavelength region in order to grasp the surrounding environment through the light guide plate. Additionally, also in order to reduce the loss of the light propagating from the light source through the light guide plate, a high transmittance characteristic is demanded. Therefore, the optical glass with a difference (λ70−λ5) between λ70 and λ5 of 70 nm or less is preferable as a light guide plate material.
The optical glass with a wavelength λ5 of more than 370 nm and less than 410 nm is optical glass for blocking an ultraviolet light, and transmitting a visible light therethrough. When a light on a short wavelength side is made incident upon the eyes, a risk such as cataract may be caused. For this reason, the optical glass having a higher transmittance characteristic than required on the short wavelength side is not preferable. In view of this point, the optical glass with a wavelength λ5 of more than 370 nm and less than 410 nm is preferable as a light guide plate material.
The difference (λ70−λ5) between λ70 and λ5 of the above optical glass is 70 nm or less, can be 68 nm or less, 66 nm or less, 64 nm or less, 62 nm or less, 60 nm or less, 58 nm or less, 56 nm or less, 54 nm or less, 52 nm or less, or 50 nm or less. The difference (λ70−λ5) between λ70 and λ5 can be, for example, 10 nm or more, 20 nm or more, 30 nm or more, or 40 nm or more.
The λ5 of the above optical glass is more than 370 nm, can be 371 nm or more, 372 nm or more, 373 nm or more, 374 nm or more, or 375 nm or more. Further, the λ5 of the above optical glass is less than 410 nm, can be 408 nm or less, 405 nm or less, 403 nm or less, 400 nm or less, 398 nm or less, 395 nm or less, 393 nm or less, 390 nm or less, 388 nm or less, 385 nm or less, or 380 nm or less.
It is sufficient for the λ70 of the above optical glass that the difference (λ70-λ5) between λ70 and λ5 falls within the foregoing range, and the λ70 has no particular restriction. In one embodiment, the λ70 of the above optical glass can be more than 400 nm and less than 480 nm.
In the present disclosure and in the present specification, the glass composition is expressed by the glass composition on an oxide basis. Herein, the term “glass composition on an oxide basis” represents the glass composition resulting from conversion on the assumption that the glass raw material is fully decomposed at the time of melting, and is present as an oxide in glass. Further, the glass composition is expressed on a mass basis (mass %, mass ratio) unless otherwise specified.
The glass composition in the present disclosure and the present specification can be determined by, for example, the method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). The quantitative analysis is performed for every element using the ICP-AES. Subsequently, the analysis value is converted to oxide notation. The analysis value by the ICP-AES may include, for example, a measurement error of about ±5% of the analysis value. Therefore, the value expressed in terms of oxide converted from the analysis value may also similarly include an error of about ±5%.
Further, in the present disclosure and in the present specification, the constituent component having a content of 0%, 0.00%, or 0.000%, or not being included nor introduced means that the constituent component is substantially not included, and indicates that the content of the constituent component is equal to or lower than approximately the impurity level. The term “being equal to or lower than approximately the impurity level” means, for example, being less than 0.01%.
In one embodiment, the above optical glass can be boric acid-based glass, and can include B2O3. Further, in one embodiment, the above optical glass can include SiO2, B2O3, TiO2, Nb2O5, Y2O3, La2O3, and Gd2O3 as essential components.
Below, the glass composition of the above optical glass will be further described in details. However, it is sufficient for the above optical glass to have a refractive index nd, λ5, and a difference (λ70−λ5) between λ5 and λ70 within the foregoing respective ranges, and is not limited to optical glasses having the glass compositions described below.
The mass ratio of the B2O3 content to the SiO2 content (B2O3/SiO2) can be less than 3.000, 2.800 or less, 2.600 or less, 2.400 or less, 2.200 or less, 2.000 or less, 1.800 or less, 1.600 or less, 1.400 or less, 1.200 or less, 1.000 or less, less than 1.000, 0.980 or less, 0.960 or less, 0.950 or less, 0.920 or less, or 0.900 or less from the viewpoint of suppressing the surface devitrification of glass, and from the viewpoint of reducing TI described later. The mass ratio (B2O3/SiO2) can be, for example, 0.100 or more, 0.200 or more, 0.300 or more, 0.400 or more, 0.500 or more, or 0.600 or more.
The mass ratio of the Y2O3 content to the total content of Y2O3, La2O3, Gd2O3, and Yb2O3 (Y2O3/(Y2O3+La2O3+Gd2O3+Yb2O3)) can be 0.010 or more, more than 0.010, 0.011 or more, 0.012 or more, 0.013 or more, 0.014 or more, 0.015 or more, 0.016 or more, 0.017 or more, 0.018 or more, 0.019 or more, 0.020 or more, more than 0.020, 0.021 or more, 0.022 or more, 0.023 or more, 0.024 or more, or 0.025 or more from the viewpoint of suppressing the surface devitrification and from the viewpoint of reducing the TI. The mass ratio (Y2O3/(Y2O3+La2O3+Gd2O3+Yb2O3)) can be, for example, 0.100 or less, 0.090 or less, 0.080 or less, 0.070 or less, 0.060 or less, and 0.050 or less.
The above optical glass can include SiO2, B2O3, TiO2, Nb2O5, Y2O3, La2O3, and Gd2O3 as essential components.
SiO2 is a network-forming oxide, and is a component capable of contributing to keeping of the glass stability, keeping of the viscosity suitable for molding molten glass and improvement of the chemical durability thereof. The enhancement of the glass stability leads to suppression of the surface devitrification of glass, and hence is preferable. The SiO2 content of the above optical glass can be 0.10% or more, 0.50% or more, 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, or 5.00% or more. From the viewpoints of the suppression of the reduction of the refractive index and keeping of the glass meltability, the SiO2 content can be 30.00% or less, 20.00% or less, 15.00% or less, 10.00% or less, 8.00% or less, or 6.00% or less.
B2O3 is a network-forming oxide, and is a component capable of contributing to keeping of the glass meltability and the improvement of the glass stability. The B2O3 content of the above optical glass can be 0.10% or more, 0.50% or more, 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, or 5.00% or more. From the viewpoints of suppression of the reduction of the refractive index and suppression of the reduction of the chemical durability, the B2O3 content can be 30.00% or less, 20.00% or less, 15.00% or less, 10.00% or less, 8.00% or less, or 6.00% or less.
From the viewpoint of the improvement of the glass stability, the total content of SiO2 and B2O3 (SiO2+B2O3) can be 1.00% or more, 3.00% or more, 5.00% or more, 8.00% or more, or 10.00% or more. From the viewpoint of increasing the refractive index of glass, the total content (SiO2+B2O3) can be 30.00% or less, 20.00% or less, 15.00% or less, 13.00% or less, or 12.00% or less.
TiO2 is a component capable of contributing to an increase in refractive index of glass, and the improvement of the chemical durability thereof. The TiO2 content of the above optical glass can be 1.00% or more, 3.00% or more, 5.00% or more, 8.00% or more, 10.00% or more, 13.00% or more, 15.00% or more, 18.00% or more, or 20.00% or more. From the viewpoint of suppression of the reduction of the glass stability, the TiO2 content can be 50.00% or less, 45.00% or less, 40.00% or less, 35.00% or less, 30.00% or less, 28.00% or less, or 26.00% or less. Further, the TiO2 content can fall within the foregoing range also from the viewpoint of controlling the λ5 within the previously described range.
The mass ratio of the TiO2 content to the total content of SiO2 and the B2O3 (TiO2/(SiO2+B2O3)) can be 1.500 or more, 1.550 or more, 1.600 or more, 1.650 or more, 1.700 or more, 1.750 or more, 1.800 or more, 1.850 or more, 1.900 or more, 1.950 or more, 1.960 or more, 1.970 or more, 1.980 or more, 1.990 or more, or 2.000 or more from the viewpoint of increasing the refractive index of glass. From the viewpoint of improving the glass stability, the mass ratio (TiO2/(SiO2+B2O3)) can be 10.000 or less, 8.000 or less, 5.000 or less, 3.000 or less, 2.800 or less, or 2.500 or less.
Nb2O5 is a component capable of contributing to an increase in refractive index of glass, and the improvement of the chemical durability thereof. The Nb2O5 content of the above optical glass can be 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, 5.00% or more, or 6.00% or more. From the viewpoint of suppression of the reduction of the glass stability, the Nb2O5 content can be 30.00% or less, 20.00% or less, 15.00% or less, 10.00% or less, or 8.00% or less.
The WO3 content of the above optical glass can be 0.00%, 0.00% or more, or more than 0.00%. WO3 is a component capable of contributing to an increase in refractive index of glass and the improvement of the chemical durability thereof. The WO3 content can be, for example, 8.00% or less, 7.00% or less, 6.00% or less, or 5.00% or less.
The total content of TiO2, Nb2O5, and WO3 (TiO2+Nb2O5+WO3) can be 10.00% or more, 15.00% or more, 20.00% or more, 25.00% or more, 28.00% or more, or 30.00% or more from the viewpoints of an increase in the refractive index of glass, and the improvement of the chemical durability thereof. From the viewpoint of improving the glass stability, the total content (TiO2+Nb2O5+WO3) can be 60.00% or less, 55.00% or less, 50.00% or less, 45.00% or less, 40.00% or less, 38.00% or less, or 35.00% or less.
Y2O3 is a component capable of contributing to an increase in refractive index of glass, keeping of the low dispersibility thereof, and the improvement of the chemical durability. The Y2O3 content of the above optical glass can be 0.10% or more, 0.30% or more, 0.50% or more, 0.80% or more, or 1.00% or more. From the viewpoints of suppression of the reduction of the glass stability and suppression of an increase in TI, the Y2O3 content can be 10.00% or less, 8.00% or less, 5.00% or less or 3.00% or less.
La2O3 is also a component capable of contributing to an increase in refractive index of glass, keeping of the low dispersibility thereof, and the improvement of the chemical durability. The La2O3 content of the above optical glass can be 10.00% or more, 15.00% or more, 20.00% or more, 25.00% or more, 30.00% or more, or 35.00% or more. From the viewpoints of suppression of the reduction of the glass stability and suppression of an increase in TI, the La2O3 content can be 60.00% or less, 55.00% or less, 50.00% or less, 45.00% or less, or 40.00% or less.
Gd2O3 is also a component capable of contributing to an increase in refractive index of glass, keeping of the low dispersibility thereof, and the improvement of the chemical durability. The Gd2O3 content of the above optical glass can be 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, 5.00% or more, or 6.00% or more. From the viewpoints of suppression of the reduction of the glass stability and suppression of an increase in TI, the Gd2O3 content can be 30.00% or less, 20.00% or less, 15.00% or less, 10.00% or less, or 8.00% or less.
The Yb2O3 content can be 0.00%, 0.00% or more, or more than 0.00%. Yb2O3 is also a component capable of contributing to an increase in refractive index of glass, keeping of the low dispersibility thereof, and the improvement of the chemical durability. The Yb2O3 content of the above optical glass can be, for example, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, 1.00% or less, 0.50% or less, or 0.10% or less.
The total content of Y2O3, La2O3, Gd2O3, and Yb2O3 (Y2O3+La2O3+Gd2O3+Yb2O3) can be 10.00% or more, 15.00% or more, 20.00% or more, 25.00% or more, 30.00% or more, 35.00% or more, 40.00% or more, 43.00% or more, or 45.00% or more, from the viewpoints of an increase in the refractive index of glass, keeping of the low dispersibility, and improving the chemical durability. From the viewpoints of suppression of the reduction of the glass stability, and suppression of an increase in TI, the total content (Y2O3+La2O3+Gd2O3+Yb2O3) can be 70.00% or less, 65.00% or less, 60.00% or less, 55.00% or less, 53.00% or less, or 50.00% or less.
Each content of Li2O, Na2O, K2O, and Cs2O can be 0.00%, 0.00% or more, more than 0.00%, 0.05% or more, or 0.10% or more. Further, each content of Li2O, Na2O, K2O, and Cs2O can be, for example, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, or 1.00% or less. All of Li2O, Na2O, K2O, and Cs2O each have an action of improving the thermal stability of glass. An increase in the content thereof tends to result in a decrease in refractive index and chemical durability. For this reason, each content of Li2O, Na2O, K2O, and Cs2O can fall within the foregoing range.
Each content of MgO, CaO, SrO, and BaO can be 0.00%, 0.00% or more, more than 0.00%, 0.05% or more, or 0.10% or more. Further, each content of MgO, CaO, SrO, and BaO can be, for example, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, or 1.00% or less.
All of MgO, CaO, SrO, and BaO have an action of improving the thermal stability of glass. An increase in content thereof tends to reduce the refractive index and the chemical durability. For this reason, each content of MgO, CaO, SrO, and BaO can fall within the foregoing range.
The ZnO content can be 0.00%, 0.00% or more, more than 0.00%, 0.05% or more, 0.10% or more, or 1.00% or more. Further, the ZnO content can be, for example, 5.00% or less, 4.00% or less, 3.00% or less, or 2.00% or less.
ZnO has an action of improving the thermal stability of glass. An increase in content of ZnO tends to result in an increase in specific gravity. For this reason, the content of ZnO can fall within the foregoing range.
The ZrO2 content can be 0.00%, 0.00% or more, more than 0.00%, 1.00% or more, 3.00% or more, or 5.00% or more. Further, the ZrO2 content can be, for example, 10.00% or less or 8.00% or less.
ZrO2 has an action of increasing the refractive index of glass. An increase in content of ZrO2 tends to result in a decrease in thermal stability of glass. For this reason, the content of ZrO2 can fall within the foregoing range.
The Ta2O5 content can be 0.00%, 0.00% or more, more than 0.00%, 0.05% or more, or 0.10% or more. Further, the Ta2O5 content can be, for example, 5.00% or less, 4.00% or less, 3.00% or less, 2.00% or less, or 1.00% or less.
Ta2O5 has an action of increasing the refractive index of glass. An increase in content of Ta2O5 tends to result in a decrease in thermal stability of glass. For this reason, the content of Ta2O5 can fall within the foregoing range.
The above optical glass can further include one or more of P2O5, Al2O3, and the like in addition to the foregoing components.
The P2O5 content can be 0.00% or more, 10.00% or less, 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, 1.00% or less, or 0.50% or less.
The Al2O3 content can be 0.00% or more, 10.00% or less, 8.00% or less, 6.00% or less, 4.00% or less, 2.00% or less, 1.00% or less, or 0.50% or less.
For the above optical glass, the content of platinum Pt can be 10 ppm or less, 8 ppm or less, 7 ppm or less or 5 ppm or less. The lower limit of the platinum content has no particular restriction, and can be, for example, 0.001 ppm or more. Setting the content of Pt within the foregoing range can reduce the coloring of glass caused by Pt. This point is preferable for reducing the difference (λ70−λ5) between λ70 and λ5. The platinum content is the content based on mass relative to the total mass of glass, and can be quantified by inductively coupled plasma mass spectrometry method (ICP-MS).
Pb, As, Cd, TI, Be, and Se respectively have toxicity. For this reason, the above elements can be prevented from being included, namely, the above elements can be prevented from being introduced into glass as glass components.
U, Th, and Ra are all radioactive elements. For this reason, the above elements can be prevented from being included, namely, the above elements can be prevented from being introduced into glass as glass components.
V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Ce increase the coloration of glass, and become the source of generation of fluorescence, and are not preferable as the elements to be included in glass for an optical element. For this reason, the above elements can be prevented from being included, namely, the above elements can be prevented from being introduced into glass as glass components.
Sb and Sn are optional elements each functioning as a clarifying agent.
The amount of Sb to be added can be set within the range of 0.000 to 0.100 mass %, within the range of 0.001 to 0.020 mass %, within the range of 0.001 to 0.010 mass %, or within the range of 0.001 to 0.005 mass % for every 100 mass % of the total content of other glass components than Sb2O3 in terms of Sb2O3. The amount of Sn to be added can be set within the range of 0.000 to 0.100 mass %, within the range of 0.000 to 0.020 mass %, within the range of 0.000 to 0.010 mass %, or within the range of 0.000 to 0.005 mass % for every 100 mass % of the total content of other glass components than SnO2 in terms of SnO2.
The Abbe's number vd is the value indicative of the property regarding the dispersibility, and is expressed as vd=(nd−1)/(nF−nC) using respective refractive indices nd, nF, and nC in the d line, the F line, and the C line. From the viewpoint of usability as a material for an optical element and a light guide plate material, the Abbe's number vd of the above optical glass can be 20.00 or more, 21.00 or more, 22.00 or more, or 23.00 or more. From the same viewpoint, the Abbe's number vd can be 30.00 or less, 28.00 or less, 26.00 or less, 25.00 or less, or 24.00 or less.
The glass transition temperature Tg of the above optical glass can be 560° C. or more from the viewpoint of machinability. Glass with a high glass transition temperature tends to be less likely to be broken upon undergoing machining of glass such as cutting, shaving, grinding, or polishing, and hence is preferable. From the viewpoint of the machinability, the glass transition temperature Tg can be 570° C. or more, 580° C. or more, 590° C. or more, or 600° C. or more. On the other hand, from the viewpoint of reducing the burden on an annealing furnace or a mold, the glass transition temperature Tg can be 800° C. or less, 790° C. or less, 780° C. or less, 770° C. or less, 760° C. or less, or 750° C. or less.
The glass transition temperature Tg is determined in the following manner. With differential scanning calorimetry, upon a temperature rise of a glass sample, endothermic behavior in association with a change in specific heat, namely, an endothermic peak occurs. Upon a further temperature rise, an exothermic peak occurs. Differential scanning calorimetric analysis provides a DSC (Differential Scanning Calorimetry) curve with the temperature on the horizontal axis, and the amount corresponding to exotherm/endotherm of the sample on the vertical axis. The point of intersection between the tangent line at the point at which the slope is maximized when the endothermic peak appears from the baseline in the curve and the baseline is assumed to be the glass transition temperature Tg. The measurement of the glass transition temperature Tg can be performed using the one obtained by sufficiently grinding glass by a mortar or the like as a sample, at a heating rate of 10° C./min using a differential scanning calorimeter.
The present inventor newly found that the glass with a temperature TI at which switching to melt is caused in the differential scanning calorimetry being low is less likely to cause surface devitrification. For glass whose surface has been devitrified, a devitrified portion thereof has to be removed for processing into a light guide plate, or the like. Therefore, the surface devitrification causes yield reduction. Further, glass whose surface has been devitrified has fogging on the glass surface. For this reason, it is difficult to perform quality check of the inside of the glass. Therefore, glass which is less likely to undergo surface devitrification is preferable. The TI of the above optical glass can be 1300° C. or less, 1295° C. or less, 1290° C. or less, 1285° C. or less, 1280° C. or less, 1275° C. or less, 1270° C. or less, 1265° C. or less, 1260° C. or less, 1255° C. or less, 1250° C. or less, 1247° C. or less, 1246° C. or less, 1245° C. or less, 1244° C. or less, 1243° C. or less, 1242° C. or less, 1241° C. or less, or 1240° C. or less. The TI of the above optical glass can be, for example, 1200° C. or more, 1210° C. or more, or 1220° C. or more. However, from the viewpoint of suppressing the surface devitrification, a lower TI is more preferable. For this reason, the TI of the above optical glass may be lower than the foregoing range.
The temperature TI is determined as the temperature of the point of intersection between the tangent line at the point at which the slope is maximized over from the top of the endothermic peak due to fusion to the baseline, and the baseline from the DSC curve. The temperature of the point of intersection is the temperature which is h in
For an optical element configuring an optical system, the refractive power is determined by the refractive index of the glass configuring the optical element and the curvature of the optical functional surface (the surface upon and from which a light beam to be controlled is incident and emitted) of the optical element. When the curvature of the optical functional surface is tried to be increased, the thickness of the optical element is also increased. As a result, the optical element becomes heavy. In contrast, when glass with a high refractive index is used, a large refractive power can be obtained even if the curvature of the optical functional surface is not increased.
From the description up to this point, when the refractive index can be increased while suppressing an increase in specific gravity of glass, it becomes possible to reduce the weight of the optical element having a given refractive power.
Further, also for glass configuring a light guide plate, a low specific gravity is preferable from the viewpoints of the weight reduction of the light guide plate and the weight reduction of an image display device.
From the viewpoints described up to this point, the specific gravity of the above optical glass can be 5.30 or less, 5.20 or less, 5.10 or less. A lower specific gravity is more preferable from the viewpoint of the weight reduction of the optical element. For this reason, the specific gravity of the optical glass has no particular restriction on the lower limit. In one embodiment, the specific gravity can be 4.00 or more, 4.40 or more, or 4.800 or more.
“T460” is the internal transmittance for a thickness of 10 mm at a wavelength of 460 nm, determined using respective spectral transmittances of a pair of samples having different thicknesses. The spectral transmittance includes the surface reflection loss as described previously. The internal transmittance T (%) can be determined using the following previously shown equation:
The T460 of the above optical glass can be 90.0% or more, 92.5% or more, 95.0% or more, 96.0% or more, or 97.0% or more from the viewpoint of reducing the loss of the light with a wavelength of a blue color propagating through the light guide plate.
The β-OH determined by the following equation (1) means the absorbance caused by a hydroxy group. Therefore, the content of water (and/or a hydroxide ion, which will be hereinafter referred to simply as “water”) in glass can be evaluated by the β-OH. Namely, a high β-OH of glass means a high content of waver in glass.
In the equation (1), t represents the thickness (mm) of glass for use in the measurement of the spectral transmittance, A represents the spectral transmittance (%) at a wavelength of 2500 nm when a light is made incident upon the glass in parallel with the thickness direction thereof, and B represents the spectral transmittance (%) at a wavelength of 2900 nm when a light is made incident upon the glass in parallel with the thickness direction thereof. In the equation (1), In is a natural logarithm. The unit of β-OH is mm−1. An increase in the value of β-OH of glass leads to a decrease in the difference (λ70−λ5) between λ70 and λ5, and hence is preferable. The β-OH of the optical glass can be 0.50 mm−1 or more, 0.60 mm−1 or more, 0.70 mm−1 or more, 0.80 mm−1 or more, or 0.90 mm−1 or more. The β-OH of the above optical glass can be, for example, 1.50 mm−1 or less, or 1.25 mm−1 or less.
The optical glass described above is useful as a glass material for a light guide plate, and is also useful as a glass material for an optical element.
The above optical glass can be obtained in the following manner. An oxide, a carbonic acid salt, a sulfuric acid salt, a nitric acid salt, hydroxide, and the like of raw materials are weighed and prepared so as to obtain the objective glass composition, and are sufficiently mixed, resulting in a mixed batch. Such a mixed batch is subjected to heating, melting, deaeration, and stirring in a melting container, thereby forming molten glass which is homogeneous and does not include foam. Specifically, molten glass can be formed using a known melting method. By molding the molten glass thus obtained, it is possible to obtain the above optical glass.
For example, at the melting step, glass raw materials are prepared so as to obtain the objective glass composition, and are sufficiently mixed, resulting in a batch raw material. The batch raw material is placed in a platinum crucible, and is coarsely molten. At the melting step, a reducing agent can be added to the glass raw materials. The reducing agent has no particular restriction. Examples thereof may include a substance exhibiting the reducibility such as Al, Si, Ti, W, H2, CO, or C. More specifically, examples of the substance exhibiting the reducibility may include a carbon compound and active carbon C. Addition of a reducing agent to the glass raw materials allows oxygen with a high reactivity generated upon vitrification of the glass raw materials and the reducing agent to react with each other. Accordingly, the oxidation reaction of platinum derived from the platinum crucible is suppressed. As a result, the platinum content in the glass can be reduced. The reduction of the platinum content leads to the reduction of the difference (λ70−λ5) between λ70 and λ5, and hence is preferable.
The melting atmosphere at the melting step of the glass can be a non-oxidizing atmosphere. By performing the melting step in a non-oxidizing atmosphere, the oxygen partial pressure in the melting atmosphere is reduced, so that the oxidation of platinum derived from the platinum crucible is suppressed. Accordingly, it is possible to reduce the amount of platinum to be molten into the molten glass.
The non-oxidizing atmosphere has no particular restriction. Examples thereof may include an inert gas atmosphere of nitrogen, carbon dioxide, argon, helium, or the like, and a water vapor added atmosphere. In order to enhance the β-OH of the finally obtainable glass, the water vapor added atmosphere is preferable.
By adding water vapor to the melting atmosphere, it is possible to enhance the β-OH of the finally obtainable glass. Further, by adding water vapor to the melting atmosphere, it is possible to effectively prevent melting of platinum or the like into the glass. Still further, by adding water vapor to the melting atmosphere, it is possible to supply a sufficient dissolved gas to the glass. As a result, it is possible to improve the defoaming and clarification of the glass.
The method for adding water vapor to the melting atmosphere has no particular restriction. As the method for adding water vapor to the melting atmosphere, for example, mention may be made of a method in which a connecting pipe is inserted from the opening provided at the melting device into the crucible, and if required, water vapor is supplied through the pipe into the space in the crucible.
At the melting step, bubbling can be involved for the purpose of stirring the molten substance. Bubbling at the time of melting may also be continued after melting the prepared material. By stirring the molten substance at the melting step, oxidation of the glass components proceeds. On the other hand, by stirring the molten substance at the melting step, oxidation of platinum derived from the platinum crucible is suppressed. This is due to the fact that the glass components tend to be more likely to be oxidized than platinum. As a result, the reduction reaction of the glass components is suppressed, so that the reduced color is decreased. Further, melting of platinum into the molten substance is suppressed, so that coloring derived from platinum is also decreased. This point leads to the reduction of the difference (λ70−λ5) between λ70 and λ5, and hence is preferable.
The gas for use in bubbling has no particular restriction, and a known gas can be used. Examples thereof may include inert gases such as nitrogen, carbon dioxide, argon, and helium, air, and gases obtained by adding water vapor to the gases.
By using a gas including water vapor as the gas for use in bubbling, it is possible to enhance the β-OH of the finally obtainable glass. Further, by using a gas including water vapor as the gas for use in bubbling, it is possible to effectively prevent melting of platinum into the glass. Still further, by using a gas including water vapor as the gas for use in bubbling, it is possible to supply a sufficient dissolved gas to the glass. As a result, the defoaming and the clarification of the glass can be improved.
The content of the water vapor in such a gas including water vapor can be 10 vol % or more, 20 vol % or more, 30 vol % or more, 40 vol % or more, 50 vol % or more, 60 vol % or more, 70 vol % or more, 80 vol % or more, or 90 vol % or more. A higher water vapor content is more preferable. By setting the content within the foregoing range, it is possible to enhance the β-OH of the finally obtainable glass.
For example, the molten product obtained by coarse melting is quenched, and crushed, thereby manufacturing a cullet. Further, the cullet is placed in a platinum crucible, and is heated and remolten, resulting in molten glass. Further, after clarification and homogenization, the molten glass is molded, and is gradually cooled. As a result, a glass molded body can be obtained. To molding and gradual cooling of the molten glass, a known method may be applied.
Reduction of a part of the components included in the glass in the melting may cause coloring (which will be hereinafter described as “reduced color”) in the glass molded body. When a reduced color is generated, by subjecting the glass molded body to a heat treatment, it is possible to decrease the reduced color. The heat treatment of the glass molded body can be performed at, for example, a temperature of approximately the glass transition temperature in an oxidizing atmosphere. When the heat treatment temperature is high, the heat treatment time can be shortened. Further, even when the oxygen partial pressure in an oxidizing atmosphere is increased, the heat treatment time can be shortened. Thus, the heat treatment time varies according to the heat treatment temperature and the oxygen partial pressure in an oxidizing atmosphere. For this reason, setting thereof may be accomplished so as to be able to sufficiently reduce coloring of glass. The heat treatment time can be set at, for example, about 0.1 hour to 100 hours. The oxidizing atmosphere is an atmosphere including oxygen, and may be, for example, an air atmosphere.
An aspect of the present disclosure relates to:
Another aspect of the present disclosure relates to:
In accordance with a still other aspect of the present disclosure also provides:
The optical element blank is an optical element base material closely analogous in shape to the objective optical element, and obtained by adding the polishing margin (the surface layer to be removed by polishing), and if required, a grinding margin (the surface layer to be removed by grinding), to the shape of the optical element. The surface of the optical element blank is ground and polished, thereby finishing an optical element. In one embodiment, an optical element blank can be manufactured by a method in which the molten glass obtained by melting the glass in a proper amount is press molded (which is referred to as a direct press method). In another embodiment, the optical element blank can also be manufactured by solidifying the molten glass obtained by melting a proper amount of the glass.
Still further, in a still other aspect, a glass material for press molding is manufactured. The manufactured glass material for press molding is press molded. As a result, an optical element blank can be manufactured.
Press molding of the glass material for press molding can be performed with a known method in which a glass material for press molding in a heated and softened state is pressed with a mold for press molding. Both of heating and press molding can be performed in the atmosphere. By reducing the strain inside the glass with annealing after press molding, it is possible to obtain a homogeneous optical element blank.
Examples of the glass materials for press molding include those to be subjected to machining such as cutting, grinding, and polishing, and to go through a glass gob for press molding for being subjected to press molding, in addition to those referred to as a glass gob for press molding to be subjected to press molding for manufacturing an optical element blank in the as-is state. Examples of the cutting methods include a method in which a groove is formed at the portion to be cut of the surface of a glass sheet with a process referred to as scribing, and the portion of the groove is applied with a local pressure from the back surface of the surface including the groove formed therein, thereby breaking the glass sheet at the portion of the groove; a method in which a glass sheet is cut by a cutting blade; and other methods. Further, examples of the grinding and polishing methods include barrel polishing, and the like.
The glass material for press molding can be manufactured, for example, in the following manner. Molten glass is casted in a mold, and molded into a glass sheet. The glass sheet is cut into a plurality of glass pieces. Alternatively, a glass gob for press molding can also be manufactured by molding a proper amount of molten glass. An optical element blank can also be manufactured by reheating and softening, and press molding the glass gob for press molding. The method in which glass is reheated and softened, and is press molded, thereby manufacturing an optical element blank is referred to as a reheat press method in contrast to the direct press method.
A still other aspect of the present disclosure relates to:
The above optical element is manufactured using the above optical glass. In the above optical element, one or more layers of coating such as a multilayer film of, for example, an antireflection film may be formed on the glass surface.
Further, one aspect of the present disclosure also provides:
With the above method for manufacturing an optical element, to grinding and polishing, a known method may be applied. After processing, the optical element surface is subjected to sufficient cleaning, and drying, and the like. As a result, it is possible to obtain an optical element with a high inside quality and surface quality. In this manner, the optical element comprised of the above glass can be obtained. Examples of the optical element include various lenses such as a spherical lens, an aspherical lens, and a microlens; prisms; and the like.
Further, the optical element comprised of the above optical glass is also preferable as a lens configuring a cemented optical element. Examples of the cemented optical element include the one including lenses cemented to each other therein (cemented lens), and the one including a lens and a prism cemented to each other therein. For example, the cemented optical element can be manufactured in the following manner. The joint surfaces of two optical elements to be cemented are precisely processed (for example, spherically polished) so that the shapes may become the inverted shapes. An ultraviolet ray curable adhesive for use in adhesion of a cemented lens is applied, and an ultraviolet ray is applied through the lens after bonding, thereby curing the adhesive. The above glass is preferable for manufacturing a cemented optical element in this manner. A plurality of optical elements to be cemented are respectively manufactured using a plurality of kinds of glasses having different Abbe's numbers vd, and are cemented, which can result in the elements preferable for correction of the chromatic aberration.
Below, the present disclosure will be described in further details by way of Examples. However, the present disclosure is not limited to the embodiments shown in Examples.
First, an oxide, a hydroxide, a carbonic acid salt, and a nitric acid salt corresponding to the constituent components of glass were prepared as raw materials. The raw materials were weighed and prepared so that the glass composition of the resulting optical glass may become each composition shown in the table below. Thus, the raw materials were sufficiently mixed. The prepared raw material (batch raw material) thus obtained was charged with a reducing agent in the amount (unit: mass %) shown in the following table for every 100 mass % of the prepared raw material into a platinum crucible, and was heated at 1250° C. to 1400° C. for 2 hours, and was molten, resulting in molten glass (melting step), and stirring was performed at 1300 to 1400° C. for 1 to 2 hours for homogenization and clarifying (homogenizing/clarifying step). The molten glass was casted in a mold preheated to an appropriate temperature. The casted glass was subjected to a heat treatment at a glass transition temperature Tg for 30 minutes, and was allowed to cool to room temperature in the furnace, resulting in a glass molded body. The resulting molded body was increased in temperature to the glass transition temperature Tg in the air atmosphere, and was held at this temperature for 48 hours for a heat treatment. Thus, a glass sample was obtained.
In the following table, the unit of the content is mass %. The Sb2O3 content is the content when the total content of glass components other than Sb2O3 is assumed to be 100 mass %.
At the melting step, and the homogenizing/clarifying step, the following operations were performed.
A pipe made of platinum was inserted into a crucible made of platinum arranged in the furnace from the outside of the melting furnace, and water vapor was supplied through the pipe made of platinum into the space in the crucible made of platinum. There was set at the flow rate shown in the following table.
Further, nitrogen was supplied through the pipe made of platinum into the space in the crucible made of platinum, and water vapor was bubbled into the molten substance from the pipe set under the crucible. The flow rates of the supplied nitrogen and water vapor were set at 30 L/min for nitrogen, and 5.0 cc/min for the water vapor.
Thus, glass samples of respective optical glasses of Nos. 1 to 10 of Example 1, and a glass sample of Comparative Example 1 were obtained.
Comparative Example 2 in the following table is TAFD55-W manufactured by HOYA Corporation, and Comparative Example 3 is E-FDS3-W manufactured by HOYA Corporation.
Various physical properties of respective optical glasses of Examples and Comparative Example are shown in the following table. The various physical properties of the optical glasses were measured in the following manner.
Using a glass sample having two optically polished planes opposed to each other, and having a thickness of 10±0.1 mm, a light with an intensity Iin was made incident upon the polished surfaces from the vertical direction, and the intensity Iout of the light transmitted through the glass sample was measured by a spectrophotometer, thereby calculating the spectral transmittance Iout/Iin. Accordingly, λ5 and λ70 were determined, where λ5 represents the wavelength providing a spectral transmittance of 5%, and λ70 represents the wavelength providing a spectral transmittance of 70%. The difference (λ70−λ5) between λ70 and λ5 was calculated from the determined λ70 and λ5.
Using respective spectral transmittances (including the surface reflection loss) of a pair of samples having different thicknesses, the internal transmittance T460 for a thickness of 10 mm at a wavelength of 460 nm was determined.
As for the glass obtained by temperature drop at a temperature dropping rate of −30° C./hour, the refractive index nd and the Abbe's number vd were measured with the refractive index measuring method of the Japan Optical Glass Manufacturers' Association standard.
With the one obtained by sufficiently grinding glass in a mortar as a sample, using a differential scanning calorie analyzer (DSC3300SA) manufactured by NETZSCH Co., DSC measurement was performed at a heating rate of 10° C./min, resulting in a DSC curve. From the resulting DSC curve, the glass transition temperature Tg and the temperature TI at which switching to melt is caused were determined as described previously.
The specific gravity was measured with the Archimedes method.
The glass sample was processed into a sheet-shaped glass sample with a thickness of 1 mm, and having planes in parallel with each other, and optically polished. A light was made incident upon the polished surface of the sheet-shaped glass sample from the vertical direction. Thus, the spectral transmittance A at a wavelength of 2500 nm and the spectral transmittance B at a wavelength of 2900 nm were measured, respectively, using a spectrophotometer, and the β-OH was calculated by the equation (1) previously shown.
The Pt content of each optical glass of Nos. 1 to 10 of Example 1 was quantified by the inductively coupled plasma mass spectrometry method (ICP-MS), and was found to fall within the range of 0.001 ppm to 10 ppm.
Each optical glass of Nos. 1 to 10 of Example 1 was visually observed. As a result, surface devitrification was not observed in the glass block of each optical glass of Example 1.
Each optical glass of Example 1 and Comparative Examples 1 to 3 was processed into a rectangular thin sheet shape with length 50 mm×width 20 mmx thickness 1.0 mm, resulting in a light guide plate 10.
The light guide plate was mounted to the head mount display 1 (which will be hereinafter abbreviated as “HMD 1”) shown in
As shown in
The image display element 24 is, for example, a transmission type liquid crystal (LCDT-LCOS) panel to be driven by a field sequential system. The image display element 24 applies the light of each wavelength with modulation in response to the image signal generated by an image engine (not shown) of the signal processing instrument 5. The light of each wavelength modulated with the pixel in the effective region of the image display element 24 is made incident with a prescribed luminous flux cross section (substantially the same shape as that of the effective region) on the light guide plate 10. The image display element 24 can also be replaced with a display element in, for example, another form such as a DMD (Digital Mirror Device), a reflection type liquid crystal (LCOS) panel, MEMS (Micro Electro Mechanical Systems), an organic EL (Electro-Luminescence), or an inorganic EL.
The display element unit 20 is not limited to the display element of a field sequential system, and may be assumed as an image forming unit of the simultaneous display element (a display element having RGB color filters in a prescribed array at the emitting surface front surface). In this case, for the light source, for example, a white light source is used.
As shown in
Both the HOEs 32R and 32L are each also a reflection type volume phase type HOE, and have the same layer structure as that of the HOEs 52R and 52L. The HOEs 32R and 32L, and 52R and 52L may have, for example, substantially the same pitch of the interference fringes pattern.
The HOEs 52R and 52L are stacked with the mutual centers in alignment with each other, and the interference fringes pattern inverted 180 (deg). Then, the HOEs 52R and 52L are fixed tightly on the second surface 10b of the light guide plate 10 in a stacked state by adhesion or the like so that the centers thereof may be in alignment with the center line X. Upon the HOEs 52R and 52L, lights with respective wavelengths modulated by the image display element 24 are sequentially made incident via the light guide plate 10.
The HOEs 52R and 52L diffract the lights with respective wavelengths sequentially made incident at a prescribed angle in order to guide the lights to the right eye and the left eye. The lights with respective wavelengths diffracted by the HOEs 52R and 52L respectively repeatedly undergo total reflection at the interface between the light guide plate 10 and air, and propagate through the inside of the light guide plate 10, to be made incident upon the HOEs 32R and 32L. Herein, the HOEs 52R and 52L give the same diffraction angle to the lights with respective wavelengths. For this reason, the lights with all the wavelengths to be made incident upon substantially the same positions with respect to the light guide plate 10 (or in other words, emitted from substantially the same coordinates in the effective region of the image display element 24) propagate through substantially the same optical paths in the inside of the light guide plate 10, and are made incident upon substantially the same positions on the HOEs 32R and 32L. From another viewpoint, the HOEs 52R and 52L diffract the lights with respective wavelengths of RGB so that the pixel positional relationship in the effective region of the image displayed in the effective region of the image display element 24 may be reproduced on the HOEs 32R and 32L truly.
As described above, in the present Example, the HOEs 52R and 52L respectively diffract the lights with all the wavelengths emitted from substantially the same coordinates in the effective region of the image display element 24 so that the lights may be made incident upon substantially the same positions of the HOEs 32R and 32L. Alternatively, the HOEs 52R and 52L may be configured such that the lights with all the wavelengths forming originally the same pixels relatively shifted in the effective region of the image display element 24 may be made incident upon substantially the same positions on the HOEs 32R and 32L.
The lights with respective wavelengths made incident upon the HOEs 32R and 32L are diffracted by the HOEs 32R and 32L, to be sequentially emitted substantially perpendicularly to the outside from the second surface 10b of the light guide plate 10. The lights with respective wavelengths thus emitted as substantially parallel lights form images on the right eye retina and the left eye retina of a user as the virtual image I of the image generated by the image display element 24, respectively. Further, the HOEs 32R and 32L may be imparted with the capacitor action so that a user may observe the virtual image I of an enlarged image. Namely, it may be configured as follows: the light made incident in each more peripheral region of the HOEs 32R and 32L is emitted at an angle so as to be closer to the center of the pupil, and forms an image at the retina of a user. Alternatively, it may be configured as follows: in order for a user to observe the virtual image I of an enlarged image, the HOEs 52R and 52L diffract the lights with respective wavelengths of RGB so that the pixel positional relationship on the HOEs 32R and 32L forms a similar shape enlarged relative to the pixel positional relationship in the effective region of the image displayed in the effective region of the image display element 24.
The air-equivalent optical path length of the light traveling in the light guide plate 10 is shortened with an increase in refractive index. For this reason, by using the respective optical glasses with a high refractive index, it is possible to increase the apparent viewing angle with respect to the width of the image display element 24. Further, since the refractive index is high but the specific gravity can be kept low, it is possible to provide a light guide plate which is lightweight and has the above effect.
The light guide plate 10 thus obtained was mounted in a HMD1, and the image was evaluated at a position of eye point. With the HMD1 including a light guide plate comprised of each optical glass of Example mounted therein, an image with a high luminance and a high contrast could be observed at a wide viewing angle. With the HMD1 including a light guide plate comprised of each optical glass of Example mounted therein, a more clear image could be obtained as compared with the HMD1 including a light guide plate comprised of each optical glass of Comparative Examples 1 to 3.
The light guide plate including each optical glass of Example can be used for a see-through transmission type head mount display, a non-transmission type head mount display, and the like.
The head mount displays each include the light guide plate comprised of glass with a high refractive index, and thereby are excellent in immersiveness due to a wide viewing angle. The head mount displays are preferable as image display devices for use in combination with information terminals, for use as for providing AR (Augmented Reality), or the like, or for use as for providing movie watching, game, VR (Virtual Reality), and the like.
In the present Example, the head mount display was taken as an example for description. However, the light guide plate may be mounted to other image display devices.
Using the various glasses obtained in Example 1, a glass block (glass gob) for press molding was manufactured. The glass block was heated and softened in the atmosphere, and was press molded in a mold for press molding, thereby manufacturing a lens blank (optical element blank). The manufactured lens blank was taken out from the mold for press molding, and was annealed, and was subjected to machining including polishing, thereby manufacturing a spherical lens including each optical glass of Example 1.
The molten glass manufactured in Example 1 was press molded in a desired amount in a mold for press molding, thereby manufacturing a lens blank (optical element blank). The manufactured lens blank was taken out from the mold for press molding, and was annealed, and was subjected to machining including polishing, thereby manufacturing a spherical lens including each optical glass of Example 1.
The glass block (optical element blank) manufactured by solidifying the molten glass manufactured in Example 1 was annealed, and was subjected to machining including polishing, thereby manufacturing a spherical lens including each optical glass of Example 1.
Each spherical lens manufactured in Examples 3 to 5 was bonded with a spherical lens including other kinds of glasses, thereby manufacturing a cemented lens.
It should be considered that the embodiments disclosed this time are illustrative in all the points, and are not restrictive. The scope of the present disclosure is shown not by the foregoing description, but by the appended claims, and is intended to include the meanings equivalent to the appended claims and all the changes within the scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-058567 | Mar 2023 | JP | national |
| 2024-016057 | Feb 2024 | JP | national |
