JPH09211207A - Light control film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light control film having a sufficient hiding property and a high light transmittance by forming a light diffusing layer with a composition prepared by mixing and dispersing a specified amt. of a polystyrene resin grain in the transparent-resin base consisting of a polyester resin. SOLUTION: A light diffusing layer 6 obtained by dispersing a fine grain in a transparent resin base is formed on the base sheet 7 consisting of a transparent resin, etc., and the light diffusing layer 6 is formed from a composition prepared by mixing 100 pts.wt. of the transparent resin base consisting of the polyester resin 6a and 60-100 pts.wt. of the polystyrene resin grain 6b. In this case, 65-100 pts.wt., preferably 80-100 pts.wt., of the polystyrene resin grain 6b is mixed. Polyethylene terephthalate is most appropriately used as the material of the base sheet, since it is highly adhesive to the polyester resin as the transparent resin base of the light diffusing layer 6, low in impurities, highly transparent and inexpensive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control film used for a backlight of a liquid crystal display, a lighting device, an illuminated signboard, a rear projection screen and the like.

[0002]

2. Description of the Related Art Conventionally, a thin display device using a liquid crystal such as a personal computer, a word processor, a liquid crystal television, etc. does not emit light from the liquid crystal itself, so that a backlight for illuminating the liquid crystal display screen from the back side is used. There is. This backlight needs to illuminate the entire liquid crystal display screen uniformly. For example, NIKKEI MATERIAL & TECHNOLOGY 1993.12, N.
o.136 Side light type or direct type surface light source devices as shown on pages 34 to 38 are adopted.

The above sidelight type surface light source device is shown in FIG.
As shown in FIG. 3, the light guide plate 21, the light sources 20 arranged on the light incident end faces on both sides of the light guide plate 21, and the light guide plate 21 arranged on the back surface side of the light guide plate 21 to emit light from the back surface of the light guide plate 21. The light that has passed through the light diffusing plate 23 and the light diffusing plate 23 that diffracts the light emitted from the light exiting surface of the light guide plate 21 to make the brightness of the irradiation surface uniform. Are provided on the light diffusion plate 23 so as to gather in the front direction. The light-condensing sheet 24 is in the form of a sheet having a large number of prism-shaped or wave-shaped concavities and convexities arranged on the surface thereof, and one sheet or two sheets are stacked. Further, on the back surface of the light guide plate 21, white dots are screen-printed or provided with projections and depressions in order to reduce variations in the brightness of the outgoing light surface.

In this device, the light from the light source 20 is guided by the light guide plate 21.
Light is incident on the entire light guide plate 21 and is emitted from the entire emission light surface. After being diffused by the light diffusion plate 23 and condensed by the condensing sheet 24, the light is condensed. A liquid crystal display screen (not shown) arranged on the upper side of the sheet 24 is uniformly illuminated. In the figure, reference numeral 25 is a reflection cover for reflecting the light of the light source 20 to the light guide plate 21 side.

Further, when it is not necessary to make it thin like a vehicle-mounted display device, as shown in FIG. 5, the light guide plate 2 is used.
Alternatively, a direct type system in which an air layer 26 is provided between the light diffusion plate 23a and the reflection plate 22a and the light source 20a is disposed in the air layer 26 is also used.

In the above surface light source device, in order to increase the brightness of the display screen and reduce the power consumption of the display device,
Each member of the surface light source device is made of a material such as a material having a high transmittance so as to suppress the loss of light. The light diffusing plate 23 is, for example, JP-A-6-5910.
No. 8, JP-A-7-209502, JP-A No. 7-209502
No. 216328, Registered Utility Model Publication No. 30108
As proposed in No. 71, etc., there is used a substrate sheet made of a transparent resin film having a light diffusion layer in which organic or inorganic fine particles are dispersed in a transparent resin binder. The light diffusing plate 23 diffuses and scatters the light passing through the light diffusing layer to make the brightness of the irradiation surface uniform.

[0007]

Recently, in order to reduce battery consumption and reduce power consumption, such as in a surface light source device used for a notebook type personal computer, the light transmittance of a light diffusion plate is reduced. It is desired to improve the brightness of the outgoing light surface to improve the brightness. Further, due to increasing consumer needs, development of a light diffusing plate having excellent concealing property is desired in order to hide white dots and irregularities on the back surface of the light guide plate. However, in the conventional light diffusing plate, generally, both the hiding property and the light transmittance are inversely proportional, and there is a problem in adjusting the balance. That is, if the light diffusing plate is to have a sufficient concealing property,
Light scattering in the light diffusing layer, loss due to reflection increases and the light transmittance decreases, and conversely, when trying to increase the light transmittance, the hiding property becomes insufficient and the white dots are visible. There was a problem that the quality of the screen deteriorates. As described above, the light diffusion plate having both the concealing property and the light transmitting property has not been developed so far.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a light control film having both sufficient concealing property and high light transmission efficiency.

[0009]

In order to achieve the above object, the light control film of the present invention has a light diffusion layer formed by laminating fine particles in a transparent resin base on the surface of a transparent substrate sheet. In the above light control film, the light diffusion layer is made of a composition in which 60 to 100 parts by weight of polystyrene resin particles are mixed and dispersed in 100 parts by weight of a transparent resin base made of a polyester resin.

That is, the present inventors disperse fine particles in a transparent resin base in the course of conducting a series of studies for the purpose of obtaining a light control film having both characteristics of hiding property and light transmittance. In the light control film having the light diffusion layer, it was thought that the light utilization efficiency could be improved by controlling the reflection and the refractive index at the interface between the transparent resin base and the fine particles. Then, further research was conducted based on the idea that if the combination of the transparent resin base and the material of the fine particles is optimized to suppress the interfacial reflection, the light utilization efficiency can be improved. As a result, they have found that the efficiency of light utilization can be improved by using a combination of polyester resin as the transparent resin and polystyrene resin particles as the fine particles. And
Further studies were conducted on the mixing ratio of polystyrene resin particles to the polyester resin, and when the polystyrene resin particles were 60 to 100 parts by weight with respect to 100 parts by weight of the polyester resin, the light transmittance was not impaired, and sufficient. The present invention has been achieved by finding out that a desired light diffusion layer having a hiding property can be obtained.

In the light diffusion layer of the present invention in which polystyrene resin particles are dispersed using a polyester resin as a transparent resin base, the polyester resin and the polystyrene resin have similar refractive index values (refractive index of the polyester resin: 1.52 to 1.52).
1.57, refractive index of polystyrene resin: 1.59 to 1.
60), interface reflection that occurs at the interface between the transparent resin base and the particles is suppressed. Therefore, it is considered that the light transmittance is improved because the light loss due to the interface reflection is reduced. Moreover, the transparent resin base made of a polyester resin and the polystyrene resin particles are mixed in a proportion of 60 to 100 parts by weight of the polystyrene resin particles to 100 parts by weight of the polyester resin. It is possible to secure a high concealment property. That is, if the polystyrene resin particles are less than 60 parts by weight with respect to 100 parts by weight of the polyester resin, the light transmittance is improved, but sufficient hiding property cannot be obtained.
When it exceeds the weight part, the light transmittance is reduced.

In the present invention, when the polystyrene resin particles are spherical, each spherical polystyrene resin particle acts as a minute lens, so that the light scattering property is improved and the brightness of the irradiation surface of the surface light source is improved. There is an advantage that variations are reduced. In the present invention, the term “spherical” means not only a true sphere but a state in which the shape is almost spherical.

[0013]

Next, an embodiment of the present invention will be described.

The light control film of the present invention comprises a base sheet made of a transparent resin or the like and a light diffusion layer having fine particles dispersed in a transparent resin base formed on the surface of the base sheet. Is formed from a composition in which 60 to 100 parts by weight of polystyrene resin particles are mixed with 100 parts by weight of a transparent resin base made of a polyester resin.

The material of the above-mentioned base sheet is preferably one having optical transparency, and examples thereof include polyethylene terephthalate, polycarbonate, polystyrene, polyester, polyvinyl chloride, acrylic resin, methacrylic resin, styrene-acrylonitrile copolymer ( AS resin), styrene-methyl methacrylate copolymer (MS resin), poly-4-methylpentene-1, vinyl chloride resin, diethylene glycol bisallyl carbonate, glass, and the like, but not limited to these. What is used. Among these, polyethylene terephthalate is most preferably used because it has good adhesion to the polyester resin used as the transparent resin base of the light diffusion layer, has few impurities, has high transparency, and is inexpensive. The thickness of the base sheet is not particularly limited, but it is preferably set to about 50 to 125 μm in consideration of use and workability.

The light diffusion layer is formed of a composition in which 60 to 100 parts by weight of polystyrene resin particles are mixed with 100 parts by weight of a transparent resin base made of polyester resin, and the polyester resin 10 is preferably used.
Polystyrene resin particles 65 to 100 parts by weight relative to 0 parts by weight
Parts by weight, more preferably 80 to 100 parts by weight.

The polyester resin is not only an ortho-based, iso-based, tele-based, bis-based, halogen-based, isophthalic acid-based, bisphenol A-based unsaturated polyester resin, but also a fatty acid-modified phthalic acid alkyd, maleic acid alkyd. Various polyester resins including saturated polyester resins such as alkyd resins, maleic acid resins, polyethylene terephthalate, polybutylene terephthalate, poly 1,4-cyclohexylene dimethylene terephthalate, polyarylate, poly-p-oxybenzoyl, etc. It is used and is not particularly limited.

The polystyrene resin particles are not limited to those made of general-purpose (GP) polystyrene resin,
Various types are used, including those made of styrene-acrylonitrile copolymer (AS resin), and are not particularly limited. Further, the polystyrene resin itself may be crosslinked, and of course, it may be uncrosslinked. The average particle size of the polystyrene resin particles is 5 to 70 μm from the viewpoint of light transmittance and hiding property.
Is preferable and 15-50 micrometers is still more preferable.
The polystyrene resin particles preferably have a spherical shape, and most preferably have a spherical shape.

Further, for the above composition, a crosslinking agent such as isocyanate, epoxy resin, methylolated melamine resin, methylolated urea resin, metal salt or metal hydroxide,
Guanidine derivatives, phosphate-containing anion activators, sulfones, quaternary ammonium salts, pyridinium salts, imidazoline derivatives, morpholine derivatives, polyoxyethylene-alkylphenols, alkylamide ethers, sorbitan fatty acid esters, and other antistatic agents, silane cups One kind or two or more kinds of subcomponents such as particles other than polystyrene resin particles such as ring agent, silicone resin particles, acrylic resin particles, nylon resin particles, urethane resin particles, polyethylene resin particles, silica particles and polyester resin particles are mixed. It may be blended. In this case, it is desirable that the total amount of the sub-component is 10 parts by weight or less based on 100 parts by weight of the polyester resin from the viewpoint of light transmittance.

In the case of producing the light control film of the present invention, the above polyester resin is dissolved in a solvent in an appropriate blending ratio, and polystyrene resin particles are mixed and dispersed in this solution to prepare a mixed dispersion solution as a base material. After being applied to the surface of the sheet, it is dried and solidified.

As the solvent, various solvents such as toluene, methyl ethyl ketone, xylene, cyclohexane and ethyl acetate are used. These may be used alone or in combination of two or more.

The number of blending parts of the polyester resin and the solvent is not particularly limited, and is set to an optimum blending part depending on the coating method, workability, kind of the solvent, etc., but 100 parts by weight of the polyester resin is used. For solvent 50 ~
It is preferably about 200 parts by weight, more preferably 100 to
It is about 150 parts by weight.

Various methods such as a comma direct method, a roll coating method, a dipping method, a knife coating method, a curtain flow method, a spray coating method, a spin coating method and a laminating method can be used as a method for applying the mixed dispersion solution on the surface of the base material sheet. Is carried out, but is not particularly limited, the number of parts of the solvent or polystyrene resin particles mixed, the viscosity of the mixed dispersion solution, the thickness of the desired light diffusion layer,
The optimum one is selected according to the surface condition of the base sheet.

The method for drying the mixed dispersion solution applied to the surface of the substrate sheet is not particularly limited, and various methods such as natural drying, hot air drying, and vacuum drying are performed.

The light diffusion layer formed as described above is
60 to 100 parts by weight of polystyrene resin particles are mixed and dispersed in 100 parts by weight of a transparent resin base made of a polyester resin. The thickness of this light diffusion layer is determined from the viewpoint of the balance between the hiding property and the light transmittance, and is preferably about 10 to 100 μm, and 30 to 75 μm.
Is more preferable. In the light diffusion layer as described above,
Since the refractive index values of the polyester resin and polystyrene resin are close to each other, the reflection of light at the interface between the transparent resin base and the particles is suppressed, and the loss of light due to interface reflection is reduced, resulting in the light transmittance of the light diffusion layer. Is improved. Further, since 60 to 100 parts by weight of polystyrene resin particles are mixed with 100 parts by weight of a transparent resin base made of a polyester resin, it is possible to obtain a sufficient light transmittance and also a good hiding property.

The above light control film may be used as it is, but in order to further suppress light loss, it may be used by applying antireflection treatment to the light incident surface or the light emitting surface. Examples of this antireflection treatment include embossing treatment by forming fine irregularities on the surface and thin film forming treatment utilizing optical interference of reflected waves. As the thin film forming treatment, for example, a thin film of a metal oxide such as silicon oxide or zinc oxide, MgF ₂ , a silicone resin, a solvent-soluble fluororesin (for example, trade name: Cytop, manufactured by Asahi Glass Co., Ltd.) is used. Forming is performed on the surface of the material sheet.

The above-mentioned thin film of metal oxide, MgF ₂ or the like is formed, for example, by a sputter deposition method, a vacuum deposition method, a CVD method, a sol-
It is formed by various methods such as a gel method. Among these, the sol-gel method is to obtain a silicon oxide layer or the like by applying a sol solution composed of silica or the like to form a dry gel, and heating and drying the dry gel to perform dehydration condensation. Most suitable. In particular, after low-temperature drying, a photo-assisted sol that irradiates ultraviolet rays or the like to cure the formed film
The gel method is more preferable because the treatment temperature is low. As a method of applying the sol solution in the sol-gel method, various methods such as a roll coating method, a dipping method, a spray coating method, a spin coating method, a laminating method, and a pouring method are performed. In particular, the spin coating method is a sheet-like method. The member is rotated, and the sol solution is dropped on the surface of the member to be uniformly applied by centrifugal force, which is preferable from the viewpoint of uniformity of the coating film.

Further, thin films of silicone resin, solvent-soluble fluororesin, etc. are coated with these solutions by various methods such as roll coating method, dipping method, spray coating, spin coating, laminating method and pouring method. Formed by drying.

By making the refractive index of the antireflection layer formed as described above lower than the refractive index of the base sheet of the light control film, reflection on the surface of the base sheet can be effectively prevented. it can. That is, generally, when the incident light enters vertically, the refractive index of air is 1.
When the refractive index of the base sheet is n and the refractive index of the base sheet is n, the ideal antireflection condition is satisfied when the refractive index of the antireflection layer is the square root of n. Therefore, for example, if the base material sheet is made of polyethylene terephthalate (refractive index: 1.58), the refractive index of the antireflection layer is ideally 1.26, and the closer the refractive index is to this, , Low reflection can be realized. Further, the film thickness of the antireflection layer satisfies the ideal antireflection condition when it is ¼ of the wavelength of light.

The above light control film is, for example,
It is used by being incorporated in a surface light source device as shown in FIG. That is, in the figure, 2 is a light guide plate, 4 is a light source such as a cold cathode tube that allows light to enter from the light incident end surface of the light guide plate 2, and 3 is a rear surface of the light guide plate 2 disposed on the back surface side of the light guide plate 2. It is a reflection plate that reflects the light that is going to be emitted from.
Further, 1 is a light control film which is arranged on the outgoing light surface side of the light guide plate 2, and 5 is two light collecting films which are arranged on the outgoing light surface side of the light controlling film 1 and have a light collecting function or the like. It is a sheet. Reference numeral 9 is a reflection cover that reflects the light rays of the light source 4 and makes them incident from the light incident end surface of the light guide plate 2.

Here, the light guide plate 2 used in the above surface light source device.
As a material for the above, a material having high transparency is preferably used. For example, acrylic resin, methacrylic resin, polyester resin, polycarbonate, polystyrene, polyethylene terephthalate, styrene-acrylonitrile copolymer (AS resin), styrene-methyl methacrylate copolymer (MS resin), poly-4-methylpentene-1. Various materials such as vinyl chloride resin, diethylene glycol bisallyl carbonate, and glass are used. Further, the shape of the light guide plate 2 is not limited to the plate shape, and can be formed in a desired shape such as a rectangular parallelepiped shape.

The light-condensing sheet 5 has, for example, prism-like or wave-like unevenness on its surface in order to collect the emitted light passing through the light control film 1 in the front direction and increase the brightness of the irradiation surface. A lot of them lined up,
A large number of minute lenses are formed side by side on the surface (the figure is a so-called prism sheet on which prism-shaped irregularities are formed). And the light control film 1
One or two sheets are arranged on the front surface side of.

In the light control film 1, as shown in FIG. 2, a light diffusion layer 6 composed of a polyester resin (transparent resin base) 6a and polystyrene resin particles 6b is formed on the surface of a base material sheet 7. This light diffusion layer 6
Then, since the polystyrene resin particles 6b are dispersed in the transparent resin base made of the polyester resin 6a, the light passing through the light diffusion layer 6 is scattered to exert the light diffusion effect. Further, by making the polystyrene resin particles 6b spherical, the polystyrene resin particles 6b themselves act as a kind of lens, and a more effective light diffusion effect is exhibited.

In the above structure, the light generated by the light source 4 enters the light guide plate 2 through the light incident end face of the light guide plate 2.
At this time, light may be directly incident from the light source 4 or may be light reflected by the reflection cover 9. The incident light passes through the inside of the light guide plate 2, and a part of the incident light passes through the inside of the light guide plate 2 while being emitted from the emission light surface side, and is directed toward the end face opposite to the light incident end face where the light source 4 is provided. proceed. As a result, the entire emission light surface emits light.
Light emitted from the light emitting surface of the light guide plate 2 is diffused by the light control film 1 and then condensed by the light condensing sheet 5 to illuminate a liquid crystal display screen (not shown).

At this time, the light control film 1
Light is scattered as it passes through. Further, since the refractive index values of the polyester resin and polystyrene resin are close, reflection of light at the interface between the transparent resin base and the particles is suppressed,
Light loss due to interface reflection is reduced, and the light transmittance of the light diffusion layer is improved. Further, since 60 to 100 parts by weight of polystyrene resin particles are mixed with 100 parts by weight of the transparent resin base, both properties of good hiding property and sufficient light transmittance can be obtained.

Further, in the above-mentioned surface light source device, when the light guide plate 2 is formed in a plate shape and the light source 4 is arranged on one of the four end faces, the light source 4 is not arranged. On the other three sides, it is desirable to dispose the same reflection plate 3 as that disposed on the back surface. By doing this,
Light leakage from the end surface of the light guide plate 2 is eliminated, and the light utilization efficiency is further improved.

In the above surface light source device, the light guide plate 2 is formed in a plate shape. However, the shape is not limited to this, and the light guide plate 2 can be formed in a desired light guide shape such as a rectangular parallelepiped. The light source 4 to be used is not limited to a linear line light source, and may be a point light source, and a desired light source 4 can be used. Further, the position of the light source 4 is not limited to one place, and may be provided at a plurality of places. Further, although the surface light source device is applied to a backlight for illuminating a liquid crystal display, it is not limited to this, and can be applied to all other surface light source devices including a direct type surface light source device. .

The light control film 1 of the present invention
Can be used not only as a light diffusing film in the above-mentioned surface light source device, but also as a light control film for controlling light from various devices such as lighting equipment, illuminated signboards, and rear projection screens. Also in this case, there is an effect that a good hiding property and a high light transmittance can be obtained.

FIG. 3 shows a light control film 1a having an antireflection layer 8 formed on one surface of the light control film 1 on which the light diffusion layer 6 is not formed. In this case, light incident on the light control film 1a from the antireflection layer 8 side does not cause reflection loss on the incident surface, so that the light transmission efficiency is further improved.

[0040]

As described above, according to the light control film of the present invention, since it has both the concealing property and the high light transmittance, when it is used in a surface light source device, a good light diffusing property is obtained. In addition to improving the quality of the screen, it is possible to obtain high brightness, and to obtain the same level of brightness as conventional ones with low power consumption.

Next, examples will be described together with comparative examples.

[0042]

Example 1 Polyethylene terephthalate (PET) film having a thickness of 100 μm (trade name: Lumirror # 100)
(T56, manufactured by Toray Industries, Inc.) is used as a base sheet, and the following composition serving as a light diffusion layer is applied to one surface of the base sheet by a comma direct method, dried at 120 ° C. for 1 minute, and light of a light diffusion layer having a thickness of 40 μm A control film was obtained. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polystyrene spherical particles (Techpolymer SBX-17, manufactured by Sekisui Plastics Co., Ltd.): 60 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone (solvent) : 50 parts by weight

[0043]

Example 2 Thickness: 100 μm polyethylene terephthalate (PE
T) A film (trade name: Lumirror # 100T56, manufactured by Toray Co., Ltd.) is used as a base sheet, and the following composition to be a light diffusing layer is applied to one side of the base sheet by a comma direct method.
It was dried at 0 ° C. for 1 minute to obtain a light control film of a light diffusion layer having a thickness of 40 μm. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polystyrene spherical particles (Techpolymer SBX-17, manufactured by Sekisui Plastics Co., Ltd.): 80 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone (solvent) : 50 parts by weight

[0044]

Example 3 Polyethylene terephthalate (PE having a thickness of 100 μm)
T) A film (trade name: Lumirror # 100T56, manufactured by Toray Co., Ltd.) is used as a base sheet, and the following composition to be a light diffusing layer is applied to one side of the base sheet by a comma direct method.
It was dried at 0 ° C. for 1 minute to obtain a light control film of a light diffusion layer having a thickness of 40 μm. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polystyrene spherical particles (Techpolymer SBX-17, manufactured by Sekisui Plastics Co., Ltd.): 100 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone (solvent) : 50 parts by weight

[0045]

Example 4 An antireflection treatment was performed by providing a thin film of silicon oxide having a thickness of 1000Å on one surface of the light control film obtained in Example 2 on the side opposite to the light diffusion layer forming surface by a vacuum deposition method. A light control film was obtained.

[0046]

Comparative Example 1 Thickness: 100 μm polyethylene terephthalate (PE
T) A film (trade name: Lumirror # 100T56, manufactured by Toray Co., Ltd.) is used as a base sheet, and the following composition to be a light diffusing layer is applied to one side of the base sheet by a comma direct method.
It was dried at 0 ° C. for 1 minute to obtain a light control film of a light diffusion layer having a thickness of 40 μm. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polystyrene spherical particles (Techpolymer SBX-17, manufactured by Sekisui Plastics Co., Ltd.): 120 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone (solvent) : 50 parts by weight

[0047]

Comparative Example 2 Polyethylene terephthalate (PE
T) A film (trade name: Lumirror # 100T56, manufactured by Toray Co., Ltd.) is used as a base sheet, and the following composition to be a light diffusing layer is applied to one side of the base sheet by a comma direct method.
It was dried at 0 ° C. for 1 minute to obtain a light control film of a light diffusion layer having a thickness of 40 μm. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polystyrene spherical particles (Techpolymer SBX-17, manufactured by Sekisui Plastics Co., Ltd.): 40 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone (solvent) : 50 parts by weight

[0048]

Comparative Example 3 Polyethylene terephthalate (PE having a thickness of 100 μm)
T) A film (trade name: Lumirror # 100T56, manufactured by Toray Co., Ltd.) is used as a base sheet, and the following composition to be a light diffusing layer is applied to one side of the base sheet by a comma direct method.
It was dried at 0 ° C. for 1 minute to obtain a light control film of a light diffusion layer having a thickness of 40 μm. Composition: Polyester resin (Byron 200, manufactured by Toyobo Co., Ltd.): 100 parts by weight Polymethylmethacrylate spherical particles (Techpolymer MBX-20, manufactured by Sekisui Plastics Co., Ltd.): 80 parts by weight Toluene (solvent): 200 parts by weight Methyl ethyl ketone ( Solvent): 50 parts by weight

The total light transmittance and haze of the light control films obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were measured. Further, the above light control film was incorporated into a light guide plate type surface light source device consisting of a light source 4, a dot printing type light guide plate 2, a reflection plate 3 and two prism sheets 5 shown in FIG. At the same time, the hiding property of the printed dots was observed. The results are shown in Table 1 below.

[0050]

[Table 1] * Concealment: ○: Dot is not visible ×: Dot is visible

As can be seen from the results in Table 1 above, Examples 1 to 3 have high total light transmittance and haze, excellent front brightness, and good hiding properties. Further, it can be seen that in Example 4 in which the antireflection layer is provided on the back surface, the total light transmittance is particularly high and the light utilization efficiency is excellent. On the other hand, it can be seen that in Comparative Example 1 in which the number of blended parts of polystyrene resin particles is higher than the predetermined value, the total light transmittance and the front luminance are inferior. Also,
It can be seen that in Comparative Example 2 in which the mixing number of polystyrene resin particles is lower than the predetermined value, the hiding property is inferior. Further, in Comparative Example 3 in which polymethylmethacrylate spherical particles were used instead of polystyrene resin particles, it was found that haze was reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a surface light source device using a light control film of the present invention.

FIG. 2 is a cross-sectional view showing a light control film of the present invention.

FIG. 3 is a cross-sectional view showing a light control film having an antireflection layer formed thereon.

FIG. 4 is an explanatory diagram showing a conventional surface light source device.

FIG. 5 is an explanatory diagram showing another conventional surface light source device.

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Claims (6)

[Claims] 1. A light control film comprising a transparent base material sheet and a light diffusion layer formed by laminating fine particles in a transparent resin base on a surface of the transparent base material sheet, wherein the light diffusion layer comprises:
An optical control film comprising a composition in which 60 to 100 parts by weight of polystyrene resin particles are compounded and dispersed in 100 parts by weight of a transparent resin base made of a polyester resin. 2. The light control film according to claim 1, wherein the polystyrene resin particles are spherical. 3. The polystyrene resin particles have an average particle diameter of 5 to 5.
The light control film according to claim 1, which has a thickness of 70 μm. 4. The light control film according to claim 1, wherein the base sheet is made of polyethylene terephthalate. 5. The light control film according to claim 1, wherein at least one surface of the light control film is subjected to antireflection treatment. 6. The light control film according to claim 1, wherein the light control film is a light diffusion film.