Glass plate

Abstract

Provided is a glass sheet which, when used as a light guide plate of an eyeglass type device such as a head mounted display, can inhibit generation of stray light.　A glass sheet 1 has: a first main surface 1a and a second main surface 1b that oppose each other; and an end surface 1c that connects the first main surface 1a and the second main surface 1b. The glass sheet 1 is characterized by having a refractive index (nd) of 1.6-2.2, having an R shape in at least a part of the end surface 1c, and having a surface roughness Ra of not more than 100 nm at the end surface 1c.

Description

[Technical field]

[0001] The present invention relates to a glass plate used as a light guide plate or the like in a wearable image display device. [Background technology]

[0002] In recent years, glasses-type devices such as head-mounted displays have been developed. These glasses-type devices may use a light guide plate with transparency. For example, see-through devices that allow users to see images displayed on a light guide plate while looking at the outside scenery are also being developed. In addition, it is possible to realize 3D display by displaying different images on light guide plates corresponding to the user's left and right pupils, or to project images directly onto the user's retina by connecting the images to the retina using the crystalline lens of the pupil.

[0003] As a method of displaying an image using a light guide plate, a diffraction grating formed on the incident surface of the light guide plate allows collimated light or laser light emitted from an image display element to enter the light guide plate, and the incident light is guided while being totally reflected inside the light guide plate, and the light is taken out by a diffraction grating formed on the exit surface and made to enter the pupil of a user. The diffraction grating formed on the surface of the light guide plate requires nano-order precision, and nanoimprinting is often used for its formation. Acrylic resin, which is mainly used as a light guide plate material, has a large minimum incident angle that causes total reflection, so it is difficult for light to propagate inside the light guide plate while repeating total reflection. In addition, resin has poor rigidity, so it is difficult to apply high-definition nanoimprinting. Therefore, it has been proposed to use a glass plate with a high refractive index and excellent rigidity as a light guide plate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-32673 A Summary of the Invention [Problem to be solved by the invention]

[0005] Of the light that enters the light guide plate, some that deviates from the correct waveguide path may become stray light. If this stray light mixes with the outgoing light, it may cause distortion in the digital image.

[0006] In view of the above, an object of the present invention is to provide a glass plate capable of suppressing the generation of stray light when used as a light guide plate for a glasses-type device such as a head-mounted display. [Means for solving the problem]

[0007] The glass plate of the present invention has a first main surface and a second main surface facing each other, and an end surface connecting the first main surface and the second main surface, and is characterized in that the refractive index (nd) is 1.6 to 2.2, at least a part of the end surface has an R shape, and the surface roughness Ra of the end surface is 100 nm or less. The glass plate is usually obtained by cutting a glass base material to a predetermined shape and thickness. In this case, as described later, light that has entered the inside of the glass plate and reached the end surface of the glass plate is likely to be totally reflected at the end surface of the glass plate and become stray light. On the other hand, when at least a part of the end surface of the glass plate has an R shape, the light that has reached the end surface of the glass plate is likely to be emitted to the outside from the end surface. In addition, since the surface roughness Ra of the end surface is small at 100 nm or less, the light that has reached the end surface of the glass plate is suppressed from scattering at the end surface, and as a result, the light is likely to be efficiently emitted to the outside from the end surface.

[0008] It is preferable that the entire end face of the glass plate of the present invention has an R-shape. In this way, of the light that has been guided inside the glass plate and has reached the end face of the glass plate, it is more likely to be emitted to the outside from the end face.

[0009] In the glass plate of the present invention, the difference between the maximum and minimum distances between the first and second main surfaces is preferably 5 μm or less. In this way, light of each wavelength that enters the inside of the glass plate is accurately guided by repeating total reflection at the first and second main surfaces, and the obtained image tends to be clear.

[0010] The glass plate of the present invention preferably has a surface roughness Ra of 10 nm or less on the first and second main surfaces, which makes it easier to obtain bright and clear images since light incident on the glass plate is less likely to suffer from scattering loss when it is guided through repeated total reflections at the first and second main surfaces.

[0011] The glass plate of the present invention preferably has a thickness of 0.5 mm or less. When the thickness of the glass plate is small, the weight of the glass plate is small, and therefore the weight of a wearable image display device using the glass plate as a light guide plate is small, thereby reducing discomfort when wearing the device.

[0012] The glass plate of the present invention preferably contains SiO2, B2O3, La2O3 and Nb2O5 as a glass composition.

[0013] The glass plate of the present invention preferably has a concave-convex structure formed on at least one of the first and second main surfaces, whereby the concave-convex structure functions as a diffraction grating, making it possible to allow light emitted from an image display element to enter the glass plate or to extract light that has been guided inside the glass to the outside.

[0014] The light guide plate of the present invention is characterized by comprising any one of the glass plates described above.

[0015] The light guide plate of the present invention is preferably used in a wearable image display device selected from glasses with a projector, a glasses-type or goggle-type display, a virtual reality (VR) or augmented reality (AR) display device, and a virtual image display device.

[0016] A wearable image display device according to the present invention is characterized by comprising any one of the light guide plates described above. Effect of the Invention

[0017] According to the present invention, it is possible to provide a glass plate capable of suppressing the generation of stray light when used as a light guide plate for a glasses-type device such as a head-mounted display. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic side view showing a portion of a glass plate according to one embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic side view showing a portion of a glass plate according to another embodiment of the present invention. [Diagram 3] FIG. 4 is a schematic side view showing a part of a glass plate according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, embodiments of the glass plate of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0020] 1 is a schematic side view showing a part of a glass plate according to one embodiment of the present invention. The glass plate 1 has a first main surface 1a and a second main surface 1b facing each other, and an end surface 1c connecting the first main surface 1a and the second main surface 1b. The planar shape of the glass plate is not particularly limited, and examples thereof include a polygon such as a rectangle, a circle, an ellipse, and the like.

[0021] At least a part of the end face 1c of the glass plate 1 has an R shape. This makes it easier for light that enters the inside of the glass plate 1 and reaches the end face of the glass plate 1 to be emitted to the outside from the end face 1c. This point will be described in detail below with reference to Figs. 1 and 3.

[0022] As shown in FIG. 1, incident light L0 enters the glass plate 1 from the first main surface 1a of the glass plate 1a. A concave-convex structure 2 functioning as a diffraction grating is formed in the region of the first main surface 1a where the incident light L0 enters. The concave-convex structure 2 changes the direction of the incident light L0 in the width direction of the glass plate 1a, and guides the light L1 between the first main surface 1a and the second main surface 1b of the glass plate 1 while repeating total reflection between them. Here, a part of the incident light L0 is emitted as light L2 toward the end surface 1c in a direction different from the light L1. However, since the end surface 1c has an R-shape, the incident angle θ1 of the light L2 with respect to the end surface 1c becomes small, and the light L2 is emitted to the outside without being reflected by the end surface 1c. In addition to the concave-convex structure 2, the diffraction grating may be, for example, a ruled line type diffraction grating or a holographic diffraction grating.

[0023] On the other hand, Fig. 3 is a schematic side view showing a part of a glass plate according to a comparative example. The glass plate 11 has a first main surface 11a and a second main surface 11b facing each other, and an end surface 11c connecting the first main surface 11a and the second main surface 11b. In the glass plate 11, the end surface 11c does not have a rounded shape but has a flat shape, which is different from the glass plate 1. In the glass plate 11, since the end surface 11c does not have a rounded shape but has a flat shape, as shown in Fig. 3, the incident angle θ2 of the light L2 with respect to the end surface 11c becomes large, and the light L2 is reflected by the end surface 11c. After that, L2 continues to be reflected inside the glass plate 11, becoming stray light.

[0024] As described above, the glass plate 1 according to one embodiment of the present invention is less susceptible to stray light generation inside, and when used as a light guide plate for a head-mounted display or the like, it is possible to suppress distortion of the digital image.

[0025] In addition, the entire end face 1c of the glass plate 1 shown in Fig. 1 has a rounded shape, and light that reaches the end face 1c can be efficiently emitted to the outside. However, the glass plate 1 is not limited to this, and only a part of the end face 1c may be rounded as shown in Fig. 2. In this way, light can be emitted to the outside from at least the part of the end face 1c that is rounded.

[0026] The surface roughness Ra of the end face 1c (at least the R-shaped portion) of the glass plate 1 is 100 nm or less, and is preferably less than 70 nm, 50 nm or less, 40 nm or less, 20 nm or less, and particularly 10 nm or less. If the surface roughness Ra of the end face 1c is too large, the light that reaches the end face 1c is scattered at the end face 1c, and as a result, it becomes difficult to emit the light to the outside from the end face 1c. The lower limit of the surface roughness Ra of the end face 1c is not particularly limited, but is practically 1 nm or more. In the present invention, the surface roughness Ra refers to a value measured according to JIS B 0601 (1994).

[0027] The refractive index (nd) of the glass plate 1 is 1.6 to 2.2, preferably 1.8 to 2.1, 1.9 to 2.05, 1.95 to 2.03, and particularly preferably 1.98 to 2.01. If the refractive index of the glass plate 1 is high, the critical angle (critical angle of total reflection) when the light inside the glass plate 1 is emitted to the outside becomes small, and light is less likely to be emitted from the end face 1c, so that stray light tends to be easily generated. Therefore, the effect of the present invention is easily obtained when the refractive index of the glass plate 1 is particularly high. If the refractive index is too low, the viewing angle tends to be narrow when used as a light guide plate for wearable image display devices such as glasses with projectors, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) displays, and virtual image displays. On the other hand, if the refractive index is too high, defects such as devitrification and striae tend to occur.

[0028] The Abbe number (νd) of the glass plate 1 is not particularly limited, but in consideration of the stability of vitrification, the lower limit is preferably 20 or more, 22 or more, and particularly preferably 25 or more, and the upper limit is preferably 35 or less, 32 or less, and particularly preferably 30 or less.

[0029] The difference between the maximum and minimum distances between the first and second main surfaces 1a and 1b of the glass plate 1 (TTV=Total Thickness Variation) is preferably 5 μm or less, 3 μm or less, and particularly preferably 1 μm or less. If the TTV is too large, it becomes difficult for the light of each wavelength incident on the inside of the glass plate 1 to be accurately guided inside the glass plate 1, and the clarity of the obtained image is likely to decrease.

[0030] The surface roughness Ra of the first main surface 1a and the second main surface 1b of the glass plate 1 is preferably 10 nm or less, 5 nm or less, 3 nm or less, particularly 2 nm or less. If the surface roughness Ra of the first main surface 1a and the second main surface 1b of the glass plate 1 is too large, scattering loss is likely to occur when light incident on the inside of the glass plate 1 is guided by repeating total reflection, making it difficult to obtain a bright and clear image. The lower limit of the surface roughness Ra of the first main surface 1a and the second main surface 1b of the glass plate 1 is not particularly limited, but is practically 1 nm or more.

[0031] The internal transmittance of glass plate 1 at 450 nm with a thickness of 10 mm is preferably 90% or more, particularly 92% or more. In this way, in a wearable image display device using glass plate 1, the brightness of the image seen by the user is likely to be increased.

[0032] Glass plate 1 has a liquidus viscosity of 10 0.5 dPa s or more, 10 0.6 dPa s or more, 10 0.7 dPa s or more, especially 10 0.8 It is preferable that the liquidus viscosity is at least 10 dPa·s. If the liquidus viscosity is too low, molding is required at a low viscosity, and defects such as striae are likely to occur in the glass, especially when the molding size is large. There is no particular upper limit for the liquidus viscosity, but in reality it is generally no more than 10 2.5 dPa·s or less, 10 1.5 dPa s or less, especially 10 1.2 It is less than dPa·s.

[0033] The thickness of the glass plate 1 is preferably 0.5 mm or less, 0.4 mm or less, and particularly preferably 0.3 mm or less. If the thickness of the glass plate 1 is too large, the weight of the wearable image display device using the glass plate 1 increases, increasing discomfort when wearing the device. If the thickness of the glass plate 1 is too small, the mechanical strength is likely to decrease, so the lower limit is preferably 0.01 mm or more, 0.02 mm or more, 0.03 mm or more, 0.04 mm or more, and particularly preferably 0.05 mm or more.

[0034] The major axis of the planar shape of the glass plate 1 (diameter in the case of a circle) 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 particularly preferably 200 mm or more. If the major axis of the glass plate 1 is too small, it becomes difficult to use it for applications such as a wearable image display device. In addition, mass productivity tends to be poor. The upper limit of the major axis of the glass plate 1 is not particularly limited, but in reality it is 1000 mm or less.

[0035] The glass plate 1 may contain, as a glass composition, SiO2, B2O3, La2O3, and Nb2O5. SiO2 and B2O3 are components that improve the stability of vitrification and chemical durability. La2O3 and Nb2O5 are components that significantly increase the refractive index. La2O3 also has the effect of improving the vitrification stability. By containing these components, it becomes easier to obtain glass that has a high refractive index and is excellent in mass productivity. Specific compositions include those that contain, in mass %, 1 to 20% SiO2, 1 to 25% B2O3, 10 to 60% La2O3, and 1 to 30% Nb2O5.

[0036] In addition to the above components, it is preferable to contain 1 to 30% TiO2 and 0 to 20% Gd2O3, which are components that increase the refractive index. In addition, Y2O3, ZrO2, etc. may be contained. On the other hand, it is preferable that As components (As2O3, etc.), Pb components (PbO, etc.), and fluorine components (F2, etc.) are not substantially contained because they have a large environmental load. In addition, Bi2O3 and TeO2 are coloring components, and are likely to reduce the transmittance in the visible range, so it is preferable that they are not substantially contained. Here, ``substantially not contained'' means that they are not intentionally contained as raw materials, and does not exclude the inclusion of unavoidable impurities. Objectively, it means that the content of each of the above components is less than 0.1%.

[0037] The uneven structure 2 can be formed by, for example, a photolithography method, a sputtering method using a mask, a method of locally etching a uniform film using a laser after the film is formed, or an imprint method using a mold.

[0038] The glass plate 1 is suitable as a light guide plate that is a component of a wearable image display device selected from glasses with a projector, a glasses-type or goggle-type display, a virtual reality (VR) or augmented reality (AR) display device, and a virtual image display device. The light guide plate is used in the so-called glasses lens portion of the wearable image display device, and plays a role in guiding light emitted from an image display element included in the wearable image display device and emitting it toward the eyes of the user.

[0039] It is preferable to use a laminate of multiple glass plates 1. In this way, when the glass plate 1 is used as a light guide plate for a wearable image display device, it becomes possible to project images in a layered manner in the depth direction of the display screen, thereby obtaining 3D images. It is preferable that the number of layers is 3 or more, and particularly 6 or more. EXAMPLES

[0040] The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

[0041] Table 1 shows the compositions and properties of the glass plates produced in the examples.

[0042] [Table 1]

[0043] The raw materials were mixed to obtain the glass compositions shown in Table 1, and melted in a platinum pot at 1250-1350°C for 2-12 hours. The resulting molten glass was poured into a carbon frame and molded. After that, the glass was held at 720-780°C for 2-48 hours, and then cooled to room temperature at a rate of 1°C / min to obtain a glass base material.

[0044] The refractive index (nd), internal transmittance, and liquidus viscosity of the obtained glass base material were measured. The results are shown in Table 1.

[0045] The refractive index was measured using a Shimadzu KPR-2000 for the d-line (587.6 nm) of a helium lamp.

[0046] The internal transmittance was measured as follows. For optically polished glass samples with thicknesses of 10 mm±0.1 mm and 5 mm±0.1 mm, the light transmittance (linear transmittance) including surface reflection loss was measured at 0.5 nm intervals using a spectrophotometer (UV-3100, manufactured by Shimadzu Corporation). Based on the measured values, the internal transmittance τ at a thickness of 10 mm was calculated using the following formula: 10 The table also shows the internal transmittance at a wavelength of 450 nm.

[0047] log τ 10 =-{(logT5-logT 10 ) / Δd}×10(%) T5: Light transmittance of a glass sample with a thickness of 5 mm ± 0.1 mm T 10 : Light transmittance of a glass sample with a thickness of 10 mm ± 0.1 mm Δd: Thickness difference between the two glass samples

[0048] The liquidus viscosity was measured as follows. After the glass base material was remelted in an electric furnace under the condition of 1200°C-0.5 hours, it was held in an electric furnace with a temperature gradient for 18 hours, then removed from the electric furnace and allowed to cool in air, and the liquidus temperature was measured by determining the precipitation position of devitrified matter with an optical microscope. Separately, the glass base material was placed in an alumina crucible and heated to melt. The viscosity of the glass at a plurality of temperatures was determined for the obtained molten glass by the platinum ball pulling method. Next, the constants of the Vogel-Fulcher formula were calculated using the measured values ​​of the glass viscosity to create a viscosity curve. The viscosity (liquidus viscosity) corresponding to the liquidus temperature was determined using the obtained viscosity curve and the liquidus temperature obtained above.

[0049] The above glass base material was cut into a plate shape of φ300 mm and thickness 0.5 mm, and then both main surfaces were sandwiched between a pair of polishing pads with different outer diameters, and both main surfaces of the plate glass base material were polished while rotating both the plate glass base material and the pair of polishing pads. Furthermore, the end surface of the plate glass base material was polished with a grinder using polishing powder to form an R shape. Specifically, as shown in FIG. 1, the entire end surface was polished to form an R shape. In this way, a glass plate having a thickness of 0.2 to 0.5 mm was obtained.

[0050] The difference TTV between the maximum and minimum distances between the two main surfaces of the glass plate obtained as described above was measured using SBW-331ML / d manufactured by Kobelco Research Institute. The surface roughness Ra of the main surface and the end surface of the glass plate was also measured using an atomic force microscope (AFM). The results are shown in Table 1.

[0051] Next, a periodic uneven structure made of SiO2 was formed on one main surface of the glass plate by photolithography, and the gaps in the uneven structure were filled with resin. Six of the obtained glass plates were stacked to obtain a laminate.

[0052] When the laminate obtained in this way is used as a light guide plate for a head mounted display or the like, the R-shaped edges of the light guide plate allow stray light to easily escape to the outside from said edges, resulting in the production of 3D images with reduced distortion of the digital image caused by stray light. [Industrial Applicability]

[0053] The glass plate of the present invention is suitable as a light guide plate for use 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. [Explanation of symbols]

[0054] 1, 11 Glass plate 1a, 11a First main surface 1b, 11b Second main surface 1c, 11c end face 2 Uneven structure

Claims

1. A glass plate having a first main surface and a second main surface facing each other, and an end surface connecting the first main surface and the second main surface, The glass plate is used for a light guide plate of a wearable image display device selected from glasses with a projector, a glasses-type or goggle-type display, a virtual reality (VR) or augmented reality (AR) display device, and a virtual image display device, and has a refractive index (nd) of 1.6 to 2.2, at least a part of the end face has an R-shape, the end face has a surface roughness Ra of 100 nm or less, and at least one of the first principal surface and the second principal surface has an uneven structure functioning as a diffraction grating, The uneven structure is formed in a region where incident light is incident, A glass plate, characterized in that, of the incident light entering the inside of the glass plate, the incident light emitted in the direction of the end face is emitted to the outside from the end face.

2. 2. The glass plate according to claim 1, wherein the entire end surface is rounded.

3. 3. The glass plate according to claim 1, wherein a difference between a maximum value and a minimum value of a distance between the first main surface and the second main surface is 5 μm or less.

4. 4. The glass plate according to claim 1, wherein the first main surface and the second main surface have a surface roughness Ra of 10 nm or less.

5. 5. The glass plate according to claim 1, having a thickness of 0.5 mm or less.

6. The glass composition is SiO ２ , B ２ O ３ , La ２ O ３ and Nb ２ O ５ The glass plate according to any one of claims 1 to 5, further comprising:

7. A glass plate according to any one of claims 1 to 6, characterized in that it is used as a laminate consisting of multiple sheets stacked together.

8. A light guide plate comprising the glass plate according to any one of claims 1 to 7.

9. A wearable image display device comprising the light guide plate according to claim 8.

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