TWI524097B - Polarizing element protective film - Google Patents

Description

Polarizing element protective film

The present invention relates to a polarizing element protective film having a light diffusing layer.

In order to prevent scratches on the surface, display surfaces of image display devices such as liquid crystal displays or plasma display panels, Brown tube (CRT, Cathode-Ray Tube) displays, and organic electroluminescence (EL) lamps A protective film having high hardness properties is usually provided. In addition, if the external light is reflected on the display surface of the image display device, the visibility is impaired. Therefore, a television or a personal computer that emphasizes image quality, a camera or a digital camera that is used outside the house with strong external light, and reflected light are used. In the mobile phone or the like for display, the protective film may be provided with a function of preventing external light from being reflected, and the incident light may be scattered by using a non-reflective treatment technique using interference of the optical multilayer film or by forming fine irregularities on the surface. It will also be reflected in the anti-glare treatment technology. In particular, the latter anti-glare treatment technology is relatively inexpensive, and thus can be preferably used for applications such as large monitors or personal computers.

Further, in the use of a large-screen image display device, for example, in a wall-mounted television application, the demand for further reduction in thickness and weight of the image display device has been surfaced, and the protective film is required to be thin and large in size corresponding to the image display device. The function of enhancing the strength of the image display element or the thinning of the protective film itself. As a protective film which meets such requirements, for example, a film containing a polyester resin can be used as a base film in terms of excellent mechanical strength, durability, and cost (refer to Japanese Patent Laid-Open Publication No. 2008-3541 (Patent Document 1)).

When a film containing a polyester resin is used as the substrate film, since it can be adjusted to a desired strength and thickness, and is advantageous in terms of cost, the resin film is usually stretched and used. Since the stretched resin film has birefringence, there is a problem that blurring caused by a phase difference is generated and visibility is poor.

Patent Document 1 describes that the haze caused by the birefringence of the base film is prevented by setting the total haze of the polarizing plate protective film to be in the range of 10 to 80%. However, the elimination of the halo is not only related to the total haze, but even if it is a protective film having a total haze within the above range, there is a case where a halo is generated. Further, if the total haze is set to a very high value, the generation of blooming can be suppressed, but in this case, the gloss of the surface is impaired and the appearance quality is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing element protective film which has a glossy surface and which suppresses a halo generated by transmitted light mainly caused by birefringence of a base film.

The present inventors have found that the generation of halos caused by transmitted light is also related to the sum of the clarity of the transmitted images. The invention includes the following.

[1] A polarizing element protective film which has a light diffusing layer, and a total value T _c (%) of the transmission image sharpness C _n (%) in the transmission image sharpness measurement test satisfies the following formula ( 1) relationship, and the total haze value H (%) satisfies the relationship of the following formula (2), and the above-described transmission image sharpness measurement test is performed at a speed orthogonal to the ray axis of the transmitted light at a speed of 10 mm/min. The light comb of the width n (mm) of the movement is measured, and the amount of transmitted light of the test piece is measured, and the highest value of the amount of transmitted light when the transmission portion of the optical comb is present on the ray axis is set in the above-described transmission image sharpness measurement test. when the minimum value of the light amount when the transmission is m _n, having the light axis of the light-shielding portion of the optical comb to m _n the case of the transmission image clarity C _n (%) according to the following equation system (3) It is calculated that the sum total value T _c is the sum of the transmission image sharpness C _0.125 , C _0.5 , C ₁ , and C ₂ when the width n (mm) of the comb is _0.125 , _0.5 , ₁ , and ₂ , respectively. 100≦T _c ≦200 type (1)

40≦H≦60 type (2)

C _n ={(M _n -m _n )/(M _n +m _n )}×100 Formula (3).

[2] The polarizing element protective film according to [1], wherein the base material film and the light diffusion layer are laminated, and the base film has birefringence.

[3] The polarizing element protective film according to [2], wherein the in-plane retardation value of the base film is 400 nm or more.

[4] The polarizing element protective film according to [2] or [3] wherein the base film is mainly composed of a polyester resin.

[5] The polarizing element protective film according to any one of [2] to [4] wherein the substrate film has a thickness of 50 μm or less.

[6] The polarizing element protective film according to any one of [1] to [5] wherein the light-diffusing layer contains a light-transmitting resin and a light-transmitting fine particle.

[7] The polarizing element protective film according to [6], wherein the light diffusion layer has a layer thickness of 10 μm or more and 20 μm or less.

[8] The polarizing element protective film according to [6] or [7], wherein the above-mentioned light transmissive micro The particles include a first light-transmitting fine particle having a weight average particle diameter of 3 to 5.5 μm and a second light-transmitting fine particle having a weight average particle diameter of 7.2 to 9 μm.

[9] The polarizing element protective film according to any one of [6] to [8] wherein the light diffusing layer is formed by a method of coating a coating containing the above-mentioned light transmitting resin And a coating liquid for forming the light-transmitting fine particles to form a coating layer; a compression step of pressing the flat surface against the surface of the coating layer to compress the coating layer; and a curing step of curing the coating layer.

[10] The polarizing element protective film according to any one of [6], wherein the light-diffusing layer has a volume filling ratio of 40% or more.

According to the polarizing element protective film of the present invention, it is possible to constitute an image display device which suppresses generation of a halo caused by transmitted light, and which has an appearance quality with a glossy surface and good display quality.

[Polarizing element protective film]

The polarizing element protective film of the present invention has a light diffusion layer. The light diffusion layer is laminated, for example, on a substrate film. The polarizing element protective film may have other layers than the above-described light diffusion layer and substrate film.

Fig. 1 is a schematic cross-sectional view showing a preferred embodiment of the protective film of the present invention. The polarizing element protective film 100 shown in FIG. 1 of the present invention includes a base film 101 and a light diffusion layer 102 laminated on the base film 101. The light-diffusing layer 102 is a layer in which the light-transmitting resin 103 is a base material, and the light-transmitting fine particles 104 are dispersed in the light-transmitting resin 103. Hereinafter, the polarizing element of the present invention will be described in further detail Protective film.

<Optical characteristics of protective film of polarizing element>

The polarizing element protective film of the present invention has a total value T _c (%) of the transmission image sharpness C _n (%) in the transmission image sharpness measurement test satisfying the relationship of the following formula (1): 100 ≦ T _c ≦ 200 Formula (1) and the total haze value H (%) satisfy the relationship of the following formula (2): 40 ≦ H ≦ 60 Formula (2).

The above-described transmission image sharpness measurement test measures the amount of transmitted light of the test piece (polarizing element protective film) by a light comb having a width n (mm) which is orthogonal to the ray axis of the transmitted light and moved at a speed of 10 mm/min. By. Specifically, it was measured using an Image Clarity measuring instrument (manufactured by Suga Test Instruments). The image sharpness measuring device records the fluctuation of the detected light amount as a waveform by an optical device that vertically transmits the light of the transmission slit as a parallel ray into the test piece, and detects the light comb by moving the transmitted light. The measurement system device is constructed. The ratio of the width of the bright portion to the dark portion of the comb is 1:1, and the width n (mm) is set to four types of 0.125, 0.5, 1, and 2, and the moving speed is set to 10 mm/min.

When the maximum value of the amount of light transmission when the light axis measured in the test has a transmission portion (bright portion) in the light transmitted image clarity of the comb to M _n, the light axis of the optical comb having a shielding portion (dark portion) When the minimum value of the transmitted light amount is set to m _n , the transmission image sharpness C _n (%) is calculated by the following formula (3): C _n = {(M _{n -} m _n ) / (M _n + m _n )}×100 Equation (3).

The total value T _c (%) is the width of the optical comb n (mm) is _0.125 , _0.5 , ₁ , 2, respectively, the four transmission images are sharp C _0.125 (%), C _0.5 (%), C ₁ The sum of (%) and C ₂ (%), so the maximum value that can be taken is 400%.

By satisfying the relationship of the above formula (1) by the sum value T _c (%), the total haze value H (%) satisfies the relationship of the above formula (2), and the surface is provided with gloss, and the haze caused by the transmitted light is suppressed. The resulting polarizing element protective film.

Here, the "total haze value" is a ratio of the total light transmittance Tt indicating the total amount of light transmitted by the light of the polarizing element protective film to the diffused light transmittance Td transmitted by the polarizing element protective film. It is obtained by the following formula (4): total haze (%) = (Td/Tt) × 100 (4).

The total light transmittance Tt is the sum of the parallel light transmittance Tp and the diffused light transmittance Td which are directly 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.

Specifically, the total haze value of the polarizing element protective film was measured in the following manner. In other words, in order to prevent warpage of the film, an optically transparent adhesive is used, and the base film 101 side is bonded to the glass substrate so that the light-diffusing layer 102 of the polarizing element protective film becomes a surface, and a test piece is produced. The total haze value was measured for the test piece. The total haze value is measured by a haze transmittance meter (for example, a haze meter "HM-150" manufactured by Murakami Color Technology Research Co., Ltd.) according to JIS K 7136, and the total light transmittance Tt and the diffused light transmittance (Td). And calculated by the above formula (4).

<Light diffusion layer>

The polarizing element protective film 100 shown in FIG. 1 includes a light diffusion layer 102 laminated on a base film 101. The light diffusion layer 102 is based on the light transmissive resin 103 The layer is formed by dispersing the light-transmitting fine particles 104 in the light-transmitting resin 103. Further, another layer (including an adhesive layer) may be provided between the base film 101 and the light diffusion layer 102.

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 a cured product of a thermosetting resin or a thermoplastic can be used. A cured product of a resin or a metal alkoxide. When an ionizing radiation-curable resin, a thermosetting resin, or a metal alkoxide is used, the resin is cured by irradiation or heating of ionizing radiation to form a light-transmitting resin 103. Among them, in the case of using a polarizing element protective film having a high hardness and provided on the surface of a liquid crystal display device, an ionizing radiation curable resin is preferable in terms of imparting high scratch resistance.

Examples of the ionizing radiation-curable resin include polyfunctional acrylates such as acrylates and methacrylates of polyhydric alcohols; and polyfunctional compounds such as diisocyanates and polyols and hydroxy esters of acrylic acid or methacrylic acid. Acrylic urethane and the like. Further, in addition to these, a polyether resin having an acrylate functional group, a polyester resin, an epoxy resin, an alkyd resin, a acetal resin, a polybutadiene resin, a polythiol polyene can also be used. Resin, etc.

Examples of the thermosetting resin include a phenol resin, a urea melamine resin, an epoxy resin, an unsaturated polyester resin, and a polyfluorene resin, in addition to a thermosetting urethane resin containing an acrylic polyol and an isocyanate prepolymer. Oxygen resin.

Examples of the thermoplastic resin include acetaminophen and nitrocellulose. a cellulose derivative such as acetyl butyl cellulose, ethyl cellulose or methyl cellulose; a vinyl resin such as vinyl acetate and a copolymer thereof, vinyl chloride and a copolymer thereof, vinylidene chloride and a copolymer thereof; An acetal resin such as polyethylene formaldehyde or polyvinyl butyral; an acrylic resin such as an acrylic resin or a copolymer thereof, a methacrylic resin or a copolymer thereof; a polystyrene resin; a polyamide resin; Polyester resin; polycarbonate resin.

As the metal alkoxide, a cerium oxide-based substrate using a decane oxide-based material as a raw material can be used. Specifically, tetramethoxy decane, tetraethoxy decane, or the like can be produced by hydrolysis or dehydration condensation to form an inorganic or organic-inorganic composite substrate (translucent resin).

Further, as the light-transmitting fine particles 104 used in the present invention, organic fine particles or inorganic fine particles having light transmissivity can be used. For example, organic fine particles containing an acrylic resin, a melamine resin, polyethylene, polystyrene, an organic polyoxynoxy resin, an acrylic-styrene copolymer, or the like; or calcium carbonate, ceria, alumina, cesium carbonate Inorganic fine particles such as barium sulfate, titanium oxide, and glass. Further, organic polymer spheres or glass hollow beads can also be used. The light-transmitting fine particles 104 may be composed of one type of fine particles, or may contain two or more kinds of fine particles. The shape of the light-transmitting fine particles 104 may be any of a spherical shape, a flat shape, a plate shape, a needle shape, and an indefinite shape, but is preferably spherical or substantially spherical.

The filling ratio of the light-transmitting fine particles 104 is preferably 40% or more, and more preferably 50% or more. When the filling ratio of the light-transmitting fine particles 104 is within this range, the production of the polarizing element protective film which satisfies the relationship of the above formulas (1) and (2) becomes easy. The filling ratio of the light-transmitting fine particles 104 described in the present specification is as follows The method is calculated. First, an image of the light diffusion layer 102 is obtained by an optical microscope, and the number of the light-transmitting fine particles 104 (5 times average) is randomly selected in an area of 50 μm × 50 μm, and the total fine particles are matched by the adjustment of the light-transmitting fine particles. The numbers are distinguished, and the total volume occupied by the microparticles is calculated from the volume of each microparticle. Further, the average layer thickness of the light diffusion layer 102 was measured and multiplied by an area of 50 μm × 50 μm, and the obtained value was taken as the total volume of the light diffusion layer in the measurement region. The filling ratio of the light-transmitting fine particles 104 is obtained by dividing the total volume occupied by the light-transmitting fine particles 104 by the total volume of the light-diffusing layer and multiplying by 100.

Here, the weight average particle diameter of the light-transmitting fine particles 104 is preferably 0.5 μm or more and 15 μm or less, and more preferably 3 μm or more and 9 μm or less. If the weight average particle diameter of the light-transmitting fine particles 104 is less than 0.5 μm, there is a case where visible light having a wavelength region of from 380 nm to 800 nm is not sufficiently scattered. In the case where the weight average particle diameter exceeds 15 μm, the thickness of the entire light diffusion layer 102 becomes thick, which hinders the thinning of the display. Further, the weight average particle diameter of the light-transmitting fine particles 104 was measured using a Coulter counter (manufactured by Beckman Coulter Co., Ltd.) using a Coulter principle (fine pore resistance method).

The light-transmitting fine particles 104 preferably include a first light-transmitting fine particle having a weight average particle diameter of 3 to 5.5 μm and a second light-transmitting fine particle having a weight average particle diameter of 7.2 to 9 μm. By disposing the light-transmitting fine particles 104 containing the two types of fine particles, the filling ratio of the light-transmitting fine particles 104 is easily made 40% or more, and further 50% or more. Further, even if the light diffusion layer is formed by the following method, the light-transmitting fine particles 104 in the light-transmitting resin can be easily filled. The charge ratio is 40% or more, and further 50% or more, and it is easy to form a polarizing element protective film so as to satisfy the relationship between the above formulas (1) and (2). The method includes a coating step in which the coating is contained. A coating layer is formed by the coating liquid of the photo-resin and the light-transmitting fine particles; a compression step of pressing the flat surface against the surface of the coating layer to compress the coating layer; and a curing step of curing the coating layer. The flat surface is not limited as long as it has a uniform plane. For example, a plate shape or a roll shape made of glass, metal or the like can be used.

It is preferable that the refractive index of the light-transmitting fine particles 104 is larger than the refractive index of the light-transmitting resin 103, and the difference is preferably in the range of from 0.04 to 0.15. When the difference in refractive index between the light-transmitting fine particles 104 and the light-transmitting resin 103 is within the above range, moderate internal scattering caused by the difference in refractive index between the light-transmitting fine particles 104 and the light-transmitting resin 103 occurs. Therefore, it is easy to control the total haze value of the polarizing element protective film in such a manner as to satisfy the relationship of the above formula (2).

Further, the surface of the light diffusion layer (the surface on the side opposite to the base film 101) is preferably formed only of the light-transmitting resin 103. That is, the light-transmitting fine particles 104 preferably do not protrude from the surface of the light-diffusing layer 102 but are completely buried in the light-diffusing layer 102. When the light-transmitting fine particles 104 protrude from the surface of the light-diffusing layer 102, it is difficult to form the polarizing element protective film so that the sum of the sharpness of the transmitted image satisfies the relationship of the above (1).

The layer thickness of the light diffusion layer 102 is preferably 10 μm or more and 20 μm or less. When the thickness is less than 10 μm, the light-transmitting fine particle particles 104 sometimes protrude from the surface of the light-diffusing layer 102. On the other hand, when it exceeds 20 μm, the entire protective film of the polarizing element becomes thick, and it becomes easy to be crimped or easily broken, which is disadvantageous in terms of handling.

Further, the polarizing element protective film of the present invention may further include an antireflection layer laminated to the light diffusion layer 102 (the surface opposite to the substrate film 101) shown in FIG. The antireflection layer is provided to reduce the reflectance as much as possible, and by forming the antireflection layer, it is possible to prevent the display screen from being reflected. Examples of the antireflection layer include a low refractive index layer composed of a material having a lower refractive index than the light diffusion layer 102, and a high refractive index layer composed of a material having a higher refractive index than the light diffusion layer 102. The laminated structure of the low refractive index layer composed of the material having a low refractive index of the high refractive index layer.

<Substrate film>

The base film 101 is a film having birefringence. Preferably, the retardation value R in the plane of the light with respect to the wavelength of 590 nm is 100 to 2500 nm, and more preferably 400 to 1500 nm. When the retardation value in the plane of the base film 11 is less than 100 nm, the haze caused by the birefringence is less likely to occur, and even if a halo is generated, it is difficult to affect the deterioration of the image quality. The retardation value R in the plane of the base film 11 is a value defined by the following formula (5): R = (n _{x -} n _y ) × d Formula (5).

In the formula (5), n _x : refractive index in the in-plane axis direction of the base film, n _y : refraction of the in-plane axis direction of the base film (direction orthogonal to the direction of the slow axis) Rate, d: average thickness of the substrate film.

The material of the base film 101 is not particularly limited, and a known material can be used. For example, a polyester resin including polyethylene terephthalate, a polyolefin resin such as polyethylene or polypropylene, an ethylene-vinyl acetate resin, or an acrylic resin such as polymethyl methacrylate may be mentioned. ,drop A synthetic polymer such as a cycloolefin resin such as an olefin resin; and a natural polymer such as a cellulose resin such as cellulose diacetate or cellulose triacetate. The base film 101 is preferably colorless and transparent, but may be colored or translucent insofar as it does not interfere with the defect detection property for surface recognition or the like.

The method for producing the base film 101 using the above materials is not particularly limited, and it can be produced by a known method such as a solvent casting method or an extrusion method. Further, the base film 101 for performing elongation treatment such as uniaxial stretching or biaxial stretching after film formation can be used. As the base film 101 in which the retardation value R in the above-described range is within the above range, it is preferable to use the base film 101 containing the polyester resin which is subjected to the stretching treatment. For example, the base film 101 containing polyethylene terephthalate which performs extension processing is mentioned.

The stretching is usually carried out continuously while the film roll is unfolded, and is extended by the heating furnace in the forward direction of the roll, in the direction perpendicular to the advancing direction, or both. The temperature of the heating furnace is usually in the range from the vicinity of the glass transition temperature of the resin constituting the base film 101 to the glass transition temperature + 100 °C.

The polyester film used as the base film 101 is a film mainly composed of polyester, and may be a single layer film mainly composed of polyester or a multilayer film having a layer mainly composed of polyester. Moreover, the surface treatment may be performed on both sides or one side of the single-layer film or the multilayer film, and the surface treatment may be surface modification by corona treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation, or the like. The quality may be formed by a film such as coating or vapor deposition of a polymer or a metal. The proportion of the weight of the polyester to the entire polyester film is usually 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more.

Examples of the polyester include polyethylene terephthalate, polyethylene isophthalate, polyethylene 2,6-naphthalenedicarboxylate, polybutylene terephthalate, and p-benzoic acid. Toluene-1,4-cyclohexanedimethyl ester, two or more of these may be used as needed. Among them, polyethylene terephthalate can be preferably used.

The polyethylene terephthalate has a polyester derived from a structural unit of terephthalic acid as a dicarboxylic acid component and a structural unit derived from ethylene glycol as a diol component, preferably a total repeating unit. More than 80% by mole is ethylene terephthalate, and may also contain structural units derived from other copolymerized components. Examples of other copolymerization components include isophthalic acid, 4-(β-oxyethoxy)benzoic acid, 4,4′-dicarboxybiphenyl, 4,4′-dicarboxybenzophenone, and double a dicarboxylic acid component such as (4-carboxyphenyl)ethane, adipic acid, sebacic acid, sodium 5-sulfoisophthalate or 1,4-dicarboxycyclohexane; or propylene glycol, butanediol, new A diol component such as pentanediol, diethylene glycol, cyclohexanediol, an ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

These dicarboxylic acid components or diol components may be used in combination of two or more kinds as needed. Further, a hydroxycarboxylic acid such as p-hydroxybenzoic acid may be used in combination with the above carboxylic acid component or diol component. As the other copolymerization component, a dicarboxylic acid component and/or a diol component containing a small amount of a guanamine bond, a urethane bond, an ether bond, a carbonate bond or the like can also be used. As a method for producing polyethylene terephthalate, a so-called direct polymerization method in which terephthalic acid is directly reacted with ethylene glycol and, if necessary, other dicarboxylic acids and/or other diols can be used; So-called transesterification of transesterification of dimethyl terephthalate with ethylene glycol, and optionally other dimethyl dicarboxylic acids and/or other diols Any manufacturing method such as a reaction method.

A known additive may be blended in the polyester as needed, and examples thereof include a lubricant, an anti-caking agent, a heat stabilizer, an antioxidant, an antistatic agent, a light stabilizer, and an impact resistance improver. However, when a polyester film is used as the base film of the anti-glare film, transparency is usually required, and therefore it is preferable to limit the amount of the additive to a minimum.

The polyester film is preferably uniaxially stretched or biaxially stretched (hereinafter, the polyester film which is uniaxially stretched or biaxially stretched in this manner is simply referred to as "stretched polyester film"). Since the polyester film is excellent in mechanical properties, solvent resistance, scratch resistance, cost, and the like, the optical film using such a polyester film is excellent in mechanical strength and the like, and the thickness can be reduced.

The stretched polyester film can be produced by forming the polyester into a film shape and performing a uniaxial stretching treatment or a biaxial stretching treatment. By performing the stretching treatment, a polyester film having a high mechanical strength can be obtained. The method for producing the stretched polyester film is not particularly limited. For example, as the uniaxially stretched polyester film, a method of melting and extruding the polyester by a tenter at a temperature higher than the glass transition temperature is exemplified. After the press-formed sheet-like unaligned film is laterally stretched, a heat setting treatment is performed. Further, in the case of the biaxially stretched polyester film, there is a method of longitudinally stretching the unaligned film which melts and extrudes the polyester into a sheet shape by a tenter at a temperature higher than the glass transition temperature, and then laterally extends. After that, heat setting treatment is performed. In this case, the stretching temperature is usually 80 to 130 ° C, preferably 90 to 120 ° C, and the stretching ratio is usually 2.5 to 6 times, preferably 3 to 5.5 times. If the stretching ratio is low, there is a tendency that the polyester film does not exhibit sufficient transparency.

Further, in order to reduce the deformation of the alignment main shaft, it is preferable to subject the polyester film to a relaxation treatment before the heat fixation treatment after stretching. The temperature during the relaxation treatment is usually from 90 to 200 ° C, preferably from 120 to 180 ° C. The amount of slack is different depending on the stretching conditions, and it is preferable to set the amount of slack and the temperature at the time of the relaxation treatment so that the heat shrinkage rate at 150 ° C of the polyester film after the relaxation treatment is 2% or less.

The heat setting treatment temperature can be set to 180 to 250 ° C, preferably 200 to 245 ° C. In the heat setting treatment, in order to reduce the deformation of the alignment main shaft and to improve the strength such as heat resistance, it is preferable to first perform the heat setting treatment by the fixed length and then perform the relaxation treatment in the width direction. The amount of relaxation in this case is preferably adjusted so that the heat shrinkage ratio at 150 ° C of the polyester film after the relaxation treatment is 1 to 10%, more preferably 2 to 5%. The maximum value of the deformation of the alignment main axis of the stretched polyester film used in the present invention is usually 10 degrees or less, preferably 8 degrees or less, more preferably 5 degrees or less. When the maximum value of the alignment main axis is larger than 10 degrees, the chromatic aberration tends to become large when it is attached to the liquid crystal display screen. Further, the "maximum deformation of the alignment main axis" of the stretched polyester film can be measured, for example, by the retardation film inspection device RETS system manufactured by Otsuka Electronics Co., Ltd.

The thickness of the base film 101 is preferably 20 to 100 μm, more preferably 30 to 50 μm. When the thickness of the base film 101 is less than 20 μm, it tends to be difficult to handle, and when the thickness exceeds 100 μm, the advantage of thinning tends to be weak.

<Method of Manufacturing Polarizing Element Protective Film>

Secondly, the method for manufacturing the protective film of the polarizing element shown in FIG. Line description. The polarizing element protective film 100 is preferably produced by a method comprising the following steps (A) and (B).

(A) a coating step of applying a coating liquid containing a light-transmitting resin in which the light-transmitting fine particles 104 are dispersed to form a coating layer on the base film 101; and (B) a hardening step of hardening the coating layer .

The coating liquid used in the above step (A) includes the light-transmitting fine particles 104, the light-transmitting resin 103 constituting the light-diffusing layer 102, or a resin forming the same (for example, an ionizing radiation-curable resin, a thermosetting resin, or a metal alkane). Oxide) and other ingredients such as solvents as needed. In the case where an ultraviolet curable resin is used as the resin for forming the light-transmitting resin 103, the coating liquid contains a photopolymerization initiator (radical polymerization initiator). As the photopolymerization initiator, for example, an acetophenone photopolymerization initiator, a benzoin photopolymerization initiator, a benzophenone photopolymerization initiator, and 9-oxosulfuric acid can be used. Photopolymerization initiator, three A photopolymerization initiator, an oxadiazole photopolymerization initiator, and the like. Further, as the photopolymerization initiator, for example, 2,4,6-trimethylbenzimidyldiphenylphosphine oxide or 2,2'-bis(o-chlorophenyl)-4,4' can also be used. ,5,5'-tetraphenyl-1,2'-biimidazole, 10-butyl-2-chloroacridone, 2-ethyl hydrazine, diphenylethylenedione, 9,10-phenanthrenequinone, Camphorquinone, methyl benzoic acid methyl ester, titanium titanate compound, and the like. The amount of the photopolymerization initiator to be used is usually 0.5 to 20 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the resin contained in the coating liquid. Further, in order to make the optical characteristics and surface shape of the light-diffusing film uniform, the dispersion of the light-transmitting fine particles 104 in the coating liquid is preferably dispersed in an isotropic manner.

The coating of the coating liquid onto the substrate film can be carried out, for example, by a gravure coating method, a micro gravure coating method, a bar coating method, a knife coating method, or a gas. It is carried out by a knife coating method, a contact coating method, a squeeze coating method, or the like. When the coating liquid is applied, as described above, it is preferable to adjust the coating layer thickness so that the thickness of the light diffusion layer 102 after curing is 10 μm or more and 20 μm or less.

In order to improve the coating property of the coating liquid or to improve the adhesion, various surface treatments may be performed on the surface (light diffusion layer side surface) of the base film 101. 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 an undercoat layer may be formed on the substrate film, and a coating liquid may be applied to the other layer.

Moreover, in order to improve the adhesion between the polarizing element protective film of the present invention and the polarizing element, it is preferred that the surface of the base film 101 (the surface on the side opposite to the light diffusing layer) is hydrophilized by various surface treatments.

In the above step (B), the coating layer is hardened. When an ionizing radiation-curable resin, a thermosetting resin, or a metal alkoxide is used as the resin for forming the light-transmitting resin 103, the coating layer is formed, and if necessary, dried (solvent removal), preferably When the flat surface is pressed against the surface of the coating layer to compress the coating layer or after compression, irradiation by ionizing radiation (in the case of using an ionizing radiation-curable resin) or heating (using a thermosetting resin) Or in the case of a metal alkoxide, the coating layer is hardened. The ionizing radiation can be appropriately selected from ultraviolet rays, electron beams, near ultraviolet rays, visible light, near infrared rays, infrared rays, X rays, and the like depending on the kind of the resin contained in the coating liquid. Among these, ultraviolet rays and electron beams are preferred, especially in terms of ease of operation and high energy availability. It is preferably ultraviolet light.

As the light source of the ultraviolet light, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra high pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, or the like can be used. Further, an ArF excimer laser, a KrF excimer laser, an excimer lamp, or a synchrotron radiation may 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 can be preferably used.

Further, examples of the electron beam include a Cockcroft-Walton type, a Van de Graaff type, a resonance transformer type, an insulating air transformer type, a linear type, and a high frequency high pressure accelerator type. An electron beam having an energy of 50 to 1000 keV, preferably 100 to 300 keV, which is released by various electron beam accelerators such as a high frequency type.

The T _c and H in the polarizing element protective film can be adjusted to the range specified by the present invention by, for example, the method shown below. First, a polarizing element protective film was produced by the above materials and methods, and T _c and H were measured. As a result, when the value of T _c is too low, any one of reducing the number of added particles of the light-transmitting fine particles, greatly reducing the particle diameter of the light-transmitting fine particles, and thinning the layer thickness of the light-diffusing layer can be performed. When two or more such treatments are disposed or combined, and the value of T _c is too high, the treatment opposite to the above is performed, that is, the number of added particles of the light-transmitting fine particles is increased, and the particles of the light-transmitting fine particles are greatly increased. Any of the treatments of the diameter and the thickness of the thickened light-diffusing layer, or a combination of two or more of these treatments, when the value of H is too low, the number of added light-transmitting fine particles is increased, and the light is transmitted. When any of the treatments of the shape of the fine particles is crushed or the like, or when the value of H is too high, the treatment opposite to the above is performed, that is, the number of added particles of the light-transmitting fine particles is reduced, and the light is transmitted. The shape of the fine particles is a spherical shape or the like, or the treatment is combined, and the polarizing element protective film is again produced, and T _c and H are measured. The production of the polarizing element protective film and the measurement of T _c and H are repeated until the target value of T _{c and} the value of H are obtained.

[Polarizer]

The polarizing element protective film of the present invention is bonded to the surface of the polarizing element to form a polarizing plate including a polarizing element and a polarizing element protective film. Since the polarizing protective film of the present invention suppresses the blooming caused by the transmitted light, the mechanical strength is excellent, and the surface gloss is excellent. Therefore, the polarizing plate using the same suppresses the generation of the halo, and the mechanical strength is excellent, and the surface gloss is excellent. Excellent polarizing plate. As the polarizing element, a known polarizing element can be used. The polarizing element usually contains a polyvinyl alcohol-based resin film that is absorbing iodine or a dichroic dye. The polarizing element protective film of the present invention is bonded to at least one surface of the polarizing element to constitute a polarizing plate. Any one of a polarizing plate disposed on the viewing side of the image display element and a polarizing plate disposed on the back side may be formed. For example, the polarizing element protective film and the polarizing element may be disposed so as to sequentially stack the light diffusion layer 102, the base film 101, and the polarizing element, and the polarizing plate on the viewing side may be formed. For example, the polarizing element protective film and the polarizing element may be disposed so as to form the polarizing element, the base film 101, and the light diffusing layer 102 in order to form the polarizing plate on the back side. The polarizing plate may be formed by bonding the polarizing element protective film of the present invention to both surfaces of one polarizing element.

[Image display device]

The polarizing plate using the polarizing element protective film of the present invention constitutes an image display element and an image display device using the same. Here, the image display element is represented by a liquid crystal panel in which a liquid crystal cell in which liquid crystal is sealed is provided between the upper and lower substrates, and an image is displayed by changing a alignment state of the liquid crystal by applying a voltage. As described above, the image display device including the polarizing element protective film of the present invention suppresses blooming caused by transmitted light, and is excellent in mechanical strength and excellent in surface gloss.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited to the examples. In the following examples, the optical characteristics of the polarizing element protective film and the method for measuring the weight average particle diameter of the light-transmitting fine particles are as follows.

(a) The sum of the clearness C _n of the transmitted image image T _c

The above-described transmission image sharpness measurement test was carried out using an image sharpness measuring device (manufactured by Suga Test Instruments), and when the widths of the optical combs were 0.125 mm, 0.5 mm, 1 mm, and 2 mm, respectively, according to the formula (3) Transmission image clarity C _0.125 , C _0.5 , C ₁ , C ₂ . Then, the total value T _{c of} C _0.125 , C _0.5 , C ₁ , and C ₂ is calculated.

(b) Total haze value H

The total light transmittance Tt and the diffused light transmitted by the diffusion of the polarizing element protective film were measured using a haze transmittance meter (a haze meter "HM-150" manufactured by Murakami Color Technology Research Co., Ltd.) according to JIS K 7136. The transmittance Td is calculated, and the total haze value H is calculated according to the formula (4).

(c) Weight average particle diameter of light-transmitting fine particles

The measurement was performed using a Coulter particle counter (manufactured by Beckman Coulter Co., Ltd.) using the Coulter principle (fine pore resistance method).

<Example 1> (1) Manufacture of mirror metal roll

Industrial chrome plating was performed on the surface of a 200 mm diameter roll (by JIS STKM13A), and then the surface was mirror-polished to produce a mirror metal roll. The chrome surface of the obtained mirror metal roll had a Vickers hardness of 1000. Further, the Vickers hardness was measured using an ultrasonic hardness meter MIC10 (manufactured by Krautkramer Co., Ltd.) in accordance with JIS Z 2244 (the Vickers hardness measurement method is the same in the following examples).

(2) Production of polarizing element protective film

60 parts by weight of pentaerythritol triacrylate and 40 parts by weight of a polyfunctional urethane acrylate (reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate) are mixed into a propylene glycol monomethyl ether solution to form a solid The ultraviolet curable resin composition was obtained by adjusting so that the concentration of the component was 60% by weight. Further, the cured product obtained by removing the propylene glycol monomethyl ether from the composition and cured by ultraviolet light had a refractive index of 1.53.

Next, 25 parts by weight of styrene-based particles having a weight average particle diameter of 7.0 μm as a light-transmitting fine particle and a photopolymerization initiator are added to 100 parts by weight of the solid content component of the ultraviolet curable resin composition. 5 parts by weight of Lucirin TPO (manufactured by BASF Corporation, chemical name: 2,4,6-trimethylbenzimidyloxydiphenylphosphine), using propylene glycol monomethyl ether in a solid content ratio of 60% by weight The coating liquid was prepared by performing dilution.

The coating liquid was applied to a polyethylene terephthalate (PET) film (base film) having a thickness of 38 μm (in-plane retardation value: 1000 nm) at a temperature of 80 ° C. Dry in a dryer for 1 minute. The base film after drying was pressed and adhered to the mirror surface of the mirror metal roll produced in the above (1) by a rubber roller so that the ultraviolet curable resin composition layer became the roll side. In this state, the light from the high-pressure mercury lamp is irradiated with a light intensity of 20 mW/cm ² from the base film side so as to be 300 mJ/cm ² in terms of an h-line converted light meter, and the ultraviolet curable resin composition layer is cured to obtain A polarizing element protective film having a thickness of 14 μm on the flat surface and a polarizing element protective film as shown in FIG. 1 of the base film. This was set as the polarizing element protective film of Example 1.

<Comparative Example 1>

As an optical film of Comparative Example 1, an optical film was used in a biaxially stretched polyethylene terephthalate (PET) film (base film) (trade name: Lumirror, manufactured by Toray Co., Ltd.) It has an anti-glare layer mainly composed of Pentaerythritol Tetraacrylate (PETA) and Trimethylol Hexyllactone (HDI), and does not contain light-transmitting fine particles in the anti-glare layer.

<Comparative Example 2>

As an optical film of Comparative Example 2, an optical film was used in a biaxially stretched polyethylene terephthalate (PET) film (base film) (trade name: Lumirror, manufactured by Toray Co., Ltd.) It has a hard coat layer mainly composed of pentaerythritol tetraacrylate (PETA), triallyl isocyanurate (trade name: TAIC (registered trademark)), and isophorone diisocyanate (IPDI, Isophorone Diisocyanate). Perfluoropolyether in the coating a lubricant and a copolymer of styrene, ethylene glycol dimethacrylate (EDMA) ).

<Comparative Example 3>

As an optical film of Comparative Example 3, an optical film was used in a biaxially stretched polyethylene terephthalate (PET) film (base film) (trade name: Lumirror, manufactured by Toray Co., Ltd.) It has a hard coat mainly composed of pentaerythritol tetraacrylate (PETA) and isophorone diisocyanate (IPDI), and contains a light-transmitting fine particle (styrene, B) having a weight average particle diameter of 6.5 μm in the hard coat layer. a copolymer of diol dimethacrylate (EDMA) and methyl methacrylate (MMA) and Al particles and Mg agglomerates having a weight average particle diameter of 100 nm.

<Comparative Example 4>

As an optical film of Comparative Example 4, an optical film having a biaxially oriented polyethylene terephthalate (PET) film (base film) (trade name: Lumirror, manufactured by Toray Co., Ltd.) was used. a hard coat mainly composed of pentaerythritol tetraacrylate (PETA) and isophorone diisocyanate (IPDI), and contains light-transmitting fine particles (styrene and ethylene glycol) having a weight average particle diameter of 3 μm in the hard coat layer. Copolymer of dimethacrylate).

<Comparative Example 5>

As an optical film of Comparative Example 5, an optical film having a biaxially oriented polyethylene terephthalate (PET) film (base film) (trade name: Lumirror, manufactured by Toray Co., Ltd.) was used. Pentaerythritol IV A hard coat layer formed of acrylate (PETA) containing an amorphous shape of cerium oxide microparticles in the hard coat layer.

(Production of liquid crystal display device)

Further, the obtained polarizing element protective film of Example 1 and the optical films of Comparative Examples 1 to 4 were used to produce a liquid crystal display device, and the haze and the surface gloss caused by the transmitted light were evaluated in accordance with the following method. First, the viewing-side polarizing plate is peeled off from the liquid crystal display device "AQUOS (registered trademark) LC-20AX5" manufactured by Sharp Co., Ltd., and is attached to the original polarizing plate in the direction coaxial with the original polarizing plate. The polarizing element protective film and the optical films of Comparative Examples 1 to 4 were used as a polarizing plate of the viewing side protective film to produce a liquid crystal display device.

(evaluation of fainting)

The obtained liquid crystal display device was white-displayed, and the generation of blooming caused by transmitted light was visually evaluated according to the following criteria:

A: Almost no vignetting

C: Faint spots are clearly visible. The results are shown in Table 1.

(Evaluation of the gloss of the surface)

The obtained liquid crystal display device was displayed in black, and the gloss of the surface was visually evaluated according to the following criteria based on the angle at which the fluorescent lamp was reflected on the surface of the liquid crystal display device:

A: The surface is shiny

B: The surface is slightly shiny

C: The surface is dull. The results are shown in Table 1.

According to Table 1, it is understood that the total value T _{c of the} transmission image clarity satisfies the relationship of the formula (1), and the polarizing element protective film of the embodiment 1 in which the total haze value H satisfies the relationship of the formula (2) is suppressed by the transmitted light. The fainting is produced and the surface is shiny.

(analysis of test results)

Fig. 2 is a graph obtained by plotting the relationship between the total haze value H of the polarizing element protective film of Example 1 of Table 1 and the optical film of Comparative Examples 1 to 5 and the total value T _c of the transmission image sharpness. As shown in Fig. 2, the relationship between the total haze value H of the optical film (usually an optical film) of Comparative Examples 1 to 5 and the total value T _c of the transmission image sharpness is derived from the plotted curve 200. On the other hand, the plot of Example 1 largely deviates from the curve 200. In the relationship with the curve 200, it is predicted that if the relationship between the total haze value H and the total value T _c of the transmission image sharpness is located in the optical film of the peripheral region 201 of the first embodiment, it can be constructed and implemented. Example 1 similarly suppresses the generation of a halo caused by transmitted light and has an image display device having a glossy surface, thereby deriving the relationship between the formulas (1) and (2).

100‧‧‧Polarized element protective film

101‧‧‧Substrate film

102‧‧‧Light diffusion layer

103‧‧‧Translucent resin

104‧‧‧Translucent fine particles

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view showing a preferred embodiment of a protective film for a polarizing element of the present invention. Surface map.

2 is a graph obtained by plotting the relationship between the total haze value H of the polarizing element protective film of Example 1 and the optical film of Comparative Examples 1 to 5 and the total value T _c of the transmission image sharpness.

100‧‧‧Polarized element protective film

101‧‧‧Substrate film

102‧‧‧Light diffusion layer

103‧‧‧Translucent resin

104‧‧‧Translucent fine particles

Claims (10)

A polarizing element protective film having a light diffusing layer, and a total value T _c (%) of transmission image sharpness C _n (%) in a transmission image sharpness measurement test satisfies the following formula (1) Relationship, and the total haze value H (%) satisfies the relationship of the following formula (2), the light diffusion layer has a flat surface, and the above-described transmission image sharpness measurement test is orthogonal to the ray axis of the transmitted light and is 10 mm a light comb of a width n (mm) of a speed of movement of /min, and the amount of transmitted light of the test piece is measured, and the amount of transmitted light when the transmission portion of the optical comb is present on the ray axis in the above-described transmission image sharpness measurement test when the maximum value is set to m _n, the light-axis has a minimum value when the amount of light transmission of the light shielding portion of the optical comb to m _n the case of the transmission image clarity C _n (%) according to the following formula based (3), the total value T _c is calculated as the transmission image clarity C _0.125 , C _0.5 , C ₁ , C ₂ when the width n (mm) of the optical comb is _0.125 , _0.5 , ₁ , _{2, respectively.} The sum of the values, 100 ≦ T _c ≦ 200 Formula (1) 40 ≦ H ≦ 60 Equation (2) C _n = {(M _{n -} m _n ) / (M _n + m _n )} × 100 Formula (3). The polarizing element protective film according to claim 1, wherein the base material film and the light diffusion layer are laminated, and the base film has birefringence. The polarizing element protective film of claim 2, wherein the substrate film is in-plane The retardation value is 400 nm or more. The polarizing element protective film of claim 2, wherein the base film is mainly composed of a polyester resin. The polarizing element protective film of claim 2, wherein the substrate film has a thickness of 50 μm or less. The polarizing element protective film of claim 1, wherein the light diffusing layer contains a light transmitting resin and a light transmitting fine particle. The polarizing element protective film of claim 6, wherein the light diffusion layer has a layer thickness of 10 μm or more and 20 μm or less. The polarizing element protective film according to claim 6, wherein the light-transmitting fine particles contain first light-transmitting fine particles having a weight average particle diameter of 3 to 5.5 μm and second light-transmitting fine particles having a weight average particle diameter of 7.2 to 9 μm. The polarizing element protective film according to claim 6, wherein the light diffusing layer is formed by a method of applying a coating liquid containing the light transmitting resin and the light transmitting fine particles. Forming a coating layer; a compression step of pressing the flat surface against the surface of the coating layer to compress the coating layer; and a hardening step of hardening the coating layer. The polarizing element protective film according to claim 6, wherein the light-diffusing layer has a volume filling ratio of 40% or more.