Optical glass plate

Abstract

To provide an optical glass plate that has a high refractive index and a good visible-light transmission rate.SOLUTION: This optical glass plate is characterized by containing, as a glass composition, at least one selected from Nb2O5, La2O3 and Gd2O3, and by having a refractive index (nd) of 1.90-2.30 and an internal transmission rate τ450 of 75% or more with respect to a wavelength of 450 nm at a thickness of 10 mm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an optical glass plate used as a light guide plate or the like in a wearable image display device.

[0002] Glass plates are used as components in wearable image display devices such as projector-equipped glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices. These glass plates function, for example, as see-through light guide plates, allowing users to view the external scenery through the glass plate while simultaneously viewing the image displayed on the glass plate. Furthermore, it is possible to achieve 3D display by utilizing technology to project different images onto the left and right sides of the glasses, or to realize a virtual reality space by utilizing technology to fuse the image to the retina using the lens of the eye. These glass plates are required to have a high refractive index in terms of widening the image angle, increasing brightness and contrast, and improving light guide characteristics. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-32673 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The glass plates used in the wearable image display devices described above often utilize elements that absorb in the visible range to increase the refractive index. Therefore, high-refractive-index glass generally suffers from low visible-range light transmittance. However, in devices with the aforementioned applications, low transmittance reduces the brightness of the image seen by the user. For this reason, optical glass for such applications requires both high refractive index and high visible light transmittance.

[0005] In light of these circumstances, the present invention aims to provide an optical glass plate with a high refractive index and excellent visible light transmittance.

Means for Solving the Problem

[0006] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by having a predetermined component as a glass composition and regulating the internal transmittance at a specific wavelength.

[0007] That is, the optical glass plate of the present invention contains at least one selected from Nb2O5, La2O3, and Gd2O3 as a glass composition, has a refractive index (nd) of 1.90 to 2.30, and an internal transmittance τ at a wavelength of 450 nm with a thickness of 10 mm 450 is 75% or more. The "internal transmittance" means the transmittance excluding the surface reflection loss on the incident side and the exit side of the glass plate, and can be calculated from the measured values of the transmittance including the surface reflection loss at thicknesses of 3 mm and 10 mm, respectively.

[0008] The optical glass plate of the present invention has an internal transmittance τ at a wavelength of 520 nm with a thickness of 10 mm 520 is preferably 85% or more.

[0009] The optical glass plate of the present invention contains TiO2 as a glass composition, and in the spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the glass cross-section, the ratio of the peak heights of Ti 2+ and Ti 4+ (Ti 2+ / Ti 4+ ) is preferably 0.3 or less. Generally, Ti in glass exists as Ti 2+ or Ti 4+ . Here, Ti 4+ does not cause a decrease in the visible light transmittance characteristic, but Ti 2+ becomes a coloring center and thus the visible light transmittance characteristic deteriorates. Therefore, by defining the ratio of the peak heights of Ti 2+ and Ti 4+ as described above, it is possible to obtain a glass excellent in visible light transmittance.

[0010] The optical glass plate of the present invention contains Nb2O5 as its glass composition, and in the spectrum obtained by X-ray photoelectron spectroscopy of the glass cross section, Nb 2+ and Nb 5+ Ratio of peak heights (Nb 2+ / Nb 5+ It is preferable that ) is 0.25 or less. Generally, Nb in glass is Nb 2+ Ya Nb 5+ It exists as such. Here, Nb 5+ This does not cause a decrease in visible light transmittance characteristics, but Nb 2+ Since it becomes the color center, the visible light transmittance characteristics decrease. Therefore, in the spectrum obtained by XPS, Nb 2+ and Nb 5+ By defining the ratio of the peak heights as described above, it becomes possible to produce glass with excellent visible light transmittance.

[0011] The optical glass plate of the present invention preferably contains, in terms of mass percent on an oxide basis, SiO2 1-20%, B2O3 1-25%, TiO2 1-30%, and Nb2O5 1-30% as a glass composition.

[0012] The optical glass plate of the present invention preferably contains, in terms of mass percent on an oxide basis, 10-60% La2O3, 20-20% Gd2O3, 15-15% ZrO2, and 5-5% Y2O3.

[0013] The optical glass plate of the present invention preferably contains 0-5% CaO and 0-5% SrO by mass percentage on an oxide basis.

[0014] The optical glass plate of the present invention contains B in the glass composition. 3+ and Si 4+ Content ratio (B 3+ / Si 4+ It is preferable that the value is between 0.5 and 5.

[0015] The optical glass plate of the present invention preferably contains substantially no arsenic, fluorine, or lead components in its glass composition. In the present invention, "substantially no" means intentionally excluding the relevant components from the glass, and does not mean completely eliminating unavoidable impurities. Objectively, it means that the content of each component, including impurities, is less than 0.1% by mass.

[0016] The optical glass plate of the present invention preferably has an Abbe number (νd) of 20 to 35.

[0017] The optical glass plate of the present invention preferably has a thickness of 1 mm or less.

[0018] In the present invention, the optical glass plate preferably has a major axis of 50 mm or more on its main surface.

[0019] The optical glass plate of the present invention has a liquid phase viscosity of 10 0.5 It is preferable that the pressure be dPa·s or higher.

[0020] The optical glass plate of the present invention has a thermal expansion coefficient of 95 × 10 at 30 to 300°C. -7 It is preferable that the temperature is below / °C. Here, the coefficient of thermal expansion refers to the average linear thermal expansion coefficient measured with a dilatometer.

[0021] The optical glass plate of the present invention has a density of 5.5 g / cm³. 3 The following is preferable:

[0022] The light guide plate of the present invention is characterized by being made of the above-mentioned optical glass plate.

[0023] The light guide plate of the present invention is preferably used in wearable image display devices selected from projector-equipped glasses, spectacle-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

[0024] The wearable image display device of the present invention is characterized by comprising the above-mentioned light guide plate. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide an optical glass plate that has a high refractive index and excellent visible light transmittance. [Modes for carrying out the invention]

[0026] The optical glass of the present invention has a minimum refractive index (nd) of 1.90, and preferably 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, and particularly 1.99. Furthermore, the maximum refractive index (nd) is 2.30, and preferably 2.20, 2.10, 2.08, 2.06, 2.05, 2.04, 2.03, 2.02, and particularly 2.01. If the refractive index is too low, the viewing angle tends to narrow when used as a light guide plate in wearable image display devices such as projector-equipped glasses, spectacle-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices. On the other hand, if the refractive index is too high, defects such as devitrification and striations tend to increase in the glass.

[0027] The optical glass of the present invention has an internal transmittance of τ at a wavelength of 450 nm at a thickness of 10 mm. 450 The internal transmittance τ at a wavelength of 450 nm is 75% or more, and is preferably 80% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, and especially preferably 93% or more. 450 By increasing this value, it becomes easier to obtain excellent light transmittance in the visible range. As a result, the brightness of the image seen by the user in the above-mentioned wearable image display device tends to increase.

[0028] For example, internal transmittance τ 450 By increasing the above, the internal transmittance τ at a wavelength of 520 nm in a thickness of 10 mm is increased. 520 This increases the brightness of the image seen by the user in the above-mentioned wearable image display device. Specifically, the internal transmittance τ 520It is possible to set the percentages to 85% or higher, 87% or higher, 89% or higher, 90% or higher, 91% or higher, 92% or higher, 93% or higher, 94% or higher, 95% or higher, 96% or higher, 97% or higher, and especially 98% or higher.

[0029] As will be described later, for example, the internal transmittance at the specified wavelength can be further increased by adjusting the valence states of Ti and Nb contained in the glass. Specifically, the internal transmittance can be further increased by increasing the valence states of Ti and Nb (i.e., shifting Ti and Nb toward oxidation).

[0030] The following provides examples of the constituent components of the optical glass plate of the present invention, along with an explanation of the preferred content ranges. In the description of the content range of each component, unless otherwise specified, percentages refer to mass percentages.

[0031] The optical glass plate of the present invention contains at least one selected from Nb2O5, La2O3, and Gd2O3 as the glass composition. Since these components increase the refractive index, it is possible to achieve the desired high refractive index characteristics by including at least one of these components as an essential component.

[0032] Nb2O5 is a component that significantly increases the refractive index. When Nb2O5 is included, its content is preferably 1-30%, 1.7-25%, 2.5-22%, 3.3-18%, 4.4-14%, 5.3-10%, and especially 6.1-9%. If the Nb2O5 content is too low, it becomes difficult to obtain the above effects. On the other hand, if the Nb2O5 content is too high, the liquid phase temperature rises rapidly, the liquid phase viscosity decreases, and mass production tends to deteriorate. Furthermore, the internal transmittance tends to decrease because the amount of Nb, which is the coloring center, increases.

[0033] Furthermore, in the spectrum obtained by XPS (X-ray photoelectron spectroscopy) of the glass cross-section of the optical glass of the present invention, Nb 2+ and Nb 5+ Ratio of peak heights (Nb 2+ / Nb 5+It is preferable that the ratio of Nb is 0.25 or less, 0.2 or less, 0.15 or less, 0.12 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, and especially 0.02 or less. 2+ / Nb 5+ If the value is too large, absorption in the visible region increases drastically, and the internal transmittance tends to decrease. Note that in the XPS spectrum, Nb 2+ and Nb 5+ The peaks are located at energy positions of 202.1 eV and 207.5 eV, respectively.

[0034] La2O3 is a component that significantly increases the refractive index. When La2O3 is included, its content is preferably 10-60%, 20-55%, 35-55%, 35-53%, 38-53%, 40-52%, 42-52%, 42-51%, and especially 45-50.5%. If the La2O3 content is too low, it becomes difficult to obtain the above effect. On the other hand, if the La2O3 content is too high, the liquid phase temperature rises rapidly, the liquid phase viscosity decreases, and mass production tends to deteriorate.

[0035] Gd2O3 is a component that increases the refractive index and improves the stability of vitrification. When Gd2O3 is included, its content is preferably 0-20%, over 0-18%, 1-17%, 2-16%, 3-15%, 4-13%, 4-12%, 5-11%, 5-10%, and especially 6-9%. If the Gd2O3 content is too high, the melting temperature becomes extremely high, making Nb and Ti more susceptible to reduction, which tends to decrease the internal transmittance.

[0036] In addition to the above-mentioned components, the optical glass of the present invention may also contain the following components.

[0037] SiO2 is a component of the glass skeleton and improves the stability of vitrification and chemical durability. The SiO2 content is preferably 1-20%, 1.2-18%, 1.5-18%, 1.8-18%, 2-15%, 2.5-15%, 2.5-13%, 2.8-13%, 3-12%, 3-11%, 3.5-10%, 3.5-9%, and especially preferably 4-8%. If the SiO2 content is too low, the viscosity of the glass decreases rapidly, the liquid phase viscosity decreases, and devitrification is more likely to occur during molding, which tends to worsen mass productivity. On the other hand, if the SiO2 content is too high, the melting temperature becomes extremely high. As a result, Nb and Ti are more easily reduced, which tends to decrease the internal transmittance. Also, the refractive index tends to decrease.

[0038] B2O3, like SiO2, is a component of the glass skeleton, but unlike SiO2, it does not increase the melting temperature of the glass; rather, it has the effect of lowering the melting temperature. It is also a component that contributes to the stability of vitrification. The B2O3 content is preferably 1-25%, 2-22%, 3-22%, 3-20%, 4-18%, 5-16%, 5-15%, 5-13%, 6-13%, 7-13%, 7.5-12%, 8-11.5%, and especially 8.3-9.5%. If the B2O3 content is too low, the melting temperature becomes extremely high, and Nb and Ti are more easily reduced, so the internal transmittance tends to decrease. On the other hand, if the B2O3 content is too high, the refractive index decreases and the chemical durability tends to decrease.

[0039] Furthermore, in order to achieve excellent light transmittance characteristics and improve the stability of vitrification and mass production, the glass composition of B is important. 3+ and Si 4+ Content ratio (cation ratio = B 3+ / Si 4+ It is preferable to appropriately adjust B 3+ / Si 4+ The values ​​are preferably 0.5-5, 0.9-4.5, 1.2-4, 1.5-4, 1.5-3.7, 1.7-3.5, and especially 1.8-3.4. 3+ / Si 4+If the value is too small, the melting temperature becomes extremely high, making Nb and Ti more susceptible to reduction, which tends to decrease the internal transmittance. On the other hand, B 3+ / Si 4+ If the ratio is too high, the chemical durability of the glass tends to decrease. Also, the viscosity of the glass decreases rapidly, leading to a decrease in liquid-phase viscosity and making mass production difficult.

[0040] Also, Si 4+ +B 3+ (Si 4+ and B 3+ The total amount of Si is preferably 20-50%, 30-50%, 31-45%, 32-45%, 33-45%, 34-45%, and especially 35-42%. 4+ +B 3+ If there is too little of it, it becomes difficult to vitrify. On the other hand, Si 4+ +B 3+ If there is too much of it, the refractive index tends to decrease.

[0041] TiO2 is a component that increases the refractive index. It also has the effect of improving chemical durability. The TiO2 content is preferably 1-30%, 1.7-25%, 2.5-23%, 3.3-21%, 8-20%, 10-18%, and especially 12-16%. If the TiO2 content is too low, it becomes difficult to obtain the above effects. On the other hand, if the TiO2 content is too high, the liquid phase temperature rises rapidly, the liquid phase viscosity decreases, and mass production tends to deteriorate. Furthermore, the internal transmittance tends to decrease because the amount of Ti, which is the coloring center, increases.

[0042] Furthermore, in the spectrum obtained by XPS (X-ray photoelectron spectroscopy) of the glass cross-section of the optical glass of the present invention, Ti 2+ and Tire 4+ Ratio of peak heights (Ti 2+ / Ti 4+ Ti 2+ / Ti 4+If the value is too large, absorption in the visible range increases drastically, and the internal transmittance tends to decrease. Note that in the XPS spectrum, Ti 2+ and Tire 4+ The peaks are located at energy positions of 455.1 eV and 459.0 eV, respectively.

[0043] ZrO2 is a component that enhances refractive index and chemical durability. However, because it acts as a crystal nucleus, its high content accelerates devitrification of the glass. Therefore, the ZrO2 content is preferably 0-15%, over 0-10%, 1-9%, 3-8%, 4-7.5%, and especially 5-7%.

[0044] Y2O3 is a component that significantly increases the refractive index. However, if its content is too high, devitrification and striations are more likely to occur. Therefore, the Y2O3 content is preferably 0-5%, over 0-5%, 0.1-4%, 0.3-2%, 0.4-1%, and especially 0.5-0.8%.

[0045] Yb2O3 is a component that significantly increases the refractive index. However, if its content is too high, devitrification and striations are more likely to occur. Therefore, the Yb2O3 content is preferably 0-5%, over 0-5%, 0.1-4%, 0.3-2%, 0.4-1%, and especially 0.5-0.8%.

[0046] Furthermore, the Y2O3+Yb2O3 content (total amount of Y2O3 and Yb2O3) is preferably 0-5%. If the Y2O3+Yb2O3 content is too high, the liquid phase temperature rises rapidly, the liquid phase viscosity decreases, and devitrification and striations are more likely to occur. The upper limit of the Y2O3+Yb2O3 content is preferably 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, and especially 0.9%. On the other hand, the lower limit of the Y2O3+Yb2O3 content is preferably 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, and especially 0.6%. This makes it easier to obtain the desired high refractive index characteristics.

[0047] In order to suppress the reduction of Nb and Ti in the optical glass of the present invention, it is preferable to add various oxidizing agents during melting. Examples of such oxidizing agents include calcium nitrate, strontium nitrate, barium nitrate, sodium nitrate, and potassium nitrate. Among these, calcium nitrate and strontium nitrate are particularly preferred. Furthermore, the total amount of oxidizing agent added is preferably 0-5%, 0-3%, and particularly 0.01-1% by mass in the glass batch.

[0048] When the aforementioned oxidizing agents are used, components such as CaO, SrO, BaO, Na2O, and K2O are included in the glass composition. The functions and ranges of content of these components are described below.

[0049] CaO is a component that contributes to the stability of vitrification. However, if its content is too high, the liquidus temperature tends to rise and the refractive index tends to decrease. Therefore, the CaO content is preferably 0-5%, 0-2%, and especially 0.01-0.5%.

[0050] SrO is a component that contributes to the stability of vitrification. However, if its content is too high, the refractive index tends to decrease. Therefore, the SrO content is preferably 0-5%, 0-2%, and especially 0.01-0.5%.

[0051] BaO contributes to the stability of vitrification and is a component that increases the refractive index. However, the inclusion of BaO increases the density of the glass, and the weight of the optical element made from the optical glass of the present invention tends to increase. For this reason, it is particularly undesirable for applications such as wearable image display devices. Accordingly, the BaO content is preferably 1% or less, 0.5% or less, or 0.2% or less, and it is particularly preferable that it is not included.

[0052] Furthermore, in order to achieve the desired refractive index and internal transmittance and to enhance the stability of vitrification, the combined amounts of CaO, SrO, and BaO are preferably 0-5%, 0-2%, 0-1%, 0-0.9%, 0-0.8%, 0-0.7%, 0-0.6%, 0-0.5%, and particularly 0.01-0.5%.

[0053] Na2O and K2O are components that lower the softening point, but if their content is too high, devitrification and striations are more likely to occur. Therefore, the content of these components is preferably 0-3% and 0-1% respectively, and it is particularly preferable that they are not present at all. Similarly, Li2O, another alkali metal component, also lowers the softening point, but if its content is too high, devitrification and striations are more likely to occur. Therefore, the content of Li2O is preferably 0-3% and 0-1%, and it is particularly preferable that it is not present at all.

[0054] Furthermore, in order to suppress the reduction of Nb and Ti, it is preferable not to include reducing agents such as carbon or metal during the melting process.

[0055] ZnO is a component that promotes devitrification in the composition system of the present invention, and its content should be as low as possible. Specifically, the ZnO content should be 1% or less, 0.5% or less, and more preferably 0.1% or less, and it is particularly preferable that it is not present at all.

[0056] WO3 is a component that increases the refractive index, but it tends to decrease the light transmittance in the visible region. Therefore, its content is preferably 1% or less, 0.6% or less, 0.5% or less, or 0.3% or less, and it is particularly preferable that it is not included.

[0057] Furthermore, it is preferable that the product is substantially free of arsenic components (such as As2O3), fluorine components (such as F2), and lead components (such as PbO) due to their significant environmental impact.

[0058] To improve clarity, the optical glass of the present invention may use clarifying agents such as CaCl2 and Sb2O3. The total amount of these clarifying agents in the glass batch is preferably 8% or less, 5% or less, 2% or less, and particularly preferably 1% or less. In this case, the content of the clarifying agent components contained in the glass component, specifically Cl and Sb2O3, is preferably 5% or less, 3% or less, and particularly preferably 0.5% or less, respectively.

[0059] The optical glass of the present invention may contain impurities such as H2, CO2, CO, H2O, He, Ne, Ar, and N2, up to 0.1% each. It may also contain Pt, Rh, and Au as impurities. However, if the content of Pt, Rh, and Au is too high, they act as coloring centers in the glass, which tends to reduce the internal transmittance. Therefore, the content of Pt, Rh, and Au is preferably 500 ppm or less, 300 ppm or less, and particularly preferably 100 ppm or less, respectively.

[0060] The optical glass of the present invention has a liquid phase viscosity of 10 0.5 dPa·s or higher, 10 0.6 dPa·s or higher, 10 0.7 dPa·s or higher, especially 10 0.8 It is preferable that the viscosity is dPa·s or higher. If the liquid-phase viscosity is too low, molding must be done at a low viscosity, which makes it easier for defects such as striations to occur in the glass, especially when the molding size is large. There is no particular upper limit to the liquid-phase viscosity, but in reality, 10 1.5 dPa·s or less, especially 10 1.2 It is less than or equal to dPa·s.

[0061] The optical glass of the present invention preferably has a liquidus temperature of 1350°C or lower, 1300°C or lower, 1250°C or lower, 1200°C or lower, and more preferably 1170°C or lower. If the liquidus temperature is too high, the load on the precious metal pots and pipes increases, requiring them to be replaced frequently, which tends to increase manufacturing costs. The lower limit of the liquidus temperature is not particularly limited, but in reality it is 1000°C or higher, and more preferably 1050°C or higher.

[0062] The liquid-phase viscosity and liquid-phase temperature can be calculated using the method described in the examples below.

[0063] The Abbe number (νd) of the optical glass of the present invention is not particularly limited, but considering the stability of vitrification, it is preferably 20 to 35, 22 to 32, and especially 25 to 30.

[0064] The optical glass of the present invention has a density of 5.5 g / cm³. 3 Below, 5.3g / cm 3The following, in particular, is 5.1 g / cm³. 3 The following is preferable. If the density is too high, the weight of the wearable device using the optical glass of the present invention will increase, increasing discomfort when wearing the device. There is no particular lower limit to the density, but if it is too low, other properties such as optical properties will deteriorate, so 4.0 g / cm³ is preferable. 3 In particular, 4.5 g / cm³ 3 It is preferable that the above conditions are met.

[0065] The optical glass of the present invention has a thermal expansion coefficient of 95 × 10 at 30 to 300°C. -7 / ℃ or below, 91×10 -7 / ℃ or lower, especially 88×10 -7 It is preferable that the coefficient of thermal expansion is below / °C. If the coefficient of thermal expansion is too high, the glass will be more prone to cracking due to thermal shock. There is no particular lower limit to the coefficient of thermal expansion, but if it is too low, other properties such as optical properties will deteriorate, so 75 × 10 -7 / ℃ or higher, especially 80×10 -7 It is preferable that the temperature is above / ℃.

[0066] The thickness of the optical glass plate of the present invention is preferably 1 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, 0.4 mm or less, and particularly 0.3 mm or less. If the thickness of the optical glass plate is too large, the weight of the wearable image display device using the optical glass plate will increase, increasing discomfort when the device is worn. There is no particular lower limit to the thickness, but considering mechanical strength, it is preferably 0.01 mm or more, 0.03 mm or more, and particularly 0.05 mm or more.

[0067] The shape of the optical glass plate of the present invention is, for example, a plate shape with a planar shape such as a circle, ellipse, or polygon such as a rectangle. In this case, the major axis (diameter in the case of a circle) of the optical glass plate is preferably 50 mm or more, 80 mm or more, 100 mm or more, 120 mm or more, 150 mm or more, 160 mm or more, 170 mm or more, 180 mm or more, 190 mm or more, and especially 200 mm or more. If the major axis of the optical glass plate is too small, it becomes difficult to use it for applications such as wearable image display devices. It also tends to be difficult to mass-produce. There is no particular upper limit to the major axis of the optical glass plate, but in reality it is 1000 mm or less.

[0068] The optical glass plate of the present invention is suitable as a light guide plate, which is a component of a wearable image display device selected from projector-equipped glasses, spectacle-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices. The light guide plate is used in the so-called spectacle lens portion of the wearable image display device and plays the role of guiding the light emitted from the image display element of the wearable image display device and directing it toward the user's pupil. Preferably, the surface of the light guide plate is provided with a diffraction grating for diffracting the light emitted from the image display element into the light guide plate. [Examples]

[0069] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0070] Tables 1-4 show examples of the present invention (Nos. 1-27).

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] First, glass raw materials were prepared to have the respective compositions shown in Tables 1 to 4. Here, for No. 8 to 10, 12, and 26, strontium nitrate was used as an oxidizing agent. Also, for No. 9 and 23, antimony oxide, and for No. 13 and 27, calcium chloride were used as fining agents.

[0076] Subsequently, the glass was melted at 1200 to 1350 °C using a platinum crucible. The melting time was 2 hours for all. Subsequently, the molten glass was poured onto a carbon plate, and after further annealing, samples suitable for each measurement were prepared.

[0077] The obtained samples were cut, and by subjecting the cut surface to XPS analysis, Ti 2+ / Ti 4+ and Nb 2+ / Nb 5+ were determined. The results are shown in Tables 1 to 4. Specifically, for the obtained XPS spectra, 9-point smoothing processing was performed, and the peak heights of Ti 2+ (455.1 eV) and Ti 4+ (459.0 eV) were read, and the ratio (Ti 2+ / Ti 4+ ) was determined. Also, the peak heights of Nb 2+ (202.1 eV) and Nb 5+ (207.5 eV) were read, and the ratio (Nb 2+ / Nb 5+ ) was determined. The XPS analysis was carried out using Quantera SXM manufactured by PHI. The excitation X-ray was Al Kα 1,2 line (1486.6 eV), the X-ray diameter was 200 μm, and the photoelectron escape angle was 45°.

[0078] Furthermore, the refractive index (nd), Abbe number (νd), internal transmittance, liquidus temperature, liquidus viscosity, density, and thermal expansion coefficient of the obtained samples were measured as follows. The results are shown in Tables 1-4.

[0079] The refractive index is shown as a measurement for the d-line (587.6 nm) of a helium lamp.

[0080] The Abbe number was calculated using the refractive index of the d line mentioned above, the refractive index of the F line (486.1 nm) of the hydrogen lamp, and the refractive index of the C line (656.3 nm) of the hydrogen lamp, using the formula (νd) = [(nd-1) / (nF-nC)].

[0081] Internal transmittance was measured as follows: Optically polished samples with thicknesses of 10 mm ± 0.1 mm and 3 mm ± 0.1 mm were prepared, and the light transmittance (linear transmittance), including surface reflection loss, was measured at 1 nm intervals using a spectrophotometer (Shimadzu UV-3100). The internal transmittance curve for the 10 mm thick sample was obtained from the linear transmittances of the 10 mm and 3 mm thick samples. The internal transmittance at wavelengths of 450 nm and 520 nm was read to obtain the measured values.

[0082] The liquidus temperature and liquidus viscosity were determined as follows.

[0083] The crushed glass sample was placed in a refractory container and melted in an electric furnace at 1250°C for 0.5 hours. Next, the refractory container was placed in an indirect heating temperature gradient furnace and left to stand in an atmospheric environment for 16 hours. After that, the refractory container was removed from the temperature gradient furnace and cooled to room temperature. The locations of crystal precipitation were determined by visual inspection of the cooled glass sample, and the liquidus temperature (crystal precipitation temperature) was determined from the temperature distribution information inside the temperature gradient furnace.

[0084] Separately, a block of glass sample was placed in an alumina crucible and heated and melted. The viscosity of the resulting glass melt was determined at multiple temperatures using the platinum ball pulling method. Subsequently, the constants of the Vogel-Fulcher equation were calculated using the measured glass viscosity values, and a viscosity curve was created.

[0085] Using the liquidus temperature and viscosity curve obtained as described above, the viscosity corresponding to the liquidus temperature (liquidus viscosity) was determined.

[0086] The density was measured using the Archimedes method with a glass sample weighing approximately 10 g.

[0087] The coefficient of thermal expansion was measured using a dilatometer with a glass sample molded to approximately 5φ × 20 mm in size, within a temperature range of 30 to 300°C.

[0088] As shown in Tables 1-4, the examples No. 1-27 have high refractive index characteristics with refractive indices of 1.95-2.00 and internal transmittance τ 450 77-98%, internal transmittance τ 520 It has excellent properties with a viscosity of 86-99%, a low liquid phase temperature of 1090-1225°C, and a liquid phase viscosity of 10 0.7 ~10 1.0 It had a high dPa·s level and excellent productivity.

[0089] Next, large glass plates having glass compositions No. 2, 5, and 10 were fabricated as follows.

[0090] First, glass raw materials were mixed to achieve compositions No. 2, 5, and 10. For composition No. 10, strontium nitrate was used as the oxidizing agent. Next, the mixture was melted at 1300°C using a large pot-type furnace, and the molten glass was poured from a platinum nozzle into a 500mm square carbon mold to a thickness of 20mm to form the glass.

[0091] After annealing the obtained ingot, the central part of the ingot was hollowed out in a circular shape, thinly sliced ​​in the planar direction, and then both sides were lapped and polished to a mirror finish. The dimensions of the fabricated optical glass plate are shown in Table 5.

[0092] [Table 5]

[0093] The optical glass plates 1-3 shown in Table 5 had the desired dimensions, with a diameter of 300-400 nm and a thickness of 0.1-0.3 mm, and no defects such as devitrification or striations were observed. [Industrial applicability]

[0094] The optical glass plate of the present invention is suitable as a light guide plate used in wearable image display devices selected from projector-equipped glasses, spectacle-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

Claims

1. As a glass composition, Nb ２ O ５ , La ２ O ３ and Gd ２ O ３ contains at least one selected therefrom, and in mass% in terms of oxide, La ２ O ３ 39.5 to 48.2%, TiO ２ 12 to 30%, SiO ２ 4 to 10.0%, B ２ O ３ 4.5 to 11.5%, WO ３ 0.5% or less, ZnO 0.1% or less, the refractive index (nd) is 1.90 to 2.00, and the internal transmittance τ ４５０ at a wavelength of 450 nm with a thickness of 10 mm is 75% or more. An optical glass plate characterized by this.

2. Internal transmittance τ at a wavelength of 520 nm with a thickness of 10 mm ５２０ The optical glass plate according to claim 1, characterized in that the content is 85% or more.

3. TiO ２ It contains and in the spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the glass fracture cross section, Ti ２＋ and Ti ４＋ Ratio of peak heights (Ti ２＋ / Ti ４＋ The optical glass plate according to claim 1 or 2, characterized in that ) is 0.3 or less.

4. Nb as the glass composition ２ O ５ It contains and in the spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the glass fracture cross-section, Nb ２＋ and Nb ５＋ Ratio of peak heights (Nb ２＋ / Nb ５＋ The optical glass plate according to any one of claims 1 to 3, characterized in that the ratio is 0.25 or less.

5. As for the glass composition, in terms of mass % on an oxide basis, Nb ２ O ５ An optical glass plate according to any one of claims 1 to 4, characterized in that it contains 1 to 30%.

6. In terms of mass percentage on an oxide basis, further Y ２ O ３ The optical glass plate according to claim 5, characterized in that it contains 0 to 5%.

7. The optical glass plate according to claim 5 or 6, further containing 0-5% CaO and 0-5% SrO in terms of mass percentage on an oxide basis.

8. B in glass composition ３＋ and Si ４＋ Content ratio (B ３＋ / Si ４＋ The optical glass plate according to any one of claims 1 to 7, characterized in that ) is 0.5 to 5.

9. An optical glass plate according to any one of claims 1 to 8, characterized in that the glass composition substantially does not contain arsenic, fluorine, or lead components.

10. An optical glass plate according to any one of claims 1 to 9, characterized in that its Abbe number (νd) is 20 to 35.

11. An optical glass plate according to any one of claims 1 to 10, characterized in that its thickness is 1 mm or less.

12. An optical glass plate according to any one of claims 1 to 11, characterized in that the major axis of the main surface is 50 mm or more.

13. Liquid phase viscosity is 10 ０．５ An optical glass plate according to any one of claims 1 to 12, characterized in that it is dPa·s or higher.

14. The coefficient of thermal expansion at 30-300°C is 95 × 10⁻⁶. －７ An optical glass plate according to any one of claims 1 to 13, characterized in that it is below / ℃.

15. Density is 5.5 g / cm³ ３ The optical glass plate according to any one of claims 1 to 14, characterized in that it is as follows:

16. A light guide plate characterized by being made of an optical glass plate as described in any one of claims 1 to 15.

17. The light guide plate according to claim 16, characterized in that it is used in a wearable image display device selected from projector-equipped glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

18. A wearable image display device characterized by comprising a light guide plate according to claim 16 or 17.

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