TWI406050B - Optical sheet and the use of its backlight unit - Google Patents

Abstract

The invention provides an optical sheet having excellent viscosity resistance, high total light transmission ratio, capability of suppressing interference phenomenon and illumination unevenness and thereby having high economical efficiency and film property, and a backlight unit using the same. The optical sheet of the invention comprises a transparent substrate film, an optical layer laminated on one side of the substrate film, and an anti-adhesion layer laminated on the other side of the substrate film, wherein the anti-adhesion layer contains filler and resin bonding agent thereof; the average thickness of a flat part of the anti-adhesion layer is more than 50 nm but less than 150 nm; the average particle diameter of the filler is more than 70 nm but smaller than 200 nm; a small-diameter filler containing main ingredients and a big-diameter filler containing auxiliary ingredients are used as filler; the average particle diameter of the small-diameter filler can be set to be more than 50 nm but less than 150 nm.

Description

Optical sheet and backlight unit using the same

The present invention relates to an optical sheet and a backlight unit using the same, and in particular, the present invention relates to an optical function having diffused transmitted light, refracted toward a normal side, concentrated, etc., and is particularly suitable for liquid crystal display. Optical sheet and backlight unit in the device.

In the liquid crystal display device, a backlight system in which a liquid crystal layer is irradiated from the back surface to emit light is generally used, and a backlight unit such as an end surface illumination type or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 5(a), the end-illuminated backlight unit 50 basically includes a linear light source 51 as a light source and a square plate-shaped light guide plate 52 whose end portion is arranged along the light source 51. And a plurality of optical sheets laminated on the light guide plate 52. The optical sheet has a predetermined optical function such as a function of refracting the peak direction of the light toward the normal direction side and a function of diffusing the luminance distribution, and specifically, the light diffusion sheet 53 and the edge disposed on the surface side of the light guide plate 52. Lens 54 and the like. Further, although not shown, in addition to the light diffusion sheet 53 and the cymbal sheet 54, the optical sheet may be provided with a reflection sheet disposed on the back side of the light guide plate 52 or a lenticular sheet having a microlens array on its surface. .

Hereinafter, the function of the backlight unit 50 will be described. First, the light incident from the light source 51 to the light guide plate 52 is reflected by the back surface of the light guide plate 52, and the reflection sheet (not shown) disposed on the back side of the light guide plate 52. And the side surfaces of the light guide plate 52 are reflected and are emitted from the surface of the light guide plate 52. The light emitted from the light guide plate 52 is incident on the light diffusion sheet 53 and is subjected to a predetermined optical action such as diffusion and refracting toward the normal direction side, and is emitted from the surface of the light diffusion sheet 53. Thereafter, the light emitted from the light-diffusing sheet 53 is incident on the cymbal sheet 54, and is emitted as a light having a distribution of peaks in a substantially normal direction by the dam portion 54a formed on the surface thereof.

As described above, the light emitted from the light source 51 is refracted toward the surface side by the light guide plate 52, and is diffused by the light diffusion sheet 53, and the peak is displayed in the substantially upper direction by the cymbal 54. The film is refracted to illuminate the entire surface of the liquid crystal layer (not shown) above. Further, although not shown, there is also a backlight unit in which another cymbal sheet or light-diffusing sheet is further disposed on the surface side of the cymbal sheet 54.

As the conventional light diffusion sheet 53, as shown in FIG. 5(b), the substrate film 55, the light diffusion layer 56 formed on the surface of the base film 55, and the back surface of the base film 55 are laminated. The anti-adhesion layer 57 (for example, refer to Japanese Patent Laid-Open Publication No. 2000-89007, etc.). The light diffusion layer 56 is configured to have a light diffusing function for transmitted light, and the light diffusing agent 59 is contained in the adhesive 58.

In the above-described conventional light-diffusing sheet 53, the anti-adhesion layer 57 is formed by applying a resin composition containing a polymer constituting a binder, a resin bead 61, a solvent, or the like to the back surface of the base film 55, in the adhesive 60. The resin beads 61 are dispersed, and the resin beads 61 have a convex portion on the back surface. The convex portion formed on the back surface of the release layer 57 prevents the back surface of the light diffusion sheet 53 from adhering to the light guide plate 52 and the like to cause interference fringes.

From the viewpoint of the anti-adhesion, the resin bead 61 of the anti-adhesion layer 57 can be an acrylate bead having an average particle diameter of 5 μm to 20 μm or the like. Therefore, the above-mentioned release layer 57 may cause a certain degree of scattering of light incident from the back surface due to reflection and refraction at the interface of the resin beads 61. Therefore, the above-described light diffusing sheet 53 may cause a decrease in optical function such as light transmittance due to the release layer 57.

Further, in order to fix the resin beads 61 having the above average particle diameter, the average thickness of the release layer 57 is set to 5 μm or more and 15 μm or less. Therefore, the above-mentioned prior light diffusing sheet 53 is required to be thinner in the current liquid crystal display device, and the transmitted light is disturbed by the refraction at the interface of the anti-adhesion layer 57, which may cause the occurrence of the rubbing. Wait.

Further, since the anti-adhesive layer 57 contains the resin beads 61, the convex portions on the back surface and the like are relatively soft, and may be damaged during assembly, storage, and transportation of the liquid crystal display device. If the back surface of the anti-adhesion layer 57 is damaged, there is a possibility that the screen brightness of the liquid crystal display device is lowered due to scattering of light, and uneven brightness is caused.

Further, since the release layer 57 is formed by coating or the like as described above, at least three steps are required in the production of the light diffusion sheet 53: a step of molding the base film 55, and the substrate film 55. The step of forming the light-diffusing layer 56 on the surface and the step of laminating the anti-adhesion layer 57 on the back surface of the base film 55, and in order to achieve the current requirements, that is, to reduce the manufacturing cost, it is required to simplify the manufacturing process.

The disadvantages of the light diffusing sheet 53 also occur in the cymbal sheet 54, or other lenticular sheet, lenticular lens sheet, Fresnel lens sheet or the like.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-89007

The present invention has been made in view of the above problems, and an object thereof is to provide an excellent anti-stick property, a high total light transmittance, an interference phenomenon and uneven brightness, and a high economical efficiency and film. Optical sheet and backlight unit using the same.

The invention completed to solve the above problems is as follows: an optical sheet comprising a transparent base film, an optical layer laminated on one surface of the base film, and an anti-adhesive layer laminated on the other side of the base film. The anti-adhesive layer contains a filler and a resin binder. The average thickness of the flat portion of the anti-adhesive layer is 50 nm or more and 150 nm or less, and the average particle diameter of the filler is 70 nm or more and 200 nm or less.

In the optical sheet, the release layer contains a filler and a resin binder, and the average thickness of the flat portion of the release layer is 50 nm or more and 150 nm or less, and the average particle diameter of the filler is 70 nm or more and 200 nm or less. The rice-sized filler can form a fine convex portion densely and uniformly on the outer surface of the anti-adhesive layer, and as a result, it can be abutted on the back side by a dense and uniform convex portion. Light guide plate, bracts, etc. Therefore, the optical sheet has high anti-sticking property and can prevent interference fringes due to adhesion.

Further, in the optical sheet, since the average particle diameter of the filler exhibiting the anti-sticking property is 70 nm or more and 200 nm or less, the average particle diameter of the filler is smaller than the wavelength of visible light, and even if the filler is blended, the light transmittance can be remarkably lowered. Sexual hindrance, so it has a higher total light transmittance.

Further, in the optical sheet, since the average thickness of the flat portion of the release layer is 50 nm or more and 150 nm or less, the average thickness of the flat portion of the release layer is smaller than the wavelength of visible light, thereby reducing the two interfaces of the release layer. The interference phenomenon of the transmitted light generated by the refraction can effectively suppress the occurrence of moiré or the like.

Further, in the optical sheet, the average thickness of the flat portion of the release layer is remarkably smaller than the previous average thickness, thereby facilitating the thinning of the currently required liquid crystal display device. Further, in the optical sheet, in order to form a fine convex portion on the outer surface and to contain a filler in the release layer, the resin beads in the prior optical sheet are not contained, so that the base using the extrusion molding method can be implemented. In the production line of the forming step of the material film, the anti-adhesive layer is laminated, and as a result, other steps such as coating before the base film such as an optical sheet can be omitted, and the manufacturing workability can be remarkably improved and the manufacturing cost can be reduced. .

The average particle size of the filler may be greater than the average thickness of the flat portion of the release layer. By making the average particle diameter of the filler larger than the average thickness of the flat portion of the release layer as described above, the fine convex portion can be remarkably formed on the outer surface of the release layer, whereby the anti-sticking property can be further improved.

The filler contains a small-diameter filler having a main component and a large-diameter filler having an average particle diameter larger than a subcomponent of the small-diameter filler, and the small-diameter filler may have an average particle diameter of 50 nm or more and 150 nm or less. As described above, the small-diameter filler containing the main component and the large-diameter filler of the subcomponent in the filler can form fine convex portions on substantially the entire surface of the outer surface of the anti-adhesive layer by the small-diameter filler of the main component. Further, a large convex portion is formed in a scattered manner by the large-diameter filler of the subcomponent, and as a result, the anti-sticking property is remarkably improved.

The content of the filler in the anti-adhesion layer is preferably 20% by mass or more and 50% by mass or less. By setting the content of the filler of the release layer in the above range as described above, the uniformity and density of the fine convex portions formed on the outer surface of the release layer are suitable for anti-adhesion, and the anti-sticking property is further improved.

The polymer constituting the above binder may have a three-dimensional crosslinked structure. By having the three-dimensional crosslinked structure of the binder polymer as described above, the fixing property and the protective property of the filler in the anti-adhesion layer are improved, thereby contributing to the uniform dispersibility of the filler and the improvement of the anti-sticking property. Further, since the binder polymer has a three-dimensional crosslinked structure, the smoothness and abrasion resistance of the anti-adhesive layer are improved.

The above binder may be formed of a polymer composition containing an acrylic polyol and a curing agent. By using a polymer composition containing an acrylic polyol and a curing agent as a material for forming a binder as described above, it is possible to easily and surely carry out a lamination operation of laminating an anti-adhesive layer on a base film, and the adhesive has The transparency is high, and further, the three-dimensional crosslinked structure can be easily formed by the selection of a hardener.

As the above filler, colloidal cerium oxide is preferred. The colloidal cerium oxide is excellent in light transmittance in the anti-adhesive layer, has good dispersibility in the binder polymer, and contributes to improvement in heat resistance and rigidity of the anti-adhesive layer.

The coefficient of variation of the particle size distribution of the small-diameter filler is preferably 20% or less. By making the coefficient of variation of the small-diameter filler 20% or less as described above, the uniformity and the protrusion height of the fine convex portions formed on the outer surface of the release layer can be made suitable for anti-adhesion, and the anti-adhesive property is further improved.

The anti-adhesive layer may be dispersed and contained in the anti-adhesive layer. By dispersing the antistatic agent in the anti-adhesion layer as described above, the anti-static property of the optical sheet can be imparted, and the anti-stick property of the optical sheet and the light guide plate, the ruthenium sheet and the like which are superposed on the back side thereof can be further improved. .

The above optical layer may contain a light diffusing agent and a binder thereof. The optical sheet is a so-called light-diffusing sheet having a function of diffusing transmitted light by a plurality of light diffusing agents in the optical layer, and has a high anti-stick property and a total light transmittance by the anti-adhesion layer. Uniformity, economy and film properties such as brightness.

Further, the optical layer may have a fine uneven shape having refractive properties. The optical sheet is an optical sheet that follows a mold shape such as a microlens sheet, a cymbal sheet, a lentil lens sheet, or a Fresnel lens sheet, and has a plurality of optical layers for condensing transmitted light and refracting toward the normal side. Various optical functions such as diffusion, such as the anti-adhesive layer, have high adhesion, uniformity of light transmittance, brightness, etc., economy, and film properties.

Therefore, in the backlight unit for the liquid crystal display device in which the light emitted from the light source is dispersed and guided to the surface side, if the optical sheet is provided, the optical sheet has high anti-stick property, total light transmittance, and the like as described above. The uniformity, economy, and film properties of the brightness and the like can significantly improve the utilization efficiency of the light emitted by the light source, and can promote the high brightness, high quality, energy saving, and thinness and light weight required by the society.

Here, the "flat portion of the anti-adhesion layer" means a region where no filler is present in the anti-adhesion layer. The "average particle size" and the "coefficient of variation of the particle size distribution" are the values of the volume basis.

As described above, the optical sheet of the present invention is excellent in anti-sticking property and has a high total light transmittance, and can effectively suppress interference phenomena and uneven brightness, and further has high economy and film properties. Therefore, the backlight unit of the present invention can promote high luminance, uniformity of brightness, cost reduction, and thickness reduction of the liquid crystal display device to be used.

Hereinafter, embodiments of the present invention will be described in detail with reference to the appropriate drawings. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention, FIG. 2 is a schematic bottom view of the optical sheet of FIG. 1, and FIG. 3 is a schematic view showing an optical sheet different from the optical sheet of FIG. FIG. 4 is a schematic cross-sectional view showing an optical sheet different from the optical sheet of FIGS. 1 and 3.

The optical sheet 1 of FIG. 1 is a light-diffusing sheet comprising a base film 2, a release layer 3 laminated on the back surface of the base film 2, and an optical layer 4 laminated on the surface of the base film 2.

The base film 2 must be transparent to light, and thus it is formed of a transparent, especially colorless, transparent synthetic resin. The synthetic resin used in the base film 2 is not particularly limited, and examples thereof include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, and diethyl fluorene fibers. Cellulose polymers such as cellulose and triethylenesulfonyl cellulose, polycarbonate polymers, acrylic polymers such as polymethyl methacrylate, and styrenic polymerization such as polystyrene and acrylonitrile-styrene copolymer. Polyethylene, polypropylene, polyolefin having a cyclic or even norbornene structure, an olefin polymer such as an ethylene-propylene copolymer, a vinyl chloride polymer, a phthalamide polymer such as nylon or an aromatic polyamide. , quinone imine polymer, fluorene polymer, polyether fluorene polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, An ethylene butyral polymer, an aryl ester polymer, a polyoxymethylene polymer, an epoxy polymer or the like. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved flexibility can be more preferable.

As the material for forming the base film 2, the above polymers may be used alone or in combination of two or more. Moreover, in order to improve and modify workability, heat resistance, weather resistance, mechanical properties, dimensional stability, and the like, various additives and the like may be mixed into the material for forming the base film 2. Examples of the additive include a lubricant, a crosslinking agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a filler, a reinforcing fiber, a reinforcing agent, an antistatic agent, a flame retardant, a flame retardant, and a foaming agent. , mold inhibitors, fillers, pigments, plasticizers, anti-deterioration agents, dispersants, etc.

The thickness (average thickness) of the base film 2 is not particularly limited, but is preferably 10 μm or more and 250 μm or less, and more preferably 20 μm or more and 188 μm or less. When the thickness of the base film 2 is less than the above range, when a polymer composition for forming an optical layer (a layer for functioning as an optical sheet) is laminated on the surface of the base film 2, curling is liable to occur. Use problems such as difficulty. On the other hand, if the thickness of the base film 2 exceeds the above range, the brightness of the liquid crystal display device in which the optical sheet 1 is mounted may be lowered, and the thickness of the backlight unit may be increased, which is also inconsistent with the thinning requirement of the liquid crystal display device. .

The release layer 3 includes a plurality of fillers 5 disposed in a layered manner and spaced apart from each other, and a binder 6 that fixes the filler 5 to the back side of the base film 2. A plurality of convex portions 7 are formed in a scattered manner on the back surface of the anti-adhesion layer 3 by the filler 5 protruding from the back surface (outer surface) of the adhesive 6. Therefore, when the optical sheet 1 and the light guide plate are laminated, the convex portion 7 on the back surface is in contact with the surface of the light guide plate or the like, and the entire back surface of the optical sheet 1 is not in contact with the light guide plate or the like. Thereby, adhesion of the optical sheet 1 to the light guide plate or the like can be prevented, and unevenness in brightness on the screen of the liquid crystal display device can be suppressed.

As a specific material of the filler 5, it can be roughly classified into an inorganic filler and an organic filler. As the inorganic filler, for example, an oxide selected from the group consisting of elements of Groups 2 to 6 of the periodic table (for example, cerium, aluminum, zinc, titanium, zirconium, etc.), aluminum hydroxide, cerium sulfide, magnesium citrate can be used. Or a mixture of these. Among them, colloidal cerium oxide having a particle size of a nanometer order and a low light shielding property is preferably obtained. Further, as the organic filler, for example, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamine or the like can be used. Among them, an acrylic resin having high transparency after curing is preferred, and polymethyl methacrylate (PMMA) is more preferred.

The shape of the filler 5 is not particularly limited, and examples thereof include a spherical shape, a spindle shape, a needle shape, a rod shape, a cubic shape, a plate shape, a scaly shape, and a fiber shape. Among them, it is preferable that the convex portion 7 is formed in the prevention. The back surface of the adhesive layer 3 is excellent in formability and exhibits a good ball-like shape.

The lower limit of the average particle diameter of the filler 5 is preferably 70 nm, more preferably 100 nm. On the other hand, the upper limit of the average particle diameter of the filler 5 is preferably 200 nm, more preferably 150 nm. If the average particle diameter of the filler 5 does not reach the above lower limit, the surface energy is increased, so that the filler may be difficult to be dispersed and contained in the binder 6, and the convex portion 7 formed on the back surface of the release layer 3 by the filler 5 becomes It is small, so it may not be able to play the anti-stick function. On the other hand, if the average particle diameter of the filler 5 exceeds the above upper limit, the effect of blocking the penetration of light is enhanced by the influence of the short wavelength, which may cause the total light transmittance of the optical sheet 1 to decrease. Further, as the release layer 3 containing the filler 5 in the above average particle diameter range, it is possible to easily and directly laminate the release layer without forming an easy-adhesion layer which is easily adhered to the back surface of the base film 2. The composition can reduce manufacturing costs, achieve weight reduction, and thin film. Further, the anti-adhesive layer 3 containing the above-described nano-sized filler 5 is excellent in antistatic effect and damage prevention effect in addition to the above-mentioned light transmittance and anti-adhesion property.

The lower limit of the content of the filler 5 in the anti-adhesive layer 3 (the content in terms of solid content in the composition for an anti-adhesive layer) is preferably 20% by mass, and more preferably 30% by mass. On the other hand, the upper limit of the content of the filler 5 is preferably 50% by mass, and more preferably 40% by mass. When the content of the filler 5 is less than the above lower limit, the uniform dispersibility and density of the convex portion 7 formed on the back surface of the release layer 3 may be lowered, and the anti-adhesive effect may not be sufficiently obtained. On the other hand, if the content of the filler 5 exceeds the above upper limit, the anti-adhesive effect cannot be further improved, and the light transmittance may be lowered.

The coefficient of variation of the particle size distribution of the filler 5 is preferably 20% or less, more preferably 10% or less. By setting the coefficient of variation of the filler 5 within the above range, the uniformity of the protrusion height of the fine convex portion 7 formed on the back surface of the release layer 3 is improved, and the anti-sticking property is further improved. Further, by setting the coefficient of variation of the filler 5 within the above range, it is possible to promote the reduction of the small-diameter filler 5 which is disadvantageous for the anti-adhesion, and the reduction of the filler 5 per unit area, and to promote the prevention of the above-mentioned anti-adhesion layer. 3 scattering or the like causes an effect of a decrease in optical function.

The binder 6 can be formed by hardening a polymer composition containing a substrate polymer. The filler 5 is fixed to the back surface of the base film 2 at substantially equal density by the adhesive 6.

From the viewpoint of improving light transmittance, the base polymer used in the adhesive 6 itself is preferably transparent, and more preferably is colorless and transparent. The base polymer is not particularly limited, and examples thereof include polymethacrylic resins such as polymethacrylic acid and polycarboxyphenylmethacrylamide, and polystyrene such as poly(biphenyl)styrene. A polyolefin-based resin represented by a resin or the like, a polyether-based resin typified by poly(2,6-dimethyl-1,4-phenylene ether), and a poly(oxycarbonyloxy-1,4- a polycarbonate resin represented by phenylisopropylene-1,4-phenylene, which is a poly(oxy-2,2,4,4-tetramethyl-1,3-cyclopropene) a polyester-based resin typified by a hydroxy-p-xylylene group, a poly(oxy-1,4-phenylphenylsulfonyl-1,4-phenylene) group, a poly(oxy-1) group , 4-phenylene isopropylidene-1,4-phenyleneoxy-1,4-phenylenesulfonyl-1,4-phenylene, etc., represented by polyfluorene-based resins, A poly(urethane-1,4-phenylenesulfonyl) group represented by poly(iminom-xylyleneimidoimino-4,4'-biphenyl) -1,4-phenylene) is a polysulfide-based resin, an unsaturated polyester resin, an epoxy resin, a melamine resin, a diallyl phthalate resin, a phenol resin, and a poly Yttrium Resins, polyphosphazenes resin, silicone resin or the like organic siloxane alkoxy silane compound consisting of silicon; such polymers may be used alone or as a mixture of two or more thereof.

In particular, the base polymer is preferably a polyol in terms of high workability and the formation of the release layer 3 by a method such as coating. Further, the base polymer is preferably a polyolefin-based copolymer from the viewpoint of the formability of the three-dimensional crosslinked structure described below.

The polymer 10 constituting the binder 6 may have a three-dimensional crosslinked structure as shown in FIG. Since the polymer 10 constituting the binder 6 as described above has a three-dimensional crosslinked structure, the fixing property and the protective property of the filler 5 in the anti-adhesion layer 3 are improved, and the uniform dispersibility of the filler 5 or even the anti-adhesive property is promoted. improve. Further, since the polymer 10 has a three-dimensional crosslinked structure, the hardness, smoothness, abrasion resistance and the like of the anti-adhesive layer 3 are improved.

The method for constituting the three-dimensional crosslinked structure is not particularly limited, and a known method can be employed. Generally, the three-dimensional crosslinked structure can have two or more unsaturations in the polymer composition of the base polymer. Formed based on a polyfunctional monomer. The polyfunctional monomer having two or more unsaturated groups means a monomer having two or more unsaturated functional groups copolymerizable with a monomer or a prepolymer, and a functional group capable of copolymerization. Examples thereof include a vinyl group, a methyl vinyl group, an acrylonitrile group, and a methacrylium group. Further, a monomer having two or more different functional groups capable of copolymerization in one molecule is also included in the polyfunctional monomer in the present invention.

Examples of the polyfunctional monomer having two or more unsaturated groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(methyl). ) acrylate, glycerin (di/tri) (meth) acrylate, trimethylolpropane (di/tri) (meth) acrylate, pentaerythritol (di/tri/tetra) (meth) acrylate, etc. Di-(meth) acrylates, tri-(meth) acrylates, tetra-(meth) acrylates of polyhydric alcohols; aromatic polyfunctional groups such as divinyl benzene and o-divinyl benzene a monomer; an ester of vinyl (meth) acrylate, allyl (meth) acrylate; a diene of butadiene, hexadiene, pentadiene or the like; and dichlorophosphazene as a raw material Further, a polyfunctional monomer having a heterocyclic ring skeleton such as a monomer having a phosphazene skeleton, a triallyl diisocyanate or the like, and a polyfunctional group are introduced.

The amount of the polyfunctional monomer having two or more unsaturated groups is preferably 2% by mass or more and 80% by mass or less in the three-dimensionally crosslinked polymer. When the blending amount is less than the above range, the three-dimensional cross-linking may not be sufficiently performed, and the heat resistance, the solvent resistance, and the like tend to be lowered. On the other hand, when the blending amount is more than the above range, the impact resistance and the like may be lowered, and the properties as a plastic may be deteriorated.

Examples of the polyhydric alcohol include a polyhydric alcohol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, or a polyester polyol obtained under conditions of an excess of a hydroxyl group, and the like, which may be used alone. Alternatively, two or more types may be used in combination.

Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and propylene alcohol. a hydroxyl group-containing unsaturated monomer such as propylene alcohol, cinnamyl alcohol or crotyl alcohol; (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4- a dihydric alcohol or an epoxy compound such as bis(hydroxymethyl)cyclohexane, phenyl glycidyl ether, glycidyl decanoate, Placcel FM-1 (manufactured by Daicel Chemical Industries, Inc.), and, for example, acrylic acid, A hydroxyl group-containing unsaturated monomer obtained by reacting an unsaturated carboxylic acid such as methacrylic acid, maleic acid, fumaric acid, crotonic acid or itaconic acid. One or two or more selected from the group of the hydroxyl group-containing unsaturated monomers may be polymerized to produce the above polyol.

Further, the above polyol may also be selected from the group consisting of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, methacrylic acid. N-propyl ester, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, ethylhexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene , vinyl toluene, 1-methylstyrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, propylene acetate, diallyl adipate, itacon Diallyl acrylate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butoxymethyl acrylamide, diacetone propylene One or two or more kinds of ethylenically unsaturated monomers of decylamine, ethylene, propylene, and isobutylene are produced by polymerizing a hydroxyl group-containing unsaturated monomer selected from the above (a) and (b).

The number average molecular weight of the polyol obtained by polymerizing the monomer component containing a hydroxyl group-containing unsaturated monomer is 1,000 or more and 500,000 or less, preferably 5,000 or more and 100,000 or less. Further, the hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.

As the polyester polyol obtained under the condition of excess hydroxyl group, (c) such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, 1,4-butanediol 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,10-decanediol, 2,2,4-trimethyl-1,3-pentanediol, trishydroxy Methylpropane, hexanetriol, glycerol, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis(hydroxymethyl)cyclohexane, hydroquinone bis(hydroxyethyl ether), isocyanuric acid tris(hydroxyl) Polyhydric alcohols such as ethyl esters and phthalic acid, and (d), for example, maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, sebacic acid, trimellitic acid And polybasic acids such as terephthalic acid, phthalic acid, and isophthalic acid, and the number of hydroxyl groups in the polyols such as propylene glycol, hexanediol, polyethylene glycol, and trimethylolpropane is more than the carboxyl group of the above polybasic acid The reaction was carried out under the conditions of several conditions.

The polyester polyol obtained by the excess of the hydroxyl group has a number average molecular weight of 500 or more and 300,000 or less, preferably 2,000 or more and 100,000 or less. Further, the hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.

The polyol used as the base polymer of the polymer composition preferably has a (meth) group obtained by polymerizing a monomer component containing the polyester polyol and the hydroxyl group-containing unsaturated monomer. An acrylic polyol such as an acrylonitrile unit. The polyester 6 or the acrylic polyol as the binder of the base polymer 6 has high weather resistance, and can suppress yellowing of the anti-adhesion layer 3 and the like. Further, either of the polyester polyol and the acrylic polyol may be used, or both may be used.

In addition, the number of the hydroxyl groups in the polyester polyol and the acrylic polyol is not particularly limited as long as it is contained in two or more molecules per molecule, but the hydroxyl value in the solid component is 10 or less. In addition, the number of crosslinking points decreases, and the physical properties of the film such as solvent resistance, water resistance, heat resistance, and surface hardness tend to decrease.

As the above substrate polymer, a polyhydric alcohol having a cycloalkyl group is preferred. As described above, by introducing a cycloalkyl group into the polyol constituting the binder 6 as the base polymer, the water repellency and water resistance of the binder 6 can be made high, and under high temperature and high humidity conditions, The bending resistance, dimensional stability, and the like of the optical sheet 1 are improved. Further, the basic properties of the coating film such as weather resistance, hardness, thickness feeling, and solvent resistance of the release layer 3 are improved. Further, the affinity between the binder 6 and the filler 5 to which the organic polymer is fixed on the surface, and the uniform dispersibility of the filler 5 are further improved.

The cycloalkyl group is not particularly limited, and examples thereof include a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecyl group, a cyclodecyl group, a cyclodecyl group, and a ring twelve. Alkyl, cyclotridecyl, cyclotetradecyl, cyclopentadecyl, cyclohexadecyl, cycloheptadecyl, cyclooctadecyl, and the like.

The polyol having the above cycloalkyl group is obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group means a polymerizable unsaturated monomer having at least one cycloalkyl group in the molecule. The polymerizable unsaturated monomer is not particularly limited, and examples thereof include cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and t-butylcyclohexyl (meth)acrylate. Cyclododecyl (meth)acrylate or the like.

When a polyol is used as the substrate polymer as described above, the polymer composition may contain a polyisocyanate compound as a curing agent. The polyisocyanate compound is a derivative such as a dimer, a trimer or a tetramer obtained by polymerization of a diisocyanate. Since the polymer composition contains a polyisocyanate hardener, the following three-dimensional crosslinked structure can be easily and surely formed, and the film properties of the release layer 3 are further improved. Further, by blending the polyisocyanate compound, the curing reaction rate of the polymer composition can be increased. Therefore, even if the polymer composition contains a cationic antistatic agent which contributes to the dispersion stability of the fine inorganic filler, The productivity of the curing reaction rate due to the cationic antistatic agent is sufficiently compensated, and the productivity can be further improved.

The polyisocyanate compound is preferably a xylene diisocyanate derivative or a mixture of the xylene diisocyanate derivative and an aliphatic diisocyanate derivative. The xylene diisocyanate derivative has a large effect of improving the reaction rate of the polymer composition, and has less yellowing and deterioration due to heat or ultraviolet rays in the aromatic diisocyanate derivative. The temporal deterioration of the light transmittance of the optical sheet 1 can be reduced. On the other hand, the aliphatic diisocyanate derivative has a smaller effect of improving the reaction rate than the aromatic diisocyanate derivative, but the yellowing and deterioration due to ultraviolet rays and the like are extremely small, and therefore, by using xylene When the isocyanate derivatives are mixed, the effect of improving the reaction rate and the effect of preventing yellowing can be achieved with good balance.

The lower limit of the amount of the polyisocyanate compound (the amount of the solid component converted based on 100 parts of the polymer component in the polymer composition) is preferably 2 parts, more preferably 5 parts. On the other hand, the upper limit of the above compounding amount of the hardener is preferably 20 parts, more preferably 15 parts. By setting the amount of the polyisocyanate compound in the above range as described above, the polymer composition can effectively exhibit the effect of increasing the rate of the curing reaction.

As the inorganic filler 5, those having an organic polymer fixed to the surface thereof can be used. By using the inorganic filler 5 to which the organic polymer is immobilized as described above, the dispersibility in the binder 6 or the affinity with the binder 6 can be improved. The organic polymer to be immobilized is not particularly limited in terms of its molecular weight, shape, composition, presence or absence of a functional group, and any organic polymer can be used. Further, the shape of the organic polymer may be any shape such as a linear chain, a branched chain or a crosslinked structure.

Specific examples of the specific resin constituting the above organic polymer include (meth)acrylic resin, polystyrene, polyvinyl acetate, polyethylene such as polyethylene or polypropylene, polyvinyl chloride, vinylidene chloride, and poly A polyester such as ethylene terephthalate or a copolymer thereof; or a resin obtained by partially modifying a functional group such as an amino group, an epoxy group, a hydroxyl group or a carboxyl group. In particular, an organic polymer containing a (meth)acrylic acid unit such as a (meth)acrylic resin, a (meth)acrylic acid-styrene resin, or a (meth)acrylic acid-polyester resin is used as an essential component. It is preferred that the film forms a function. On the other hand, a resin having compatibility with the base polymer of the above polymer composition is preferred, and therefore, it is preferably one having the same composition as the base polymer contained in the polymer composition.

Further, the fine particles of the inorganic filler 5 may also contain an organic polymer. Thereby, it is possible to impart moderate softness and toughness to the inorganic material which is the core of the filler 5.

The organic polymer may be used in an amount of 0.01 mmol or more and 50 mmol or less per 1 g of the organic polymer-containing filler. By the alkoxy group, the affinity with the matrix resin constituting the binder 6 and the dispersibility in the binder 6 can be improved.

The above alkoxy group means an RO group bonded to a metal element forming a fine particle skeleton. The R is an alkyl group which may be substituted, and the RO groups in the fine particles may be the same or different. Specific examples of R include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, and an n-butyl group. It is preferred to use an alkoxy group of the same metal as the metal constituting the filler 5, and when the filler 5 is a colloidal cerium oxide, it is preferred to use an alkoxy group having ruthenium as a metal.

The content of the organic polymer in the inorganic filler 5 to which the organic polymer is immobilized is not particularly limited, but is preferably 0.5% by mass or more and 50% by mass or less based on the filler 5 .

The above-mentioned organic polymer to be fixed to the filler 5 is a polymer composition containing a hydroxyl group, and the polymer composition constituting the binder 6 may contain a polyfunctional isocyanate compound selected from two or more functional groups reactive with a hydroxyl group. At least one of a melamine compound and an amine resin. Thereby, the matrix resin of the filler 5 and the binder 6 is bonded by a crosslinked structure, thereby improving storage stability, stain resistance, flexibility, weather resistance, storage stability, and the like, thereby making the obtained film glossy. .

Further, the antistatic agent may be mixed in the polymer composition in a finely dispersed state. By forming the binder 6 with the polymer composition in which the antistatic agent is mixed, the optical sheet 1 can exhibit an antistatic effect, thereby preventing adsorption of dust or being difficult to overlap with the ruthenium or the like due to static electricity. The problem. Further, when the antistatic agent is applied to the surface, the surface is sticky or dirty, but the disadvantage can be reduced by kneading the antistatic agent in the polymer composition as described above. The antistatic agent is not particularly limited, and examples thereof include an anionic antistatic agent such as an alkyl sulfate or an alkyl phosphate; a cationic antistatic agent such as a quaternary ammonium salt or an imidazoline compound, and a polyethylene glycol system. Non-ionic antistatic agent such as polyoxyethylene sorbitan monostearate or ethanol decylamine, polymer antistatic agent such as polyacrylic acid, and conductive metal powder, metal oxide powder, carbon Nano tube and so on. Among them, a cationic antistatic agent having a large antistatic effect is preferable, and an antistatic effect can be exhibited by adding a small amount of the cationic antistatic agent.

Further, as the polymer composition for forming the binder 6, in addition to the base polymer, the filler 5, the hardener, and the antistatic agent, for example, a plasticizer, a dispersant, and various leveling agents may be appropriately blended. Agent, UV absorber, antioxidant, viscous modifier, lubricant, light stabilizer, etc.

The lower limit of the average thickness T of the flat portion of the release layer 3 (the average thickness in the region without the filler 5) is preferably 50 nm, more preferably 70 nm. On the other hand, the upper limit of the average thickness T of the flat portion of the release layer 3 is preferably 150 nm, more preferably 120 nm. If the average thickness T of the release layer 3 is less than the above lower limit, it may be difficult to fix the filler 5 to the back surface of the base film 2. On the other hand, if the average thickness T of the release layer 3 exceeds the above upper limit, the convex portion 7 formed on the back surface of the adhesion preventing layer 3 by the filler 5 becomes small, and as a result, the anti-adhesive function of the optical sheet 1 may be weakened. . Further, if the average thickness T of the anti-adhesive layer 3 exceeds the above upper limit, interference due to transmitted light may occur due to refraction at the two interfaces of the anti-adhesion layer 3, so that embossing or the like may occur.

The arithmetic mean roughness (Ra) of the back surface of the release layer 3 is preferably 0.05 μm or more and 0.15 μm or less, more preferably 0.08 μm or more and 0.12 μm or less. The maximum height (Ry) of the back surface of the release layer 3 is preferably 0.4 μm or more and 0.9 μm or less, more preferably 0.6 μm or more and 0.7 μm or less. The ten-point average roughness (Rz) of the back surface of the release layer 3 is preferably 0.3 μm or more and 0.8 μm or less, more preferably 0.5 μm or more and 0.6 μm or less. If the arithmetic mean roughness (Ra), the maximum height (Ry), and the ten-point average roughness (Rz) of the back surface of the release layer 3 are smaller than the above range, the fine convex portion of the back surface of the release layer 3 may be reduced, The anti-sticking property is lowered. On the other hand, if the arithmetic mean roughness (Ra) of the back surface of the release layer 3 exceeds the above range, glare may occur on the screen of the liquid crystal display device, resulting in deterioration in quality.

The optical layer 4 includes a plurality of light diffusing agents 8 that are substantially uniformly disposed on the surface of the base film 2, and a binder 9 of the plurality of light diffusing agents 8. The plurality of light diffusing agents 8 are covered by the binder 9. The light transmitted from the back side of the optical layer 4 to the front side can be uniformly diffused by the plurality of light diffusing agents 8 contained in the optical layer 4 as described above. Further, fine irregularities are formed substantially uniformly on the surface of the optical layer 4 by the plurality of light diffusing agents 8. The light can be more diffused by the refraction of the fine meniscus lens formed on the surface of the optical sheet 1 as described above. In addition, the average thickness of the optical layer 4 is not particularly limited, and is, for example, about 1 μm or more and 30 μm or less.

The light diffusing agent 8 is a particle having a property of diffusing light, and is roughly classified into a filler and an organic filler. As the filler, for example, cerium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, cerium sulfide, magnesium citrate, or a mixture thereof can be used. As a material of the organic filler, for example, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamine or the like can be used. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is more preferred.

The shape of the light diffusing agent 8 is not particularly limited, and examples thereof include a spherical shape, a spindle shape, a needle shape, a rod shape, a cubic shape, a plate shape, a scaly shape, and a fibrous shape. Among them, it is preferable to have excellent light diffusibility. Spherical beads.

The lower limit of the average particle diameter of the light diffusing agent 8 is preferably 1 μm, more preferably 2 μm, and most preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the light diffusing agent 8 is preferably 50 μm, more preferably 20 μm, and most preferably 15 μm. When the average particle diameter of the light diffusing agent 8 is less than the above range, the unevenness of the surface of the optical layer 4 formed by the light diffusing agent 8 becomes small, and the light diffusibility necessary as a light diffusing sheet may not be satisfied. On the other hand, when the average particle diameter of the light diffusing agent 8 exceeds the above range, the thickness of the optical sheet 1 increases, and it is difficult to uniformly spread.

The lower limit of the amount of the light diffusing agent 8 (the amount of the solid content conversion of 100 parts of the base polymer in the polymer composition as the material for forming the binder 9) is preferably 10 parts, more preferably The amount of the compounding amount is preferably 500 parts, more preferably 300 parts, and most preferably 200 parts. The reason for this is that when the amount of the light diffusing agent 8 is less than the above range, the light diffusibility is insufficient. On the other hand, if the blending amount of the light diffusing agent 8 exceeds the above range, the effect of fixing the diffusing agent 8 is obtained. Will fall. Further, in the case of a so-called upper light-diffusing sheet disposed on the surface of the cymbal sheet, it is necessary to have a high light diffusibility. Therefore, the amount of the light diffusing agent 8 is preferably 10 parts or more and 40 parts or less, more preferably It is 10 or more and 30 or less.

The binder 9 is formed by crosslinking and curing a polymer composition containing a base polymer. The light diffusing agent 8 is disposed and fixed to the surface of the base film 2 at substantially equal density by the binder 9. The polymer composition for forming the binder 9 is the same as the polymer composition of the binder 6 for forming the above-mentioned release layer 3.

The polymer composition forming the binder 9 may contain a minute inorganic filler. The heat resistance of the optical layer 4 and the optical sheet 1 is improved by including the fine inorganic filler in the binder 9. The inorganic substance constituting the fine inorganic filler is not particularly limited, and is preferably an inorganic oxide. The inorganic oxide is defined as a metal element that forms a three-dimensional network structure of a plurality of oxygen-containing metal compounds mainly via bonding with oxygen atoms. The metal element constituting the inorganic oxide is preferably, for example, an element selected from Groups 2 to 6 of the periodic table, and more preferably an element selected from Groups 3 to 5 of the periodic table. More preferably, it is an element selected from the group consisting of Si, Al, Ti, and Zr. In terms of the effect of improving heat resistance and uniform dispersibility, colloidal cerium oxide having a metal element of Si is preferable as a fine inorganic filler. Further, the shape of the fine inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scaly shape, or a crushed shape, and is not particularly limited.

The lower limit of the average particle diameter of the fine inorganic filler is preferably 5 nm, more preferably 10 nm. On the other hand, the upper limit of the average particle diameter of the fine inorganic filler is preferably 50 nm, more preferably 25 nm. The reason for this is that if the average particle diameter of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler becomes high, and aggregation or the like is liable to occur. On the other hand, if the average particle diameter exceeds the above range, the short wavelength is obtained. The influence is white turbid, so that the transparency of the optical sheet 1 cannot be completely maintained.

The lower limit of the amount of the fine inorganic filler to be added to 100 parts of the base polymer (the amount of the inorganic component only) is preferably 5 parts, more preferably 50 parts, in terms of solid content. On the other hand, the upper limit of the above-mentioned compounding amount of the fine inorganic filler is preferably 500 parts, more preferably 200 parts, and most preferably 100 parts. The reason for this is that if the amount of the fine inorganic filler is less than the above range, the heat resistance of the optical sheet 1 may not be sufficiently exhibited. On the other hand, if the amount exceeds the above range, it is difficult to blend into the polymer composition. It is possible to lower the light transmittance of the optical layer 4.

As the fine inorganic filler, as in the case of the above-described filler 5, those having an organic polymer fixed on the surface thereof can be used. By using the fine inorganic filler to which the organic polymer is fixed as described above, the dispersibility in the binder 9 and the affinity with the binder 9 can be improved.

The method for producing the optical sheet 1 is not particularly limited as long as it can produce the above-described structure, but it is preferable to use a production method having the following steps: (a) a substrate film forming step by using a T-die Forming a base film extrudate composed of a thermoplastic resin by extrusion molding, and (b) laminating step, laminating a composition for an anti-adhesive layer on one side of the base film extrudate; (c) stretching a step of stretching the substrate film extrudate and the anti-adhesive layer layer of the composition layer; (d) forming the optical layer 4 by mixing the polymer composition of the binder 9 with a light diffusing agent The optical layer composition of 8 is laminated on the surface of the base film 2, and is then cured to form the optical layer 4. Further, the base film forming step and the laminating step described above may be simultaneously performed by a co-extrusion molding method using a T-die. By using the above-described extrusion molding method, one of the substrate film extrudates is applied before the stretching step of stretching the substrate film extrudate and the anti-adhesive layer composition layer. The step of laminating the composition for the anti-adhesive layer is carried out, so that the laminating step and the substrate film forming step and the stretching step can be carried out on the same production line (that is, as an in-line lamination step), and as a result, it can be suppressed. An optical sheet is manufactured by manufacturing cost, improving productivity, and work efficiency.

In the optical sheet 1, the light diffusing function (directional diffusion) is exhibited by reflection or refraction at the interface of the light diffusing agent 8 contained in the optical layer 4 and refraction formed on the fine unevenness on the surface of the optical layer 4. Features). Further, the anti-adhesive layer 3 of the optical sheet 1 contains a filler 5 and a resin-made adhesive 6, and the average thickness of the flat portion of the anti-adhesive layer 3 is 50 nm or more and 150 nm or less, and the average particle diameter of the filler 5 is 70 nm or more. Since it is 200 nm or less, the fine convex portion 7 is formed more frequently and uniformly on the outer surface of the release layer 3 by the nano-sized filler 5, and as a result, the convex portion 7 which is densely dispersed can be abutted in a scattered manner. The light guide plate, the cymbal sheet, and the like are superposed on the back side. Therefore, the optical sheet 1 has a high anti-stick property and may prevent interference fringes due to adhesion.

Further, in the optical sheet 1, since the average particle diameter of the filler 5 exhibiting the anti-sticking property is 70 nm or more and 200 nm or less, the average particle diameter of the filler 5 is smaller than the wavelength of visible light, and even if the filler 5 is blended, the filler 5 can be remarkably lowered. The effect of light transmission, thus having a higher total light transmittance.

Further, in the optical sheet 1, since the average thickness of the flat portion of the release layer 3 is 50 nm or more and 150 nm or less, the average thickness of the flat portion of the release layer 3 is smaller than the wavelength of visible light, so that the release layer 3 can be lowered. The interference phenomenon of transmitted light generated by the refraction at the two interfaces can effectively suppress the occurrence of moiré or the like.

Further, the average thickness of the flat portion of the release layer 3 of the optical sheet 1 is extremely small as compared with the previous average thickness, and the thickness of the liquid crystal display device which is currently required can be promoted. Further, in the optical sheet 1, in order to form the convex portion 7 on the outer surface, the filler 5 is contained in the release layer 3, but the resin beads of the previous optical sheet are not contained, so that extrusion molding can be carried out. In the step of forming the base film 2, the anti-adhesive layer 3 is laminated in the line. As a result, other steps such as coating before the base film such as an optical sheet can be omitted, and the manufacturing workability and the promotion can be remarkably improved. Manufacturing costs have fallen.

The optical sheet 11 of FIG. 3 includes a base film 2, a release layer 12 laminated on the back surface of the base film 2, and an optical layer 4 laminated on the surface of the base film 2. The type, content, shape, and the like of the base film 2, the optical layer 4, and the filler 5, and the adhesive 6 and the manufacturing method are the same as those of the optical sheet 1 of Fig. 1, and the same reference numerals are attached thereto, and the description thereof is omitted.

Similarly to the optical sheet 1 of FIG. 1 , the anti-adhesive layer 12 has a plurality of fillers 5 arranged in a layered manner and spaced apart from each other, and the binder 6 is fixed to the back surface side of the base film 2 . The filler 5 contains a small-diameter filler 5a having a main component and a large-diameter filler 5b having an average particle diameter larger than that of the minor component of the small-diameter filler 5a.

The optical sheet 11 contains a small-diameter filler 5a having a main component and a large-diameter filler 5b as a filler as a filler 5, whereby the small-diameter filler 5a of the main component is used to form a relatively denser surface on the back surface (outer surface) of the release layer 12. The fine convex portion 7a which is dispersed is formed by the large-diameter filler 5b of the subcomponent, and the relatively large convex portion 7b is formed in a scattered manner, so that the sticking resistance is remarkably improved.

The lower limit of the average particle diameter of the small-diameter filler 5a is preferably 50 nm, more preferably 80 nm. On the other hand, the upper limit of the average particle diameter of the small-diameter filler 5a is preferably 150 nm, more preferably 120 nm. If the average particle diameter of the small-diameter filler 5a does not reach the above lower limit, the surface energy may increase, so that it is difficult to disperse the convex portion contained in the adhesive 6 and formed on the back surface of the release layer 3 by the small-diameter filler 5a. 7a will become smaller and will not play the anti-stick function. On the other hand, if the average particle diameter of the small-diameter filler 5a exceeds the above upper limit, the effect of transmitting the masking light due to the influence of the short wavelength may be increased, resulting in a decrease in the total light transmittance of the optical sheet 11.

The lower limit of the average particle diameter of the large-diameter filler 5b is preferably 200 nm, more preferably 300 nm. On the other hand, the upper limit of the average particle diameter of the large-diameter filler 5b is preferably 1.2 μm, more preferably 1 μm. When the average particle diameter of the large-diameter filler 5b is less than the above lower limit, the convex portion 7b which is formed in a scattered manner on the back surface of the release layer 12 is reduced, and the effect of improving the anti-sticking property cannot be achieved. On the other hand, when the average particle diameter of the large-diameter filler 5b exceeds the above upper limit, the fixing property of the large-diameter filler 5b in the anti-adhesion layer 12 is lowered, which is further required to be thinned by the anti-adhesion layer 12.

The blend of the large-diameter filler 5b with respect to the total filler 5 is preferably 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less. When the mixing ratio of the large-diameter filler 5b is less than the above range, the density of the large convex portion 7b formed on the back surface of the release layer 12 in a scattered manner as described above is lowered, and the effect of improving the above-described release property cannot be achieved. On the other hand, when the blending ratio of the large-diameter filler 5b exceeds the above range, the effect of improving the anti-sticking property cannot be achieved, and conversely, the light-transmitting linearity of the optical sheet 11 may be lowered due to the blending of the large-diameter filler 5b.

The optical sheet 20 of Fig. 4 is a so-called microlens sheet having a high optical function such as condensing, refraction toward the normal side, and diffusion. The optical sheet 20 has a base film 2, an optical layer 21 laminated on the surface of the base film 2, and an anti-adhesion layer 3 laminated on the back surface of the base film 2. The base film 2 and the release layer 3 are the same as those of the optical sheet 1 of Fig. 1 described above, and the same reference numerals are attached thereto, and the description thereof is omitted.

The optical layer 21 includes a sheet portion 22 laminated on the surface of the base film 2 and a microlens array 23 formed on the surface of the sheet portion 22. Further, the sheet portion 22 may not be present in the optical layer 21, and the optical layer 21 may be constituted only by the microlens array 23. In short, the microlens array 23 can also be formed directly on the surface of the substrate film 2. Further, the optical layer 21 and the base film 2 may be integrally molded.

The optical layer 21 must transmit light, and thus it is formed of a transparent, especially colorless, transparent synthetic resin. Examples of the synthetic resin used in the optical layer 21 include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, and cellulose acetate. Weather-resistant vinyl chloride, active energy ray-curable resin, and the like. Among them, a radiation curable resin such as an ultraviolet curable resin or an electron beam curable resin excellent in moldability of the microlens array 23 or polyethylene terephthalate having excellent transparency and strength is particularly preferable. Further, in the optical layer 21, in addition to the above synthetic resin, for example, a filler, a plasticizer, a stabilizer, an anti-deterioration agent, a dispersant, or the like may be blended.

The microlens array 23 is composed of a plurality of microlenses 24. The microlens 24 is formed in a hemispherical shape (including an approximately hemispherical shape) and is protruded from the surface side of the base film 2. Further, the microlens 24 is not limited to the above-described hemispherical convex lens, and may be a microlens of a hemispherical concave lens. The microlens of the hemispherical concave lens also has an excellent optical function as the above-described microlens 24.

The microlens 24 is densely and geometrically disposed on the surface of the substrate film 2. Specifically, the microlenses 24 are disposed on the surface of the base film 2 in an equilateral triangle lattice pattern. Therefore, the distance between the microlenses 24 (P) and the distance between the lenses (S) are all fixed. The arrangement pattern can be arranged with the microlenses 24 in the most dense arrangement. Furthermore, the arrangement pattern of the microlenses 24 is not limited to the above-described equilateral triangular lattice pattern which can be densely filled, and may be, for example, a square lattice pattern or a random pattern. By the random pattern, the generation of the moiré can be reduced when the optical sheet 20 is overlapped with other optical members.

The lower limit of the diameter (D) of the microlens 24 is preferably 10 μm, more preferably 100 μm, and most preferably 200 μm. On the other hand, the upper limit of the diameter (D) of the microlens 24 is preferably 1000 μm, more preferably 700 μm. If the diameter (D) of the microlens 24 is less than 10 μm, the influence of diffraction becomes large, and it is liable to cause a drop in optical performance or color separation, resulting in deterioration in quality. On the other hand, if the diameter (D) of the microlens 24 exceeds 1000 μm, thickness increase or unevenness in brightness tends to occur, resulting in deterioration in quality. In addition, by making the diameter (D) of the microlens 24 100 μm or more, the number of microlenses 24 per unit area is reduced, and the area of the optical sheet 20 as a lenticular sheet is increased, thereby reducing the area. The technical and cost burden of manufacturing.

The lower limit of the surface roughness (Ra) of the microlens 24 is preferably 0.01 μm, more preferably 0.03 μm. On the other hand, the upper limit of the surface roughness (Ra) of the microlens 24 is preferably 0.1 μm, more preferably 0.07 μm. By setting the surface roughness (Ra) of the microlens 24 to the above lower limit or more as described above, the formability of the microlens array 23 of the optical sheet 20 can be made easy, thereby reducing the technical and cost in manufacturing. The burden. On the other hand, by reducing the surface roughness (Ra) of the microlens 24 to the above upper limit, the scattering of light on the surface of the microlens 24 is lowered, and the condensing function of the microlens 24 or the normal line can be improved. The refractive function on the direction side achieves high luminance in the front direction due to the good optical function.

The lower limit of the height ratio (H) of the microlens 24 with respect to the radius of curvature (R) (H/R) is preferably 5/8, more preferably 3/4. On the other hand, the upper limit of the height ratio (H/R) is preferably 1. By setting the height ratio (H/R) of the microlens 24 to the above range as described above, the lens refraction in the microlens 24 is effectively exerted, and the optical function such as the condensing of the optical sheet 20 is remarkably improved. .

The upper limit of the ratio (S/D) of the inter-lens distance (S; P-D) to the diameter (D) of the microlens 24 is preferably 1/2, more preferably 1/5. By setting the inter-lens distance (S) of the microlens 24 to the above upper limit or less as described above, the flat portion which is disadvantageous to the optical function is reduced, and the optical function such as condensing of the optical sheet 20 is remarkably improved.

The lower limit of the filling ratio of the microlens 24 is preferably 40%, more preferably 60%. By setting the filling ratio of the microlens 24 to the above lower limit or more as described above, the area occupied by the microlens 24 on the surface of the optical sheet 20 is increased, and the optical function such as condensing of the optical sheet 20 is remarkably improved.

Furthermore, the numerical ranges of the height ratio (H/R), the spacing ratio (S/D), and the filling ratio are derived based on the luminance analysis simulation of the non-sequential ray tracing using the Monte Carlo method. By.

The lower limit of the refractive index of the material constituting the optical layer 21 is preferably 1.3, more preferably 1.45. On the other hand, the upper limit of the refractive index of the material is preferably 1.8, more preferably 1.6. Within this range, the refractive index of the material constituting the optical layer 21 is preferably 1.5. By setting the refractive index of the material constituting the optical layer 21 to the above range as described above, the lens refraction in the microlens 24 is effectively exhibited, and the optical function such as condensing of the optical sheet 20 is further improved.

The manufacturing method of the optical sheet 20 is not particularly limited as long as it can be manufactured. It is preferable to employ a manufacturing method including the following steps: (a) a substrate film forming step by an extrusion molding method using a T-die. Forming a substrate film extrudate composed of a thermoplastic resin; (b) a laminating step of laminating a composition for an anti-adhesive layer on one side of the substrate film extrudate; (c) a stretching step of the base film The extruded body and the anti-adhesive layer are stretched by a laminate of the composition layer; (d) a step of forming the optical layer 21 on the surface of the base film 2.

As a method of forming the optical layer 21 described above, specifically, there are:

(a) a method of laminating a synthetic resin and a substrate film 2 on a sheet mold having an inverted shape of a surface of the microlens array 23, and peeling the sheet mold to form the optical layer 21;

(b) a method of reheating the sheet-form resin and then pressing it together with the base film 2 and pressing it between the mold having the reverse shape of the surface of the microlens array 23 and the metal plate, and transferring the shape ;

(c) an extrusion sheet forming method in which the resin and the base film 2 in a molten state are passed through a kneading port between the roll mold having the reverse shape of the surface of the microlens array 23 on the circumferential surface and the other roll ;

(d) applying an ultraviolet curable resin to the base film 2, and then extruding it on a sheet mold, a mold or a roll mold having the same reverse shape as described above, thereby transferring the shape to the uncured ultraviolet rays. a method of curing a UV-curable resin by curing ultraviolet rays on a curing resin;

(e) The uncured ultraviolet curable resin is applied to a mold or a roll mold having the same reverse shape as described above, and is pressed by the base film 2 to be flattened, and irradiated with ultraviolet rays to cure the ultraviolet rays. a method of hardening a resin;

(f) a method of forming an uncured (liquid) ultraviolet curable resin or the like from a fine nozzle or releasing it onto the base film 2 to form the microlens 24 and hardening it;

(g) A method of using an electron beam curing resin instead of the ultraviolet curable resin.

Further, the substrate film forming step and the layering step described above may be simultaneously performed by a coextrusion molding method using a T-die. Further, the step of forming the optical layer 21 may be carried out simultaneously with the substrate film forming step and the layering step by a co-extrusion molding method using a T-die. Specifically, the molten synthetic resin is pressed from the T-die to a nip having a circumferential shape opposite to the surface of the microlens array 23 and the other roller, and is hardened. This can simultaneously form the optical sheet 20. By the production method of the extrusion molding method, the substrate film extrudate is subjected to a stretching step of stretching the substrate film extrudate and the anti-adhesive layer composition layer. a lamination step of the composition for laminating the anti-adhesive layer and an optical layer forming step, so that the laminating step and the optical layer forming step can be performed on the same production line as the substrate film forming step and the stretching step (that is, as a lamination step in the production line) The optical sheet can be produced by suppressing the manufacturing cost, improving the productivity, and operating efficiency.

Further, as a manufacturing method of a mold (mold) having an opposite shape to the microlens array 23, for example, a method of forming a speckled three-dimensional pattern on a substrate by using a photoresist material, the three-dimensional pattern can be produced by a method Heating is performed to make it curved, thereby forming a microlens array model, and then a metal layer is laminated on the surface of the microlens array model by electroforming, and the metal layer is peeled off. Further, as the method of fabricating the microlens array model, the method described in the above (f) may be employed.

The optical sheet 20 has an optical function such as high condensing, refracting toward the normal direction side, and diffusion by the microlens array 23, and the optical function can be easily and surely controlled. Therefore, the optical sheet 20 can control, for example, the peak direction in which incident light rays are incident on the wafer of the backlight unit, and the tilt angle which is optimal for the refraction toward the normal direction side. Further, the optical sheet 20 has high uniformity, economy, and film properties such as high anti-adhesive property, total light transmittance, and brightness by the anti-adhesive layer 3.

In addition, the above-mentioned "microlens" refers to a microlens having a partial spherical shape at the interface, such as a hemispherical convex lens or a hemispherical concave lens. The term "diameter (D)" refers to the diameter of the base or opening of the microlens. The "height (H)" refers to the vertical distance from the base surface to the top of the microlens when the microlens is a convex lens. When the microlens is a concave lens, it refers to the open surface of the microlens. The vertical distance to the bottom. The term "distance between lenses" means the shortest distance between one of the adjacent microlenses. The "filling rate" refers to the area ratio of the microlens per unit area in the surface projection shape. The "triangular lattice pattern" refers to a pattern in which the surface is divided into the same shape and the microlenses are arranged at the vertices of the equilateral triangle.

The backlight unit for a liquid crystal display device of the present invention includes a square light guide plate, a light source disposed along a long side edge of the light guide plate, and a light optical sheet such as a light diffusion sheet or a slab laminated on the surface of the light guide plate; The optical sheets 1, 11, and 20 are used as the light diffusion sheet, the ruthenium sheet, or the like. Because the optical sheet has high uniformity, economy, and film properties, such as high anti-stick property, total light transmittance, brightness, etc., the backlight unit can significantly improve the utilization efficiency of light emitted by the light source. It can promote the high brightness, high quality, energy saving and thin weight reduction required by the society.

Furthermore, the optical sheet and the backlight unit of the present invention are not limited to the above embodiment. For example, the optical sheet is not limited to the above-described light-diffusing sheet and lenticular sheet, and can be applied to other optical sheets such as a cymbal sheet, a lenticular lens sheet, and a Fresnel lens sheet. By laminating the release layer on the back surface of the optical sheet such as the enamel sheet, the lentil lens sheet, or the Fresnel lens sheet, the uniformity, economy, and film of the anti-stick property, total light transmittance, and brightness can be improved. Sex.

Further, in addition to the base film, the optical layer, and the anti-adhesive layer, other layers such as an ultraviolet absorber layer, an antistatic agent layer, an overcoat layer, and an easy-adhesion layer may be laminated on the optical sheet.

Further, the polymer composition may contain an ultraviolet absorber. By forming the binder 6 from the polymer composition containing the ultraviolet absorber as described above, the optical sheet can be imparted with an ultraviolet ray-proof function, thereby preventing a small amount of ultraviolet ray from the light source of the backlight unit from being damaged by the ultraviolet ray of the liquid crystal layer. .

The ultraviolet absorber is not particularly limited as long as it is a known compound which can absorb ultraviolet rays and efficiently convert it into heat energy and is stable to light. Among them, a salicylic acid-based ultraviolet absorber or a benzophenone-based ultraviolet absorber which has a high ultraviolet absorption function and is excellent in compatibility with the base polymer and which can be stably present in the base polymer is preferable. And a benzotriazole-based ultraviolet absorber and a cyanoacrylate-based ultraviolet absorber; one or two or more selected from the group consisting of these may be used. Further, as the ultraviolet absorber, a polymer having an ultraviolet absorbing group in a molecular chain (for example, "Yudaburu UV" series manufactured by Nippon Shokubai Co., Ltd.) can be preferably used. By using a polymer having an ultraviolet absorbing group in the molecular chain, the compatibility with the main polymer of the binder 6 is high, and deterioration of the ultraviolet absorbing function due to bleeding of the ultraviolet absorbing agent or the like can be prevented. Further, a polymer having an ultraviolet absorbing group in a molecular chain may be used as a base polymer of the binder 6, or a polymer having an ultraviolet absorbing group bonded thereto may be used as a base polymer of the binder 6. Furthermore, the base polymer may further contain an ultraviolet absorber, thereby further improving the ultraviolet absorption function.

The lower limit of the content of the ultraviolet absorber relative to the base polymer of the binder 6 is preferably 0.1% by mass, more preferably 1% by mass, most preferably 3% by mass; and the upper limit of the above content of the ultraviolet absorber is Preferably, it is 10% by mass, more preferably 8% by mass, most preferably 5% by mass. The reason is that if the mass ratio of the ultraviolet absorber to the base polymer is less than the lower limit, the optical sheet cannot effectively exhibit the ultraviolet absorption function; if the mass ratio of the ultraviolet absorber exceeds the upper limit, the substrate is The polymer causes adverse effects and causes a decrease in strength, durability, and the like of the binder 6.

Instead of the above ultraviolet absorber, a UV stabilizer (including a base polymer having an ultraviolet stabilizing group bonded to a molecular chain) may be used, or a UV stabilizer may be used together with the ultraviolet absorber. By the ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen, and the like can be deactivated, thereby improving ultraviolet stability, weather resistance, and the like. As the ultraviolet stabilizer, a hindered amine-based ultraviolet stabilizer having high stability to ultraviolet rays can be suitably used. Further, by using the ultraviolet absorber together with the ultraviolet stabilizer, the deterioration of the ultraviolet rays and the weather resistance can be remarkably improved.

Example

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the description based on the description of the examples.

[Example 1]

Polyethylene terephthalate (hereinafter referred to as "PET") was supplied to a T-die, and extrusion molding was carried out to form a PET film extrudate, and the PET film extrudate was stretched along the film length direction. Times. Next, 100 parts of polyester polyol ("Vylonal MD1250" manufactured by Toyobo Co., Ltd.) and 120 parts of blocked isocyanate ("Elastron H-3" manufactured by Daiichi Kogyo Co., Ltd.), and 50 parts of a composition for an anti-adhesive layer of colloidal cerium oxide having an average particle diameter of 100 nm, which is coated on a PET film extrudate by a roll coating method to form the anti-adhesive layer A laminate of the layer of the composition and the extruded body of the PET film described above. Then, the laminate was stretched three times in the film width direction, whereby a substrate sheet for an optical sheet having an average thickness of 188 μm (the average thickness of the release layer was 100 nm) was obtained. These steps are all carried out continuously on the same production line.

Next, a polymer composition containing 100 parts of an acrylic polyol ("RUB MEDIUM SA" manufactured by Dairi Seiki Co., Ltd.) and 5 parts of a hardener ("Coronate HX" manufactured by Japan Polyurethane Co., Ltd.) in terms of solid content In the above, 100 parts of acrylic resin beads having an average particle diameter of 15 μm ("MBX-15" manufactured by Sekisui Seisakusho Co., Ltd.) were mixed to prepare a composition for an optical layer. The composition for an optical layer is applied to the surface of the substrate sheet for an optical sheet by a roll coating method to a thickness of 15 g/m ² (in terms of solid content), and is cured to form an optical layer. Finally, it was cut into 20 cm squares, whereby the optical sheet of Example 1 was obtained.

[Embodiment 2]

The anti-adhesive layer composition and the PET which are the same as those of the user in Example 1 were respectively supplied to a multilayer mold, and co-extrusion molding was carried out, thereby forming a composition layer for the anti-adhesion layer and a PET film. A coextruded body formed of a body. Then, the co-extruded molded body was simultaneously biaxially stretched at a draw ratio of 3 times in the film length direction and 3 times in the film width direction, whereby a substrate sheet for an optical sheet having an average thickness of 188 μm was obtained (prevention The average thickness of the adhesive layer is 100 nm). These steps are all carried out continuously on the same production line.

Then, in the same manner as in Example 1, the composition for an optical layer was applied onto the surface of the substrate sheet for an optical sheet to form an optical layer, and cut into 20 cm squares, whereby the optical of Example 2 was obtained. sheet.

[Comparative example]

A film made of transparent polyethylene terephthalate having a thickness of 188 μm as a base film was used as a composition for an optical layer, and the same composition for an optical layer as in the above Example 1 was used as a composition for an anti-adhesion layer. In a polymer composition containing 100 parts of acrylic polyol ("RUB MEDIUM SA" manufactured by Dairi Seiki Co., Ltd.) and 5 parts of a hardener ("Coronate HX" manufactured by Japan Polyurethane Co., Ltd.) in terms of solid content A composition comprising 1.5 parts of acrylic resin beads having an average particle diameter of 3 μm ("MBX-3" manufactured by Sekisui Kogyo Co., Ltd.). The composition for the optical layer was laminated on the surface of the base film so as to be 15 g/m ² (in terms of solid content), and the composition for the release layer was laminated to 3 g/m ² (calculated as solid content). On the back surface of the substrate film, an optical sheet of a comparative example was obtained.

[Feature evaluation]

Using the optical sheets of the above Examples 1 and 2 and the optical sheets of the comparative examples, the evaluation of the anti-stick properties of the optical sheets and the measurement of the relative values of the total light transmittance, the haze value and the front luminance were carried out. The results are shown in Table 1 below.

The anti-adhesive property is to be placed under the environmental test conditions (70 ° C × RH 95%) for 24 hours under the condition that the back surface of the optical sheet is overlapped with the acrylic plate in a water-interval state, and an optical sheet and an acrylic sheet are tried. In the case of peeling, the case where peeling was easy was evaluated as ○, and the case where peeling was not easy was evaluated as ×. Further, the relative values of the total light transmittance, the fog value, and the front luminance were measured in accordance with JIS-K7105 using a haze meter manufactured by Suga Test Instrument Co., Ltd.

As shown in Table 1 above, the optical sheets of Examples 1 and 2 were compared with the optical sheets of the comparative examples, and had high anti-stick properties, and had excellent total light transmittance, haze value, and relative brightness of front surface. .

Further, the arithmetic mean roughness (Ra), the maximum height (Ry), and the ten-point average roughness (Rz) of the back surface of the anti-adhesive layer of the optical sheet of Example 1 were measured, and the results were 0.09 μm and 0.63 μm, respectively. 0.52 μm. The pencil hardness of the anti-adhesive layer of the optical sheet is H to 2H. The arithmetic mean roughness (Ra), the maximum height (Ry), and the ten-point average roughness (Rz) of the surface properties are set to 2.5 mm in the cutoff wavelength λc and 12.5 mm in the evaluation length according to JIS B0601-1994. The measurement was carried out using a stylus type surface roughness measuring machine "Surfcom 470A" manufactured by Tokyo Precision Co., Ltd.

Industrial availability

As described above, the optical sheet of the present invention can be used as a constituent element of a backlight unit of a liquid crystal display device, and is particularly suitable for a transmissive liquid crystal display device.

1, 11, 20. . . Optical sheet

2, 55. . . Substrate film

3, 12, 57. . . Anti-adhesion layer

4, 21. . . Optical layer

5. . . filler

5a. . . Small diameter filler

5b. . . Large diameter packing

6, 9, 58, 60. . . Adhesive

7, 7a, 7b. . . Convex

8, 59. . . Light diffusing agent

10. . . polymer

twenty two. . . Sheet portion

twenty three. . . Microlens array

twenty four. . . Microlens

50. . . End-illuminated backlight unit

51. . . Linear light source

52. . . Light guide

53. . . Light diffuser

54. . . Bract

54a. . . Crotch

56. . . Light diffusion layer

61. . . Resin beads

D. . . Diameter of microlens 24

H. . . Height of microlens 24

P. . . Between the microlenses 24

R. . . Curvature radius of microlens 24

S. . . Inter-lens distance

T. . . Average thickness of the flat portion

Fig. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention.

Figure 2 is a schematic bottom view of the optical sheet of Figure 1.

Fig. 3 is a schematic cross-sectional view showing an optical sheet different from the optical sheet of Fig. 1.

Fig. 4 is a schematic cross-sectional view showing an optical sheet different from the optical sheet of Figs. 1 and 3.

Fig. 5(a) is a schematic perspective view showing a conventional end-illuminated backlight unit, and Fig. 5(b) is a schematic cross-sectional view showing a general optical sheet.

1. . . Optical sheet

2. . . Substrate film

3. . . Anti-adhesion layer

4. . . Optical layer

5. . . filler

6. . . Adhesive

7. . . Convex

8. . . Light diffusion layer

9. . . Adhesive

T. . . Average thickness of the flat portion

Claims (11)

An optical sheet comprising a transparent base film, an optical layer laminated on one surface of the base film, and an anti-adhesive layer laminated on the other side of the base film, wherein the anti-adhesive layer contains a filler And a resin-made adhesive, the average thickness of the flat portion of the anti-adhesive layer is 50 nm or more and 150 nm or less, and the average particle diameter of the filler is 70 nm or more and 200 nm or less, and the filler contains a small-diameter filler having a main component, and The large-diameter filler having an average particle diameter larger than the auxiliary component of the small-diameter filler, and the average diameter of the small-diameter filler is 50 nm or more and 150 nm or less. The optical sheet of claim 1, wherein the filler has an average particle diameter larger than an average thickness of the flat portion of the anti-adhesive layer. The optical sheet of claim 1, wherein the content of the filler in the anti-adhesion layer is 20% by mass or more and 50% by mass or less. The optical sheet of claim 1, wherein the polymer constituting the binder has a three-dimensional crosslinked structure. The optical sheet of claim 1, wherein the adhesive is formed from a polymer composition comprising an acrylic polyol and a hardener. The optical sheet of claim 1, wherein the filler is colloidal ceria. For example, the optical sheet of claim 1 of the patent scope, wherein: The coefficient of variation of the particle size distribution of the small-diameter filler is 20% or less. The optical sheet of claim 1, wherein the anti-adhesive layer contains an antistatic agent dispersed therein. The optical sheet of claim 1, wherein the optical layer comprises a light diffusing agent and a binder thereof. The optical sheet of claim 1, wherein the optical layer has a fine concavo-convex shape with refraction. A backlight unit for a liquid crystal display device, which is characterized in that the light emitted from the light source is dispersed and guided to the surface side, and is characterized in that the optical sheet of any one of the above claims 1 to 10 is provided.