JPH09113709A - Light diffusion film and display device - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To widen the vision of a liquid crystal display, and to suppress a decrease in brightness in the front direction. A liquid crystal display includes a reflective sheet.
And a light guide plate 11 having printed scattering dots 12 provided on the front surface side of the reflection sheet 14. The prism sheet 15 and the liquid crystal panel 7 are sequentially provided on the front surface side of the light guide plate 11, and the light diffusion sheet 1 is provided on the front surface side of the liquid crystal panel 7.
Is arranged. On the surface side of the light diffusion sheet 1,
The convex portion having a light diffusing property and the flat portion having a light transmitting property are mixedly formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device such as a liquid crystal display and a light diffusing film used for the display device, and more particularly, it can minimize the decrease in brightness in the front direction and widen the viewing angle. The present invention relates to a display device and a light diffusion film.

[0002]

2. Description of the Related Art In various displays or lighting equipment, a light diffusing plate or a light diffusing film is used in order to uniformly spread the light of a light source and enhance the visibility. The conventional light diffusing plate or light diffusing film has unevenness formed on the surface of a light transmitting resin such as polymethylmethacrylate resin or polycarbonate resin, or a light transmitting resin such as polymethylmethacrylate resin or polycarbonate resin. It is prepared by dispersing a diffusing agent, or by coating a film substrate with a composition in which a light diffusing agent is mixed and dispersed in a light transmissive resin.

These light diffusion films are usually installed between a light source and a display, and are often used for the purpose of converting a point light source or a line light source into a uniform surface light source. The light diffusion film for such a purpose is often used. Has been proposed.

[0004]

Brightness and viewing angle are particularly important items for evaluating the visibility of the display. In particular, among displays, it has been pointed out that a liquid crystal display capable of providing high quality display has a narrow viewing angle as a disadvantage. The liquid crystal display has a light source and a liquid crystal panel, and the light diffusion film is provided between the light source and the liquid crystal panel. Therefore, the incident light on the liquid crystal panel is
Although it has a wide distribution in the viewing angle direction due to the light diffusion film, the viewing angle of light is narrowed thereafter by the liquid crystal panel.

On the other hand, it is conceivable to provide a light diffusion film on the light emitting surface side of the display to widen the viewing angle of the display. However, if the conventional light diffusion film is installed as it is, the viewing angle is widened but the brightness of the display is large. Will fall.

The present invention has been made in consideration of the above points, and it is possible to suppress the decrease in the brightness of the front surface of the display to a minimum and to expand the field of view and the display. The purpose is to provide a device.

[0007]

According to the first aspect of the present invention,
In a light diffusing film in which one surface or both surfaces are convex portion forming surfaces, the convex portion forming surface has a light diffusing convex portion having an area of 10 to 90% and a light transmitting portion having the remaining area. Is a light-diffusing film, which is characterized in that it comprises a flat portion having good properties.

According to a third aspect of the present invention, there is provided a first substrate having a first polarizing plate, a second substrate having a second polarizing plate, and the first substrate.
A light-diffusing film according to claim 1 is provided on a front surface side of a liquid crystal panel including a liquid crystal layer provided between a substrate and the second substrate.

According to the present invention, a convex portion having an area of 10 to 90% and a flat portion having the remaining area are mixed on the surface side of the light diffusing film, and the convex portion having a light diffusing property and the light transmitting portion are provided. The light-diffusing film having appropriate light-diffusing property and light-transmitting property can be obtained by the flat portion having the property. By arranging this light diffusion film on the front surface side of the liquid crystal panel, it is possible to widen the visual sense of the display device and to suppress the decrease in the brightness in the front direction.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 are views showing an embodiment of the present invention.

First, the display device (liquid crystal display) according to the present invention will be described with reference to FIG. As shown in FIG. 6, the liquid crystal display 10 includes a light guide plate 11 having scattering dots 12 formed on the back surface by pattern printing or the like, a reflection sheet 14 provided on the back surface side of the light guide plate 11,
A light source 13 that makes light enter the light guide plate 11.

A prism sheet 15 and a liquid crystal panel 7 are further sequentially provided on the front surface side (viewing side) of the light guide plate 11, and the light diffusion film 1 is arranged on the front surface side of the liquid crystal panel 7. Of these, the liquid crystal panel 7 includes a first glass substrate 17 having a first polarizing plate 16 on the back surface side, a second glass substrate 19 having a second polarizing plate 20 on the front surface side, a first glass substrate 17 and a second glass substrate. And a liquid crystal layer 18 provided therebetween.

An additional light diffusion film may be provided between the light guide plate 11 and the prism sheet 15, and the scattering dots 12 of the light guide plate 11 may be hidden from the front surface side by the additional light diffusion film.

Next, the light diffusion film 1 will be described with reference to FIGS. As shown in FIGS. 1 to 5, at least the surface of the light diffusing film 1 on the surface side is a convex portion forming surface, and the convex portion forming surface of the light diffusing film 1 is
The convex portion 1a occupies an area of 10 to 90%, and the flat portion 1b occupies the remaining area. Of these, the convex portion 1a
Is a part having a light diffusing property, and the flat part 1b is a part having a light transmitting property.

The convex portion 1a and the flat portion 1b of the light diffusing film 1 can be formed by directly shaping the surface of the light transmissive substrate 2 (FIG. 1 (a)). However, by providing the convex portion 1a formed by shaping the transparent resin 3 on the transparent substrate 2, the convex portion 19 and the flat portion 1b are formed.
May be formed (FIG. 1 (b)). Furthermore, a bead-shaped light diffusing agent 4 is provided in the light-transmitting resin 3 on the light-transmitting substrate 2.
The convex portion 1a and the flat portion 1b may be formed by coating a composition in which is dispersed (see FIG. 1).
(C)).

Next, the shape of the convex portion 1a of the light diffusion film 1 will be described in detail. As shown in FIG. 2A, the convex portions 1a of the light diffusing film 1 may be provided in stripes on the convex portion forming surface of the light diffusing film 1, or the convex portions 1a may be provided in a fixed pattern. (FIG.2 (b)). Further, the convex portions 1a may be provided randomly on the convex portion forming surface of the light diffusion film 1 (FIG. 2 (c)).

As shown in FIG. 4 (a), the protrusions 1a may be provided in stripes and may have a triangular cross section, or the protrusions 1a may be provided in stripes and have a semicircular cross section. Good (Fig. 4
(B)). Further, as shown in FIG. 4C, the convex portion 1a may be composed of a large number of pyramids or a large number of hemispheres (FIG. 4D).

By the way, the convex portion 1a of the light diffusion film 1
Occupies an area of 10 to 90%, but this is
If the area ratio of a is larger than 90%, the brightness decrease on the front surface of the liquid crystal display becomes 10% or more as in the case of the conventional light diffusing film, and if it is smaller than 10%, the effect of widening the viewing angle is hardly recognized. Is.

As shown in FIG. 3, an adhesive or pressure-sensitive adhesive 5 is formed on the back side of the light-transmissive substrate 2 of the light diffusion film 1.
May be provided. Further, as shown in FIG. 5, the convex portion 1 a may be provided on the front surface side of the substrate 2 with a light transmitting resin, and the antireflection layer 6 may be provided on the front surface of the substrate 2. Instead of the antireflection layer 6 on the surface of the substrate 2, a hard coat layer may be provided, or an antireflection layer and a hard coat layer may be provided in an overlapping manner.

Next, the material of each component of the light diffusion film 1 will be described. First, as the light-transmissive substrate 2, it is desirable to use a film containing a polycarbonate resin, an acrylic resin, a polyethylene terephthalate resin, or a polystyrene resin as a main component in terms of shapeability, transparency, light resistance, coating suitability, etc. The thickness is not particularly limited, but is preferably 25 to 200 μ from the viewpoint of easy handling.

Examples of the light-transmitting resin 3 include polyester resin, acrylic resin, polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyethylene resin, polypropylene resin, polyurethane resin, polyamide. Resins, polyvinyl acetate resins, polyvinyl alcohol resins, epoxy resins,
Cellulose resins, organosiloxane resins, polyimide resins, polysulfone resins, polyarylate resins and the like are used. Among these, polypropylene resin, polycarbonate resin, polyethylene terephthalate resin, and acrylic resin are preferable as the light-transmissive resin 3 suitable for shaping the convex portion 1a as shown in FIG. Acrylic resins are particularly excellent in shapeability. The light-transmitting resin 3 suitable for forming the convex portion 1a as shown in FIG. 1C varies depending on the base material 2 and the light diffusing agent 4 used, but it is a polyester resin or an acrylic resin. Urethane resins are particularly desirable because of problems such as coating suitability.

As the material used for the light diffusing agent 4, there are beads or fillers containing acrylic, organic silicone, polystyrene, polyethylene, urea resin, silica, calcium carbonate, titanium oxide as a main component and hollow beads thereof. Is desirable. Of these, acrylic beads are particularly desirable in terms of weather resistance, and the average particle size of the light diffusing agent 4 used is preferably 1 to 50 μm. These light diffusing agents 4 may be used alone or in combination of two or more.

The preferable blending ratio of the light diffusing agent and the light transmitting resin depends on the material used, the refractive index, the particle size of the light diffusing agent, etc., but is 10 to 100 parts by weight of the light transmitting resin. 1
It is about 50 parts by weight.

In addition, a light stabilizer, a heat stabilizer, an antistatic agent, and other additives are separately added and blended in the base material 2, the light transmissive resin 3 and the light diffusivity 4 in order to enhance the commercial value. Is also good.

As the adhesive 5, for example, urea resin, melamine resin, phenol resin, epoxy resin, polyvinyl acetate, polyvinyl chloride, polystyrene, nylon, acrylic polymer and the like are preferable, and the thickness is 5
It is preferably about 30 μm. As the adhesive 5, a rubber-based, acrylic-based, silicone-based adhesive or the like is used.

Further, the antireflection layer 6 is not publicly known, and is formed by, for example, dry or wet coating of magnesium fluoride, a fluororesin or the like having a low refractive index, and the hard coat layer is, for example, an ultraviolet curing type. It is formed by coating with acrylic resin or the like.

Next, a method for manufacturing the light diffusion film will be described. As shown in FIG. 1 (a), as a method for directly forming the convex portion 1 a on the light-transmitting base material 2, a hot pressing method of pressing a high temperature mold against the base material 2 or a resin at a high temperature is used. An EC embossing method is used in which the convex portion 1a is formed on the surface by an embossing roll at the same time when the extruded substrate 2 is formed into a film. As shown in FIG. 1B, the light transmissive substrate 2
As a method of forming the convex portion 1a made of a light-transmissive resin on the upper surface, in addition to the EC embossing method, the light-transmissive radiation-curable resin 3 is shaped on the substrate 2 by a mold and then cured 2P.
Method is used.

As the shape of the convex portion 1a formed by these methods, a semicylindrical cross section of a plane perpendicular to the surface of the convex portion 1a is triangular, trapezoidal, semicircular, or hemispherical. A prism shape, a pyramid shape and the like are conceivable, but a prism shape or a pyramid shape having a vertex angle of 50 to 90 ° is particularly desirable.

As shown in FIG. 1C, the light transmissive substrate 2
As a method for coating the light-transmissive resin 3 and the light diffusing agent 4 on the surface, a screen printing method, a curtain flow method, a roll coating method, a knife coating method or the like can be used. Select the most suitable one in consideration of the film thickness and the surface condition of the substrate.

According to this embodiment, the convex portion 1a having an appropriate light diffusing property and occupying an area of 10 to 90% on the surface side of the light diffusing film 1, and the flat portion having a light transmitting property and occupying the remaining area. By installing the light diffusion film 1 on the front surface side of the display in a mixed manner with the portion 1b, it is possible to widen the viewing angle of the display and minimize the decrease in the brightness in the front direction.

[Examples] Examples of experiments conducted on the present invention will be described below. In the present example, various light diffusion films were prepared, and the following optical characteristic evaluation was performed on each light diffusion film 1. (Evaluation of optical characteristics) -6 when the sample was set to 0 ° with respect to the normal direction of the light diffusion film with a three-dimensional goniometer.
The viewing angle characteristics of 0 to 60 ° were measured. Also, the luminance measurement is 9.
A light diffusion film was placed on the surface of a 4-inch STN color liquid crystal display, and measurement was performed using a luminance meter at a spot size of 0.95 mmφ from a distance of 28.5 cm. (Experimental Example 1) Using a Labo Plastomill and a film sheet take-up device, an acrylic resin (base material) is set to 200 μm.
And a hemispherical shape having a diameter of 100 μm was formed on the surface by a plate on a metal roll at the time of extrusion to obtain a light diffusion film. The molding conditions are as follows.・ Extruder heater set temperature: (second half) (first half) 180 ° C → 220 ° C → 240 ° C → 250 ° C ・ Resin temperature: (second half) (first half) 215 ° C → 225 ° C → 238 ° C ・ Melted resin extrusion Pressure: P ₁ = 24 kg / cm ² , P ₂ = 40 kg / cm ²・ Cylinder rotation speed: 95.3 rpm ・ Metal roll temperature: 80 ° C. (Experimental example 2) 100 μm acrylic resin (light The transparent resin) was extruded onto a polycarbonate film (base material) of 100 μm, and at the time of extrusion, a hemispherical shape having a diameter of 100 μm was formed on the surface by a plate on a metal roll to obtain a light diffusion film. (Experimental Example 3) A roll-shaped intaglio in which a reverse shape of a kamaboko shape (having the same shape but the concavities and convexities) is engraved on the surface of a metal cylinder is prepared. UV curable resin (light transmissive resin) containing functional polyester acrylate oligomer and photoinitiator as main components
The liquid was supplied to the plate surface to cover the inverted concavo-convex surface of the kamaboko shape. Then, a polyethylene terephthalate film (base material) of 50 μm is unwound from a winding roll at a speed that is synchronized with the rotational peripheral speed of the roll-shaped intaglio plate, and the polyethylene terephthalate film is pressed onto the roll intaglio plate with a pressing roll.
The resin solution was laminated and adhered with the resin solution interposed therebetween, and in that state, ultraviolet rays from a mercury lamp were irradiated from the polyethylene terephthalate film side to cross-link and cure the resin solution in the reverse mold, and at the same time, adhered to the polyethylene terephthalate film. Next, the poly (ethylene terephthalate) film running using a peeling roll was peeled off together with the molded cured resin in the shape of a kamaboko that was adhered to it to obtain a light diffusion film having a rough surface in a kamaboko shape. (Experimental Example 4) A polyethylene terephthalate film of 100 μm was used as a substrate, a polyester resin and an isocyanate curing agent were diluted as a light diffusion ink in a solvent to adjust the viscosity, and a thickness of 15 μm was formed in a stripe pattern by a screen printing method. A convex portion having a coating width of 150 μm and a pitch of 300 μm was formed to obtain a light diffusion film. (Experimental Example 5) Polyethylene terephthalate film 100 μm was used as a substrate, polyester resin and isocyanate curing agent as light diffusion ink, acrylic beads having an average particle size of 10 μm as a light diffusing agent were decomposed and diluted with a solvent to obtain a viscosity. And adjust the thickness to 2 by roll coating.
A light diffusion film was obtained by applying 0 μm and a coating amount of 10 g / m ² . (Experimental Example 6) In each of the experimental examples described above, an acrylic adhesive (BPS manufactured by Toyo Ink Co., Ltd.) was formed on the surface different from the convex-formed surface.
4940) and a curing agent (BPS408 manufactured by Toyo Ink Co., Ltd.)
9B) was blended, diluted with a solvent to adjust the viscosity, and coated by a roll coating method to a thickness of 20 μm. (Experimental results) As a result of arranging and evaluating the light diffusing film produced by each of the above-mentioned experimental examples on the surface of the liquid crystal display, any of the samples widened the viewing angle of the display, and the decrease in the luminance in the front direction was 10% or less. . By thus disposing the light diffusion film especially on the front surface of the liquid crystal display, the viewing angle can be widened and the decrease in the brightness in the front direction can be suppressed to a minimum, which brings about the effect of improving the display quality of the display.

[0032]

As described above, according to the present invention,
It is possible to obtain a light diffusing film having an appropriate light diffusing property and light transmitting property, and by arranging this light diffusing film on the front surface side of the liquid crystal panel, it is possible to widen the visual sense of the display device and to The decrease in brightness can be suppressed. Therefore, a high quality display can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a light diffusion film according to the present invention.

FIG. 2 is a plan view of a light diffusion film according to the present invention.

FIG. 3 is a side sectional view showing a modified example of the light diffusion film.

FIG. 4 is a perspective view showing a convex shape of the light diffusion film.

FIG. 5 is a side sectional view showing a modified example of the light diffusion film.

FIG. 6 is a side sectional view showing a display device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light-diffusing film 1a Convex part 1b Flat part 2 Light-transmissive base material 3 Light-transmissive resin 4 Light-diffusing agent 7 Liquid crystal panel 10 Liquid crystal display 11 Light guide plate 12 Scattering dot 13 Light source 14 Reflective sheet 15 Prism sheet 16 First polarizing plate 17 First Glass Substrate 18 Liquid Crystal Layer 19 Second Glass Substrate 20 Second Polarizing Plate

Claims (3)

[Claims] 1. A light-diffusing film having one surface or both surfaces serving as a convex-forming surface, wherein the convex-forming surface has a light-diffusing convex portion having an area of 10 to 90%, and the remaining surface. A light-diffusing film comprising a light-transmissive flat portion having an area. 2. The light diffusing convex portion provided on the convex portion forming surface of the light diffusing film has a hemispherical shape, a prism shape, a pyramid shape or a semi-cylindrical shape, and is perpendicular to the light diffusing convex portion. The light diffusion film according to claim 1, wherein the cross-sectional shape is a triangle, a trapezoid, or a semicircle. 3. A liquid crystal panel comprising a first substrate having a first polarizing plate, a second substrate having a second polarizing plate, and a liquid crystal layer provided between the first substrate and the second substrate. A display device provided with the light diffusion film according to claim 1 on the front surface side.