WO2015033866A1

WO2015033866A1 - Light guide plate

Info

Publication number: WO2015033866A1
Application number: PCT/JP2014/072704
Authority: WO
Inventors: 加藤　嘉成
Original assignee: 日本電気硝子株式会社
Priority date: 2013-09-03
Filing date: 2014-08-29
Publication date: 2015-03-12
Also published as: CN105264284A; KR20160051683A; TWI678563B; CN105264284B; TW201512719A; KR102138067B1

Abstract

Provided is a light guide plate characterized by having at least a glass plate, and in that the maximum transmittance of the glass plate is at least 50% at an optical path length of 100mm and in a wavelength range of 350-750nm.

Description

Light guide plate

The present invention relates to a light guide plate, and more particularly to a light guide plate suitable for an edge light type surface light emitting device.

Conventionally, liquid crystal display devices are used for liquid crystal televisions and the like. The liquid crystal display device includes a surface light emitting device and a liquid crystal panel arranged on the light emitting surface side of the surface light emitting device. As the surface light emitting device, for example, a direct type and an edge light type are known.

In the direct type surface light emitting device, the light source is disposed on the back surface opposite to the light emitting surface. When a point light source such as a light emitting diode (Light Emitting Diode) is used as the light source, a large number of LED chips are required to supplement the brightness, and the variation in luminance characteristics becomes very large.

Therefore, at present, edge light type surface light emitting devices are mainly used. The edge light type surface light emitting device includes a light source such as an LED, a light guide plate, a reflection plate (or reflection film), and the like. A light source is arrange | positioned at the side surface which becomes a orthogonal direction with respect to a light-projection surface. The light guide plate is arranged to propagate light from the light source to the inside by total reflection and to emit the light in a planar shape. A resin plate such as an acrylic resin is generally used as the light guide plate (see Patent Documents 1 to 4). The reflecting plate is disposed on the light reflecting surface opposite to the light emitting surface, and is disposed to reflect light passing through the light reflecting surface to emit light on a display surface such as a liquid crystal panel. In addition, in order to emit light uniformly on a display surface such as a liquid crystal panel, a diffusion plate (diffusion film) may be disposed on the light exit surface side of the light guide plate.

FIG. 1 is a conceptual cross-sectional view showing an example of an edge light type surface light emitting device 1. The edge light type surface light emitting device 1 includes a light source 2 such as an LED, a light guide plate 3, a reflection plate 4, and a diffusion plate 5. Light from the light source 2 enters from the end face of the light guide plate 3 and propagates into the light guide plate 3. The light that reaches the light reflecting surface 6 is reflected by the reflecting plate 4, travels toward the light emitting surface 7, and is diffused by the diffusion plate 5. As a result, a display surface such as a liquid crystal panel disposed above the diffusion plate 5 can emit light uniformly.

JP 2012-123933 A JP 2012-138345 A JP 2012-216523 A JP 2012-216528 A

In the edge light type surface emitting device, when light is generated from the light source, heat is generated, and accordingly, the temperature of the light guide plate also increases. When a resin plate is used as the light guide plate, the dimensional change due to heat of the light guide plate is larger than the dimensional change of the liquid crystal panel. This is due to the high thermal expansion coefficient of the resin plate. For example, the thermal expansion coefficient of the acrylic resin plate is about 700 × 10 ⁻⁷ / ° C. For this reason, until now, a dimensional change of the light guide plate has been corrected by providing a gap in the frame portion of the liquid crystal display device so that an undue stress is not generated due to a difference in dimensional change.

However, in recent years, due to the narrow frame of the liquid crystal display device, it is difficult to correct the dimensional change of the light guide plate at the frame portion of the liquid crystal display device.

Also, when a resin plate is used as the light guide plate, the amount of light is reduced when light from the light source enters from the end face and exits to the light exit surface. As a result, the luminance characteristics of the display device are likely to deteriorate.

From such a point of view, the first object of the present invention is to create a light guide plate that hardly undergoes a dimensional change with a rise in temperature and that does not easily deteriorate the luminance characteristics of the display device.

Also, the liquid crystal panel uses polarized light. Further, the edge light type surface light emitting device has a different distance from the light source on the light emitting surface. Therefore, in recent years, with an increase in the size of the liquid crystal display device, the polarization state is different within the panel surface, and uneven luminance characteristics are likely to occur.

From this point of view, the second object of the present invention is to create a light guide plate that is less likely to undergo dimensional changes with increasing temperature and that can uniformize the luminance characteristics of the display device.

As a result of intensive studies, the present inventor has solved the first problem by adopting a glass plate having a small dimensional change due to temperature change as the light guide plate and restricting the transmittance of the glass plate to a predetermined range. It finds out and obtains and proposes as this invention (1st invention). That is, the light guide plate of the present invention (first invention) has at least a glass plate, and has an optical path length of 100 mm and a maximum transmittance of 50% or more in a wavelength range of 350 to 750 nm. To do. The “maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm” can be measured by a commercially available transmittance measuring device, and can be measured by, for example, UV-3100PC manufactured by Shimadzu Corporation.

A display panel such as a liquid crystal panel has a structure in which a display element such as a liquid crystal element is sandwiched between a pair of glass plates. Therefore, when a glass plate is adopted as the light guide plate, a difference in dimensional change between the display panel and the light guide plate is reduced, and it is possible to appropriately cope with a narrow frame of a display device such as a liquid crystal display device.

The present inventor has found that the maximum transmittance in the optical path length of 100 mm and the wavelength range of 350 to 750 nm of the glass plate affects the luminance characteristics of the display device. Therefore, in the present invention (first invention), the maximum transmittance in the optical path length of 100 mm and the wavelength range of 350 to 750 nm of the glass plate is regulated to 50% or more to enhance the luminance characteristics of the display device.

In the light guide plate of the present invention (first present invention), the content of Fe ₂ O ₃ in the glass plate is preferably 0.1% by mass or less. By doing so, it is possible to increase the maximum transmittance of the glass plate in the optical path length of 100 mm and the wavelength range of 350 to 750 nm. Fe ₂ O ₃ exists in the state of Fe ³⁺ or Fe ^{2+ in} the glass. Fe ³⁺ has an absorption peak in the vicinity of a wavelength of 380 nm, and lowers the transmittance in the visible region in the ultraviolet region and the short wavelength side. Fe ²⁺ has an absorption peak in the vicinity of a wavelength of 1080 nm, and lowers the transmittance in the visible region on the long wavelength side. Therefore, when the content of Fe ₂ O ₃ increases, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease. In general, a large amount of Fe ₂ O ₃ is mixed in the glass plate from the glass raw material and the manufacturing process. Therefore, the conventional glass plate, because the content of Fe ₂ O ₃ is large, it is difficult to increase the luminance characteristics of the display device. Therefore, when the content of Fe ₂ O ₃ in the glass plate is regulated to 0.1% by mass or less, the luminance characteristics of the display device can be improved. Note that “Fe ₂ O ₃ ” referred to in the present invention includes divalent iron oxide and trivalent iron oxide, and the divalent iron oxide is handled in terms of Fe ₂ O ₃ . Similarly, other oxides are handled based on the indicated oxide.

The light guide plate of the present invention (first invention) preferably has a glass plate with a dimension of at least one side of 1000 mm or more. In this way, it is possible to satisfy the demand for an increase in the size of the display device.

In the light guide plate of the present invention (first present invention), the surface roughness Ra of the end surface of the glass plate is preferably 2 μm or less. Here, “surface roughness Ra” refers to a value measured by a method in accordance with JIS B0601: 2001, with an evaluation length of 8 mm, a cutoff value λc = 0.8 mm, and a cutoff ratio λc / λs = 100. Refers to the value measured under conditions.

In the light guide plate of the present invention (first invention), the glass plate preferably has a thermal expansion coefficient of 120 × 10 ⁻⁷ / ° C. or less. Here, “thermal expansion coefficient” refers to a value obtained by measuring an average thermal expansion coefficient at 30 to 380 ° C. based on JIS R3102 using a dilatometer.

The light guide plate of the present invention (first invention), a glass plate, as a glass composition, in _{_{_{mass%, SiO 2 40 ~ 70%}}} , Al 2 O 3 2 ~ 25%, B 2 O 3 0 ~ 20% , R ₂ O (R is one or more of Li, Na and K) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 It is preferable to contain ˜10%, ZrO ₂ 0˜10%, Fe ₂ O ₃ 0.001˜0.1%. This makes it possible to reduce the thermal expansion coefficient while increasing the maximum transmittance in the optical path length of 100 mm and the wavelength range of 350 to 750 nm.

The light guide plate of the present invention (first present invention) is preferably a glass plate formed by an overflow downdraw method. Here, the “overflow down-draw method” is a method in which molten glass overflows from both sides of a heat-resistant bowl-shaped molded body, and the molten glass overflows and joins at the lower end of the molded body to be stretched and formed downward. It is a method of manufacturing.

The light guide plate of the present invention (first invention) is characterized by being used for an edge light type surface light emitting device.

The edge light type surface light emitting device of the present invention (the first present invention) includes the light guide plate described above.

In addition, as a result of intensive studies, the present inventor adopted a glass plate having a small dimensional change due to a temperature change as a light guide plate, and restricting the retardation of the glass plate to a predetermined range, thereby solving the second problem. It has been found that the problem can be solved, and is proposed as the present invention (second present invention). That is, the light guide plate of the present invention (second invention) has at least a glass plate and has a retardation of 30 nm or less at an optical path length of 50 mm. The “retardation at an optical path length of 50 mm” can be measured by a commercially available birefringence measuring apparatus, and can be measured by, for example, an optical heterodyne method using PEL-3A-XR manufactured by UNIOPT.

The present inventor has found that the retardation of the glass plate at an optical path length of 50 mm affects the luminance characteristics of the display device. Therefore, in the present invention (second present invention), the retardation of the glass plate in the optical path length of 50 mm is regulated to 30 nm or less to achieve uniform luminance characteristics of the display device.

In the light guide plate of the present invention (second invention), it is preferable that the dimension of at least one side of the glass plate is 1000 mm or more. In this way, it is possible to satisfy the demand for an increase in the size of the display device.

In the light guide plate of the present invention (second present invention), the surface roughness Ra of the end face of the glass plate is preferably 2 μm or less. In this way, light from the light source can be uniformly incident on the light guide plate. Here, “surface roughness Ra” refers to a value measured by a method in accordance with JIS B0601: 2001, with an evaluation length of 8 mm, a cutoff value λc = 0.8 mm, and a cutoff ratio λc / λs = 100. Refers to the value measured under conditions.

In the light guide plate of the present invention (second invention), the glass plate preferably has a thermal expansion coefficient of 120 × 10 ⁻⁷ / ° C. or less. Here, “thermal expansion coefficient” refers to a value obtained by measuring an average thermal expansion coefficient at 30 to 380 ° C. based on JIS R3102 using a dilatometer.

In the light guide plate of the present invention (second invention), the strain point of the glass plate is preferably 550 ° C. or higher. If it does in this way, the heat resistance of a light-guide plate will improve. Here, “strain point” refers to a value measured based on JIS R3103.

The light guide plate of the present invention (second invention), a glass plate, as a glass composition, in _{_{_{mass%, SiO 2 40 ~ 70%}}} , Al 2 O 3 2 ~ 25%, B 2 O 3 0 ~ 20% , R ₂ O (R is one or more of Li, Na and K) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 Preferably, it contains up to 10% and 0 to 10% of ZrO ₂ . In this way, it is possible to achieve both a low thermal expansion coefficient and a high strain point.

The light guide plate of the present invention (second invention) is preferably a glass plate formed by the overflow down draw method. Here, the “overflow down-draw method” is a method in which molten glass overflows from both sides of a heat-resistant bowl-shaped molded body, and the molten glass overflows and joins at the lower end of the molded body to be stretched and formed downward. It is a method of manufacturing.

The light guide plate of the present invention (second invention) is used for an edge light type surface light emitting device.

An edge light type surface light emitting device according to the present invention (second present invention) includes the light guide plate described above.

The glass plate of the present invention (second invention) has a retardation at an optical path length of 50 mm of 20 nm or less, and is used for a light guide plate.

It is a section conceptual diagram showing an example of an edge light type surface emitting device. It is the measurement data of the transmittance | permeability in the optical path length of 100 mm and the wavelength range of 300-750 nm of the glass plate which concerns on Examples 1-3. FIG. 6 shows transmittance measurement data of an optical path length of 100 mm and a wavelength range of 300 to 750 nm of a glass plate according to Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

In the light guide plate of the present invention (first invention), the maximum transmittance of the glass plate in the optical path length of 100 mm and the wavelength range of 350 to 750 nm is 50% or more, preferably 70% or more, 75% or more, 80% or more. 81% or more or 82% or more, particularly preferably 83% or more. If the maximum transmittance in the optical path length of 100 mm and the wavelength range of 350 to 750 nm is too low, the luminance characteristics of the display device are likely to deteriorate.

In the light guide plate of the present invention (first invention), it is preferable to reduce the content of the colored oxide in the glass plate as much as possible. Examples of the colored oxide include Fe ₂ O ₃ , Cr ₂ O ₃ , V ₂ O ₅ , NiO, MnO ₂ , Nd ₂ O ₃ , CeO ₂ , Er ₂ O _{3 and the} like.

In the light guide plate of the present invention (first invention), the content of the transition metal oxide in the glass plate is preferably 0.1% by mass or less, 0.05% by mass or less, 0.03% by mass or less, 0.02 mass% or less, 0.015 mass% or less, 0.01 mass% or less, 0.009 mass% or less, 0.008 mass% or less, 0.007 mass% or less, 0.006 mass% or less, 0 0.005 mass% or less or 0.004 mass% or less, particularly preferably 0.001 to 0.01 mass%. When the content of the transition metal oxide is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease. In addition, when content of a transition metal oxide will be less than 0.001 mass%, raw material cost and the manufacturing cost of a glass plate will rise.

The content of Fe ₂ O ₃ in the glass plate is preferably 0.1% by mass or less, 0.05% by mass or less, 0.03% by mass or less, 0.02% by mass or less, or 0.015% by mass or less, Particularly preferred is 0.001 to 0.01% by mass. If the content of Fe ₂ O ₃ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease. Incidentally, when the content of _Fe 2 _{O 3} is less than 0.001 wt%, the raw material cost, the cost of manufacturing the glass sheet to rise.

The content of Cr ₂ O ₃ in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, 0.005% by mass or less, 0.003 mass% or less, 0.001 mass% or less, 0.0005 mass% or less, 0.0004 mass% or less, 0.0003 mass% or less or 0.0002 mass% or less, particularly preferably 0.0001 mass% It is as follows. When the content of Cr ₂ O ₃ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease. Incidentally, when the content of Cr ₂ O ₃ is too small, the raw material cost, the cost of manufacturing the glass sheet to rise. The preferred lower limit content is 0.00001% by mass or more, particularly 0.00005% by mass or more.

The content of V ₂ O ₅ in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, Especially preferably, it is 0.003 mass% or less. When the content of V ₂ O ₅ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

The content of NiO in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, particularly preferably 0.003 mass% or less. When the content of NiO is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

The content of MnO ₂ in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, particularly preferably. Is 0.003 mass% or less. When the content of MnO ₂ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

The content of Nd ₂ O ₃ in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, Especially preferably, it is 0.003 mass% or less. When the content of Nd ₂ O ₃ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

The CeO ₂ content in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, particularly preferably. Is 0.003 mass% or less. When the content of CeO ₂ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

The content of Er ₂ O ₃ in the glass plate is preferably 0.03% by mass or less, 0.02% by mass or less, 0.015% by mass or less, 0.01% by mass or less, or 0.005% by mass or less, Especially preferably, it is 0.003 mass% or less. When the content of Er ₂ O ₃ is too large, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm tends to decrease.

In order to eliminate the contamination of colored oxides such as Fe ₂ O ₃ and Cr ₂ O ₃ as much as possible, a high-purity glass raw material is used, or from a raw material preparation facility or the like to the raw material, Fe ₂ O ₃ and Cr ₂ O ₃ Manufacturing equipment designed so that colored oxides such as the above may not be mixed may be used.

In the light guide plate of the present invention (first present invention), the size of at least one side of the glass plate is preferably 1000 mm or more, 1500 mm or more, 2000 mm or more, or 2500 mm or more, and particularly preferably 3000 mm or more. In this way, it is possible to satisfy the demand for an increase in the size of the display device.

The surface roughness Ra of the end face of the glass plate is preferably 2 μm or less, 1.5 μm or less, 1 μm or less, or 0.7 μm or less, particularly preferably 0.5 μm or less. If it does in this way, it will become easy to scatter the light from a light source on the end surface of a glass plate, and it will become difficult to make the light from a light source inject into a light-guide plate uniformly.

The thermal expansion coefficient of the glass plate is preferably 120 × 10 ⁻⁷ / ° C. or lower, 90 × 10 ⁻⁷ / ° C. or lower, 60 × 10 ⁻⁷ / ° C. or lower, 55 × 10 ⁻⁷ / ° C. or lower, 50 × 10 ^{− 7} / ° C. or lower or 45 × 10 ⁻⁷ / ° C. or lower, particularly preferably 25 × 10 ⁻⁷ to 40 × 10 ⁻⁷ / ° C. or lower. If the thermal expansion coefficient is too high, the difference in dimensional change due to heat between the display panel and the light guide plate becomes large.

The strain point of the glass plate is preferably 550 ° C. or higher, 580 ° C. or higher, 600 ° C. or higher, 615 ° C. or higher, 630 ° C. or higher, or 640 ° C. or higher, particularly preferably 650 ° C. or higher. If the strain point is too low, the heat resistance of the glass plate is likely to be lowered. For example, when a reflective film, a diffusion film, or the like is formed on the surface of the glass plate at a high temperature, the glass plate is likely to be thermally deformed. Here, the “strain point” is a value measured based on JIS R3103.

The glass plate has a glass composition of mass%, SiO ₂ 40 to 70%, Al ₂ O ₃ 2 to 25%, B ₂ O ₃ 0 to 20%, R ₂ O (R is one of Li, Na and K) Or 2 or more types) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 10%, ZrO ₂ 0 to 10%, Fe ₂ O ₃ It is preferable to contain 0.001 to 0.1%. The reason why the content of each component is regulated as described above will be described below. In addition, in description of the containing range of each component,% display means the mass%.

SiO ₂ is a component that serves as a network former of glass, and is a component that reduces a thermal expansion coefficient and reduces a dimensional change due to heat. It is a component that increases acid resistance and strain point. The content of SiO ₂ is preferably 40 to 70% or 50 to 67%, particularly preferably 57 to 64%. When the content of SiO ₂ is increased, the high temperature viscosity is increased, the meltability is lowered, and the devitrification blisters of cristobalite are liable to precipitate at the time of molding. On the other hand, when the content of SiO ₂ decreases, the coefficient of thermal expansion increases and the dimensional change due to heat tends to increase. In addition, acid resistance and strain point are likely to be lowered.

Al ₂ O ₃ is a component that lowers the thermal expansion coefficient and reduces dimensional changes due to heat. It also has the effect of increasing the strain point and suppressing the precipitation of devitrified cristobalite during molding. The content of Al ₂ O ₃ is preferably 2 to 25% or 10 to 20%, particularly preferably 14 to 17%. When the content of Al ₂ O ₃ increases, the liquidus temperature rises and it becomes difficult to form a glass plate. On the other hand, when the content of Al ₂ O ₃ decreases, the thermal expansion coefficient increases and the dimensional change due to heat tends to increase. In addition, the strain point tends to decrease.

B ₂ O ₃ is a component that acts as a flux, lowers the high temperature viscosity, and improves the meltability. Moreover, it is a component which reduces a thermal expansion coefficient and reduces the dimensional change by heat. The content of B ₂ O ₃ is preferably 0 to 20% or 5 to 15%, particularly preferably 7.5 to 12%. When the content of B ₂ O ₃ is increased, the strain point and acid resistance are likely to be lowered. On the other hand, when the content of B ₂ O ₃ decreases, the thermal expansion coefficient increases and the dimensional change due to heat tends to increase. In addition, the meltability tends to be lowered.

R ₂ O is a component that lowers the high temperature viscosity and improves the meltability. The content of R ₂ O is preferably 0 to 25% or 0 to 20%, particularly preferably 0 to 15%. When the content of R ₂ O increases, the strain point tends to decrease, and the maximum transmittance around the wavelength of 550 nm tends to decrease. From the viewpoint of reducing the thermal expansion coefficient, it is preferable to reduce the content of R ₂ O as much as possible, and the content is preferably 5% or less or 1% or less, particularly preferably 0.5% or less. The contents of Li ₂ O, Na ₂ O, and K ₂ O are also preferably 5% or less or 1% or less, particularly preferably 0.5% or less, respectively.

MgO is a component that improves the meltability by lowering only the high temperature viscosity without lowering the strain point. The content of MgO is preferably 0 to 10% or 0 to 5%, particularly preferably 0 to 3.5%. When the content of MgO is increased, devitrification beads are likely to precipitate during molding.

CaO is a component that improves the meltability by lowering only the high temperature viscosity without lowering the strain point. The content of CaO is preferably 0 to 15% or 2 to 12%, particularly preferably 3.5 to 10%. When there is too much content of CaO, devitrification will become easy to precipitate at the time of fabrication.

SrO is a component that improves chemical resistance and devitrification resistance. The content of SrO is preferably 0 to 10% or more than 0.5 to 8%, particularly preferably 1 to 8%. When the SrO content is increased, the thermal expansion coefficient is increased, and the dimensional change due to heat tends to increase.

BaO is a component that increases chemical resistance and devitrification resistance in the same manner as SrO. The content of BaO is preferably 0 to 15% or 0 to 10%, particularly preferably 0.1 to 8%. When the content of BaO increases, the density increases or the thermal expansion coefficient increases, and the dimensional change due to heat tends to increase. In addition, the meltability tends to be lowered.

ZnO is a component that improves meltability. The content of ZnO is preferably 0 to 10% or 0 to 5%, particularly preferably 0 to 1%. When the content of ZnO is increased, the devitrification resistance and the strain point are liable to be lowered.

ZrO ₂ is a component that increases the strain point. The content of ZrO ₂ is preferably 0 to 10% or 0 to 7%, particularly preferably 0 to 5%. When the ZrO ₂ content is increased, the density is remarkably increased, and devitrification spots caused by ZrO ₂ are liable to precipitate during molding.

Colored oxide is a component that decreases the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm. The preferred content and the like of the colored oxide are as described above.

In addition to the above components, other components may be introduced. For example, in order to lower the liquidus temperature, Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O ₅ , P ₂ O ₅ are each up to 3%, As ₂ O ₃ , Sb ₂ O ₃ , SnO as refining agents ₂ , SO ₃ , F, Cl or the like may be introduced up to 2% in total. However, As ₂ O ₃ and Sb ₂ O ₃ are environmentally hazardous substances, and when a glass plate is formed by the float process, it is reduced in the float bath to become a metal foreign object, so avoid substantial introduction. More specifically, the content is preferably less than 0.01%.

In the light guide plate of the present invention (first invention), the glass plate is preferably formed by an overflow down draw method. In this way, it is difficult to produce a temperature difference and composition difference between the front and back surfaces of the glass ribbon during molding, and it becomes easy to form a glass plate that is unpolished and has good surface quality. As a result, the manufacturing cost of the light guide plate is low. And uniform brightness characteristics. The reason for this is that, in the case of the overflow downdraw method, the surface to be the surface does not come into contact with the bowl-like refractory and is molded in a free surface state. The structure and material of the bowl-shaped structure are not particularly limited as long as desired dimensions and surface quality can be realized. Moreover, in order to perform the downward extending | stretching shaping | molding, the method of applying force with respect to a glass ribbon will not be specifically limited if a desired dimension and surface quality are realizable. For example, a method may be adopted in which a heat-resistant roll having a sufficiently large width is rotated and stretched in contact with the glass ribbon, or a plurality of pairs of heat-resistant rolls are only near the end face of the glass ribbon. You may employ | adopt the method of making it contact and extending | stretching.

In addition to the overflow downdraw method, the glass plate can be formed by a slot downdraw method, a float method, a rollout method, a redraw method, or the like. In the float process, a temperature difference and a composition difference between the front and back surfaces of the glass ribbon are likely to occur during molding. However, if the temperature control during the molding is strictly performed, the temperature difference and the composition difference can be reduced.

The light guide plate of the present invention (first invention) preferably includes a reflective film on one surface (light reflecting surface) side, and includes a diffusion film on the other surface (light emitting surface) side. preferable. In this way, it becomes easy to make the luminance characteristics of the display device uniform.

The edge light type surface light emitting device of the present invention (the first present invention) includes the light guide plate described above. In addition, the edge light type surface light emitting device of the present invention preferably includes a reflecting plate on one surface (light reflecting surface) side of the light guide plate, and diffuses on the other surface (light emitting surface) side of the light guiding plate. It is preferable to provide a plate. In this way, it becomes easy to make the luminance characteristics of the display device uniform.

The glass plate of the present invention (first invention) has an optical path length of 100 mm, a maximum transmittance of 50% or more in a wavelength range of 350 to 750 nm, and is characterized by being used for a light guide plate. Here, the technical features (preferable characteristics, effects, etc.) of the glass plate of the present invention are the same as the technical features of the light guide plate of the present invention. Therefore, detailed description is abbreviate | omitted about the glass plate of this invention.

The glass plate of the present invention (first present invention) can also be applied to a glass plate used for a display panel to have the function of a light guide plate. In this way, the member configuration of the display device can be simplified.

In the light guide plate of the present invention (second invention), the retardation of the glass plate at an optical path length of 50 mm is 30 nm or less, preferably 25 nm or less or 20 nm or less, particularly preferably 0.1 to 17.5 nm or less. . If the retardation is too large, it is difficult to make the luminance characteristics of the display device uniform.

In order to reduce the retardation of the glass plate, for example, when molten glass is formed into a glass ribbon in a molding furnace (molded body), the thickness of the end of the glass ribbon is substantially the same as the thickness of the central portion of the glass ribbon. The glass ribbon may be cooled so that the temperature distribution in the width direction of the glass ribbon is as small as possible when the glass ribbon is slowly cooled (cooled) in a slow cooling furnace.

In the molding process, the reason for forming the glass ribbon so that the thickness of the end of the glass ribbon is substantially the same as the thickness of the center of the glass ribbon is that the thickness of the end of the glass ribbon is different from the thickness of the center of the glass ribbon. In the cooling process after molding, the cooling rate is different between the end and the center of the glass ribbon, and as a result, the retardation increases. For example, when the rotational speed of a forming roll or the like for drawing molten glass into a glass ribbon is adjusted, the thickness of the end portion of the glass ribbon and the thickness of the center portion of the glass ribbon are easily made uniform.

Moreover, in the cooling process in a slow cooling furnace, the following method is mentioned as a method of making temperature distribution in the width direction of a glass ribbon as small as possible.
(1) The number of heaters is increased so that the glass ribbon is uniformly heated, and the temperature difference between the heaters is reduced as much as possible. For example, the temperature difference between the heaters is regulated within ± 1 ° C.
(2) A soaking plate is installed between the heater and the glass ribbon so that the heat from the heater is uniformly transmitted to the glass ribbon.
(3) An enclosure is installed at the end of the glass ribbon or a large number of heaters are arranged at the end so that the difference in the cooling rate between the center and the end of the glass ribbon is reduced.
(4) Lower (slow) the drawing speed.

Unlike the float method, the overflow downdraw method always increases the low temperature air flow along the surface of the glass ribbon in the direction from the cutting process, which is a low temperature atmosphere, to the slow cooling furnace and the forming furnace, which is a high temperature atmosphere. After the air flow is heated inside a slow cooling furnace or the like, a part of the air leaks into the external atmosphere through a gap in the peripheral wall portion, so that the atmospheric temperature of the slow cooling furnace or the molding furnace is likely to fluctuate. As a result, the glass plate formed by the overflow downdraw method tends to have a large retardation. Therefore, when forming a glass plate by the overflow down draw method, in addition to making the end portions and the center portion of the glass ribbon substantially the same thickness, and reducing the temperature distribution in the width direction of the glass ribbon, a slow cooling furnace It is preferable to suppress an increase in the low-temperature air flow in the molding furnace.

In order to suppress the rise in the low-temperature air flow in the slow cooling furnace or the forming furnace, for example, a convection prevention plate is provided in the slow cooling furnace or the air pressure in the external atmosphere of the forming furnace or the slow cooling furnace is adjusted using a blower or the like. The air in the molding furnace or the slow cooling furnace may be made difficult to leak into the external atmosphere.

In addition to the above method, increase the content of SiO ₂ , Al ₂ O ₃ , B ₂ O _{3 in} the glass composition to decrease the thermal expansion coefficient or increase the content of alkaline earth metal oxides If the photoelastic constant is lowered, the retardation of the glass plate tends to be lowered.

In the light guide plate of the present invention (second invention), the size of at least one side of the glass plate is preferably 1000 mm or more, 1500 mm or more, 2000 mm or more, or 2500 mm or more, particularly preferably 3000 mm or more. In this way, it is possible to satisfy the demand for an increase in the size of the display device.

The strain point of the glass plate is preferably 550 ° C. or higher, 580 ° C. or higher, 600 ° C. or higher, 615 ° C. or higher, 630 ° C. or higher, or 640 ° C. or higher, particularly preferably 650 ° C. or higher. If the strain point is too low, the heat resistance of the glass plate is likely to be lowered. For example, when a reflective film, a diffusion film, or the like is formed on the surface of the glass plate at a high temperature, the glass plate is likely to be thermally deformed.

The glass plate has a glass composition of mass%, SiO ₂ 40 to 70%, Al ₂ O ₃ 2 to 25%, B ₂ O ₃ 0 to 20%, R ₂ O (R is one of Li, Na and K) (Or two or more) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 10%, ZrO ₂ 0 to 10% Is preferred. The reason why the content of each component is regulated as described above will be described below. In addition, in description of the containing range of each component,% display means the mass%.

SiO ₂ is a component that becomes a glass network former, and is a component that lowers the thermal expansion coefficient to reduce dimensional change and retardation due to heat. It is a component that increases acid resistance and strain point. The content of SiO ₂ is preferably 40 to 70% or 50 to 67%, particularly preferably 57 to 64%. When the content of SiO ₂ is increased, the high temperature viscosity is increased, the meltability is lowered, and the devitrification blisters of cristobalite are liable to precipitate at the time of molding. On the other hand, when the content of SiO ₂ decreases, the thermal expansion coefficient increases, and the dimensional change and retardation due to heat tend to increase. In addition, acid resistance and strain point are likely to be lowered.

Al ₂ O ₃ is a component that lowers the coefficient of thermal expansion and reduces dimensional changes and retardation due to heat. It also has the effect of increasing the strain point and suppressing the precipitation of devitrified cristobalite during molding. The content of Al ₂ O ₃ is preferably 2 to 25% or 10 to 20%, particularly preferably 14 to 17%. When the content of Al ₂ O ₃ increases, the liquidus temperature rises and it becomes difficult to form a glass plate. On the other hand, when the content of Al ₂ O ₃ decreases, the thermal expansion coefficient increases, and the dimensional change and retardation due to heat tend to increase. In addition, the strain point tends to decrease.

B ₂ O ₃ is a component that acts as a flux, lowers the high temperature viscosity, and improves the meltability. Moreover, it is a component which reduces a thermal expansion coefficient and reduces the dimensional change and retardation by a heat | fever. The content of B ₂ O ₃ is preferably 0 to 20% or 5 to 15%, particularly preferably 7.5 to 12%. When the content of B ₂ O ₃ is increased, the strain point and acid resistance are likely to be lowered. On the other hand, when the content of B ₂ O ₃ decreases, the thermal expansion coefficient increases, and the dimensional change and retardation due to heat tend to increase. In addition, the meltability tends to be lowered.

R ₂ O is a component that lowers the high temperature viscosity and improves the meltability. The content of R ₂ O is preferably 0 to 25% or 0 to 20%, particularly preferably 0 to 15%. As the R ₂ O content increases, the strain point tends to decrease. From the viewpoint of reducing the thermal expansion coefficient, it is preferable to reduce the content of R ₂ O as much as possible, and the content is preferably 5% or less or 1% or less, particularly preferably 0.5% or less. The contents of Li ₂ O, Na ₂ O, and K ₂ O are also preferably 5% or less or 1% or less, particularly preferably 0.5% or less, respectively.

MgO is a component that improves the meltability by lowering only the high temperature viscosity without lowering the strain point. It is also a component that lowers the photoelastic constant. The content of MgO is preferably 0 to 10% or 0 to 5%, particularly preferably 0 to 3.5%. When the content of MgO is increased, devitrification beads are likely to precipitate during molding.

CaO is a component that improves the meltability by lowering only the high temperature viscosity without lowering the strain point. It is also a component that lowers the photoelastic constant. The content of CaO is preferably 0 to 15% or 2 to 12%, particularly preferably 3.5 to 10%. When there is too much content of CaO, devitrification will become easy to precipitate at the time of fabrication.

SrO is a component that improves chemical resistance and devitrification resistance. It is also a component that lowers the photoelastic constant. The content of SrO is preferably 0 to 10% or more than 0.5 to 8%, particularly preferably 1 to 8%. When the SrO content is increased, the coefficient of thermal expansion is increased, and dimensional change and retardation due to heat are likely to increase.

BaO is a component that increases chemical resistance and devitrification resistance in the same manner as SrO. It is also a component that lowers the photoelastic constant. The content of BaO is preferably 0 to 15% or 0 to 10%, particularly preferably 0.1 to 8%. When the content of BaO increases, the density increases and the thermal expansion coefficient increases, and the dimensional change and retardation due to heat tend to increase. In addition, the meltability tends to be lowered.

In the light guide plate of the present invention (second invention), the glass plate is preferably formed by an overflow down draw method. In this way, it is difficult to produce a temperature difference and composition difference between the front and back surfaces of the glass ribbon during molding, and it becomes easy to form a glass plate that is unpolished and has good surface quality. As a result, the manufacturing cost of the light guide plate is low. And uniform brightness characteristics. The reason for this is that, in the case of the overflow downdraw method, the surface to be the surface does not come into contact with the bowl-like refractory and is molded in a free surface state. The structure and material of the bowl-shaped structure are not particularly limited as long as desired dimensions and surface quality can be realized. Moreover, in order to perform the downward extending | stretching shaping | molding, the method of applying force with respect to a glass ribbon will not be specifically limited if a desired dimension and surface quality are realizable. For example, a method may be adopted in which a heat-resistant roll having a sufficiently large width is rotated and stretched in contact with the glass ribbon, or a plurality of pairs of heat-resistant rolls are only near the end face of the glass ribbon. You may employ | adopt the method of making it contact and extending | stretching.

The light guide plate of the present invention (second invention) preferably includes a reflective film on one surface (light reflecting surface) side, and includes a diffusion film on the other surface (light emitting surface) side. preferable. In this way, it becomes easy to make the luminance characteristics of the display device uniform.

An edge light type surface light emitting device according to the present invention (second present invention) includes the light guide plate described above. In addition, the edge light type surface light emitting device of the present invention preferably includes a reflecting plate on one surface (light reflecting surface) side of the light guide plate, and diffuses on the other surface (light emitting surface) side of the light guiding plate. It is preferable to provide a plate. In this way, it becomes easy to make the luminance characteristics of the display device uniform.

The glass plate of the present invention (second invention) has a retardation at an optical path length of 50 mm of 30 nm or less, and is used for a light guide plate. Here, the technical features (preferable characteristics, effects, etc.) of the glass plate of the present invention are the same as the technical features of the light guide plate of the present invention. Therefore, detailed description is abbreviate | omitted about the glass plate of this invention.

The glass plate of the present invention (second present invention) can also be applied to a glass plate used for a display panel to have the function of a light guide plate. In this way, the member configuration of the display device can be simplified.

Hereinafter, the present invention (first invention) will be described in detail based on examples. The following examples are merely illustrative. The present invention (first invention) is not limited to the following examples.

Example 1
First, the glass composition is glass so that it contains 60% SiO ₂ , 15% Al ₂ O ₃ , 10% B ₂ O ₃ , 1% MgO, 8% CaO, 5% SrO, and 1% BaO. After mixing and mixing the raw materials, the raw glass was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass was formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 2200 mm × 1950 mm × thickness 1.1 mm, and the surface roughness Ra of the end face was 0.5 μm. The glass plate was obtained by polishing. As in the content of _Fe 2 _{O 3} of the glass plate in is 0.013 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Fe 2 _{O 3,} the glass plates A glass production facility designed so that coloring components such as Fe ₂ O ₃ were not mixed into the glass from the production facility was used. Further, as the content of _Cr 2 _{O 3} of the glass plate in it is 0.0005% by mass, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Cr 2 _{O 3,} the glass plates Glass manufacturing equipment designed so that coloring components such as Cr ₂ O ₃ were not mixed into the glass from the manufacturing equipment was used.

A sample for measuring the thermal expansion coefficient was prepared from the obtained glass plate, and the average thermal expansion coefficient at 30 to 380 ° C. was measured based on JIS R3102 using a dilatometer. As a result, the thermal expansion coefficient was 38 × 10 ⁻⁷ / ° C.

A glass block having a size of 25 mm × 25 mm × 100 mm was obtained by collecting glass dough from the saddle portion of the bowl-shaped refractory used in the overflow downdraw method and performing a predetermined slow cooling treatment and processing. Next, after optically polishing the surface of the obtained glass block, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm was measured using UV-3100PC manufactured by Shimadzu Corporation. As a result, the maximum transmittance was 82% in an optical path length of 100 mm and a wavelength range of 350 to 750 nm. FIG. 2 shows measurement data of the transmittance of the glass plate according to Example 1 in an optical path length of 100 mm and a wavelength range of 350 to 750 nm.

From the above results, it is considered that the light guide plate having this glass plate is less likely to undergo dimensional changes with increasing temperature and can improve the luminance characteristics of the display device.

(Example 2)
First, as a glass composition, glass contains 60% SiO ₂ , 19% Al ₂ O ₃ , 7% B ₂ O ₃ , 3% MgO, 5% CaO, 1% SrO, and 5% BaO. After mixing and mixing the raw materials, the raw glass was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass was formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 2200 mm × 1950 mm × thickness 1.1 mm, and the surface roughness Ra of the end face was 0.5 μm. The glass plate was obtained by polishing. As in the content of _Fe 2 _{O 3} of the glass plate in is 0.009 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Fe 2 _{O 3,} the glass plates A glass production facility designed so that coloring components such as Fe ₂ O ₃ were not mixed into the glass from the production facility was used. Further, as the content of _Cr 2 _{O 3} of the glass plate in is 0.0003 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Cr 2 _{O 3,} the glass plates Glass manufacturing equipment designed so that coloring components such as Cr ₂ O ₃ were not mixed into the glass from the manufacturing equipment was used.

A glass block having a size of 25 mm × 25 mm × 100 mm was obtained by collecting glass dough from the saddle portion of the bowl-shaped refractory used in the overflow downdraw method and performing a predetermined slow cooling treatment and processing. Next, after optically polishing the surface of the obtained glass block, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm was measured using UV-3100PC manufactured by Shimadzu Corporation. As a result, the maximum transmittance was 84% in an optical path length of 100 mm and a wavelength range of 350 to 750 nm. FIG. 2 shows measurement data of transmittance of the glass plate according to Example 2 in an optical path length of 100 mm and a wavelength range of 350 to 750 nm.

Example 3
First, as a glass composition, it contains SiO ₂ 62%, Al ₂ O ₃ 18%, B ₂ O ₃ 0.5%, MgO 3%, Na ₂ O 14.5%, K ₂ O 2% by mass%. Thus, after glass material was prepared and mixed, it was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass is formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 1800 mm × 1500 mm × thickness 1.1 mm, and the surface roughness Ra of the end face is 0.5 μm. The glass plate was obtained by polishing. As in the content of _Fe 2 _{O 3} of the glass plate in is 0.006 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Fe 2 _{O 3,} the glass plates A glass production facility designed so that coloring components such as Fe ₂ O ₃ were not mixed into the glass from the production facility was used. Further, as the content of _Cr 2 _{O 3} of the glass plate in it is 0.00015 wt%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Cr 2 _{O 3,} the glass plates Glass manufacturing equipment designed so that coloring components such as Cr ₂ O ₃ were not mixed into the glass from the manufacturing equipment was used.

A sample for measuring the thermal expansion coefficient was prepared from the obtained glass plate, and the average thermal expansion coefficient at 30 to 380 ° C. was measured based on JIS R3102 using a dilatometer. As a result, the thermal expansion coefficient was 91 × 10 ⁻⁷ / ° C.

A glass block having a size of 25 mm × 25 mm × 100 mm was obtained by collecting glass dough from the saddle portion of the bowl-shaped refractory used in the overflow downdraw method and performing a predetermined slow cooling treatment and processing. Next, after optically polishing the surface of the obtained glass block, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm was measured using UV-3100PC manufactured by Shimadzu Corporation. As a result, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm was 80%. FIG. 2 shows measurement data of the transmittance of the glass plate according to Example 3 in an optical path length of 100 mm and a wavelength range of 350 to 750 nm. *

Example 4
First, the glass composition is glass so that it contains 60% SiO ₂ , 15% Al ₂ O ₃ , 10% B ₂ O ₃ , 1% MgO, 8% CaO, 5% SrO, and 1% BaO. After mixing and mixing the raw materials, the raw glass was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass is formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 2200 mm × 1950 mm × thickness 1.8 mm, and the end surface roughness Ra is 0.5 μm. The glass plate was obtained by polishing. As in the content of _Fe 2 _{O 3} of the glass plate in becomes 0.005 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Fe 2 _{O 3,} the glass plates A glass production facility designed so that coloring components such as Fe ₂ O ₃ were not mixed into the glass from the production facility was used. Further, as the content of _Cr 2 _{O 3} of the glass plate in is 0.0001 mass%, as a glass raw material, the use of high-purity glass material colored impurities is small, such as _Cr 2 _{O 3,} the glass plates Glass manufacturing equipment designed so that coloring components such as Cr ₂ O ₃ were not mixed into the glass from the manufacturing equipment was used.

8 sheets of the obtained glass plate were cut out to a size of 1.8 mm × 40 mm × 100 mm. Next, light from a light source is incident from a surface of 14.4 mm × 40 mm using a UV-3100PC manufactured by Shimadzu Corporation with the 8 glass plates stacked in a block shape of 14.4 mm × 40 mm × 100 mm. The maximum transmittance was measured at an optical path length of 100 mm and a wavelength range of 350 to 750 nm. As a result, the maximum transmittance in an optical path length of 100 mm and a wavelength range of 350 to 750 nm was 85%. FIG. 3 shows measurement data of transmittance of the glass plate according to Example 4 in an optical path length of 100 mm and a wavelength range of 350 to 750 nm.

Next, the present invention (second invention) will be described in detail based on examples. The following examples are merely illustrative. The present invention (second invention) is not limited to the following examples.

(Example 5)
First, the glass composition is glass so that it contains 60% SiO ₂ , 15% Al ₂ O ₃ , 10% B ₂ O ₃ , 1% MgO, 8% CaO, 5% SrO, and 1% BaO. After mixing and mixing the raw materials, the raw glass was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass was formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 2200 mm × 1950 mm × thickness 1.1 mm, and the surface roughness Ra of the end face was 0.5 μm. The glass plate was obtained by polishing. During molding and slow cooling, the temperature distribution between each heater is controlled within ± 1 ° C, and the atmospheric pressure in the external atmosphere of the molding furnace and slow cooling furnace is controlled to suppress the generation of ascending airflow. did.

From the obtained glass plate, measurement samples of thermal expansion coefficient and strain point were prepared, and each measurement was performed. As a result, the strain point was 650 ° C. and the thermal expansion coefficient was 38 × 10 ⁻⁷ / ° C. The thermal expansion coefficient is a value obtained by measuring an average thermal expansion coefficient at 30 to 380 ° C. based on JIS R3102 using a dilatometer. The strain point is a value measured based on JIS R3103.

The obtained glass plate was further cut into dimensions of 50 mm × 50 mm × thickness 1.1 mm, and the opposite end surfaces were mirror-polished. Next, the retardation at an optical path length of 50 mm was measured by the optical heterodyne method using PEL-3A-XR manufactured by UNIOPT. During the measurement, laser light was irradiated perpendicularly to the optically polished end face. As a result, the retardation was 17.3 nm.

From the above results, it is considered that the light guide plate having this glass plate is less likely to undergo a dimensional change with increasing temperature and can make the luminance characteristics of the display device uniform.

(Example 6)
First, as a glass composition, it contains SiO ₂ 62%, Al ₂ O ₃ 18%, B ₂ O ₃ 0.5%, MgO 3%, Na ₂ O 14.5%, K ₂ O 2% by mass%. Thus, after glass material was prepared and mixed, it was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass is formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 1800 mm × 1500 mm × thickness 1.1 mm, and the surface roughness Ra of the end face is 0.5 μm. The glass plate was obtained by polishing. During molding and slow cooling, the temperature distribution between each heater is controlled within ± 1 ° C, and the atmospheric pressure in the external atmosphere of the molding furnace and slow cooling furnace is controlled to suppress the generation of ascending airflow. did.

From the obtained glass plate, measurement samples of thermal expansion coefficient and strain point were prepared, and each measurement was performed. As a result, the strain point was 560 ° C. and the thermal expansion coefficient was 91 × 10 ⁻⁷ / ° C. The thermal expansion coefficient is a value obtained by measuring an average thermal expansion coefficient at 30 to 380 ° C. based on JIS R3102 using a dilatometer. The strain point is a value measured based on JIS R3103.

The obtained glass plate was further cut into dimensions of 50 mm × 50 mm × thickness 1.1 mm, and the opposite end surfaces were mirror-polished. Next, the retardation at an optical path length of 50 mm was measured by the optical heterodyne method using PEL-3A-XR manufactured by UNIOPT. During the measurement, laser light was irradiated perpendicularly to the optically polished end face. As a result, the retardation was 18 nm.

(Comparative example)
First, the glass composition is glass so that it contains 60% SiO ₂ , 15% Al ₂ O ₃ , 10% B ₂ O ₃ , 1% MgO, 8% CaO, 5% SrO, and 1% BaO. After mixing and mixing the raw materials, the raw glass was melted at a maximum temperature of 1650 ° C. in a continuous melting furnace to obtain molten glass. Next, the obtained molten glass was formed into a plate shape by the overflow down draw method, and then slowly cooled, then cut into dimensions of 2200 mm × 1950 mm × thickness 1.1 mm, and the surface roughness Ra of the end face was 0.5 μm. The glass plate was obtained by polishing. During molding and slow cooling, the temperature distribution between the heaters was not strictly controlled, and the ascending air current was not suppressed.

The obtained glass plate was further cut into dimensions of 50 mm × 50 mm × thickness 1.1 mm, and the opposite end surfaces were mirror-polished. Next, the retardation at an optical path length of 50 mm was measured by the optical heterodyne method using PEL-3A-XR manufactured by UNIOPT. During the measurement, laser light was irradiated perpendicularly to the optically polished end face. As a result, the retardation was 39.4 nm.

From the above results, it is considered that the light guide plate having this glass plate is likely to undergo dimensional changes as the temperature rises and the luminance characteristics of the display device are likely to be non-uniform.

DESCRIPTION OF SYMBOLS 1 Edge light type surface emitting device 2 Light source 3 Light guide plate 4 Reflection plate 5 Diffusing plate 6 Light reflection surface 7 Light emission surface

Claims

A light guide plate having at least a glass plate, an optical path length of 100 mm, and a maximum transmittance of 50% or more in a wavelength range of 350 to 750 nm.
The light guide plate according to claim 1, wherein the content of Fe 2 O 3 in the glass plate is 0.1% by mass or less.
The light guide plate according to claim 1 or 2, wherein a dimension of at least one side of the glass plate is 1000 mm or more.
The light guide plate according to any one of claims 1 to 3, wherein the surface roughness Ra of the end face of the glass plate is 2 µm or less.
5. The light guide plate according to claim 1, wherein the glass plate has a thermal expansion coefficient of 120 × 10 −7 / ° C. or less.
The glass plate has a glass composition of 40% by mass to SiO 2 40 to 70%, Al 2 O 3 2 to 25%, B 2 O 3 0 to 20%, R 2 O (R is one of Li, Na, and K) Or 2 or more types) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 10%, ZrO 2 0 to 10%, Fe 2 O 3 0.001 the light guide plate according to any one of claims 1 to 5, characterized in that it contains 0.1%.
The light guide plate according to any one of claims 1 to 6, wherein the glass plate is formed by an overflow down draw method.
The light guide plate according to any one of claims 1 to 7, wherein the light guide plate is used for an edge light type surface light emitting device.
An edge light type surface light emitting device comprising the light guide plate according to any one of claims 1 to 7.
A glass plate having an optical path length of 100 mm, a maximum transmittance of 50% or more in a wavelength range of 350 to 750 nm, and being used for a light guide plate.
A light guide plate having at least a glass plate and a retardation of the glass plate at an optical path length of 50 mm of 30 nm or less.
The light guide plate according to claim 11, wherein a dimension of at least one side of the glass plate is 1000 mm or more.
The light guide plate according to claim 11 or 12, wherein the surface roughness Ra of the end face of the glass plate is 2 µm or less.
14. The light guide plate according to claim 11, wherein the glass plate has a thermal expansion coefficient of 120 × 10 −7 / ° C. or less.
The light guide plate according to any one of claims 11 to 14, wherein the strain point of the glass plate is 550 ° C or higher.
The glass plate has a glass composition of 40% by mass to SiO 2 40 to 70%, Al 2 O 3 2 to 25%, B 2 O 3 0 to 20%, R 2 O (R is one of Li, Na, and K) (Or two or more) 0 to 25%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 15%, ZnO 0 to 10%, ZrO 2 0 to 10% The light guide plate according to any one of claims 11 to 15, wherein:
The light guide plate according to any one of claims 11 to 16, wherein the glass plate is formed by an overflow downdraw method.
The light guide plate according to any one of claims 11 to 17, wherein the light guide plate is used in an edge light type surface light emitting device.
An edge light type surface light emitting device comprising the light guide plate according to any one of claims 11 to 17.
A glass plate having a retardation of 30 nm or less at an optical path length of 50 mm and being used for a light guide plate.