CN107533187B

CN107533187B - Glass plate for light guide plate

Info

Publication number: CN107533187B
Application number: CN201680022098.8A
Authority: CN
Inventors: 奥隼人; 下津浩一; 山田真史; 国友一伸
Original assignee: Nippon Electric Glass Co Ltd
Current assignee: Nippon Electric Glass Co Ltd
Priority date: 2015-07-24
Filing date: 2016-07-04
Publication date: 2020-02-07
Anticipated expiration: 2036-07-04
Also published as: CN107533187A; WO2017018131A1; JP6583623B2; TW201712380A; KR102524354B1; JP2017027850A; KR20180034303A; TWI673525B

Abstract

The invention provides a glass plate for a light guide plate. An edge part (9) of a light guide plate glass plate (1) along the edge on the light incident side where light from a light source (3) is introduced has chamfered surfaces (13, 14) between an end surface (12) and main surfaces (7, 8), the external angle (theta 1) formed by the chamfered surfaces (13, 14) and the main surfaces (7, 8) is 45 DEG or less, the length (L1) of the chamfered surfaces (13, 14) in the direction along the main surfaces (7, 8) is 5 [ mu ] m or more, and the surface roughness (Ra) of the end surface (12) is 0.5 [ mu ] m or less.

Description

Glass plate for light guide plate

Technical Field

The present invention relates to a glass plate used as a substrate of a light guide plate, and more particularly, to a glass plate for a light guide plate, which is treated at an edge portion along a side of a light incident side and/or an edge portion along an opposite side to the side of the light incident side.

Background

As is well known, a liquid crystal display used as a display device of a thin information apparatus includes a backlight. As such a backlight, an edge-light type backlight is mainly used. The edge-light type backlight includes a light guide plate for introducing light from a light source (for example, an LED) from an edge portion along a side on a light incident side to perform surface light emission.

As a substrate of a conventional light guide plate, a resin plate is generally used. Under such a background, a conventional light guide plate is provided with a diffusion plate or the like on a light-emitting surface of a resin plate, and a reflection plate or the like on the opposite surface.

However, when a resin plate is used as a substrate of the light guide plate, various problems such as deformation by heat of the light source, deterioration of dimensional stability, difficulty in thinning, and influence of moisture are caused due to the characteristics of the resin.

For this reason, patent document 1 discloses that a glass plate is used as a substrate of a light guide plate instead of a resin plate. Specifically, this document discloses a light guide plate in which a diffusion plate (diffusion film) is provided on one main surface of a glass plate, and a reflection plate (reflection film) is provided on the other main surface.

In this way, when a glass plate is used as the substrate of the light guide plate, various problems in the case of using the above-described resin plate can be expected to be solved.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-72896

Disclosure of Invention

Problems to be solved by the invention

However, when a glass plate is used as a substrate of a light guide plate, a new problem arises due to the characteristics of the glass plate, that is, a new problem such as a defect or a breakage is likely to occur. In addition, in an attempt to avoid such a problem, consideration has to be given to making the glass plate satisfy optical characteristics required for the light guide plate.

From the above-described viewpoints, an object of the present invention is to provide a glass substrate for a light guide plate, which is less likely to cause defects, damage, and the like, and which easily satisfies optical characteristics required for the light guide plate.

Means for solving the problems

The present invention has been made to solve the above problems, and is characterized in that a chamfered surface is provided between the end surface and the main surface along the edge portion of the edge on the light incident side into which light from the light source is introduced, the chamfered surface forming an external angle θ 1 of 45 ° or less with the main surface, a length L1 of the chamfered surface in the direction along the main surface is 5 μm or more, and a surface roughness Ra of the end surface is 0.5 μm or less.

According to such a configuration, when light is introduced into the glass plate for a light guide plate from the edge portion along the light incident side, a sufficient amount of light can be introduced, and the glass plate is less likely to be lost or damaged. That is, in the case where the chamfered surface is formed along the edge portion of the light incident side edge, the amount of light introduced may be reduced by the chamfered surface, although it can be roughly coped with the absence, breakage, and the like of the glass plate. In contrast, in the present invention, the external angle θ 1 formed by the chamfered surface and the main surface is set to 45 ° or less, thereby sufficiently drawing in light. Even if the chamfer surface is formed at such an angle, if the chamfer width is insufficient, it becomes difficult to reliably suppress the occurrence of a defect, a breakage, or the like. In contrast, in the present invention, by setting the length L1 of the chamfered surface in the direction along the main surface to 5 μm or more, the chamfer width is sufficiently ensured and the occurrence of a defect, a breakage, or the like is reliably suppressed. The end face of the edge portion is a portion capable of significantly increasing the amount of light to be introduced compared to the chamfered face. In contrast, in the present invention, by setting the surface roughness Ra of the end face to 0.5 μm or less, the introduction of light due to the large surface roughness of the end face is less likely to be inhibited. As described above, according to the present invention, it is possible to provide a glass plate for a light guide plate that can easily satisfy optical characteristics required for a light guide plate while eliminating the problem that defects, damages, and the like are likely to occur, which is a problem that occurs due to the characteristics inherent to a glass plate.

In the above-described configuration, it is preferable that the end face is a flat face, and a maximum separation dimension L2 between the end face and a virtual vertical face perpendicular to the main surface and in contact with the end face is 5% or less of a thickness dimension of the glass sheet.

In this way, the end face of the end edge portion along the light incident side becomes a surface perpendicular or substantially perpendicular to the main surface, so that light is favorably taken in from the end face, and the efficiency of taking in the amount of light toward the glass substrate is improved.

In the above configuration, it is preferable that the chamfered surface is provided between the end surface and the main surface along the end edge portion of the opposite side to the light entrance side edge, and an external angle θ 2 formed by the chamfered surface and the main surface exceeds 45 °.

Thus, the phenomenon that strong light emission appears in a band shape along the opposite side is reduced at the edge portion along the opposite side opposite to the side on the light incident side. That is, when the external angle θ 2 formed by the chamfer and the main surface along the edge side portion of the opposite edge is 45 ° or less, the above phenomenon may be conspicuously caused along the opposite edge. Therefore, when the glass plate is applied to a light guide plate, light emission from the main surface, that is, surface light emission becomes uneven. However, if the external angle θ 2 exceeds 45 °, the above phenomenon can be reduced, and the surface emission can be made uniform.

In this case, the chamfered surface may not be provided between the end surface and the main surface along the end edge portion of the opposite side to the light entrance side edge.

In this way, since the chamfered surface causing the above phenomenon does not exist, the phenomenon is reliably converged, and the uniformity of surface light emission when the glass plate is applied to a light guide plate is further promoted.

In the above configuration, it is preferable that the drawing direction of the glass plate is along a traveling direction of light introduced from an end edge portion along the light incident side. Here, the "drawing direction" refers to a direction in which a drawing force acts in a process of forming a glass sheet, which is a raw material of the glass sheet, from a molten glass.

Even if foreign matter (defect) such as bubbles is mixed into the glass sheet, the foreign matter has a high probability of being a long and thin shape extending in the drawing direction, and therefore, the foreign matter is not likely to become an element that hinders the light introduced into the glass sheet from traveling. Therefore, the probability of adversely affecting the optical characteristics required for the light guide plate also becomes extremely low.

In the present invention, a chamfered surface may be provided between the end surface and the main surface along an end edge portion of an opposite side to a side on which light from the light source is introduced, the chamfered surface forming an external angle θ 2 with the main surface of more than 45 °.

The operational effects based on this configuration are the same as those described above, and therefore, the description thereof will be omitted here.

In the present invention, the chamfered surface may not be provided between the end surface and the main surface along the edge portion of the opposite side to the side on which the light from the light source is introduced.

The operational effects based on this configuration are also overlapped with the above-described matters, and therefore, the description thereof is omitted here.

Effects of the invention

According to the present invention, it is possible to provide a glass substrate for a light guide plate, which is less likely to cause defects, damage, and the like and which easily satisfies optical characteristics required for a light guide plate.

Drawings

Fig. 1 is a schematic perspective view showing an arrangement state of a light guide plate using a glass plate for a light guide plate as a substrate and a light source on which an LED is placed according to an embodiment of the present invention.

Fig. 2 is an exploded arrangement perspective view showing a detailed structure of an example of a light guide plate using a glass plate for a light guide plate according to an embodiment of the present invention as a substrate.

Fig. 3 is an enlarged view showing the peripheral shape of the edge portion along the light incident side edge of the glass plate for a light guide plate according to the embodiment of the present invention, and more specifically, an enlarged cross-sectional view orthogonal to the light incident side edge and cut in the plate thickness direction.

Fig. 4 is an enlarged view showing a peripheral shape of an edge portion along an opposite side facing a side on a light incident side of a glass plate for a light guide plate according to an embodiment of the present invention, and more specifically, is an enlarged cross-sectional view orthogonal to the opposite side facing the side on the light incident side and cut in a plate thickness direction.

Fig. 5 is a schematic cross-sectional view of a principal part of a glass plate for a light guide plate, which illustrates a principle of occurrence of a phenomenon (a light banding phenomenon) which is a conventional problem, along a periphery of an edge portion of an opposite side to a side on a light incident side.

Fig. 6 is a front view schematically showing a glass plate for a light guide plate in a state where a phenomenon (light banding phenomenon) which has been a problem in the related art has occurred.

Fig. 7 is a schematic cross-sectional view of a main portion showing a peripheral shape of an edge portion along a light incident side edge of a glass plate for a light guide plate according to a second embodiment of the present invention.

Fig. 8 is a schematic cross-sectional view of a main portion showing a peripheral shape of an edge portion along a light incident side edge of a glass plate for a light guide plate according to a third embodiment of the present invention.

Fig. 9 is a partial cross-sectional view showing a peripheral shape of an edge portion of a light guide plate glass plate according to a fourth embodiment of the present invention along a light incident side.

Fig. 10 is a schematic cross-sectional view of a main portion showing a peripheral shape of an edge portion along an opposite side to a light incident side of a glass plate for a light guide plate according to a fifth embodiment of the present invention.

Fig. 11 is a schematic cross-sectional view of a main part showing a peripheral shape of an edge portion along an opposite side to a light incident side of a glass plate for a light guide plate according to a sixth embodiment of the present invention.

Fig. 12 is a schematic cross-sectional view of a main part showing a peripheral shape of an edge portion along an opposite side to a side on a light incident side of a glass plate for a light guide plate according to a seventh embodiment of the present invention.

Fig. 13 is a schematic perspective view for explaining a state of inspection in the embodiment of the present invention.

Detailed Description

Hereinafter, a glass plate for a light guide plate and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings.

Fig. 1 is a schematic perspective view showing a light guide plate 2 using a glass plate 1 for a light guide plate (hereinafter, simply referred to as a glass plate 1) as a substrate, and a light source 3 on which an LED is placed. As shown in the figure, the light sources 3 are arranged on one end side (lower end side) of the light guide plate 2 with a gap therebetween. The light guide plate 2 introduces light emitted from the light source 3 into the inside, propagates inside by total reflection, and emits the light in a planar manner, thereby generating surface light emission. The surface light emitting device having the light source 3 and the light guide plate 2 is used as an edge type backlight of a liquid crystal display, for example.

Fig. 2 is an exploded perspective view of elements showing a detailed structure of an example of the light guide plate 2. As shown in the figure, the light guide plate 2 includes a glass plate 1 serving as a substrate, a diffusion plate (including a diffusion film) 4 and a prism sheet 5 disposed on the front side of the glass plate 1, and a reflection plate (including a reflection film) 6 disposed on the back side of the glass plate 1. The diffusion plate 4 and the prism sheet 5 are sequentially attached to one main surface 7 of the glass plate 1 by bonding or the like, and the reflection plate 6 is attached to the other main surface 8 by bonding or the like.

The glass plate 1 includes an edge side 9 (hereinafter referred to as a light-incident side edge 9) along a side on which light from the light source 3 is incident, an edge side 10 (hereinafter referred to as an opposite side edge 10) along an opposite side to the light-incident side edge, and a pair of side edges 11 connected to the light-incident side edge 9 and the opposite side edge 10. Therefore, the one main surface 7 of the glass plate 1 is set as a light exit surface that exits light introduced from the light entrance side end portion 9 to perform surface light emission, and the other main surface 8 of the glass plate 1 is set as a reflection surface that reflects light introduced in the same manner. In the present embodiment, the glass plate 1 has a plate thickness of 0.2mm to 4.0mm, preferably, the lower limit is 0.3mm or 0.4mm, and the upper limit is 3.0mm or 2.0 mm.

In the glass plate 1 of the present embodiment, SiO is preferably contained as the glass composition in mass%₂40 to 80% (preferably 55 to 70%) of Al₂O₃1 to 25% (preferably 2 to 15%) of B₂O₃0 to 20% (preferably 5 to 15%) of Na₂O0-20% (preferably 5-16%), MgO 0-10%, CaO 0-15% (preferably 3-12%), SrO 0-15%, and BaO 0-35%. Thus, the glass plate 1 is less likely to be dimensionally changed by heat because of the improved heat resistance. Further, since the devitrification resistance is improved, the glass sheet 1 becomes easy to mold.

Further, it is preferable to reduce Fe in the glass plate 1 as much as possible₂O₃The content of (a). If the Fe content is reduced₂O₃The content (b) improves the maximum transmittance of the glass plate 1 in the wavelength range of 400 to 750nm, and thus the luminance characteristics of a display device using the glass plate 1 can be improved. Fe in glass plate 1₂O₃The content of (B) is preferably 50ppm or less, 40ppm or less, 30ppm or less, 1 to 28ppm or 5 to 25ppm by mass, and particularly preferably 10 to 22ppm by mass. If Fe is desired₂O₃If the content of (b) is too small, the cost of raw materials may increase.

Fig. 3 is an enlarged view showing the peripheral shape of the light-incident-side edge portion 9 of the glass plate 1, and more specifically, an enlarged cross-sectional view taken perpendicular to the light-incident-side edge and cut along the plate thickness direction. As shown in the drawing, the light-entrance-side end portion 9 of the glass plate 1 has a chamfered surface 13 between the one main surface 7 and the end surface 12, and also has a chamfered surface 14 between the other main surface 8 and the end surface 12. The external angles θ 1 of the

main surfaces

7 and 8 and the chamfered surfaces 13 and 14 are 45 ° or less. In addition, the lengths L1 of the chamfered surfaces 13 and 14 in the direction along the

main surfaces

7 and 8 are both 5 μm or more. The chamfered surfaces 13 and 14 are both polished surfaces, and the chamfered surfaces 13 and 14 have a surface roughness Ra of 1.0 μm or less.

In the present embodiment, the chamfered surfaces 13 and 14 are flat surfaces, and the end surface 12 is also flat. The chamfered surfaces 13 and 14 are polished surfaces, but the end surface 12 may be a cut surface or a polished surface. Here, the cutting plane is a cutting plane such as a plane obtained by forming a scribe line in the starting glass plate and breaking the scribe line, a plane obtained by breaking the starting glass plate by applying only bending stress, or a plane obtained by laser cutting the starting glass plate by using thermal stress.

The surface roughness Ra of the end face 12 is preferably 0.5 μm or less. The maximum separation dimension L2 between the end face 12 and the virtual vertical plane 15 perpendicular to the

main surfaces

7 and 8 and in contact with the end face 12 is preferably 5% or less of the plate thickness dimension T. In addition, length L3 in the direction orthogonal to

main surfaces

7 and 8 in end surface 12 is preferably 50% or more of plate thickness dimension T.

The direction from the light-incident-side end edge 9 toward the opposite-side end edge 10 is preferably along the drawing direction of the glass sheet 1. That is, the glass plate 1 is pulled in a direction along the traveling direction of the light introduced from the light-incident-side end portion 9 (the left-right direction in the figure). Here, the drawing direction of the glass sheet 1 means a direction in which a drawing force acts in a process of forming a glass sheet, which is a raw material of the glass sheet 1, from molten glass. Therefore, the defect (for example, bubble) 16 such as a foreign substance mixed into the glass sheet 1 has a long and thin shape elongated in the drawing direction of the glass sheet 1. In this way, the defect 16 has a shape in which the elongated shape that becomes a long strip in the drawing direction of the glass sheet 1 does not cover all the defects, but the defect 16 having such an elongated shape is much larger than a defect not having such a shape.

Fig. 4 is an enlarged view showing the peripheral shape of the opposite side end edge portion 10 of the glass plate 1, and more specifically, an enlarged cross-sectional view taken perpendicular to the opposite side facing the light incident side and cut along the plate thickness direction. As shown in this figure, the opposite side end portion 10 of the glass plate 1 has a chamfered surface 18 between the one main surface 7 and the end surface 17, and also has a chamfered surface 19 between the other main surface 8 and the end surface 17. The respective external angles θ 2 of these

main surfaces

7, 8 and the chamfer surfaces 18, 19 preferably exceed 45 °. In addition, the length L4 of each of the chamfered surfaces 18 and 19 in the direction along the

main surfaces

7 and 8 is preferably less than 30% of the plate thickness T. Preferably, the chamfered surfaces 18 and 19 are both polished surfaces, and the chamfered surfaces 18 and 19 have a surface roughness Ra of 1.0 μm or less.

In the present embodiment, the chamfered surfaces 18 and 19 are flat surfaces, and the end surface 17 is also flat. The chamfered surfaces 18 and 19 are polished surfaces, but the end surface 17 may be a cut surface or a polished surface. The meaning of the cutting plane is the same as above. The surface roughness Ra of the end face 17 is preferably 0.5 μm or less. It is preferable that the maximum separation dimension L5 between the end face 17 and the virtual vertical plane 20 perpendicular to the

main surfaces

7 and 8 and in contact with the end face 17 is less than 5% of the plate thickness dimension T. The length L6 in the direction perpendicular to the

main surfaces

7 and 8 in the end surface 17 is preferably 30% or more of the plate thickness T. Note that the case where the drawing direction of the glass plate 1 is along the traveling direction (the left-right direction in the drawing) of the light introduced from the light-incident-side end portion 9, and the case where the defect (for example, bubble) 21 such as a foreign substance mixed into the glass plate 1 has a long and thin shape elongated in the drawing direction of the glass plate 1 are the same as described above.

The pair of side edge portions 11 may have a cross-sectional shape perpendicular to the side edges and cut in the plate thickness direction, and may have a chamfered surface, a cut surface without a chamfered surface, a polished surface, or a polished surface curved like an arc or the like between the

main surfaces

7 and 8 and the end surfaces.

Next, the operational effects of the glass plate 1 having the above-described structure will be described.

First, the operation and effect based on the peripheral structure of the light incident side end portion 9 shown in fig. 3 will be described. Since the chamfered surfaces 13 and 14 are formed in the light-incident-side end portion 9, it is possible to cope with a loss, a breakage, or the like of the glass plate 1, but it may be difficult to introduce light from the chamfered surfaces 13 and 14. In contrast, in the present embodiment, since each of the external angles θ 1 formed by the chamfered surfaces 13 and 14 and the

main surfaces

7 and 8 is set to 45 ° or less, the light is sufficiently drawn. From such a viewpoint, at least one of the external angles θ 1 is preferably 40 ° or less, 35 ° or less, 30 ° or less, 20 ° or less, or 15 ° or less, and may be 10 ° or less or 5 ° or less. Among them, from the viewpoint of suppressing the occurrence of chipping, breakage, and the like of the glass plate 1, it is preferably 3 ° or more.

Even if the chamfer widths S1 are insufficient by forming the chamfer surfaces 13, 14 at the outer angle θ 1 as described above, it is difficult to reliably suppress the occurrence of a defect, a breakage, or the like in the glass plate 1. In contrast, in the present embodiment, since the length L1 in the direction along the

main surfaces

7 and 8 of the chamfered surfaces 13 and 14 is set to 5 μm or more, a sufficient chamfer width S1 is ensured, and the occurrence of chipping, breakage, or the like of the glass plate 1 is reliably suppressed. From such a viewpoint, at least one of the lengths L1 is preferably 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more, and may be 35 μm or more, or 40 μm or more. Among them, from the viewpoint of sufficiently drawing light from the end face 12, it is preferably 200 μm or less or 100 μm or less.

The end face 12 of the light entrance side end portion 9 is a portion capable of greatly increasing the amount of light to be introduced compared to the chamfered surfaces 13 and 14. Therefore, in the present embodiment, by setting the surface roughness Ra of the end face 12 to 0.5 μm or less, the introduction of light is less likely to be hindered due to the large surface roughness of the end face 12. From such a viewpoint, the surface roughness Ra of the end face 12 is preferably 0.3 μm or less, 0.1 μm or less, 0.08 μm or less, 0.07 μm or 0.06 μm or less, and more preferably 0.05 μm or less. In the present embodiment, the chamfer surfaces 13 and 14 are also set to have a surface roughness Ra of 1.0 μm or less, so that the amount of light introduced from the chamfer surfaces 13 and 14 is increased. Therefore, the surface roughness Ra of at least one of the chamfered surfaces 13 and 14 is preferably 0.5 μm or less, 0.1 μm or less, 0.08 μm or less, 0.07 μm or less, or 0.06 μm or less, and more preferably 0.05 μm or less.

Further, by shortening the maximum separation dimension L2 between the end face 12 and the virtual vertical plane 15, the amount of light introduced from the end face 12 can be increased efficiently. In contrast, in the present embodiment, the maximum separation dimension L2 is set to 5% or less of the thickness dimension T, thereby achieving efficiency for increasing the amount of drawn light. From such a viewpoint, the maximum separation dimension L2 is preferably 4% or less, 3% or less, or 2% or less, and more preferably 1% or less of the plate thickness dimension T.

In addition, even when the length L3 in the direction orthogonal to

main surfaces

7 and 8 of end surface 12 is increased, the amount of light introduced from end surface 12 can be increased efficiently. In contrast, in the present embodiment, the length L3 is set to 50% or more of the thickness dimension T, thereby achieving efficiency for making the amount of drawn light large. From such a viewpoint, the length L3 is preferably 55% or more, 60% or more, 65% or more, or 70% or more, and may be 75% or more, or 80% or more. Among them, from the viewpoint of suppressing the occurrence of chipping, breakage, and the like of the glass plate 1, it is preferably 95% or less or 90% or less.

When the direction of pulling the glass plate 1 does not follow the direction of travel of the light introduced from the light-incident-side end portion 9, the longitudinal direction of the defect 16 mixed in the elongated shape of the glass plate 1 does not follow the direction of travel of the light. Therefore, the travel of the light described above may be hindered by the defect 16 of an elongated shape. In contrast, in the present embodiment, the draw direction of the glass plate 1 is made to follow the traveling direction of the light, thereby efficiently avoiding such a problem.

By performing the above-described processing, in the present embodiment, the problem of the glass plate 1 having the original characteristics, that is, the problem of the glass plate 1 being likely to be lost or damaged, is solved with respect to the light incident side edge portion 9, and the glass plate 1 can sufficiently have the optical characteristics required for the light guide plate 2.

Next, the operational effects based on the peripheral structure of the opposite side end portion 10 shown in fig. 4 will be described. Since the chamfered surfaces 18 and 19 are formed on the opposite side end portion 10, it is possible to roughly cope with a defect, a breakage, and the like of the glass plate 1, but a phenomenon (hereinafter, referred to as a light banding phenomenon) in which strong light emission appears in a band shape along the longitudinal direction of the opposite side end portion 10 may occur. As shown in fig. 5, the band phenomenon of light is explained in that light 22 introduced from the light-incident side end portion 9 and reaching the opposite side end portion 10 is reflected by the chamfered surface 19(18), and the reflected light is condensed at the periphery of the opposite side end portion 10, thereby generating the band phenomenon. Therefore, as shown in fig. 6, when light enters from the light-incident-side end portion 9 into the glass plate 1 and travels toward the opposite-side end portion 10, a band phenomenon of light, as indicated by a one-dot chain line, may occur in the periphery of the opposite-side end portion 10. When the glass plate 1 in which the banding phenomenon of light occurs is applied to the light guide plate 2, light emission from the

main surfaces

7 and 8, that is, surface light emission may become uneven. Such a problem may be conspicuously caused when each external angle θ 2 between the chamfered surfaces 18 and 19 and the

main surfaces

7 and 8 is 45 ° or less.

In contrast, in the present embodiment, since each of the outer angles θ 2 exceeds 45 °, the band phenomenon of light generated at the opposite side end edge portions 10 is reduced, and the uniformity of surface light emission in the light guide plate 2 is not easily hindered. From such a viewpoint, at least one of the outer angles θ 2 is preferably more than 50 °, more than 60 °, or more than 70 °, and may be more than 80 ° or more than 90 °.

Even if the chamfered surfaces 18 and 19 having the external angle θ 2 as described above are formed, if the chamfer width S2 is too large, the banding phenomenon of light may not be sufficiently reduced, or the machining operation of the chamfered surfaces 18 and 19 may become complicated. In contrast, in the present embodiment, since the length L4 of the chamfered surfaces 18 and 19 in the direction along the

main surfaces

7 and 8 is set to be less than 30% of the plate thickness T, an excessive increase in the chamfer width S2 can be avoided. From such a viewpoint, at least one of the lengths L4 is preferably less than 25% or less than 20% of the thickness T, and may be less than 15% or less than 10% of the thickness T.

In order to improve the quality of the glass plate 1, it is preferable that the end surface 17 of the opposite-side end portion 10 has a surface roughness Ra equal to that of the end surface 12 of the light-entrance end portion 9. Therefore, in the present embodiment, the surface roughness Ra of the end face 17 of the opposite side end edge portion 10 is also set to 0.5 μm, but may be 0.3 μm or less, 0.1 μm or less, 0.08 μm or less, 0.07 μm or less, or 0.06 μm or less, and further may be 0.05 μm or less. From the same viewpoint, the chamfer surfaces 18, 19 of the opposite side end edge portion 10 also have a surface roughness Ra of 1.0 μm or less, but at least one of the chamfer surfaces 18, 19 may have a surface roughness Ra of 0.5 μm or less, 0.1 μm or less, 0.08 μm or less, 0.07 μm or 0.06 μm or less, and further 0.05 μm or less.

Further, if the maximum separation dimension L5 between the end face 17 of the opposite side end side edge portion 10 and the virtual vertical plane 20 is increased, there is a possibility that the optical characteristics are disturbed. In contrast, in the present embodiment, the maximum separation dimension L5 is set to 5% or less of the thickness dimension T, thereby reliably preventing the end face 17 from becoming an element of deterioration of optical characteristics. In addition, from the viewpoint of ensuring the quality of the plate glass, the maximum separation dimension L5 may be 4% or less, 3% or less, or 2% or less, and further 1% or less of the plate thickness dimension T.

In addition, when the length L6 in the direction orthogonal to the

main surfaces

7 and 8 in the end surface 17 is shortened, the chamfer width S2 may become too long to reliably prevent the occurrence of the light banding phenomenon, or the work of machining the chamfer surfaces 18 and 19 may become complicated. In contrast, in the present embodiment, the length L6 is set to 30% or more of the sheet thickness dimension T, but may be 40% or more, 50% or more, 60% or more, or 70% or more, or may be 80% or more, or 90% or more.

By performing the above-described processing, in the present embodiment, the opposite side edge portions 10 are free from problems due to the characteristics inherent to the glass plate 1, that is, problems such as easy occurrence of a defect, a breakage, and the like, and are less likely to cause a banding phenomenon of light, thereby being able to cope with the uniformization of the surface light emission of the light guide plate 2.

In the above embodiment, the end surface 12 and the chamfered surfaces 13 and 14 of the light-incident-side end portion 9 are flat surfaces, and the end surface 17 and the chamfered surfaces 18 and 19 of the opposite-side end portion 10 are also flat surfaces, but the present invention can be variously modified as described below.

An end surface 12 of the light entrance side end portion 9 shown in fig. 7 is a convexly curved surface, and chamfered

surfaces

13 and 14 each formed of a flat surface are formed between the end surface 12 and the

main surfaces

7 and 8. In this case, the light entrance side end portion 9 may be an end surface that is curved in an arc shape or the like over the entire region between the

main surfaces

7 and 8, and a chamfered surface is not formed.

The light incident side end portion 9 shown in fig. 8 has no chamfered surface formed between the end surface 12 (cut surface or polished surface) and the

main surfaces

7 and 8. In this case, the opposite side end portions 10, not shown, are formed with chamfered surfaces 18 and 19(18a and 19a) as described above or as described below between the end surface 17 and the

main surfaces

7 and 8.

The light entrance side end portion 9 shown in fig. 9 has R chamfered

surfaces

13a and 14a formed between the end surface 12 formed of a flat surface and the

main surfaces

7 and 8, respectively. The radius of curvature of each of the R-chamfered

surfaces

13a and 14a is preferably 20% or less, 15% or less, or 10% or less of the plate thickness dimension T, and the lower limit value is preferably 5%, 3%, or 1%.

The end face 17 of the opposite side end portion 10 shown in fig. 10 is a convexly curved surface, and chamfered

surfaces

18 and 19 each formed of a flat surface are formed between the end face 17 and the

main surfaces

7 and 8. In this case, the opposite side end portion 10 may be an end surface that is curved in an arc shape or the like over the entire region between the

main surfaces

7 and 8, and a chamfered surface is not formed.

The opposite side end portion 10 shown in fig. 11 has no chamfered surface formed between the end surface 17 (cut surface or ground surface) and the

main surfaces

7 and 8. In this case, the chamfered surfaces 13 and 14(13a and 14a) are formed between the end surface 12 and the

main surfaces

7 and 8, as described above, with respect to the light-entrance-side end portion 9 outside the figure.

The opposite side end portion 10 shown in fig. 12 has R chamfered

surfaces

18a and 19a formed between the end surface 17 formed of a flat surface and the

main surfaces

7 and 8, respectively. The radius of curvature of each of the R chamfered

surfaces

18a and 19a is preferably 20% or less, 15% or less, or 10% or less of the plate thickness dimension T, and the lower limit value is preferably 5%, 3%, or 1%.

In the above embodiment, one of the four sides of the glass plate 1 is the light entrance side end portion 9, but two or three or all of the adjacent sides may be the light entrance side end portion 9.

Example 1

Four glass plates having a longitudinal dimension of 400mm, a transverse dimension of 300mm and a plate thickness of 2.0mm were prepared for the sample of example 1. The four glass plates were prepared as shown in fig. 3, and sample nos. 1 to 4 were prepared as the glass plates in which the external angles θ 1 formed by the chamfered surfaces 13 and 14 of the light incident side end portion 9 and the

main surfaces

7 and 8 were 35 °, 45 °, 55 °, and 65 °, respectively. As shown in fig. 13, in each of the samples Nol to 4, light from the light source 23 composed of a halogen lamp was emitted through the diffusion plate, the emitted light was taken in from the light-incident-side end portion 9 of the glass plate 1 of each sample, and illuminance was measured and evaluated by the illuminometer 24 in contact with the opposite-side end portion 10. In this case, the opposite side end portion 10 is a cut surface having no chamfered surface for all the samples. The traveling direction of light is the longitudinal direction of the glass sheet (draw direction). The results are shown in table 1 below. In table 1, the "reduction rate" is a rate at which the illuminance measured for each sample is reduced from the illuminance measured by the illuminometer in the same manner as described above with respect to the glass plate having the incident-side end portion 9 formed as a cut surface without a chamfered surface.

[ Table 1]

Sample No.	Angle θ 1(°)	Reduction ratio (%)
			1	35	5
2	45	15
			3	55	45
4	65	55

Example 2

For the sample of example 2, four glass plates having the same size and the same plate thickness as those of the sample of example 1 were prepared. The four glass plates were prepared as sample nos 5 to 8, in which the maximum separation dimensions L2 between the end face 12 and the virtual vertical plane 15 in the incident-side end edge portion 9 shown in fig. 3 were 0.05mm (2.5% of the plate thickness), 0.10mm (5.0% of the plate thickness), 0.15mm (7.5% of the plate thickness), and 0.20mm (10% of the plate thickness), respectively. As shown in FIG. 13, the illuminance of the samples No. 5 to No. 8 was measured by the illuminance meter 24 and evaluated in the same manner as in example 1. The results are shown in table 2 below. In table 2, the "reduction rate" is a rate at which the illuminance measured for each sample is reduced with respect to the illuminance measured by the illuminometer 24 provided at the same position as that shown in fig. 13 in a state where the glass plate is not present.

[ Table 2]

Sample No.	Verticality (mm)	Verticality (%)	Reduction ratio (%)
				5	0.05	2.5	10
6	0.10	5.0	14
				7	0.15	7.5	35
8	0.20	10	47

Example 3

For the sample of example 3, a plurality of glass plates having a longitudinal dimension of 130mm, a transverse dimension of 65mm and a plate thickness of 1.1mm were prepared. These multiple glass sheets are classified into a glass sheet manufactured by a float method and a glass sheet manufactured by an overflow down-draw method. First, from among a plurality of glass plates produced by the respective methods, it was examined whether or not the major diameter of a bubble (the dimension in the longitudinal direction of the bubble) as a defect was 300 μm or more by an inspection based on light irradiation of 2000lux, and the group of glass plates not containing a bubble having a major diameter of 300 μm or more was set as group a, and the group of glass plates containing a bubble having a major diameter of 300 μm or more was set as group B. Then, for the glass sheets of group B, the correlation between the major axis of the bubble and the percentage of the long side direction of the bubble that becomes parallel to the drawing direction of the glass sheet was examined. The results of the examination are shown in table 3 below.

[ Table 3]

Major diameter of defect (μm)	The long edge direction of the defect is parallel to the direction of the pulling plate
		≤100μm	20％
101～200	40％
		201～300	60％
≥301	90％

According to table 3, the percentage of the long-diameter bubbles that have a large influence on the diffused reflection that are parallel to the drawing direction of the glass sheet is higher than the percentage of the long-diameter bubbles that have a short length.

Next, as shown in fig. 13, the glass plates of the above-described group a and group B were evaluated by measuring the illuminance with the illuminometer 24 in the same manner as in example 1. The illuminance in this case is measured in a manner that the plate pulling direction of the glass plate in the group a and the group B is orthogonal to the traveling direction (incident direction) of light and in a manner that the plate pulling direction is parallel to the traveling direction of light. The pulling direction of the glass sheet can be determined according to the surface properties such as the undulation state of the main surface. The measurement results in this case are shown in table 4 below. In table 4, "%" indicates transmission efficiency, and "transmission efficiency" refers to the ratio of the illuminance of light actually passing through the glass plate based on the original illuminance (29000lux) of the light source at the measurement position.

[ Table 4]

According to table 4, the transmission efficiency is higher in the case where both the glass plates of the group a and the group B are made parallel to the pulling direction than in the case where both directions are made orthogonal to each other. When the incident direction and the drawing direction are parallel to each other, the same transmission efficiency is obtained in group a including glass plates with few defects mixed with small bubbles and group B including glass plates with many defects mixed with large bubbles. This means that, if the incident direction is parallel to the direction of the tab, the transmission efficiency is high regardless of the size of the defect (bubble). As the glass sheet produced by the float method, a glass sheet having a lower transmittance than that of a glass sheet produced by the overflow down-draw method was used, and a difference was generated between the two.

Description of reference numerals:

1 glass plate for light guide plate

2 light guide plate

3 light source

7 major surface

8 major surface

9 end edge (incident light side edge)

10 end edge (opposite side edge)

12 end face

13 chamfer surface

13a chamfer

14 chamfered surface

14a chamfer

15 imaginary vertical plane

17 end face

18 chamfered surface

18a chamfer

19 chamfer surface

19a chamfer surface

20 imaginary vertical plane

Claims

1. A glass plate for a light guide plate, characterized in that,

the glass plate for a light guide plate has a chamfered surface between an end surface and a main surface along an edge on a side on which light from a light source is introduced, the chamfered surface forming an external angle (theta 1) of 45 DEG or less with the main surface, a length (L1) of the chamfered surface in a direction along the main surface being 5 [ mu ] m or more, a surface roughness (Ra) of the end surface being 0.5 [ mu ] m or less,

a chamfered surface is provided between the end surface and the main surface along an end edge portion of an opposite side to the light entrance side, and an external angle (theta 2) formed by the chamfered surface and the main surface exceeds 45 degrees.

2. The glass plate for a light guide plate according to claim 1,

the end face of the edge portion along the light incident side is a plane, and a maximum separation dimension (L2) between the end face and a virtual vertical plane perpendicular to the main surface and in contact with the end face is 5% or less of a thickness dimension (T) of the glass sheet.

3. The glass plate for a light guide plate according to claim 1 or 2,

the glass plate is drawn in a direction along a traveling direction of light introduced from an end edge portion along the light incident side.