JP2009008991A - Light diffusion plate - Google Patents

Abstract

[PROBLEMS] To prevent the position of a light source from being visually recognized through a light diffusing plate even when a light source having high directivity and high luminance is used, and has a high total light transmittance, and diffusing ability is not significantly reduced even if other layers are laminated. Providing a light diffusing plate, particularly a light diffusing plate that is thin and incapable of being visually recognized even when installed near the light source.
A light in which a filler is dispersed in a transparent resin matrix, the refractive index of the transparent resin matrix is larger than the refractive index of the filler, and the difference is 0.08 or more. Diffusion plate.
[Selection figure] None

Description

  The present invention relates to a light diffusing plate exhibiting sufficient diffusivity even for a light source having high light directivity and high luminance such as an LED.

Conventionally, various light diffusion plates having a function of uniformly diffusing light from a light source, which are used in electric / electronic devices such as personal computers, mobile phones, and car navigation systems, have been proposed. For example, a liquid crystal display device such as a car navigation system is configured to irradiate the liquid crystal display screen from the back side with a light source because the liquid crystal itself does not emit light. The light diffusion plate is arranged between the light source and the liquid crystal display screen in order to make the luminance on the liquid crystal display screen uniform. Here, many light diffusion plates have a structure in which fine particles such as organic or inorganic fillers are uniformly dispersed in a transparent resin matrix. For example, the light diffusion plate according to Patent Document 1 sets the average particle diameter of the fine particles to 1 to 50 μm, causes a part of the fine particles to protrude from the surface of the transparent resin, and sets the refractive index of the fine particles to itself. The difference in refractive index generated at the interface between the transparent resin and the fine particles is set in the range of 0.03 to 0.06, which is different between the surface portion and the inside (claims, etc.). By adopting such a configuration, light is reflected at the interface between the transparent resin and the fine particles, and the problem that the light that should originally pass through the light diffusion layer is reflected and lost is solved. As a result, the light utilization efficiency is increased. It is possible to improve the surface brightness of a surface light source device or the like.
Japanese Patent No. 3499064

  By the way, in recent years, among various light sources, LEDs (light-emitting diodes) have attracted attention because of their low power consumption, high brightness, and long life. However, the light emitted from the LED has been proposed so far, including Patent Document 1, which is exclusively intended for conventional light sources (fluorescent tubes, neon tubes, etc.) whose directivity is not so high because of its strong directivity. In fact, there is no light diffusing plate that has a sufficient diffusing capacity that can be applied to LEDs. Specifically, when a plurality of LEDs are arranged as a light source, the light diffusion plate is thickened (eg, an acrylic plate having a thickness of several millimeters), the installation distance of the light diffusion plate from the light source is increased, or the light diffusion Unless a filler having a high refractive index is used in the matrix of the plate, the positions of the plurality of LEDs can be visually recognized through the light diffusion plate. On the other hand, when these measures are taken so that the light source cannot be visually recognized, there is a problem that the total light transmittance (illuminance) is lowered. Thus, the light diffusivity and the total light transmittance are generally in a trade-off relationship, and a light diffusing plate in which both performances are sufficiently exhibited has not been provided so far.

  In addition, there is a method of improving the diffusibility by forming an uneven shape on the surface of the light diffusing plate, but in this method, if an adhesive layer or the like is laminated on the light diffusing plate, the diffusing ability is almost lost. There is also.

  Therefore, the present invention makes it impossible to visually recognize the position of the light source through the light diffusing plate even when a light source having high directivity and high brightness is used, has a large total light transmittance, and can diffuse even if other layers are laminated. An object of the present invention is to provide a light diffusing plate that does not significantly decrease, particularly a light diffusing plate that is thin and has a light source that is not visible even when installed near the light source.

  The present invention (1) is a light diffusing plate in which a filler is dispersed in a transparent resin matrix. The refractive index of the transparent resin matrix is larger than the refractive index of the filler, and the difference is 0.08 or more. There is a light diffusing plate.

  The present invention (2) is the light diffusing plate according to the invention (1), wherein the transparent resin matrix is a cycloolefin resin, and the filler is a silicone resin.

  The present invention (3) is the light diffusing plate of the invention (1), wherein the transparent resin matrix is an acrylic-styrene resin and the filler is a silicone resin.

  According to the present invention (1), even if a light source having high directivity and high luminance such as an LED is used, the position of the light source cannot be visually recognized through the light diffusion plate, and a light diffusion plate having a large total light transmittance is provided. There is an effect that it becomes possible to do.

  Furthermore, according to the present invention (2) or (3), in addition to the above effects, the light diffusing plate is made thinner by adopting a specific combination of cycloolefin resin or acrylic-styrene resin and silicone resin. (For example, 50 to 100 μm) and can be easily bent. As a result, there is an effect that it can be applied to an object having a curved surface such as a thin advertising light or a specially-shaped signboard. Furthermore, regarding the present invention (2), by adopting a cycloolefin resin as the transparent resin matrix, there is also a production effect of improving the dispersibility of the filler due to the low polarity of the resin matrix.

BEST MODE FOR CARRYING OUT THE INVENTION

  First, the light diffusion plate according to the present invention will be described. The light diffusion plate is formed by dispersing a filler in a transparent resin matrix. Here, the light diffusion plate is not particularly limited, but usually has a thickness of 50 to 500 μm, preferably 50 to 200 μm, more preferably 60 to 150 μm. Hereinafter, each component will be described in detail.

  The transparent resin matrix is not particularly limited as long as it has optical transparency, but is preferably a resin having a refractive index in the range of 1.50 to 1.60. For example, acrylic-styrene resin, acrylic-urethane resin, and various types of cycloolefin resins can be used, and cycloolefin resins are preferably used. The cycloolefin-based resin is preferably a cycloolefin copolymer (COC). The cycloolefin-based resin can be obtained from Polyplastics Co., Ltd., JSR Co., Ltd., Nippon Zeon Co., Ltd., Mitsui Chemicals Co., Ltd., and the following structural formulas are available.

  Next, the filler is not particularly limited as long as it has optical transparency, but is preferably a resin having a refractive index in the range of 1.40 to 1.50. Specific examples include silicone resin particles, acrylic resin particles, and nylon resin particles. The particle size of the filler is not particularly limited, but those having an average particle size of 1 μm to 50 μm, more preferably 1 to 20 μm are preferably used.

  Here, in particular, when targeting a light source having high light directivity and high brightness such as an LED, the refractive index of the resin matrix is larger than the refractive index of the filler, and the difference is 0.08 or more. It is essential. The upper limit of the refractive index difference is not particularly limited, but is preferably 0.20 or less in consideration of the degree of freedom in material selection. The reason will be explained. First, by setting the difference between the refractive index of the resin matrix and the refractive index of the filler to be 0.08 or more, even when a light source having high light directivity and high luminance such as an LED is targeted, light diffusion is performed. It is possible to provide light diffusibility to such an extent that the position of the light source cannot be visually recognized through the plate. Also, by making the refractive index of the resin matrix larger than the refractive index of the filler, light reflection at the interface between the resin matrix and the filler is less likely to occur, so less light is reflected to the light source side, that is, all light rays. The transmittance is improved. In addition, in this specification, the refractive index of a resin matrix or a filler shall be measured based on the B method as described in JIS K-7142 (1996).

Next, the properties of the light diffusion plate according to the present invention will be described in detail. First, the light diffusing plate has such a property that the position of the light source cannot be visually recognized through the light diffusing plate even when a light source having strong light directivity and high luminance such as an LED is used (LED high diffusing property). Here, the “LED high diffusibility” refers to the property that the position of the LED becomes invisible when measured according to the following method.
<< Measurement test method of LED high diffusivity >>
As the light source, 9 LEDs (1500 candela / piece) were arranged at equal intervals in 1 inch (2.54 cm) square. A light diffusing plate was placed at a distance of 3 cm from the tip of the light source (LED), and observation and photography were taken from a point 30 cm away from the diffusing plate on the side opposite to the light source.

  Further, the light diffusing plate also has a property that the total light transmittance is large, and preferably the total light transmittance (JIS K7361-1) is 70% or more, and more preferably 74% or more.

The light diffusing plate according to the present invention may be a single light diffusion plate or may be combined with another base material. For example, it may be combined with a base film in order to increase strength or have heat resistance, and a condensing sheet (one or two, for example, It may be combined with a mode in which a large number of prismatic or wave-like irregular stripes are arranged on the surface or a mode in which a large number of microlenses are arranged on the surface. Furthermore, in order to suppress light loss, antireflection treatment on the light incident surface and / or light exit surface {for example, embossing treatment by forming micro unevenness on the surface, thin film (for example, metal oxide or MgF ₂ ) on the surface } May be applied to the light diffusion plate.

  Next, the manufacturing method of the light diffusing plate according to the present invention will be described. The light diffusing plate can be obtained by preparing a paint in which the filler is blended in an appropriate blending amount with the transparent resin, applying the paint on a predetermined substrate and drying it. Here, although the compounding quantity of the filler with respect to transparent resin is not specifically limited, For example, it is 20-50 weight part with respect to 100 weight part of transparent resin, More preferably, it is 25-40 weight part. Here, the application method is not particularly limited, and examples thereof include well-known methods such as a roll coating method, a spray coating method, a dipping method, and a spin coating method.

  The light diffusing plate according to the present invention can be used for electrical / electronic devices such as a backlight of a liquid crystal display, a lighting fixture, an electric signboard, and a rear projection screen. In particular, it is also useful for electrical / electronic devices using a light source with high directivity and high brightness such as LED. The type, number, position, and the like of the light source are not particularly limited, and may be a linear light source, a point light source, one or a plurality of locations, a direct type, or a side light type.

Example 1
After stirring the paint having the following composition, it was coated on a stainless steel belt by a roll coating method, dried, and the cured sheet was peeled off from the stainless steel belt to obtain a light diffusion plate of this example having a thickness of 60 μm. .
[paint]
Cycloolefin resin (trade name: Arton, manufactured by JSR, refractive index: 1.51) 100 parts by weight Silicone resin particles (trade name: High Plessica UF, manufactured by Ube Nitto Kasei Co., Ltd., refractive index: 1.43, average Particle size: 2.0 μm) 30 parts by weight / toluene 300 parts by weight

Example 2
A light diffusion plate of this example having a thickness of 70 μm was obtained in the same manner as in Example 1 except that the coating material was changed to the following and the coating thickness was changed.
[paint]
・ Acrylic-styrene resin (trade name: Acryt, manufactured by Taisei Fine Chemical Co., Ltd., refractive index: 1.53) 100 parts by weight ・ Silicone resin particles (trade name: High Plessica UF, Ube Nitto Kasei Co., Ltd., refractive index: 1.43, (Average particle size: 4.0 μm) 30 parts by weight / 300 parts by weight of methyl isobutyl ketone

<< Comparative Example 1 >>
A light diffusing plate of a comparative example was obtained in the same manner as in Example 1 except that the coating material was changed as follows.
[paint]
・ Acrylic-styrene resin (trade name: ACRITO, manufactured by Taisei Fine Chemical Co., Ltd., refractive index: 1.53) 100 parts by weight ・ Acrylic resin particles (trade name: MX300, manufactured by Soken Chemical Co., Ltd., refractive index: 1.49, average particle Diameter: 3.0 μm) 30 parts by weight / methyl isobutyl ketone 300 parts by weight

<< Comparative Example 2 >>
A light diffusing plate of a comparative example was obtained in the same manner as in Example 1 except that the coating material was changed as follows.
[paint]
Acrylic resin (trade name: SK Dyne TM2094, manufactured by Soken Chemical Co., Ltd., refractive index: 1.47) 100 parts by weight Silicone resin particles (trade name: High Plessica UF, Ube Nitto Kasei Co., Ltd., refractive index: 1.43, (Average particle size: 4.0 μm) 30 parts by weight / 400 parts by weight of methyl isobutyl ketone

<< Comparative Example 3 >>
A diffusion plate (thickness of about 2 mm) used for a backlight of a liquid crystal display (trade name: Aquos, manufactured by Sharp Corporation) was cut out to obtain a light diffusion plate of a comparative example.

<Effect confirmation test>
1. Diffusivity Confirmation Test A diffusivity test was performed on the light diffusion plates according to the above Examples and Comparative Examples according to the above “LED High Diffusivity Measurement Test Method”. 1 to 6 are photographs showing the results {FIG. 1: Example 1, FIG. 2: Example 2, FIG. 3: Comparative Example 1, FIG. 4: Comparative Example 2, FIG. 5: Comparative Example 3, FIG. 6: Light source only (blank)}. As can be seen from these figures, the position can be visually recognized in any light diffusion plate according to the comparative example, whereas the position of the LED arranged behind the light diffusion plate according to the example cannot be visually recognized. Became.
2. Linear transmitted light amount, total light transmittance, and haze measurement test About the light diffusing plate which concerns on the said Example and comparative example, the linear transmitted light amount, the total light transmittance, and haze were measured. Here, the linear transmitted light amount was measured in accordance with the following << Method for measuring linear transmitted light amount >>. Moreover, the measurement of the total light transmittance (JIS K7361-1) and the haze value (JIS K7136) used the maze meter (brand name: NDH2000, Nippon Denshoku Co., Ltd. make). FIG. 7 shows the result of the linear transmitted light amount, and Table 1 shows the measured values of haze value and total light transmittance.
<< Measurement method of linear transmitted light quantity >>
Using a goniophotometer (trade name: GP-5, manufactured by Murakami Color Co., Ltd.), the light receiving part is fixed at a position where it receives straight light from the light source, and the anisotropic diffusion obtained in the above production example is placed on the sample holder in the meantime. A medium and a light diffusing plate were set.

FIG. 1 is a diagram (photograph) showing a state when a diffusion test of the light diffusion plate according to Example 1 was performed. FIG. 2 is a diagram (photograph) showing a state when a diffusion test of the light diffusion plate according to Example 2 was performed. FIG. 3 is a diagram (photograph) showing a state when a diffusion test of the light diffusing plate according to Comparative Example 1 is performed. FIG. 4 is a diagram (photograph) showing a state when a diffusion test of the light diffusing plate according to Comparative Example 2 is performed. FIG. 5 is a diagram (photograph) showing a state when a diffusion test of the light diffusing plate according to Comparative Example 3 is performed. FIG. 6 is a diagram (photograph) showing only the light source. FIG. 7 is a diagram showing the results of a linear transmitted light amount test on the light diffusion plates according to Examples 1 and 2 and Comparative Examples 1 to 3.

Claims (3)

  A light diffusing plate, wherein a filler is dispersed in a transparent resin matrix, the refractive index of the transparent resin matrix is larger than the refractive index of the filler, and the difference is 0.08 or more.   The light diffusing plate according to claim 1, wherein the transparent resin matrix is a cycloolefin resin, and the filler is a silicone resin.   The light diffusing plate according to claim 1, wherein the transparent resin matrix is an acrylic-styrene resin and the filler is a silicone resin.