JP7429093B2 - Light guide plate - Google Patents

Description

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

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

In the direct type surface emitting device, the light source is arranged on the back surface opposite to the light exit surface. When a point light source such as a light emitting diode is used as a light source, a large number of LED chips are required to compensate for brightness, resulting in very large variations in brightness.

Due to these circumstances, edge-light type surface emitting devices are currently the mainstream. An edge-light surface emitting device includes a light source such as an LED, a light guide plate, a reflective plate (or reflective film), and the like. The light source is arranged on a side surface perpendicular to the light exit surface. The light guide plate is arranged to propagate the light from the light source inside by total reflection and emit it in a planar shape. Generally, a resin plate such as an acrylic resin is used as a light guide plate, but recently, a low expansion glass plate is being used as a light guide plate (see Patent Documents 1 to 4). The reflecting plate is arranged on the light emitting surface and the light reflecting surface on the opposite side thereof, and is arranged to reflect the light passing through the light reflecting surface to cause a display surface such as a liquid crystal panel to emit light. Note that in order to uniformly emit light from a display surface of a liquid crystal panel or the like, 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 diagram showing an example of an edge-light surface emitting device 1. As shown in FIG. The edge light type surface 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 the end face of the light guide plate 3 and propagates inside the light guide plate 3. The light that has reached the light reflecting surface 6 is reflected by the reflecting plate 4, travels toward the light emitting surface 7, and is diffused by the diffusing plate 5. As a result, it becomes possible to uniformly emit light from the display surface of a liquid crystal panel or the like disposed above the diffuser plate 5.

Japanese Patent Application Publication No. 2012-123933 Japanese Patent Application Publication No. 2012-138345 JP2012-216523A JP2012-216528A

By the way, if a glass plate is used as the light guide plate instead of a resin plate, the difference in dimensional change between the display panel and the light guide plate becomes smaller, eliminating the need to provide a large gap in the frame of the liquid crystal display device. Display devices such as liquid crystal display devices can have narrower frames (see Patent Documents 1 to 4).

However, glass plates have a problem in that they absorb light in the visible range (wavelengths of 380 to 750 nm), leading to a decrease in brightness.

The main factor in light absorption is Fe ₂ O ₃ contained in the glass. Further, Fe ₂ O ₃ is an impurity that is inevitably mixed in from the introduced raw material. Therefore, it is not easy to remove Fe ₂ O ₃ from the glass composition.

The present invention has been made in view of the above circumstances, and its technical objective is to devise a light guide plate whose brightness is unlikely to decrease in the visible range even when a glass plate is used.

As a result of intensive studies, the present inventor found that the raw materials for introducing MgO and CaO contained a large amount of Fe ₂ O ₃ as an impurity, and also found that MgO and CaO were It has been discovered that the above technical problem can be solved by reducing the content ratio of , and this is proposed as the present invention. That is, the light guide plate of the present invention is a light guide plate having at least a glass plate, and the glass plate includes, as a glass composition, 55 to 80% by mass of SiO ₂ , 0 to 15% of Al ₂ O ₃ , and B. ₂ O ₃ 1-20%, Li ₂ O + Na ₂ O + K ₂ O 1-20%, MgO + CaO + SrO + BaO 0.1-10%, SnO ₂ 0-0.5%, Sb ₂ O ₃ 0-0.5%, Fe ₂ It is characterized by containing 0 to 0.005% (50 mass ppm or less) of O ₃ and having a mass ratio (MgO+CaO)/(Li ₂ O+Na ₂ O+K ₂ O+MgO+CaO+SrO+BaO) of less than 0.40. Here, " _Li2O + _Na2O + _K2O " refers to the total amount of _Li2O , _Na2O and _K2O . "MgO+CaO+SrO+BaO" refers to the total amount of MgO, CaO, SrO and BaO. "(MgO+CaO)/( _Li2O + _Na2O + _K2O +MgO+CaO+SrO+BaO)" is the value obtained by dividing the total amount of MgO and CaO by the total amount of _Li2O , _Na2O , K2O, _MgO , CaO, SrO, and BaO. refers to

The light guide plate of the present invention has at least a glass plate. If a glass plate is used instead of a resin plate for the light guide plate, the difference in dimensional change between the display panel and the light guide plate will be smaller, eliminating the need for a large gap in the frame of the liquid crystal display, and as a result, the liquid crystal display Display devices such as devices can have narrower frames.

Moreover, in the light guide plate of the present invention, the mass ratio (MgO+CaO)/(Li ₂ O+Na ₂ O+K ₂ O+MgO+CaO+SrO+BaO) of the glass plate is less than 0.40. In this way, it becomes difficult for Fe ₂ O ₃ impurities to be mixed in, so that the brightness of the display device can be increased.

Moreover, in the light guide plate of the present invention, the content of Fe ₂ O ₃ in the glass plate is 50 mass ppm or less. In this way, the optical path length of the glass plate is 200 mm, and the maximum transmittance in the visible range can be increased. 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 reduces transmittance in the ultraviolet region and visible region on the short wavelength side. Fe ²⁺ has an absorption peak near a wavelength of 1080 nm, and reduces 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 the visible range tends to decrease. Therefore, by regulating the content of Fe ₂ O ₃ in the glass plate to 50 mass ppm or less, the brightness of the display device can be increased. Note that "Fe ₂ O ₃ " as used in the present invention includes divalent iron oxide and trivalent iron oxide, and divalent iron oxide is treated in terms of Fe ₂ O ₃ . Other polyvalent oxides shall be treated in the same manner based on the indicated oxide.

Further, the light guide plate of the present invention has a glass plate in which the content of Cr ₂ O ₃ is 5 mass ppm or less, the content of TiO ₂ is 50 mass ppm or less, the content of Pt is 5 mass ppm or less, and the content of Rh is It is preferable that the amount is 5 ppm by mass or less. In this way, the transmittance in the visible range can be increased.

Further, in the light guide plate of the present invention, it is preferable that the basicity of the glass plate is 0.54 or less. In order to improve the light scattering properties of the light guide plate, a dot pattern is formed on one of the surfaces of the glass plate (usually the surface facing the light exit surface), and this dot pattern is formed by irradiation with ultraviolet rays. Sometimes. However, when a glass plate is irradiated with ultraviolet rays, the glass plate becomes colored and its transmittance in the visible range decreases. When the transmittance in the visible range decreases, the amount of light from the light source is reduced when it enters from the end face and passes through the light exit surface. As a result, the brightness of the display device tends to decrease. According to the research conducted by the present inventors, when the basicity of the glass plate increases, the number of non-crosslinking oxygens in the glass network increases, resulting in a state where there are many colored centers. As a result, the glass plate tends to be colored by ultraviolet irradiation, and the transmittance in the visible region tends to decrease. Therefore, in the light guide plate of the present invention, it is preferable that the basicity of the glass plate is regulated to 0.54 or less. This makes it difficult for the transmittance in the visible range to decrease even when irradiated with ultraviolet rays. Here, "basicity" is an index indicating the electron donating property of oxygen atoms in the glass, and serves as an index for evaluating the average Lewis basicity of oxide ions in the glass. Specifically, it is a value calculated using Equation 1 below. In addition, in the following formula 1, Λ is the basicity, c _i is the proportion of oxygen brought in by compound i, Z _i is the valence of the cation, and r _i is the number of cations expressed per oxygen (compound i molar ratio of cation to oxygen), γ _i is a parameter called basicity moderating power and is determined by the electronegativity χ _i of the cation.

To reduce the basicity of the glass plate, for example, increase the amount of network-forming oxides such as SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, ZnO, Li ₂ O, The content of network modifying oxides such as Na ₂ O and K ₂ O may be reduced.

Figure 2 shows the difference in basicity and average transmittance in the visible range before and after UV irradiation (average transmittance in optical path length 2 mm, wavelength range 400 to 750 nm, output 0.1 mW, wavelength 185 nm UV rays, output 13. 3 mW, wavelength 254 nm ultraviolet rays and 0.4 mW, wavelength 365 nm ultraviolet rays are simultaneously irradiated for 12 hours, optical path length 2 mm, wavelength range 400-750 nm It is a graph showing the relationship between average transmittance in the wavelength range 400 to 750 nm). As can be seen from FIG. 2, the lower the basicity, the smaller the average transmittance difference in the visible range before and after ultraviolet irradiation.

Further, the light guide plate of the present invention has a maximum transmittance of 85% or more in the optical path length of the glass plate of 200 mm and a wavelength range of 400 to 750 nm, and a minimum transmittance of 85% or more in the optical path length of the glass plate of 200 mm and the wavelength range of 400 to 750 nm. % or more, and the difference between the highest transmittance and the lowest transmittance is preferably 10% or less. Here, "transmittance" can be measured with a commercially available transmittance measuring device, for example, with UV-3100PC manufactured by Shimadzu Corporation, and unless otherwise specified, it can be measured with an internal transmittance calculated using Formula 2. Refers to transmittance.

Further, in the light guide plate of the present invention, it is preferable that a dot pattern is formed on at least one surface of the glass plate.

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

FIG. 3 is a conceptual perspective view showing an example of the light guide plate of the present invention. As shown in FIG. 3, the light guide plate 10 includes a glass plate 11. Light from the light source 12 enters from the end surface 13 of the glass plate 11, propagates inside the glass plate 11, and exits from the light exit surface. Furthermore, a dot pattern 15 is formed on the light reflecting surface 14 of the glass plate 11. The diameter of the dots in the dot pattern 15 gradually increases from the end surface 13 toward the end surface 16. This dot pattern 15 makes the light emitted from the light emitting surface uniform within the surface. Further, reflective layers 19 are formed on the end faces 16, 17, and 18 of the glass plate, respectively. The light that has reached the end surfaces 16, 17, and 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.

It is also possible to use a plurality of glass plates 11 of the present invention joined together. For example, two glass plates 11 are prepared, and a reflective layer is not formed on the end face 17 of one glass plate 11, and a reflective layer is not formed on the end face 18 of the other glass plate 11, and both reflective layers are formed. It is possible to produce a large-area light guide plate by joining the other end faces with a transparent adhesive whose refractive index is matched.

FIG. 2 is a conceptual cross-sectional diagram showing an example of an edge-light surface emitting device. It is a graph showing the relationship between basicity and the difference in average transmittance in the visible range before and after ultraviolet irradiation. FIG. 1 is a conceptual perspective view showing an example of a light guide plate of the present invention.

In the light guide plate of the present invention, the glass plate has, as a glass composition, SiO ₂ 55 to 80%, Al ₂ O ₃ 0 to 15%, B ₂ O ₃ 1 to 20%, Li ₂ O + Na ₂ O + K ₂ O 1-20%, MgO+CaO+SrO+BaO 0.1-10%, SnO ₂ 0-0.5%, Sb ₂ O ₃ 0-0.5%, Fe ₂ O ₃ 0-0.005% (50 mass ppm or less) The mass ratio (MgO+CaO)/(Li ₂ O+Na ₂ O+K ₂ O+MgO+CaO+SrO+BaO) is less than 0.40. The reasons for regulating the content of each component as described above are shown below. In addition, in the description of the content range of each component, % indication means mass %.

SiO ₂ is a component that becomes a network former for glass, and is a component that lowers the coefficient of thermal expansion and reduces dimensional changes due to heat. It is also a component that increases acid resistance and strain point. The content of SiO ₂ is 55-80%, preferably 58-78%, 60-75%, 62-74%, especially 64-72%. When the content of SiO ₂ decreases, the basicity tends to increase, the coefficient of thermal expansion increases, and dimensional changes due to heat tend to increase. In addition, acid resistance and strain point tend to decrease. On the other hand, when the content of SiO ₂ increases, the high-temperature viscosity increases, the meltability decreases, and devitrified cristobalite particles tend to precipitate during molding.

Al ₂ O ₃ is a component that lowers the coefficient of thermal expansion and reduces dimensional changes due to heat. It also has the effect of increasing the strain point and suppressing the precipitation of cristobalite devitrification lumps during molding. The content of Al ₂ O ₃ is 0-15%, preferably 0.1-13%, 1-12%, especially 4-11%. When the content of Al ₂ O ₃ decreases, the basicity tends to increase, the coefficient of thermal expansion increases, and dimensional changes due to heat tend to increase. Moreover, the strain point tends to decrease. On the other hand, when the content of Al ₂ O ₃ increases, the liquidus temperature increases, making it difficult to form into a glass plate.

B ₂ O ₃ is a component that acts as a flux, lowers high temperature viscosity, and improves meltability. It is also a component that lowers the coefficient of thermal expansion and reduces dimensional changes due to heat. The content of B ₂ O ₃ is 1-20%, preferably 5-18%, 7-17%, 9-16%, especially 10-15%. When the content of B ₂ O ₃ decreases, the basicity tends to increase, the high temperature viscosity increases, and the meltability tends to decrease. In addition, devitrified particles such as cristobalite tend to precipitate. On the other hand, when the content of B ₂ O ₃ increases, the strain point and acid resistance tend to decrease. In addition, the glass becomes easier to undergo phase separation.

The content of SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ is preferably 83% or more, 85% or more, 86% or more, 88% or more, especially 90 to 93%. When the content of SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ decreases, the basicity tends to increase. In addition, " _SiO2 + _{Al2O3 + B2O3 "} refers to _the total amount _{of SiO2} , _Al2O3 , and _B2O3 .

The content of Li ₂ O + Na ₂ O + K ₂ O is 1-20%, preferably 2-15%, 3-13%, 4-12%, especially 5-11%. When the content of Li ₂ O + Na ₂ O + K ₂ O decreases, the high temperature viscosity increases and the meltability tends to decrease. On the other hand, when the content of Li ₂ O + Na ₂ O + K ₂ O increases, the basicity tends to increase, the coefficient of thermal expansion increases, and dimensional changes due to heat tend to increase. Note that the content of Li ₂ O is preferably 0 to 5%, 0 to 3%, 0 to 1%, 0 to 0.5%, particularly 0 to 0.1%. The content of Na ₂ O is preferably 0-13%, 2-10%, 3-9%, 4-8%, especially 5-7%. The content of K ₂ O is preferably 0-9%, 0-7%, 0-5%, 0-4%, especially 0.1-3%.

The content of MgO+CaO+SrO+BaO is 0.1-10%, preferably 0.3-8%, especially 0.5-5%. When the content of MgO+CaO+SrO+BaO decreases, high-temperature viscosity increases and meltability tends to decrease. On the other hand, when the content of MgO+CaO+SrO+BaO increases, Fe ₂ O ₃ impurities are likely to be mixed in from the introduced raw materials. Moreover, basicity tends to increase.

The mass ratio (SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ )/(MgO+CaO+SrO+BaO) is preferably 15 or more, particularly 20 or more. If the mass ratio (SiO ₂ +Al ₂ O ₃ +B ₂ O ₃ )/(MgO+CaO+SrO+BaO) is too small, the basicity tends to increase.

The mass ratio (MgO+CaO)/( _Li2O + _Na2O + _K2O +MgO+CaO+SrO+BaO) is less than 0.40, 0.35 or less, 0.32 or less, 0.30 or less, 0.28 or less, 0.26 or less, 0. 24 or less, 0.22 or less, 0.20 or less, 0.18 or less, 0.16 or less, 0.14 or less, 0.12 or less, 0.10 or less, 0.08 or less, 0.06 or less, especially 0 .04 or less. When the mass ratio (MgO+CaO)/(Li ₂ O+Na ₂ O+K ₂ O+MgO+CaO+SrO+BaO) increases, Fe ₂ O ₃ impurities are likely to be mixed in from the introduced raw material.

MgO is a component that reduces high-temperature viscosity and improves meltability, but it is a component that reduces the brightness of the display device due to Fe ₂ O ₃ impurities in the introduced raw material. The content of MgO is preferably 0-5%, 0-4%, 0.2-3%, especially 0.5-2%. When the content of MgO decreases, high temperature viscosity increases and meltability tends to decrease. On the other hand, when the content of MgO increases, it becomes easier for Fe ₂ O ₃ impurities to be mixed in from the introduced raw material, and the basicity becomes easier to increase. In addition, devitrification particles tend to precipitate during molding.

CaO is a component that improves meltability by lowering only high-temperature viscosity without lowering the strain point, but it is a component that lowers the brightness of the display device due to Fe ₂ O ₃ impurities in the introduced raw material. The content of CaO is preferably 0-10%, 0.1-8%, 0.2-7%, 0.3-6%, 0.4-5%, especially 0.5-4%. . When the content of CaO decreases, high temperature viscosity increases and meltability tends to decrease. On the other hand, when the content of CaO increases, it becomes easier for Fe ₂ O ₃ impurities to be mixed in from the introduced raw material and the basicity tends to increase. In addition, devitrification particles tend to precipitate during molding.

SrO is a component that reduces high temperature viscosity, improves meltability, and increases chemical resistance and devitrification resistance. The content of SrO is preferably 0-10%, 0.1-8%, 0.2-7%, 0.3-6%, 0.4-5%, especially 0.5-4%. . When the SrO content decreases, high temperature viscosity increases and meltability tends to decrease. On the other hand, when the content of SrO increases, the density and basicity tend to increase, the coefficient of thermal expansion increases, and dimensional changes due to heat tend to increase.

BaO is a component that reduces high-temperature viscosity, improves meltability, and increases chemical resistance and devitrification resistance. The BaO content is preferably 0-10%, 0-8%, 0-7%, 0-6%, 0-5%, especially 0.1-4%. When the BaO content decreases, high-temperature viscosity increases and meltability tends to decrease. On the other hand, when the BaO content increases, the density and basicity tend to increase, the thermal expansion coefficient increases, and dimensional changes due to heat tend to increase.

SnO ₂ and Sb ₂ O ₃ are components that act as clarifying agents. The content of SnO ₂ is 0-0.5%, preferably 0.01-0.5%, 0.05-0.5%, 0.07-0.5%, especially 0.1-0. .4%. The content of Sb ₂ O ₃ is 0-0.5%, preferably 0.01-0.5%, 0.05-0.5%, 0.07-0.5%, especially 0.1 ~0.4%. When the content of SnO ₂ and Sb ₂ O ₃ decreases, it becomes difficult to enjoy the clarification effect. On the other hand, when the content of SnO ₂ and Sb ₂ O ₃ increases, devitrification particles tend to precipitate during molding.

Fe ₂ O ₃ is a component that absorbs light and reduces transmittance in the visible range. The content of Fe ₂ O ₃ is 0 to 0.005% (50 mass ppm or less), preferably 40 mass ppm or less, 30 mass ppm or less, 25 mass ppm or less, 20 mass ppm or less, especially 4 to 25 mass ppm. It is ppm. When the content of Fe ₂ O ₃ increases, the brightness of the display device tends to decrease. Note that if the content of Fe ₂ O ₃ is too low, the raw material cost and the manufacturing cost of the glass plate will increase.

The content of Cr ₂ O ₃ is preferably less than 10 mass ppm, 8 mass ppm or less, 6 mass ppm or less, 0.1 to 5 mass ppm, 0.2 to 4 mass ppm, especially 0.3 to 3 mass ppm. It is. When the content of Cr ₂ O ₃ increases, the transmittance in the visible range tends to decrease. Note that if the content of Cr ₂ O ₃ is too low, the raw material cost and the manufacturing cost of the glass plate will increase.

TiO ₂ is a component that absorbs light and reduces transmittance in the visible range. The content of TiO ₂ is preferably 50 mass ppm or less, 30 mass ppm or less, 20 mass ppm or less, 15 mass ppm or less, 10 mass ppm or less, especially 1 to 5 mass ppm or less. When the content of TiO ₂ increases, the brightness of the display device tends to decrease. Note that if the content of TiO ₂ is too low, the raw material cost and the manufacturing cost of the glass plate will increase.

In order to eliminate the contamination of Fe ₂ O ₃ , Cr ₂ O ₃ , TiO _{2 ,} etc. as much as possible, in addition to reducing the content of MgO and CaO, Fe ₂ O ₃ , Cr etc. should be added to the raw materials from raw material preparation equipment, etc. It is effective to use manufacturing equipment designed to prevent the contamination of colored oxides such as ₂ O ₃ and TiO ₂ .

The content of Pt (Pt ions) is preferably 5 ppm or less, 3 ppm or less, 2 ppm or less, 0.01 to 1 ppm by mass, particularly 0.05 to 0.8 ppm by mass. When the content of Pt increases, the transmittance in the visible range tends to decrease. In addition, when the content of Pt is too small, it becomes difficult to use high-strength Pt in glass manufacturing equipment, and the manufacturing cost of the glass plate increases.

The content of Rh (Rh ion) is preferably 5 mass ppm or less, 3 mass ppm or less, 2 mass ppm or less, 0.01 to 1 mass ppm, 0.05 to 0.8 mass ppm, especially 0.1 to It is 0.7 mass ppm. When the Rh content increases, the difference in transmittance between the highest transmittance and the lowest transmittance in the visible range tends to become excessive. Note that if the Rh content is too low, it becomes difficult to use a high-strength Pt-Rh alloy in glass manufacturing equipment, and the manufacturing cost of the glass plate increases. In order to reduce the Rh content as much as possible, it is necessary to use high-purity glass raw materials, adjust glass manufacturing conditions to prevent Rh from being mixed in, and change the locations where Pt-Rh alloy is used in glass manufacturing equipment. Just reduce it.

In addition to the above components, other components may be introduced. For example, Y ₂ O ₃ , Nb ₂ O ₅ , P ₂ O ₅ up to 3% each to lower the liquidus temperature, Cs ₂ O up to 5% each to lower the melting temperature, fining agent As such, SO ₃ , F, Cl, etc. may be introduced in a total amount of up to 0.5%. As ₂ O ₃ is an environmentally hazardous substance, and when glass plates are formed by the float method, it is reduced in the float bath and becomes metallic foreign matter, so it is preferable to avoid its substantial introduction. , the content thereof is preferably 0.5% or less and less than 0.01%, respectively.

The water content is preferably 500 ppm or less, 400 ppm or less, 300 ppm or less, particularly 250 ppm or less. When the water content increases, the strain point tends to decrease and bubbles tend to occur at the interface between platinum and molten glass. Here, the "moisture content" can be calculated by multiplying the β-OH value (/mm) by a coefficient specific to the glass composition. Then, the β-OH value can be calculated using Equation 3.

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

The basicity is preferably 0.54 or less, 0.53 or less, 0.52 or less, 0.51 or less, 0.50 or less, 0.49 or less, especially 0.30 to 0.48. If the basicity is too high, the transmittance tends to decrease due to ultraviolet irradiation, and the brightness of the display device tends to decrease.

The maximum transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm is preferably 85% or more, 86% or more, 87% or more, particularly 88% or more. If the maximum transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm is too low, the brightness of the display device tends to decrease.

The minimum transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm is preferably 75% or more, 82% or more, 84% or more, particularly 85% or more. If the minimum transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm is too low, the brightness of the display device tends to decrease.

The difference between the highest transmittance and the lowest transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm is preferably 10% or less, 7% or less, 5% or less, 3% or less, 2% or less, particularly 1% or less. When the difference between the highest transmittance and the lowest transmittance in the optical path length of 200 mm and the wavelength range of 400 to 750 nm increases, the brightness of the display device tends to decrease.

In the light guide plate of the present invention, the glass plate has an optical path length of 2 mm, an average transmittance in the wavelength range of 400 to 750 nm of When Y (%) is the average transmittance in the wavelength range of 400 to 750 nm with an optical path length of 2 mm after simultaneous 12-hour irradiation with 0.4 mW and 365 nm wavelength ultraviolet rays, it is possible to satisfy the relationship X-Y < 1%. Preferably, XY is less than 0.9%, less than 0.8%, less than 0.7%, less than 0.6%, less than 0.5%, especially less than 0.4%. If the difference in average transmittance before and after irradiation with ultraviolet rays is too large, it becomes difficult to ensure the brightness of the display device.

The coefficient of thermal expansion in the temperature range of 30 to 380°C is preferably 120×10 ⁻⁷ /°C or less, 95×10 ⁻⁷ /°C or less, 75×10 ⁻⁷ /°C or less, particularly 30×10 ⁻⁷ to 70 ×10 ⁻⁷ /°C. If the coefficient of thermal expansion of the glass plate is too high, the difference in dimensional change due to heat between the display panel and the light guide plate will increase. Here, the "thermal expansion coefficient in the temperature range of 30 to 380°C" is an average value measured with a dilatometer in accordance with JIS R3102.

The strain point is preferably 400°C or higher, 420°C or higher, 440°C or higher, 460°C or higher, 470°C or higher, 480°C or higher, particularly 490°C or higher. If the strain point is too low, heat resistance tends to decrease, and for example, when a reflective film or the like is formed on the surface of a glass plate at high temperature, the glass plate tends to be thermally deformed. Here, the "strain point" is a value measured based on JIS R3103.

The liquidus temperature is preferably 1000°C or lower, particularly 970°C or lower. The liquidus viscosity is preferably 10 ^4.6 dPa·s or more, particularly 10 ^5.0 dPa·s or more. The "liquidus temperature" was set at 1100°C to 1350°C by crushing each sample, passing it through a standard sieve of 30 mesh (500 μm), and placing the remaining glass powder on the 50 mesh (300 μm) in a platinum boat. After holding the glass in a temperature gradient furnace for 24 hours, the platinum boat was taken out and the temperature was such that devitrification (crystalline foreign matter) was observed in the glass. "Liquidus viscosity" is the value of the viscosity of glass at liquidus temperature measured by the platinum ball pulling method.

The dimension of at least one side of the glass plate is preferably 1000 mm or more, 1500 mm or more, 2000 mm or more, 2500 mm or more, particularly 3000 mm or more. In this way, the demand for larger display devices can be met.

The glass plate is preferably formed by an overflow down-draw method. In this way, temperature differences and composition differences between the front and back surfaces of the glass ribbon are less likely to occur during molding, and it becomes easier to mold an unpolished glass plate with good surface quality, resulting in lower manufacturing costs for the light guide plate. It becomes easier to achieve uniform brightness and brightness. The reason for this is that in the case of the overflow down-draw method, the surface that should become the surface does not come into contact with the trough-like refractory and is molded in a free surface state. The structure and material of the gutter-like structure are not particularly limited as long as desired dimensions and surface quality can be achieved. Further, the method of applying force to the glass ribbon in order to perform downward stretching molding is not particularly limited as long as desired dimensions and surface quality can be achieved. For example, a method may be adopted in which a heat-resistant roll having a sufficiently large width is rotated and stretched while in contact with the glass ribbon, or a plurality of pairs of heat-resistant rolls may be used only near the end face of the glass ribbon. You may adopt the method of making it contact and stretching.

In addition to the overflow downdraw method, the glass plate can also be formed by a slot downdraw method, a float method, a rollout method, a redraw method, or the like. Note that in the float method, temperature differences and composition differences between the front and back surfaces of the glass ribbon tend to occur during molding, but these temperature differences and composition differences can be reduced by strictly controlling the temperature during molding.

In the light guide plate of the present invention, it is preferable that a dot pattern is formed on at least one surface (preferably the light exit surface) of the glass plate. When a dot pattern is formed on the surface of a glass plate, air with a low refractive index can be brought into contact between the dots forming the dot pattern. Thereby, the total reflection condition is satisfied, and light can be sufficiently propagated inside the glass plate. As a result, it becomes easier to make the light emitted from the light emitting surface uniform within the surface.

It is further preferable that the diameter of the dots constituting the dot pattern gradually increases as the distance from the end surface onto which the light from the light source is to be incident is increased. In this way, it becomes easier to make the light emitted from the light emitting surface uniform within the surface. Note that the dot pattern can be formed, for example, by printing heat-resistant paint or glass frit on the surface of a glass plate and baking it.

The shape of the dots constituting the dot pattern is not particularly limited, and examples thereof include a circle, an ellipse, a square, a triangle, and a polygon. Among them, a circular shape is preferable as the shape of the dot.

In the light guide plate of the present invention, the average surface roughness Ra of the end face of the glass plate (preferably the end face on which light from the light source should enter) is preferably 0.5 μm or less, 0.3 μm or less, 0.2 μm or less, particularly It is 0.1 μm or less. This makes it easier to reduce light loss when light from the light source enters the end face. Furthermore, it becomes easier to form a high-quality reflective layer on the end face.

For example, by polishing the end face of the glass plate with a #2000 grindstone, the average surface roughness Ra of the end face of the glass plate can be reduced as much as possible. Furthermore, by etching the end face of the glass plate, the average surface roughness Ra of the end face of the glass plate can be reduced without causing polishing scratches.

It is preferable that the end surface of the glass plate does not have a chamfered portion. In this way, it becomes easier to take in the light from the light source into the inside of the glass plate.

In the light guide plate of the present invention, it is preferable that a reflective layer is formed on all or part of the end face other than the end face on which the light from the light source should enter, and the light guide plate of the present invention preferably has a reflective layer formed on all or part of the end face on which the light from the light source should enter. It is particularly preferable that a reflective layer is formed on the surface. This makes it difficult for light propagated inside the glass plate to leak from the end face. Note that as the reflective layer, a reflective film may be directly formed on the end face, or a reflective sticker may be attached to the end face.

The light guide plate of the present invention preferably includes a diffusion plate on one surface (preferably the light exit surface) of the glass plate, and has a diffusion plate on one surface (preferably the surface opposite the light exit surface) of the glass plate. Preferably, a plate is provided. In this way, it becomes easier to equalize the brightness of the display device.

The present invention will be described below based on Examples. However, the following examples are merely illustrative. The present invention is not limited to the following examples.

Tables 1 to 10 show Examples (Samples No. 1 to 193) of the present invention. In addition, in the table, "R ₂ O" indicates Li ₂ O+Na ₂ O+K ₂ O, and "RO" indicates MgO+CaO+SrO+BaO. Moreover, "cri" in the primary phase in the table indicates cristobalite, and "Quartz" indicates quartz.

First, a glass batch containing glass raw materials prepared to have the glass composition shown in the table was placed in a platinum crucible, and then melted at 1200 to 1650°C for 24 hours. When melting the glass batch, it was stirred using a platinum stirrer to achieve homogenization. Next, the molten glass was poured onto a carbon plate, formed into a plate shape, and then annealed for 30 minutes at a temperature near the annealing point. For each sample obtained, water content H ₂ O, optical path length 200 mm, maximum transmittance in the wavelength range 400 to 750 nm, optical path length 200 mm, minimum transmittance in the wavelength range 400 to 750 nm, and optical path length 200 mm, wavelength range 400 to 750 nm. Difference between the highest transmittance and the lowest transmittance in the optical path length of 200 mm and the wavelength range of 400 to 750 nm, the coefficient of thermal expansion α in the temperature range of 30 to 380°C, density ρ, strain point Ps, annealing point Ta, softening point Ts , temperature at high temperature viscosities of 10 ^4.0 , 10 ^3.0 , and 10 ^2.5 dPa·s, liquidus temperature TL, liquidus viscosity logη at TL, and initial phase were evaluated.

The water content H ₂ O was calculated by multiplying the β-OH value (/mm) by a coefficient of 0.09 specific to the glass composition. Then, the β-OH value can be calculated using Equation 3 above.

The maximum transmittance and minimum transmittance at an optical path length of 200 mm and a wavelength range of 400 to 750 nm were calculated using the above formula 2, and were measured using UV-3100PC manufactured by Shimadzu Corporation.

The thermal expansion coefficient α in the temperature range of 30 to 380° C. is an average value measured with a dilatometer in accordance with JIS R3102.

The density ρ is a value measured by the well-known Archimedes method.

The strain point Ps, annealing point Ta, and softening point Ts are values measured based on the methods of ASTM C336 and C338.

The temperatures at high-temperature viscosities of 10 ^4.0 , 10 ^3.0 , and 10 ^2.5 dPa·s are values measured by the platinum ball pulling method.

The liquidus temperature TL is determined by crushing each sample, passing it through a standard sieve of 30 mesh (500 μm), and placing the remaining glass powder on the 50 mesh (300 μm) in a platinum boat, and setting the temperature gradient from 1100°C to 1350°C. After being kept in the furnace for 24 hours, the platinum boat was taken out and the temperature was such that devitrification (crystalline foreign matter) was observed in the glass. Then, crystals precipitated in the temperature range from liquidus temperature TL to (liquidus temperature TL - 50° C.) were observed with an electron microscope and evaluated as the primary phase. Furthermore, the viscosity of the glass at the liquidus temperature was measured by the platinum ball pulling method, and this was defined as the liquidus viscosity logη at TL.

As can be seen from Tables 1 to 10, sample No. Nos. 1 to 193 had a small mass ratio (MgO+CaO)/(Li ₂ O+Na ₂ O+K ₂ O+MgO+CaO+SrO+BaO) and a low content of Fe ₂ O ₃ , so the transmittance in the visible range was high. Therefore, sample no. Nos. 1 to 193 are considered to be suitable as light guide plates for use in edge-light type surface emitting devices.

1 Edge light type surface emitting device 2, 12 Light source 3, 10 Light guide plate 4, 19 Reflective layer 5 Diffusion plate 6, 14 Light reflecting surface 7 Light emitting surface 11 Glass plate 13, 16 to 18 End surface 15 Dot pattern 19 Reflecting layer

Claims (6)

A light guide plate having at least a glass plate,
The glass plate has, as a glass composition, SiO ₂ 55-80%, Al ₂ O ₃ 0-15%, B ₂ O ₃ 1-20%, Li ₂ O 0-5%, Li ₂ O + Na ₂ Contains O+K ₂ O 5.8-13%, MgO+CaO+SrO+BaO 0.1-10%, SnO ₂ 0-0.5%, Sb ₂ O ₃ 0-0.5%, Fe ₂ O ₃ 0-0.005% and the mass ratio (MgO+CaO)/( _Li2O + _Na2O + _K2O +MgO+CaO+SrO+BaO) is 0.18 or less,
A light guide plate characterized in that the glass plate has an optical path length of 200 mm and a minimum transmittance of 80% or more in a wavelength range of 400 to 750 nm . The content of Cr ₂ O ₃ in the glass plate is not more than 5 ppm by mass, the content of TiO ₂ is not more than 50 ppm by mass, the content of Pt is not more than 5 ppm by mass, and the content of Rh is not more than 5 ppm by mass. The light guide plate according to claim 1, characterized by: 3. The light guide plate according to claim 1, wherein the glass plate has a basicity of 0.54 or less. A claim characterized in that the glass plate has an optical path length of 200 mm and a maximum transmittance of 85% or more in a wavelength range of 400 to 750 nm, and a difference between the maximum transmittance and the minimum transmittance is 10% or less. The light guide plate according to any one of 1 to 3. 5. The light guide plate according to claim 1, 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 5, characterized in that it is used in an edge-light type surface emitting device.