JP2008249995A - Light diffusion sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion thermoplastic resin sheet which attains effective use of the edge material thereof and improvement in the efficiency of production, is advantageous in terms of the cost and suitable for a fresnel lens base material. <P>SOLUTION: The light diffusion sheet comprises: a layer (1) made by dispersing fine particles with refractive index Na into a thermoplastic resin (1) with refractive index N1; and a layer (2) made by dispersing fine particles with refractive index Na into a thermoplastic resin (2) with refractive index N2, and satisfies: equation (I) ¾N1-Na¾≤0.005; equation (II) 0.005<¾N2-Na¾≤0.04; and equation (III) 0.005<¾N2-N1¾≤0.04. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light diffusing sheet.

  An optical screen such as a transmissive screen of a projection television is usually composed of a lens sheet such as a Fresnel lens sheet or a lenticular lens sheet. Further, for the purpose of protecting the lens sheet, a configuration in which a front panel is mounted is also employed. In the Fresnel lens sheet, a Fresnel lens obtained by curing an ultraviolet curable resin on a light diffusing sheet base is usually formed. In addition, recently, as the pitch of lenticular lenses has become finer, the number of cases where film-like lenticular lenses are used is increasing. In this case, a light diffusive sheet is usually used to support the lenses. Is done. Further, depending on the application of the projection screen, the light diffusing sheet may be used alone as a screen.

  These light diffusing sheets for transmissive screens are designed for the purpose of adjusting the image quality and viewing angle obtained through the screen. Recently, since the light source of the projection television has become very bright, so-called scintillation has been a problem as a glare of the screen, and various studies have been made to reduce this scintillation. As a technique for reducing scintillation, various studies have been made to devise the configuration and prescription of the above-described light diffusive sheet. For example, in the pamphlet of International Publication No. 98/03898 (Patent Document 1), it is proposed to provide two separated light diffusion portions in the light transmission direction in the transmission screen. Japanese Patent Laid-Open No. 8-313865 (Patent Document 2) discloses a rear projection image display apparatus including a first diffusing element on a side close to a light source and a second diffusing element on a side close to an observer. Proposed. In both documents, a two-layer sheet or a three-layer sheet is exemplified as a light diffusive sheet, and these sheets may be a layer containing light diffusing fine particles (hereinafter referred to as a fine particle-containing layer). ) And a layer not containing light diffusing fine particles (hereinafter sometimes referred to as a fine particle-free layer).

International Publication No. 98/03898 Pamphlet JP-A-8-313865

  The light diffusing sheet having a multilayer structure disclosed in the above document is usually obtained by multilayer extrusion using two or more extruders, and has a fine particle-containing layer and a fine particle-free layer. In the extrusion molding, there are the following problems.

  As the thermoplastic resin used for the fine particle-containing layer and the fine particle-free layer, resins having the same composition are usually used. On the other hand, in the resin sheet obtained by extrusion molding, from the viewpoint of cost, the end material other than the part to be a product is usually reused as a raw material after pulverization. Usually, in the case of a single-layer board or a multilayer board of fine particle-containing layer / fine particle-containing layer, it is possible to reuse the raw material obtained from the end material at an appropriate ratio. However, in the case of a multilayer plate having a fine particle-containing layer / a fine particle-free layer, particularly when the proportion of the fine particle-free layer in the total thickness of the plate is large, the fine particles are not contained when trying to reuse the mill ends as a raw material. If a milled product of milled material is introduced into the layer-containing layer, the pulverized product contains the light diffusing fine particles contained in the fine particle-containing layer, so that the light diffusing fine particles are mixed into the fine particle-free layer. The fine particle-free layer becomes a diffusion layer. Therefore, the milling material cannot be introduced to the fine particle-free layer side, and the utilization efficiency of the milling material becomes very bad, which is very disadvantageous in terms of cost.

  Moreover, adjustment at the time of extrusion molding becomes very difficult. Normally, in extrusion molding, the thickness of the sheet is adjusted, the sheet is flattened, and the sheet surface state is optimized by passing between three or more mirror rolls that are appropriately temperature-controlled. Since the surface tends to be uneven due to the influence of the diffusible fine particles, the adhesion to the mirror surface roll tends to be deteriorated, and it is general to cope by setting the mirror surface roll temperature to a relatively high setting. On the other hand, the fine particle-free layer has a very smooth surface and is easy to adhere to a mirror roll, so if the roll temperature is too high, the fine particle-free layer is taken off by the roll when the fine particle-free layer surface side is separated, A streak defect called a so-called tack mark is likely to occur in a direction parallel to the roll.

  From the above, in a multilayer sheet, when one side of the sheet surface is a fine particle-containing layer surface and the other side is a fine particle-free layer surface, it is difficult to obtain a sheet having a good appearance, and as a result, adjustment leading to product removal Time is required, and defects are likely to occur during product collection, resulting in a decrease in yield and a disadvantage in cost.

  Further, in the case of a multilayer sheet having a fine particle-containing layer and a fine particle-free layer, particularly when one surface of the sheet surface is a fine particle-containing layer surface and the other surface is a fine particle-free layer surface, the multilayer sheet is used as a basis for forming a Fresnel lens. When it is intended to be used as a material, it is preferable to arrange a fine particle-containing layer on the light source side from the viewpoint of reducing scintillation when molding a commonly used refractive Fresnel lens. The Fresnel lens will be molded. A Fresnel lens is usually obtained by curing an ultraviolet curable resin, but adhesion to a substrate is manifested by chemical bonds and physical bonds. If the surface of the base material to be molded with Fresnel lens is very smooth with a fine particle-free surface, the latter physical bond (so-called anchor effect) is hardly expressed, so the Fresnel lens is not sufficiently adhered to the base material. There is a concern that it is likely to be. In particular, when chemical bonds cannot be sufficiently expressed from the viewpoint of the composition of the substrate, physical bonds (anchor effect) due to fine irregularities on the surface of the substrate are considered to contribute greatly to the adhesion. If the surface is a fine particle-free layer and is very smooth, physical bonding cannot be expected, resulting in insufficient adhesion.

  Therefore, as a result of intensive investigations from the viewpoint of cost advantage of effective utilization of mill ends and improvement of production efficiency, and the viewpoint of being suitable as a Fresnel lens base material, the present inventor has 2 The present inventors have found a light diffusing thermoplastic resin sheet having a multilayer structure of more than one layer, and have reached the present invention.

That is, in the present invention, the layer (1) in which fine particles of refractive index Na are dispersed in the thermoplastic resin (1) having a refractive index N1, and the fine particles of refractive index Na are formed in the thermoplastic resin (2) having a refractive index N2. A layer (2) dispersed, and having the formulas (I) to (III):
| N1-Na | ≦ 0.005 (I)
0.005 <| N2-Na | ≦ 0.04 (II)
0.005 <| N2-N1 | ≦ 0.04 (III)
The light diffusive sheet | seat characterized by satisfy | filling is provided.

  By using the light diffusing sheet of the present invention, it is possible to effectively use mill ends and improve production efficiency, which is advantageous in terms of cost. In particular, when used as a base material for a transmission screen, it is possible to reduce scintillation. It becomes.

  As the thermoplastic resin used in the light diffusing sheet of the present invention, a highly transparent resin is suitable, for example, a methyl methacrylate resin, a styrene resin, a methyl methacrylate-styrene copolymer resin, a polycarbonate resin. An alicyclic olefin resin, a polyester resin, an acrylonitrile-styrene copolymer resin, or the like is used. Among these, methyl methacrylate resin, styrene resin, and methyl methacrylate-styrene copolymer resin are preferably used.

  The methyl methacrylate resin is a polymer mainly composed of methyl methacrylate, and may be a homopolymer of methyl methacrylate, or 50% by mass or more of methyl methacrylate and 50% by mass of other monomers. It may be a copolymer with: In the case of a copolymer, the proportion of methyl methacrylate is preferably 70% by mass or more, and more preferably 90% by mass or more.

  Monomers other than methyl methacrylate have one or more double bonds capable of radical polymerization in the molecule, and (meth) acrylic acid esters and styrene monomers other than methyl methacrylate are preferably used. . Examples of (meth) acrylic esters other than methyl methacrylate include methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, (meth ) 2-ethylhexyl acrylate, 2-hydroxyethyl (meth) acrylate, and the like. Examples of styrenic monomers include styrene and nuclei such as o-methyl styrene, p-methyl styrene, m-methyl styrene, 2,4-dimethyl styrene, p-ethyl styrene, pt-butyl styrene. Alkyl-substituted styrenes; α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-p-methylstyrene; halogenated styrenes such as o-chlorostyrene and p-chlorostyrene. Examples of monomers other than (meth) acrylic acid esters and styrenic monomers include acrylonitrile, methacrylonitrile, acrylamide, diacetone acrylamide, acrylic acid, methacrylic acid, maleic anhydride, phenylmaleimide, cyclohexyl And maleimide.

  The styrene-based resin is a polymer mainly composed of styrene, and may be a homopolymer of styrene, or a copolymer of 50% by mass or more of styrene and 50% by mass or less of other monomers. May be. In the case of a copolymer, the proportion of styrene is preferably 70% by mass or more, and more preferably 90% by mass or more.

  Monomers other than styrene have at least one double bond capable of radical polymerization in the molecule. Examples thereof include methyl methacrylate and other monomers of methyl methacrylate resin. Examples include (meth) acrylic acid esters other than methyl methacrylate, styrene monomers other than styrene, and monomers other than (meth) acrylic acid esters and styrene monomers. .

  The methyl methacrylate-styrene copolymer resin is a copolymer having methyl methacrylate and styrene as essential monomers, and the monomer composition overlaps with the above methyl methacrylate resin and styrene resin. It is possible. The monomer composition is preferably 15 to 85% by mass of methyl methacrylate, 15 to 85% by mass of styrene, and 0 to 30% by mass of other monomers.

  Monomers other than methyl methacrylate and styrene have at least one double bond capable of radical polymerization in the molecule, and as an example of the monomer of methyl methacrylate resin, Examples thereof include (meth) acrylic acid esters other than methyl methacrylate, styrene monomers other than styrene, and monomers other than (meth) acrylic acid esters and styrene monomers.

  The thermoplastic resin may contain a rubber-like polymer. In this case, the rubber-like polymer usually has a refractive index substantially the same as the portion other than the rubber-like polymer of the thermoplastic resin. (With a refractive index difference of 0.005 or less) is used.

  In particular, when the portion other than the rubber-like polymer of the thermoplastic resin is a methyl methacrylate resin, acrylic rubber particles are suitable as the rubber-like polymer. The acrylic rubber particle is a particle containing an elastic polymer mainly composed of an acrylate ester as a rubber component, and may be a particle having a single layer structure made of only this elastic polymer, or a layer of this elastic polymer. It may be a multi-layered particle having The elastic polymer may be a homopolymer of an acrylate ester or a copolymer of 50% by mass or more of an acrylate ester and 50% by mass or less of other monomers. .

  In particular, when the portion other than the rubber-like polymer of the thermoplastic resin is a methyl methacrylate-styrene copolymer resin, a diene rubber copolymer is suitable as the rubber-like polymer. Examples of the diene monomer include butadiene, 2-methylbutadiene, 2,3-dimethylbutadiene, and the like, and two or more of them can be used as necessary. Of these, butadiene is preferred. As the diene rubbery copolymer, styrene-butadiene copolymer rubber is most commonly mentioned. The diene rubbery copolymer may be a random copolymer or a block copolymer. Further, a monomer component other than the rubber-like polymer of the thermoplastic resin may be graft polymerized.

  The thermoplastic resin can be produced, for example, by a bulk polymerization method, a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, or the like.

  As the diffusing fine particles used in the light diffusing sheet of the present invention, organic polymer particles and inorganic particles are usually used. Examples of the organic polymer particles include methyl methacrylate polymer particles, styrene polymer particles, and siloxane polymer particles.

  The methyl methacrylate polymer particle is a polymer particle mainly composed of methyl methacrylate, and this polymer has methyl methacrylate and one double bond capable of radical polymerization in the other molecule. A cross-linked polymer obtained by copolymerizing a monofunctional monomer and a polyfunctional monomer having two or more double bonds capable of radical polymerization in the molecule is preferable.

  Here, as an example of a monofunctional monomer other than methyl methacrylate, (meth) acrylic acid esters other than methyl methacrylate and styrene-based monomers mentioned above as examples of monomers of methyl methacrylate resin And the same as the monomer other than (meth) acrylic acid ester and styrene monomer, and styrene is preferably used.

Examples of polyfunctional monomers include 1,4-butanediol dimethacrylate, neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, propylene ethylene glycol dimethacrylate, tetrapropylene Methacrylates of polyhydric alcohols such as ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate; 1,4-butanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, tetraethylene Glycol diacrylate, propylene ethylene glycol dia Relate, tetrapropylene glycol diacrylate, trimethylolpropane triacrylate, methacrylates of polyhydric alcohols such as pentaerythritol tetraacrylate; divinylbenzene, such as aromatic polyfunctional compounds of diallyl phthalate, and the like. Such polyfunctional monomers are used alone or in combination of two or more.

  The refractive index of such methyl methacrylate polymer particles is usually about 1.46 to 1.55, and there is a tendency that the higher the benzene skeleton and halogen atom content, the higher the refractive index. The methyl methacrylate polymer particles can be produced by, for example, a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, or a dispersion polymerization method.

  Styrenic polymer particles are particles of a polymer mainly composed of styrene, and this polymer includes styrene and a monofunctional monomer having one double bond capable of radical polymerization in other molecules. A crosslinked polymer obtained by copolymerizing a polyfunctional monomer having two or more double bonds capable of radical polymerization in the molecule is preferable.

  Here, as an example of a monofunctional monomer other than styrene, in addition to methyl methacrylate, (meth) acrylic acid esters other than methyl methacrylate listed above as examples of methyl methacrylate resin monomers, Examples of the styrene monomer and those other than the (meth) acrylic acid ester and the styrene monomer are listed, and methyl methacrylate is preferably used.

  Moreover, as an example of a polyfunctional monomer, the thing similar to what was mentioned as an example of the polyfunctional monomer of the methyl methacrylate polymer particle | grains previously is mentioned, Each is single or in combination of 2 or more types. Can be used.

  The refractive index of such styrenic polymer particles is usually about 1.53 to 1.61, and there is a tendency that the larger the benzene skeleton or halogen atom content, the larger the refractive index. The styrenic polymer particles can be produced, for example, by suspension polymerization, micro suspension polymerization, emulsion polymerization, or dispersion polymerization.

  The ratio of the polyfunctional monomer used in the methyl methacrylate polymer particles and the styrene polymer particles is usually about 0.05 to 15% by mass, preferably 0.1% based on the total monomers. -10 mass%. If the amount of the polyfunctional monomer is too small, the degree of crosslinking of the particles is not sufficient, and the particles are likely to be greatly deformed when subjected to heat or shear during extrusion, and as a result, it is difficult to obtain a desired light diffusion effect. Become. Moreover, when there is too much quantity of a polyfunctional monomer, an external appearance defect will generate | occur | produce easily at the time of extrusion molding.

  Siloxane polymer particles are, for example, polymer particles produced by a method of hydrolyzing and condensing chlorosilanes. Examples of chlorosilanes include dimethyldichlorosilane, diphenyldichlorosilane, phenylmethyldichlorosilane, methyltrichlorosilane, and phenyltrichlorosilane. The siloxane polymer may be cross-linked. For crosslinking, for example, siloxane-based polymer is benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl-2,5-dimethyl peroxide. A peroxide such as -2,5- (t-butylperoxy) hexane may be allowed to act. Moreover, when it has a terminal silanol group, you may carry out condensation bridge | crosslinking with alkoxysilanes. The crosslinked polymer preferably has a structure in which about 2 to 3 organic residues are bonded per silicon atom. Such a siloxane-based polymer is a polymer also called a silicone rubber or a silicone resin, and is preferably a solid at room temperature. Siloxane polymer particles can be obtained by grinding the siloxane polymer. It is good also as granular particle | grains by hardening the curable polymer which has a linear organosiloxane block, or its composition in a sprayed state. Alternatively, the alkyltrialkoxysilane or a partially hydrolyzed condensate thereof may be obtained as granular particles by hydrolytic condensation in an aqueous solution of ammonia or amines. The refractive index of such siloxane polymer particles is usually about 1.40 to 1.47.

  Examples of the inorganic particles include calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica (silicon oxide), inorganic glass, talc, mica, white carbon, magnesium oxide, and zinc oxide. Such inorganic particles may be surface-treated with a surface treatment agent such as fatty acid so as to be uniformly dispersed in the thermoplastic resin.

  The weight average particle diameter of the organic polymer particles and inorganic particles used as the light diffusing fine particles may be appropriately selected in terms of the light diffusing properties, but is usually 1 to 40 μm, preferably 3 from the viewpoint of light diffusing performance. It is -20 micrometers, More preferably, it is 5-15 micrometers. The light diffusing fine particles are generally spherical, but those having a rectangular shape, a scale shape, a needle shape, a plate shape, or the like can also be used.

  The light diffusing sheet of the present invention is a sheet in which light diffusing fine particles are dispersed in the thermoplastic resin described above, and is a thermoplastic resin sheet having a multilayer structure of two or more layers, and having a refractive index. Layer (1) in which fine particles of refractive index Na are dispersed in N1 thermoplastic resin (1), and layer (2) in which fine particles of refractive index Na are dispersed in thermoplastic resin (2) with refractive index N2. It has. The fine particles dispersed in the thermoplastic resin (2) are preferably the same as the fine particles dispersed in the thermoplastic resin.

And this light diffusive sheet | seat is following formula (I)-(III):
| N1-Na | ≦ 0.005 (I)
0.005 <| N2-Na | ≦ 0.04 (II)
0.005 <| N2-N1 | ≦ 0.04 (III)
It satisfies.

That is, first, as shown in the formula (I), fine particles are dispersed in the thermoplastic resin (1) by making the refractive index N1 of the thermoplastic resin (1) substantially equal to the refractive index Na of the fine particles. Layer (1) can be substantially transparent similar to the fine particle-free layer. The relationship between N1 and Na is preferably the formula (I ′):
| N1-Na | ≦ 0.003 (I ′)
It is good to satisfy.

Further, as shown in the formula (II), by providing a predetermined refractive index difference between the refractive index N2 of the thermoplastic resin (2) and the refractive index Na of the fine particles, the fine particles are dispersed in the thermoplastic resin (2). The layer (2) formed can be a light diffusing layer. This relationship between N2 and Na is preferably (formula II ′):
0.01 ≦ | N2-Na | ≦ 0.03 (II ′)
It is good to satisfy.

  By forming the layer (1) as a transparent layer and the layer (2) as a light diffusion layer as described above, for example, a two-layer plate of transparent layer / light diffusion layer [layer (1) / layer (2)] A transparent screen substrate having a transparent layer and a light diffusion layer, such as a three-layer plate of light diffusion layer / transparent layer / light diffusion layer [layer (2) / layer (1) / layer (2)] When used as, a light diffusion sheet advantageous in terms of scintillation reduction can be obtained. In addition, since the transparent layer [layer (1)] contains fine particles, the surface becomes difficult to be taken by the roll, so that a tuck mark is hardly generated, and the surface easily exhibits an anchor effect. When a Fresnel lens is molded, the adhesion becomes high.

Then, as shown in the formula (III), the difference between the refractive index N1 of the thermoplastic resin (1) and the refractive index N2 of the thermoplastic resin (2) is set to a predetermined value or less, so that the thermoplastic resin (1) When mixing the thermoplastic resin (2) and the thermoplastic resin (2), even if they are not compatible, apparently they can be in a compatible state. Later, it becomes easy to reuse as a raw material, which is advantageous in terms of cost. The relationship between N1 and N2 is preferably the formula (III ′):
0.005 <| N2-N1 | ≦ 0.02 (III ′)
It is good to satisfy. If only the relationship between N2 and N1 is considered, the smaller the difference, the more advantageous in terms of reuse of the scrap material. In order to satisfy the relationship between N1 and Na and the relationship between N2 and Na. , N2 and N1 should have a predetermined difference.

In the light diffusing sheet of the present invention, the layer (1) in which the fine particles are dispersed in the thermoplastic resin (1), that is, the thickness of the transparent layer is T1, and the fine particles are dispersed in the thermoplastic tree (2). When the thickness of the layer (2), that is, the light diffusion layer is T2, the formula (IV):
0.5 ≦ T1 / (T1 + T2) ≦ 0.98 (IV)
It is preferable to satisfy. If T1 / (T1 + T2) is too small, the thickness of the transparent layer with respect to the total thickness becomes small, and there is a concern that the scintillation reduction effect described above may not be sufficient. On the other hand, if T1 / (T1 + T2) is too large, the thickness of the light diffusing layer with respect to the entire thickness becomes small, so that it becomes difficult to obtain sufficient light diffusing performance, and when trying to obtain sufficient light diffusing performance. It is necessary to make the concentration of the fine particles very high, resulting in a poor appearance of the resulting sheet. In addition, when there are a plurality of layers (1), the thickness T1 may be considered as the total thickness of the plurality of layers. When there are a plurality of layers (2), the thickness T2 is the sum of the plurality of layers. What is necessary is just to think as thickness.

Moreover, in the light diffusable sheet | seat of this invention, the relationship of refractive index N1 and N2 and thickness T1 and T2 is Formula (V):
T2 / (T1 + T2) × | N1-N2 | ≦ 0.01 (V)
It is preferable to satisfy the relationship. When T2 / (T1 + T2) × | N1-N2 | exceeds 0.01, T2 and | N1-N2 | become relatively large values, and the thermoplastic resin (1) and heat It becomes difficult for the plastic resin (2) to be compatible with each other, and a decrease in transmittance due to phase separation tends to occur, which is not preferable.

  In the light diffusing sheet of the present invention, for example, various additives such as an antioxidant, a plasticizer, a release agent, a colorant, an antistatic agent, an ultraviolet absorber, a flame retardant, etc. It may be added as described above.

  Such a light diffusive sheet of the present invention can be obtained by an ordinary multilayer extrusion molding method or press molding method. In view of cost and the like, it is preferably obtained by a multilayer extrusion molding method. The mixture of each layer may be prepared by mixing a thermoplastic resin and diffusing fine particles in advance and mixing them with additives as necessary, and supplying them to an extruder as they are, and melt extrusion sheeting. Alternatively, the thermoplastic resin and diffusing fine particles may be used in advance. The additive to be added as necessary may be obtained as a resin molded body (pellet) obtained by melt-kneading at a temperature equal to or higher than the melting temperature, and then supplied to an extruder for melt extrusion sheeting.

  In multi-layer extrusion, multiple extruders are prepared according to the number of layers in the sheet, and they are laminated and integrated through feed block dies or multi-manifold dies corresponding to the number of layers. By sandwiching and cooling, a desired multilayer light diffusion sheet can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this Example. The evaluation method in each example is as follows.

(Light diffusion performance)
Haze was evaluated as an index of light diffusivity. The light diffusing sheet (1.5 mm thickness) obtained by the experiment is cut out to 4 × 6 cm, the sample is set so that the light diffusing layer (surface layer) side is the light incident surface, and according to JIS K7136, Murakami Color Technology Evaluation was performed using HM-150 manufactured by Research Laboratory.

[Layer thickness]
The thickness of the entire sheet was measured with a micrometer. The thickness of the light diffusion layer was measured by observing the cross section with an optical microscope.

[Scintillation]
What was integrated with the lenticular lens which has a black stripe with a pitch of 0.25 mm was used for evaluation so that the light-diffusion layer (surface layer) side of the obtained light-diffusion sheet might become the incident surface of the light from a light source. . For evaluation, a 62-inch rear projection TV screen with a commercially available DLP light source was replaced with a transparent acrylic plate, a white screen was output, and a screen set was diffused in the center of the screen. The sheet was attached so that the light diffusion layer (surface layer) side of the adhesive sheet was the light source side. Then, visual sensory evaluation of scintillation was performed from a place 1 m away from the screen, and indicated by ○ (good) and Δ (somewhat bad). Scintillation was judged as good or bad as a comparative evaluation of equivalent haze levels.

  The following were used as the thermoplastic resin. The refractive index was measured according to JIS K7142.

Resin (1): Copolymer resin (refractive index 1.533) of methyl methacrylate / styrene = 60/40 (mass ratio).

Resin (2): Copolymer resin of methyl methacrylate / styrene = 80/20 (mass ratio) (refractive index 1.512)

  As the light diffusing fine particles, the following were used. The refractive index was measured according to JIS K7142.

Particle (1): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 58/37/5 (mass ratio) (refractive index 1.535, weight average particle diameter 7.9 μm).

Particle (2): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 38/57/5 (mass ratio) (refractive index 1.555, weight average particle diameter 8.8 μm).

Examples 1-5, Comparative Examples 1-6, Reference Examples 1-6
[Mixing of thermoplastic resin and light diffusing fine particles]
After mixing the thermoplastic resin and light diffusing fine particles shown in Table 1 at a mass ratio shown in Table 1 and mixing them in a plastic bag at room temperature, an extruder (uniaxial, screw diameter φ40 mm, with vent, Melted and kneaded at a resin temperature of about 230 ° C while being heated by Tanabe Plastics Machine), the resin strand extruded from the strand die is cut with a pelletizer device, processed into a pellet shape, thermoplastic resin and light diffusion The mixture (light diffusable composition) with diffusing fine particles was obtained.

[Production of light diffusive sheet (multilayer sheet)]
The thermoplastic resins shown in Table 1 are used in the first extruder (Tanabe Plastics Machine; screw diameter 40 mm, uniaxial, with vent) and the second extruder (Tanabe Plastics Machine; screw diameter 20 mm, uniaxial, with vent). And a mixture of diffusing fine particles were added. A two-kind, two-layer distribution type multi-manifold die is placed at the tip of the extruder, and the layer from the first extruder is the main layer and the layer from the second extruder is light-diffused with the die maintained at about 250 ° C. The layers were integrated into two layers (surface layers). The two-layer light diffusing sheet coming out of the die is sandwiched between the first cooling roll and the second cooling roll, and tightly wound around the second cooling roll, while being sandwiched between the second cooling roll and the third cooling roll. And was tightly wound around the third cooling roll and cooled. Each of the first cooling roll, the second cooling roll, and the third cooling roll was made of stainless steel with a diameter of 25 cm and the surface was mirror-finished after chrome plating. The total thickness of the two-layer light diffusing sheet was about 1.5 mm, and the surface layer thickness was about 0.1 mm [T1 / (T1 + T2) = 0.93]. The evaluation results of the light diffusing sheet thus obtained are shown in Table 1.

Claims (4)

A layer (1) in which fine particles of refractive index Na are dispersed in a thermoplastic resin (1) having a refractive index N1, and a layer (in which fine particles of refractive index Na are dispersed in a thermoplastic resin (2) having a refractive index N2 ( 2) having the formulas (I) to (III):
| N1-Na | ≦ 0.005 (I)
0.005 <| N2-Na | ≦ 0.04 (II)
0.005 <| N2-N1 | ≦ 0.04 (III)
A light diffusing sheet characterized by satisfying Formula (I ′):
0.005 <| N2-N1 | ≦ 0.02 (III ′)
The light diffusive sheet according to claim 1 satisfying When the thickness of the layer (1) is T1, and the thickness of the layer (2) is T2, the formula (IV):
0.5 ≦ T1 / (T1 + T2) ≦ 0.98 (IV)
The light diffusable sheet according to claim 1 or 2 satisfying Formula (V):
T2 / (T1 + T2) × | N1-N2 | ≦ 0.01 (V)
The light diffusable sheet | seat of Claim 3 satisfy | filling these.