WO2017209254A1 - Light diffusing plate, surface light-emitting device, and liquid crystal display device - Google Patents

Abstract

Provided is a light diffusing plate that diffuses and transmits light from a plurality of light sources from one to the other of two main surfaces facing each other, wherein: letting, when light with a wavelength of 550 nm is made orthogonally incident to the one main surface, T_t be total light ray transmittance, I₀ be the intensity of transmitted light when the output direction is identical to the direction of incidence, and I₃₀ be the intensity of transmitted light for an output direction that is a direction at an inclination of 30° to the direction of incidence, T_t is 10 - 70% and I₃₀/I₀ is 0.6 or greater; and the light diffusion plate is formed from glass such that the specific elastic modulus is at least 26.0 GPa∙cm³/g, and in the mol% content for the oxide basis, MgO is 1 - 16%, P₂O₅ 0 - 5%, and Al₂O₃ 1 - 9%.

Description

Light diffusing plate, surface emitting device, and liquid crystal display device

The present invention relates to a light diffusion plate, a surface light emitting device, and a liquid crystal display device.

The direct type backlight of the liquid crystal display device has a plurality of light sources on the back side of the liquid crystal panel, and has a light diffusion plate between the liquid crystal panel and the light source. The plurality of light sources are arranged on the same plane, and the light diffusion plate diffuses and transmits the light from the plurality of light sources.

The light diffusion plate of Patent Document 1 is formed by dispersing a light diffusion agent in a polycarbonate resin in order to suppress luminance unevenness caused by a plurality of light sources. As the light diffusing agent, one having a difference in refractive index with the polycarbonate resin of 0.02 to 0.20 in absolute value is used, and inorganic particles or organic particles are used.

Japanese Patent Laid-Open Publication No. 2006-98912

A large area and a thin structure of a surface light emitting device such as a backlight are required, and a large area and a thin structure of a light diffusion plate are required. Therefore, the light diffusion plate is easily bent by an external force such as gravity.

The inventors of the present invention have found that the distance between the light diffusion plate and the light source varies from light source to light source, resulting in uneven brightness on the light emitting surface of the light diffusion plate. The uneven brightness is more remarkable as the distance between the light diffusion plate and the light source is narrower for thinning the surface light emitting device.

This invention is made in view of the said subject, Comprising: It aims mainly at provision of the light-diffusion plate which reduced the brightness nonuniformity resulting from using a several light source.

According to one aspect of the present invention, in order to solve the above problems,
A light diffusing plate that diffuses and transmits light from a plurality of light sources from one of two main surfaces facing each other to the other,
The total light transmittance is T _t when the light having a wavelength of 550 nm is perpendicularly incident on the one main surface, the intensity of the transmitted light having an exit direction in the same direction as the exit direction is I ₀ , and the exit direction is incident. Assuming that the intensity of transmitted light, which is a direction inclined by 30 ° with respect to the direction, is I ₃₀ , T _t is 10 to 70%, and I ₃₀ / I ₀ is 0.6 or more,
The specific modulus is 26.0 GPa · cm ³ / g or more, and it is 1 to 16% of MgO, 0 to 5% of P ₂ O _5, and 1 to 5% of Al ₂ O ₃ in terms of mol% on an oxide basis. A light diffusing plate is provided which is made of glass containing 9%.

According to one aspect of the present invention, there is provided a light diffusion plate in which unevenness in brightness caused by using a plurality of light sources is reduced.

FIG. 1 is a cross-sectional view of a liquid crystal display according to one embodiment. It is a top view of the surface emitting apparatus of FIG. 1, Comprising: It is a top view which fractures | ruptures and shows a part of light diffusing plate. It is drawing which shows the transmitted light diffused and transmitted through the light diffusing plate of FIG. It is a figure which exaggerates and shows the change of the space | interval of the light-diffusion plate and the light source resulting from self-weight bending of the light-diffusion plate of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same or corresponding reference numerals, and the description thereof will be omitted.

FIG. 1 is a cross-sectional view of a liquid crystal display according to one embodiment. FIG. 2 is a plan view of the surface light emitting device of FIG. 1 and is a plan view showing a part of the light diffusion plate in a cutaway state.

The surface light emitting device 10 is used, for example, as a direct type backlight of a liquid crystal display device, is disposed on the back side of the liquid crystal panel 12, and emits light to the liquid crystal panel 12. The liquid crystal panel 12 has, for example, an array substrate, a liquid crystal layer, and a color filter substrate in this order. The array substrate has an active element such as a TFT and a transparent pixel electrode on the liquid crystal layer side. The color filter substrate has a color filter and a transparent counter electrode on the liquid crystal layer side. The surface light emitting device 10, the liquid crystal panel 12, and the like constitute a liquid crystal display device.

The surface light emitting device 10 may have any light emitting surface as long as it intersects with the user's line of sight or its extended line, and the application is not particularly limited. For example, the surface emitting device 10 may be used as a lighting device that illuminates the inside of a room.

The surface light emitting device 10 includes, for example, a frame 20, a plurality of light sources 30 supported by the frame 20, a light diffusion plate 40 which diffuses and transmits light from the plurality of light sources 30, and light from the plurality of light sources 30. And a light reflection plate 50 that reflects toward the diffusion plate 40.

The frame 20 supports the plurality of light sources 30, the light diffusion plate 40, and the light reflection plate 50. When the plurality of light sources 30 are fixed to the light reflecting plate 50 as shown in FIG. 1, the frame 20 supports the light reflecting plate 50 to support the plurality of light sources 30. The plurality of light sources 30 may be fixed to a dedicated fixing plate, and the frame 20 may support the plurality of light sources 30 by supporting the fixing plate.

The plurality of light sources 30 may be arranged in a matrix on the same plane as shown in FIG. Each light source 30 is, for example, a light emitting diode (LED). Although LED in particular is not limited, it is white LED, for example. Each light source 30 may be a cold cathode tube or the like.

The light diffusion plate 40 diffuses and transmits the light from the plurality of light sources 30 from one of the two main surfaces 41, 42 facing each other to the other. Hereinafter, among the two main surfaces 41 and 42, the main surface 41 on the light source 30 side is also referred to as a light irradiation surface 41, and the main surface 42 on the opposite side to the light source 30 is also referred to as a light emitting surface 42. A light diffusion sheet made of a resin may be adhered to the light emitting surface 42 in order to suppress unevenness in brightness caused by using the plurality of light sources 30.

The light reflection plate 50 is provided on the opposite side of the light diffusion plate 40 with respect to the light source 30 in order to increase the luminance of the light emitting surface 42 of the light diffusion plate 40, and light from the plurality of light sources 30 is diffused to the light diffusion plate 40. Reflect towards. Reflection of light by the light reflecting plate 50 may be either regular reflection or diffuse reflection.

FIG. 3 is a drawing showing transmitted light diffused and transmitted through the light diffusion plate of FIG. In FIG. 3, L0 indicates the irradiation light vertically incident on the light irradiation surface 41, L1 indicates the transmitted light whose emission direction is the same as the incident direction (hereinafter referred to as “linear transmission light”), and L2 indicates the same. The transmitted light (hereinafter, referred to as “diffuse transmitted light”) in which the emission direction is a direction inclined by 30 ° with respect to the incident direction is respectively shown. The angle θ between the ray of the linearly transmitted light L1 and the ray of the diffused transmitted light L2 is 30 °.

The light diffusion plate 40 diffuses the total light transmittance T _t , the intensity of the linear transmitted light L 1 I ₀ , and diffuses the light having a wavelength of 550 nm perpendicularly to the light irradiation surface 41 as shown in FIG. When the intensity of the transmitted light L2 and _{I 30, T t} is 10 percent or _more, I 30 / _{I 0} is 0.6 or more.

The total light transmittance T _t is measured using an integrating sphere unit of a spectrophotometer (not shown). The “total light transmittance” is the remaining one main surface (for example, the light diffusion plate 40) with respect to incident light that is incident at an incident angle of 0 ° to one main surface (for example, the light irradiation surface 41) of the light diffusion plate 40. It means the percentage of the total transmitted light transmitted to the light emitting surface 42). The total light transmittance is measured by the method described in JIS K7361: 1997 (ISO 13468-1: 1996) using the d-line (wavelength 589 nm) of a sodium lamp as incident light.

The total light transmittance T _t is 10% or more, preferably 15% or more, more preferably 15% or more, and further preferably 30% or more, in order to improve the light extraction efficiency. The total light transmittance T _t is 70% or less, more preferably 50% or less, more preferably 50% or less, from the viewpoint of further enhancing the diffusion performance by utilizing the diffuse reflection toward the light source 30 inside the light diffusion plate 40. 40% or less.

The intensity I ₀ of the linear transmission light L ₁ and the intensity I ₃₀ of the diffuse transmission light L 2 are measured by the photometer 60. The photometer 60 is pivoted between a position at which the intensity I ₀ of the linear transmitted light L ₁ is measured and a position at which the intensity I ₃₀ of the diffuse transmitted light L 2 is measured. Intensity I ₃₀ of the diffuse transmitted light L2 may employ an average of measured values at a plurality of positions, but may employ a value measured at any one location.

The ratio I ₃₀ / I ₀ of the intensity I ₃₀ of the diffuse transmission light L ₂ to the intensity I ₀ of the linear transmission light L ₁ (hereinafter also simply referred to as “intensity ratio I ₃₀ / I ₀ ”) does not show through the shape of the light source In order to scatter light uniformly and to suppress unevenness in luminance on the light emitting surface 42, it is 0.6 or more, preferably 0.7 or more, and more preferably 0.8 or more.

FIG. 4: is a figure which exaggerates and shows the change of the space | interval of the light-diffusion plate and the light source resulting from self-weight bending of the light-diffusion plate of FIG. In FIG. 4, the solid line exaggerates the self-weight deflection of the light diffusion plate 40 horizontally placed on the frame 20, and the two-dot chain line indicates a state in which no external force such as gravity acts (hereinafter referred to as “natural state And the light diffusion plate 40 of FIG. In FIG. 4, the light diffusion plate 40 is only mounted on the frame 20 and not fixed, but may be fixed.

When the light diffusion plate 40 is bent due to gravity or the like, the distance D between the light diffusion plate 40 and the light source 30 varies from one light source 30 to another. In addition, since the light reflection plate 50 to which the light source 30 is fixed is placed on a table or the like, it hardly bends due to gravity or the like.

The specific elastic modulus of the light diffusing plate 40 is expressed by E / d obtained by dividing the Young's modulus E by the density d, and is 26.0 GPa · cm ³ / g or more. By this, the bending of the light diffusion plate 40 can be reduced, and the variation of the distance D between the light diffusion plate 40 and the light source 30 can be suppressed. As a result, it is possible to suppress luminance unevenness caused by using the plurality of light sources 30.

The specific elastic modulus E / d of the light diffusion plate 40 is preferably 26.5 GPa · cm ³ / g or more, more preferably 27.0 GPa · cm ³ / g or more, still more preferably 27.5 GPa · cm ³ / g or more , particularly preferably 28.0GPa · ^cm 3 / g or more, particularly more preferably 29. 0GPa · ^cm 3 / g or more, and most preferably 30GPa · ^cm 3 / g or more.

The density d of the light diffusion plate 40 is preferably 3.0 g / cm ³ or less, more preferably 2.8 g / cm ³ or less, and further preferably 2. to increase the specific elastic modulus E / d of the light diffusion plate 40. It is 6 g / cm ³ or less, particularly preferably 2.5 g / cm ³ or less.

The diagonal lengths of the light irradiation surface 41 and the light emitting surface 42 of the light diffusion plate 40 are preferably 1200 mm or more in order to increase the area of the surface light emitting device 10.

The plate thickness t (see FIG. 3) of the light diffusion plate 40 is preferably 2.0 mm or less, more preferably 1.8 mm or less, still more preferably 1.6 mm or less, particularly for thinning the surface light emitting device 10 Is 1.4 mm or less. The thickness t of the light diffusion plate 40 is preferably 0.5 mm or more.

The amount of height displacement (also referred to as flatness) in any 300 mm square area in the plane of the light irradiation surface 41 or the light emitting surface 42 of the light diffusion plate 40 is measured in a state where the influence of the self weight deflection can be ignored. In this case, it is preferably 0.5 mm or less, more preferably 0.3 mm or less, still more preferably 0.1 mm or less, and most preferably 0.05 mm or less. By setting the height displacement amount to 0.5 mm or less, the usage pattern of the light diffusion plate 40, in particular, the luminance distribution in the state where the light diffusion plate 40 is mounted on the frame can be made more uniform. In order to make the self-weight deflection negligible, the light diffusion plate 40 is placed on a plane to measure the amount of height displacement (flatness). In order to reduce the in-plane height displacement, it is preferable to use the float method or the fusion method as a method of forming the light diffusion plate 40.

The distance D between the light diffusion plate 40 and each light source 30 in a natural state (for example, a state shown by a two-dot chain line in FIG. 4) is preferably 15 mm or less, more preferably 10 mm or less, for thinning the surface light emitting device 10. More preferably, it is 8 mm or less, and particularly preferably 6 mm or less. The distance D between the light diffusion plate 40 in the natural state and each light source 30 is preferably 1 mm or more, more preferably 3 mm or more, so that the light from each light source 30 is not concentrated in a narrow range of the light irradiation surface 41.

The light diffusion plate 40 is made of glass containing 1 to 16% of MgO, 0 to 5% of P ₂ O ₅ , and 1 to 9% of Al ₂ O ₃ in terms of mol% on an oxide basis. The glass may be a crystallized glass, but in the present embodiment it is a phase separated glass. The phase-separated glass is a phase separated into plural types of glass phases. The multiple glass phases have different refractive indices and scatter light. Phase-separated glass may have a glass phase of a matrix and a glass phase dispersed in the matrix. The phase-separated glass can be obtained, for example, by heat-treating a glass having the following composition.

The phase-separated glass contains, for example, 55 to 70% of SiO ₂ , 1 to 7% of Al ₂ O ₃ , and 1 to 20% of B ₂ O ₃ in terms of mol% on an oxide basis. The phase-separated glass contains, in addition to the above three components, one or more components selected from eight components of MgO, CaO, SrO, BaO, Na ₂ O, K ₂ O, P ₂ O ₅ , and TiO ₂ You may The Na ₂ O content may be 17% or less, and the TiO ₂ content may be 3% or less.

Preferably, phase-separated glass, in mol% based on oxides, SiO ₂ 55 - 70% of _{Al 2 O 3 1 ~ 7%} , B 2 O 3 1-20% ~ 1 MgO 15 %, the CaO 1 ~ 15%, the SrO 1 ~ 15%, 1 ~ 15% of BaO, Na ₂ O 17% or less, the _{K 2} O 5% or _less, P 2 _{O 5} to 1 ~ 8%, TiO ₂ contains 3% or less. Assuming that the total content of these 11 components is 100 mol%, the F content is 2 mol% or less in external ratio.

More preferably, phase-separated glass is in mol% based on oxides, SiO ₂ 58 - 68%, the _{Al 2 O 3 2 ~ 7%} , B 2 O 3 and 3 - 18%, MgO 4 to 10%, 3-10% of CaO, SrO and 3-10%, BaO of 3-10%, Na ₂ O 15% or less, the _{K 2} O 5% or _less, P 2 _{O 5} 2-7% It contains 3% or less of TiO ₂ . Assuming that the total content of these 11 components is 100 mol%, the F content is 1 mol% or less in external ratio.

More preferably, phase-separated glass is in mol% based on oxides, SiO ₂ 60 - 65%, the _{Al 2 O 3 2 ~ 7%} , a _{B 2 O 3 5 ~ 15%} , MgO 4 to 10%, the CaO 3 ~ 10%, the SrO 3 ~ 10%, a _{BaO 3 ~ 10%, Na 2} O 10% or less, the _{K 2} O 5% or _less, P 2 _{O 5} 3-6% It contains 3% or less of TiO ₂ . Assuming that the total content of these 11 components is 100 mol%, the F content is 1 mol% or less in external ratio.

Hereinafter, each component of phase-separated glass is demonstrated. In the description of each component, "%" means mol%.

The SiO ₂ content is 55% or more, preferably 58% or more, more preferably 60% or more, in order to improve the specific modulus of phase-separated glass. In addition, the SiO ₂ content is 70% or less, preferably 68% or less, more preferably 65% or less, in order to maintain the solubility of the glass raw material and hence the homogeneity of the phase-separated glass.

The Al ₂ O ₃ content is 1% or more, preferably 2% or more, more preferably 3% or more, and still more preferably 4% or more, in order to improve the specific modulus of phase-separated glass. The Al ₂ O ₃ content is 9% or less, preferably 8% or less, and more preferably 7% or less, in order to maintain the solubility of the glass material and thus the homogeneity of the phase-separated glass.

The B ₂ O ₃ content is 1% or more, preferably 3% or more, more preferably 5% or more, in order to improve the solubility of the glass raw material and thus the homogeneity of the phase-separated glass. Further, B ₂ O ₃ content, in order to suppress deterioration of the homogeneity of the molten glass due to volatilization of B ₂ O ₃ component from the liquid surface of the molten glass, 20% or less, preferably 18% or less, more preferably 15% or less.

The content of MgO is 1% or more, preferably 3% or more, more preferably 4% or more, in order to improve the specific modulus of phase-separated glass. The MgO content is 16% or less, more preferably 15% or less, still more preferably 12% or less, and most preferably 10% or less, in order to suppress the devitrification of the molten glass during cooling.

The CaO content is preferably 1% or more, more preferably 3% or more, in order to improve the specific elastic modulus of the phase-separated glass. Further, the CaO content is preferably 15% or less, more preferably 10% or less, in order to suppress devitrification at the time of cooling of the molten glass. In particular, when it is desired to increase the diffuse transmittance to increase the luminance of the light emitting surface 42 of the light diffusing plate 40, it is preferably 4% or less, more preferably 2% or less, and still more preferably 1% or less.

The SrO content is preferably 1% or more, more preferably 3% or more, in order to reduce the proportion of linear transmittance in the total light transmittance of the phase-separated glass and to improve the diffuse transmittance of the phase-separated glass. . The SrO content is preferably 15% or less, more preferably 10% or less, in order to suppress devitrification at the time of cooling of the molten glass. In particular, when it is desired to increase the diffuse transmittance to increase the luminance of the light emitting surface 42 of the light diffusing plate 40, it is preferably 4% or less, more preferably 2% or less, and still more preferably 1% or less.

Although the content of BaO may be 0%, it is preferably 1% or more, more preferably, in order to reduce the ratio of linear transmittance to the total light transmittance of the phase separated glass and to improve the diffuse transmittance of the phase separated glass. Is 3% or more. The BaO content is preferably 15% or less, more preferably 10% or less, in order to reduce the thermal expansion coefficient of the phase-separated glass. In particular, when it is desired to reduce the deflection of the light diffusion plate 40, BaO increases the density d and lowers the specific elastic modulus E / d, so it is preferably 4% or less, more preferably 3% or less, still more preferably 2%. Below, most preferably it is 1% or less.

Na ₂ O improves the solubility of the glass material and thus the homogeneity of phase-separated glass. However, the Na ₂ O content is preferably 17% or less, more preferably 15% or less, and more preferably, in order to suppress deterioration of the homogeneity of the molten glass due to volatilization of the Na ₂ O component from the liquid surface of the molten glass. Is less than 10%. The Na ₂ O content may be substantially zero.

K ₂ O improves the solubility of the glass material and thus the homogeneity of phase-separated glass. However, in order to reduce the thermal expansion coefficient of phase-separated glass, the K ₂ O content is preferably 5% or less. The K ₂ O content may be substantially zero percent.

Although the P ₂ O ₅ content may be 0%, it is preferably 1% or more in order to reduce the ratio of the linear transmittance to the total light transmittance of the phase separated glass and to improve the diffusion transmittance of the phase separated glass More preferably, it is 2% or more, further preferably 3% or more. Further, the P ₂ O ₅ content is preferably 8% or less, more preferably 7% or less, in order to suppress deterioration of the homogeneity of the molten glass due to volatilization of the P ₂ O ₅ component from the liquid surface of the molten glass. More preferably, it is at most 6%, particularly preferably at most 5%, most preferably at most 4.5%, most preferably at most 4%.

TiO ₂ reduces the ratio of the linear transmittance to the total light transmittance of the phase separated glass, and improves the diffuse transmittance of the phase separated glass. However, in order to suppress devitrification during cooling of the molten glass, TiO ₂ content is preferably 3% or less. The TiO ₂ content may be substantially zero.

F improves the clarity of the molten glass. However, in order to suppress the devitrification at the time of cooling of the molten glass and also to suppress the deterioration of the homogeneity of the molten glass due to the volatilization of the F component from the liquid surface of the molten glass, the F content is % Or less. The F content may be substantially zero.

ZrO ₂ improves the Young's modulus and specific modulus of phase-separated glass. However, in order to suppress devitrification at the time of cooling of the molten glass, the ZrO ₂ content is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less. The ZrO ₂ content may be substantially zero percent.

A light scattering layer may be provided on both sides or one side of the main surface of the light diffusion plate of the present invention to further improve the light diffusion property. In addition, the surface of the main surface of the light scattering plate of the present invention is subjected to surface treatment to give an uneven structure having a center line average roughness of 50 μm or less and an average interval of the uneven portions of 5 mm or less It may be improved. In Test Examples 1 to 18 described later, no light scattering layer was provided, and no surface treatment was applied to give a structure such as unevenness.

[Test Examples 1 to 12]
In Test Examples 1 to 12, phase-divided glasses of the glass compositions described in Tables 1 to 3 were prepared, and density d, Young's modulus E, specific elastic modulus E / d, total light transmittance T _t , and intensity ratio I ₃₀ / I ₀ was measured.

Phase-separated glass was produced by the following method. First, a glass material prepared in advance was melted, homogenized, and degassed at 1650 ° C. to produce a molten glass. The molten glass is cooled to the phase separation temperature described in Tables 1 to 3 at a cooling rate of 50 ° C. per minute, held at the phase separation temperature for 30 minutes, poured into a mold, and 30 ° C. from the glass transition temperature. After holding at high temperature for 1 hour, the glass was cooled to room temperature at a cooling rate of 1 ° C./min to prepare phase-separated glass. It was observed by a scanning electron microscope that the glass was phase separated and divided into two phases.

As a measurement sample for measuring the total light transmittance T _t , the intensity I ₀ of linear transmission light, the intensity I ₃₀ of diffuse transmission light, etc., those having a plate thickness t of 1.0 mm with both main surfaces mirror-polished Using.

The total light transmittance T _t was measured using an integrating sphere unit of a Perkin Elmer spectrophotometer (trade name: Lamda 950).

The angular distribution of the transmitted light intensity was measured by an ultraviolet visible infrared spectrophotometer (manufactured by JASCO Corporation: V-670 DS) and an automatic absolute reflectance measurement unit (manufactured by JASCO Corporation: ARMN-735). Applying light from the normal direction with respect to one side of the main surface of the measurement sample, by measuring the intensity of the light of wavelength 550nm which angle is transmitted in the direction of 0 ° and 30 ° with the normal direction, I ₀ and was _{I 30.} From these values was calculated _I 30 / _{I 0.}

The measurement results are shown in Tables 1 to 3 together with the glass composition. In Tables 1 to 3, the F content is expressed by an external division when the total content of the 11 components other than F is 100 mol%.

As shown in Tables 1 to 3, phase-divided glasses of the glass compositions of Test Examples 1 to 11 had T _t of 10 to 70%, I ₃₀ / I ₀ of 0.6 or more, and E / d of 26.0 GPa · It was cm ³ / g or more. On the other hand, the phase-differentiated glass of the glass composition of Test Example 12 had a T _t of 10 to 70% and an I ₃₀ / I ₀ of 0.6 or more, but an E / d of less than 26.0 GPa · cm ³ / g Met.

The flatness was measured by a laser displacement meter according to JIS B 0621 1984. Using the glass of Example 5, five plate-like light diffusion plates with a thickness t of 1.0 mm and 300 × 300 mm with mirror-polished on both main surfaces are prepared, and one main surface of each light diffusion plate is determined. It was installed on a board, and the remaining one main surface (upper surface) of the light diffusion plate was scanned with a laser displacement meter to measure the flatness of each main surface. The flatness of the ten major surfaces had a maximum value of 0.4 mm and a minimum value of 0.05 mm.

[Test Examples 13 to 18]
In Test Examples 13 to 18, the relationship between the specific elastic modulus E / d of the light diffusing plate and the luminance distribution of the light emitting surface of the light diffusing plate was examined by simulation. LightTools (manufactured by Synopsys) was used for the simulation. Test Examples 13 to 14 are Examples, and Test Examples 15 to 18 are Comparative Examples.

The light diffusing plate had a rectangular shape with a light emitting surface and a light emitting surface, a vertical dimension (short side length) of 622 mm, a horizontal dimension (long side length) of 1105 mm, and a diagonal length of 1270 mm. The light diffusion plate was placed on a rectangular frame-like horizontal frame having the same outer shape as the light diffusion plate but was not fixed but was bent by its own weight as shown in FIG. The amount of deflection of the light diffusion plate was a maximum value ΔD _max at the center of the light diffusion plate.

The light diffusion plate was composed of a matrix and spherical particles dispersed in the matrix. In Test Examples 13 to 18, the particle diameter, the volume fraction of particles, the refractive index of particles, the refractive index of the matrix, and the total light transmittance T _t and the intensity ratio I ₃₀ / I ₀ agree with the results of Test Example 5 , And decided the thickness t.

Specifically, in Test Examples 13 to 16, assuming that the light diffusion plate is formed of the phase-separated glass of Test Example 5, the particle diameter is 268 nm, the volume fraction of particles is 9%, and the refractive index of the particles The refractive index of the matrix is 1.51, and the plate thickness t is 1.0 mm.

On the other hand, in Test Examples 17 to 18, assuming that the light diffusion plate is composed of polystyrene resin and particles dispersed in polystyrene resin, the particle diameter is 1000 nm, the volume fraction of particles is 22%, and the refractive index of particles Is 1.49, the refractive index of the matrix is 1.59, and the plate thickness t is 2.2 mm.

An LED was used for each of the plurality of light sources. Each LED is a cube of 2 mm on a side, and light is emitted only from the upper surface of the cube. The number of rays from each LED was one million, and the relationship between the direction of the rays and the density of the rays was approximated by a Lambert distribution. The lower surface of each LED was fixed to the upper surface of the light reflection plate. The light reflectance of the upper surface of the light reflection plate was 100%.

The plurality of LEDs were arranged in a matrix on the top surface of the light reflection plate. Specifically, as shown in FIG. 2, an LED group is constituted by 10 LEDs arranged in the lateral direction at a pitch of 100 mm, and five LED groups are arranged in the longitudinal direction at a pitch of 100 mm.

In Test Examples 13 to 17, the distance D between the light diffusion plate in the natural state and each LED was constant at 10 mm. On the other hand, in Test Example 18, the distance D between the light diffusion plate in the natural state and each LED was constant at 30 mm.

The luminance of the light emitting surface (upper surface) of the light diffusing plate was measured in a state where the light diffusing plate was bent by its own weight. The measurement position is on the optical axis of each of the 10 LEDs belonging to the longitudinally central LED group, and in Test Examples 13 to 17, the position is 13 mm above the upper surface of each LED, and in Test Example 18, each LED is The position was 33 mm above the top surface. The measurement area was a rectangular shape having a horizontal dimension of 2.2 mm and a vertical dimension of 1.0 mm.

The results are summarized in Table 4. In Table 4, the numbers of the LEDs represent the order in which the LEDs are arranged, and were set to increase from one lateral end to the other lateral end. In Table 4, the relative luminance is the luminance when the maximum luminance is 1 in each test example.

As apparent from Table 4, in the test examples 13 to 14, since the specific elastic modulus E / d was 26.0 GPa · cm ³ / g or more, the maximum value ΔD _max of the deflection amount is small, and the maximum value of the relative luminance is The difference between the and the minimum value was small. On the other hand, in the test examples 15 to 17, since the specific elastic modulus E / d was less than 26.0 GPa · cm ³ / g, the maximum value ΔD _max of the deflection amount is large, and the difference between the maximum value and the minimum value of the relative luminance Was great. When the maximum value ΔD _{max of the} amount of deflection is large, the distance between the light diffusion plate and the LED is too close due to the deflection at the lateral center, so that the shape of the LED can be seen through and the brightness directly above the LED is increased . Therefore, the difference in relative luminance between the lateral center and the lateral end became large. Further, in Test Examples 17 to 18, in order to obtain sufficient light diffusion in a natural state, a thickness of 2.2 mm is required, and it is difficult to reduce the thickness as a backlight unit.

As mentioned above, although embodiment of a light-diffusion plate etc. was described, this invention is not limited to the said embodiment etc., A various deformation | transformation and improvement are possible within the range of the summary of this invention described in the claim. It is.

Although the deflection of the light diffusion plate 40 is the self weight deflection in the above embodiment, it is not limited to the self weight deflection, and may be a deflection caused by being restrained by the frame 20, for example. Therefore, the light diffusion plate 40 is arranged horizontally in FIG. 4 but may be arranged vertically. The light diffusion plate 40 may be disposed obliquely with respect to the horizontal plane.

Priority is claimed on Japanese Patent Application No. 2016-110849 filed with the Japanese Patent Office on June 2, 2016, and Japanese Patent Application No. 2016-160187 filed on the Japanese Patent Office on August 17, 2016. The entire contents of Japanese Patent Application Nos. 2016-110849 and 2016-160187 are incorporated into the present application.

10 surface emitting device 12 liquid crystal panel 20 frame 30 light source 40 light diffusion plate 41 main surface (light irradiation surface)
42 Main surface (emitting surface)
50 light reflector

Claims (9)

1. A light diffusing plate that diffuses and transmits light from a plurality of light sources from one of two main surfaces facing each other to the other,
   The total light transmittance is T _t when the light having a wavelength of 550 nm is perpendicularly incident on the one main surface, the intensity of the transmitted light having an exit direction in the same direction as the exit direction is I ₀ , and the exit direction is incident. Assuming that the intensity of transmitted light, which is a direction inclined by 30 ° with respect to the direction, is I ₃₀ , T _t is 10 to 70%, and I ₃₀ / I ₀ is 0.6 or more,
   The specific modulus is 26.0 GPa · cm ³ / g or more, and it is 1 to 16% of MgO, 0 to 5% of P ₂ O _5, and 1 to 5% of Al ₂ O ₃ in terms of mol% on an oxide basis. A light diffuser made of glass containing 9%.
2. The light diffusing plate according to claim 1, wherein the glass contains 0 to 2% of BaO and 0 to 2% of ZrO ₂ in terms of mol% on an oxide basis.
3. The diagonal length of each of the main surfaces is at least 1200 mm,
   The light diffusing plate of Claim 1 or 2 whose board thickness is 2.0 mm or less.
4. The light diffusion plate according to any one of claims 1 to 3, wherein the glass is a phase separated glass.
5. The partial phase glass is in mol% based on oxides, SiO ₂ 55 ~ 70%, the _{Al 2 O 3 1 ~ 7%} , including _{B 2 O 3 1 ~ 20%} , according to claim 4 Light diffuser.
6. The light diffusing plate according to claim 4 or 5, wherein the phase-separated glass has a Na ₂ O content of 17% or less and a TiO ₂ content of 3% or less in terms of mol% on an oxide basis. .
7. The light diffusion plate according to any one of claims 1 to 6, wherein the height displacement amount in an arbitrary 300 mm square area in the plane of each of the main surfaces is 0.5 mm or less.
8. A surface light emitting device comprising the light diffusion plate according to any one of claims 1 to 7 and a plurality of the light sources,
   The surface emitting apparatus whose space | interval of the said light-diffusion board and each said light source in the state which is not acting external force is 15 mm or less.
9. A liquid crystal display device comprising: the surface light emitting device according to claim 8; and a liquid crystal panel to which the surface light emitting device emits light.

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