glass sheet

Abstract

Provided is a glass sheet that can suppress the generation of stray light when used as a light guide plate for eyeglass-type devices such as head-mounted displays. A glass sheet (1) has opposing first and second main faces (1a, 1b) and an end face (1c) connecting the first and second main faces (1a, 1b), the glass sheet (1) having a refractive index (nd) of 1.6 to 2.2, at least a portion of the end face (1c) having a rounded shape, and a surface roughness Ra of the end face (1c) of 100 nm or less.

Description

Technical Field

[0001] This invention relates to a glass plate used as a light guide plate or the like in wearable image display devices. Background Technology

[0002] In recent years, eyeglass-type devices such as head-mounted displays have been developed. These eyeglass-type devices sometimes use translucent light guides. For example, see-through devices that allow users to view both the external scenery and the image displayed on the light guide are also under development. Furthermore, 3D displays can be achieved by displaying different images on light guides corresponding to the user's left and right eyes, or by utilizing the lens of the eye and the retina to project images directly onto the user's retina.

[0003] One method for displaying images using a light guide plate involves using a diffraction grating formed on the incident-side surface of the light guide plate to guide collimated light or laser light emitted from an image display element into the light guide plate. This light undergoes total internal reflection and waveguided within the light guide plate, and the diffraction grating formed on the exit-side surface extracts the light outwards, directing it towards the user's eye. The diffraction grating formed on the surface of the light guide plate requires nanometer-level precision, and nanoimprinting is frequently used in its formation. Acrylic resin, primarily used as a light guide plate material, has a large minimum incident angle for total internal reflection, making it difficult for light to propagate through repeated total internal reflection within the light guide plate. Furthermore, the resin's poor rigidity makes high-precision nanoimprinting difficult to implement. Therefore, the use of a glass plate with a high refractive index and excellent rigidity as a light guide plate has been proposed (see, for example, Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-32673 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Sometimes, a portion of the light incident inside the light guide plate that deviates from the proper waveguide path becomes stray light. If this stray light mixes with the outgoing light, it can sometimes cause distortion in the digital image.

[0009] In view of the above, the object of the present invention is to provide a glass plate that can suppress the generation of stray light when used as a light guide plate in eyeglass-type devices such as head-mounted displays.

[0010] Solution for solving the problem

[0011] The glass plate of the present invention has opposing first and second main surfaces and an end face connecting the first and second main surfaces. The glass plate is characterized by a refractive index (nd) of 1.6 to 2.2, a rounded corner shape at least a portion of the end face, and a surface roughness Ra of 100 nm or less. The glass plate is typically obtained by cutting a glass substrate into a predetermined shape and thickness. In this case, as described later, light incident inside the glass plate that reaches the end face is easily totally internally reflected at the end face and becomes stray light. On the other hand, when at least a portion of the end face of the glass plate has a rounded corner shape, light reaching the end face is easily emitted outward from that end face. Furthermore, the surface roughness Ra of the end face is as small as 100 nm or less, thus suppressing the scattering of light reaching the end face at that end face, resulting in efficient emission outward from that end face.

[0012] Preferably, in the glass plate of the present invention, the end face is entirely rounded. In this way, the light that has been guided inside the glass plate and reaches the end face of the glass plate can be more easily emitted from the end face to the outside.

[0013] Preferably, in the glass plate of the present invention, the difference between the maximum and minimum distances between the first principal surface and the second principal surface is less than 5 μm. In this way, light of various wavelengths incident on the interior of the glass plate undergoes repeated total internal reflection and accurate waveguided behavior on the first and second principal surfaces, thus easily resulting in a sharp image.

[0014] Preferably, in the glass plate of the present invention, the surface roughness Ra of the first principal surface and the second principal surface is less than 10 nm. In this way, when light incident on the interior of the glass plate undergoes repeated total internal reflection and waveguided ...

[0015] Preferably, the thickness of the glass plate in this invention is 0.5 mm or less. With such a small thickness, the weight of the glass plate is reduced, thus reducing the weight of the wearable image display device that uses this glass plate as a light guide plate, and reducing discomfort when wearing the device.

[0016] Preferably, the glass plate of the present invention contains SiO2, B2O3, La2O3 and Nb2O5 as glass components.

[0017] Preferably, in the glass plate of the present invention, at least one of the first main surface and the second main surface has an uneven structure. In this way, the uneven structure acts as a diffraction grating, enabling light emitted from the image display element to enter the interior of the glass plate or to extract light that has been guided inside the glass plate to the outside.

[0018] The light guide plate of the present invention is characterized in that it is composed of any of the glass plates described above.

[0019] Preferably, the light guide plate of the present invention is used in wearable image display devices selected from eyeglasses with projectors, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

[0020] The wearable image display device of the present invention includes any one of the above-mentioned light guide plates.

[0021] Invention Effects

[0022] According to the present invention, a glass plate capable of suppressing the generation of stray light can be provided when used as a light guide plate in eyeglass-type devices such as head-mounted displays. Attached Figure Description

[0023] Figure 1 This is a schematic side view illustrating a portion of a glass plate according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic side view of a portion of a glass plate illustrating another embodiment of the invention.

[0025] Figure 3 This is a schematic side view showing a portion of the glass plate of the comparative example. Detailed Implementation

[0026] Hereinafter, embodiments of the glass plate of the present invention will be described using the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0027] Figure 1 This is a schematic side view illustrating a portion of a glass plate according to an embodiment of the present invention. The glass plate 1 has a first main surface 1a and a second main surface 1b opposite to 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; for example, polygons such as rectangles, circles, ellipses, etc., can be included.

[0028] The end face 1c of the glass plate 1 has a rounded corner shape in at least a portion. Therefore, light incident inside the glass plate 1 that reaches the end face of the glass plate 1 can easily exit from the end face 1c to the outside. Regarding this, using... Figure 1 as well as Figure 3 The following is a detailed explanation.

[0029] like Figure 1As shown, incident light L0 enters the interior of glass plate 1a from the first principal surface 1a. A concave-convex structure 2, functioning as a diffraction grating, is formed in the region of the first principal surface 1a where the incident light L0 enters. The incident light L0 changes direction along the width direction of glass plate 1a by passing through the concave-convex structure 2, and is guided as light L1 between the first principal surface 1a and the second principal surface 1b of glass plate 1 through repeated total internal reflection. Here, a portion of the incident light L0 exits as light L2 towards the end face 1c in a direction different from light L1. However, the end face 1c has a rounded corner shape, so the incident angle θ1 of light L2 relative to the end face 1c becomes smaller, and light L2 is not reflected at the end face 1c but exits outwards. It should be noted that, in addition to the concave-convex structure 2, the component functioning as a diffraction grating can also be, for example, a scribed diffraction grating, a holographic diffraction grating, etc.

[0030] on the other hand, Figure 3 This is a schematic side view showing a portion of a glass plate of a comparative example. Glass plate 11 has opposing first main surfaces 11a and second main surfaces 11b, and an end surface 11c connecting the first main surfaces 11a and the second main surfaces 11b. In glass plate 11, the end surface 11c does not have a rounded corner shape but is flat, unlike glass plate 1. In glass plate 11, the end surface 11c does not have a rounded corner shape but is flat, therefore... Figure 3 As shown, the incident angle θ2 of light L2 relative to end face 11c increases, and light L2 is reflected at end face 11c. Subsequently, L2 is repeatedly reflected inside the glass plate 11 and becomes stray light.

[0031] As described above, in the glass plate 1 of one embodiment of the present invention, when stray light is not easily generated inside and it is used as a light guide plate for head-mounted displays or the like, the disorder of digital images can be suppressed.

[0032] It should be noted that, Figure 1 The end face 1c of the glass plate 1 shown is rounded, which allows light reaching the end face 1c to be efficiently emitted outwards. It should be noted that the glass plate 1 is not limited to this shape and can also be as shown... Figure 2 As shown, only a portion of the end face 1c is rounded. In this way, at least the rounded portion of the end face 1c allows light to be emitted outward.

[0033] The surface roughness Ra of the end face 1c (at least the rounded corner portion) of the glass plate 1 is 100 nm or less, preferably less than 70 nm, preferably less than 50 nm, preferably less than 40 nm, preferably less than 20 nm, and particularly preferably less than 10 nm. If the surface roughness Ra of the end face 1c is too large, the light reaching the end face 1c will be scattered at the end face 1c, resulting in difficulty in escaping from the end face 1c to the outside. There is no particular limitation on the lower limit of the surface roughness Ra of the end face 1c, but in practice it is 1 nm or more. It should be noted that in this invention, the surface roughness Ra refers to the value measured according to JIS B 0601 (1994).

[0034] The refractive index (nd) of glass plate 1 is 1.6 to 2.2, preferably 1.8 to 2.1, more preferably 1.9 to 2.05, more preferably 1.95 to 2.03, and particularly preferably 1.98 to 2.01. If the refractive index of glass plate 1 is high, the critical angle (critical angle for total internal reflection) for light to exit from inside glass plate 1 becomes smaller, making it difficult for light to exit from end face 1c, thus tending to generate stray light. Therefore, the effects of the present invention are particularly easily achieved when the refractive index of glass plate 1 is high. If the refractive index is too low, when used as a light guide plate for wearable image display devices such as projector glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices, there is a tendency for the field of view to narrow. On the other hand, if the refractive index is too high, defects such as devitrification and ripples are easily generated.

[0035] The Abbe number (vd) of glass plate 1 is not particularly limited, but considering the stability of vitrification, the lower limit is 20 or more, preferably 22 or more, and especially preferably 25 or more, and the upper limit is 35 or less, preferably 32 or less, and especially preferably 30 or less.

[0036] The difference between the maximum and minimum distances (TTV = Total Thickness Variation) between the first principal surface 1a and the second principal surface 1b of the glass plate 1 is 5 μm or less, preferably 3 μm or less, and particularly preferably 1 μm or less. If the TTV is too large, it will be difficult for light of various wavelengths incident on the interior of the glass plate 1 to be accurately guided inside the glass plate 1, and the sharpness of the obtained image will easily be reduced.

[0037] The surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1 is less than 10 nm, preferably less than 5 nm, more preferably less than 3 nm, and particularly preferably less than 2 nm. If the surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1 is too large, the light incident inside the glass plate 1 will easily suffer scattering loss when repeatedly subjected to total internal reflection and waveguided, making it difficult to obtain a bright and clear image. The lower limit of the surface roughness Ra of the first principal surface 1a and the second principal surface 1b of the glass plate 1 is not particularly limited, but in practice it is above 1 nm.

[0038] The internal transmittance of the 10mm thick glass plate 1 at 450nm is 90% or more, particularly preferably 92% or more. As a result, in wearable image display devices using the glass plate 1, the brightness of the image seen by the user is easily improved.

[0039] Glass plate 1 has a liquid phase viscosity of 10. 0.5 dPa·s or higher, preferably 10 0.6 dPa·s or higher, preferably 10 0.7 dPa·s or higher, especially preferably 10 0.8 Above dPa·s. If the liquid phase viscosity is too low, low viscosity forming is required, which can easily lead to defects such as ripples in the glass, especially when the forming size becomes larger. There is no specific upper limit to the liquid phase viscosity, but in practice it is around 10 dPa·s. 2.5 Below dPa·s, it is 10 1.5 Below dPa·s, especially for 10 1.2 Below dPa·s.

[0040] The thickness of the glass plate 1 is 0.5 mm or less, preferably 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 will increase, and the discomfort when wearing the device will increase. It should be noted that if the thickness of the glass plate 1 is too small, the mechanical strength will easily decrease. Therefore, the lower limit is 0.01 mm or more, preferably 0.02 mm or more, preferably 0.03 mm or more, preferably 0.04 mm or more, and particularly preferably 0.05 mm or more.

[0041] The major axis (diameter in the case of a circle) of the planar shape of glass plate 1 is 50 mm or more, preferably 80 mm or more, preferably 100 mm or more, preferably 120 mm or more, preferably 150 mm or more, preferably 160 mm or more, preferably 170 mm or more, preferably 180 mm or more, preferably 190 mm or more, and particularly preferably 200 mm or more. If the major axis of glass plate 1 is too small, it is difficult to use it for applications such as wearable image display devices. In addition, there is a tendency for poor mass production. There is no particular upper limit to the major axis of glass plate 1, but in reality it is 1000 mm or less.

[0042] Glass plate 1, as a glass composition, can include glass compositions containing SiO2, B2O3, La2O3, and Nb2O5. SiO2 and B2O3 are components that improve vitrification stability and chemical durability. La2O3 and Nb2O5 are components that significantly increase the refractive index. La2O3 also improves vitrification stability. By including these components, glass with a high refractive index and excellent mass production properties can be easily obtained. Specific compositions can include those containing 1–20% SiO2, 1–25% B2O3, 10–60% La2O3, and 1–30% Nb2O5 by mass%.

[0043] It should be noted that, in addition to the above-mentioned components, it is also preferable to contain 1-30% TiO2 and 0-20% Gd2O3 by mass, which are components that improve the refractive index. Y2O3, ZrO2, etc., may also be included. On the other hand, As components (As2O3, etc.), Pb components (PbO, etc.), and fluorine components (F2, etc.) have a significant environmental burden, and therefore are preferably substantially absent. Furthermore, Bi2O3 and TeO2 are coloring components that easily reduce the transmittance in the visible region, and are therefore preferably substantially absent. Here, "substantially absent" means not intentionally included as a raw material, but does not exclude the unavoidable contamination of impurities. Objectively speaking, it means that the content of each of the above components is less than 0.1%.

[0044] The uneven structure 2 can be formed by, for example, photolithography, sputtering using a mask, local etching using a laser after forming a uniform film, or imprinting using a mold.

[0045] The glass plate 1 is preferably a light guide plate, which is a component of a wearable image display device selected from eyeglasses with a projector, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices. This light guide plate is used in the so-called eyeglass lens portion of the wearable image display device and serves to guide the light emitted from the image display elements of the wearable image display device toward the user's eyes.

[0046] The glass plate 1 is preferably used as a laminated body by stacking multiple sheets. In this way, when the glass plate 1 is used as a light guide plate for a wearable image display device, images can be superimposed and projected in the depth direction of the displayed image, thus obtaining a 3D image. The number of laminated sheets is 3 or more, and more preferably 6 or more.

[0047] Example

[0048] The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

[0049] Table 1 shows the composition and properties of the glass plates manufactured in the embodiments.

[0050] [Table 1]

[0051]

[0052] The raw materials were blended to form the glass compositions shown in Table 1, and melted in a platinum kettle at 1250–1350°C for 2–12 hours. The resulting molten glass was then poured into a carbon frame and shaped. Afterward, it 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 the glass matrix.

[0053] The refractive index (nd), internal transmittance, and liquid phase viscosity of the obtained glass matrix were measured. The results are shown in Table 1.

[0054] The refractive index is expressed as the d-line (587.6 nm) of a helium lamp measured using a Shimadzu KPR-2000.

[0055] 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 transmittance (linear transmittance), including surface reflection loss, was measured at 0.5 nm intervals using a spectrophotometer (Shimadzu Corporation UV-3100). Based on the measured values, the internal transmittance τ for a thickness of 10 mm was calculated using the following mathematical formula. 10 It should be noted that the table shows the internal transmittance values ​​under the condition of a wavelength of 450 nm.

[0056] logτ 10 =-{(logT5-logT)} 10 ) / Δd}×10(%)

[0057] T5: Light transmittance of a glass sample with a thickness of 5 mm ± 0.1 mm.

[0058] T 10 Light transmittance of a glass sample with a thickness of 10 mm ± 0.1 mm

[0059] Δd: The thickness difference between the two glass samples

[0060] The liquid phase viscosity was measured as follows. After remelting the glass matrix in an electric furnace at 1200°C for 0.5 hours, it was held in an electric furnace with a temperature gradient for 18 hours. The melt was then removed from the furnace and cooled in air. The precipitation sites of devitrifications were determined using an optical microscope, and the liquid phase temperature was measured. The glass matrix was then placed in an alumina crucible and heated to melt. The viscosity of the resulting molten glass was determined at multiple temperature conditions using the platinum ball pulling method. Next, using the measured glass viscosity, the constant of the Vogel-Fulcher equation was calculated to create a viscosity curve. Using the obtained viscosity curve and the liquid phase temperature determined above, the viscosity at the liquid phase temperature (liquid phase viscosity) was calculated.

[0061] After cutting and processing the above-mentioned glass matrix into After forming a 0.5mm thick plate, a pair of grinding pads with different outer diameters clamp the two main surfaces of the plate-shaped glass substrate. The plate-shaped glass substrate is then rotated together with the grinding pads, and the two main surfaces are ground. Furthermore, the end faces of the plate-shaped glass substrate are ground into rounded corners using a grinding machine and grinding powder. Specifically, as... Figure 1 The end face is ground and rounded as shown. In this way, a glass plate with a thickness of 0.2 to 0.5 mm is obtained.

[0062] The difference between the maximum and minimum distances (TTV) between the two principal faces of the glass plate obtained as described above was measured using an SBW-331ML / d microscope manufactured by Kobe Steel Research Institute. Furthermore, the surface roughness Ra of the principal and end faces of the glass plate was measured using an atomic force microscope (AFM). The results are shown in Table 1.

[0063] Next, a periodic uneven structure composed of SiO2 is formed on one side of the glass plate using photolithography, and the gaps between the uneven structure are filled with resin. Six glass plates are stacked to obtain a laminate.

[0064] When such a laminate is used as a light guide plate for head-mounted displays, stray light easily escapes from the rounded ends of the light guide plate. As a result, 3D images that suppress digital image distortion caused by stray light can be obtained.

[0065] Industrial applicability

[0066] The glass plate of the present invention is preferably used as a light guide plate in a wearable image display device selected from eyeglasses with projectors, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

[0067] Explanation of reference numerals in the attached figures

[0068] 1.11 Glass Plate

[0069] 1a, 11a First Main Face

[0070] 1b, 11b Second Main Face

[0071] 1c and 11c end faces

[0072] 2. Concave-convex structure.

Claims

1. A glass plate having an opposing first main surface and a second main surface, and an end surface connecting the first main surface and the second main surface. The glass plate is characterized in that... The refractive index (nd) is 1.6 to 2.2, at least a portion of the end face has a rounded corner shape, the surface roughness (Ra) of the end face is less than 100 nm, and at least one of the first main surface and the second main surface has an uneven structure that functions as a diffraction grating. The uneven structure is formed in the region where incident light is incident. The incident light incident into the interior of the glass plate includes a first light that undergoes repeated total internal reflection and waveguided wave between the first main surface and the second main surface, and a second light that exits in a direction different from the waveguided direction of the first light at the end face. The second light emitted toward the end face can easily be emitted outward from the end face.

2. The glass plate according to claim 1, characterized in that, The end face is rounded.

3. The glass plate according to claim 1 or 2, characterized in that, The difference between the maximum and minimum distances between the first main surface and the second main surface is less than 5 μm.

4. The glass plate according to claim 1 or 2, characterized in that, The surface roughness (Ra) of the first main surface and the second main surface is less than 10 nm.

5. The glass plate according to claim 1 or 2, characterized in that, The thickness is less than 0.5mm.

6. The glass plate according to claim 1 or 2, characterized in that, It contains SiO2, B2O3, La2O3 and Nb2O5 as a glass component.

7. A light guide plate, characterized in that, The light guide plate is composed of a glass plate as described in any one of claims 1 to 6.

8. The light guide plate according to claim 7, characterized in that, The light guide plate is used in wearable image display devices selected from eyeglasses with projectors, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR) display devices, and virtual image display devices.

9. A wearable image display device, characterized in that, The wearable image display device includes the light guide plate as described in claim 7 or 8.

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