JP2009109702A - Light diffusion sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet having favorable light diffusion and light transmission and capable of preferably suppressing generation of ghost or double images or scintillation even when the sheet is used for a Fresnel lens. <P>SOLUTION: The light diffusion sheet is characterized in that: the 20-degree mirror face gloss on at least one surface specified by JIS Z8741-1997 is not more than 5; the 60-degree mirror face gloss on the above surface specified by JIS Z8741-1997 is not more than 20; and the 85-degree mirror face gloss on the surface specified by JIS Z8741-1997 is not more than 27. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light diffusing sheet. The light diffusing sheet is useful for a transmissive screen of a projection television, a backlight member of a liquid crystal television, and the like.

  Light diffusive sheets are known to be used for transmissive screens for projection televisions, backlight members for liquid crystal televisions, and the like, and such optically diffusable sheets are required to have various optical performances.

  For example, such a light diffusion sheet is required to have high light transmittance while maintaining sufficient light diffusion. In addition, when the light diffusive sheet is used in a Fresnel lens, which is one of the transmissive screens of projection televisions, the ability to suppress the generation of so-called ghosts and double images derived from reflected light, Therefore, there is a demand for performance to suppress glare (hereinafter sometimes referred to as scintillation) that is considered to be caused by uneven brightness.

  As a light diffusing sheet having such a performance, for example, in Japanese Patent Application Laid-Open No. 2003-215716 (Patent Document 1), a matte surface is provided on one side, and the matte surface has a 60-degree specular glossiness defined in JIS K7105. Is 20 to 45 (%), and a transparent base sheet having a 20 degree specular gloss of 5 to 15 (%) as defined in JIS K7105 of the mat surface is described.

JP 2003-215716 A

  However, even when the sheet described in the above document is used for the Fresnel lens, it is not always satisfactory in terms of the performance of suppressing the generation of ghosts and double images and the performance of suppressing scintillation. Further improvement was desired.

  Accordingly, an object of the present invention is to provide a light diffusibility that has good light diffusibility and light transmittance, and can suppress generation of ghosts and double images and scintillation even when used in the Fresnel lens. To provide a sheet.

  As a result of intensive studies, the present inventor has found that the above object can be achieved by a light diffusing sheet having a predetermined specular gloss on at least one surface, and has completed the present invention.

  That is, according to the present invention, the 20-degree specular gloss specified in JIS Z8741-1997 in at least one surface is 5 or less, and the 60-degree specular gloss defined in JIS Z8741-1997 in the surface is 20 or less. The light diffusive sheet is characterized in that the 85 ° specular glossiness defined in JIS Z8741-1997 is 27 or less.

  Furthermore, the present invention is a light diffusing sheet for a Fresnel lens for forming a Fresnel lens shape on one surface, as defined in JIS Z8741-1997 on the surface opposite to the surface for forming the Fresnel lens shape. The specular glossiness is 5 or less, the 60 ° specular glossiness defined in JIS Z8741-1997 on the opposite surface is 20 or less, and the 85 ° specular glossiness defined in JIS Z8741-1997 on the opposite surface is 27. The present invention provides a light diffusive sheet for a Fresnel lens characterized by the following.

  According to the present invention, there is provided a light diffusive sheet that has a good light diffusibility and a light transmissive property, and can suppress generation of ghosts and double images and scintillation even when used in the Fresnel lens. Can be provided.

  Hereinafter, the present invention will be described in detail. The light diffusing sheet of the present invention is mainly composed of a base resin made of a thermoplastic resin, and the light diffusing sheet may have a so-called single layer structure, or two or two types or two or three types. A multilayer structure such as a layer may be used.

  The light diffusing sheet of the present invention has, on at least one surface of the sheet, (1) a 20-degree specular gloss specified in JIS Z8741-1997 is 5 or less, and (2) a 60-degree specular specified in JIS Z8741-1997. The glossiness is 20 or less, and (3) the 85 ° specular glossiness defined in JIS Z8741-1997 is 27 or less. Here, at least one surface means one surface or both surfaces, and therefore, in the sheet, one surface satisfies the above (1) to (3), or both surfaces are It satisfies the above (1) to (3). And by satisfying such conditions, it has good light diffusibility and light transmittance, for example, when the light diffusive sheet is used for a Fresnel lens which is one of the transmission type screens of a projection television. In addition, the generation of ghosts and double images and scintillation can be suppressed more satisfactorily. Note that recent projection televisions have been made thinner, and the incident angle of light from the light source may exceed 60 degrees. Therefore, the light diffusing sheet for the Fresnel lens in particular has 20 In addition to the specular glossiness of 60 degrees and the specular glossiness of 60 degrees, the specular glossiness of 85 degrees is also a necessary element. If the 85-degree specular gloss is higher than 27, it is insufficient in terms of suppressing the generation of ghosts and double images and suppressing scintillation.

  Further, the light diffusing sheet preferably has a haze value defined in JIS K7136: 2000 of 45% or more, and more preferably 50% or more. When the haze value is less than 45%, the light diffusibility is insufficient. For example, when used in the Fresnel lens, it is insufficient in terms of suppressing scintillation.

  As a thermoplastic resin which comprises base resin, it is a thermoplastic resin which has transparency normally, and a highly transparent thing is more preferable. Suitable examples include methyl methacrylate resin, styrene resin, methyl methacrylate-styrene copolymer resin, methyl methacrylate-butadiene-styrene resin, polycarbonate resin, alicyclic olefin resin, polyester resin, acrylonitrile. -Styrene copolymer resin etc. are mentioned. Of these, methyl methacrylate resin, styrene resin, methyl methacrylate-styrene copolymer resin, and methyl methacrylate-butadiene-styrene resin are more preferable.

  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. Examples include 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 Examples include 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 that of the thermoplastic resin other than the rubber-like polymer. (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. The rubber-like copolymer-containing resin is a so-called methyl methacrylate-butadiene-styrene resin. 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, the monomer component of the thermoplastic resin (A) other than the rubber-like polymer may be obtained by graft polymerization.

  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.

  The light diffusing sheet of the present invention has a surface with a physically fine uneven shape, or a base resin containing fine particles such as inorganic particles and organic polymer particles. It is also possible to have both of these. Thus, by giving a predetermined shape or containing fine particles, a desired specular gloss or haze value can be obtained.

  As a method for physically giving the surface of the light diffusive sheet a fine uneven shape, for example, as a rolling roll in melt extrusion of a thermoplastic resin, a rolling roll having a fine mat shape on the surface is used. There are a method for transferring the mat form on the surface of the sheet, a method for producing a sheet on which the mat form is transferred by polymerizing and curing after injecting a polymerizable monomer between a glass plate or a SUS plate having a fine mat shape on the surface. Can be mentioned.

  In addition, examples of a method for causing the base resin to contain fine particles such as inorganic particles and organic polymer particles include a method of melt extrusion molding a mixture of a thermoplastic resin serving as the base resin and the fine particles.

  Among the above-described methods, a method in which the fine particles are contained in the base resin is preferable in terms of precisely controlling the specular gloss and the haze value.

  From the viewpoint of light diffusibility, the fine particles are usually particles having a weight average particle diameter of 50 μm or less, and preferably 20 μm or less. Further, when such fine particles are contained in the surface layer of the light diffusive sheet and surface irregularities are formed by the fine particles, the specular glossiness is set within a predetermined range, and ghosts and two when used in a Fresnel lens are used. From the viewpoint of suppressing the generation of multiple images and scintillation, the fine particles are more preferably particles having a weight average particle diameter of 7 μm or less.

  Further, as the fine particles, those having a refractive index different from that of the base resin are usually used. However, for example, when such fine particles are contained in the surface layer of the light diffusive sheet and the surface unevenness is formed by the fine particles, the surface resin has a bendability because the surface unevenness acquires light diffusibility. And the refractive index of the fine particles may be the same. As the light diffusing sheet of the present invention, those having fine irregularities formed on the surface layer are preferable, and those having many fine particles having a relatively small particle diameter are preferable. In order to employ such a preferred embodiment, the refractive index difference | X−Y | between the refractive index X of the base resin and the refractive index Y of the fine particles is determined from the balance between light diffusibility and light transmittance. , 0.005 or less is preferable.

  When inorganic particles are used as the fine particles, examples of the inorganic particles include calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica, glass, talc, mica, white carbon, magnesium oxide, and zinc oxide. These may be subjected to a surface treatment with a fatty acid or the like. When organic polymer particles are used as the fine particles, examples of the organic polymer particles include styrene polymer particles, acrylic polymer particles, and siloxane polymer particles, and the weight average molecular weight is 50. Ten to five million high molecular weight polymer particles, crosslinked polymer particles, and the like are preferably used. Moreover, these 2 or more types can also be used as needed.

  As the styrene polymer particles, polymer particles containing 50% by mass or more of a styrene monomer having one double bond capable of radical polymerization in one molecule as the monomer unit are suitably used (hereinafter referred to as “the styrene polymer particles”). A monomer having one radical-polymerizable double bond in one molecule is called a monofunctional monomer, and a monomer having at least two radical-polymerizable double bonds in one molecule is multifunctional. For example, high molecular weight polymer particles obtained by polymerizing styrene monofunctional monomers, obtained by polymerizing styrene monofunctional monomers and other monofunctional monomers. High molecular weight polymer particles, cross-linked polymer particles obtained by polymerizing styrenic monofunctional monomers and polyfunctional monomers, styrenic monofunctional monomers and other monofunctional monomers and polyfunctional monomers Crosslinked polymer particles obtained by polymerizing monomers are used.As a polymerization method for obtaining these styrene polymer particles, a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method and the like are usually employed.

  Examples of the styrene monofunctional monomer in the styrene polymer particles include styrene, halogenated styrene such as chlorostyrene and bromostyrene, alkyltoluene such as vinyltoluene and α-methylstyrene, and the like. Two or more of them can be used as necessary.

  Examples of the monofunctional monomer other than the styrene monofunctional monomer in the styrenic polymer particles include, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, methacrylic acid. Methacrylic acid esters such as 2-ethylhexyl acid and 2-hydroxyethyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, acrylic Acrylic acid esters such as 2-hydroxyethyl acid; acrylonitrile and the like can be mentioned, and two or more of them can be used as necessary. Among these, methacrylic acid esters such as methyl methacrylate are preferable.

  Examples of the polyfunctional monomer in the styrenic polymer particles include 1,4-butanediol dimethacrylate, neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and propylene glycol dimethacrylate. Di-or higher methacrylates such as tetrapropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate; 1,4-butanediol diacrylate, neopentyl glycol diacrylate, ethylene Glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate , Di- or higher acrylates of polyhydric alcohols such as propylene glycol diacrylate, tetrapropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate; A functional monomer etc. are mentioned and those 2 or more types can also be used as needed.

  The refractive index of the styrenic polymer particles is usually about 1.53 to 1.61 although it depends on its constituent components. In general, the more phenyl groups and more halogeno groups, the higher the refractive index.

  As the acrylic polymer particles, polymer particles containing 50% by mass or more of an acrylic monofunctional monomer as a monomer unit are used. For example, a polymer particle obtained by polymerizing an acrylic monofunctional monomer is used. Molecular weight polymer particles, high molecular weight polymer particles obtained by polymerizing acrylic monofunctional monomers and other monofunctional monomers, obtained by polymerizing acrylic monofunctional monomers and polyfunctional monomers Cross-linked polymer particles obtained by polymerizing an acrylic monofunctional monomer, another monofunctional monomer, and a polyfunctional monomer are used. As a polymerization method for obtaining these acrylic polymer particles, a suspension polymerization method, a micro suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method and the like are usually employed.

  Examples of the acrylic monofunctional monomer in the acrylic polymer particles include, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, methacrylic acid. Methacrylic acid esters such as 2-hydroxyethyl; methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc. Acrylic acid esters; methacrylic acid, acrylic acid and the like can be mentioned, and two or more of them can be used as necessary.

  Examples of the monofunctional monomer other than the acrylic monofunctional monomer in the acrylic polymer particles include those similar to the styrene monofunctional monomer in the styrene polymer particles and acrylonitrile. Two or more of them can be used accordingly. Of these, styrene is preferred. In addition, examples of the polyfunctional monomer in the acrylic polymer particles include those similar to the polyfunctional monomer in the styrene polymer particles, and two or more of them can be used as necessary. .

  The refractive index of the acrylic polymer particles is usually about 1.46 to 1.55, although it depends on its constituent components. Similarly to the styrene polymer particles, generally, the more phenyl groups and the more halogeno groups, the higher the refractive index.

  As the siloxane polymer particles, those generally called silicone rubber and those called silicone resin, which are solid at room temperature, are used. The siloxane polymer can be preferably produced by hydrolyzing and condensing chlorosilanes such as dimethyldichlorosilane, diphenyldichlorosilane, phenylmethyldichlorosilane, methyltrichlorosilane, and phenyltrichlorosilane. The polymer thus obtained is further benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 2, It may be crosslinked by the action of a peroxide such as 5-dimethyl-2,5-di (t-butylperoxy) hexane, and if it has a silanol group at the terminal, it is an alkoxysilane. It may be condensed and cross-linked. The polymer is preferably a crosslinked polymer in which 2 to 3 organic groups are bonded per silicon atom.

  The siloxane polymer particles may be obtained, for example, by mechanically pulverizing the siloxane polymer, and in the production thereof, as described in JP-A-59-68333, a line is used. The curable polymer having the organosiloxane block or its composition may be cured in a sprayed state to obtain spherical particles, or as described in JP-A-60-13813, The alkoxysilane or its partially hydrolyzed condensate may be obtained as spherical particles by hydrolysis and condensation in an aqueous solution of ammonia or amines.

  The refractive index of the siloxane polymer particles is usually about 1.40 to 1.47, although it depends on its constituent components. Generally, the refractive index tends to increase as the number of phenyl groups increases and the number of organic groups directly bonded to silicon atoms increases.

  Although the thickness of the light diffusable sheet of this invention is suitably adjusted with a use etc., it is about 0.05-6 mm normally, Preferably it is 0.1-5 mm. In addition, as described above, the light diffusing sheet of the present invention may have a single layer configuration or a multilayer configuration such as two types, two layers, and two types, three layers. From the viewpoint of obtaining the desired light diffusion performance, it is preferable that the outermost surface has a fine uneven shape. In order to form such a shape, in the case of a single layer configuration, a gold such as a rolling roll is used. A mat shape transfer on the surface of the mold and a mat shape transfer on the surface of the glass plate or SUS plate are suitable. In the case of a multilayer structure, it is preferable that the outermost layer contains a large amount of the fine particles. In addition, the light diffusive sheet which contains many said microparticles | fine-particles in the outermost layer in the latter multilayer structure is preferable at the point which controls a specular glossiness and a haze value precisely.

  Examples of the method for obtaining a light diffusing sheet having a multilayer structure include methods such as a coextrusion molding method, a bonding method, a thermal bonding method, a solvent bonding method, a polymerization bonding method, a cast polymerization method, and a surface coating method.

  In the production by the co-extrusion molding method, the resin (A) and the resin (B) in which necessary components are blended are melt-kneaded using separate uniaxial or biaxial extruders, and both of them are fed block die or multi-manifold. After stacking and integrating via a die, it can be performed by cooling and solidifying using a roll unit.

  Manufacturing by the bonding method is performed by, for example, processing one of the resin (A) and the resin (B) in which necessary components are blended into a plate shape, and pasting the other resin in a molten state. This can be done by combining them.

  In the production by the thermal bonding method, for example, the resin (A) and the resin (B) in which necessary components are blended are each processed into a plate shape, and both plate-like products are at a temperature higher than the softening point of both. It can carry out by pressing and integrating.

  In the production by the solvent bonding method, the resin (A) and the resin (B) in which necessary components are blended are processed into plates, and both plates are dissolved in either one or both resins. It can be performed by adhering using a solvent to be used.

  For example, the resin (A) and the resin (B) in which necessary components are blended are processed into a plate shape, and both plate-like products are bonded to each other by thermal polymerization or photopolymerization. It can be performed by adhering using an agent. Here, as an adhesive, what added the thermal-polymerization initiator or the photoinitiator to the monomer used as the raw material of resin (A) or resin (B) or its partial polymer is used suitably. .

  In the production by the cast polymerization method, for example, one of the resin (A) and the resin (B) in which necessary components are blended is processed into a plate shape, and this is applied to the inner surface of the cast molding cell. It can be carried out by installing and injecting into this cell a monomer that is a raw material for the other resin, or a mixture of components necessary for its partial polymer, and polymerizing.

  In the production by the surface coating method, for example, one of the resin (A) and the resin (B) in which necessary components are blended is processed into a plate shape, and this is used as a raw material for the other resin. It can be carried out by coating and polymerizing a monomer or a partial polymer blended with necessary components.

  The light diffusing sheet of the present invention includes one kind of various additives such as an antioxidant, a plasticizer, a release agent, a lubricant, a colorant, an antistatic agent, an ultraviolet absorber, and a flame retardant as necessary. Or you may contain 2 or more types.

  The light diffusing sheet of the present invention can be used for a transmissive screen of a projection television, a backlight member of a liquid crystal television, and the like. Among these, it can be suitably used for a Fresnel lens that is one of the transmission screens of projection televisions.

  Such a Fresnel lens is a sheet in which one surface is formed in the shape of a Fresnel lens, and projection light enters from a surface opposite to the surface. When the light diffusing sheet of the present invention is used for the Fresnel lens, one surface of the light diffusing sheet is formed into a Fresnel lens shape, and (1) JIS Z8741- The 20-degree specular gloss specified in 1997 is 5 or less, (2) the 60-degree specular gloss specified in JIS Z8741-1997 is 20 or less, and (3) the 85-degree specular gloss specified in JIS Z8741-1997 is 27 or less. Configured. By adopting such a configuration, generation of ghosts and double images and scintillation can be suppressed more favorably.

  As a method for forming such a Fresnel lens shape, for example, a cast molding method using a cell in which the Fresnel lens shape is processed may be mentioned. As a specific example in this case, a glass plate or SUS plate having a fine mat shape is used on the cell surface on one side, and a glass plate or SUS plate having a Fresnel lens shape on the other cell surface is used. Examples thereof include a method of polymerizing and curing after injecting a polymerizable monomer between the plates. In addition, as other methods, the light diffusive sheet of the present invention is hot press molded using a mold having a Fresnel lens shape, or an ultraviolet curable resin is applied to the surface of the light diffusable sheet of the present invention. Examples include a method of curing so that a shape is formed.

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

(Light diffusion performance)
The haze value was measured as an index of light diffusivity. A light diffusing sheet (thickness 1.3 to 2.0 mm) obtained by [Manufacture of a light diffusing sheet] described later is cut into 4 × 6 cm so that the strong matte surface (surface layer) side becomes a light incident surface. A sample was set, and the haze value was measured using HM-150 manufactured by Murakami Color Research Laboratory in accordance with JIS K7136: 2000.

[Total light transmittance]
The total light transmittance was measured as an index of the transmission characteristics of the light diffusing sheet. A light diffusing sheet (thickness 1.3 to 2.0 mm) obtained by [Manufacture of a light diffusing sheet] described later is cut into 4 × 6 cm so that the strong matte surface (surface layer) side becomes a light incident surface. A sample was set, and the total light transmittance was measured using HM-150 manufactured by Murakami Color Research Laboratory in accordance with JIS K7361-1: 1997.

[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.

[Specular gloss (20 degrees, 60 degrees, 85 degrees)]
A light diffusing sheet (thickness 1.3 to 2.0 mm) obtained by [Manufacture of a light diffusing sheet] to be described later is cut out to about 5 × 8 cm, and the glossiness on the strong matte surface (surface layer) side is JIS Z8741- Based on 1997, 20-degree specular gloss, 60-degree specular gloss, and 85-degree specular gloss were measured using micro-TRI-gloss manufactured by BYK-Gardner GmBH.

[Surface roughness (Ra, Rz, Sm)]
Regarding the surface roughness of the light diffusable sheet (thickness 1.3 to 2.0 mm) on the strong matte surface (surface layer) side obtained by [Manufacture of light diffusive sheet] described later, a surface roughness measuring machine (stock) The average roughness Ra (μm), the ten-point average roughness Rz (μm), and the average crest pitch Sm (μm) were measured using “SJ-201P” manufactured by Mitutoyo Corporation. Based on B0601: 1994, the cutoff value was 0.8 mm, the evaluation length was 4 mm, and the other measurement conditions were default values.

[Scintillation]
On the surface opposite to the light diffusing sheet obtained by [Manufacture of light diffusing sheet] described later, the surface opposite to the light matting surface (surface layer) side is a light incident surface for light from the light source. A lenticular lens sheet having a black stripe of 25 mm was used for evaluation as a screen set. For evaluation, a 62-inch thin rear-projection television screen with a DLP light source was replaced with a transparent acrylic plate, a white screen was output, and a screen set was placed in the center of the screen. Affixing was performed so that the strong matte surface (surface layer) side 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), Δ (slightly bad), and × (bad).

[Ghost / double image]
A Fresnel lens made of a cured product of an ultraviolet curable resin is molded on the surface opposite to the strong matte surface (surface layer) of the light diffusing sheet obtained by [Manufacture of a light diffusing sheet] described later. Obtained. A lenticular lens sheet having black stripes with a pitch of 0.15 mm on the observation surface side of the Fresnel lens sheet is directed so that the strong matte surface (surface layer) of the obtained Fresnel lens sheet becomes a light incident surface of light from a light source. Further, the superposed product was set on a thin rear projection television having a DLP light source. In the state where the image was projected, the ghost and double image states resulting from the reflection of the light incident surface of the Fresnel lens sheet were observed, and indicated by ○ (good), Δ (slightly bad), and × (bad).

  As the base resin, the following two types of thermoplastic resins were used.

[Resin (1)]
Random copolymer of styrene / butadiene = 25/75 (mass ratio) [Nippon Elastomer Co., Ltd., Toughden 2000A] 6.7 parts by mass, methyl methacrylate 53.2 parts by mass, styrene 40.1 parts by mass And a polymerization initiator were mixed, and a two-stage stirring type continuous reaction apparatus was used to retain the polymer at 150 ° C. for 225 seconds for partial polymerization. The obtained partial polymer was transferred to another polymerization tank, a polymerization initiator, a suspension stabilizer and water were further added, and suspension polymerization was carried out with stirring to complete the polymerization. The obtained slurry was washed and filtered to obtain a resin (1) in which a rubbery copolymer was dispersed. The total light transmittance (measured in accordance with JIS K7361-1: 1997) of a resin plate having a thickness of 3 mm obtained by extrusion molding of the resin (1) is 91%, and the haze value (in compliance with JIS K7136: 2000). Measured) was 2%. Further, the refractive index of the resin plate (measured in accordance with JIS K7142-1996) was 1.535.

[Resin (2)]
A copolymer resin of methyl methacrylate / styrene = 20/80 (mass ratio) obtained by bulk polymerization was used as the resin (2). The total light transmittance (measured in accordance with JIS K7361-1: 1997) of the resin plate having a thickness of 3 mm obtained by extrusion molding of the resin (2) is 90%, and the haze value (in compliance with JIS K7136: 2000). Measured) was 0.5%. Moreover, the refractive index (measured according to JIS K7142-1996) of the resin plate was 1.570.

  The following were used as the fine particles. The refractive index was measured according to JIS K7142-1996.

Particle (1): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 58/32/10 (mass ratio) (refractive index 1.535, weight average particle diameter 5 μm).

Particle (2): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 68/27/5 (mass ratio) (refractive index 1.525, weight average particle diameter 12 μm).

Particle (3): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 32 / 67.5 / 0.5 (mass ratio) (refractive index 1.560, weight average particle diameter 8 μm).

Particle (4): Copolymer particles of methyl methacrylate / styrene / divinylbenzene = 68/27/5 (mass ratio) (refractive index 1.525, weight average particle diameter 5 μm).

Examples 1-2 and Comparative Examples 1-5
[Production of light diffusive sheet]
The first extruder (screw diameter 130 mm, uniaxial, with a vent) was charged with the thermoplastic resin and fine particles forming the main layer shown in Table 1, and the second extruder (slew diameter 65 mm, uniaxial, with a vent) A thermoplastic resin and fine particles forming a strong mat layer (surface layer) shown in Table 1 were added. Next, a two-type two-layer distribution type multi-manifold die is disposed at the tip of the extruder, and the layer extruded from the first extruder is used as the main layer in the die maintained at about 250 ° C. The two layers having the layer extruded from the above as a strong mat layer (surface layer) were integrated. The two-layer light diffusive 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 the second cooling roll and the third cooling roll It pinched | interposed in between, it closely_contact | adhered to the 3rd cooling roll, it wound and cooled, and also it pinched | interposed between the 3rd cooling roll and the 4th cooling roll, and closely wound on the 4th cooling roll and cooled. Then, after passing through the conveyance roller, a two-layer light diffusing sheet was obtained by cutting with a saw so as to have a desired size on the downstream side. The 1st cooling roll, the 2nd cooling roll, the 3rd cooling roll, and the 4th cooling roll were each made from stainless steel, and used what finished the mirror surface after the chromium plating process. The total thickness of the two-layer light diffusing sheet was about 1.3 to 2.0 mm, and the surface layer thickness was about 0.04 to 0.20 mm. The evaluation results of the light diffusing sheet thus obtained are shown in Table 1.

Claims (8)

The 20-degree specular gloss specified in JIS Z8741-1997 on at least one surface is 5 or less,
The 60-degree specular glossiness defined in JIS Z8741-1997 on the surface is 20 or less,
A light diffusive sheet characterized in that the 85-degree specular glossiness defined in JIS Z8741-1997 on the surface is 27 or less.   The light diffusable sheet according to claim 1, wherein the haze value defined in JIS K7136: 2000 is 45% or more.   The light diffusable sheet according to claim 1 or 2, wherein the base resin contains particles having a weight average particle diameter of 7 µm or less.   The light diffusive sheet according to claim 3, wherein a refractive index difference | X−Y | between the refractive index X of the base resin and the refractive index Y of the particles is 0.005 or less. A light diffusing sheet for a Fresnel lens for forming a Fresnel lens shape on one surface,
The 20-degree specular gloss specified in JIS Z8741-1997 on the surface opposite to the surface for forming the Fresnel lens shape is 5 or less,
The 60 degree specular glossiness defined in JIS Z8741-1997 on the opposite surface is 20 or less,
A light diffusive sheet for a Fresnel lens, characterized in that the 85 ° specular glossiness defined in JIS Z8741-1997 on the opposite surface is 27 or less.   The light diffusable sheet for Fresnel lenses according to claim 5, wherein a haze value defined in JIS K7136: 2000 is 45% or more.   The light-diffusing sheet for Fresnel lenses according to claim 5 or 6, wherein the base resin contains particles having a weight average particle diameter of 7 µm or less.   The light diffusing sheet for Fresnel lens according to claim 7, wherein a refractive index difference | X−Y | between the refractive index X of the base resin and the refractive index Y of the particles is 0.005 or less.