JP2002174705A - Method for manufacturing light diffusing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to efficiently manufacture a light diffusing film having high transmission efficiency, excellent viewing angle characteristics and little concentration irregularity. SOLUTION: In the method for manufacturing a light diffusing film by applying a coating liquid for an undercoating transparent layer on the surface of a transparent base material to form a base transparent layer, embedding transparent beads in the undercoating transparent layer and applying a coating liquid for a light absorbing layer to form a light absorbing layer, the light absorbing layer is formed by producing metal fine particles. It is preferable that the coating liquid for the light absorbing layer contains a color developing agent, that the coating liquid for the undercoating transparent layer contains a reducing agent, that the color developing agent is silver behenate, that the reducing agent is gallic acid, that the volume average particle size (D50) of the transparent beads ranges from 3 to 15 μm, that the volume average particle size (D50) of the transparent beads ranges from 10 to 50 μm, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a light-diffusing film used for a transmission screen or a liquid crystal display of a rear projection display.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device known as a technique for remarkably improving the viewing angle characteristics such as gradation and chromaticity is, as shown by a liquid crystal display device 100 in FIG. The liquid crystal panel 2 includes a backlight unit 4 that causes a bundle (collimated light) to enter the liquid crystal panel 2 and a light diffusion film 6 that diffuses image light spatially modulated by the liquid crystal panel 2.

As shown schematically in FIG. 2, a light diffusion film 6 is formed on a light-transmitting substrate (transparent substrate) 10 on a light-transmitting microsphere transparent bead (hereinafter, referred to as a “transparent bead”). 14) is fixed by the light absorbing layer 20. The transparent beads 14 are partially buried in the light absorbing layer 20 in contact with the transparent substrate 10.

[0004] The parallel light beam (collimated light) incident on the liquid crystal panel 2 is refracted by the transparent beads 14 in the light diffusion film 6 as shown by the one-dot chain line, and the contact portion between the transparent beads 14 and the transparent substrate 10. Is diffused through. Since the light absorbing layer 20 has a light absorbing property, a portion other than the contact portion between the transparent beads 14 and the transparent substrate 10 becomes a black mask, and external light from the observer side is reflected and scattered by the light diffusion film 6. Since there is no contrast and no decrease in contrast, a good contrast ratio can be obtained over a wide viewing angle.

As a method for manufacturing the light diffusion film, Japanese Patent Application Laid-Open No. 9-318801 discloses the following methods for manufacturing a light diffusion film having an excellent incident light amount. A transparent substrate 10 is prepared (FIG. 3A), and
The undercoat transparent layer 12 and the light absorbing layer 20 are sequentially formed as a binder (FIG. 3B). The transparent beads 14 are dispersed on the light absorbing layer 20 (FIG. 3C). The light absorbing layer 20 in which the transparent beads 14 are dispersed and the transparent substrate 10 are pressed from above and below (FIG. 3D), and a part of the transparent beads 14 penetrates the light absorbing layer 20 and the undercoating transparent layer 12. The light diffusing film 6 is manufactured by being buried and fixed (FIG. 3E).

In the light diffusing film 6 obtained by the above-described manufacturing method, the transparent beads 14 are partially buried in the undercoating transparent layer 12 and are surrounded by the light absorbing layer 20. Since the light is exposed from the light receiving surface 20, the incident light is efficiently incident on the densely arranged transparent beads 14, and the incident light flux is once converged and diffused by the lens action of the transparent beads 14, thereby improving the viewing angle. I do. Also, of the light incident on the light diffusion film 6, the light not incident on the transparent beads 14, that is, the transparent beads 1
The light that has not been affected by the lens due to the
And transmission to the front is blocked. Further, external light incident from the front of the light diffusion film 6 (that is, the light exit side) is also almost absorbed by the light absorption layer 20, so that it is not observed as stray light from the front and the contrast is reduced. improves.

However, in the above manufacturing method, FIG.
As shown in (f), when the sizes of the transparent beads 14 are not uniform, that is, in addition to the standard size of the transparent beads 14, small transparent beads 142, large transparent beads 143, and the like are mixed. If present, all transparent beads 14,
There is a problem that the parts 142, 143 and the like are not always buried in contact with the transparent base material 10 evenly. That is, the smaller transparent beads 142 are arranged in a state of floating in the light absorbing layer 20 without contacting the transparent base material 10, and there is a problem that the amount of incident light is reduced. In addition, the large transparent beads 143 have a problem that they are damaged by the pressing force at the time of pressing, and image defects such as light leakage occur.

As a technique for solving the above problem, Japanese Patent Laid-Open No.
In the publication No. 1-102025, when the melt viscosity of the undercoat transparent layer is n and the melt viscosity of the light absorption layer is n ′, the relationship of n> n ′, that is, the melt viscosity n of the undercoat transparent layer is An invention has been disclosed in which the transmittance of incident light is increased by increasing the melt viscosity n ′. According to the invention,
When the transparent beads are embedded by hot pressing, the light absorbing layer is deformed before the undercoating transparent layer, so that the light emitting portion of the transparent beads is easily exposed to the undercoating transparent layer, and the transmission efficiency of the incident light amount is high.

However, when the pressing force at the time of hot pressing is low and uneven, the area of the light emitting portion is still insufficient, and there are problems such as the existence of transparent beads not in contact with the undercoat transparent layer. Was. In particular, when the size of the transparent beads is largely distributed, this problem is remarkable, and there is still a problem that the transmission efficiency of incident light is insufficient. Also, when the pressure at the time of pressing is high, the transparent beads are broken, and there is a problem that a planar defect of light leakage occurs.
Still remained.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, an object of the present invention is to provide a method for efficiently producing a light diffusion film having high transmission efficiency, excellent viewing angle characteristics, and less density unevenness.

[0011]

Means for solving the above problems are as follows. That is, <1> transparent (meaning “transparent” with respect to visible light; the same applies to the following.) An undercoating transparent layer coating solution is applied to the surface of a base material to form an undercoating transparent layer. A method for producing a light-diffusing film in which a light-absorbing layer is formed by applying a coating solution for a light-absorbing layer after embedding the transparent beads, wherein the light-absorbing layer is formed by generation of metal fine particles. This is a method for producing a light diffusion film. <2> The coating solution for a light absorbing layer contains a color former.
1> The method for producing a light diffusion film described in <1>. <3> The method for producing a light diffusion film according to <1> or <2>, wherein the coating liquid for an undercoat transparent layer contains a reducing agent.

<4> The method according to <2>, wherein the color former is silver behenate. <5> The method for producing a light diffusing film according to <3>, wherein the reducing agent is gallic acid. <6> The volume average particle diameter of the transparent beads (D ₅₀₎ is 3 to 1
The method for producing a light diffusion film according to any one of <1> to <5>, wherein the thickness is 5 μm. <7> The volume average particle diameter of the transparent beads (D ₅₀₎ is 10
The method for producing a light diffusion film according to any one of <1> to <5>, wherein the thickness is 50 μm.

<8> The production of the light diffusing film according to any one of <1> to <7>, wherein the transparent beads are placed on the undercoating transparent layer and heated to embed the transparent beads in the undercoating transparent layer. Is the way. <9> The method for producing a light-diffusing film according to <8>, wherein the heat-conductive flexible substance is placed on the transparent beads and pressed. <10> The method for producing a light diffusing film according to <9>, wherein the heat conductive flexible substance is a silicone rubber.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The method for producing a light-diffusing film of the present invention comprises the steps of: forming an undercoating transparent layer on the surface of a transparent substrate, embedding a transparent bead in the undercoating transparent layer, and applying a light absorbing layer coating solution to absorb light. A light absorption layer forming step of forming a layer, and other steps as necessary.

[Embedding Step] In the embedding step, an undercoating transparent layer is formed on the surface of the transparent substrate, and transparent beads are embedded in the undercoating transparent layer.

-Transparent Substrate-The material of the transparent substrate is not particularly limited, and various materials may be used as long as they have a sufficient light transmittance and a sufficient mechanical strength according to the application. Is available. Specifically, various types of glass, polyester, polyolefin, polyamide, polyether, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polystyrene, polyester amide, polycarbonate,
Various resin materials such as polyphenylene sulfide, polyetherester, polyvinyl chloride, and polymethacrylic acid ester are preferably exemplified. The thickness of the transparent substrate is not particularly limited, but is preferably 50 to 500 μm.

For the purpose of improving the observability of the liquid crystal display device, a known antireflection treatment such as an AR coat is applied to the transparent substrate on the observation surface (the surface opposite to the surface where the transparent beads are embedded). It is preferred to apply.

—Undercoating Transparent Layer— The undercoating transparent layer is formed by applying an undercoating transparent layer coating solution. As components of the undercoating transparent layer coating solution,
There is no particular limitation as long as the undercoating transparent layer can embed transparent beads, but it is particularly preferable that the undercoating layer contains a reducing agent and, if necessary, various resins. The undercoating transparent layer coating solution contains a reducing agent, and if the light absorbing layer coating solution contains a color former, as described below, by appropriately selecting conditions, by the action of the reducing agent. The color former is reduced to produce fine metal particles (color is formed), and the light absorbing layer is suitably formed.

The thickness of the undercoating transparent layer is not particularly limited, but is preferably such a thickness that the transparent beads can be fixed uniformly and the transparent beads are not buried. Although it cannot be said unconditionally because it depends on the particle size of the transparent beads to be used, it is preferably about 1/10 of the volume average particle diameter (D ₅₀ ) of the transparent beads.

--- Reducing Agent-- The reducing agent is not particularly limited as long as the metal fine particles can be suitably produced. For example, JP-A-53-1
No. 020 (p. 227, lower left column, line 14 to 229)
And the reducing agent described in the upper right column of the page, line 11), among which mono, bis, tris or tetrakisphenols, mono or bisnaphthols, di or polyhydroxynaphthalenes, di or polyhydroxybenzenes, Hydroxy monoethers, ascorbic acids, 3-pyrazolidones, pyrazolines, pyrazolones, reducing sugars,
Phenylenediamines, hydroxylamines, reductones, hydrooxamines, hydrazides, amide oximes, N-hydroxyureas and the like are preferred. Among these, aromatic organic reducing agents such as phenols, polyphenols, sulfonamidephenols, and naphthols are preferable, and gallic acid and esters thereof are particularly preferable in terms of the color reaction rate and the color density. These reducing agents may be used alone or may be used alone.
More than one species may be used in combination.

The content of the reducing agent in the undercoating transparent layer coating solution is preferably 5 to 50% by weight.
20-40% by weight is more preferred. When the content is less than 5% by weight, the generation of metal fine particles is not sufficient, and the light absorbing layer may not be suitably formed. On the other hand, when the content exceeds 50% by weight, the amount of the reducing agent becomes excessive, The thickness of the formed light absorbing layer may be too large to cover the transparent beads and reduce the area of the light incident part. In the present invention, by appropriately selecting the content of the reducing agent, the thickness of the light absorbing layer to be formed (the amount of the generated metal fine particles) can be easily controlled. As a result, while securing a sufficient light incident area,
A light absorbing layer having a sufficient thickness can be easily formed.

-Resin-Specific examples of the resin include vinyl acetate resin, ethylene-vinyl acetate copolymer, vinyl chloride resin, vinyl chloride-vinylidene chloride copolymer, and (meth) acrylate resin. Butyral resin, silicone resin, polyester, polyamide, vinylidene fluoride resin, nitrocellulose resin, polystyrene, styrene-acryl copolymer, urethane resin, polyethylene, polypropylene, polyethylene chloride, rosin derivative, and the like. Among these, polyamide is preferable in that it has appropriate adhesiveness required for forming a single-layer transparent bead layer, and thermoplasticity required for embedding by heating, and the like. Especially, nylon is preferred. These resins and the like may be used alone or in combination of two or more.

Other components contained in the undercoating transparent layer coating solution include solvents such as water, alcohol and cresol, as well as surfactants effective for uniformizing the coating film.

-Transparent beads-The material of the transparent beads is not particularly limited, and various materials may be used as long as they are transparent. For example, the material of the transparent substrate may be used. Acrylic resins, glass, and the like are preferred from the viewpoint of goodness and the like.

The shape of the transparent beads is particularly preferably spherical. As the particle size of the transparent beads, the observer,
There is no particular limitation as long as the size does not cause roughness of the screen, but the preferred size varies depending on the use of the light diffusion film. Specifically, when used for a desktop display or the like (when the distance from the observer to the display is about 300 mm), the volume average particle diameter (D ₅₀ ) is preferably 50 μm or less, more preferably 30 μm or less, 3-15 μm is more preferred. When used in a home television or the like (when the distance from the observer to the television is about 2 m), the volume average particle diameter (D ₅₀ ) is preferably 300 μm or less, and 200 μm or less.
μm or less, more preferably 10 to 50 μm.

-Embedding- In the embedding step, the transparent beads are embedded in the undercoating transparent layer. Therefore, unlike the conventional case, after the light absorption layer is formed, the light absorption layer is not buried from above the light absorption layer. Therefore, even if the burying is somewhat uneven, the depth is easily set to a depth sufficient for light emission. The transparent beads are embedded, and a light diffusion film having high transmission efficiency and high viewing angle characteristics can be obtained.

In the embedding step, the transparent beads are
It is preferable that the undercoating transparent layer is evenly embedded. By uniformly burying the transparent beads, a light diffusion film having high uniformity of the light emitting portion and high transmission efficiency can be obtained. In the embedding step, the transparent beads are preferably embedded in the undercoating transparent layer in a closely arranged manner. When the transparent beads are densely embedded, a light diffusion film having high transmission efficiency can be obtained. As a method for embedding the transparent beads densely in the undercoating transparent layer, for example, arranging and embedding the transparent beads having different particle diameters may be mentioned.

In the embedding step, it is particularly preferable that the transparent beads are embedded such that at least half of the volume of the transparent beads is exposed from the undercoat transparent layer. By embedding in this way, a light diffusion film having high transmission efficiency can be obtained.

In the embedding step, heating may be performed as appropriate, and the heating temperature is preferably about 100 to 150 ° C. By the heating, the transparent beads are easily and sufficiently embedded in the softened transparent layer.

At the time of the heating, on the transparent beads,
It is preferable to load the heat conductive flexible material and pressurize. Due to the pressure, the uniformity of embedding of the transparent beads becomes higher. The heat conductive flexible substance is not particularly limited, but silicone rubber or the like is preferable because it is excellent in heat conductivity and flexibility and is easily available. The pressing pressure is not particularly limited as long as the transparent beads are not damaged.

[Light Absorbing Layer Forming Step] In the light absorbing layer forming step, after the embedding step, a light absorbing layer coating solution is applied to form a light absorbing layer.

-Coating Liquid for Light Absorbing Layer- The coating liquid for light absorbing layer is transparent to visible light, and after coating, only a portion where metal fine particles are formed under predetermined conditions develops a color to form a light absorbing layer. Become. Therefore, by controlling the amount of the generated metal fine particles, the thickness of the formed light absorbing layer can be adjusted to a desired thickness, and the thickness of the light absorbing layer can be adjusted so that the transparent beads do not cover the head. With this setting, it is possible to easily secure a sufficient amount of incident light.

The component of the light absorbing layer coating solution is not particularly limited as long as the fine particles are formed by the coating to form the light absorbing layer, but it is particularly preferable to contain a coloring agent. . If the light absorbing layer coating solution contains a color former, the undercoating transparent layer coating solution contains a reducing agent,
Under a predetermined condition, the color former is reduced by the action of the reducing agent to generate fine metal particles (color is formed), and the light absorbing layer is suitably formed. Since the predetermined condition varies depending on the amount of the reducing agent and the like, it cannot be said unconditionally.
Conditions such as heating to 150 ° C. are preferred.

The color forming agent is not particularly limited as long as the metal fine particles are suitably formed, and for example, an organic metal salt is preferable. As the organic metal salt, specifically,
Silver salts of long-chain aliphatic carboxylic acids such as silver laurate, myristic acetate, silver palmitate, silver stearate, silver arachiate and silver behenate, silver benzotriazole, silver benzimidazole, silver carbazole and phthalazinone A silver salt of an organic compound having an imino group such as a silver salt;
Silver salts of sulfur-containing compounds such as alkylthioglycolates, silver salts of aromatic carboxylic acids such as silver benzoate and silver phthalate, silver salts of sulfonic acids such as silver ethanesulfonate, o-
Silver salts of sulfinic acid such as silver toluenesulfinate, silver salts of phosphoric acid such as silver phenylphosphate, silver barbiturates, silver saccharinate, silver salts of salicylaldoxime and the like can be mentioned. Among these, long-chain aliphatic carboxylic acid silver salts are preferred, and silver behenate is particularly preferred. These may be used alone or in combination of two or more.

Other components contained in the coating solution for the light absorbing layer include solvents such as water, alcohol and cresol, as well as a surfactant effective for making the coating film uniform.

-Coating of Coating Solution for Light Absorbing Layer- The thickness of the coating solution for the light absorbing layer is not particularly limited, but is approximately equal to the volume average particle diameter (D ₅₀ ) of the transparent beads. preferable. As described above, since only the portion where the metal fine particles are generated develops a color and becomes a light absorbing layer, it is necessary to expose and apply the transparent beads in order to secure the amount of incident light in the light diffusion film. There is no. Therefore, the coating solution for the light absorbing layer can be applied efficiently.

-Light Absorbing Layer- The light absorbing layer is formed by generation of the metal fine particles. As described above, the thickness of the light absorbing layer must be appropriately adjusted according to the size of the transparent beads in consideration of securing the amount of incident light on the transparent beads. the volume average particle diameter of the beads (D ₅₀₎ is 3
In the case of 15 μm, it is preferably about 0.5 to 5 μm,
In the case of の 50 μm, it is preferably about 2 to 15 μm.

<Light-diffusing film> The light-diffusing film obtained by the above-described method for producing a light-diffusing film of the present invention may be a rigid sheet or a flexible sheet or film. The material, thickness, and the like of the transparent substrate may be appropriately selected depending on the required mechanical strength and application.

As described above, the light diffusion film is suitably used for various liquid crystal display devices having a liquid crystal panel, a backlight unit, and a light diffusion film. In the liquid crystal display device, as the liquid crystal panel, liquid crystal displays of various known modes including a TN mode are suitably used. As the backlight unit, if it is possible to emit a parallel light beam with sufficient light quantity for image observation,
All known various light source devices are available.

[0040]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 Embedding Step A resin (water-soluble nylon: P-70, manufactured by Toray Industries, Inc.) is provided on one surface of polyethylene terephthalate (transparent substrate).
And an undercoating transparent layer coating solution (aqueous solution) containing 10 parts by weight and a reducing agent (methyl gallate) 4 parts by weight was applied with a wire bar to form an undercoating transparent layer (thickness after drying:
7 μm). In the undercoating transparent layer, transparent beads (made of glass, volume average particle diameter (D ₅₀ ): 30 μm) are densely arranged,
After holding at 120 ° C. for 9 minutes, the mixture was cooled to room temperature, and transparent beads were embedded in the undercoat transparent layer.

-Light absorbing layer forming step-Next, 7 parts by weight of a color former (silver behenate) and 2 parts of gelatin were added.
A light absorbing layer coating solution (aqueous solution) containing 0 parts by weight was applied so as to have a coating thickness of 15 μm.
At 30 ° C. for 30 seconds) to form metal fine particles (metal silver fine particles) to form a black light absorbing layer (thickness: 5 μm).

<Measurement / Evaluation> The obtained light diffusing film was measured and evaluated for density unevenness (surface failure), transmission efficiency, and viewing angle characteristics by the following measurement methods.

-Measurement / Evaluation of Density Unevenness (Surface Failure)-The density unevenness (surface failure) was visually evaluated by sensory evaluation.

—Measurement / Evaluation of Transmission Efficiency— The transmission efficiency was measured with a haze meter (HR100: manufactured by Murakami Color Research Laboratory) according to JISK7361-1.

-Measurement / Evaluation of Viewing Angle Characteristics- The viewing angle characteristics are obtained by irradiating a parallel light beam having a divergence angle of 5 degrees or less into a light diffusion film, transmitting transmitted light, and measuring the intensity of radiated light using a silicon photodiode as a sensor. It was measured with an angle distribution measuring device.

From the above measurements and evaluations, in Example 1, there was no density unevenness, and both the transmission efficiency and the viewing angle characteristics were excellent. Further, by observing a liquid crystal display device using the obtained light diffusion film, the light diffusion film was particularly suitable for a liquid crystal display device such as a home-use television and the like in which an observer observes at a distance of about 2 m.

(Embodiment 2) "Embedding process" of "Embodiment 1"
, The volume average particle diameter (D ₅₀ ) of the transparent beads is 8 μm
In the “light absorbing layer forming step”, the coating thickness of the light absorbing layer coating solution (aqueous solution) was changed to 8 μm,
A light diffusion film was obtained in the same manner as in “Example 1”, and “density unevenness (planar failure)”, “transmission efficiency”, and “viewing angle characteristics” were measured and evaluated in the same manner as in Example 1. There was no density unevenness, and both transmission efficiency and viewing angle characteristics were excellent. Further, by observing a liquid crystal display device using the obtained light diffusion film, the light diffusion film is particularly suitable for a desktop display device or the like, and a liquid crystal display device or the like in which an observer observes at a short distance of about 300 mm. Even at a distance, a smooth image was visually recognized by the observer.

(Embodiment 3) "Embedding process" of "Embodiment 1"
At the time, silicone rubber (thickness: 1 mm,
A light-diffusing film was obtained in the same manner as in "Example 1", except that a light-diffusing film was obtained in the same manner as in "Example 1", except that the sample was heated (120.degree. C.) and pressed (0.01 kg weight cm.sup.- ² ). When "density unevenness (surface failure)", "transmission efficiency", and "viewing angle characteristics" were measured and evaluated, there was no density unevenness, and both the transmission efficiency and the viewing angle characteristics were excellent. Because the silicone rubber is placed on the transparent beads and heated and pressed, the transparent beads are sufficiently and evenly embedded in the undercoat transparent layer,
In particular, the transmission efficiency was high.

[0050]

According to the present invention, it is possible to provide a method for efficiently producing a light diffusion film having high transmission efficiency, excellent viewing angle characteristics, and less density unevenness.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conventionally known liquid crystal display device.

FIG. 2 is a diagram illustrating a state in which a parallel light beam is incident on a liquid crystal panel and a light diffusion film.

FIG. 3 is a diagram illustrating a conventional method for manufacturing a light diffusion film.

[Explanation of symbols]

 Reference Signs List 2 liquid crystal panel 4 backlight unit 6 light diffusion film 10 transparent base material 12 undercoat transparent layer 14 transparent beads 20 light absorption layer 100 liquid crystal display device 142 transparent beads 143 transparent beads

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shintaro Washinasu 200 Onakazato, Fujinomiya City, Shizuoka Prefecture Fuji Photo Film F-term (reference) 2H042 BA02 BA12 BA15 BA19 BA20 2H091 FA34Y FA35Y LA30

Claims (10)

[Claims] 1. An undercoating transparent layer coating solution is applied to the surface of a transparent base material to form an undercoating transparent layer, and the undercoating transparent layer is embedded with transparent beads, and then a light absorbing layer coating solution is applied. A method for producing a light diffusion film for forming a light absorption layer, wherein the light absorption layer is formed by generation of metal fine particles. 2. The method for producing a light diffusing film according to claim 1, wherein the coating solution for a light absorbing layer contains a color former. 3. The method for producing a light diffusing film according to claim 1, wherein the coating liquid for the undercoating transparent layer contains a reducing agent. 4. The method for producing a light diffusing film according to claim 2, wherein the color former is silver behenate. 5. The method for producing a light diffusion film according to claim 3, wherein the reducing agent is gallic acid. 6. The transparent beads having a volume average particle diameter (D ₅₀ )
The method for producing a light diffusing film according to claim 1, wherein the thickness is 3 to 15 μm. 7. The transparent beads having a volume average particle diameter (D ₅₀ )
The method for producing a light diffusion film according to any one of claims 1 to 5, wherein the thickness is 10 to 50 µm. 8. The method for producing a light diffusion film according to claim 1, wherein the transparent beads are placed on the undercoating transparent layer, and the transparent beads are buried in the undercoating transparent layer by heating. 9. The method for producing a light diffusing film according to claim 8, wherein a heat-conductive flexible substance is placed on the transparent beads and pressure is applied. 10. The method according to claim 9, wherein the heat conductive flexible substance is a silicone rubber.