WO2012067046A1 - Light dispersion film, polarization plate and image display device - Google Patents

Abstract

A light dispersion film (100), as well as a polarization plate in which the same is applied and an image display device, wherein the light dispersion film (100) comprises a substrate film (101), a light dispersion layer (102) layered on the substrate film (101), and an overcoat layer (105) layered on the light dispersion layer (102), the light dispersion layer (102) containing a first translucent resin (103) and translucent microparticles (104) dispersed in the first translucent resin (103), the overcoat layer (105) containing a second translucent resin, and, when a laser beam with a wavelength of 543.5nm is incident on the light dispersion film (100) from the overcoat layer (105) side at an angle of incidence of 30°, the reflectance (R₃₀) of the light dispersion film (100) in an angle of reflection of 30° being 2%~5%, and the reflectance (R₄₀) of the light dispersion film (100) in an angle of reflection of 40° being no more than 0.0001%.

Description

Light diffusion film, polarizing plate and image display device

The present invention relates to a light diffusion film provided with a light diffusion layer on a base film. The present invention also relates to a polarizing plate and an image display device using the light diffusion film.

In recent years, liquid crystal display devices have been rapidly applied to mobile phones, personal computer monitors, televisions, liquid crystal projectors, and the like. Generally, a liquid crystal display device operates a liquid crystal in a display mode such as a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an IPS (In-Plane Switching) mode, and electrically transmits light passing through the liquid crystal. Control the difference between light and dark on the screen and display characters and images.

Conventionally, in a liquid crystal display device, when the display screen is viewed from an oblique direction, high contrast cannot be obtained, and further, good display characteristics cannot be obtained due to a gradation reversal phenomenon in which the contrast of the image is reversed. The problem, that is, the problem that the viewing angle is narrow has been pointed out.

As a method for solving the above problems, a technique of providing a light diffusion film on the viewing side surface of a liquid crystal display device is conventionally known. For example, Patent Documents 1 and 2 disclose a light diffusing film (light diffusing sheet) having a high-haze light diffusing layer formed by applying a coating solution containing fine particles on a substrate. By disposing such a light diffusing film on the viewing side surface of the liquid crystal display device, the viewing angle can be reduced by reducing the contrast of the image and improving the gradation inversion phenomenon when the display screen of the liquid crystal display device is observed obliquely. It is possible to spread. However, the light diffusing film containing fine particles as described in Patent Documents 1 and 2 has a so-called whitish color in which the entire display surface becomes whitish due to irregular reflection caused by surface unevenness due to the fine particles, and the display becomes cloudy. (White turbidity) is likely to occur.

On the other hand, in Patent Document 3, the surface of the antiglare layer is provided with a fluidity regulator such as colloidal silica on the surface of the antiglare layer provided on the light-transmitting substrate. It is described that the surface irregularity structure is controlled by forming a surface adjustment layer having good followability of the surface, and both glossy black and antiglare properties are achieved. The “glossy blackness” as referred to in Patent Document 3 is related to the above-mentioned whitishness and can be reduced by improving the glossy blackness. There was room.

JP 2007-94369 A JP 2002-107512 A JP 2008-32845 A

An object of the present invention is a light diffusing film provided on a base film with a light diffusing layer in which translucent fine particles are dispersed, and a high front contrast is obtained, and furthermore, occurrence of whitening is effectively prevented. It is to provide a light diffusion film. Another object of the present invention is to provide a polarizing plate and an image display device to which the light diffusion film is applied.

The present invention is a light diffusion film comprising a base film, a light diffusion layer laminated on the base film, and an overcoat layer laminated on the light diffusion layer, wherein the light diffusion layer Contains a first translucent resin and translucent fine particles dispersed in the first translucent resin, the overcoat layer contains a second translucent resin, When a laser beam with a wavelength of 543.5 nm is incident on the light diffusion film from the overcoat layer side at an incident angle of 30 °, the reflectance R ₃₀ of the light diffusion film at a reflection angle of 30 ° is 2% to 5%. Provided is a light diffusion film having a reflectance R ₄₀ of 0.0001% or less at a reflection angle of 40 °.

In the light diffusing film of the present invention, the relative scattered light intensity T ₄₀ when a laser beam having a wavelength of 543.5 nm is incident on the light diffusing film from the base film side in the normal direction of the light diffusing film is 0. It is preferably 0.0008% to 0.001%. The relative scattered light intensity T ₄₀ is 40 ° from the normal of the light diffusion film from the overcoat layer side of the light diffusion film with respect to the intensity of the laser light having a wavelength of 543.5 nm incident on the light diffusion film. This is the ratio of the intensity of laser light emitted in the tilted direction.

The light diffusion film of the present invention preferably has a sum of reflection sharpness measured by using optical combs having a width of 0.5 mm, 1.0 mm and 2.0 mm, respectively, of 200% or more. Further, it is preferable that the sum of the transmission sharpness measured using optical combs having a width of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm, respectively, is 70% to 230%.

In the light diffusion film of the present invention, the center line average roughness Ra of the surface of the overcoat layer is preferably 0.1 μm or less. Further, the light diffusion film of the present invention has a total haze of 40% to 70%, an internal haze of 40% to 70%, and a surface haze of less than 1% due to the surface shape of the overcoat layer. Is preferred.

The absolute value of the difference between the refractive index of the first translucent resin constituting the light diffusion layer and the refractive index of the second translucent resin constituting the overcoat layer is preferably 0.02 or less. The thickness of the overcoat layer is preferably 1 μm to 10 μm. The present invention also provides an antireflection light diffusion film further comprising an antireflection layer laminated on the light diffusion film of the present invention and the overcoat layer of the light diffusion film.

The present invention also comprises a polarizing film and the light diffusing film or antireflective light diffusing film of the present invention, wherein the substrate film is closer to the polarizing film than the overcoat layer. Provided is a polarizing plate on which a light diffusion film or the antireflection light diffusion film is disposed.

Furthermore, the present invention provides an image display device comprising the polarizing plate of the present invention and an image display element. In the image display device, the polarizing plate is disposed on the image display element such that the polarizing film is closer to the image display element than the overcoat layer.

According to the present invention, it is possible to provide a light diffusing film and a light diffusing polarizing plate in which high front contrast is obtained and whitish generation is effectively prevented. A liquid crystal display device to which a light diffusing film or a polarizing plate having such excellent optical properties is applied exhibits high front contrast, and is effectively prevented from whitening due to surface irregular reflection.

It is a schematic sectional drawing which shows a preferable example of the light-diffusion film of this invention. Is a diagram for explaining the reflectance R ₃₀ and reflectance R _40, is a perspective view schematically illustrating a and the reflection direction incident direction of the laser beam from the overcoat layer side. The incident direction of the laser beam when measuring the transmitted scattered light intensity of the laser beam incident from the normal direction on the base film side and transmitted in a direction inclined by 40 ° from the normal direction on the overcoat layer side It is a perspective view which shows typically the transmitted scattered light intensity | strength measurement direction. It is a schematic sectional drawing which shows an example of the polarizing plate of this invention. It is a schematic sectional drawing which shows an example of the image display apparatus of this invention.

<Light diffusion film>
FIG. 1 is a schematic cross-sectional view showing a preferred example of the light diffusion film of the present invention. A light diffusion film 100 shown in FIG. 1 according to the present invention includes a base film 101, a light diffusion layer 102 laminated on the base film 101, and an overcoat layer 105 laminated on the light diffusion layer 102. Is provided. The light diffusion layer 102 is a layer having the first light-transmitting resin 103 as a base material, and the light-transmitting fine particles 104 dispersed in the first light-transmitting resin 103 and the first light-transmitting resin 103. And formed from. The light diffusion layer 102 is typically a layer having an uneven shape on the surface. The overcoat layer 105 is a layer formed of a second light-transmitting resin that is laminated on the light diffusion layer 102 so as to fill the concave portions of the surface unevenness of the light diffusion layer 102. The surface of the overcoat layer 105 is preferably a smooth surface (centerline average roughness Ra is 0.1 μm or less). Hereinafter, the light diffusion film 100 of the present invention will be described in more detail.

[Base film]
The base film 101 only needs to be translucent, and for example, glass and plastic films can be used. The plastic film only needs to have appropriate transparency and mechanical strength. Specific examples include cellulose acetate resins such as TAC (triacetyl cellulose); polyester resins such as acrylic resins, polycarbonate resins, and polyethylene terephthalate; polyolefin resins such as polyethylene and polypropylene. The thickness of the base film 101 is, for example, 10 to 500 μm, preferably 20 to 300 μm.

(Light diffusion layer)
The light diffusion film 100 of the present invention includes a light diffusion layer 102 laminated on a base film 101. The light diffusion layer 102 is a layer having the first translucent resin 103 as a base material, and the first translucent resin 103 and the translucent fine particles dispersed in the first translucent resin 103. 104. The light diffusion film 100 may have another layer (including an adhesive layer) between the base film 101 and the light diffusion layer 102.

(1) First Translucent Resin The first translucent resin 103 is not particularly limited as long as it has translucency. For example, the activity of an ultraviolet curable resin, an electron beam curable resin, etc. A cured product of an energy beam curable resin and a thermosetting resin, a cured product of a thermoplastic resin, a cured product of a metal alkoxide, or the like can be used. Among these, an active energy ray-curable resin is preferable because it has high hardness and can impart high scratch resistance as a light diffusion film provided on the surface of the image display device. When an active energy ray curable resin, a thermosetting resin, or a metal alkoxide is used, the first light-transmitting resin 103 is formed by curing the resin by irradiation or heating with an active energy ray.

The active energy ray-curable resin can contain a polyfunctional (meth) acrylate compound. The polyfunctional (meth) acrylate compound is a compound having at least two (meth) acryloyloxy groups in the molecule.

Specific examples of the polyfunctional (meth) acrylate compound include, for example, ester compounds of polyhydric alcohol and (meth) acrylic acid, urethane (meth) acrylate compounds, polyester (meth) acrylate compounds, epoxy (meth) acrylate compounds, and the like. And a polyfunctional polymerizable compound containing two or more (meth) acryloyl groups.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, propanediol, butanediol, and pentanediol. , Divalent alcohols such as hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, 2,2′-thiodiethanol, 1,4-cyclohexanedimethanol; trimethylolpropane, glycerol, pentaerythritol , Trihydric or higher alcohols such as diglycerol, dipentaerythritol and ditrimethylolpropane.

Specific examples of esterified products of polyhydric alcohol and (meth) acrylic acid include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and neopentyl glycol. Di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, tetramethylol methane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, tetramethylol methane tetra ( (Meth) acrylate, pentaglycerol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerin tri (meth) acrylate, Pentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate.

Examples of the urethane (meth) acrylate compound include urethanization reaction products of an isocyanate having a plurality of isocyanate groups in one molecule and a (meth) acrylic acid derivative having a hydroxyl group. Examples of organic isocyanates having a plurality of isocyanate groups in one molecule include hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, and the like. Organic isocyanate having a group; organic isocyanate having three isocyanate groups in one molecule, such as isocyanurate-modified, adduct-modified, biuret-modified, etc. Examples of the (meth) acrylic acid derivative having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- Examples include hydroxy-3-phenoxypropyl (meth) acrylate and pentaerythritol triacrylate.

Preferred as the polyester (meth) acrylate compound is a polyester (meth) acrylate obtained by reacting a hydroxyl group-containing polyester with (meth) acrylic acid. The hydroxyl group-containing polyester preferably used is a hydroxyl group-containing polyester obtained by an esterification reaction between a polyhydric alcohol and a carboxylic acid or a compound having a plurality of carboxyl groups and / or an anhydride thereof. Examples of the polyhydric alcohol include the same compounds as those described above. Moreover, bisphenol A etc. are mentioned as phenols other than a polyhydric alcohol. Examples of the carboxylic acid include formic acid, acetic acid, butyl carboxylic acid, benzoic acid and the like. The compounds having a plurality of carboxyl groups and / or their anhydrides include maleic acid, phthalic acid, fumaric acid, itaconic acid, adipic acid, terephthalic acid, maleic anhydride, phthalic anhydride, trimellitic acid, cyclohexanedicarboxylic anhydride Thing etc. are mentioned.

Among the polyfunctional (meth) acrylate compounds as described above, hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and diethylene glycol diene from the viewpoint of improving the strength of the cured product (coating film) and availability. Ester compounds such as (meth) acrylate, tripropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate; hexamethylene diisocyanate and 2- Adduct of hydroxyethyl (meth) acrylate; adduct of isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate; tolylene diisocyanate and 2-hydroxyethyl (meth) acrylate Adducts of over preparative; adduct-modified isophorone diisocyanate with 2-adduct of hydroxyethyl (meth) acrylate; adducts of, and biuret-modified isophorone diisocyanate with 2-hydroxyethyl (meth) acrylate. Further, the active energy ray-curable resin preferably contains a urethane (meth) acrylate compound because it exhibits good flexibility (a property showing flexibility) when it is thickened. These polyfunctional (meth) acrylate compounds can be used alone or in combination of two or more.

The active energy ray-curable resin may contain a monofunctional (meth) acrylate compound in addition to the polyfunctional (meth) acrylate compound. Examples of monofunctional (meth) acrylate compounds include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-hydroxyethyl (meth) ) Acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, glycidyl (meth) acrylate, acryloylmorpholine N-vinylpyrrolidone, tetrahydrofurfuryl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, aceto (Meth) acrylate, benzyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, ethyl carbitol (meth) acrylate, phenoxy (meth) acrylate, ethylene oxide modified phenoxy (meta ) Acrylate, propylene oxide (meth) acrylate, nonylphenol (meth) acrylate, ethylene oxide modified (meth) acrylate, propylene oxide modified nonylphenol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, 2- (meth) acryloyloxyethyl-2 -Hydroxypropyl phthalate, dimethylaminoethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, etc. Meth) acrylate can be given. These compounds can be used alone or in combination of two or more.

The active energy ray curable resin may contain a polymerizable oligomer. By including the polymerizable oligomer, the hardness of the light diffusion layer 102 can be adjusted. The polymerizable oligomer is, for example, the polyfunctional (meth) acrylate compound, that is, an ester compound of a polyhydric alcohol and (meth) acrylic acid, a urethane (meth) acrylate compound, a polyester (meth) acrylate compound, or an epoxy (meth). It can be an oligomer such as a dimer, trimer or the like such as an acrylate.

In addition, as other polymerizable oligomer, urethane (meth) acrylate obtained by reaction of polyisocyanate having at least two isocyanate groups in the molecule and polyhydric alcohol having at least one (meth) acryloyloxy group. There may be mentioned oligomers. Examples of the polyisocyanate include hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate polymer, and the like. As the polyhydric alcohol having at least one (meth) acryloyloxy group, Hydroxyl group-containing (meth) acrylic acid ester obtained by esterification reaction of alcohol and (meth) acrylic acid, wherein polyhydric alcohol is, for example, 1,3-butanediol, 1,4-butanediol, 1,6 -Hexanediol, diethylene glycol, triethylene glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, glycerin, pentaerythritol, di Include those which is pentaerythritol and the like. In this polyhydric alcohol having at least one (meth) acryloyloxy group, a part of the alcoholic hydroxyl group of the polyhydric alcohol is esterified with (meth) acrylic acid, and the alcoholic hydroxyl group is present in the molecule. It remains.

Furthermore, as another example of the polymerizable oligomer, a polyester (meta) obtained by reacting a compound having a plurality of carboxyl groups and / or an anhydride thereof with a polyhydric alcohol having at least one (meth) acryloyloxy group. ) Acrylate oligomers. Examples of the compound having a plurality of carboxyl groups and / or anhydrides thereof are the same as those described as the polyester (meth) acrylate of the polyfunctional (meth) acrylate compound. Examples of the polyhydric alcohol having at least one (meth) acryloyloxy group include those described as the urethane (meth) acrylate oligomer.

In addition to the polymerizable oligomers as described above, examples of urethane (meth) acrylate oligomers are obtained by reacting isocyanates with hydroxyl groups of a hydroxyl group-containing polyester, a hydroxyl group-containing polyether or a hydroxyl group-containing (meth) acrylic acid ester. Compounds. The hydroxyl group-containing polyester preferably used is a hydroxyl group-containing polyester obtained by an esterification reaction between a polyhydric alcohol and a carboxylic acid or a compound having a plurality of carboxyl groups and / or an anhydride thereof. Examples of the polyhydric alcohol and the compound having a plurality of carboxyl groups and / or anhydrides thereof are the same as those described as the polyester (meth) acrylate compound of the polyfunctional (meth) acrylate compound. The hydroxyl group-containing polyether preferably used is a hydroxyl group-containing polyether obtained by adding one or more alkylene oxides and / or ε-caprolactone to a polyhydric alcohol. The polyhydric alcohol may be the same as that which can be used for the hydroxyl group-containing polyester. Examples of the hydroxyl group-containing (meth) acrylic acid ester preferably used include the same as those described as the polymerizable oligomer urethane (meth) acrylate oligomer. As the isocyanates, compounds having one or more isocyanate groups in the molecule are preferable, and divalent isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate are particularly preferable.

These polymerizable oligomer compounds can be used alone or in combination of two or more.

Examples of thermosetting resins include phenolic resins, urea melamine resins, epoxy resins, unsaturated polyester resins, and silicone resins, in addition to thermosetting urethane resins prepared from acrylic polyols and isocyanate prepolymers.

Examples of thermoplastic resins include cellulose derivatives such as acetylcellulose, nitrocellulose, acetylbutylcellulose, ethylcellulose, and methylcellulose; vinyl acetate and copolymers thereof, vinyl chloride and copolymers thereof, vinylidene chloride and copolymers thereof, and the like. Acetal resins such as polyvinyl formal and polyvinyl butyral; Acrylic resins and copolymers thereof, Acrylic resins such as methacrylic resins and copolymers; Polystyrene resins; Polyamide resins; Polyester resins; Polycarbonate resins Etc.

As the metal alkoxide, a silicon oxide matrix made of a silicon alkoxide material can be used. Specifically, it is tetramethoxysilane, tetraethoxysilane, or the like, and can be made into an inorganic or organic-inorganic composite matrix (first translucent resin) by hydrolysis or dehydration condensation.

(2) Translucent fine particles The translucent fine particles 104 are not particularly limited as long as they have translucency, and conventionally known ones can be used. For example, organic fine particles made of acrylic resin, melamine resin, polyethylene, polystyrene, organic silicone resin, acrylic-styrene copolymer, calcium carbonate, silica, aluminum oxide, barium carbonate, barium sulfate, titanium oxide, glass, etc. And inorganic fine particles. Organic polymer balloons and glass hollow beads can also be used. These fine particles may be used alone or in combination of two or more. The shape of the translucent fine particles 104 may be any of a spherical shape, a flat shape, a plate shape, a needle shape, an indefinite shape, etc., but a spherical shape or a substantially spherical shape is preferable.

The weight average particle diameter of the translucent fine particles 104 is not particularly limited, but is preferably 0.5 μm to 20 μm, more preferably 1 μm to 15 μm. If the weight average particle size is less than 0.5 μm, the internal haze cannot be sufficiently exhibited, the light diffusibility becomes insufficient, and as a result, it may be difficult to obtain a wide viewing angle. On the other hand, when the weight average particle diameter exceeds 20 μm, the light diffusibility becomes excessively large, and the front contrast may be easily lowered. In addition, the weight average particle diameter of the translucent fine particles 104 is measured using a Coulter multisizer (manufactured by Beckman Coulter, Inc.) using the Coulter principle (pore electrical resistance method).

The content of the translucent fine particles 104 in the light diffusion layer 102 is preferably 3 to 60 parts by weight with respect to 100 parts by weight of the first translucent resin 103, and 5 to 50 parts by weight. It is more preferable that When the content of the light transmissive fine particles 104 is less than 3 parts by weight with respect to 100 parts by weight of the first light transmissive resin 103, the light diffusibility of the light diffusing film 100 becomes insufficient and a wide viewing angle is obtained. It may be difficult to be confused. In addition, when the content of the translucent fine particles 104 exceeds 60 parts by weight with respect to 100 parts by weight of the first translucent resin 103, the light diffusibility becomes excessively large and the front contrast tends to be lowered. There is. Further, the transparency of the light diffusion film 100 may be easily lost.

The absolute value of the difference between the refractive index of the translucent fine particles 104 and the refractive index of the first translucent resin 103 is preferably 0.04 to 0.15. Thereby, moderate internal haze (hence appropriate light diffusibility) can be obtained.

In this specification, “the thickness of the light diffusion layer” refers to the maximum thickness from the surface of the light diffusion layer 102 that contacts the base film 101 to the opposite surface. Therefore, when the light diffusion layer 102 has irregularities in the light diffusion film 100 of the present invention, the thickest portion corresponding to A shown in FIG. 1 is the thickness of the light diffusion layer 102. The thickness A of the light diffusion layer 102 is preferably 1 μm to 30 μm. When the thickness A of the light diffusing layer 102 is less than 1 μm, sufficient scratch resistance required for the light diffusing film 100 disposed on the viewing side surface of the liquid crystal display device may not be provided. Moreover, when thickness A exceeds 30 micrometers, the quantity of the curl which generate | occur | produces in the produced light-diffusion film 100 becomes large, and it exists in the tendency for the handleability in the bonding to another film, a board | substrate, etc. to worsen. In a portion where the thickness from the surface in contact with the base film 101 to the opposite surface of the light diffusion layer 102 is not the maximum (for example, the concave portion of the light diffusion layer 102 having unevenness), the thickness of the light diffusion layer 102 is 1 μm or more. It does not have to be.

The center line average roughness Ra according to JIS B 0601 on the surface of the light diffusion layer 102 (the surface on the side opposite to the base film 101 (in the positive direction side of the Z axis in FIG. 1)) is not particularly limited. In order to prevent the thickness from becoming excessively large, the thickness is preferably 0.5 μm or less, and more preferably 0.2 μm or less. The centerline average roughness Ra in accordance with JIS B 0601 is the reference curve l is extracted from the roughness curve in the direction of the average line, and the x-axis is plotted in the direction of the average line of the extracted portion. When the y-axis is taken in the direction and the roughness curve is expressed by y = f (x), the following formula (1):

Is a value expressed in units of micrometers (μm). Centerline average roughness Ra is a program software that can calculate Ra based on the above formula (1) using a confocal interference microscope (for example, “PLμ2300” manufactured by Optical Solution Co., Ltd.) in accordance with JIS B 0601. Can be calculated.

[Overcoat layer]
The light diffusing film 100 of the present invention has an overcoat layer 105 having a predetermined surface reflection characteristic to be described later, which is laminated on the light diffusing layer 102 so as to fill the concaves and convexes on the surface of the light diffusing layer 102. Lamination of the light diffusion film 100 can be effectively prevented by laminating the overcoat layer 105 that imparts predetermined surface reflection characteristics to the light diffusion film on the light diffusion layer 102.

The overcoat layer 105 is a layer made of the second light-transmitting resin, and has substantially no internal haze in order to avoid that the light diffusion property imparted to the light diffusion layer 102 deviates from the designed range. It is preferable. That is, the light-diffusing property is imparted only to the light-diffusing layer 102 without imparting light-diffusing property to the overcoat layer 105, while only the surface reflection property is imparted to the over-coating layer 105. And surface reflection characteristics are preferably controlled independently of each other. This makes it possible to easily design and manufacture a light diffusion film that can obtain high front contrast and wide viewing angle characteristics and can effectively prevent the occurrence of whitening.

For example, when the resin layer contains a light diffusing agent (fine particles) and when phase separation occurs in the resin layer (for example, a crystalline region and an amorphous region are mixed) The overcoat layer 105 preferably does not contain these internal haze expression factors.

As the second translucent resin constituting the overcoat layer 105, those described above for the first translucent resin 103 can be similarly used. However, the absolute value of the difference between the refractive index of the first translucent resin 103 and the refractive index of the second translucent resin is preferably 0.02 or less, and preferably 0.01 or less. More preferred. If the difference in refractive index is large, light diffusion at the interface between the light diffusion layer 102 and the overcoat layer 105 cannot be ignored, and it becomes difficult to control the light diffusion characteristics and the surface reflection characteristics independently. It may be difficult to obtain diffusion characteristics.

In this specification, “the thickness of the overcoat layer” refers to the minimum thickness from the surface of the overcoat layer 105 (the surface opposite to the light diffusion layer 102) to the surface in contact with the light diffusion layer 102. Therefore, when the light diffusion layer 102 has irregularities in the light diffusion film 100 of the present invention, the thinnest portion corresponding to B shown in FIG. The thickness B of the overcoat layer 105 is not particularly limited as long as the concave and convex portions on the surface of the light diffusion layer 102 can be filled, but is preferably 1 μm to 10 μm, more preferably 2 μm to 9 μm. If the thickness B of the overcoat layer 105 is less than 1 μm, the influence of surface irregular reflection due to the surface unevenness of the light diffusion layer 102 cannot be completely eliminated, and there is a possibility that whitening is likely to occur. Moreover, when thickness B exceeds 10 micrometers, the quantity of the curl which generate | occur | produces in the produced light-diffusion film becomes large, and manufacturing cost also becomes high. In the portion where the thickness from the surface of the overcoat layer 105 (the surface opposite to the light diffusion layer 102) to the surface in contact with the light diffusion layer 102 is not minimum (for example, the portion in contact with the concave portion of the light diffusion layer 102) The thickness of the overcoat layer 105 may not be 10 μm or less.

The center line average roughness Ra according to JIS B 0601 on the surface of the overcoat layer 105 (surface opposite to the light diffusion layer 102) is to obtain predetermined surface reflection characteristics (reflectances R ₃₀ and R ₄₀ ) described later. Preferably, it is 0.1 μm or less. In addition, by adjusting the center line average roughness Ra within this range, reflection of external light can be more effectively prevented when an antireflection layer is provided on the overcoat layer 105.

[Optical characteristics of light diffusion film]
(1) Reflectivity of the surface of the overcoat layer The light diffusion film 100 of the present invention has a reflection angle when laser light having a wavelength of 543.5 nm is incident on the light diffusion film at an incident angle of 30 ° from the overcoat layer 105 side. The reflectance R ₃₀ of the light diffusion film at 30 ° is 2% to 5%, preferably 3% to 5%, and the reflectance R ₄₀ of the light diffusion film at a reflection angle of 40 ° is 0.0001% or less, preferably 0.00008% or less. By setting the reflectance R ₃₀ and the reflectance R ₄₀ within the above ranges, it is possible to effectively prevent whitish while sufficiently suppressing reflection due to surface reflection. When the reflectance R ₃₀ exceeds 5%, reflection due to surface reflection cannot be sufficiently suppressed, and visibility is deteriorated. On the other hand, when the reflectance R ₃₀ is less than 2%, the front contrast is lowered. On the other hand, if the reflectance R ₄₀ exceeds 0.0001%, whitening occurs and visibility decreases.

The reflectance when laser light enters the light diffusion film at an incident angle of 30 ° from the overcoat layer 105 side will be described. FIG. 2 is a diagram for explaining the reflectance R ₃₀ and the reflectance R ₄₀ , and is a perspective view schematically showing the incident direction and the reflecting direction of the laser light from the overcoat layer 105 side. In FIG. 2, a laser beam 205 (He−) from a direction inclined by 30 ° with respect to the normal line 202 of the light diffusion film 200 on the overcoat layer 105 side of the light diffusion film 200 (in the positive direction side of the Z axis in FIG. 2). Ne laser parallel light (wavelength: 543.5 nm) is incident and reflected in a direction inclined by φ ° from the normal line 202 to the opposite side of the incident light 205 in a plane 209 including the incident light 205 and the normal line 202. The intensity of the reflected light 206 is measured. The value obtained by dividing the intensity of the reflected light at φ = 30 ° (reflected light in the regular reflection direction) by the light intensity of the light source is the reflectance R ₃₀ , and the intensity of the reflected light at φ = 40 ° is the light intensity of the light source. divided by the value the reflectance R _40. In order to adjust the reflectances R ₃₀ and R ₄₀ , the ratio of the thickness of the light diffusion layer to the particle diameter of the light-transmitting fine particles, the thickness of the overcoat layer, and the like may be adjusted.

The optical power meter (for example, “3292 03 Optical Power Sensor” manufactured by Yokogawa Electric Corporation and “3292 Optical Power Meter” manufactured by the same company) can be used for the reflectance measurement. In addition, in measuring the reflectance, an optically transparent adhesive is used to eliminate the possibility that reflection from the back of the light diffusing film will affect the measured value and to prevent warping of the light diffusing film. And it is preferable to use as a measurement sample what stuck the light-diffusion film to the black board by the base film side. Thereby, measurement accuracy and measurement reproducibility can be improved.

The reflectances R ₃₀ and R ₄₀ in the state where the overcoat layer 105 is not laminated on the light diffusion layer 102 (that is, the reflectances R ₃₀ and R _{40 on the} surface of the light diffusion layer 102) are 0.05 respectively. % To 2%, preferably 0.0001% to 0.1%.

(2) Relative scattered light intensity The light diffusing film of the present invention has a relative scattered light when a laser beam having a wavelength of 543.5 nm is incident on the light diffusing film from the base film 101 side in the normal direction of the light diffusing film. The strength T ₄₀ is preferably 0.00008% to 0.001%, and more preferably 0.0001% to 0.0006%. The relative scattered light intensity T ₄₀ is to the intensity of the laser beam with a wavelength of 543.5nm entering the light diffusion film, the overcoat layer 105 side of the light diffusion film, the normal from 40 ° inclined direction of the light diffusing film This is the ratio of the intensity of the emitted laser light. When the relative scattered light intensity _{T 40} is less than 0.00008%, light scattering is insufficient, there is a tendency that the viewing angle is narrowed. On the other hand, if it exceeds 0.001%, light scattering is too strong and the front contrast tends to decrease.

The relative scattered light intensity will be described with reference to FIG. FIG. 3 shows a case where laser light is incident from the base film side in the normal direction of the light diffusion film and the transmitted scattered light intensity of the laser light transmitted in the direction inclined by 40 ° from the normal line is measured on the overcoat layer side. It is a perspective view which shows typically the incident direction of a laser beam, and the direction of the transmitted scattered light which measures light intensity. In FIG. 3, laser light (He—Ne) is applied to the light diffusing film 300 from the base film 101 side of the light diffusing film 300 (in the negative direction side of the Z axis in FIG. 3) to the normal 301 direction of the light diffusing film. The parallel light of the laser, the wavelength 543.5 nm) is incident, and the light diffusing film 300 is over in the plane 309 including the tangent 305 of the light diffusing film 300 and the normal 302 on the overcoat layer 105 side of the light diffusing film 300. The intensity of laser light emitted from the coat layer 105 side in a direction 303 inclined by 40 ° from the normal 302 of the light diffusion film 300, that is, the intensity of transmitted scattered light is measured. Value obtained by dividing the light intensity of the intensity of the transmitted scattered light source is a relative scattered light intensity T _40. To adjust the relative scattered light intensity T _40, the particle size of the translucent particles, the ratio of the particle diameter of thickness and the transparent fine particles of the light diffusing layer, the refractive index difference between the light diffusing layer and the transparent fine particles, light The difference in refractive index between the diffusion layer and the overcoat layer, the thickness of the overcoat layer, and the like may be adjusted.

For the measurement of the relative scattered light intensity T ₄₀ , an optical power meter (for example, “3292 03 Optical Power Sensor” manufactured by Yokogawa Electric Co., Ltd. and “3292 Optical Power Meter” manufactured by the same company can be used. In order to prevent the light diffusing film from warping, the scattered light intensity T ₄₀ is measured by using an optically transparent adhesive and bonding the light diffusing film to the glass substrate on the base film side. Is preferably used as a measurement sample, thereby improving measurement accuracy and measurement reproducibility.

The relative scattered light intensity T ₄₀ in the state where the overcoat layer 105 is not laminated on the light diffusion layer 102 is 0.00008% to 0.001% as in the case where the overcoat layer 105 is laminated. It is preferable that

(3) Reflection sharpness The light diffusion film of the present invention is obtained through optical combs having widths of 0.5 mm, 1.0 mm and 2.0 mm, respectively, that is, the sum of reflection sharpness measured using an optical comb ( Hereinafter, it is preferably simply “reflection sharpness”) of 200% or more, and preferably 300% or less. “The sum of reflection sharpness measured using optical combs of 0.5 mm, 1.0 mm and 2.0 mm” is based on JIS K 7105, and the ratio of the width between the dark part and the bright part is 1: 1. The sum of reflection sharpness (image sharpness) measured using three types of optical combs whose widths are 0.5 mm, 1.0 mm, and 2.0 mm. Therefore, the maximum value of “reflection sharpness” here is 300%.

When the reflection definition of the light diffusing film is less than 200%, the scattering of incident light onto the surface of the overcoat layer 105 is too strong. Therefore, when this light diffusing film is applied to a liquid crystal display device, There is a tendency to mess up. The reflection definition of the light diffusion film is more preferably 240% to 300%. In order to adjust the reflection definition, the ratio of the thickness of the light diffusion layer to the particle diameter of the light-transmitting fine particles, the thickness of the overcoat layer, etc. may be adjusted.

Similar to the measurement of reflectance, the measurement of reflection definition can be performed on a measurement sample in which a light diffusion film is bonded to a black plate on the base film 101 side using an optically transparent adhesive. preferable. Thereby, measurement accuracy and measurement reproducibility can be improved. As the measuring device, a image clarity measuring device (for example, “ICM-1DP” manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7105 can be used.

It should be noted that the reflection sharpness in the state where the overcoat layer 105 is not laminated on the light diffusion layer 102 is preferably 10% to 150%.

(4) Transmission sharpness The light diffusion film of the present invention is obtained through optical combs having a width of 0.125 mm, 0.5 mm, 1.0 mm, and 2.0 mm, respectively, that is, transmission sharpness measured using an optical comb. The sum of degrees (hereinafter simply referred to as “transmission definition”) is preferably 70% to 230%. “Sum of transmitted sharpness measured using optical combs of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm” is based on JIS K 7105, and the ratio of the width of the dark part to the bright part Is the sum of transmitted sharpness (image sharpness) measured using four types of optical combs having a width of 1: 1 and a width of 0.125 mm, 0.5 mm, 1.0 mm, and 2.0 mm. Therefore, the maximum value of “transmission definition” here is 400%.

When the transmission definition of the light diffusion film is less than 70%, light scattering is too strong. Therefore, when this light diffusion film is applied to a liquid crystal display device, for example, in white display, light in the front direction of the liquid crystal display device is light. The front contrast tends to decrease due to causes such as excessive scattering by the diffusion layer, and the display quality tends to deteriorate. Also, when the transmitted sharpness exceeds 230%, transmitted light moiré occurs due to interference between the uneven surface structure of the prism film on the backlight side of the liquid crystal display device and the regular matrix structure of the color filter of the liquid crystal cell. Tend to. The transmission definition of the light diffusion film is more preferably 70% to 200%, and still more preferably 90% to 200%. To adjust the transmission clarity, the particle diameter of the light-transmitting fine particles, the ratio of the thickness of the light diffusion layer to the particle diameter of the light-transmitting fine particles, the difference in refractive index between the light diffusion layer and the light-transmitting fine particles, What is necessary is just to adjust thickness etc. FIG.

Similar to the measurement of relative scattered light intensity, the measurement of the transmission clarity is performed on a measurement sample in which a light diffusion film is bonded to a glass substrate on the base film 101 side using an optically transparent adhesive. It is preferable. Thereby, the curvature of the film at the time of a measurement can be prevented, and measurement reproducibility can be improved. As the measuring device, a image clarity measuring device (for example, “ICM-1DP” manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7105 can be used.

It should be noted that the transmission sharpness in the state where the overcoat layer 105 is not laminated on the light diffusion layer 102 is preferably 50% to 200%.

(5) Haze The light diffusion film of the present invention preferably has a total haze of 40% to 70% and an internal haze of 40% to 70%. Moreover, it is preferable that the surface haze resulting from the shape of the surface of the overcoat layer 105 (surface opposite to the light diffusion layer 102) is less than 1%. Here, “total haze” refers to the total light transmittance (Tt) representing the total amount of light transmitted through irradiation of the light diffusing film and the diffused light transmittance (Td) diffused and transmitted by the light diffusing film. ) And the following formula (2):
Total haze (%) = (Td / Tt) × 100 (2)
Is required.

The total light transmittance (Tt) is the sum of the parallel light transmittance (Tp) and the diffuse light transmittance (Td) that are transmitted coaxially with the incident light. The total light transmittance (Tt) and the diffused light transmittance (Td) are values measured in accordance with JIS K 7361.

The “internal haze” of the light diffusing film is a haze other than the haze (surface haze) caused by the surface shape of the overcoat layer 105 among all the hazes.

When the total haze and / or internal haze is less than 40%, the light diffusibility is insufficient and the viewing angle tends to be narrow. When the total haze and / or internal haze exceeds 70%, the light diffusion is too strong and the front contrast tends to decrease. Moreover, when the total haze and / or internal haze exceeds 70%, the transparency of the light diffusion film tends to be impaired. The total haze and internal haze are each preferably 45% to 65%. To adjust the total haze and internal haze, the particle diameter of the light transmissive fine particles, the ratio of the thickness of the light diffusing layer to the particle diameter of the light transmissive fine particles, the refractive index difference between the light diffusing layer and the light transmissive fine particles, the light diffusion The refractive index difference between the layer and the overcoat layer, the thickness of the overcoat layer, and the like may be adjusted.

In addition, when the surface haze due to the surface shape of the overcoat layer 105 exceeds 1%, there is a tendency for whitening to occur due to surface irregular reflection. In order to prevent whitening more effectively, the surface haze is preferably 0.9% or less. In order to adjust the surface haze, the ratio of the thickness of the light diffusion layer and the particle diameter of the light-transmitting fine particles, the thickness of the overcoat layer, etc. may be adjusted.

The total haze, internal haze, and surface haze of the light diffusion film are specifically measured as follows. That is, first, in order to prevent warping of the film, the light diffusion film is bonded to the glass substrate with the optically transparent adhesive so that the overcoat layer 105 becomes the surface. A measurement sample is prepared, and the total haze value of the measurement sample is measured. For the total haze value, the total light transmittance (Tt) and diffuse light transmittance are measured using a haze transmittance meter (for example, a haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136. The rate (Td) is measured and calculated by the above equation (2).

Next, a triacetyl cellulose film having a haze of approximately 0% is bonded to the surface of the overcoat layer 105 using glycerin, and the haze is measured in the same manner as the measurement of the total haze described above. The haze can be regarded as “internal haze” of the light diffusion film because the surface haze due to the surface shape of the overcoat layer 105 is almost canceled by the bonded triacetyl cellulose film. Therefore, the “surface haze” of the light diffusion film is expressed by the following formula (3):
Surface haze (%) = Total haze (%)-Internal haze (%) (3)
More demanded.

The total haze and the internal haze when the overcoat layer 105 is not laminated on the light diffusion layer 102 are both 40% to 70%, as in the case where the overcoat layer 105 is laminated. preferable.

[Production method of light diffusion film]
Next, a method for producing the light diffusion film of the present invention will be described. The light-diffusion film of this invention can be suitably manufactured by the method containing the following process (A) and (B).
As will be described later, the steps (A) and (B) can be performed simultaneously.
(A) A step of forming the light diffusion layer 102 on the base film 101,
(B) A step of forming an overcoat layer 105 on the light diffusion layer 102.

In the step (A), first, the translucent fine particles 104, the first translucent resin 103 or a resin forming the same (for example, active energy ray curable resin, thermosetting resin, thermoplastic resin or metal alkoxide) In addition, a resin liquid containing other components such as a solvent such as an organic solvent, a leveling agent, a dispersant, an antistatic agent, and an antifouling agent is prepared as necessary. Work. When an ultraviolet curable resin is used as the resin that forms the first light-transmitting resin 103, the resin liquid further contains a photopolymerization initiator (radical polymerization initiator).

Examples of the photopolymerization initiator include acetophenone photopolymerization initiator, benzoin photopolymerization initiator, benzophenone photopolymerization initiator, thioxanthone photopolymerization initiator, triazine photopolymerization initiator, and oxadiazole photopolymerization initiator. An initiator or the like is used. Examples of the photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,2′-bis (o-chlorophenyl) -4,4 ′, 5,5′-tetraphenyl-1,2 '-Biimidazole, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, benzyl, 9,10-phenanthrenequinone, camphorquinone, methyl phenylglyoxylate, titanocene compounds and the like can also be used. The amount of the photopolymerization initiator used is usually 0.5 to 20 parts by weight, preferably 1 to 5 parts by weight with respect to 100 parts by weight of the resin contained in the resin liquid.

Examples of organic solvents include aliphatic hydrocarbons such as hexane, cyclohexane, and octane; aromatic hydrocarbons such as toluene and xylene; alcohols such as ethanol, 1-propanol, isopropanol, 1-butanol, and cyclohexanol; methyl ethyl ketone, methyl isobutyl Ketones such as ketone and cyclohexanone; esters such as ethyl acetate, butyl acetate and isobutyl acetate; glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether Ethers; ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, etc. Esterified glycol ethers; Cellsolves such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol; 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, 2- (2- It can be selected from carbitols such as butoxyethoxy) ethanol, etc. in consideration of viscosity and the like. These solvents may be used alone or as a mixture of several kinds as required. After coating, it is necessary to evaporate the organic solvent. Therefore, the boiling point of the organic solvent is desirably in the range of 60 ° C to 160 ° C. The saturated vapor pressure of the organic solvent at 20 ° C. is preferably in the range of 0.1 kPa to 20 kPa.

In addition, in order to make the optical characteristics and surface shape of the light diffusion film 100 uniform, the dispersion of the translucent fine particles 104 in the resin liquid is preferably isotropic dispersion.

Application of the resin liquid onto the base film 101 can be performed by, for example, a gravure coating method, a micro gravure coating method, a rod coating method, a knife coating method, an air knife coating method, a kiss coating method, a die coating method, or the like. .

Various surface treatments may be applied to the surface of the base film 101 (surface on the light diffusion layer 102 side) for the purpose of improving the coating property of the resin liquid or improving the adhesion to the light diffusion layer 102. Examples of the surface treatment include corona discharge treatment, glow discharge treatment, acid surface treatment, alkali surface treatment, and ultraviolet irradiation treatment. Further, another layer such as a primer layer may be formed on the base film 101, and the resin liquid may be applied on the other layer.

Moreover, when using the light-diffusion film 100 of this invention as a protective film of the polarizing film mentioned later, in order to improve the adhesiveness of the base film 101 and a polarizing film, the surface (light It is also preferable to hydrophilize the surface on the side opposite to the diffusion layer 102 by various surface treatments.

Next, the light diffusion layer 102 is formed by fixing the coating layer on the base film 101. Specifically, when an active energy ray curable resin, a thermosetting resin, or a metal alkoxide is used as the resin that forms the first translucent resin 103, drying (removal of the solvent) was performed as necessary. Thereafter, the coating layer is cured by irradiating the coating layer with active energy rays (when using an active energy ray-curable resin) or heating (when using a thermosetting resin or metal alkoxide). . The active energy ray can be appropriately selected from ultraviolet rays, electron beams, near ultraviolet rays, visible rays, near infrared rays, infrared rays, X-rays, etc., depending on the type of resin contained in the resin liquid. An electron beam is preferable, and ultraviolet rays are particularly preferable because of easy handling and high energy.

As the ultraviolet light source, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon arc lamp, or the like can be used. An ArF excimer laser, a KrF excimer laser, an excimer lamp, synchrotron radiation, or the like can also be used. Among these, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a xenon arc lamp, and a metal halide lamp are preferably used.

As the electron beam, 50 to 1000 keV emitted from various electron beam accelerators such as Cockloft Walton type, Bande graph type, resonance transformation type, insulation core transformation type, linear type, dynamitron type, and high frequency type, preferably 100 Mention may be made of electron beams having an energy of ˜300 keV.

On the other hand, when a thermoplastic resin is used as the first translucent resin 103, the coating layer is softened after drying (removing the solvent) as necessary or drying as necessary. Alternatively, the light diffusion layer 102 can be formed by melting and then cooling the coating layer.

For example, in the case of using an ultraviolet curable resin, for example, a step of continuously feeding a base film 101 wound in a roll shape, a resin liquid containing translucent fine particles 104 and an ultraviolet curable resin as a base film Coating on 101, drying as necessary, curing the coating layer to form the light diffusion layer 102, and winding the substrate film 101 on which the light diffusion layer 102 is formed The light diffusing layer 102 can be continuously formed by the method including this. Note that when the overcoat layer 105 is performed subsequent to or simultaneously with the formation of the light diffusion layer 102, a winding step is not necessary.

Specific embodiments are as follows. First, the base film 101 is continuously unwound by the unwinding device. Next, a resin liquid containing the translucent fine particles 104 and the ultraviolet curable resin is applied onto the unwound base film 101 using a coating apparatus and a backup roll facing the coating apparatus. Next, when the resin liquid contains a solvent, it is dried by passing it through a dryer. Next, the coating layer is cured by irradiating the substrate film 101 provided with the coating layer with ultraviolet rays from an ultraviolet irradiation device in a state where the substrate film 101 side is in contact with the backup roll. Since the irradiated surface becomes hot due to ultraviolet irradiation, the backup roll preferably includes a cooling device for adjusting the surface temperature of the backup roll to about room temperature to 80 ° C. Further, one or a plurality of ultraviolet irradiation devices can be used. The base film 101 on which the light diffusion layer 102 obtained as described above is formed is wound up by a winding device. At this time, for the purpose of protecting the light diffusing layer 102, it may be wound up with a protective film made of polyethylene terephthalate, polyethylene, or the like attached to the surface of the light diffusing layer 102 through a pressure-sensitive adhesive layer having removability. Good.

Next, the step (B) will be described. As a method for forming the overcoat layer 105 on the light diffusion layer 102, for example, a second light-transmitting resin or a resin forming the same (for example, active energy ray curing) A resin liquid containing a mold resin, a thermosetting resin, a thermoplastic resin, or a metal alkoxide) is applied onto the light diffusion layer 102 and dried as necessary, and then the application layer is fixed onto the light diffusion layer 102. A method is mentioned. The resin liquid is a solvent such as an organic solvent, a leveling agent, a dispersant, an antistatic agent, an antifouling agent, a photopolymerization initiator (radical polymerization initiator), etc. Of other ingredients.

The coating method of the resin liquid, the fixing method of the coating layer to the light diffusion layer 102 (for example, the curing method in the case of using an ultraviolet curable resin), and the like are the same as in the case of forming the light diffusion layer 102 described above. It's okay. Further, in order to obtain an overcoat layer 105 having higher surface smoothness, the coating layer may be fixed to the light diffusion layer 102 in a state where the mirror surface of the mold is pressed against the surface of the coating layer.

Also, the light diffusion layer 102 and the overcoat layer 105 can be simultaneously laminated on the base film 101. As a method for laminating at the same time, a method using a coating device having two coaters in one pass line, or a coater capable of two-layer simultaneous coating with two slits in one coater. Mention may be made of the methods used. Examples of such a coater include a multilayer slot die coater, a multilayer slide coater, and a multilayer curtain coater. After performing the two-layer coating using the apparatus as described above, the light diffusing film 100 is dried in the same manner as described above, and then the two layers are fixed (cured, etc.). Can be obtained.

<Antireflection light diffusion film>
By further laminating an antireflection layer on the overcoat layer 105 (surface opposite to the light diffusion layer 102) of the light diffusion film of the present invention, an antireflection light diffusion film can be obtained. The antireflection light diffusing film includes the light diffusing film of the present invention and an antireflection layer laminated on the overcoat layer of the light diffusing film. The antireflection layer may be formed directly on the overcoat layer 105, or an antireflection film in which an antireflection layer is formed on a transparent film is separately prepared, and this is applied to the overcoat layer 105 using an adhesive or an adhesive. May be laminated. The antireflection layer is provided to reduce the reflectance as much as possible, and reflection on the display screen can be more effectively prevented by forming the antireflection layer. As the antireflection layer, a low refractive index layer composed of a material lower than the refractive index of the overcoat layer 105; a high refractive index layer and a low refractive index composed of a material lower than the refractive index of the high refractive index layer And a laminated structure with a layer. When the antireflection film is laminated on the overcoat layer 105 using an adhesive or an adhesive, a commercially available antireflection film can be used.

When providing the anti-reflection layer, reflectance R ₃₀ of the anti-reflection light-diffusing film having an antireflection _layer, i.e., the reflectance R ₃₀ of the surface of the antireflection layer is preferably 2% or less.

<Polarizing plate>
Then, with reference to FIG. 4, the polarizing plate 400 of this invention is demonstrated. The polarizing plate 400 of the present invention includes the polarizing film 41 and the light diffusion film 100 described above, and the light diffusion film 100 has the base film 101 side facing the polarizing film 41, that is, the overcoat layer 105. The base film 101 is laminated on the polarizing film 41 so that the base film 101 is closer to the polarizing film 41. The polarizing film 41 has a function of extracting linearly polarized light from incident light, and the type thereof is not particularly limited. As an example of a suitable polarizing film, there can be mentioned a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin. Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol, which is a saponified product of vinyl acetate, partially formalized polyvinyl alcohol, and a saponified product of an ethylene / vinyl acetate copolymer. As the dichroic dye, iodine or a dichroic organic dye is used. Further, a polyene-oriented film of a polyvinyl alcohol dehydrated product or a polyvinyl chloride dehydrochlorinated product can be the polarizing film 41. The thickness of the polarizing film 41 is usually about 5 to 80 μm.

The polarizing plate of the present invention may be obtained by laminating the light diffusion film 100 of the present invention on one side or both sides (usually one side) of the polarizing film 41. As shown in FIG. The transparent protective layer 42 may be laminated on one surface of 41, and the light diffusion film 100 of the present invention may be laminated on the other surface. At this time, the light diffusion film 100 also has a function as a transparent protective layer of the polarizing film 41. When the surface unevenness shape is given to the light diffusion layer 102 of the light diffusion film 100, the light diffusion layer 102 also has a function as an antiglare layer. The transparent protective layer 42 can be formed on the polarizing film 41 by a method of pasting a transparent resin film using an adhesive or the like, a method of applying a transparent resin-containing coating liquid, or the like. Similarly, the light diffusion film 100 of the present invention can be bonded to the polarizing film 41 using an adhesive or the like.

The transparent resin film used as the transparent protective layer 42 is preferably excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like. Examples of such a transparent resin film include triacetyl cellulose, diacetyl cellulose, cellulose acetate Cellulose resins such as cellulose acetate such as pionate; polycarbonate resins; (meth) acrylic resins such as polyacrylate and polymethyl methacrylate; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; chains such as polyethylene and polypropylene Examples thereof include a film formed from a glassy polyolefin resin; a cyclic polyolefin resin; a styrene resin; a polysulfone; a polyether sulfone; a polyvinyl chloride resin. These transparent resin films may be optically isotropic, or have optical anisotropy for the purpose of compensating the viewing angle when incorporated in an image display device. Also good.

<Image display device>
The image display device of the present invention is a combination of the polarizing plate 400 of the present invention and an image display element that displays various information on a screen. FIG. 5 is a schematic diagram showing an example of the image display device 500 according to the present invention. The image display device 500 of FIG. 5 includes a backlight device 52, an image display element 51, and the polarizing plate 400 of the present invention in this order. The kind of the image display device 500 of the present invention using the image display element is not particularly limited, and in addition to a liquid crystal display (LCD) using a liquid crystal panel, a cathode ray tube display or plasma display panel using a cathode ray tube (CRT). Plasma display using (PDP), field emission display (FED) using field emission device, surface conduction electron emission device display (SED) using surface conduction electron emission device, organic EL using organic EL device Examples thereof include a display and a laser display using a laser element. The screen including the polarizing plate 400 of the present invention and the projector television including the image display element may be combined to form the image display apparatus of the present invention.

For example, in the case of manufacturing a liquid crystal panel display by arranging the polarizing plate 400 of the present invention on a liquid crystal cell, the polarizing plate 400 has the overcoat layer 105 on the outside, that is, the polarizing film 41 than the overcoat layer 105. It is arranged on the liquid crystal cell so that is closer to the liquid crystal cell. The same applies to other image display apparatuses. The polarizing plate 400 may be disposed on the viewing side of the image display element 51, may be disposed on the backlight device 52 side, or may be disposed on both. When the polarizing plate 400 is arranged on the viewing side, that is, when the light diffusing film 100 is arranged on the viewing side, the light diffusing film effectively prevents glare, reflection of external light, and whitish, and has a light diffusing function. Thus, the viewing angle and the like are improved while maintaining a sufficient front contrast. On the other hand, when the polarizing plate 400 is disposed on the backlight device side, that is, when the light diffusing film 100 is disposed on the backlight device 52 side, the light diffusing film 100 diffuses the light incident on the liquid crystal cell, and moire or the like. Functions as a diffusion plate (or diffusion sheet) to prevent. In addition, you may provide the light-diffusion film 100 independently in the visual recognition side or the backlight apparatus side separately from the polarizing plate 400. FIG.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The measuring method of various physical properties is as follows.

(A) Light Diffusion Layer and Overcoat Layer Thickness The thickness of the laminate formed from the base film on which the overcoat layer is not laminated and the light diffusion layer is measured by a contact-type film thickness meter [DIGIMICRO MH-15 manufactured by NIKON Corporation ( Main body) and ZC-101 (counter)], and the thickness of the light diffusion layer was measured by subtracting 80 μm of the thickness of the base film from this value. Moreover, the thickness of the light-diffusion film was measured using the same apparatus, and the thickness of the overcoat layer was measured by subtracting the thickness of the laminate formed from the base film and the light-diffusion layer from this value.

(B) Weight average particle diameter and standard deviation of translucent fine particles Measured using a Coulter Multisizer (manufactured by Beckman Coulter, Inc.) based on the Coulter principle (pore electrical resistance method).

(C) Overcoat layer surface reflectivity R ₃₀ and R ₄₀
Using an optically transparent adhesive, measurement was performed using a measurement sample in which the light diffusion film was bonded to a black plate on the base film side. Parallel light of He—Ne laser (wavelength 543.5 nm) is incident from a direction inclined by 30 ° with respect to the normal line of the light diffusion film on the overcoat layer side of the measurement sample, and includes incident light and normal line. In the plane, the intensity of the reflected light reflected in the directions inclined by 30 ° and 40 ° on the opposite side to the incident light from the normal line is measured, and the reflectance is obtained by dividing each reflected light intensity by the light intensity of the light source. It was calculated R ₃₀ and _{R 40.} For measurement, a “3292 03 optical power sensor” manufactured by Yokogawa Electric Corporation and a “3292 optical power meter” manufactured by the same company were used.

In performing this measurement, the light source for irradiating the He—Ne laser was disposed at a position of 430 mm from the black plate. A power meter, which is a light receiver, was placed at a position 280 mm from the emission point of the laser beam on the overcoat layer, and the power meter was moved to the predetermined angle to measure the intensity of the reflected laser beam. In addition, the intensity of the laser light irradiated to the light diffusion film, that is, the intensity of the laser light irradiated from the light source is measured by directly measuring the intensity of the light incident on the power meter from the light source without installing a measurement sample. I asked for it. The intensity was measured by placing a power meter at a position of 710 mm (= 430 mm + 280 mm) from the light source.

(D) Relative scattered light intensity T ₄₀
Using an optically transparent adhesive, measurement was performed using a measurement sample in which the light diffusion film was bonded to the glass substrate on the base film side. From the glass substrate surface side of the measurement sample, parallel light (wavelength 543.5 nm) of a He—Ne laser is incident in the normal direction of the light diffusion film, and the tangent line of the light diffusion film and the overcoat layer side of the light diffusion film are incident. Measure the intensity of transmitted and scattered light transmitted through the light diffusing film in a direction inclined by 40 ° from the normal in a plane including the normal, and calculate the relative scattering as the value obtained by dividing the intensity of the transmitted and scattered light by the light intensity of the light source. and it calculates the light intensity _{T 40.} For measurement, a “3292 03 optical power sensor” manufactured by Yokogawa Electric Corporation and a “3292 optical power meter” manufactured by the same company were used.

In performing this measurement, a light source for irradiating a He—Ne laser was disposed at a position of 430 mm from the glass substrate. A power meter, which is a light receiver, was placed at a position 280 mm from the emission point of the laser light on the overcoat layer, and the power meter was moved to the predetermined angle to measure the intensity of transmitted scattered light. In addition, the intensity of the laser light irradiated to the light diffusion film, that is, the intensity of the laser light irradiated from the light source is measured by directly measuring the intensity of the light incident on the power meter from the light source without installing a measurement sample. I asked for it. The intensity was measured by placing a power meter at a position of 710 mm (= 430 mm + 280 mm) from the light source.

(E) Reflection sharpness Using an image clarity measuring instrument (made by Suga Test Instruments Co., Ltd.) “ICM-1DP” compliant with JIS K 7105, the width ratio between the dark part and the bright part is compliant with JIS K 7105. The sum of reflection sharpness measured at 1: 1 with optical combs having widths of 0.5 mm, 1.0 mm and 2.0 mm was calculated. The measurement was performed using a sample for measurement in which a light diffusion film was bonded to a black plate on the base film side using an optically transparent adhesive.

(F) Transmission sharpness Using an image clarity measuring device (made by Suga Test Instruments Co., Ltd.) “ICM-1DP” compliant with JIS K 7105, the width ratio between the dark part and the bright part is compliant with JIS K 7105. The sum of transmitted sharpness measured with an optical comb with a width of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm at 1: 1 was calculated. The measurement was performed using a measurement sample in which a light diffusion film was bonded to a glass substrate on the base film side using an optically transparent adhesive.

(G) Haze Using an optically transparent adhesive, measurement was performed using a measurement sample in which a light diffusion film was bonded to a glass substrate on the base film side. For the measurement of the total haze value and internal haze, a haze transmittance meter (haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd.) according to JIS K 7136 was used. Based on the result, the surface haze was calculated from the above formula (3).

(H) Centerline average roughness Ra
It measured using the confocal interference microscope ("PL (micro | micron | mu) 2300" by an optical solution company) based on JISB0601.

[Production of light diffusion film]
<Example 1>
(1) Formation of light diffusion layer The following components were mixed to prepare an ultraviolet curable resin liquid for forming a light diffusion layer.

[I] A mixture of 60 parts by weight of pentaerythritol triacrylate and 40 parts by weight of polyfunctional urethanized acrylate (reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate), totaling 100 parts by weight,
[Ii] 40 parts by weight of polystyrene-based particles (weight average particle diameter: 6.9 μm, standard deviation: 1.3 μm),
[Iii] 5 parts by weight of a photopolymerization initiator “Lucirin TPO” (manufactured by BASF, chemical name: 2,4,6-trimethylbenzoyldiphenylphosphine oxide)
[Iv] 80 parts by weight of diluting solvent (propylene glycol monomethyl ether).

The light diffusion layer forming resin solution is applied on a triacetyl cellulose (TAC) film (base film) having a thickness of 80 μm with a die coater so that the thickness after curing is about 10 μm. It formed and obtained the laminated body of a base film and a coating layer. After the obtained laminate is dried in a drying furnace, the base film and the light diffusion layer are obtained by irradiating ultraviolet rays so that the light integrated light amount in UVA is 400 mJ / cm ² and curing the coating layer. A laminate was obtained. The thickness of the light diffusion layer was 10 μm.

(2) Formation of Overcoat Layer The following components were mixed to prepare an ultraviolet curable resin solution for forming an overcoat layer.

[I] A mixture of 60 parts by weight of pentaerythritol triacrylate and 40 parts by weight of polyfunctional urethanized acrylate (reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate), totaling 100 parts by weight,
[Ii] 5 parts by weight of a photopolymerization initiator “Lucirin TPO” (manufactured by BASF, chemical name: 2,4,6-trimethylbenzoyldiphenylphosphine oxide),
[Iii] 100 parts by weight of diluting solvent (ethyl acetate).

The overcoat layer forming resin solution is applied to the surface of the light diffusion layer of the laminate of the base film and the light diffusion layer by a die coater so that the thickness after curing is about 3 to 4 μm. A construction layer was formed. After the obtained laminate is dried in a drying furnace, the base film and the light diffusion layer are obtained by irradiating ultraviolet rays so that the light integrated light amount in UVA is 400 mJ / cm ² and curing the coating layer. A light diffusion film which was a laminate with the overcoat layer was obtained. The thickness of the overcoat layer was 4.6 μm.

<Example 2>
A light diffusing film was produced in the same manner as in Example 1 except that the overcoat layer-forming resin solution was applied so that the thickness after curing was about 7 to 8 μm. The thickness of the overcoat layer was 7.8 μm.

<Example 3>
A light diffusion film was produced in the same manner as in Example 1 except that the blending amount of the polystyrene-based particles in the light diffusion layer forming resin liquid was changed to 20 parts by weight. The thickness of the overcoat layer was 2.5 μm.

<Example 4>
A light diffusion film was produced in the same manner as in Example 2 except that the blending amount of the polystyrene-based particles in the light diffusion layer forming resin liquid was changed to 20 parts by weight. The thickness of the overcoat layer was 8.6 μm.

<Comparative Example 1>
A light diffusion film was produced in the same manner as in Example 1 except that no overcoat layer was provided.

<Comparative Example 2>
A light diffusion film was produced in the same manner as in Example 2 except that the overcoat layer was not provided.

[Evaluation of light diffusion film]
The obtained light diffusion film, the reflectance _{R 30, R 40,} relative scattered light intensity _{T 40,} reflection sharpness, clarity of vision through was measured haze, the center line average roughness Ra. The results are shown in Table 1. Further, according to the following method, the degree of whitening and the front contrast when applied to a liquid crystal display device were evaluated. The results are shown in Table 1.

(1) White turbidity
Using an optically transparent adhesive, the light diffusing film was bonded to a black plate on the base film side, visually observed in a bright room with a fluorescent lamp, and the degree of whitening was evaluated. The evaluation criteria are as follows.
○: The light diffusion film does not look whitish and no whitening is observed.
X: The light diffusion film looks whitish and whiteness is recognized.

(2) Front contrast A liquid crystal display device was produced by the following procedure. First, two prism films in which a plurality of linear prisms with apex angles of 95 ° are arranged in parallel are used on the backlight device of a VA mode SUMSUNG 32-inch liquid crystal television “UN32C6500”. It arrange | positioned between the light-guide plate of a light apparatus, and the backlight side polarizing plate. At this time, one prism film (the prism film closer to the backlight device) is arranged so that the direction of the ridgeline of the linear prism is substantially parallel to the transmission axis of the backlight-side polarizing plate, and the other prism The film (the prism film closer to the backlight side polarizing plate) was arranged so that the direction of the ridgeline of the linear prism was substantially parallel to the transmission axis of the viewing side polarizing plate described later. Also, the viewing side polarizing plate is peeled off, and an iodine type polarizing plate (“TRW842AP7” manufactured by Sumitomo Chemical Co., Ltd.) is bonded to the liquid crystal cell so as to be crossed Nicol with respect to the backlight side polarizing plate. The light diffusing films prepared in Examples 1 to 4 or Comparative Examples 1 to 2 were bonded via an adhesive layer to form a viewing-side polarizing plate to obtain a liquid crystal display device.

The obtained liquid crystal display device was activated in a dark room, and using a luminance meter BM5A type (manufactured by Topcon Co., Ltd.), the front luminance in the black display state and the white display state was measured, and the front contrast was calculated. The front contrast is a ratio of the front luminance in the white display state to the front luminance in the black display state.

As shown in Table 1, according to the light diffusion films (Examples 1 to 4) according to the present invention, it can be seen that high front contrast can be obtained and whitish can be effectively prevented. On the other hand, in the light diffusion films of Comparative Examples 1 and 2 that do not have a predetermined surface reflection characteristic by not having an overcoat layer, it is not possible to prevent whitening, and in the light diffusion film of Comparative Example 1, Front contrast decreased.

DESCRIPTION OF SYMBOLS 100,200,300 ... Light diffusing film, 101 ... Base film, 102 ... Light diffusing layer, 103 ... 1st translucent resin, 104 ... Translucent fine particle, 105 ... Overcoat layer, 202 ... Light diffusing film 205: laser light incident from a direction inclined by 30 ° with respect to the normal of the light diffusion film, 206: reflected light reflected in a direction inclined by φ ° with respect to the normal of the light diffusion film, 209 ... Plane including incident light (laser light) and normal of light diffusion film, 301: base film side normal of light diffusion film, 302: overcoat layer side normal of light diffusion film, 303: light diffusion film A direction inclined by 40 ° from the normal line on the overcoat layer side, 305 ... a tangent line of the light diffusion film, 309 ... a plane including the tangent line of the light diffusion film and the normal line on the overcoat layer side, 400 ... a polarizing plate, 1 ... polarizing film, 42 ... transparent protective layer, 51 ... image display device, 52 ... backlight device.

Claims (11)

1. A base film;
   A light diffusion layer laminated on the base film;
   An overcoat layer laminated on the light diffusion layer;
   A light diffusing film comprising:
   The light diffusion layer contains a first translucent resin and translucent fine particles dispersed in the first translucent resin,
   The overcoat layer contains a second translucent resin,
   When a laser beam with a wavelength of 543.5 nm is incident on the light diffusion film from the overcoat layer side at an incident angle of 30 °, the reflectance R ₃₀ of the light diffusion film at a reflection angle of 30 ° is 2% to 5%. A light diffusion film having a reflectance R ₄₀ of 0.0001% or less at a reflection angle of 40 °.
2. When the laser light having a wavelength of 543.5 nm is incident on the light diffusing film from the base film side in the normal direction of the light diffusing film, the relative scattered light intensity T ₄₀ is 0.00008% to 0.001. %
   The relative scattered light intensity T ₄₀ is 40 ° from the normal of the light diffusion film from the overcoat layer side of the light diffusion film with respect to the intensity of the laser light having a wavelength of 543.5 nm incident on the light diffusion film. The light diffusion film according to claim 1, wherein the light diffusion film has a ratio of the intensity of laser light emitted in an inclined direction.
3. The light diffusion film according to claim 1 or 2, wherein the sum of reflection sharpness measured using optical combs each having a width of 0.5 mm, 1.0 mm, and 2.0 mm is 200% or more.
4. The sum of transmitted sharpness values measured using optical combs having a width of 0.125 mm, 0.5 mm, 1.0 mm, and 2.0 mm, respectively, is 70% to 230%. The light diffusion film as described.
5. The light diffusing film according to any one of claims 1 to 4, wherein a center line average roughness Ra of the surface of the overcoat layer is 0.1 µm or less.
6. A surface haze of less than 1% due to a total haze of 40% to 70%, an internal haze of 40% to 70%, and a surface shape of the overcoat layer, according to any one of claims 1 to 5. The light diffusion film as described.
7. The absolute value of the difference between the refractive index of the first translucent resin and the refractive index of the second translucent resin is 0.02 or less. Light diffusion film.
8. The light diffusion film according to any one of claims 1 to 7, wherein the overcoat layer has a thickness of 1 to 10 µm.
9. An antireflection light diffusing film comprising the light diffusing film according to any one of claims 1 to 8 and an antireflection layer laminated on an overcoat layer of the light diffusing film.
10. A polarizing film;
    A light diffusing film according to any one of claims 1 to 8 or an antireflective light diffusing film according to claim 9,
    The polarizing plate in which the light diffusion film or the antireflection light diffusion film is disposed so that the base film is closer to the polarizing film than the overcoat layer.
11. A polarizing plate according to claim 10 and an image display element,
    The image display device, wherein the polarizing plate is disposed on the image display element such that the polarizing film is closer to the image display element than the overcoat layer.

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