JPH0713002A - Light-diffusing film - Google Patents

Abstract

PURPOSE:To solve problems such as a complicated structure and high cost of a light diffusing film comprising a plastic film, and to provide a light- diffusing film consisting of a single plastic film excellent in light-diffusing property. CONSTITUTION:This light-diffusing film has a layer of solid fine particles having <=10mum average particle size on the surface of a transparent plastic film. The rear surface of the plastic film is coated with a layer of spherical particles comprising polyolefin resin having <=30mum average particle size. This light- diffusing film is used for a back light illuminating panel of a liquid crystal display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing film applied to a backlight illumination panel in a liquid crystal display device.

[0002]

2. Description of the Related Art In a liquid crystal display device, in order to make the displayed image easy to see, an illumination panel is arranged behind the liquid crystal display panel, and light from this backlight illumination panel is transmitted from the rear side to the front side of the liquid crystal display panel. It is known to do. An example of the structure of such a backlight illumination panel is shown in FIGS. 1 and 2. 1 shows a cross-sectional view of a side lamp type lighting panel in which a lamp is arranged at one side end of a light guide plate, and FIG. 2 shows a lamp in which both sides of the light guide plate are arranged. The cross-sectional block diagram of the side lamp type illumination panel is shown. In these figures, 1 is a light guide plate, which is made of a transparent plastic plate such as an acrylic plate,
A white dot pattern 2 for reflection is printed on the back surface thereof. Reference numeral 3 is a lamp, 4 is a lamp cover, and a reflection sheet 6 is laminated on the inner surface of the lamp cover. 5
Is a reflector, and 7 is a light diffusion film. In the lighting panel having such a structure, the light from the lamp 3 is
The light enters the light guide plate 1, passes through the light diffusing film 7 arranged on the surface thereof, and is led out in the direction of the liquid crystal panel arranged in front of the light diffusing film 7.

By the way, as a light diffusing film 7 applied to such an illumination panel, conventionally, a plastic film having solid fine particle layers formed on both surfaces or the upper surface of the film, the surface of which is made into a fine uneven surface by embossing. A stack of formed plastic films was used. In particular, when high brightness is required for an illumination panel, a plurality of these films are laminated and used. However, when a plurality of films are laminated and used as described above, there is a problem that the cost becomes high due to the complexity of the manufacturing process, the inclusion of dust, the defective lamination, and the like.

[0004]

SUMMARY OF THE INVENTION The present invention solves the problems of structural complexity and high cost found in the conventional light diffusing film made of plastic film, and is made of one plastic film and has a light diffusing property. It is an object to provide an excellent light diffusion film.

[0005]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a solid fine particle layer having an average particle diameter of 10 μm or less is provided on the surface of a transparent plastic film, and a spherical particle layer made of a polyolefin resin having an average particle diameter of 30 μm or less is provided on the back surface of the plastic film. There is provided a light diffusion film applied to a backlight illumination panel in a liquid crystal display device, which has a structure in which

Examples of the transparent plastic film used in the present invention include polycarbonate, polyester, nylon, polyacrylate, polyvinyl chloride and polyolefin. In the present invention, it is particularly preferable to use a plastic having a refractive index of 1.46 to 1.70. The thickness of the plastic film is 0.
05-0.5 mm, preferably 0.075-0.3 mm
Is. It is not necessary to perform embossing on the front surface or the back surface of this plastic film, but if necessary, fine irregularities having a center line average roughness of 0.1 to 6 μm can be formed.

To obtain the light diffusing film of the present invention, a solid fine particle layer (A) is formed on the surface side of the plastic film. The solid fine particle layer (A) can be formed by dispersing solid fine particles in a binder resin liquid, applying the dispersion liquid onto the surface of the embossed film, and drying. As the binder resin liquid, a solution in which the binder resin is dissolved in a solvent, or a dispersion liquid (emulsion) in which the binder resin is dispersed in the solvent is used. As the binder resin, a thermoplastic resin, a thermosetting resin, a photocurable resin or the like is used. As the solid fine particles, organic and inorganic fine particles are used. Examples of the organic fine particles include synthetic resin fine particles (crosslinked styrene polymer beads, etc.) and formalin resin. As the inorganic fine particles, silica, alumina, zirconia, titania, zeolite, kaolin, clay,
Calcium carbonate, barium sulfate, magnesium hydroxide,
Examples include calcium carbonate and calcium phosphate. The average particle size of the solid fine particles is 10 μm or less, preferably 1 to
It is 7 μm. The weight ratio of the solid fine particles to the binder resin in the solid fine particle layer (A) is 1/10 to 4 /.
1, preferably 1/5 to 2/1. The thickness of the solid fine particle layer (A) is 1 to 30 μm, preferably 3 to 2
It is 0 μm. The center line average roughness of the solid fine particle layer (A) is 0.2 to 5.0 μm, preferably 0.3 to 3.0 μm.
m, and if it deviates from this range, a film having good light diffusivity cannot be obtained.

In the present invention, the spherical particle layer (B) made of a polyolefin resin is formed on the back surface side of the plastic film. The spherical particle layer (B) can be formed by dispersing spherical particles of a polyolefin resin in a binder resin, applying the dispersion on the back surface of the film, and drying. As the binder resin liquid, a solution obtained by dissolving the binder resin in a solvent,
A dispersion liquid (emulsion) in which a binder resin is dispersed in a solvent is used. As the binder resin, a thermoplastic resin, a thermosetting resin, a photocurable resin or the like is used. As the spherical particles of the polyolefin resin, spherical particles made of a polymer or copolymer mainly containing olefin such as polyethylene, polypropylene, polybutylene, and ethylene / propylene copolymer are used. The average particle size of the spherical particles is 30 μm or less, preferably 5 to 20 μm.
m. The weight ratio of the spherical particles to the binder resin in the spherical particle layer (B) is 0.1 / 1 to 4 /.
1, preferably 0.6 / 1 to 2/1. The thickness of the spherical particle layer (B) is 2 to 30 μm, preferably 5 to 20 μm.
And the center line average roughness of the surface is 0.2 to
It is 2.0, preferably 0.5 to 1.5.

In the light diffusing film of the present invention, the solid fine particle layer (A) formed on the surface side thereof is preferably a spherical particle layer made of formalin resin. in this case,
The formalin resin means a resin containing formalin as a condensation reaction component. Examples of such formalin resin include benzoguanamine / formaldehyde condensate, melamine / formaldehyde condensate, benzoguanamine / melamine / formaldehyde condensate, and the like. Among those resins, the benzoguanamine / melamine / formaldehyde condensate shows a particularly excellent light diffusion effect.
The average particle diameter of the spherical particles of the formalin resin is 10 μm or less, preferably 1 to 8 μm, more preferably 2.2 to 5
μm.

The benzoguanamine / melamine / formaldehyde condensate (hereinafter also referred to as BMF resin) is a resin represented by the following formula.

[Chemical 1] (In the formula, n and m represent integers of 1 or more)

The average particle size of the BMF resin used in the present invention is 1 to 8 μm, preferably 2.2 to 5 μm. The particle range is usually 0.5 to 8 μm. BMF resins provide films with superior light diffusion properties compared to other formalin resins such as benzoguanamine / formaldehyde condensates and melamine / formaldehyde condensates.

The light diffusion film having the spherical particle layer (A) made of the formaldehyde resin described above can be obtained by applying a coating solution containing the resin particles and the binder resin on the surface side of the film and drying. . In this case, the weight ratio of the formaldehyde resin to the binder resin is 0.7 to 2.0, preferably 1 to 1.5.
If it deviates from this range, the light diffusivity of the obtained film will deteriorate. The formaldehyde resin particle layer (A) has a thickness of 2 to 30 μm, preferably 3 to 2
The center line average roughness is 0.2 to 5 μm.
m, preferably 0.3 to 1.5 μm.

[0013]

EXAMPLES Next, the present invention will be described in more detail by way of examples. All parts and% shown below are based on weight.

Example 1 A polyethylene terephthalate film having a thickness of 130 μm was used as a base film. The surface of the base film is coated with the following synthetic silica dispersion liquid at 130 ° C.
And dried for 3 minutes to form a synthetic silica layer (A) (thickness: 15 μm) having a center line average roughness of 0.52 μm. (Synthetic silica dispersion) Synthetic silica: 8.0 parts (Syloid 244,
Fuji Devison Chemical Co., Ltd., average particle size 1.8 μm) Water: 50 parts Nonionic surfactant: 0.1 parts 5 wt% ammonia water: 0.9 parts Pre-crosslinked acrylic emulsion: 66 parts On the back side of the material film, apply the dispersion liquid of the following white polyolefin-based resin particles at 110 ° C.
For 5 minutes to form a polyolefin resin particle layer (B) (thickness: 12 μm) having a center line average roughness of 0.96 μm. (Polyolefin resin particle dispersion) Chemipearl W-800: 35.6 parts Ethanol: 20.0 parts Nonionic surfactant: 0.12 parts Melamine resin: 13.2 parts Self-crosslinking acrylic emulsion: 55.2 parts Modified Poval: 4.0 parts Ammonium chloride: 0.12 parts Funnel oil: 2.8 parts The Chemipearl W-800 (manufactured by Mitsui Petrochemical Co., Ltd.)
Is an aqueous dispersion of spherical particles made of low molecular weight polyolefin (softening point 130 ° C.) having an average particle size of 7 μm and having a solid content concentration of 40%.

(Measurement of Performance of Light Diffusing Film) The light diffusing film obtained above is placed on the light guide plate 1 of the illumination panel having the structure shown in FIG. In this case, the light diffusing film is placed so that the back surface side (the surface having the spherical particle layer made of polyolefin resin) contacts the light guide plate. next,
Set the luminance meter in the direction perpendicular to the light guide plate. Then, the lamp is turned on and the brightness of the light transmitted through the diffusion film is measured. The results are shown in Table 1. For comparison, the performance of the conventional light diffusing film was also measured in the same manner. The results are shown in Table 1. As the conventional light diffusion film, one obtained by laminating one light diffusion film (F-300HS, manufactured by Somar Co., Ltd.) and the embossed base film shown in Example 1 (conventional product A),
Further, a laminate of the same light diffusion film A and the same embossed base film (conventional product B) was used. As shown in Table 1 in comparison with the product of the present invention, the brightness of the conventional product A is not sufficient. Further, in the case of the conventional product B, the brightness was sufficient, but the number of laminated films was 3,
Work efficiency is significantly deteriorated. On the other hand, the product of the present invention has sufficient brightness, requires only one film, and has very good working efficiency.

[0016]

[Table 1]

Example 2 A polyethylene terephthalate film having a thickness of 130 μm was used as a base film. A dispersion containing white BMF resin particles shown below was applied to the surface side of this substrate film and dried at 130 ° C. for 3 minutes to obtain a BMF resin particle layer (A) having a center line average roughness of 0.1 μm. (Thickness 5 μm) was formed. Then, in the same manner as in Example 1, a spherical particle layer (B) made of a polyolefin resin was formed on the back surface of the film to obtain a light diffusion film. (BMF resin particle dispersion liquid) BMF resin particles: 8.0 parts (average particle diameter of about 3 μm) Nonionic surfactant: 0.4 parts 5 wt% ammonia water: 3.0 parts Melamine resin: 6.1 parts Self-crosslinking Acrylic emulsion: 23 parts Ammonium chloride: 0.24 parts Funnel oil: 5.0 parts Water: 23.4 parts

Example 3 A benzoguanamine / formaldehyde condensate (average particle size: about 2) was used in place of the BMF resin particles in Example 2.
A light diffusion film was obtained in the same manner except that (.mu.m) was used.

Example 4 In Example 2, instead of the BMF resin particles, a melamine / formaldehyde condensate (average particle size: about 1.2 μm) was used.
A light diffusion film was obtained in the same manner except that m) was used.

(Measurement of Performance of Light Diffusing Film) Each of the light diffusing films obtained above is placed on the light guide plate 1 of the illumination panel having the structure shown in FIG. 1 so that the back side thereof contacts the light guide plate. . Next, the luminance meter is set in the direction perpendicular to the light guide plate. Then, the lamp is turned on and the brightness of the light transmitted through the diffusion film is measured. The results are shown in Table 2. For comparison, the performance of the conventional light diffusing film was also measured in the same manner. The results are shown in Table 2.
As the conventional light diffusion film, one light diffusion film (manufactured by Somar Co., F-300HS) and the embossed base film shown in Example 1 were laminated (conventional product A), and the same. A laminate of two light diffusion films A and the same embossed base film (conventional product B) was used. As shown in Table 2 in comparison with the product of the present invention, the brightness of the conventional product A is not sufficient. Further, in the case of the conventional product B, the brightness was sufficient, but the number of films to be laminated was 3, and the working efficiency was significantly deteriorated. On the other hand, the product of the present invention has sufficient brightness, requires only one film, and has very good working efficiency.

[0021]

[Table 2]

[0022]

The light diffusing film of the present invention is excellent in its light diffusing effect, and transmits the light guided from the surface of the light guide plate with high brightness in the direction of the liquid crystal display panel. Therefore, the liquid crystal display device using the illumination panel to which the light diffusion film of the present invention is applied as a backlight has high brightness and the displayed image is easy to see.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a side-lamp type illumination panel in which a lamp is arranged at one side end of a light guide plate.

FIG. 2 is a cross-sectional configuration diagram of a side lamp type illumination panel in which lamps are arranged at both ends of a light guide plate.

[Explanation of symbols]

 1 Light guide plate 2 White dot pattern 3 Lamp 4 Lamp cover 5 Reflector 6 Reflective sheet 7 Light diffusion film

Claims (3)

[Claims] 1. A solid particle layer having an average particle size of 10 μm or less is provided on the surface of a transparent plastic film, and a spherical particle layer made of a polyolefin resin having an average particle size of 30 μm or less is provided on the back surface of the plastic film. A light diffusion film applied to a backlight illumination panel in a liquid crystal display device having the above structure. 2. A spherical particle layer made of formalin resin having an average particle diameter of 10 μm or less is disposed on the surface of a transparent plastic film, and spherical particles made of a polyolefin resin having an average particle diameter of 30 μm or less are provided on the back surface of the plastic film. A light diffusion film applied to a backlight illumination panel in a liquid crystal display device, which has a structure in which layers are arranged. 3. A benzoguanamine / melamine / having an average particle diameter of 2.2 to 5 μm on the surface of a transparent plastic film.
Arrange a spherical particle layer made of formaldehyde condensate,
A light diffusion film applied to a backlight illumination panel in a liquid crystal display device, which has a structure in which a spherical particle layer made of a polyolefin resin having an average particle diameter of 30 μm or less is arranged on the back surface of the plastic film.