JP2012078736A - Light diffusion film and manufacturing method for the same, light diffusion polarization plate, and liquid crystal display device - Google Patents

Abstract

A light diffusing film exhibiting good optical characteristics such as high front contrast and wide viewing angle is obtained stably.
A light diffusing film having a base film and a light diffusing layer laminated on the base film, wherein the light diffusing layer is a resin containing translucent fine particles and a solvent. It is a layer comprising a dried product or a cured product thereof, and the resin composition has the formula (A): S = 100− (100 × M / 30) [M is a 100 ml graduated cylinder of 30 ml of the resin composition. The scale (ml) of the interface between the transparent supernatant layer and the suspension layer of the resin composition observed when left for 6 hours. ] The light diffusion film whose sedimentation degree S represented by this is 30 or less.
[Selection] Figure 1

Description

  The present invention relates to a light diffusion film including a light diffusion layer in which translucent fine particles are dispersed on a base film, and a method for producing the same. The present invention also relates to a light diffusing polarizing plate and a liquid crystal display device using the light diffusing film.

  In recent years, application of liquid crystal display devices to mobile phones, personal computer monitors, televisions, liquid crystal projectors, and the like is rapidly progressing. 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 and display 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. By arranging a light diffusing film on the viewing side surface of the liquid crystal display device and imparting light diffusivity, when the display screen of the liquid crystal display device is observed obliquely, the contrast of the image is reduced and the gradation inversion phenomenon is improved. Wide viewing angle can be achieved. In general, a light diffusing film is manufactured by applying a coating liquid containing fine particles on a substrate, and forming a light diffusing layer containing fine particles on the substrate through drying or curing treatment. (For example, Patent Documents 1 to 4).

JP 2003-43218 A JP 2008-152268 A JP 2000-121809 A JP 2010-160527 A

  In conventional light diffusing films, in order to obtain a wide viewing angle, if sufficient light diffusibility is imparted, for example, by increasing the content of fine particles in the light diffusing layer, the transmission clarity of the displayed image decreases, and accordingly There is a problem that the front contrast of the display image is lowered and the entire screen is felt whitish due to the irregular reflection of the surface of the light diffusing layer, so-called whitish is likely to occur. On the other hand, if the content of fine particles in the light diffusion layer is kept low to increase the front contrast, the light diffusibility becomes insufficient and a wide viewing angle cannot be obtained.

  In particular, when the content of fine particles in the light diffusion layer forming coating liquid is large, the coating liquid is continuously applied on the substrate for a long time in the continuous production of the light diffusion film. Stable optical characteristics due to accumulation of fine particles on the die that supplies the liquid, which can contaminate the light diffusion film and manufacturing equipment, or the degree of sedimentation of the fine particles in the coating liquid increases over time. In addition, there is a problem that a light diffusion film having an appearance cannot be obtained.

  An object of the present invention is to provide a light diffusing film having a high front contrast and a wide viewing angle, and a light diffusing polarizing plate and a liquid crystal display device to which the light diffusing film is applied. Another object of the present invention is to provide a method capable of stably and continuously producing a light diffusion film exhibiting good optical characteristics including high front contrast and wide viewing angle characteristics.

The present invention is a light diffusion film having a base film and a light diffusion layer laminated on the base film, wherein the light diffusion layer is a dried resin composition containing translucent fine particles and a solvent. Or a cured product thereof, and the resin composition has the following formula (A):
S = 100− (100 × M / 30) (A)
(In the formula, M represents a scale [ml] at the interface between the transparent supernatant layer and the suspension layer of the resin composition observed when 30 ml of the resin composition is placed in a 100 ml measuring cylinder and left for 6 hours. The light diffusion film whose sedimentation degree S represented by this is 30 or less is provided.

  The translucent fine particles are preferably organic fine particles having a weight average particle diameter of 3 μm or more and 10 μm or less. The content of the light-transmitting fine particles in the resin composition is preferably 25 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the resin solid content. The viscosity at 25 ° C. of the resin composition is preferably 10 mPa · s or more and 60 mPa · s or less. The resin composition can be a curable resin composition. In this case, the light diffusion layer is a layer made of the cured product.

  In the light diffusing film of the present invention, it is preferable that the sum of transmitted sharpness obtained through optical combs of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm is 45% or more and 220% or less. The haze is preferably 40% or more and 70% or less, and the surface haze resulting from the surface shape of the light diffusion layer is preferably 6% or less. The surface haze is more preferably 3% or less. The center line average roughness Ra of the surface of the light diffusion layer is preferably 1 μm or less.

  The light diffusion film of the present invention may further include an antireflection layer laminated on the light diffusion layer.

  Moreover, this invention provides the method for manufacturing the said light-diffusion film. The manufacturing method of this invention includes the process of coating the coating liquid which consists of the said predetermined | prescribed resin composition on a base film, and the process of drying the obtained coating layer. When the resin composition is a curable resin composition, the method further includes a step of curing the dried coating layer.

  Furthermore, the present invention provides a light diffusing polarizing plate comprising at least a polarizing plate having a polarizing film and the light diffusing film of the present invention laminated on the polarizing plate so that the base film side faces the polarizing plate. provide. In the light diffusing polarizing plate according to a preferred embodiment, the polarizing film and the light diffusing film are bonded together via an adhesive layer.

  The present invention further provides a liquid crystal display device comprising the light diffusing film or the light diffusing polarizing plate.

  According to the present invention, a light diffusion film and a light diffusing polarizing plate having high front contrast and a wide viewing angle can be provided. Moreover, according to the method of the present invention, a light diffusion film exhibiting good optical characteristics including high front contrast and wide viewing angle characteristics can be stably and continuously produced. A liquid crystal display device to which a light diffusing film or a light diffusing polarizing plate having such excellent optical characteristics is applied exhibits a high front contrast and a wide viewing angle.

It is a schematic sectional drawing which shows a preferable example of the light-diffusion film of this invention. It is a schematic sectional drawing which shows another preferable example of the light-diffusion film of this invention. It is a schematic sectional drawing which shows another preferable example of the light-diffusion film of this invention. It is the schematic which shows an example of the apparatus for manufacturing the light-diffusion film of this invention. It is a schematic sectional drawing which shows a preferable example of the light diffusable polarizing plate of this invention. It is a schematic sectional drawing which shows a preferable example of the liquid crystal display device of this invention. It is a schematic perspective view for demonstrating the relationship between the ridgeline direction of the linear prism which a prism film has, and the transmission-axis direction of a polarizing plate. It is a schematic sectional drawing which shows another preferable example of the liquid crystal display device of this invention.

<Light diffusion film>
1 and 2 are schematic cross-sectional views showing preferred examples of the light diffusion film of the present invention. The light diffusion films 100 and 200 shown in FIGS. 1 and 2 according to the present invention include a base film 101 and a light diffusion layer 102 laminated on the base film 101. The light diffusing layer 102 is a layer having a translucent resin 103 as a base material, and translucent fine particles 104 are dispersed in the translucent resin 103. The light diffusion layer 102 is a layer formed by coating and drying a resin composition (coating liquid) containing the translucent fine particles 104 and a solvent, or a layer obtained by further curing the layer. In the light diffusing film of the present invention, the surface of the light diffusing layer 102 may be composed of a flat surface as in the example shown in FIG. 1, or it is composed of an uneven surface as in the example shown in FIG. It may be. Hereinafter, the light diffusion film of the present invention will be described in more detail.

[Base film]
The base film 101 used in the present invention may be a translucent film, and for example, glass or plastic film 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), acrylic resins, polycarbonate resins, and polyester resins such as polyethylene terephthalate. The thickness of the base film 101 is, for example, 10 to 200 μm, and preferably 20 to 100 μm.

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

(1) Translucent resin The translucent resin 103 is not particularly limited as long as it has translucency. For example, an ionizing radiation curable resin such as an ultraviolet curable resin or an electron beam curable resin, or heat. A cured product of a curable resin; a thermoplastic resin; a cured product of a metal alkoxide, or the like can be used. Among these, an ionizing radiation 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 liquid crystal display device. In the case of using an ionizing radiation curable resin, a thermosetting resin, or a metal alkoxide, the translucent resin 103 is formed by curing the resin by irradiation or heating with ionizing radiation.

  The ionizing radiation 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. , Hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, 2,2'-thiodiethanol, divalent alcohols such as 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, tetramethylolmethane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, tetramethylolmethanetetra ( (Meth) acrylate, pentaglycerol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol tri (meth) acrylate, di Pentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate.

  Examples of the urethane (meth) acrylate compound include urethanized 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 two isocyanates in one molecule such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and dicyclohexylmethane diisocyanate. Organic isocyanate having a group, organic isocyanate having three isocyanate groups in one molecule obtained by subjecting these organic isocyanates to isocyanurate modification, adduct modification, biuret modification, and the like. 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.

  A preferable 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 of a polyhydric alcohol, a carboxylic acid, 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 Adduct adduct modified isophorone diisocyanate with 2-hydroxyethyl (meth) acrylate; adducts and adducts of biuret of isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate. Furthermore, the ionizing radiation curable resin preferably contains a urethane (meth) acrylate compound because it exhibits good flexibility (a property exhibiting flexibility) when it is thickened. These polyfunctional (meth) acrylate compounds can be used alone or in combination of two or more.

  The ionizing radiation curable resin may contain a monofunctional (meth) acrylate compound in addition to the polyfunctional (meth) acrylate compound. Examples of the monofunctional (meth) acrylate compound include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, and 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 ionizing radiation curable resin may contain a polymerizable oligomer. By containing the polymerizable oligomer, the hardness of the light diffusion layer 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, and a polymer of xylylene diisocyanate. The polyhydric alcohol having at least one (meth) acryloyloxy group includes Hydroxyl group-containing (meth) acrylic acid ester obtained by esterification reaction of alcohol and (meth) acrylic acid, and as polyhydric alcohol, for example, 1,3-butanediol, 1,4-butanediol, 1,6 -Hexanediol, diethylene glycol, triethylene glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, glycerin, pentaerythritol What is dipentaerythritol 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 for 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 for 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 of a polyhydric alcohol, a carboxylic acid, a compound having a plurality of carboxyl groups, and / or an anhydride thereof. Examples of the polyhydric alcohol, the compound having a plurality of carboxyl groups, and / or the anhydride thereof are the same as those described for 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 for the polymerizable oligomeric 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 the thermosetting resin that forms the translucent resin 103 include a phenol resin, a urea melamine resin, an epoxy resin, an unsaturated polyester resin, and a silicone resin in addition to a thermosetting urethane resin composed of an acrylic polyol and an isocyanate prepolymer. Can be mentioned.

  Examples of the thermoplastic resin that forms the translucent resin 103 include cellulose derivatives such as acetylcellulose, nitrocellulose, acetylbutylcellulose, ethylcellulose, and methylcellulose; vinyl acetate and copolymers thereof, vinyl chloride and copolymers thereof, and vinylidene chloride. And vinyl resins such as copolymers thereof; acetal resins such as polyvinyl formal and polyvinyl butyral; acrylic resins and copolymers thereof, acrylic resins such as methacrylic resins and copolymers thereof; polystyrene resins; polyamide resins Polyester resin; polycarbonate resin and the like.

  As the metal alkoxide for forming the translucent resin 103, a silicon oxide matrix using a silicon alkoxide material as a raw material can be used. Specifically, it is tetramethoxysilane, tetraethoxysilane, or the like, and can be made into an inorganic or organic-inorganic composite matrix (translucent resin) by hydrolysis or dehydration condensation.

(2) Translucent fine particles As the translucent fine particles 104, organic fine particles or inorganic fine particles having translucency 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. Examples include inorganic fine particles. Organic polymer balloons and glass hollow beads can also be used. In particular, it is preferable to use organic fine particles as the light-transmitting fine particles 104 because preparation of a resin composition (coating liquid) having a predetermined sedimentation degree S described later is facilitated.

  The translucent fine particles 104 may be composed of one kind of fine particles, or may contain two or more kinds of fine particles having different weight average particle diameters and refractive indexes. 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, and the like, but a spherical shape or a substantially spherical shape is preferable.

  The weight average particle size of the translucent fine particles 104 (in the case where two or more types of translucent fine particles having different weight average particle sizes are used, the respective weight average particle sizes) is preferably 3 μm or more and 10 μm or less. More preferably, it is 8 μm or less. When the weight average particle diameter of the light-transmitting fine particles 104 is less than 3 μm, visible light having a wavelength region of 380 nm to 800 nm cannot be sufficiently scattered, and the light diffusibility of the light diffusion film becomes insufficient. A corner may not be obtained. In addition, when the weight average particle size exceeds 10 μm, if the transmission definition is adjusted to a preferable range described later, light scattering becomes too weak, so that sufficient light scattering properties cannot be obtained, and a wide viewing angle is obtained similarly. There may not be. In addition, the use of translucent fine particles having a weight average particle diameter exceeding 10 μm is necessary to obtain a resin composition (coating liquid) exhibiting a predetermined sedimentation degree S and to adjust the viscosity of the resin composition. May need to be adjusted.

  The weight average particle diameter of the translucent fine particles 104 is measured using a Coulter Multisizer (manufactured by Beckman Coulter, Inc.) based on the Coulter principle (pore electrical resistance method).

  The difference in refractive index between the translucent fine particles 104 and the translucent resin 103 is preferably in the range of 0.04 to 0.15. By setting the refractive index difference within the above range, moderate internal scattering due to the refractive index difference occurs, and it becomes easy to control the total haze and the internal haze of the light diffusion film within a preferable range described later, and transmission. It becomes easy to moderately control the sharpness and control within a preferable range described later.

(3) Surface shape and thickness of light diffusing layer In the light diffusing film of the present invention, the center line average roughness Ra according to JIS B 0601 on the surface of the light diffusing layer 102 (surface opposite to the base film 101) is preferably It is 1 μm or less, more preferably 0.2 μm or less. When the center line average roughness Ra on the surface of the light diffusing layer 102 exceeds 1 μm, so-called whitishness in which the entire screen is felt whitish due to surface irregular reflection of the light diffusing layer becomes prominent. The centerline average roughness Ra according to JIS B 0601 means that only the reference length l (el) is extracted from the roughness curve in the direction of the average line, the x-axis is extracted 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 represented 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 Solutions Co., Ltd.) in accordance with JIS B 0601. Can be calculated.

  Moreover, it is preferable that the surface of the light diffusion layer (the surface on the side opposite to the base film 101) is formed only by the translucent resin 103. That is, it is preferable that the translucent fine particles 104 do not protrude from the surface of the light diffusion layer 102 and are completely buried in the light diffusion layer 102. Therefore, the thickness of the light diffusion layer 102 is set to the weight average particle diameter of the light transmitting fine particles 104 (the largest weight average particle diameter when two or more kinds of light transmitting fine particles having different weight average particle diameters are used). On the other hand, it is preferably 1 to 3 times. When the thickness of the light diffusion layer 102 is less than 1 times the weight average particle diameter of the translucent fine particles 104, it is difficult to control the surface haze of the light diffusion film to be described later within a preferable range, thereby causing whiteness There is. In addition, when the thickness of the light diffusion layer 102 exceeds three times the weight average particle diameter of the translucent fine particles 104, the thickness of the light diffusion layer 102 becomes too thick, and the light diffusibility of the light diffusion film increases accordingly. As a result, when this light diffusion film is applied to a liquid crystal display device, for example, in black display, light leaking obliquely with respect to the front direction of the liquid crystal display device is scattered in the front direction by the light diffusion layer. For example, the front contrast may be lowered due to the cause of the display quality and the display quality may be deteriorated.

  The thickness of the light diffusion layer 102 is preferably in the range of 3 to 30 μm. When the thickness of the light diffusion layer 102 is less than 3 μm, sufficient scratch resistance required for the light diffusion film disposed on the viewing side surface of the liquid crystal display device may not be provided. In addition, when the thickness exceeds 30 μm, the amount of curl generated in the produced light diffusion film increases, and the handleability in bonding to other films and substrates, application to liquid crystal display devices, etc. tends to deteriorate. .

[Resin composition for forming light diffusion layer (coating liquid)]
The resin composition (coating liquid) that forms the light diffusion layer 102 includes at least a resin (for example, an ionizing radiation curable resin, a thermosetting resin, or a metal alkoxide) that forms the translucent resin 103, and translucent fine particles 104. And solvent. Here, in the present invention, the resin composition (coating liquid) is represented by the following formula (A):
S = 100− (100 × M / 30) (A)
Is set to 30 or less, preferably 20 or less, and more preferably 10 or less.

  In formula (A), M is a scale of the interface between the transparent supernatant layer and the suspension layer of the resin composition observed when 30 ml of the resin composition is placed in a 100 ml measuring cylinder and left at 25 ° C. for 6 hours. ml]. The maximum value of M is 30 [ml], which means that no sedimentation of translucent fine particles has occurred at all even after 6 hours, and is completely dispersed (sedimentation degree S = 0). The minimum value of M is 0 [ml] (however, it is not completely zero because of the volume of the translucent fine particles themselves), which is completely or almost completely translucent fine particles after 6 hours. Is settled (sedimentation degree S≈100). That is, the sedimentation degree S is an index for evaluating the degree of sedimentation of the translucent fine particles by leaving a predetermined amount of the resin composition (coating liquid) in which the translucent fine particles are dispersed for a predetermined time. The larger the degree S (the smaller M) means that the translucent fine particles settle faster, and the smaller the degree of sedimentation S (the larger M) means that the translucent fine particles settle slower. .

  When the sedimentation degree S exceeds 30, translucent fine particles accumulate on a die or the like that supplies the coating liquid, which causes contamination of the light diffusing film or the manufacturing apparatus. Since the sedimentation degree of the light-sensitive fine particles increases, it becomes difficult to stably obtain a light diffusion film having good optical characteristics and appearance. That is, even if the specific configuration of the light diffusion layer is designed as described above in order to achieve the desired optical characteristics as the light diffusion film, if the sedimentation degree S exceeds 30, the translucent fine particles are relatively Due to the quick sedimentation, the optical properties of the light diffusion film manufactured in the initial stage of coating and the light diffusion film manufactured after a certain amount of coating time are greatly different, The optical properties and the like of the light diffusing film manufactured after the coating time elapses depart from the designed desirable optical properties and the like. For these reasons, when the sedimentation degree S exceeds 30, it is difficult to stably obtain a light diffusion film having a high front contrast and a wide viewing angle.

  The sedimentation degree S is the viscosity of the resin composition (coating liquid), the weight average particle diameter of the translucent fine particles, the specific gravity difference between the specific gravity of the translucent fine particles and the solvent containing the resin that forms the translucent resin, etc. It is controllable by adjusting. In particular, the viscosity of the resin composition tends to greatly affect the sedimentation degree S. Adjustment of the viscosity of a resin composition can be performed by adjusting the quantity and kind of solvent. In order to reduce the viscosity of the resin composition, it is sufficient to use a large amount of solvent and a solvent having a low viscosity. To increase the viscosity of the resin composition, the amount of solvent is small and the solvent has a high viscosity. Can be used. More specifically, the viscosity at 25 ° C. of the resin composition is preferably 10 mPa · s or more and 60 mPa · s or less, although it depends on the weight average particle diameter and specific gravity of the translucent fine particles.

  From the viewpoint of obtaining a resin composition exhibiting a predetermined sedimentation degree S, the weight average particle diameter of the translucent fine particles is preferably 3 μm or more and 10 μm or less as described above. However, the weight average particle diameter of the translucent fine particles should be determined in consideration of desired optical characteristics.

  The specific gravity of the translucent fine particles, that is, the material can be selected from many options as exemplified above, but contains the specific gravity of the translucent fine particles and the resin that forms the translucent resin. It is preferable to select the difference in specific gravity with the solvent as small as possible. From this point, the translucent fine particles are preferably organic fine particles. The material of the translucent fine particles should be determined in consideration of desired optical characteristics.

  The content of the translucent fine particles 104 in the resin composition (coating liquid) is preferably 25 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the resin solid content of the resin composition. More preferably, it is 40 parts by weight or less. When the content of the translucent fine particles 104 is less than 25 parts by weight with respect to 100 parts by weight of the resin solid content, the light diffusibility of the light diffusion film becomes insufficient, and as a result, a wide viewing angle cannot be obtained. In some cases, moire may occur as a result of the transmission clarity that will be described later exceeding 220%. Further, when the content of the translucent fine particles 104 exceeds 50 parts by weight with respect to 100 parts by weight of the resin solid content, the light scattering effect is too strong, and the total haze and / or internal haze described later exceeds 70%. In some cases, a decrease in front contrast and a decrease in transparency of the light diffusion film may occur.

  When an ultraviolet curable resin is used as the resin that forms the translucent resin 103, the resin composition includes 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 compound and the like can also be used. The usage-amount of a photoinitiator is 0.5-20 weight part normally with respect to 100 weight part of resin solid content, Preferably, it is 1-5 weight part.

  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 and methyl isobutyl ketone Ketones such as cyclohexanone; esters such as ethyl acetate, butyl acetate, and isobutyl acetate; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether Class: Ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, etc. Celluloses 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 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 solvent. Therefore, the boiling point is desirably in the range of 60 ° C to 160 ° C. The saturated vapor pressure at 20 ° C. is preferably in the range of 0.1 kPa to 20 kPa.

  The resin composition (coating liquid) may contain other additives such as a leveling agent (fluorine-based or silicone-based leveling agent), an antistatic agent, and an antifouling agent, if necessary.

[Optical characteristics of light diffusion film]
(1) Transmission clarity The light diffusing film of the present invention is a sum of transmission clarity obtained through optical combs of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm (in this specification, simply “transmission”). The sharpness "is sometimes 45% or more and 220% or less. “The sum of transmitted sharpness obtained through 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 between the dark part and the bright part is 1: 1 is the sum of transmitted sharpness (image sharpness) measured using four types of optical combs whose widths are 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 45%, the light scattering is too strong. Therefore, when this light diffusion film is applied to a liquid crystal display device, for example, in white display, the 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 transmission definition exceeds 220%, a moire of transmitted light is generated 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. There is a tendency. The transmission definition of the light diffusion film is more preferably 90% or more and 150% or less.

  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. 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.

(2) 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 surface shape of the light-diffusion layer 102 is 6% or less. Here, “total haze” refers to the total light transmittance (Tt) representing the total amount of light transmitted through the light diffusion film and the diffused light transmittance (Td) diffused and transmitted by the light diffusion 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 diffused 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 according to JIS K 7361.

  The “internal haze” of the light diffusion film is a haze other than the haze (surface haze) caused by the surface shape of the light diffusion layer 102 among all the hazes.

  When the total haze and / or internal haze is less than 40%, the light scattering property is insufficient and the viewing angle tends to be narrow. Further, when the total haze and / or internal haze exceeds 70%, light scattering is too strong. Therefore, when this light diffusion film is applied to a liquid crystal display device, for example, in black display, in the front direction of the liquid crystal display device. On the other hand, the light that leaks obliquely is scattered in the front direction by the light diffusion layer, and the front contrast is lowered and the display quality tends to deteriorate. Moreover, when the total haze and / or internal haze exceeds 70%, the transparency of the light diffusion film tends to be impaired. More preferably, the total haze and the internal haze are 50% or more and 65% or less, respectively.

  Moreover, when the surface haze resulting from the surface shape of the light-diffusion layer 102 exceeds 6%, there exists a tendency for whitening to generate | occur | produce by surface irregular reflection. In order to prevent whitening more effectively, the surface haze is more preferably 3% or less.

  Specifically, the total haze, internal haze, and surface haze of the light diffusion film are measured as follows. That is, first, in order to prevent warping of the film, an optically transparent adhesive is used to bond the light diffusion film to the glass substrate so that the light diffusion layer 102 is the surface. A measurement sample is prepared, and the total haze value of the measurement sample is measured. The total haze value is determined by 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, and a total light transmittance (Tt) and diffused light transmission. The rate (Td) is measured and calculated by the above equation (2).

Next, a triacetylcellulose film having a haze of approximately 0% is bonded to the surface of the light diffusion layer 102 using glycerin, and the haze is measured in the same manner as the measurement of the total haze described above. The haze is almost countered by the triacetyl cellulose film to which the surface haze due to the surface shape of the light diffusion layer 102 is bonded, and thus can be regarded as “internal haze” of the light diffusion 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.

[Other layers that the light diffusion film may have]
The light diffusion film of the present invention may have a resin layer 105 made of a translucent resin laminated on the light diffusion layer 102 as in the light diffusion film 300 shown in FIG. In this case, the center line average roughness Ra of the surface of the resin layer 105 is preferably 1 μm or less.

  The light diffusion film of the present invention may further include an antireflection layer laminated on the light diffusion layer 102 (surface opposite to the base film 101). The antireflection layer is provided to reduce the reflectance as much as possible, and reflection on the display screen can be 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 light diffusion layer 102; a high refractive index layer composed of a material higher than the refractive index of the light diffusion layer 102, and the high refractive index A laminated structure with a low refractive index layer composed of a material lower than the refractive index of the layer can be exemplified.

[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 the present invention preferably comprises the following steps:
(I) A step of applying a coating liquid comprising a resin composition containing translucent fine particles 104 and a solvent and exhibiting the predetermined sedimentation degree S on the substrate film 101, and (II) obtained. It is manufactured by a method including a step of drying the coating layer. When the resin composition is a curable resin composition, the method further includes a step (III) of curing the dried coating layer.

  Application of the coating liquid onto the base film can be performed, for example, by 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. In coating the coating liquid, as described above, the coating film thickness is set so that the thickness of the light diffusion layer 102 is 1 to 3 times the weight average particle diameter of the translucent fine particles 104. It is preferable to adjust.

  Various surface treatments may be applied to the surface of the base film 101 (light diffusion layer side surface) for the purpose of improving the coating property of the coating 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. In addition, another layer such as a primer layer may be formed on the base film, and the coating solution may be applied on the other layer.

  Moreover, when using the light-diffusion film 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-diffusion) of the base film 101 is used. It is preferable to hydrophilize the surface opposite to the layer) by various surface treatments.

  Next, the coating layer is dried (step (II). When the resin composition is a curable resin composition such as an ultraviolet curable resin, the dried coating layer is cured (step (III)). In the curing step (III) (when the resin forming the translucent resin 103 is a thermoplastic resin, cooling after drying), the mirror surface or uneven surface of the mold is transferred to the surface of the coating layer. Specifically, in order to obtain a light diffusion layer having a flat surface as shown in Fig. 1, a mold having a mirror surface on the surface of the coating layer (mirror surface mold). In order to obtain a light diffusing layer having an uneven surface shape as shown in Fig. 2, a mold having an uneven surface on the surface of the coating layer ( The uneven surface of the embossing mold) is brought into close contact with the uneven surface, and the uneven surface is transferred. The embossing mold may be an embossing metal roll, and thus the translucent fine particles are obtained by transferring the mirror surface or the uneven surface of the mold to the surface of the light diffusion layer 102. Can be reliably prevented from projecting to the surface of the light diffusion layer, and a light diffusion layer having a desired surface shape can be formed.

  More specifically, when an ionizing radiation curable resin, a thermosetting resin or a metal alkoxide is used as a resin for forming the translucent resin 103, after forming a coating layer and drying (removing the solvent) In a state where the mirror surface or uneven surface of the mold is in close contact with the surface of the coating layer, or after close contact, irradiation with ionizing radiation (when using ionizing radiation curable resin) or heating (thermosetting resin or When the metal alkoxide is used, the coating layer is cured. The ionizing radiation can be appropriately selected from ultraviolet rays, electron beams, near ultraviolet rays, visible light, near infrared rays, infrared rays, X-rays, etc. depending on the type of resin contained in the resin liquid. Among these, ultraviolet rays, 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 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, and a metal halide lamp are preferably used.

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

  Next, a preferred embodiment for producing the light diffusion film of the present invention will be described. In the production method according to the preferred embodiment, in order to continuously produce the light diffusion film of the present invention, the step of continuously feeding the base film 101 wound in a roll shape, the translucent fine particles 104 and the solvent are provided. It includes a step of coating and drying the coating liquid to be contained, a step of curing the coating layer, and a step of winding up the obtained light diffusion film. Such a manufacturing method can be implemented using, for example, a manufacturing apparatus shown in FIG. Hereinafter, the manufacturing method according to the preferred embodiment will be described with reference to FIG.

  First, the base film 101 is continuously unwound by the unwinding device 501. Subsequently, the coating liquid containing the translucent fine particles 104 and the solvent is applied onto the unwound base film 101 using the coating apparatus 502 and the backup roll 503 facing the coating apparatus 502. Next, it is dried by passing through a dryer 504. Next, the base film 101 provided with the coating layer is provided between the mirror surface metal roll or the embossing metal roll 505 and the nip roll 506, and the coating layer is the mirror surface metal roll or the embossing metal. It is wound around in close contact with the roll 505. Thereby, the mirror surface of the mirror surface metal roll or the uneven surface of the metal roll for embossing is transferred to the surface of the coating layer. Next, the coating layer is cured by irradiating ultraviolet rays from the ultraviolet irradiation device 508 through the substrate film 101 in a state where the substrate film 101 is wound around the mirror surface metal roll or the embossing metal roll 505. Let Since the irradiated surface becomes high temperature due to ultraviolet irradiation, the mirror surface metal roll or the embossing metal roll 505 preferably includes a cooling device for adjusting the surface temperature to about room temperature to about 80 ° C. . Further, one or a plurality of ultraviolet irradiation devices 508 can be used. The base film 101 (light diffusion film) on which the light diffusion layer 102 is formed is peeled off from the mirror surface metal roll or the embossing metal roll 505 by the peeling roll 507. The light diffusion film produced as described above is taken up by the take-up device 509. 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.

  In addition, after peeling from the mirror surface metal roll or the embossing metal roll 505 by the peeling roll 507, additional ultraviolet irradiation may be performed. Moreover, instead of performing ultraviolet irradiation in a state of being wound around a mirror surface metal roll or an embossing metal roll 505, the base film 101 on which an uncured coating layer is formed is mirror surface metal roll or embossing. After peeling from the metal roll 505 for use, it may be cured by irradiating with ultraviolet rays.

<Light diffusing polarizing plate>
The light diffusing film of the present invention described above can be made into a light diffusing polarizing plate by combining with the polarizing plate. The light diffusing polarizing plate is a multifunctional film having a polarizing function and a light diffusing (antiglare) function. The light diffusing polarizing plate of the present invention is a polarizing plate having at least a polarizing film and the above laminated on the polarizing plate via an adhesive layer or an adhesive layer so that the base film side faces the polarizing plate. The light diffusing film of the present invention is provided. A polarizing plate may be a conventionally well-known structure, for example, what has a protective film on the single side | surface or both surfaces of a polarizing film is common. The polarizing plate may be the polarizing film itself.

  FIG. 5 is a schematic cross-sectional view showing a preferred example of the light diffusing polarizing plate of the present invention. A light diffusing polarizing plate 600 shown in FIG. 5 includes a polarizing film 601, a protective film 602 attached to one surface of the polarizing film 601, and a light diffusing film 100 attached to the other surface. . The light diffusion film 100 is stuck so that the base film 101 side faces the polarizing film 601 of the polarizing plate. The light diffusion film 100 and the protective film 602 are attached to the polarizing film 601 via an adhesive layer (not shown). Such a configuration in which the polarizing film and the light diffusing film are attached via the adhesive layer, that is, the configuration in which the light diffusing film is used as a protective film for the polarizing film is used to reduce the thickness of the light diffusing polarizing plate. It is advantageous.

  As the polarizing film 601, for example, a dichroic dye or iodine is adsorbed and oriented on a film made of polyvinyl alcohol resin, polyvinyl acetate resin, ethylene / vinyl acetate (EVA) resin, polyamide resin, polyester resin, or the like. Examples thereof include a polyvinyl alcohol / polyvinylene copolymer containing a molecular chain oriented with a dichroic dehydrated product of polyvinyl alcohol (polyvinylene) in a molecularly oriented polyvinyl alcohol film. In particular, a film obtained by adsorbing and orienting a dichroic dye or iodine on a polyvinyl alcohol-based resin film is suitably used as a polarizing film. Although there is no limitation in particular in the thickness of a polarizing film, generally 100 micrometers or less are preferable from viewpoints, such as thickness reduction of a polarizing plate, More preferably, it is the range of 10-50 micrometers, More preferably, it is the range of 25-35 micrometers.

  The protective film 602 of the polarizing film 601 is preferably a film made of a polymer that has low birefringence and is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like. Examples of such films include cellulose acetate resins such as TAC (triacetyl cellulose); acrylic resins; fluorine resins such as tetrafluoroethylene / hexafluoropropylene copolymers; polycarbonate resins; polyethylenes Polyester resins such as terephthalate; polyimide resins; polysulfone resins; polyethersulfone resins; polystyrene resins; polyvinyl alcohol resins; polyvinyl chloride resins; polyolefin resins or polyamide resins What was formed and processed is mentioned. Among these, a triacetyl cellulose film whose surface is saponified with alkali or the like, or a norbornene-based thermoplastic resin film can be preferably used from the viewpoints of polarization characteristics and durability. The norbornene-based thermoplastic resin film is particularly suitable because it has high moisture and heat resistance and can greatly improve the durability of the polarizing plate and has high dimensional stability because of low hygroscopicity. For forming into a film, a conventionally known method such as a casting method, a calendar method, and an extrusion method can be used. The thickness of the protective film is not limited, but is preferably 500 μm or less from the viewpoint of thinning the polarizing plate. More preferably, it is the range of 5-300 micrometers, More preferably, it is the range of 5-150 micrometers.

  Typically, the light diffusing polarizing plate having the above-described configuration is applied through a pressure-sensitive adhesive layer or the like so that the light diffusing film is on the light emitting side (viewing side) when applied to a liquid crystal display device. Affixed to the glass substrate of the liquid crystal cell.

<Liquid crystal display device>
Next, the liquid crystal display device according to the present invention will be described. The liquid crystal display device of the present invention comprises the light diffusing film or light diffusing polarizing plate of the present invention. In one preferred embodiment, the liquid crystal display device of the present invention includes a backlight device, a light deflecting unit, a backlight side polarizing plate, a liquid crystal cell, and the light diffusing polarizing plate of the present invention in this order. . FIG. 6 is a schematic sectional view showing a preferred example of the liquid crystal display device of the present invention. The liquid crystal display device of FIG. 6 is a normally white mode TN liquid crystal display device, and includes a backlight device 702, a light diffusion plate 703, two prism films 704a and 704b as light deflecting means, and a backlight side. A polarizing plate 705, a liquid crystal cell 701 in which a liquid crystal layer 712 is provided between a pair of transparent substrates 711a and 711b, and a light diffusing polarizing plate comprising a viewing side polarizing plate 706 and the light diffusion film 707 according to the present invention. Are arranged in this order.

  As shown in FIG. 7, the backlight-side polarizing plate 705 and the viewing-side polarizing plate 706 are arranged so that their transmission axes have a crossed Nicols relationship. Each of the two prism films 704a and 704b has a flat surface on the light incident side (backlight device side) and a surface on the light emitting side (viewing side) (a surface facing the backlight side polarizing plate 705). ), A plurality of linear prisms 741a and 741b are formed in parallel. The prism film 704a is arranged so that the direction of the ridge line 742a of the linear prism 741a is substantially parallel to the transmission axis direction of the backlight-side polarizing plate 705, and the prism film 704b is formed of the linear prism 741b. It arrange | positions so that the direction of the ridgeline 742b may become substantially parallel with the transmission-axis direction of the visual recognition side polarizing plate 706 which comprises a light diffusable polarizing plate. However, the direction of the ridgeline 742b of the linear prism 741b of the prism film 704a is arranged so that the direction of the ridgeline 742b of the linear prism 741b of the prism film 704b is substantially parallel to the transmission axis direction of the backlight side polarizing plate 705. Can be arranged so as to be substantially parallel to the transmission axis direction of the viewing-side polarizing plate 706 constituting the light diffusing polarizing plate. Hereinafter, the constituent members constituting the liquid crystal display device of the present invention will be described in more detail.

[Liquid crystal cell]
The liquid crystal cell 701 includes a pair of transparent substrates 711a and 711b disposed to face each other with a predetermined distance by a spacer, and a liquid crystal layer 712 formed by sealing liquid crystal between the pair of transparent substrates 711a and 711b. A pair of transparent substrates 711a and 711b are formed by laminating transparent electrodes and alignment films, respectively, and a liquid crystal is aligned by applying a voltage based on display data between the transparent electrodes. The display method of the liquid crystal cell 701 is the TN method in the above example, but a display method such as an IPS method or a VA method is also used.

[Backlight device]
The backlight device 702 includes a rectangular parallelepiped case 721 having an upper surface opening, and a plurality of cold cathode tubes 722 as linear light sources arranged in parallel in the case 721. The case 721 is formed of a resin material or a metal material, and at least the case inner peripheral surface is preferably white or silver from the viewpoint of reflecting the light emitted from the cold cathode tube 722 on the case inner peripheral surface. As a light source, LEDs of various shapes such as a linear shape can be used in addition to a cold cathode tube. When the linear light source is used, the number of the linear light sources to be arranged is not particularly limited, but the distance between the centers of the adjacent linear light sources is in the range of 15 mm to 150 mm from the viewpoint of suppressing luminance unevenness on the light emitting surface. It is preferable. Note that the backlight device 702 used in the present invention is not limited to the direct type shown in FIG. 6, but is a sidelight type in which a linear light source or a point light source is arranged on the side surface of the light guide plate, or a flat surface. Various types such as a shape light source type can be used.

[Light diffusion means]
The liquid crystal display device of the present invention can include a light diffusing plate 703 as a light diffusing unit disposed between the backlight device 702 and the light deflecting unit. The light diffusing plate 703 is a film or sheet in which a diffusing agent is dispersed and mixed with a base material. As the base material, polycarbonate resin, methacrylic resin, methyl methacrylate and styrene copolymer resin, acrylonitrile and styrene copolymer resin, methacrylic acid and styrene copolymer resin, polystyrene resin, polyvinyl chloride resin, Polyolefin resins such as polypropylene and polymethylpentene, cyclic polyolefin resins, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyamide resins, polyarylate resins, polyimide resins and the like can be used. The light diffusing means may be a combination of a light diffusing plate and a light diffusing film.

  In addition, as the diffusing agent to be mixed and dispersed in the base material, organic fine particles composed of acrylic resin, melamine resin, polyethylene resin, polystyrene resin, organic silicone resin, copolymer of acrylic and styrene, etc., which are different from the base material And inorganic fine particles composed of calcium carbonate, silica, aluminum oxide, barium carbonate, barium sulfate, titanium oxide, glass and the like. The kind of diffusing agent to be used may be one kind or two or more kinds. Organic polymer balloons and glass hollow beads can also be used as the diffusing agent. The weight average particle size of the diffusing agent is preferably in the range of 0.5 to 30 μm. The shape of the diffusing agent may be spherical, flat, plate-like, or needle-like, but is preferably spherical.

[Prism film (light deflection means)]
The prism films 704a and 704b have a flat surface on the light incident surface side (backlight device side), and a polygonal shape having a tapered cross section on the light emitting surface (surface facing the backlight side polarizing plate 705), preferably A plurality of triangular linear prisms 741a and 741b are formed in parallel. Examples of the material of the prism films 704a and 704b include polycarbonate resin, ABS resin, methacrylic resin, copolymer resin of methyl methacrylate and styrene, polystyrene resin, copolymer resin of acrylonitrile and styrene, polyolefin such as polyethylene and polypropylene Examples of the resin include ionizing radiation curable resins such as ultraviolet curable resins and electron beam curable resins. The prism film can be produced by a known method such as a profile extrusion method, a press molding method, an injection molding method, a roll transfer method, a laser ablation method, a mechanical cutting method, a mechanical grinding method, or a photopolymer process method. Each of these methods may be used alone, or two or more methods may be combined. The thickness of the prism films 704a and 704b is usually 0.1 to 15 mm, preferably 0.5 to 10 mm.

  The cross-sectional shape in the vertical cross section orthogonal to the ridgelines 742a and 742b of the linear prisms 741a and 741b is, for example, a triangle. In this case, the apex angle θ (see FIG. 7) of the apexes forming the ridge line among the apexes of the triangle is preferably in the range of 90 to 110 °. In addition, this triangle may be either an equal side or an unequal side, but when concentrating in the front direction (the normal direction of the display surface of the liquid crystal display device), the triangle may have two sides on the light emitting side. It is preferably an isosceles triangle with equal sides. The cross-sectional shape of the linear prism can be set in accordance with the characteristics of the light emitted from the surface light source, and may have a shape other than a triangle, such as a curved line.

  In the prism films 704a and 704b, for example, a plurality of linear prisms 741a and 741b having a triangular cross section are sequentially arranged so that the bases relative to the apex angle θ of the triangle are adjacent to each other, and the plurality of linear prisms 741a are arranged. , 741b preferably have a structure in which the ridge lines 742a and 742b are arranged so as to be substantially parallel to each other. In this case, as long as the light collecting ability is not significantly reduced, each of the vertices of the triangular shape of the linear prisms 741a and 741b may have a curved shape. The distance between the ridge lines is usually in the range of 10 to 500 μm, preferably in the range of 30 to 200 μm.

〔Polarizer〕
As the backlight side polarizing plate 705 constituting the light diffusing polarizing plate, those described above can be used. Moreover, as a visual recognition side polarizing plate 706, a conventionally well-known thing can be used.

[Phase difference film]
The liquid crystal display device of the present invention can include a retardation plate 708 as shown in FIG. In FIG. 8, the retardation film 708 is disposed between the backlight side polarizing plate 705 and the liquid crystal cell 701. This phase difference plate 708 has a phase difference of almost zero in a direction perpendicular to the surface of the liquid crystal cell 701, has no optical effect from the front, and has a phase difference when viewed from an oblique direction. It is expressed and compensates for the phase difference generated in the liquid crystal cell 701. As a result, a wider viewing angle can be obtained, and better display quality and color reproducibility can be obtained. The retardation film 708 can be disposed between the backlight side polarizing plate 705 and the liquid crystal cell 701 and between one or both of the viewing side polarizing plate 706 and the liquid crystal cell 701.

  As the phase difference plate 708, for example, a polycarbonate resin or a cyclic olefin polymer resin is used as a film, and this film is further biaxially stretched, or a liquid crystalline monomer is applied to the film, and its molecular arrangement is changed by a photopolymerization reaction. Immobilized ones are listed. The retardation plate 708 optically compensates for the alignment of the liquid crystal, so that a retardation plate having a refractive index characteristic opposite to that of the liquid crystal alignment is used. Specifically, for a TN mode liquid crystal cell, for example, “WV film” (manufactured by FUJIFILM Corporation), for an STN mode liquid crystal display cell, for example, “LC film” (manufactured by Nippon Oil Corporation), For IPS mode liquid crystal display cells, for example, a biaxial retardation film, for VA mode liquid crystal display cells, for example, a retardation plate or a biaxial retardation film combining a A plate and a C plate, a π cell For the mode liquid crystal display cell, for example, “OCB WV film” (manufactured by FUJIFILM Corporation) can be suitably used.

  In the liquid crystal display device configured as described above, with reference to FIG. 6, the light emitted from the backlight device 702 is diffused by the light diffusion plate 703 and then enters the prism film 704a. In a vertical cross section perpendicular to the transmission axis direction of the backlight-side polarizing plate 705, light incident obliquely with respect to the lower surface of the prism film 704a is emitted with its path changed in the front direction. Next, in the prism film 704b, in the cross section orthogonal to the transmission axis direction of the viewing side polarizing plate 706, the light incident obliquely with respect to the lower surface of the prism film 704b is changed in the front direction in the same manner as described above. Are emitted. Therefore, the light that has passed through the two prism films 704a and 704b is condensed in the front direction in any vertical section, and the luminance in the front direction is improved.

  Next, the light having directivity in the front direction is polarized by the backlight side polarizing plate 705 and enters the liquid crystal cell 701. The light incident on the liquid crystal cell 701 is emitted from the liquid crystal cell 701 with the plane of polarization controlled for each pixel by the orientation of the liquid crystal layer 712 controlled by the electric field. And the light radiate | emitted from the liquid crystal cell 701 passes the visual recognition side polarizing plate 706, and further radiate | emits to the display surface side through the light-diffusion film 707. FIG.

  As described above, when the two prism films 704a and 704b are used as the light deflecting means, the directivity of the light incident on the liquid crystal cell 701 in the front direction can be further increased, thereby further increasing the luminance in the front direction. Can be improved. Moreover, since the light-diffusion film of this invention is used, the outstanding light-diffusion and high permeation | transmission clearness are obtained, without causing the fall of front contrast.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples. In the following examples, the optical properties and surface shape of the light diffusing film, the thickness of the light diffusing layer, the weight average particle diameter of the light-transmitting fine particles used, the sedimentation degree S of the resin composition (coating liquid) for forming the light diffusing layer The method for measuring the viscosity is as follows.

(A) Transmission clarity 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, an image clarity measuring device (“ICM-1DP” manufactured by Suga Test Instruments Co., Ltd.) based on JIS K 7105 was used. The transmission definition here is based on JIS K 7105 as defined above, and the ratio of the width between the dark part and the bright part is 1: 1, and the width is 0.125 mm, 0.5 mm, 1.0 mm. And transmission sharpness (image sharpness) measured using four types of optical combs of 2.0 mm.

(B) Haze It measured using the sample for a measurement which bonded the light-diffusion film to the glass substrate on the base film side using the optically transparent adhesive. A haze transmittance meter (haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd.) conforming to JIS K 7136 was used to measure all haze values and internal haze according to the measurement method described above. Based on the result, the surface haze was calculated from the above formula (3).

(C) Centerline average roughness Ra
It measured based on the said Formula (1) using the confocal interference microscope (For example, "PL (micro | micron | mu) 2300" by an optical solution company) based on JISB0601.

(D) Thickness of light diffusing layer The thickness of the light diffusing film is measured using DIGIMICRO MH-15 (main body) and ZC-101 (counter) manufactured by NIKON, and the thickness of the base film is subtracted from the measured layer thickness. Thus, the thickness of the light diffusion layer was measured.

(E) Weight average particle diameter of translucent fine particles Measurement was performed using a Coulter Multisizer (manufactured by Beckman Coulter, Inc.) based on the Coulter principle (pore electrical resistance method).

(F) Sedimentation degree S of resin composition (coating liquid)
The M value at 25 ° C. was measured according to the measurement method described above, and the sedimentation degree S at 25 ° C. was determined according to the above formula (A).

(G) Viscosity of Resin Composition (Coating Liquid) The viscosity at 25 ° C. was measured using a B-type viscometer (“viscomter TVB10” manufactured by Toki Sangyo Co., Ltd.).

[Production of light diffusion film]
<Example 1>
(1) Production of mirror surface metal roll An industrial chromium plating process was performed on the surface of a 200 mm diameter iron roll (STKM13A by JIS), and then the surface was mirror-polished to produce a mirror surface metal roll. The Vickers hardness of the chrome-plated surface of the obtained mirror surface metal roll was 1000. The Vickers hardness was measured according to JIS Z 2244 using an ultrasonic hardness tester MIC10 (manufactured by Krautkramer).

(2) Production of light diffusion film 60 parts by weight of pentaerythritol triacrylate and 40 parts by weight of polyfunctional urethanized acrylate (reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate) were mixed with propylene glycol monomethyl ether (PGME). And it adjusted so that it might become solid content concentration 60weight%, and obtained the ultraviolet curable resin composition. The refractive index of the cured product after removing propylene glycol monomethyl ether from the composition and curing with ultraviolet rays was 1.53.

  Next, with respect to 100 parts by weight of the resin solid content of the ultraviolet curable resin composition, polystyrene particles having a weight average particle size of 7.3 μm as transparent fine particles (SX713L manufactured by Soken Chemical Co., Ltd., refractive index: 1. 59, 26 parts by weight of specific gravity 1.01) and 17 parts by weight of polystyrene-based particles (XX342K, refractive index 1.59, specific gravity 1.01 manufactured by Sekisui Plastics Co., Ltd.) having a weight average particle diameter of 3.8 μm, Add 5 parts by weight of photopolymerization initiator “Lucirin TPO” (manufactured by BASF, chemical name: 2,4,6-trimethylbenzoyldiphenylphosphine oxide), and propylene glycol so that the solid content is 60% by weight. A coating solution was prepared by diluting with monomethyl ether.

Next, this coating solution was applied onto a triacetyl cellulose (TAC) film (base film) having a thickness of 80 μm using a slot die coater and dried for 1 minute in a dryer set at 80 ° C. I let you. The base film after drying was brought into close contact with the mirror surface of the mirror surface metal roll prepared in (1) above with a rubber roll so that the coating layer was on the roll side. In this state, light from a high-pressure mercury lamp with an intensity of 20 mW / cm ² is irradiated from the base film side so that the amount of light in terms of h-line is 300 mJ / cm ² to cure the coating layer and have a flat surface. A light diffusing film having a structure shown in FIG. 1, which is composed of a light diffusing layer and a base film, was obtained.

<Example 2>
A coating solution was prepared in the same manner as in Example 1 except that the solvent was changed to ethyl acetate (EA) to prepare a light diffusion film.

<Example 3>
A coating solution was prepared in the same manner as in Example 1 except that the amount of the solvent was adjusted so that the solid content of the coating solution was 40% by weight, and a light diffusion film was produced.

<Comparative Example 1>
A coating solution was prepared in the same manner as in Example 1 except that the solvent was changed to ethyl acetate and the amount of the solvent was adjusted so that the solid content of the coating solution was 40% by weight, and a light diffusion film was produced. did.

<Comparative example 2>
Addition amount of polystyrene particles having a weight average particle size of 7.3 μm (SX713L manufactured by Soken Chemical Co., Ltd.) and polystyrene particles having a weight average particle size of 3.8 μm with respect to 100 parts by weight of the resin solid content of the ultraviolet curable resin composition (Sekisui Plastics Co., Ltd. XX342K) addition amount was changed to 12 parts by weight and 8 parts by weight, respectively, except that the amount of solvent was adjusted so that the solid content of the coating solution was 40% by weight. A coating solution was prepared in the same manner as in Example 1 to produce a light diffusion film.

  Table 1 summarizes the measurement results of the above (a) to (d), (f) and (g) for the obtained light diffusion film and the coating solution used. In addition, all of these measurement results are values when a light diffusing film is produced by coating a base film immediately after preparing a coating solution.

[Evaluation of die contamination]
Each of the coating liquids prepared in the above Examples and Comparative Examples was applied to a base film continuously for 3 hours using a slot die coater, and the translucency settled and accumulated in the slot at the discharge part of the slot die coater. The degree of accumulation of fine particles was visually confirmed and evaluated according to the following criteria. The results are shown in Table 2.
○: No sediment of translucent fine particles is observed.
Δ: Slight sediment of translucent fine particles is observed.
X: A large amount of sediment is observed.

[Evaluation of optical property variability]
Each coating solution was prepared according to the procedure of the above-mentioned Examples and Comparative Examples, and allowed to stand for 6 hours. Using the coating solution after standing for 6 hours, a light diffusing film was prepared in the same manner as in the above Examples and Comparative Examples, and the total haze of the light diffusing film was measured according to the above-described measurement method. It compared with the total haze at the time of producing a light-diffusion film using a process liquid. The results are shown in Table 2.

[Production of liquid crystal display device and evaluation of its display characteristics]
A liquid crystal display device was produced using the obtained light diffusion film. First, on a backlight device of an IPS mode 32-inch liquid crystal television “VIERA TH-32LZ85” manufactured by Panasonic, a light diffusion whose luminance value in the direction of 70 ° with respect to the normal direction is 10% of the luminance value in the normal direction Two prism films in which a plurality of linear prisms each having an apex angle of 95 ° were arranged in parallel were used, and these were arranged between the light diffusion plate and the backlight side polarizing plate. At this time, one prism film (prism film close 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 film ( The prism film near 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. Moreover, the viewing-side polarizing plate was peeled off, and an iodine-based polarizing plate (“TRW842AP7” manufactured by Sumitomo Chemical Co., Ltd.) was bonded to the backlight-side polarizing plate so as to be crossed Nicol. The light diffusing film of 1-3 or Comparative Examples 1-2 was bonded through the adhesive layer, and the liquid crystal display device was obtained. The light diffusing film used here is the one prepared in the above [Evaluation of variability of optical characteristics], that is, the light diffusing film prepared using the coating liquid after standing for 6 hours.

  The liquid crystal display device thus obtained was evaluated for front contrast and 60 ° viewing angle. The results are shown in Table 3. These evaluation methods are as follows.

(A) Front contrast The liquid crystal display device was activated in a dark room, and the front luminance in the black display state and the white display state was visually observed to evaluate the front contrast. The evaluation criteria are as follows.
A: A level with no problem as a product.
○: Slightly inferior to ◎, but at a level where there is no problem as a product.

(B) 60 degree viewing angle Display quality was visually evaluated from the direction of 60 ° viewing angle (angle formed with the front direction of the liquid crystal display device). The evaluation criteria are as follows.
A: No abnormality is observed in the display quality.
○: There is almost no abnormality in the display quality.
X: Tone crushing and inversion are recognized.

  100, 200, 300, 707 Light diffusing film, 101 base film, 102 light diffusing layer, 103 translucent resin, 104 translucent fine particles, 105 resin layer, 501 unwinding apparatus, 502 coating apparatus, 503 backup roll , 504 dryer, 505 mirror surface metal roll or metal roll for embossing, 506 nip roll, 507 peeling roll, 508 ultraviolet irradiation device, 509 winding device, 600 light diffusing polarizing plate, 601 polarizing film, 602 protective film, 701 liquid crystal cell, 702 backlight device, 703 light diffusion plate, 704a, 704b prism film, 705 backlight side polarizing plate, 706 viewing side polarizing plate, 708 retardation plate, 711a, 711b transparent substrate, 712 liquid crystal layer, 721 case 722 Cold Cathode tube, 741a, 741b Linear prism, 742a, 742b Ridge line of linear prism.

Claims (13)

A light diffusion film having a base film and a light diffusion layer laminated on the base film,
The light diffusion layer is a layer composed of a dried product of a resin composition containing translucent fine particles and a solvent or a cured product thereof,
The resin composition has the following formula (A):
S = 100− (100 × M / 30) (A)
(In the formula, M is the scale [ml] at the interface between the transparent supernatant layer and the suspension layer of the resin composition observed when 30 ml of the resin composition is placed in a 100 ml measuring cylinder and left for 6 hours. To express.)
The light diffusion film whose sedimentation degree S represented by is 30 or less.   The light diffusing film according to claim 1, wherein the translucent fine particles are organic fine particles having a weight average particle diameter of 3 μm or more and 10 μm or less.   3. The light diffusing film according to claim 1, wherein a content of the translucent fine particles in the resin composition is 25 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the resin solid content.   The light diffusion film according to claim 1, wherein the resin composition has a viscosity at 25 ° C. of 10 mPa · s to 60 mPa · s.   The light diffusion film according to claim 1, wherein the resin composition is a curable resin composition, and the light diffusion layer is a layer made of the cured product.   The light diffusing film according to any one of claims 1 to 5, wherein a sum of transmission clarity obtained through optical combs of 0.125 mm, 0.5 mm, 1.0 mm and 2.0 mm is 45% or more and 220% or less.   The light diffusion film according to any one of claims 1 to 6, wherein the total haze is 40% or more and 70% or less, and the surface haze resulting from the surface shape of the light diffusion layer is 6% or less.   The light diffusion film according to any one of claims 1 to 7, wherein a center line average roughness Ra of the surface of the light diffusion layer is 1 µm or less.   The light diffusion film according to claim 1, further comprising an antireflection layer laminated on the light diffusion layer. It is a manufacturing method of the light-diffusion film of Claim 1, Comprising:
Applying a coating liquid comprising the resin composition on the base film;
A step of drying the coating layer;
The manufacturing method of the light-diffusion film containing this.   The manufacturing method of the light-diffusion film of Claim 10 which further includes the process of hardening the dried coating layer. A polarizing plate having at least a polarizing film;
The light diffusion film according to any one of claims 1 to 9, which is laminated on the polarizing plate such that the base film side faces the polarizing plate,
A light diffusing polarizing plate.   A liquid crystal display device comprising the light diffusing film according to claim 1 or the light diffusing polarizing plate according to claim 12.

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