OPTICAL GLASS PLATE

Abstract

Provided is an optical glass plate having a high refractive index and excellent visible light transmittance. An optical glass plate characterized by containing as a glass composition at least one selected from Nb.sub.2O.sub.5, La.sub.2O.sub.3, and Gd.sub.2O.sub.3, the optical glass plate having a refractive index (nd) of 1.90 to 2.30 and an internal transmittance τ.sub.450 of 75% or greater for a thickness of 10 mm at a wavelength of 450 nm.

Claims

1. An optical glass plate containing as a glass composition at least one selected from Nb.sub.2O.sub.5, La.sub.2O.sub.3, and Gd.sub.2O.sub.3, the optical glass plate having: a refractive index (nd) from 1.90 to 2.30; and an internal transmittance τ.sub.450 of 75% or greater for a thickness of 10 mm at a wavelength of 450 nm.

2. The optical glass plate according to claim 1, having an internal transmittance τ520 of 85% or greater for a thickness of 10 mm at a wavelength of 520 nm.

3. The optical glass plate according to claim 1, containing TiO.sub.2 as a glass composition, wherein a ratio of peak heights of Ti.sup.2+ and Ti.sup.4+, that is Ti.sup.2+/Ti.sup.4+, is 0.3 or less, in a spectrum obtained by X-ray photoelectron spectroscopy (XPS) on a glass cut surface.

4. The optical glass plate according to claim 1, containing Nb.sub.2O.sub.5 as a glass composition, wherein a ratio of peak heights of Nb.sup.2+ and Nb.sup.5+, that is Nb.sup.2+/Nb.sup.5+ is 0.25 or less, in a spectrum obtained by X-ray photoelectron spectroscopy (XPS) on a glass cut surface.

5. The optical glass plate according to claim 1, containing, as glass compositions, from 1 to 20% of SiO.sub.2, from 1 to 25% of B.sub.2O.sub.3, from 1 to 30% of TiO.sub.2, and from 1 to 30% of Nb.sub.2O.sub.5 in terms of an oxide in mass %.

6. The optical glass plate according to claim 5, further containing from 10 to 60% of La.sub.2O.sub.3, from 0 to 20% of Gd.sub.2O.sub.3, from 0 to 15% of ZrO.sub.2, and from 0 to 5% of Y.sub.2O.sub.3 in terms of an oxide in mass %.

7. The optical glass plate according to claim 5, further containing from 0 to 5% of CaO or from 0 to 5% of SrO in terms of an oxide in mass %.

8. The optical glass plate according to claim 1, wherein a content ratio of B.sup.3+ and Si.sup.4+, that is B.sup.3+/Si.sup.4+, in a glass composition is from 0.5 to 5.

9. The optical glass plate according to claim 1, containing as a glass composition substantially no arsenic component, no fluorine component, and no lead component.

10. The optical glass plate according to claim 1, having an Abbe number (νd) from 20 to 35.

11. The optical glass plate according to claim 1, having a thickness of 1 mm or less.

12. The optical glass plate according to claim 1, having a long diameter of a main surface of 50 mm or longer.

13. The optical glass plate according to claim 1, having a liquidus viscosity of 10.sup.0.5 dPa.Math.s or greater.

14. The optical glass plate according to claim 1, having a thermal expansion coefficient of 95×10.sup.−7/° C. or lower at 30 to 300° C.

15. The optical glass plate according to claim 1, having a density of 5.5 g/cm.sup.3 or less.

16. A light guide plate comprising the optical glass plate described in claim 1.

17. The light guide plate according to claim 16, which is for use in a wearable image display device selected from: eyeglasses with a projector; an eyeglasses-type or goggle-type display; a virtual reality (VR) or augmented reality (AR) display device; and a virtual image display device.

18. A wearable image display device comprising the light guide plate described in claim 16.

Description

EXAMPLES

[0069] Hereinafter, the present invention will now be described in detail using examples, but the present invention is not limited to these examples.

[0070] Tables 1 to 4 list Examples (Nos. 1 to 27) of the present invention.

TABLE-US-00001 TABLE 1 Unit 1 2 3 4 5 6 7 Glass SiO.sub.2 mass % 5.2 6.6 5.2 5.0 4.9 6.6 10.0 composition B.sub.2O.sub.3 10.4 8.8 10.1 9.8 9.7 10.8 4.7 TiO.sub.2 14.6 14.6 14.5 12.4 13.9 15.1 14.9 Nb.sub.2O.sub.5 8 7.4 8.1 12.9 7.7 2.9 7.9 ZrO.sub.2 5.9 5.9 5.9 5.7 3.3 6.4 5.9 La.sub.2O.sub.3 48.1 48.2 47.9 46.2 45.7 49.9 48.3 Gd.sub.2O.sub.3 7.7 7.7 7.7 7.4 14.2 8.0 7.7 Y.sub.2O.sub.3 0.1 0.8 0.6 0.6 0.6 0.6 0.6 Sb.sub.2O.sub.3 SrO CaO Cl Ti.sup.2+/Ti.sup.4+ — <0.02 <0.02 <0.02 <0.02 <0.03 <0.02 Not measured Nb.sup.2+/Nb.sup.5+ — <0.02 <0.02 <0.02 <0.02 <0.03 <0.02 Not Measured B.sup.3+/Si.sup.4+ — 3.5 2.3 3.4 3.4 3.4 2.8 0.8 B.sup.3+ + Si.sup.4+ Cation % 38.0 36.5 37.3 36.7 36.6 40.5 32.1 Refractive index — 1.98 1.99 1.99 2.00 1.99 1.96 1.98 (nd) Abbe number (vd) — 17.2 28.8 28.5 29.8 29.1 29.9 19.2 τ.sub.450 % 89 94 89 91 90 87 77 τ.sub.520 % 95 98 95 96 97 91 86 Liquidus temperature ° C. 1090 1130 1115 1205 1160 1120 1225 Liquidus viscosity dPa .Math. s 10.sup.1.0 10.sup.1.0 10.sup.0.9 10.sup.0.8 10.sup.0.7 10.sup.1.0 10.sup.0.7 Density g/cm.sup.3 4.95 5.00 4.98 5.00 5.12 4.92 Not Measured Thermal expansion ×10.sup.−7/° C. 83 83 85 82 82 82 Not coefficient measured

TABLE-US-00002 TABLE 2 Unit 8 9 10 11 12 13 14 Glass SiO.sub.2 mass % 6.6 6.6 6.6 6.6 6.4 6.6 7.4 composition B.sub.2O.sub.3 8.8 8.8 8.7 8.6 9.0 8.8 10.4 TiO.sub.2 14.6 14.6 14.5 15.6 14.0 14.7 15.0 Nb.sub.2O.sub.5 7.4 7.4 7.4 7.2 7.8 7.5 6.6 ZrO.sub.2 5.9 5.9 5.9 5.5 6.1 5.9 2.7 La.sub.2O.sub.3 48.0 48.0 48.2 48.0 48.1 47.6 49.6 Gd.sub.2O.sub.3 7.8 7.7 7.6 7.3 7.7 7.8 8.0 Y.sub.2O.sub.3 0.8 0.8 0.8 0.8 0.8 0.8 Sb.sub.2O.sub.3 0.1 SrO 0.1 0.1 0.2 0.4 0.1 0.1 0.3 CaO 0.1 Cl 0.1 Ti.sup.2+/Ti.sup.4+ — <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nb.sup.2+/Nb.sup.5+ — <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 B.sup.3+/Si.sup.4+ — 2.3 2.3 2.3 2.2 2.4 2.3 2.4 B.sup.3+ + Si.sup.4+ Cation % 36.5 36.5 36.2 35.8 36.7 36.3 40.9 Refractive index — 1.99 1.99 1.99 1.99 1.99 1.99 1.96 (nd) Abbe number (vd) — 28.8 28.7 28.7 28.7 28.6 28.6 29.4 τ.sub.450 % 98 96 95 89 96 91 91 τ.sub.520 % 99 97 98 95 99 97 98 Liquidus temperature ° C. 1135 1135 1135 1135 1135 1135 1115 Liquidus viscosity dPa .Math. s 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.0.9 Density g/cm.sup.3 5.00 5.00 5.00 5.00 5.00 5.00 Not Measured Thermal expansion ×10.sup.−7/° C. 83 83 83 83 83 83 Not coefficient measured

TABLE-US-00003 TABLE 3 Unit 15 16 17 18 19 20 21 Glass SiO.sub.2 mass % 5.5 6.5 5 5 5 4 10 composition B.sub.2O.sub.3 10.5 8.8 10 10 10 11.5 4.5 TiO.sub.2 14.5 14.5 14.5 12.5 14 14.5 15 Nb.sub.2O.sub.5 8.0 7.5 8 13 7.5 8 8 ZrO.sub.2 6 6 6 5.5 3.5 6 6 La.sub.2O.sub.3 48 48 48 46 45.5 48 48 Gd.sub.2O.sub.3 7.5 8 8 7.5 14 7.5 8 Y.sub.2O.sub.3 0.7 0.5 0.5 0.5 0.5 0.5 Sb.sub.2O.sub.3 SrO CaO Cl Ti.sup.2+/Ti.sup.4+ — <0.02 <0.02 <0.02 <0.02 <0.03 <0.02 Not Measured Nb.sup.2+/Nb.sup.5+ — <0.02 <0.02 <0.02 <0.02 <0.03 <0.02 Not measured B.sup.3+/Si.sup.4+ — 3.3 2.3 3.5 3.5 3.5 5.0 0.8 B.sup.3+ + Si.sup.4+ Cation % 38.6 36.4 36.9 37.1 37.4 38.6 31.6 Refractive index — 1.97 1.99 1.99 2.00 1.99 1.95 1.98 (nd) Abbe number (vd) — 17.2 28.8 28.5 29.8 29.1 29.9 19.2 τ.sub.450 % 89 94 89 91 90 87 77 τ.sub.520 % 95 98 95 96 97 91 86 Liquidus temperature ° C. 1090 1130 1115 1205 1160 1095 1225 Liquidus viscosity dPa .Math. s 10.sup.1.0 10.sup.1.0 10.sup.0.9 10.sup.0.8 10.sup.0.7 10.sup.0.9 10.sup.0.7 Density g/cm.sup.3 4.95 5.00 4.98 5.00 5.12 4.96 Not Measured Thermal expansion ×10.sup.−7/° C. 83 83 85 82 82 82 Not coefficient measured

TABLE-US-00004 TABLE 4 Unit 22 23 24 25 26 27 Glass SiO.sub.2 mass % 5 6.5 8 6.5 6.5 6.5 compo- B.sub.2O.sub.3 10 8.8 7.5 8.8 9 8.8 sition TiO.sub.2 14 14.5 14.5 14.5 14 14.5 Nb.sub.2O.sub.5 8 7.5 8 7.5 8 7.5 ZrO.sub.2 3.5 6 6 6 6 6 La.sub.2O.sub.3 39.5 47.8 48 47.6 47.4 47.7 Gd.sub.2O.sub.3 19.5 8 7.5 8 8 8 Y.sub.2O.sub.3 0.5 0.7 0.5 0.7 1 0.7 Sb.sub.2O.sub.3 0.1 SrO 0.1 0.4 0.1 0.1 CaO 0.1 Cl 0.1 Ti.sup.2+/Ti.sup.4+ — <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nb.sup.2+/Nb.sup.5+ — <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 B.sup.3+/Si.sup.4+ — 3.5 2.3 1.6 2.3 2.4 2.3 B.sup.3+ + Si.sup.4+ Cation % 37.5 36.4 35.6 36.3 36.8 36.2 Refractive — 1.95 1.99 1.96 1.99 1.99 1.99 index (nd) Abbe number — 28.8 28.7 2.87 28.7 28.6 28.6 (vd) τ.sub.450 % 95 92 95 89 96 91 τ.sub.520 % 97 97 98 95 99 97 Liquidus ° C. 1220 1135 1190 1135 1135 1135 temperature Liquidus dPa .Math. s 10.sup.0.7 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.1.0 10.sup.1.0 viscosity Density g/cm.sup.3 5.18 5.00 5.00 5.00 5.00 5.00 Thermal ×10.sup.−7/° C. 83 83 83 83 83 83 expansion coefficient

[0071] First, glass raw materials were blended to give each composition shown in Tables 1 to 4. Here, in Nos. 8 to 10, 12, and 26, strontium nitrate was used as an oxidizing agent. For a fining agent, antimony oxide was used in Nos. 9 and 23, and calcium chloride was used in Nos. 13 and 27.

[0072] The glass was then melted at a temperature from 1200 to 1350° C. using a platinum crucible. The melting time was 2 hours for all. The molten glass was poured onto a carbon plate, annealed, and then a sample suitable for each measurement was produced.

[0073] The resulting sample was cut to analyze the cut surface by XPS, and Ti.sup.2+/Ti.sup.4+ and Nb.sup.2+/Nb.sup.5+ were determined. The results are shown in Tables 1 to 4. Specifically, the resulting XPS spectrum was subjected to a 9-point smoothing process to determine peak heights of Ti.sup.2+ (455.1 eV) and Ti.sup.4+ (459.0 eV), and the ratio, Ti.sup.2+/Ti.sup.4+, was obtained. In addition, peak heights of Nb.sup.2+ (202.1 eV) and Nb.sup.5+ (207.5 eV) were determined, and the ratio, Nb.sup.2+/Nb.sup.5+, was obtained. The XPS analysis was performed using a Quantera SXM available from PHI under the conditions that the excited X-ray was Al Kα.sub.1,2 line (1486.6 eV), the X-ray spot diameter was 200 μm, and the photoelectron escape angle was 45°.

[0074] In addition, the resulting sample was measured for the refractive index (nd), Abbe number (νd), internal transmittances, liquidus temperature, liquidus viscosity, density, and thermal expansion coefficient as follows. The results are shown in Tables 1 to 4.

[0075] The refractive index was presented as a measured value for a d-line (587.6 nm) of a helium lamp.

[0076] The Abbe numbers were calculated from the Abbe number formula, (νd)=[(nd−1)/(nF−nC)], using the above refractive index for a d-line, a refractive index value for an F-line (486.1 nm) of a hydrogen lamp, and a refractive index value for a C-line (656.3 nm) of the hydrogen lamp.

[0077] The internal transmittances were measured as follows. Optically polished samples each having a thickness of 10 mm±0.1 mm or 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 (UV-3100 available from Shimadzu Corporation). From the linear transmittances for thicknesses of 10 mm and 3 mm, an internal transmittance curve for the thickness of 10 mm was determined. From the internal transmittances at wavelengths of 450 nm and 520 nm, the measured values were obtained.

[0078] The liquidus temperature and liquidus viscosity were determined as follows.

[0079] A pulverized glass sample was filled in a refractory container and melted in an electric furnace under conditions of 1250° C. for 0.5 hours, The refractory container was then placed in an indirect heating type temperature gradient furnace and allowed to stand in air atmosphere for 16 hours. The refractory container was then taken out from the temperature gradient furnace and cooled to room temperature. The glass sample after cooling was visually observed to determine the location of crystal precipitation, and the liquidus temperature (crystal precipitation temperature) was determined from the temperature distribution information in the temperature gradient furnace.

[0080] Separately, a bulk glass sample was charged in an alumina crucible and heated to melt. From the resulting glass melt, viscosities of the glass at a plurality of temperatures were determined by the platinum ball pulling-up method. The constant of the Vogel-Fulcher equation was calculated using the measured values of the glass viscosities, and a viscosity curve was created.

[0081] The viscosity liquidus viscosity) corresponding to the liquidus temperature was determined using the liquidus temperature and the viscosity curve determined as described above.

[0082] The density was measured by the Archimedes method using a glass sample about 10 g in weight.

[0083] The thermal expansion coefficient was measured with a dilatometer in a temperature range from 30 to 300° C. using a glass sample molded in about 5φ×20 mm.

[0084] As shown in Tables 1 to 4, samples Nos. 1 to 27 from examples had high refractive index properties with refractive indexes from 1.95 to 2.00, excellent internal transmittances with internal transmittances τ.sub.450 from 77 to 98% and internal transmittances τ.sub.520 from 86 to 99%, low liquidus temperatures from 1090 to 1225° C., and high liquidus viscosities from 10.sup.0.7 to 10.sup.1.0 dPa.Math.s, having excellent productivity.

[0085] Large glass plates having a glass composition of No. 2, 5, or 10 were then produced as follows.

[0086] First, glass raw materials were blended to give each composition of No. 2, 5, or 10. In No. 10, strontium nitrate was used as an oxidizing agent. Each composition was then melted at 1300° C. using a pot-type large furnace, and the molten glass was poured from a platinum nozzle into a 500-mm square carbon mold to give a thickness of 20 mm and molded.

[0087] The resulting ingot was annealed, then the central portion of the ingot was hollowed out in a circular shape, sliced thinly in the surface direction, then both sides were lap-polished and finished to a mirror surface by further polishing. Dimensions of the produced optical glass plates are shown in Table 5.

TABLE-US-00005 TABLE 5 Optical glass Optical glass Optical glass plate 1 plate 2 plate 3 Composition No. 2 No. 5 No. 10 Diameter (mm) 300 320 400 Thickness (mm) 0.3 0.2 0.1

[0088] The optical glass plates 1 to 3 shown in Table 5 had desired dimensions with diameters of 300 to 400 nm and thicknesses from 0.1 to 0.3 mm, and no defects, such as devitrification or a stria, were not observed.

INDUSTRIAL APPLICABILITY

[0089] The optical glass plate according to an embodiment of the present invention is suitable as a light guide plate for use in a wearable image display device selected from: eyeglasses with a projector; an eyeglasses-type or goggle-type display; a virtual reality (VR) or augmented reality (AR) display device; and a virtual image display device.