JP2015055833A - Polarizer protective film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film that has excellent visibility and adhesiveness.SOLUTION: A polarizer protective film has, at least on one surface, a coating layer including a copolymer latex having a diolefin monomer and vinyl monomer as constituents, and is composed of an orientation polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.

Description

  The present invention relates to a polarizer protective film and a polarizing plate and a liquid crystal display device using the same. Specifically, the present invention relates to a polarizer protective film, a polarizing plate, and a liquid crystal display device that can suppress generation of rainbow spots.

  A polarizing plate used in a liquid crystal display device (LCD) is usually composed of a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like and sandwiched between two polarizer protective films. In general, a triacetyl cellulose (TAC) film is used. In recent years, with the thinning of LCDs, there has been a demand for thinner polarizing plates. However, if the thickness of the TAC film used as the protective film is reduced for this purpose, sufficient mechanical strength cannot be obtained and moisture permeability deteriorates. Further, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

  Therefore, it has been proposed to use a polyester film instead of the TAC film so that the polarizing plate can be made thin so that high durability can be maintained even if the thickness is small as a polarizer protective film (Patent Documents 1 to 3). ).

  The polyester film is superior to the TAC film in durability, but unlike the TAC film, the polyester film has birefringence. Therefore, when the polyester film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, a rainbow-like color spot is generated when observed from an oblique direction, and the image quality is deteriorated. . Therefore, in patent documents 1-3, the countermeasure which makes retardation small is made by using copolyester as polyester. However, even in that case, the iridescent color spots could not be completely eliminated.

  Moreover, since the polyester film has lower adhesion to the polarizer than the TAC film, it has been studied to improve the adhesion by forming an easy adhesion layer on the surface layer of the film.

In Patent Document 4, the corona treatment is applied to the polyester film, and the adhesiveness is expressed by laminating two easy-adhesion layers. However, a plurality of steps are necessary, and productivity is sacrificed. Also, a hard coat layer may be provided on the surface of the polarizer protective film opposite to the side on which the polarizer is laminated in order to improve the scratch resistance of the film and prevent sticking during lamination on other films. . However, it was necessary to provide a hard coat layer having sufficient light diffusibility in order to reduce iridescent unevenness due to birefringence interference generated in a film using a polyester resin by scattering.

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A JP 2008-3541 A WO2011-162198

  As means for solving the above problems, it is disclosed that a white light emitting diode is used as a backlight light source and an oriented polyester film having a certain retardation is used as a polarizer protective film (Patent Document 5). However, the inventors have made further studies on the liquid crystal display device having such a configuration, and even in such an improved liquid crystal display device, polyester as a polarizer protective film is provided on both of the pair of polarizing plates. In the case of using a film, when observed from an oblique direction, rainbow spots may still occur depending on the angle, and a new problem has been discovered that adhesion to the polarizer and hard coat layer is insufficient. . Therefore, the present invention does not require a light-diffusing hard coat layer, and suppresses the occurrence of rainbow spots when an oriented polyester film is used as a polarizer protective film for both of a pair of polarizing plates of a liquid crystal display device. The main problem is to improve the adhesion with a polarizer or the like.

  As a result of examining the above problems day and night, the present inventor has controlled the retardation of the oriented polyester film used as the polarizer protective film and the characteristic of the Nz coefficient represented by | ny-nz | / | ny-nx |. In the case where a polyester film is used as a polarizer protective film for both of a pair of polarizing plates of a liquid crystal display device, the generation of rainbow spots is effectively suppressed, and a coating layer having a specific composition is provided on the surface layer to provide polarized light. It has been found that the adhesiveness with the child can be improved. The present invention has been completed as a result of further research and improvement based on such knowledge.

The representative present invention is as follows.
Item 1.
From an oriented polyester film having a coating layer containing a copolymer latex comprising a diolefin monomer and a vinyl monomer as constituent components on at least one surface and having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less A polarizer protective film.
Item 2.
Item 2. The polarizer protective film according to Item 1, wherein the orientation degree of the oriented polyester film is 0.13 or less.
Item 3.
Item 3. The polarizer protective film according to Item 1 or 2, wherein the oriented polyester film comprises at least three layers, an ultraviolet absorber is contained in a layer other than the outermost layer, and the light transmittance at 380 nm is 20% or less.
Item 4.
Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
The polarizing plate whose polarizer protective film of at least one side is the polarizer protective film in any one of claim | item 1-3.
Item 5.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
The polarizer according to any one of Items 1 to 3, wherein at least one of the polarizer protective films of the polarizing plate disposed on the incident light side and at least one of the polarizer protective films of the polarizing plate disposed on the outgoing light side are A liquid crystal display device which is a protective film.
Item 6.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
Item 4. The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side, and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side, A liquid crystal display device which is a polarizer protective film.
Item 7.
Item 7. The liquid crystal display device according to item 5 or 6, wherein the white light source having a continuous emission spectrum is a white light emitting diode.

  If it is a polarizer protective film of this invention, even if it is a case where an orientation polyester film is used as both polarizer protective films of a pair of polarizing plate which a liquid crystal display device has, generation | occurrence | production of an rainbow spot can be suppressed. Excellent visibility. Moreover, the polarizer protective film of this invention is excellent in adhesiveness with a polarizer etc., and can improve the durability of a polarizing plate and a liquid crystal display device. Therefore, the present invention makes it possible to further reduce the thickness of the liquid crystal display device while maintaining sufficient mechanical strength, and in turn reduce the manufacturing cost.

1. 2. Liquid Crystal Display Device In general, a liquid crystal display device is composed of a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight light source toward the image display side (viewing side or outgoing light side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the side facing the backlight light source in the rear module, and is disposed on the image display side (viewing side or outgoing light side) in the front module.

2. Backlight Light Source The liquid crystal display device of the present invention includes at least a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may have other constituent members other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film and the like as appropriate.

  The configuration of the backlight may be an edge light method using a light guide plate, a reflection plate, or the like as a constituent member, or a direct type. In the present invention, it is preferable to use a white light source having a continuous broad emission spectrum as a backlight light source of a liquid crystal display device. Here, the continuous broad emission spectrum means an emission spectrum in which there is no wavelength at which light intensity becomes zero in a wavelength region of at least 450 nm to 650 nm, preferably in the visible light region. As such a white light source having a continuous broad emission spectrum, for example, a white LED can be exemplified, but the present invention is not limited thereto.

  The white LED usable in the present invention includes a phosphor type, that is, an element that emits white light by combining a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor, or an organic light emitting diode (Organic light diode). -Emitting diode (OLED). Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. Among white LEDs, white light-emitting diodes, consisting of light-emitting elements that combine blue light-emitting diodes using compound semiconductors with yttrium, aluminum, and garnet-based yellow phosphors, have a continuous and broad emission spectrum and have a luminous efficiency. Therefore, it is suitable as the backlight light source of the present invention. Since the white LED has low power consumption, the liquid crystal display device of the present invention using the white LED contributes to energy saving.

  Fluorescent tubes such as cold-cathode tubes and hot-cathode tubes that have been widely used as backlight light sources have a discontinuous emission spectrum whose emission spectrum has a peak at a specific wavelength. Therefore, since it is difficult to obtain the desired effect of the present invention, it is not preferable as the light source of the liquid crystal display device of the present invention.

3. Polarizer Protective Film The polarizing plate has a configuration in which two polarizer protective films are bonded to a polarizer in which PVA or the like is dyed with iodine. The polarizing plate used in the present invention is an oriented polyester that satisfies at least one of two polarizer protective films with a specific range of retardation and a physical property of Nz coefficient represented by | ny-nz | / | ny-nx |. Use film.

3-1. Retardation It is preferable that the oriented polyester film used for the polarizer protective film used in the present invention has a retardation of 4000 to 30000 nm. This is because when the retardation is less than 4000 nm, an interference color is exhibited when the liquid crystal display device is observed from an oblique direction, so that good visibility cannot always be ensured. The preferred retardation of the oriented polyester film is 4500 nm or more, then preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, and even more preferably 10,000 nm or more.

  The upper limit of the retardation of the oriented polyester film is 30000 nm. Even if an oriented polyester film having a retardation higher than that is used, a further improvement effect of visibility is not substantially obtained, and as the retardation increases, the thickness of the film is considerably increased, and the handleability as an industrial material is improved. It is because it falls.

  The retardation value of the oriented polyester film can be determined by measuring the biaxial refractive index and thickness according to a known method. For example, it can also measure using commercially available automatic birefringence measuring apparatuses, such as KOBRA-21ADH (Oji Scientific Instruments).

  As shown in Patent Document 5, when an oriented polyester film is used as a polarizer protective film for only one of a pair of polarizing plates, the retardation of the oriented polyester film is controlled in the range of 3000 to 30000 nm and is continuously used as a light source. By adopting a white light source having a broad spectrum of emission, the generation of rainbow spots is suppressed. The principle is considered as follows.

  That is, when a birefringent or oriented polyester film is disposed on one side of the polarizer, the linearly polarized light emitted from the polarizer is disturbed when passing through the polyester film. And the transmitted light shows the interference color peculiar to the retardation which is the product of the birefringence and the thickness of the polyester film. Therefore, when a light source having a discontinuous emission spectrum, such as a cold cathode tube or a hot cathode tube, is used as the light source, the transmitted light intensity varies depending on the wavelength, and a rainbow-like color spot is exhibited.

  On the other hand, when light having a continuous and broad emission spectrum in a wavelength region of at least 450 nm to 650 nm, preferably in the visible light region, passes through the birefringent body, the interference color spectrum becomes an envelope shape. Therefore, by controlling the retardation of the polyester film, a spectrum similar to the emission spectrum of the light source can be obtained. In this way, by making the emission spectrum of the light source similar to the envelope shape of the interference color spectrum by the transmitted light that has passed through the birefringent body, visibility is not noticeable without rainbow-like color spots. It is thought to improve.

  However, as described above, when the oriented polyester film is used as the polarizer protective film in both of the pair of polarizing plates, rainbow spots may still be observed. Although the present invention makes it possible to suppress the occurrence of such rainbow spots, the principle has not been fully elucidated.

3-2. Nz coefficient The oriented polyester film used for the polarizer protective film is
| Ny-nz | / | nynx |
It is preferable that the Nz coefficient represented by is 1.7 or less. The Nz coefficient can be obtained as follows. The orientation axis direction of the film is determined using a molecular orientation meter (manufactured by Oji Scientific Instruments, MOA-6004 type molecular orientation meter), and the biaxial refractive index (ny, nx, However, ny> nx) and the refractive index (nz) in the thickness direction are determined by an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). The Nz coefficient can be obtained by substituting nx, ny, and nz obtained in this way into an expression represented by | ny-nz | / | ny-nx |.

  If the Nz coefficient of the oriented polyester film exceeds 1.7, rainbow spots may occur depending on the angle when the liquid crystal display device is observed from an oblique direction. The Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less. The lower limit value of the Nz coefficient is 1.2. This is because it is difficult in terms of manufacturing technology to obtain a film of less than 1.2. In order to maintain the mechanical strength of the film, the lower limit value of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and further preferably 1.45 or more.

3-3. Arrangement of Polarizer Protective Film In the liquid crystal display device of the present invention, the oriented polyester film having the specific retardation and the Nz coefficient is used as both polarizer protective films of a pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate disposed on the incident light side with respect to the liquid crystal and a polarizing plate disposed on the outgoing light side with respect to the liquid crystal. That is, the oriented polyester film is used for both a polarizing plate on the incident light side and a polarizing plate on the outgoing light side. The oriented polyester film only needs to be used as at least one of the two polarizer protective films constituting each polarizing plate, and may be used for both.

  In a preferred embodiment, the oriented polyester film is used as a polarizer protective film on the incident light side of the polarizing plate on the incident light side, and as a polarizer protective film on the outgoing light side of the polarizing plate on the outgoing light side. used. When the oriented polyester film is used for only one of the two polarizer protective films constituting the polarizing plate, an arbitrary polarizer protective film (for example, a TAC film) can be used for the other. When the oriented polyester film is used as the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the incident light side and the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the outgoing light side, the polarization of the liquid crystal cell Since there is a possibility of changing the characteristics, the polarizer protective film at these positions is a polarizer protective film other than the oriented polyester film (for example, a TAC film, an acrylic film, or a norbornene-based film). It is preferable to use a film having no birefringence.

3-4. Planar orientation coefficient In addition to controlling the retardation value and Nz coefficient of the oriented polyester film to the specific range described above, the plane orientation degree represented by (nx + ny) / 2-nz is more reliably reduced to a specific value or less. Iridescents can be completely eliminated when a polyester film is used as a polarizer protective film for both of the pair of polarizing plates. Here, the values of nx, ny, and nz are obtained by the same method as for the Nz coefficient. The degree of plane orientation of the oriented polyester film is preferably 0.13 or less, more preferably 0.125 or less, and still more preferably 0.12 or less. By setting the degree of plane orientation to 0.13 or less, it is possible to completely eliminate rainbow spots observed depending on the angle when the liquid crystal display device is observed from an oblique direction. The plane orientation degree is preferably 0.08 or more, and more preferably 0.10 or more. If the degree of plane orientation is less than 0.08, the film thickness varies, and the retardation value may be non-uniform in the film plane.

3-5. Retardation ratio The ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the oriented polyester film is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6. Above, especially preferably 0.89 or more. This is because as the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is larger, the birefringence action is more isotropic, and the occurrence of rainbow-like color spots due to the observation angle is less likely to occur. In a complete uniaxial (uniaxial symmetry) film, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2. However, as will be described later, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered as the film approaches a complete uniaxial (uniaxial symmetry) film.

  Therefore, the upper limit of the ratio of retardation in the thickness direction (Re / Rth) is preferably 1.2 or less, more preferably 1 or less. In order to completely suppress the occurrence of rainbow-like color spots due to the observation angle, the ratio of retardation to thickness direction retardation (Re / Rth) does not have to be 2, and 1.2 or less is sufficient. Even if the ratio is 1.0 or less, it is possible to satisfy the viewing angle characteristics (180 degrees left and right, 120 degrees up and down) required for the liquid crystal display device.

3-6. Thickness unevenness In order to suppress the variation in retardation of the oriented polyester film, it is preferable that the thickness unevenness of the film is small. In this respect, the uneven thickness of the oriented polyester film is preferably 5% or less, more preferably 4.5% or less, still more preferably 4% or less, and more preferably 3% or less. Particularly preferred.

3-7. Thickness The thickness of the oriented polyester film is not particularly limited as long as the effect of the present invention is not hindered, but is usually 15 to 300 μm, preferably 15 to 200 μm. When the film thickness is less than 15 μm, the anisotropy of the mechanical properties of the film becomes remarkable, and tearing, tearing, and the like may occur. A particularly preferable lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes too thick, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. A particularly preferable upper limit of the thickness is 100 μm, which is about the same as a general TAC film.

3-8. Polyester resin The oriented polyester film used in the present invention can be obtained from any polyester resin. The type of the polyester resin is not particularly limited, and any polyester resin obtained by condensing a dicarboxylic acid and a diol using a known antimony, titanium, germanium-based catalyst, or the like can be used.

  Examples of the dicarboxylic acid component that can be used in the production of the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 , 5-Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid , Hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyl Adipine , Pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

  Examples of the diol component that can be used for the production of the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1 , 3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. Can be mentioned.

  The dicarboxylic acid component and the diol component constituting the polyester resin can be used alone or in combination of two or more. Suitable polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and more preferably polyethylene terephthalate and polyethylene naphthalate. Furthermore, other copolymer components may be included. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and a large retardation can be obtained relatively easily even if the film is thin.

3-9. Light Transmittance The oriented polyester film desirably has a light transmittance of 20% or less at a wavelength of 380 nm from the viewpoint of suppressing deterioration of optical functional dyes such as iodine dyes contained in the polarizer. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the optical functional dye can be prevented from being deteriorated by ultraviolet rays. The light transmittance is measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

  The transmittance of the oriented polyester film at a wavelength of 380 nm can be controlled to 20% or less by appropriately adjusting the type and concentration of the ultraviolet absorber to be blended and the thickness of the film. As the ultraviolet absorber used in the present invention, a known ultraviolet absorber can be appropriately selected and used. Specific examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency.

  Examples of the organic ultraviolet absorber include benzotriazole, benzophenone, and cyclic imino ester, and combinations thereof. However, the organic ultraviolet absorber is not particularly limited as long as it is within the absorbance range defined in the present invention. However, from the viewpoint of durability, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

  Examples of the benzophenone ultraviolet absorber, benzotriazole ultraviolet absorber, and acrylonitrile ultraviolet absorber include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2 ′ -Dihydroxy-4,4'-dimethoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- (2′-Hydroxy-3′-tert-butyl-5′- Tilphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2′-methylenebis (4- ( 1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, etc. Examples of cyclic imino ester UV absorbers include 2,2 ′-(1 , 4-phenylene) bis (4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazine-4- ON, 2-phenyl-3,1-benzoxazin-4-one, etc. These UV absorbers may be used alone or in combination of two or more.

  When an ultraviolet absorbent is blended in the oriented polyester film, it is preferable that the oriented polyester film has a multilayer structure of three or more layers, and the ultraviolet absorbent is added to a layer other than the outermost layer (ie, the intermediate layer) of the film.

3-10. Other components, etc. In addition to the ultraviolet absorber, it is also preferable to add various additives to the oriented polyester film as long as the effects of the present invention are not hindered. Examples of additives include inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants, and antigelling agents. And surfactants.

3-11. Lubricant Particles as a lubricant may be blended in the oriented polyester film in order to improve handling and lubricity. However, in order to achieve high transparency, it is preferable to reduce the particle content in the polyester film. More preferably, the oriented polyester film has a multilayer structure of three or more layers, and particles are added to the outermost layer of the film.

  As a method of blending the inert particles with polyester, a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder It can be carried out.

  The inert particles contained in the outermost layer include calcium carbonate, calcium phosphate, amorphous silica, spherical silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, fluoride. Inorganic particles such as calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, Examples thereof include heat-resistant polymer fine particles such as polytetrafluoroethylene particles. Of these, silica is most suitable in that it can ensure a film with higher transparency because its refractive index is relatively close to that of polyester.

4). Easy-adhesive layer In the present invention, in order to improve the adhesion to a polarizer or the like, at least one side of the oriented polyester film, from a copolymer latex comprising a diolefin monomer and a vinyl monomer on at least one side It is preferable to have a coating layer. The copolymer latex composed of the diolefin monomer and the vinyl monomer may contain other monomers. Examples of the other monomer include monomers having an acryloyl group, a methacryloyl group, or an allyl group. These polymerization methods are not particularly limited, and examples thereof include emulsion polymerization in an aqueous medium in the presence of a polymerization initiator, an emulsifier, and a polymerization chain transfer agent.
The copolymer latex may be used alone, but may be used in combination with other acrylate latex, methacrylic latex, styrene latex, polyester resin, polyurethane resin emulsion, and the like.

  Examples of the diolefin monomer that is one monomer forming the copolymer include conjugated dienes such as butadiene, isoprene, and chloroprene, and butadiene is particularly preferably used.

  The vinyl monomer that is the other component of the copolymer may be any monomer that is inherent to a vinyl group, but is preferably the following: styrene, 2-vinylpyridine, acrylonitrile, methacrylic acid Methyl, vinyl chloride, vinyl acetate and their derivatives, alkyl esters of acrylic acid, acrylamide, methacrylamide, acrolein, methacrolein, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, allyl acrylate, allyl Examples include methacrylate, N-methylol acrylamide, N-methylol methacrylamide, vinyl isocyanate, allyl isocyanate, and the like.

  Examples of the styrene derivatives include methyl styrene, dimethyl styrene, ethyl styrene, diethyl styrene, isopropyl styrene, butyl styrene, hexyl styrene, cyclohexyl styrene, decyl styrene, benzyl styrene, chloromel styrene, trifluoromethyl styrene, and ethoxymethyl. Styrene, acetoxymethylstyrene, methoxystyrene, 4-methoxy-3-methylstyrene, dimethoxystyrene, chlorostyrene, dichlorostyrene, trichlorostyrene, tetrachlorostyrene, pentachlorostyrene, bromostyrene, dibromostyrene, iodostyrene, fluoro Styrene, trifluorostyrene, 2-bromo-4-trifluoromethylstyrene, 4-fluoro-3-trifluoromethylstyrene, It can be exemplified sulfonyl benzoic acid methyl ester.

  As other copolymer components, acrylates such as acrylate, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, divinylbenzene, 1,5-hexadiene-3-in, hexa Mention may be made of divinyls such as triene, divinyl ether, divinyl sulfone, diallyl phthalate, diallyl carbinol, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane dimethacrylate, allyls, di or trimethacrylates.

  It is preferable that content of the diolefin monomer in a copolymer is 10-60 mass% of the whole copolymer, More preferably, it is 15-40 mass%. The vinyl monomer is preferably 90 to 40% by mass of the whole, and particularly preferably the vinyl monomer, particularly styrenes, is 70 to 40% by mass of the total copolymer. Moreover, it is preferable that monomer components other than a diolefin monomer and a vinyl monomer are 10 mass% or less as the whole copolymer. The content of these copolymers in the easy-adhesion layer is preferably 50% by mass or more, more preferably 75% by mass or more. If the content of the copolymer in the easy-adhesion layer is less than 50% by mass, characteristics such as sufficient adhesiveness with a water-based or UV-curing type polarizer or the like cannot be obtained.

  It is preferable to use a crosslinking agent in combination with the copolymer latex. Examples of the crosslinking agent include epoxy-based, oxazoline-based, carbodiimide-based, isocyanate-based, aziridine-based, melamine-based, and triazine-based crosslinking agents. The crosslinking agent is particularly preferably used in combination with a dichloro-s-triazine-based crosslinking agent. The combined use of the dichloro-s-triazine-based crosslinking agent significantly improves the adhesive strength under normal humidity conditions, high humidity conditions, and low humidity conditions.

  The dichloro-s-triazine-based crosslinking agent used is shown below.

  General formula (1)

  (In general formula (1), A represents an alkyl group, a cyclic alkyl group, an aryl group, an alkyl group, a metal, or a hydrogen atom.)

And / or general formula (2)

(In the general formula (2), R ¹ and R ² are hydrogen, an alkyl group, a cyclic alkyl group, an aryl group, an alkyl group, —NHR ³ (R ³ is an alkyl group, an acyl group), R ¹ and R ² are And may form a 5- to 6-membered ring containing O, S, and N—R ⁴ (R ⁴ is an alkyl group).

  These dichloro-s-triazine crosslinking agents can be added in an amount of 0.1 to 100 parts by mass with respect to 100 parts by mass of the monomer mixture. When the addition amount of the dichloro-s-triazine-based crosslinking agent is less than 0.1 parts by mass, the adhesion is not sufficiently improved, and the crack prevention effect, antistatic property, scratch resistance and water resistance under low humidity conditions are also insufficient. Such effects as solvent resistance tend to be insufficient. On the other hand, when the added amount of the dichloro-s-triazine-based crosslinking agent exceeds 100 parts by mass, a large amount of unreacted crosslinking agent remains and the adhesiveness is lowered, which is not preferable.

  Specific examples of these dichloro-s-triazine-based crosslinking agents include 2,4-dichloro-6-hydroxy-s-triazine sodium salt, 2,4-dichloro-6-methylhydrazino-s-triazine, 2, 4-dichloro-6-phenylhydrazino-s-triazine and the like.

  By providing a second easy-adhesive layer (second adhesive layer) containing a hydrophilic polymer as the main binder on the above-mentioned easy-adhesive layer, it is possible to further improve the adhesiveness with a polarizer or the like. .

  Here, as the hydrophilic polymer, for example, acylated gelatin such as gelatin, phthalated gelatin, maleated gelatin, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, acrylic acid, methacrylic acid, amide or the like was grafted onto gelatin. Grafted gelatin, polyvinyl alcohol, polyhydroxyalkyl acrylate, polyvinyl pyrrolidone, copoly-vinyl pyrrolidone-vinyl acetate, casein, agarose, albumin, sodium alginate, polysaccharide, agar, starch, grafted starch, polyacrylamide, N-substituted acrylamide, A synthetic or natural hydrophilic polymer compound such as a homo- or copolymer such as N-substituted methacrylamide or a partial hydrolyzate thereof is used. These are used alone or in combination. A preferred hydrophilic polymer is gelatin or a derivative thereof.

  The easy-adhesion layer of the oriented polyester film can be provided by applying a coating solution containing the above composition on the polyester film surface during or after film formation. In film formation, after apply | coating to the single side | surface or both surfaces of the unstretched film or the uniaxially stretched film extended | stretched to the vertical direction, it can dry at 100-150 degreeC, and can be further obtained by extending | stretching to a horizontal direction. In addition, after film formation, the surface of the stretched film is subjected to surface treatment with corona, plasma, flame or the like, if necessary, and then applied to one or both sides and then dried at 100 to 180 ° C. be able to.

Since the oriented polyester film has a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less, the adhesiveness between the easy adhesion layer and the film surface is better than that of a normal oriented polyester film. Details are unknown, but since the oriented polyester film controls the ratio of the longitudinal draw ratio and the transverse draw ratio as described later, the orientation of the polyester molecules on the film surface differs in the biaxial direction, and the resin molecules in the coating layer It is presumed that it becomes easy to get involved with. As a result, when an easy-adhesion layer is provided after film formation, the film surface has sufficient coatability and adhesion with the easy-adhesion layer even without surface treatment such as corona. Processing is not essential.

The oriented polyester film is not indispensable in order to enhance the adhesion with a polarizer or the like, but an easy adhesion layer may be further provided on the easy adhesion layer. That is, you may provide the 2nd layer of an easily bonding layer. When the second easy-adhesion layer is provided, it may be applied twice by the same method described above, or the first layer may be provided during film formation, and the second layer may be provided after film formation. Is possible. The final coating amount of the first easy-adhesion layer is preferably controlled to 0.05 to 0.2 g / m ² . If the coating amount is less than 0.05 g / m ² , adhesion with the obtained polarizer or the like may be insufficient. On the other hand, when the coating amount exceeds 0.2 g / m ² , blocking resistance may be lowered. When providing an easily bonding layer on both surfaces of a polyester film, the application quantity of an easily bonding layer on both surfaces may be the same or different, and can be independently set within the above range. Moreover, when providing a 2nd layer, it is preferable to manage the application quantity of the final easily bonding layer of the 2nd layer to 0.05-1.0 g / m < ² >. If it is thinner than 0.05 μm, it is difficult to obtain sufficient adhesiveness, and if it is thicker than 1.0 μm, the adhesive effect is saturated.

  It is preferable to add particles to the easy-adhesion layer according to the necessity of slipperiness, such as the presence or absence of particles in the polyester film itself. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the coating layer. As particles to be included in the easy adhesion layer, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, Examples include inorganic particles such as calcium fluoride, and organic polymer particles such as styrene, acrylic, melamine, benzoguanamine, and silicone. These may be added to the easy-adhesion layer alone or in combination of two or more.

  The measurement of the average particle diameter of said particle | grain can be performed with the following method. Take a picture of the particles with a scanning electron microscope (SEM) and at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) Distance) is measured, and the average value is taken as the average particle diameter.

  The coating solution can be applied using a known method. Examples include reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method and the like. These methods can be performed alone or in combination.

5. Functional layer The polarizer protective film used in the present invention is for the purpose of improving scratch resistance, preventing sticking at the time of lamination, preventing reflection, and suppressing glare, that is, a hard coat layer, a diffusion layer, an antiglare layer, a reflection It is also preferable to provide a functional layer comprising a prevention layer, a low reflection layer, etc. on one side of the oriented polyester film. When providing various functional layers, the oriented polyester film preferably has an easy adhesion layer on the surface thereof. At that time, from the viewpoint of suppressing interference by reflected light with the hard coat layer, etc., the refractive index of the easy-adhesion layer is adjusted to be close to the geometric mean of the refractive index of the hard coat layer and the refractive index of the oriented polyester film. It is preferable. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

6). The manufacturing method of an oriented polyester film The oriented polyester film which is a protective film of this invention can be manufactured in accordance with the manufacturing method of a general polyester film. For example, the polyester resin is melted and the non-oriented polyester extruded and formed into a sheet shape is stretched in the longitudinal direction by utilizing the speed difference of the roll at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. The method of performing heat processing is mentioned.

  The oriented polyester film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as a polarizer protective film, even if observed from directly above the film surface, rainbow-like color spots are observed. Although it is not seen, it should be noted that rainbow-like color spots may be observed when observed from an oblique direction.

  This phenomenon is that a biaxially stretched film is composed of refractive index ellipsoids having different refractive indexes in the running direction, width direction, and thickness direction, and the retardation becomes zero depending on the light transmission direction inside the film (refractive index ellipse). This is because there is a direction in which the body appears to be a perfect circle. Therefore, when the liquid crystal display screen is observed from a specific oblique direction, a point where the retardation becomes zero may be generated, and a rainbow-like color spot is generated concentrically around that point. When the angle from the position directly above the film surface (normal direction) to the position where the rainbow-like color spots are visible is θ, the angle θ increases as the birefringence in the film increases, and the rainbow-like color increases. Spots are difficult to see. The biaxially stretched film tends to reduce the angle θ, and therefore the uniaxially stretched film is more preferable because rainbow-like color spots are less visible.

  However, a perfect uniaxial (uniaxial symmetry) film is not preferable because the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced. The present invention has biaxiality (biaxiality) in a range that does not substantially cause rainbow-like color spots or a range that does not cause rainbow-like color spots in the viewing angle range required for a liquid crystal display screen. It is preferable. Such biaxial objectivity is obtained by producing an oriented polyester film under the following conditions.

  The oriented polyester film having the specific retardation and Nz coefficient described above can be obtained by adjusting the conditions during film formation (for example, the draw ratio, the draw temperature, the film thickness, etc.). For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the higher the retardation. On the other hand, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation.

  As specific film forming conditions, for example, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 145 ° C, and particularly preferably 90 to 140 ° C. The longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. The transverse draw ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times.

  In order to control the retardation within the specific range described above, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio. If the difference between the vertical and horizontal draw ratios is too small, it is difficult to increase the retardation, which is not preferable. It is also preferable to set the stretching temperature low in order to increase the retardation. The temperature of the subsequent heat treatment is preferably 100 to 250 ° C, particularly preferably 180 to 245 ° C.

  In order to set the Nz coefficient to the above-described specific value, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio, and most preferably a uniaxially stretched film. In order to reduce the Nz coefficient, it is also preferable to add a copolymer component in order to increase the molecular weight of the polymer and to decrease the crystallinity. Furthermore, in order to control the Nz coefficient of the film within a specific range, the total stretching ratio and the stretching temperature can be appropriately set. For example, the lower the total draw ratio and the higher the drawing temperature, the lower the Nz coefficient can be obtained.

  In order to set the degree of plane orientation to the above specific value, it is preferable to control the total draw ratio. If the total draw ratio is too high, the degree of plane orientation becomes too high, which is not preferable. It is also preferable to control the stretching temperature in order to reduce the degree of plane orientation. By increasing the difference between the longitudinal draw ratio and the transverse draw ratio, setting the total draw ratio low, and setting the draw temperature high, the Nz coefficient and the degree of plane orientation can be made to be below specific values.

  Since the stretching temperature and the stretching ratio have a great influence on the thickness unevenness of the film, it is preferable to optimize the film forming conditions from the viewpoint of the thickness unevenness. In particular, if the longitudinal stretching ratio is lowered to increase the retardation, the longitudinal thickness unevenness may be deteriorated. Since there is a region where the vertical thickness unevenness becomes very bad in a specific range of the draw ratio, it is desirable to set the film forming conditions outside this range.

  The blending of the ultraviolet absorber into the oriented polyester film can be carried out by combining known methods. For example, using a kneading extruder, the dried UV absorber and polymer raw material are blended to prepare a master batch in advance, and blended by a method of mixing the predetermined master batch and polymer raw material during film formation. be able to.

  The UV absorber concentration of the master batch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and economically blend it. As conditions for producing the master batch, a kneading extruder is used, and the extrusion temperature is preferably from 1 to 15 minutes at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. Extrusion for 1 minute or less makes it difficult to uniformly mix the UV absorber. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

  The blending of the ultraviolet absorber into the intermediate layer of the oriented polyester film having a multilayer structure of three or more layers can be carried out by the following method. Polyester pellets alone for the outer layer, master batches containing UV absorbers for the intermediate layer and polyester pellets are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder, which is slit-shaped. Extruded into a sheet form from a die and cooled and solidified on a casting roll to make an unstretched film. That is, using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, An unstretched film is formed by extruding a three-layer sheet from the die and cooling with a casting roll.

  In order to remove foreign substances contained in the raw material polyester, which cause optical defects, it is preferable to perform high-precision filtration during melt extrusion in the process of producing an oriented polyester film. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filter particle size of the filter medium exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

    Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all possible and are within the scope of the present invention.

The physical property evaluation methods in the examples are as follows.
(1) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | nx−ny |) and the film thickness d (nm) on the film. Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes the long side, for measurement A sample was used. For this sample, the biaxial refractive index (nx, ny) orthogonal to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (NAR-4T manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The absolute value (| nx−ny |) of the difference between the biaxial refractive indexes was defined as the refractive index anisotropy (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (ΔNxy × d) of refractive index anisotropy (ΔNxy) and film thickness d (nm).

(2) Nz coefficient | ny-nz | / | ny-nx | However, the values of ny and nx were selected so that ny> nx.

(3) Degree of plane orientation (ΔP)
The value obtained by (nx + ny) / 2−nz was defined as the degree of plane orientation (ΔP).

(4) Thickness direction retardation (Rth)
Thickness direction retardation is obtained by multiplying two birefringences ΔNxz (= | nx−nz |) and ΔNyz (= | ny-nz |) by film thickness d when viewed from the cross section in the film thickness direction. It is a parameter which shows the average of retardation obtained. Thickness direction retardation (Rth) is calculated by calculating nx, ny, nz and film thickness d (nm) in the same manner as the retardation measurement, and calculating an average value of (ΔNxz × d) and (ΔNyz × d). )

(6) Observation of rainbow spots A polarizer protective film (polyester film) prepared by a method described later on one side of a polarizer composed of PVA and iodine so that the polarization axis of the polarizer and the orientation main axis of the polarizer protective film are perpendicular to each other. A fully saponified polyvinyl alcohol 5 mass% aqueous solution was attached as an adhesive, and a TAC film (Fuji Film Co., Ltd., thickness 80 μm) was attached to the opposite surface to prepare a polarizing plate. The obtained polarizing plate was placed on both sides of the liquid crystal so that each polarizing plate was in a crossed nicols condition to produce a liquid crystal display device. Each polarizing plate was arrange | positioned so that the said polarizer protective film might be on the opposite side (distal) from a liquid crystal. As a light source of the liquid crystal display device, a white LED composed of a light emitting element in which a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor were combined was used as a light source (Nichia Chemical, NSPW500CS). The liquid crystal display device was visually observed from the front and oblique directions, and the presence or absence of rainbow spots was determined as follows.

A: No rainbow spots are observed in any direction.
◯: When observed from an oblique direction, very thin rainbow spots are observed depending on the angle.
(Triangle | delta): When observed from the diagonal direction, a thin iridescence is observed by an angle.
X: When observed from an oblique direction, rainbow spots are observed.
Xx: When observing from the front direction and the oblique direction, rainbow spots are observed.

(7) Punching workability The polarizing plate produced above was punched from the TAC film side with an SD-type lever-type sample cutter (SDL-200, manufactured by Dumbbell) using a 50 mm × 50 mm blade.
The degree of peeling or cracking on the polyester film side at the end of the punched polarizing plate was visually observed and evaluated in the following four stages. The same evaluation was performed five times for the same polarizing plate, and the stage with the highest frequency in the five evaluations was regarded as the punching workability evaluation of the polarizing plate.
A: No peeling or cracking is observed at all. ○: Peeling or cracking is observed in less than 5% of the entire end portion.
Δ: Peeling or cracking is observed in less than 5 to 20% of the entire end portion ×: Peeling or cracking is observed in 20% or more of the entire end portion

(8) Moist heat resistance
The polarizing plate prepared above was carefully cut to a size of 50 mm × 50 mm so as not to peel off at the end, and was exposed for 500 hours under conditions of 60 ° C. and 95% RH. After the exposure, the degree of peeling on the polyester film side at the end of the polarizing plate was visually evaluated in the following three stages. The same evaluation was performed 5 times on the same polarizing plate, and the most frequent stage in the 5 evaluations was regarded as the wet heat resistance evaluation of the polarizing plate.
○: No peeling is observed Δ: Peeling is observed in less than 50% of the entire end portion X: Peeling is observed in 50% or more of the entire end portion

(9) Adhesion with light scattering layer A light scattering layer coating solution described below is applied to one side of a polarizer protective film prepared by the method described below, dried at 60 ° C. for 150 seconds, and then using a UV irradiator. The coating layer was cured by irradiating ultraviolet rays with an irradiation amount of 300 mJ / cm ² to provide a light scattering layer having a thickness of 5 μm. The light diffusion layer was evaluated for adhesion according to JIS K5400 with a cut interval of 2 mm. However, the following evaluation was made according to the ratio of the area of the cells that were not peeled off. The same evaluation was performed 5 times on the same film, and the most frequent stage in the 5 evaluations was defined as the adhesion evaluation of the light diffusion layer of the film.
◎: No peeling is seen in all 100 squares ○: No peeling is seen in 96-99 squares Δ: No peeling is seen in 80-95 squares ×: 79-50 squares No peeling is observed XX: No peeling is observed with 49 or fewer squares

(Preparation of coating solution for light scattering layer)
50 g of a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (PETA, Nippon Kayaku Co., Ltd.) was diluted with 38.5 g of toluene. Furthermore, 2 g of a polymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals Co., Ltd.) was added and mixed and stirred.

  Further, a 30% toluene dispersion of crosslinked polystyrene particles having an average particle diameter of 3.5 μm (refractive index: 1.60, SX-350, manufactured by Soken Chemical Co., Ltd.) dispersed in this solution for 20 minutes at 10,000 rpm with a homogenizer disperser. Add 13.3 g of a 30% toluene dispersion of 1.7 g and crosslinked acrylic-styrene particles having an average particle size of 3.5 μm (refractive index 1.55, manufactured by Soken Chemical Co., Ltd.), and finally, fluorine-based surface modification 0.75 g of an agent (Surflon S-386, manufactured by AGC Seimi Chemical Co., Ltd.) and 10 g of a silane coupling agent (KBM-5103, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to obtain a finished solution.

  The liquid mixture was filtered through a polypropylene filter having a pore size of 30 μm to prepare a coating solution for the light scattering layer.

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged and 0.017 parts by mass of antimony trioxide as a catalyst while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Next, the pressure was raised and the pressure esterification reaction was carried out under the conditions of gauge pressure 0.34 MPa and 240 ° C., then the esterification reaction can was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and 0.012 mass part of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and subjected to polycondensation reaction at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, it is filtered through a NASRON filter with a 95% cut diameter of 5 μm, extruded into a strand from a nozzle, and cooled and solidified using cooling water that has been filtered (pore diameter: 1 μm or less) in advance. And cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles and internally precipitated particles. (Hereafter, abbreviated as PET (A).)

(Production Example 2-Polyester B)
10 parts by weight of a dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one), PET (A) containing no particles (inherent viscosity Was 0.62 dl / g) and 90 parts by mass were mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (B)).

(Production Example 3-Polyester C)
Amorphous bulk silica particles having an average particle size of 2.3 μm and a pore volume of 1.6 ml / g were dispersed in ethylene glycol to prepare an ethylene glycol slurry containing 15 mass% of the amorphous bulk silica particles.

It contains inert particles in the same manner as in Production Example 1 except that the glycol slurry is added to 2000 ppm with respect to the generated PET in a state where the liquid is kept at 30 ° C. or lower before the temperature is increased under pressure. A polyester resin (C) having an intrinsic viscosity of 0.62 dl / g was prepared (hereinafter abbreviated as PET (C)).

(Production Example 4-Styrene-butadiene latex A>
After a 10 L pressurized reactor equipped with a stirrer, thermometer, cooler, and nitrogen gas inlet and continuously charged with a monomer, an emulsifier, and a polymerization initiator was replaced with nitrogen, butadiene 30 After charging parts by weight, 70 parts by weight of styrene, 0.5 parts by weight of sodium dodecylbenzenesulfonate, 0.3 parts by weight of t-dodecyl mercaptan, 0.4 parts by weight of sodium bicarbonate, and 150 parts by weight of ion-exchanged water, The temperature was raised to 82 ° C. A polymerization initiator, 0.8 part by weight of calcium persulfate, was added thereto and polymerized while stirring for about 300 minutes to produce a styrene-butadiene latex (A).

(Production Example 5—Styrene-butadiene latex B>
A styrene-butadiene latex (B) was produced in the same manner as in Production Example 4 except that the comonomer was changed to 35 parts by weight of butadiene, 55 parts by weight of styrene, and 10 parts by weight of methyl methacrylate.

(Production Example 6 2-vinylpyridine-styrene-butadiene latex>
A 2-vinylpyridine-styrene-butadiene latex was produced in the same manner as in Production Example 4 except that the comonomer was changed to 40 parts by weight of butadiene, 15 parts by weight of styrene, and 15 parts by weight of 2-vinylpyridine.

(Production Example 7—Water-dispersible copolymerized polyester resin liquid)
A transesterification reaction and a polycondensation reaction are performed by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal group-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol (relative to the entire glycol component) was prepared as a glycol component. Next, 60 parts by mass of water, 20 parts by mass of n-butyl cellosolve, and 0.03 parts by mass of a nonionic surfactant were mixed and then heated and stirred. When the temperature reached 77 ° C, the above-mentioned water-dispersible sulfonic acid metal base was contained. After adding 20 parts by mass of the copolyester resin and continuing to stir until the resin is no longer solidified, the resin water dispersion is cooled to room temperature to obtain a uniform water dispersible copolyester resin liquid having a solid content of 20% by mass. Got.

The latex obtained above was mixed in the solid content ratio shown in Table 1 to prepare a coating solution having a solid content concentration of 5% by mass. The silica particle used the liquid which disperse | distributed 3 mass parts of aggregate silica particles (Fuji Silysia Co., Ltd. product, silicia 310) to 50 mass parts of water. Further, water and isopropyl alcohol were used as the solvent for the coating solution, and the ratio of isopropyl alcohol in the solvent was adjusted to 15% by mass.

(Coating solution composition)

(Polarizer protective film 1)
After drying 90 parts by mass of PET (A) resin pellets containing no particles as a raw material for the base film intermediate layer and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) , And supplied to the extruder 2 (for the intermediate layer II layer). Also, the PET (A) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III) and dissolved at 285 ° C. . After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, coating solution No1 was applied on both surfaces of the unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m ^2, and then dried at 80 ° C. for 20 seconds.

  The unstretched film on which the coating layer was formed was guided to a tenter stretching machine, guided to a hot air zone at a temperature of 135 ° C. while being gripped by a clip, and stretched 3.8 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 100 μm.

(Polarizer protective film 2)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as the polarizer protective film 1 except that the coating liquid No2 was used instead of the coating liquid No1.

(Polarizer protective film 3)
Using a method similar to that of the polarizer protective film 2, a uniaxially oriented PET film having a thickness of about 100 μm was obtained. On the coating layer on one side, a corona discharge treatment is performed, and a coating solution (coating solution 8) containing a hydrophilic polymer having the following composition as a main binder is applied to a dry film thickness of 100 nm to provide a second easy adhesion. The layer was formed and the polarizing plate protective film 3 was obtained.

Coating liquid 8
A coating solution 8 having the composition described below was prepared.
3 parts by weight of gelatin, 2 parts by weight of a 20% by weight aqueous acetic acid solution, 190 parts by weight of water

(Polarizer protective film 4)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as the polarizer protective film 1 except that the coating liquid No4 was used instead of the coating liquid No1.

(Polarizer protective film 5)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as the polarizer protective film 1 except that the coating liquid No5 was used instead of the coating liquid No1.

(Polarizer protective film 6)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as that for the polarizer protective film 1 except that the coating liquid No6 was used instead of the coating liquid No1.

(Polarizer protective film 7)
After drying 90 parts by mass of PET (A) resin pellets containing no particles as a raw material for the base film intermediate layer and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) The extruder 2 (for the intermediate layer II layer) is supplied, and 95 parts by mass of the PET (A) resin pellets and 5 parts by mass of the PET (C) resin pellets are dried by an ordinary method, and the extruder 1 (outer layer I layer) And for outer layer III) and dissolved at 285 ° C. After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

  The unstretched film was guided to a tenter stretching machine, and the end of the film was held by a clip while being guided to a hot air zone at a temperature of 135 ° C. and stretched 3.8 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 100 μm.

Next, coating liquid No. 3 was applied to one side of the obtained uniaxially oriented PET film by a bar coating method so that the coating amount after drying was 0.08 g / m ^2, and then heated and dried at 150 ° C. for 50 seconds. . Further, the opposite surface was coated in the same manner, and a coating layer was provided on both surfaces.

(Polarizer protective film 8)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained by using the same method as that for the polarizer protective film 7 except that the corona treatment was performed before applying to the uniaxially oriented PET film by the bar coating method.

(Polarizer protective film 9)
Using the polarizer protective film 8, a film having a second easy-adhesion layer on one surface was obtained in the same manner as the polarizer protective film 3.

(Polarizer protective film 10)
A coating film No. 2 was used to introduce a uniaxially oriented PET film having a film thickness of about 100 μm by the same method as for the polarizer protective film 1 except that the coating liquid No. 2 was guided to a hot air zone at a temperature of 125 ° C. Obtained.

(Polarizer protective film 11)
The unstretched film was heated to 105 ° C. using a heated roll group and an infrared heater, and then stretched 3.3 times in the running direction by a roll group having a difference in peripheral speed, and led to a hot air zone having a temperature of 110 ° C. Thereafter, a biaxially oriented PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 10 except that the film was stretched 3.9 times in the width direction.

(Polarizer protective film 12)
The unstretched film was heated to 105 ° C. using a heated roll group and an infrared heater, and then stretched 3.3 times in the running direction by a roll group having a difference in peripheral speed, and led to a hot air zone having a temperature of 110 ° C. Thereafter, a biaxially oriented PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 7 except that the film was stretched 3.9 times in the width direction.

(Polarizer protective film 13)
A biaxially oriented PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 12 except that the corona treatment was performed before coating.

(Polarizer protective film 14)
Using the polarizer protective film 13, a film having a second easy-adhesion layer on one side was obtained in the same manner as the polarizer protective film 3.

(Polarizer protective film 15)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as the polarizer protective film 1 except that the coating liquid No7 was used instead of the coating liquid No1.

(Polarizer protective film 16)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained using the same method as for the polarizer protective film 7 except that the coating solution was not applied.

    Table 2 shows details and optical properties of the polarizer protective film.

(Details of polarizer protective film)

Table 3 below shows the results of rainbow spot observation and evaluation of the film performance of the liquid crystal display device produced as described above using the polarizer protective films 1 to 16.

(Evaluation results)

  In the rainbow spot observation of the polarizer protective film 1, when a cold cathode tube was used as the light source instead of the white LED, the evaluation result was “XX”. Furthermore, the above-mentioned diffusion layer was provided on the surface opposite to the adhesive surface between the polarizer protective film 9 and the polarizer of the polarizer protective film 14, and rainbow spots were observed. These results were “◎” with almost no change in the polarizer protective film 9, but improved to “◯” in the polarizer protective film 14.

  From the results shown in Table 3, the retardation of the oriented polyester film having a coating layer composed of a copolymer latex composed of a diolefin monomer and a vinyl monomer on at least one side is 4000 or more, and It was shown that when the Nz coefficient is 1.7 or less, the occurrence of rainbow spots is remarkably suppressed, and the adhesion with the polarizer and the diffusion layer and the durability of the heat and humidity resistance are improved. In addition to this condition, it has been shown that by controlling the degree of plane orientation of the oriented polyester film to 0.13 or less, it is possible to more effectively suppress the occurrence of rainbow spots.

  By using the liquid crystal display device, polarizing plate and polarizer protective film of the present invention, it is excellent in durability during processing without reducing visibility due to rainbow-like color spots, making the LCD thinner and lower in cost. It is possible to contribute. Therefore, the industrial applicability of the present invention is extremely high.

Claims (7)

From an oriented polyester film having a coating layer containing a copolymer latex comprising a diolefin monomer and a vinyl monomer as constituent components on at least one surface and having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less A polarizer protective film. The polarizer protective film of Claim 2 whose plane orientation degree of the said oriented polyester film is 0.13 or less. The polarizer protective film according to claim 1, wherein the oriented polyester film comprises at least three layers, contains an ultraviolet absorber in a layer other than the outermost layer, and has a light transmittance of 380 nm of 20% or less. Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
The polarizing plate whose polarizer protective film of at least one side is the polarizer protective film in any one of Claims 1-3. A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
The polarization according to any one of claims 1 to 3, wherein at least one of the polarizer protective films of the polarizing plate arranged on the incident light side and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side are A liquid crystal display device which is a child protective film. A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side, and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side, according to any one of claims 1 to 3. A liquid crystal display device, which is a polarizer protective film. The liquid crystal display device according to claim 5 or 6, wherein the white light source having the continuous emission spectrum is a white light emitting diode.