JP2614191B2 - Light diffusion film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion film used for a liquid crystal display, an illuminator, a signboard, etc. for diffusing light.

[0002]

2. Description of the Related Art Conventionally, as a light diffusion film, a light diffusion film in which a resin layer in which beads having a smooth surface are dispersed is formed on the surface of a plastic film is known (Nikkei Micro Device (published by Nikkei BP)). February 1993, pages 98-99). The light diffusion film has a higher luminance than the conventional light diffusion film in order to increase the luminous efficiency. The light-diffusing film is disposed between the light source and the display to enhance the efficiency of light passing through the light-guide plate for uniformly spreading light and forming a surface light source. Usually two pieces are installed and used between them. However, since the conventional light diffusion film is placed on a light guide plate made of an acrylic plate or the like, the light diffusion film is adsorbed to the light guide plate, thereby causing a moiré pattern and a variation in luminance. Conventionally, in order to prevent the occurrence of the moire pattern, the back surface of the plastic film of the light diffusion film has been coated with ordinary silica as a matting agent.

[0003]

However, the conventional light diffusion film in which ordinary silica is coated on the back surface of a plastic film using a matting agent as a matting agent has a lower luminance than that of a film which is not coated with silica. This is presumed to be because light passing through the light guide plate does not sufficiently pass through the light diffusion film due to phenomena such as reflection, diffusion, or blocking of light at the silica particle interface when passing through the light diffusion film. Is done. The present invention eliminates the above disadvantages,
It is an object of the present invention to provide a light diffusion film that prevents the occurrence of a moiré pattern and causes a variation in luminance, and also prevents a decrease in luminance.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a light diffusion film comprising a resin film in which beads are dispersed on the surface of a plastic film, wherein a smectite having a particle diameter of several hundred nm is formed on the back surface of the plastic film. A light diffusion film characterized by forming a resin layer in which is dispersed. As the plastic film, various plastic films such as a polyester film, a polycarbonate film, an acrylic film, a weather-resistant vinyl chloride film, an embossed polycarbonate film, and a cellulose acetate film can be used. The thickness of the plastic film is not particularly limited, but is 38 to 188 μm.
Is preferred. When the thickness of the plastic film is less than 38 μm, the film is easily curled. If the thickness of the plastic film is greater than 188 μm, the brightness will not improve much.

[0005] A resin layer in which beads are dispersed is formed on the surface of a plastic film. The resin used for the resin layer in which the beads are dispersed is not particularly limited, and various resins can be used, but a resin having transparency, bead dispersibility, light resistance, moisture resistance, and heat resistance is particularly preferable. Specifically, for example, polyester polyol, acrylic resin, melamine resin, silicone resin, epoxy resin and the like can be mentioned.

As beads, plastic beads and glass beads can be used. Although beads having a smooth surface, which are used in conventional light diffusion films, can be used as beads, it is more preferable to use beads having a fine uneven surface for improving brightness. The brightness can be further improved by using beads having fine irregularities on the surface.

[0007] A fluorescent dye may be added to the resin layer in which the beads are dispersed, and such a resin is also included in the present invention. When a fluorescent dye is added to the resin layer in which the beads are dispersed,
Brightness is further improved. When the fluorescent dye is added to the resin layer in which the beads are dispersed, the fluorescent dye is not particularly limited as long as the luminance is improved. ２2% by weight may be added. Also, the color of the fluorescent dye is not particularly limited, and for example, any of blue, red, yellow and the like can be used alone or in combination. In addition, an appropriate amount of an appropriate dispersant may be mixed in the resin layer in which the beads are dispersed, and such a configuration is also included in the present invention.

On the back surface of the plastic film, a resin layer in which smectite having a particle diameter of several hundred nm is dispersed is formed. By doing so, it is possible to prevent the occurrence of moiré patterns and variations in luminance, and also to prevent the luminance from decreasing. Before forming a resin layer in which smectite is dispersed, on the back surface of the plastic film, perform a primer treatment with an appropriate resin such as an aqueous acrylic resin, a solvent acrylic polyol, an aqueous polyester polyol, or a solvent polyester polyol to form an easily adhesive layer. The present invention also includes a resin layer in which smectite is dispersed on the easy-adhesion layer.

The resin used for the resin layer in which smectite is dispersed is not particularly limited, and various resins can be used. The resin has transparency, smectite dispersibility, light resistance,
Resins having moisture resistance and heat resistance are particularly preferred. Specific examples include acrylic resins, polyester polyols, acrylic resins, melamine resins, silicone resins, epoxy resins, and the like. The resin layer in which smectite is dispersed may be mixed with an appropriate amount of an appropriate dispersing agent, and such a configuration is included in the present invention.

The thickness of the resin layer in which smectite is dispersed is not particularly limited, but is preferably 1 to 3 μm. If the thickness of the resin layer in which smectite is dispersed is less than 1 μm, the resin layer is too thin and a moiré pattern easily occurs in the resin layer itself due to interference. The thickness of the resin layer in which smectite is dispersed is 3μ
When the thickness is more than m, the resin layer is too thick, and the smectite particles overlap, so that the transparency of the resin layer is reduced and the luminance is apt to be reduced.

The amount of smectite dispersed in the resin layer in which smectite having a particle diameter of several hundred nm is dispersed is not particularly limited, but is preferably 6 to 10% by weight based on the resin in the resin layer. If the amount of smectite is less than 6% by weight of the resin in the resin layer, a moiré pattern is generated and the luminance tends to vary, and if it is more than 10% by weight, the transparency is lowered and the luminance is liable to be lowered.

When a resin layer in which smectite having a particle diameter of several hundred nm is dispersed is formed on the back surface of the plastic film, it is possible to prevent the occurrence of moire patterns and variations in luminance, and also to prevent the luminance from lowering. There is not enough theoretical elucidation at this time to see what can be done. However, smectite with a particle size of several hundred nm is very fine and easily dispersed enough for several reasons, such as light diffusion, diffusion, or shielding at the smectite particle interface. By producing a synergistic effect of preventing light from passing through the film sufficiently, it can be presumed that this is very effective in preventing the variation in luminance and the reduction in luminance due to the generation of moiré patterns.

[0013]

【Example】

Examples 1 to 5 On the surface of a 100 μm-thick wide and long polyester film (O-300E manufactured by Diafoil Co., Ltd.), polyacrylic acid ester-based beads having fine irregularities as surface beads (Techpolymer manufactured by Sekisui Chemical Co., Ltd.) EAX-15)
Using a polyester polyol (Polyester Polyol manufactured by Toyobo Co., Ltd.) as a resin, applying a paint in which 10 parts by weight of fine surface irregular beads are dispersed in 16 parts by weight of a resin by a reverse method, and then drying the resin. A resin layer having a thickness of 17 μm in which fine irregular beads were dispersed was formed.
Next, the back surface of the polyester film is subjected to a primer treatment with an aqueous acrylic resin to form an easy-adhesion layer, and a particle diameter of about 500 to 600 nm is formed on the easy-adhesion layer.
(Smectite SPN manufactured by Corp Chemical Co., Ltd.), polymethyl methacrylate acrylic (Alloset UW5160 manufactured by Nippon Shokubai Co., Ltd.), and 6 parts by weight and 7 parts by weight of smectite based on 100 parts by weight of the resin. , 8 parts by weight, 9 parts by weight and 10 parts by weight of 5
The dispersions of various types were applied by a gravure method (200 mesh) and dried to form a resin layer having a thickness of 1 μm in which smectite was dispersed, and 6%, 7%, and 8% by weight of smectite based on the resin. , 9% by weight and 10% by weight of the dispersion film of the present invention were obtained.

Comparative Examples 1-2 In place of smectite, silica (Nibseal E-220A manufactured by Nippon Kagaku Kogyo Co., Ltd.) was used in an amount of 6% by weight and 1% by weight of the resin.
Two kinds of light diffusion films were obtained in the same manner as in Example 1 except that the dispersion was 0% by weight. Comparative Examples 3 and 4 In place of smectite, silica (Nippon Aerosil R)
972) was dispersed in 6% by weight and 10% by weight with respect to the resin, and two types of light diffusion films were obtained in the same manner as in Example 1. Comparative Examples 5 and 6 A light diffusion film 2 was prepared in the same manner as in Example 1 except that silica (Aerosil TT-600, manufactured by Nippon Aerosil Co., Ltd.) was dispersed in 6% by weight and 10% by weight of resin in place of smectite. Got the kind. Comparative Examples 7 and 8 Two kinds of light diffusing films were obtained in the same manner as in Example 1, except that silica (Sildix H51 manufactured by Asahi Glass Co., Ltd.) was dispersed in the resin at 6% by weight and 10% by weight instead of smectite. . Comparative Examples 9 and 10 Two kinds of light diffusing films were obtained in the same manner as in Example 1 except that silica (Aerosil 300 manufactured by Nippon Aerosil Co., Ltd.) was dispersed in the resin at 6% by weight and 10% by weight, instead of smectite. . Comparative Example 11 One kind of light diffusing film was obtained in the same manner as in Example 1 except that an easy-adhesion layer and a resin layer in which smectite was dispersed were not formed on the back surface of the polyester film.

The total of Examples 1 to 5 and Comparative Examples 1 to 11 was 1
The luminance was measured for the six types of obtained light diffusion films. The method of measuring the luminance is as follows. Two kinds of the obtained 11 kinds of light diffusion films are placed on the light guide plate having the screen print dots, respectively, and light is emitted from the side of the light guide plate using a cold cathode tube having a thickness of 5 mm as a light source. And the amount of light diffused through the light guide plate and the two light diffusion films was measured by a luminance meter (SL-110 manufactured by Minolta) fixed at a position 30 cm from the light diffusion film. The light transmittance was measured for the parallel light transmittance (PT) and the haze (HZ). The measuring method is about 5cm x light diffusion film.
The sample was cut into 5 cm to obtain a measurement sample, which was irradiated with light from the side of the resin layer in which smectite was dispersed (the polyester film side in Comparative Example 11), and measured with a haze meter (1001 DH manufactured by Nippon Denshoku Industries Co., Ltd.). Furthermore, the occurrence of moiré patterns was visually observed. The results of measurement or observation of the luminance, light transmittance and moiré pattern were as shown in Table 1.

Table 1 Smectite or luminance Light transmittance Moire pattern Silica dispersion (%) (cd / m ² ) Presence or absence of PT HZ Example 1 6 700 88.6 1.2 None Example 2 7 700 88.4 1.4 None Example 3 8 700 88.1 1.6 None Example 4 9 699 87.7 2.0 None Example 5 10 699 87.5 2.1 None Comparative Example 1 6 664 53.5 41.8 None Comparative Example 2 10 649 22.9 70.5 None Comparative Example 3 6 688 84.6 5.3 None Comparative Example 4 10 675 82.1 8.2 None Comparative Example 5 6 665 82.3 8.4 None Comparative Example 6 10 655 67.6 25.4 None Comparative Example 7 6 645 49.5 46.1 None Comparative Example 8 10 639 44.8 46.8 None Comparative Example 9 6 679 66.5 25.7 None Comparative Example 10 10 677 59.7 33.8 None Comparative Example 11-690 88.5 1.3 Yes

[0017]

Since the present invention is constructed as described above, since a moire pattern does not occur as is clear from Table 1, there is no variation in luminance. In addition, it is possible to prevent a decrease in luminance. In particular, in the case of using beads having a fine uneven surface, not only the decrease in luminance can be prevented as is clear from Table 1, but also the luminance can be prevented. Can be further improved.

Claims (3)

(57) [Claims] 1. A light diffusion film having a resin layer in which beads are dispersed on the surface of a plastic film, wherein the particle diameter is several hundred nm on the back surface of the plastic film.
A light diffusion film, wherein a resin layer in which smectite is dispersed is formed. 2. The method according to claim 1, wherein the smectite has a resin content of 6%.
The light diffusion film according to claim 1, wherein the content of the light diffusion film is from 10 to 10% by weight. 3. The light diffusion film according to claim 1, wherein the beads are beads having a fine uneven surface.