JPH1010304A - Light diffusion sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the reflection of the impression of the dots on the rear surface of a light guide plate on an optical display surface by laminating a bead layer dispersed with beads having transparency with a binder having transparency atop a sheet base material formed by kneading the beads having the transparency with a synthetic resin having the transparency. SOLUTION: A mixture formed by melting and mixing the beads 16 having the transparency with the binder having the transparency is applied atop the sheet base material 11 formed by melting and mixing the beads 13 having the transparency with the synthetic resin 15 having the transparency, by which the bead layer 12 is laminated. At the actual use, the bead layer is used by laminating the layer atop the light guide plate in such a manner that the sheet base material 11 side faces the light guide plate. Then, the light transmitted from the front surface of the light guide plate toward the light diffusion sheet 1 is made incident on the sheet from the rear surface of the sheet base material 11 of the light diffusion sheet 1 and is diffused toward the bead layer 12 by the beads 13 in the sheet base material 11. Then, further, the uniform diffusion of the light toward the optical display screen is made possible by the beads 16 of the bead layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-reflecting sheet material for use with a light guide plate for guiding a light beam from a light source to a display element in an optical display device such as a liquid crystal display device or an electric signboard. More specifically, it is a light diffusion sheet for preventing dot printing on the lower surface of the light guide plate from being reflected on an optical display screen.

[0002]

2. Description of the Related Art A light diffusion sheet is used together with a light guide plate as an internal structure of an optical display device such as a liquid crystal display device.

FIG. 3 shows an internal structure of an optical display device. A light source 70 as an edge light and a light guide plate 40 for receiving the light are arranged on the same plane on the lower surface of an optical display screen 60. ing. Then, dots 30 are printed on the lower surface of the light guide plate 40 so as to reflect and diffuse light repeatedly reflected in the light guide plate 40 toward the upper surface of the light guide plate 40.

A light reflection sheet 20 is provided below the dots 30 to reflect light transmitted from the dots 30 to the upper surface of the light guide plate 40.

[0005] The light diffusing sheet 50 is provided on the light guide plate 40.
The light transmitted from the upper surface is provided on the upper surface of the light guide plate 40 to supply the light to the optical display screen 60 with uniform brightness.

As shown in FIG. 4, the light diffusing sheet 50 has a substrate 51 made of a transparent material, one surface of which is optically smooth or non-smooth, and the other surface of which has an uneven surface. What has formed the surface 52 or the light diffusion layer 53 was generally used. Here, the shape of the light diffusion surface 52 is, for example, a saw blade shape (FIG. 4A) or a wave shape (FIG. 4B), and the light diffusion layer 53 is formed of beads or silica particles (FIG. 4C). and so on.

However, the light diffusing sheet is preferably
It has only a thickness of about 0 μm and has a haze effect, but is made of a transparent material such as acrylic resin.
When only one light diffusing sheet is laminated on the upper surface of the light guide plate, as shown in FIG.
There is a problem that the zero shape is reflected on the optical display screen through the light diffusion sheet 50.

Therefore, conventionally, in order to enhance the haze effect of the light diffusion sheet, the light diffusion sheet must be
By stacking them on the upper surface of the light guide plate, the dots on the lower surface of the light guide plate were prevented from transmitting to the optical display screen.

[0009]

As described above, when a plurality of light diffusing sheets are used in a stacked manner, the haze effect is improved, so that the dots can be prevented from being reflected on the optical display screen. However, the light transmittance of the light diffusion sheet is reduced due to the lamination of a plurality of sheets, and therefore, a decrease in the luminance of light supplied to the optical display screen cannot be prevented when the same light source is used.

[0010] Further, in order to stack the light diffusion sheets as described above, it is necessary to consider the deviation of the positions of the respective sheets, and thus there is a problem that the manufacturing process of the optical display device is complicated. .

[0011] Therefore, a light diffusion sheet capable of simultaneously eliminating the impression of dots on the lower surface of the light guide plate while maintaining the light transmittance has been desired.

[0012]

SUMMARY OF THE INVENTION A light diffusion sheet according to the present invention has been made in view of the above-mentioned problems, and has an impression of dots on the lower surface of a light guide plate while maintaining light transmittance. Provided is a light diffusion sheet that can prevent light from being reflected on an optical display screen.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A light diffusion sheet according to the present invention is obtained by kneading a transparent synthetic resin with a transparent bead and kneading the transparent bead with a transparent binder and a transparent binder. It is characterized in that a dispersed bead layer is laminated.

Therefore, if the light diffusion sheet of the present invention is laminated on the upper surface of the light guide plate, the light incident on the light diffusion sheet from the upper surface of the light guide plate is first diffused by the beads of the sheet base material, The light can be diffused again by the beads to uniformly diffuse the light toward the optical display screen and guided.

Since the impression of dots on the lower surface of the light guide plate is also diffused with the diffusion of the light in the two stages, the light diffusion sheet of the present invention is laminated on the upper surface of the light guide plate of the optical display device and used for optical display. It is possible to prevent the impression of dots on the screen.

Further, since the impression of dots can be eliminated with one light diffusion sheet, it is not necessary to use a plurality of light diffusion sheet materials laminated on the upper surface of the light guide plate, and high brightness light can be optically displayed. Can be supplied on the screen.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of the light diffusing sheet 1 according to the present invention. The light diffusing sheet 1 is prepared by melting and mixing transparent beads 13 with a transparent synthetic resin 15. The bead layer 12 is laminated by applying a mixture obtained by melt-mixing transparent beads 16 to a transparent binder 14.

In practice, when the present invention is used, the light guide plate 4 is set so that the sheet substrate 11 faces the light guide plate 40 in FIG.
0 on the upper surface. Thereby, the light guide plate 40
The light transmitted from the upper surface toward the light diffusion sheet 1 is
The light is made to enter from the lower surface of the sheet substrate 11 of the light diffusion sheet 1 and diffused toward the bead layer 12 by the beads 13 inside the sheet substrate 11, and further, by the beads 16 of the bead layer 12, toward the optical display screen 60 in FIG. The light can be uniformly diffused toward.

That is, since the present application has the sheet substrate 11 and the bead layer 12, two-stage light diffusion can be performed by the beads 13 and beads 16 of each layer,
Thereby, it is possible to supply the light diffused uniformly to the optical display screen 60. At the same time, it is possible to diffuse the impression of the dots 30 on the lower surface of the light guide plate 40 and to eliminate the impression on the optical display screen 60.

Hereinafter, each component of the present invention will be described in more detail.

First, the sheet substrate 11 is
The transparent synthetic resin 15 is used to transmit light from the upper surface, and the transparent beads 13 are kneaded with the synthetic resin to diffuse the light.

Here, the synthetic resin 15 having transparency is used.
In consideration of heat deformation temperature, light transmittance, refractive index, and the like, it is preferable to use a polyacrylic resin, a polystyrene resin, a polycarbonate resin, or the like, and particularly preferable to use a polycarbonate resin.

As the transparent beads 13, it is preferable to use beads made of polyacrylic resin, polystyrene resin or polyurethane resin, taking into account light transmittance, refractive index, light diffusion and the like. , Particle size 2-20
It is preferable to use those having a diameter of about μm, more preferably about 5 to 10 μm.

The synthetic resin 15 and the beads 1
3 is a synthetic resin 1 in consideration of light transmittance, light diffusion, and the like.
It is preferable to mix 1 to 100% by weight of beads with respect to 00 parts by weight. It is preferable that the synthetic resin 15 and the beads 13 are mixed by using a well-known extrusion molding method.

The sheet substrate 11 composed of the transparent synthetic resin 15 and beads 13 described above has a thickness of 50 to 500 μm, especially 80 to 500 μm, in consideration of light diffusion and light transmission.
It preferably has a thickness of about 200 μm.

Next, the bead layer 12 is obtained by dispersing beads 16 in a binder 14 in order to further diffuse the light diffused by the sheet substrate 11.

Here, as the beads 16, it is preferable to use beads such as polyacrylic resin, polystyrene resin or polyurethane resin which is a substance having transparency like the beads 13 used in the above-mentioned sheet substrate 11. ,
Considering light transmittance, refractive index, light diffusion, etc.
It is preferable to use one having a thickness of 50 μm, more preferably about 5 to 30 μm.

As the binder 14, it is preferable to use a polyacrylic resin or a polyurethane resin in consideration of heat deformation temperature, light transmittance, refractive index and the like.

When mixing the beads 13 and the binder 14, 10 to 3 parts by weight with respect to 100 parts by weight of the binder 14 (solid content) in consideration of light diffusion and light transmission.
00% by weight and even 50-200% by weight of beads 13
It is preferable to mix the beads 16 into the binder 14 at this time. It is preferable to use a so-called dissolver dispersion method or the like.

Furthermore, if the refractive index of the binder 14 used for the above-described bead layer 12 and the synthetic resin 15 used for the sheet substrate 11 are made to be the same, the binder 14 From synthetic resin 11
Thus, it is possible to reduce loss when light is transmitted to the optical display screen 60 and supply light with higher luminance to the optical display screen 60.

The state of application of the beads 16 and the binder 14 on the bead layer 12 is preferably as shown in the following partially enlarged sectional view of FIG. That is, the beads 16a protruding only partially from the binder 14 and the beads 16b entirely embedded in the binder 14 are present in a mixed state, whereby the light diffusivity is further improved.

The above-mentioned bead layer 12 preferably has a thickness of about 2 to 50 μm, particularly about 10 to 30 μm in consideration of light diffusivity, refractive index, coating difficulty, handling properties, and the like. is there.

Example 1 Example 1 Polycarbonate resin containing acrylic beads (“DS-300
2 "(trade name) (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was formed into a sheet having a thickness of 130 μm by an extrusion molding method to obtain a sheet corresponding to the sheet substrate of the light diffusion sheet of the present invention.

Example 2 The lower surface of the sheet obtained in Example 1 was embossed to a depth of 30 μm to prevent adhesion to the light guide plate. Also,
20 sheets of binder containing acrylic beads are placed on the upper surface of the sheet.
Apply with a roll coater to a thickness of μm,
The light diffusion sheet of the present invention was obtained.

Comparative Example A polyester film having a thickness of 100 μm (“HP-
7 "(trade name) (manufactured by Teijin Limited) on the upper surface was coated with the same binder containing acrylic beads as used in Example 2.
It was applied by a roll coater to a thickness of μm to obtain a conventional light diffusion sheet.

[0037] The sheet obtained in Comparative Test Examples 1 and 2 and Comparative Examples was laminated to the upper surface of the light guide plate of the apparatus shown in FIG. 3, light is incident from the edge light side of the light guide plate, a haze value , Light transmittance, and whether or not dots were visible were observed from the optical display screen on the upper surface of the light guide plate. Table 1 shows the results.

[0038]

[Table 1]

From the results shown in Table 1, it can be seen that the light diffusion sheet of the present invention obtained in Example 2 has almost no difference in light transmittance as compared with the case of using only the sheet base material of Example 1. It can be seen that the haze effect is high. Further, as for the light transmittance, it can be seen that the light diffusion sheet of Example 2 has significantly improved both the haze value and the light transmittance as compared with the conventional light diffusion sheet of the comparative example.

[0040]

The light diffusing sheet of the present invention is laminated on the upper surface of the light guide plate to perform two-stage light diffusion by the beads of the sheet base and the bead layer. The light can be more uniformly diffused and supplied to the optical display screen.

In the light diffusion sheet of the present invention, the impression of the dots on the lower surface of the light guide plate is also diffused in two stages simultaneously with the two stages of light diffusion, thereby preventing the impression of the dots from being reflected on the optical display screen. I can do it.

Further, since the present invention having the light diffusing property and the haze effect as described above can exert its effect without superposing a plurality of sheets, the light transmitting property is secured and the luminance of the optical display screen is reduced. Can be prevented.

Accordingly, the present invention is a light diffusing sheet having excellent light diffusing properties and haze effects and excellent light transmissivity.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of an embodiment of a light diffusion sheet of the present invention.

FIG. 2 is a partially enlarged sectional view of a bead layer of the light diffusion sheet of the present invention.

FIG. 3 is an internal cross-sectional view of the optical display device.

FIG. 4 is a partial cross-sectional view of a conventional light diffusion sheet;
(A) is a light diffusion sheet having a light diffusion surface having a sawtooth cross section,
(B) is a light diffusion sheet having a light diffusion surface having a wave-shaped cross section,
(C) shows a light diffusion sheet having a light diffusion layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light diffusion sheet (this invention) 5 ... Light diffusion sheet (conventional) 11 ... Sheet base material 12 ... Bead layer 13 ... Beads 15 ... Synthetic resin 16 ... Beads 16a and 16b ... Beads 14 ... Binder 20 ... Light reflection sheet 30 .. Dot 40 light guide plate 50 light diffusion sheet 51 base material 52 light diffusion surface 53 light diffusion layer 60 optical display screen 70 light source

Claims (8)

[Claims] 1. A bead layer in which transparent beads are dispersed in a transparent binder is laminated on an upper surface of a sheet substrate in which transparent beads are kneaded with a transparent synthetic resin. Light diffusion sheet. 2. The light diffusion sheet according to claim 1, wherein the synthetic resin is made of a polyacrylic resin, a polystyrene resin, or a polycarbonate resin. 3. The light diffusion sheet according to claim 1, wherein the beads are made of a polyacrylic resin, a polystyrene resin, or a polyurethane resin. 4. The method according to claim 1, wherein the binder is a polyacrylic resin or a polyurethane resin.
4. The light diffusion sheet according to any one of items 1 to 3. 5. The sheet base, wherein the beads are added to the synthetic resin in an amount of 1 to 100 parts by weight of the synthetic resin.
The light-diffusing sheet according to any one of claims 1 to 4, wherein the light-diffusing sheet is mixed in an amount of from 100 to 100% by weight. 6. The light diffusion sheet according to claim 1, wherein in the bead layer, the beads are used in an amount of 10 to 300% by weight based on 100 parts by weight of the binder. . 7. The light diffusion sheet according to claim 1, wherein the sheet base has a thickness of 50 to 500 μm. 8. The light diffusion sheet according to claim 1, wherein the bead layer has a thickness of 2 to 50 μm.