TW201837366A - Light guide plate - Google Patents

Abstract

This light guide plate according to the present invention is characterized by at least including a glass plate, wherein: said glass plate has a light path length of 200 mm and a maximum transmission factor of at least 80% in a wavelength range of 400-750 nm; and the glass composition of said glass plate has a degree of basicity of 0.56 or less.

Description

Light guide

The invention relates to a light guide plate, in particular to a light guide plate suitable for an edge light type surface light emitting device.

A liquid crystal display device is used in a liquid crystal television or the like. The liquid crystal display device includes a surface light emitting device and a liquid crystal panel disposed on a light emitting surface side of the surface light emitting device. As the surface emitting device, for example, a direct type and an edge type are known.

In the direct type surface emitting device, the light source is disposed on a back surface that is opposite to the light emitting surface. When a point light source such as a light emitting diode (Light Emitting Diode) is used as a light source, a plurality of LED wafers are required to compensate for the brightness, and unevenness in brightness characteristics becomes very large.

In this case, edge light type surface light emitting devices are becoming mainstream at present. The edge light type surface emitting device includes a light source such as an LED, a light guide plate, a reflection plate (or a reflection film), and the like. The light source is disposed on a side surface that is orthogonal to the light exit surface. The light guide plate is arranged to transmit light from the light source to the inside by total reflection and to cause the light to be emitted in a planar shape. As the light guide plate, a resin plate such as an acrylic resin is generally used. Recently, in order to suppress dimensional changes due to heat, a low-expansion glass plate is used as the light guide plate (see Patent Documents 1 to 4). The reflecting plate is arranged on a light reflecting surface opposite to the light emitting surface, and is arranged to reflect light transmitted through the light reflecting surface and to cause a display surface such as a liquid crystal panel to emit light. Further, in order to uniformly emit light on a display surface such as a liquid crystal panel, a diffusion plate (diffusion film) may be disposed on the light emitting surface side of the light guide plate.

FIG. 1 is a schematic 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 such as an LED 2, a light guide plate 3, a reflection plate 4, and a diffusion plate 5. The light from the light source 2 is incident from the end surface of the light guide plate 3 and propagates to the inside of the light guide plate 3. The light reaching the light reflecting surface 6 is reflected by the reflecting plate 4, proceeds toward the light emitting surface 7, and is diffused by the diffusion plate 5. As a result, a display surface of a liquid crystal panel or the like arranged above the diffusion plate 5 can be made to emit light uniformly. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2012-123933 [Patent Literature 2] Japanese Patent Laid-Open Publication No. 2012-138345 [Patent Literature 3] Japanese Patent Laid-Open Publication No. 2012-216523 [Patent Literature 4] Japanese Patent Special Publication No. 2012-216528

[Problems to be Solved by the Invention] In the case where a glass plate is used for a light guide plate, in order to improve the light scattering property of the light guide plate, a point is formed on any surface of the glass plate (normally, the surface facing the light emission surface). In some cases, the dot pattern is formed by irradiation of ultraviolet rays.

However, when the glass plate is irradiated with ultraviolet rays, the glass plate is colored, and the transmittance in the visible region decreases. If the transmittance in the visible region is reduced, when the light from the light source is incident from the end surface and penetrates to the light exit surface, the amount of light is weakened. As a result, the brightness characteristics of the display device are liable to decrease.

In order to suppress the coloration of glass plates caused by ultraviolet irradiation, a method for reducing the amount of impurities in Fe ₂ O ₃ is generally known. Fe ₂ O ₃ is an unavoidable impurity, so it is impossible to use even high-purity raw materials. Completely removed from glass composition.

The present invention has been made in view of the foregoing circumstances, and a technical problem thereof is to invent a light guide plate that is difficult to cause dimensional change due to heat, and that it is difficult to reduce the transmittance in the visible region even when irradiated with ultraviolet rays. [Means for solving problems]

As a result of diligent research, the present inventors have found that by using a glass plate with a high transmittance as a light guide plate and reducing the alkalinity of the glass composition of the glass plate, the technical problem can be solved, and the present invention is proposed . That is, the light guide plate of the present invention has at least a glass plate, and the highest transmittance of the glass plate in the optical path length of 200 mm and the wavelength range of 400 nm to 750 nm is 80% or more, and The alkalinity of the glass composition is 0.56 or less. Here, the "transmittance" can be measured by a commercially available transmittance measuring device, for example, UV-3100PC manufactured by Shimadzu Corporation, and unless specifically stated otherwise, it is calculated based on Equation 1. Internal transmittance.

[Number 1] logT _in = log (I ₁ / I ₀ ) -logR logT _in : internal transmittance (%) I ₀ : intensity of incident light (%) I ₁ : intensity of light after passing through a specific optical path length (%) R: attenuation rate of light caused by reflection (%)

The "basicity of the glass composition" is an index indicating the electron donating property of oxygen atoms in the glass, and is an index for evaluating the average Lewis basicity of the oxide ions in the glass. Specifically, it is a value calculated using the following formula 2.

[Number 2] Δ _cal : basicity Zi: atomic valence of cation i in glass ri: number of cation i when expressed by each oxygen γi: basicity moderating parameter

In addition, γi can be calculated by Pauling's degree of electronegativity χ and Equation 3.

[Equation 3] γi = 1.36 (χi-0.26)

The light guide plate of the present invention includes at least a glass plate. If a glass plate is used for the light guide plate instead of the resin plate, the difference in the dimensional change between the display panel and the light guide plate becomes smaller, so there is no need to provide a large gap in the frame portion of the liquid crystal display device. As a result, the liquid crystal display can be used. Display devices such as devices perform narrower bezels.

In the light guide plate of the present invention, the highest transmittance of the glass plate in an optical path length of 200 mm and a wavelength range of 400 nm to 750 nm is 80% or more. In this way, the brightness characteristics of the display device can be improved.

According to the investigation by the present inventors, when the alkalinity of the glass composition of the glass plate is high, the number of non-crosslinked oxygen in the glass mesh is increased, and the number of colored centers is increased. As a result, the glass plate is easily colored by ultraviolet irradiation, and the transmittance in the visible region is liable to decrease. Therefore, in the light guide plate of the present invention, the alkalinity of the glass composition of the glass plate is limited to 0.56 or less. This makes it difficult to reduce the transmittance in the visible region even when irradiated with ultraviolet rays.

In addition, the light guide plate of the present invention is preferably a glass plate containing 40% to 80% SiO ₂ , 0% to 20% Al ₂ O ₃ , 0% to 25% B ₂ O ₃ , and 0% by mass. ～ 25% Na ₂ O, 0% ～ 15% K ₂ O, 0% ～ 25% CaO, 0% ～ 25% SrO, 0% ～ 35% BaO, 0% ～ 0.5% SnO ₂ 0% to 0.5% of Sb ₂ O ₃ , and 0% to 0.5% of As ₂ O _{3 were} used as the glass composition. This makes it easy to increase the alkalinity of the glass composition of the glass plate.

In addition, the light guide plate of the present invention is preferably a glass plate having an average transmittance of 2 mm in the optical path length and a wavelength range of 400 nm to 750 nm as X (%), that is, glass immediately before the irradiation of the following ultraviolet rays. The average transmittance of the panel in the optical path length of 2 mm and the wavelength range of 400 nm to 750 nm is set to X (%), and it will be irradiated with ultraviolet light with an output power of 0.1 mW and a wavelength of 185 nm for 12 hours, an output power of 13.3 mW Ultraviolet light with a wavelength of 254 nm and an output power of 0.4 mW and ultraviolet light with a wavelength of 365 nm have a glass path length of 2 mm and an average transmittance in a wavelength range of 400 nm to 750 nm is set to Y (%), which satisfies XY <1% relationship.

In addition, the light guide plate of the present invention is preferably a glass plate having a difference between a maximum transmittance and a minimum transmittance in a wavelength range of 200 mm and a wavelength range of 400 nm to 750 nm of 10% or less. In this way, the brightness characteristics of the display device can be improved.

In the light guide plate of the present invention, the content of Fe ₂ O ₃ in the glass plate is preferably 100 mass ppm or less. In this way, it is possible to increase the optical path length of the glass plate by 200 mm and the highest transmittance in the visible region. Fe ₂ O ₃ exists in the state of Fe ³⁺ or Fe ²⁺ in the glass. Fe ³⁺ has an absorption peak near a wavelength of 380 nm, and decreases the transmittance in the ultraviolet region and the visible region on the short wavelength side. Fe ²⁺ has an absorption peak near a wavelength of 1080 nm, and decreases the transmittance in the visible region on the long wavelength side. Therefore, as the content of Fe ₂ O ₃ increases, the highest transmittance in the visible region tends to decrease. In general, a glass plate is mixed with a large amount of Fe ₂ O ₃ from a glass raw material or a manufacturing step. Since the conventional glass plate has a large content of Fe ₂ O ₃ , it is difficult to improve the brightness characteristics of a display device. Therefore, if the content of Fe ₂ O ₃ in the glass plate is limited to 100 mass ppm or less, the brightness characteristics of the display device can be improved. The "Fe ₂ O ₃ " in the present invention includes divalent iron oxide and trivalent iron oxide, and the divalent iron oxide is converted to Fe ₂ O ₃ and processed. The other oxides are treated similarly based on the expressed oxides.

In addition, the light guide plate of the present invention preferably has a dot pattern formed on at least one surface of the glass plate.

In addition, in the light guide plate of the present invention, the thermal expansion coefficient of the glass plate is preferably 120 × 10 ^-7 / ° C or lower. Here, the "thermal expansion coefficient" refers to a value obtained by measuring an average thermal expansion coefficient at 30 ° C to 380 ° C based on JIS R3102 using a dilatometer.

In addition, the light guide plate of the present invention is preferably used in an edge light type surface emitting device.

FIG. 2 is a conceptual perspective view showing an example of a light guide plate of the present invention. As shown in FIG. 2, the light guide plate 10 includes a glass plate 11. The light from the light source 12 is incident from the end surface 13 of the glass plate 11, propagates inside the glass plate 11, and exits from the light exit surface. Here, the highest transmittance of the glass plate 11 in a 200 mm optical path length and a wavelength range of 400 nm to 750 nm is 80% or more, and the basicity of the glass composition of the glass plate 11 is 0.56 or less. A dot pattern 15 is formed on the light reflecting surface 14 of the glass plate 11. The dot diameter of the dot pattern 15 gradually increases from the end surface 13 to the end surface 16. With this dot pattern 15, the light emitted from the light emitting surface is uniformized in the plane. Furthermore, a reflection layer 19 is formed on each of the end surface 16, the end surface 17, and the end surface 18 of the glass plate. The light reaching the end face 16, end face 17, and end face 18 of the glass plate is reflected by the reflective layer 19, returns to the inside of the glass plate 11, and finally exits from the light exit surface.

In addition, a plurality of glass plates 11 according to the present invention may be bonded and used. For example, two glass plates 11 are prepared. A reflective layer is not formed on the end surface 17 of one of the glass plates 11 and a reflective layer is not formed on the end surface 18 of the other glass plate 11. The end faces of which the reflection layer is not formed are bonded to each other, whereby a large area light guide plate can be manufactured.

The light guide plate of the present invention preferably includes at least a glass plate having the following characteristics.

The highest transmittance of a glass plate with a 200 mm optical path length and a wavelength range of 400 nm to 750 nm is 80% or more, preferably 82% or more, 84% or more, 85% or more, 86% or more, 87% or more, Particularly good is over 88%. If the optical path length is 200 mm and the highest transmittance in the wavelength range of 400 nm to 750 nm is too low, the brightness characteristics of the display device tends to decrease.

The alkalinity of the glass composition of the glass plate is 0.56 or less, preferably 0.55 or less, 0.54 or less, 0.53 or less, 0.52 or less, and 0.51 or less, particularly preferably 0.30 to 0.50. When the alkalinity of the glass composition of a glass plate is too high, the transmittance will fall easily by irradiation of an ultraviolet-ray, and the brightness characteristic of a display device will fall easily.

It is preferable that the average transmittance of the glass plate with an optical path length of 2 mm and a wavelength range of 400 nm to 750 nm be set to X (%), and ultraviolet rays with an output power of 0.1 mW and a wavelength of 185 nm be simultaneously irradiated for 12 hours. The average transmittance of a glass plate with an output power of 13.3 mW and a wavelength of 254 nm and an output power of 0.4 mW and a wavelength of 365 nm is 2 mm in optical path length and 400 nm to 750 nm. %), The relationship of XY <1% is satisfied, and further preferably XY is less than 0.9%, less than 0.8%, less than 0.7%, less than 0.6%, less than 0.5%, and particularly preferably less than 0.4%. If the transmittance difference before and after the ultraviolet irradiation is too large, it becomes difficult to secure the brightness characteristics of the display device.

The content of Fe ₂ O ₃ in the glass plate is preferably 100 mass ppm or less, 70 mass ppm or less, 50 mass ppm or less, 40 mass ppm or less, and 30 mass ppm or less, and particularly preferably 5 to 25 mass ppm. When the content of Fe ₂ O ₃ is too large, the highest transmittance in the visible region tends to decrease. Furthermore, when the content of Fe ₂ O ₃ is too small, the raw material cost and the manufacturing cost of the glass plate increase.

The content of Cr ₂ O ₃ in the glass plate is preferably less than 10 mass ppm, 8 mass ppm or less, 6 mass ppm or less, 0.1 mass ppm to 5 mass ppm, 0.2 mass ppm to 4 mass ppm, and particularly preferably 0.3 mass. ppm to 3 mass ppm. When the content of Cr ₂ O ₃ is too large, the highest transmittance in the visible region tends to decrease. Furthermore, when the content of Cr ₂ O ₃ is too small, the raw material cost and the manufacturing cost of the glass plate increase.

In order to eliminate the mixing of Fe ₂ O ₃ and Cr ₂ O ₃ as much as possible, only high-purity glass raw materials are used, or colored oxides such as Fe ₂ O ₃ and Cr ₂ O _{3 are used} . The manufacturing equipment designed by the method of mixing in may be sufficient.

The content of Rh ₂ O ₃ in the glass plate is preferably less than 1 mass ppm, 0.8 mass ppm or less, 0.6 mass ppm or less, 0.01 mass ppm to 0.5 mass ppm, 0.05 mass ppm to 0.4 mass ppm, and particularly preferably 0.1 mass. ppm to 0.3 mass ppm. When the content of Rh ₂ O ₃ is too large, the difference in transmittance between the highest transmittance and the lowest transmittance in the visible region is likely to be too large. Furthermore, when the content of Rh ₂ O ₃ is too small, it is difficult to use a high-strength Pt-Rh alloy in a glass manufacturing facility, and the manufacturing cost of a glass plate increases.

In order to reduce the content of Rh ₂ O ₃ as much as possible, as long as high-purity glass raw materials are used, or the glass manufacturing conditions are adjusted so as not to be mixed with Rh ₂ O ₃ , or the use of Pt-Rh alloy in glass manufacturing equipment is reduced, can.

Thermal expansion coefficient of the glass sheet is preferably 120 × 10 ^-7 / ℃ less, 95 × 10 ^-7 / ℃ less, 75 × 10 ^-7 / ℃ less, and particularly preferably ^{30 × 10 -7 / ℃ ~ 70} × 10 - ⁷ / ℃ or less. When the thermal expansion coefficient of a glass plate is too high, the difference of the dimensional change by the heat of a display panel and a light-guide plate will become large.

The strain point of the glass plate is preferably 400 ° C or higher, 420 ° C or higher, 440 ° C or higher, 460 ° C or higher, 480 ° C or higher, or 500 ° C or higher, and particularly preferably 520 ° C or higher. If the strain point is too low, the heat resistance of the glass plate is liable to decrease. For example, if a reflective 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 preferably contains 40% to 80% SiO ₂ , 0% to 20% Al ₂ O ₃ , 0% to 25% B ₂ O ₃ , and 0% to 25% Na ₂ O. 0% to 15% K ₂ O, 0% to 25% CaO, 0% to 25% SrO, 0% to 35% BaO, 0% to 0.5% SnO ₂ , 0% to 0.5% Sb ₂ O ₃ and 0% to 0.5% of As ₂ O _{3 were} used as the glass composition. The reasons for limiting the content of each component as described below are described below. In addition, in description of the content range of each component, the expression of% means the mass%.

SiO ₂ is a component that becomes a network-formed body of glass, and is a component that lowers the coefficient of thermal expansion and reduces dimensional changes due to heat. Moreover, it is a component which improves acid resistance and a strain point. The content of SiO ₂ is preferably 40% to 80%, 60% to 78%, and particularly preferably 67% to 77%. When the content of SiO ₂ decreases, the thermal expansion coefficient tends to increase, and the dimensional change due to heat tends to increase. In addition, acid resistance and strain points are liable to decrease. On the other hand, when the content of SiO ₂ is increased, the alkalinity is likely to decrease, the high-temperature viscosity is increased, the meltability is decreased, and the devitrified substances of the silicate are easily precipitated during molding.

Al ₂ O ₃ is a component that lowers the thermal expansion coefficient and reduces dimensional changes due to heat. In addition, it also has the effect of increasing the strain point or suppressing the precipitation of devitrified matter of aragonite during molding. When the content of Al ₂ O ₃ decreases, the thermal expansion coefficient tends to increase, and the dimensional change due to heat tends to increase. In addition, the strain point is liable to decrease. On the other hand, the content of Al ₂ O ₃ is preferably 0% to 20%, 1% to 15%, 2% to 12%, and particularly preferably 5% to 8%. When the content of Al ₂ O ₃ increases, the alkalinity tends to decrease, and the liquidus temperature rises, making it difficult to shape the glass plate.

B ₂ O ₃ is a component that functions as a flux and reduces high-temperature viscosity and improves 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 25%, 0% to 20%, 1% to 18%, 3% to 16%, and particularly preferably 5% to 15%. When the content of B ₂ O ₃ decreases, there is a tendency that the thermal expansion coefficient becomes higher and the dimensional change due to heat becomes larger. In addition, meltability is liable to decrease. On the other hand, when the content of B ₂ O ₃ is increased, the alkalinity is liable to decrease, and the strain point and the acid resistance are liable to decrease.

Na ₂ O is a component that increases alkalinity, and is a component that lowers high-temperature viscosity and improves meltability. The content of Na ₂ O is preferably 0% to 25%, 3% to 20%, 5% to 18%, 8% to 17%, 10% to 16%, and particularly preferably 12% to 15%. When the content of Na ₂ O decreases, the meltability tends to decrease. On the other hand, when the content of Na ₂ O is increased, there is a tendency that the thermal expansion coefficient becomes high and the dimensional change due to heat becomes large.

K ₂ O is a component that increases alkalinity and is a component that lowers high-temperature viscosity and improves meltability. The content of K ₂ O is preferably 0% to 15%, 0% to 10%, 0% to 8%, and particularly preferably 0% to 5%. When the content of K ₂ O decreases, the meltability tends to decrease. On the other hand, when the content of K ₂ O is increased, there is a tendency that the thermal expansion coefficient becomes higher and the dimensional change due to heat becomes larger.

MgO is a component that lowers the viscosity at high temperatures and improves the meltability. The content of MgO is preferably 0% to 10%, 0% to 6%, and particularly preferably 0% to 1%. When the content of MgO is too large, devitrified substances are liable to precipitate during the molding.

CaO is a component that increases alkalinity, and is a component that only lowers the high-temperature viscosity without improving the strain point and improves the meltability. The content of CaO is preferably 0% to 25%, 3% to 18%, 7% to 17%, and particularly preferably 11% to 15%. When the content of CaO is too large, devitrified substances are liable to precipitate during molding.

SrO is a component that increases alkalinity and is a component that improves chemical resistance and devitrification resistance. The content of SrO is preferably 0% to 25%, 0% to 12%, and particularly preferably 0% to 5%. When the content of SrO is too large, there is a tendency that the density becomes high, or the thermal expansion coefficient becomes high, and the dimensional change due to heat becomes large. In addition, meltability is liable to decrease.

BaO is a component that increases alkalinity and is a component that improves chemical resistance and devitrification resistance. The content of BaO is preferably 0% to 35%, 0% to 30%, and particularly preferably 10% to 28%. When the content of BaO is increased, the density is increased, or the thermal expansion coefficient is increased, and the dimensional change due to heat tends to be increased. In addition, meltability is liable to decrease.

SnO ₂ is a component that functions as a fining agent. The content of SnO ₂ is preferably 0% to 0.5%, 0.01% to 0.5%, and particularly preferably 0.1% to 0.4%. When the content of SnO ₂ is too large, devitrified substances are liable to precipitate during molding.

The preferable contents of Fe ₂ O ₃ , Cr ₂ O ₃ and Rh ₂ O ₃ are as described above.

In addition to the components described above, other components may be introduced. For example, in order to lower the liquidus temperature, up to 3% of each of Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O ₅ , and P ₂ O ₅ may be introduced. In order to lower the melting temperature, up to 5% of each may also be introduced. Li ₂ O, Cs ₂ O, SO ₃ , F, Cl, etc. as fining agents in a total amount of 1%. As ₂ O ₃ and Sb ₂ O ₃ are environmentally-loaded substances. In addition, when a glass plate is formed by a float method, it is reduced in a floating bath and becomes a foreign metal substance. Therefore, it is preferable to avoid substantial Introducing, specifically, it is preferable to set the contents to 0.5% or less and 0.01% or less, respectively.

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, and 2500 mm or more, and particularly preferably 3000 mm or more. In this way, it is possible to meet the requirements for increasing the size of the display device.

The glass plate is preferably formed by an overflow down-draw method. In this way, it is difficult to produce a temperature difference between the front and back surfaces of the glass ribbon during molding, and the composition is poor, and it is easy to form a glass plate that has good surface quality without polishing. Homogenize. The reason is that in the case of the overflow down-draw method, the surface to be the surface is formed in a free surface state without contacting the flow channel-shaped refractory. The structure or material of the gutter-like structure is not particularly limited as long as it can achieve a desired size or surface quality. The method of applying a force to the glass ribbon in order to perform downward forming is not particularly limited as long as it can achieve a desired size or surface quality. For example, a method may be adopted in which a heat-resistant roller having a sufficiently large width is rotated while being brought into contact with the glass ribbon, and a plurality of pairs of heat-resistant rollers may be extended to contact only near the end surface of the glass ribbon. Methods.

In addition to the overflow down-draw method, the glass sheet may be formed by a flow-hole down method, a float method, a flattening method, a redraw method, and the like. Furthermore, in the float method, temperature difference and composition difference between the front and back surfaces of the glass ribbon are easily generated during molding. However, strict temperature control during molding can reduce the temperature difference and composition difference.

The light guide plate of the present invention preferably forms a dot pattern on at least one surface of the glass plate (preferably a surface facing the light emitting surface, that is, a light reflecting surface). When a dot pattern is formed on the surface of a glass plate, the air of a low refractive index can be made to contact between the points which comprise a dot pattern. Thereby, the total reflection condition can be satisfied, and light can be sufficiently transmitted to the inside of the glass plate. As a result, it is easy to make the light emitted from the light emitting surface uniform within the plane.

The diameter of the dots constituting the dot pattern is further preferably gradually increased as it moves away from the end surface where the light from the light source should be incident. In this way, it is easy to make the light emitted from the light emitting surface uniform within the plane. The dot pattern can be formed, for example, by printing a heat-resistant paint or glass frit on the surface of a glass plate and firing it.

The shape of the dots constituting the dot pattern is not particularly limited, and examples thereof include a circle, an oval, a square, a triangle, and a polygon. Among these, a shape having a circle as a point is preferable.

In the light guide plate of the present invention, the average surface roughness Ra of the end surface of the glass plate (preferably the end surface where the light from the light source should be incident) is preferably 0.5 μm or less, 0.3 μm or less, 0.2 μm or less, and particularly preferably 0.1 μm. the following. In this way, it is easy to reduce the loss of light when the light from the light source is incident on the end surface. In addition, it is easy to form a high-quality reflective layer on the end surface.

For example, if the end surface of the glass plate is polished with a # 2000 abrasive stone, the average surface roughness Ra of the end surface of the glass plate can be reduced as much as possible. In addition, if the end surface of the glass plate is etched, the average surface roughness Ra of the end surface of the glass plate can be reduced without causing abrasion damage.

It is preferable that the end surface of a glass plate does not have a chamfered part. In this way, it is easy to introduce light from the light source into the glass plate.

In the light guide plate of the present invention, it is preferable that a reflection layer is formed on all or a part of the end face other than the end face where the light from the light source should be incident, and it is particularly preferable that the end face other than the end face where the light from the light source should be incident has a reflection layer. Floor. In this way, it is difficult for the light propagating inside the glass plate to leak from the end surface. Furthermore, as the reflection layer, a reflection film may be directly formed on the end surface, or a reflection sheet may be attached to the end surface.

The light guide plate of the present invention is preferably provided with a diffusion plate on one surface (preferably a light emitting surface) side of the glass plate, and more preferably on one surface (preferably a surface facing the light emitting surface) side of the glass plate With reflector. In this way, it is easy to make the brightness characteristics of the display device uniform. [Example]

Hereinafter, the present invention will be described based on examples. The following examples are merely examples. The present invention is not limited in any way by the following examples.

Table 1 shows Examples (Sample No. 1 to Sample No. 6) and Comparative Examples (Sample No. 7) of the present invention.

[Table 1]

First, a glass ingredient prepared by blending glass raw materials so as to have a glass composition in a table is put into a platinum crucible, and then melted at 1200 ° C to 1450 ° C for 24 hours. When the glass ingredients are melted, they are stirred with a platinum stirrer for homogenization. Then, the molten glass was caused to flow out onto the carbon plate to be formed into a plate shape, and then cooled slowly at a temperature near the slow cooling point for 30 minutes. The obtained samples were evaluated for the coefficient of thermal expansion CTE, the strain point Ps, the optical path length 200 mm, and the highest transmittance in the wavelength range 400 nm to 750 nm and the optical path length 200 mm in the temperature range of 30 ° C to 380 ° C. And the lowest transmittance in the wavelength range of 400 nm to 750 nm and the optical path length of 200 mm and the highest transmittance in the wavelength range of 400 nm to 750 nm and the lowest transmittance in the wavelength range of 200 mm and the wavelength range of 400 nm to 750 nm Rate difference.

The coefficient of thermal expansion CTE in a temperature range of 30 ° C to 380 ° C is an average value measured using a dilatometer in accordance with JIS R3102. The strain point Ps is a value measured in accordance with JIS R3103.

The highest transmittance and lowest transmittance in an optical path length of 200 mm and a wavelength range of 400 nm to 750 nm are values measured using UV-3100PC manufactured by Shimadzu Corporation.

After measuring the average transmittance of a glass plate with an optical path length of 2 mm and a wavelength range of 400 nm to 750 nm, the UV irradiation was performed using an Eye UV-ozone cleaning device, and the output power was 0.1 mW and the wavelength was 185 nm for 12 hours. UV, output power of 13.3 mW and wavelength of 254 nm and output power of 0.4 mW and UV of 365 nm were measured, and the average transmittance of a glass plate with an optical path length of 2 mm and a wavelength range of 400 nm to 750 nm was measured. Then, the difference in average transmittance before and after ultraviolet irradiation was evaluated.

Based on the above results, since the transmittance in the visible region of Sample No. 1 to Sample No. 6 is high and the alkalinity of the glass composition is low, the difference in transmittance before and after ultraviolet irradiation is small. Therefore, Sample No. 1 to Sample No. 6 are considered to be suitable as light guide plates for edge-light-type surface-emitting devices. On the other hand, the glass composition of Sample No. 7 has high alkalinity, and therefore, the transmittance difference before and after ultraviolet irradiation is large.

1‧‧‧Edge light type surface light emitting device

2.12‧‧‧light source

3.10‧‧‧light guide plate

4‧‧‧ reflector

5‧‧‧ diffuser

6, 14‧‧‧ light reflecting surface

7‧‧‧ light exit surface

11‧‧‧ glass plate

13, 16 ～ 18‧‧‧ face

15‧‧‧dot pattern

19‧‧‧Reflective layer

FIG. 1 is a cross-sectional conceptual view showing an example of an edge-light-type surface light-emitting device. FIG. 2 is a conceptual perspective view showing an example of a light guide plate of the present invention.

Claims (8)

A light guide plate, characterized in that it has at least a glass plate, and the highest transmittance of the glass plate in a light path length of 200 mm and a wavelength range of 400 nm to 750 nm is 80% or more, and the glass of the glass plate The basicity of the composition is 0.56 or less. The light guide plate according to item 1 of the scope of patent application, wherein the glass plate contains 40% to 80% SiO ₂ , 0% to 20% Al ₂ O ₃ , and 0 to 25% B ₂ O in terms of mass%. ₃ , 0% to 25% Na ₂ O, 0% to 15% K ₂ O, 0% to 25% CaO, 0% to 25% SrO, 0% to 35% BaO, 0% to 0.5 % Of SnO ₂ , 0% to 0.5% of Sb ₂ O ₃ , and 0% to 0.5% of As ₂ O _{3 were} used as glass compositions. The light guide plate according to item 1 or item 2 of the scope of patent application, wherein the average transmittance of the glass plate in the optical path length of 2 mm and the wavelength range of 400 nm to 750 nm is set to X%, and simultaneous irradiation is performed. 12 hours of output power of 0.1 mW with ultraviolet wavelength of 185 nm, output power of 13.3 mW with ultraviolet wavelength of 254 nm and output power of 0.4 mW and ultraviolet wavelength of 365 nm with a glass path length of 2 mm and a wavelength range of 400 When the average transmittance in the range of nm to 750 nm is set to Y%, the relationship of XY <1% is satisfied. The light guide plate according to any one of claims 1 to 3, wherein the difference between the highest transmittance and the lowest transmittance of the glass plate in the optical path length of 200 mm and the wavelength range of 400 nm to 750 nm It is below 10%. The light guide plate according to any one of claims 1 to 4, wherein the content of Fe ₂ O ₃ in the glass plate is 100 mass ppm or less. The light guide plate according to any one of claims 1 to 5, wherein a dot pattern is formed on at least one surface of the glass plate. The light guide plate according to any one of claims 1 to 6, in which the thermal expansion coefficient of the glass plate is 120 × 10 ^-7 / ° C or lower. The light guide plate according to any one of claims 1 to 7 of the scope of patent application, which is used in an edge light type surface light emitting device.