WO2018181653A1

WO2018181653A1 - Polarizer protection film, polarizing plate and image display device

Info

Publication number: WO2018181653A1
Application number: PCT/JP2018/013099
Authority: WO
Inventors: 達郎山下; 村田　浩一; 章太早川; 佐々木　靖
Original assignee: 東洋紡株式会社
Priority date: 2017-03-31
Filing date: 2018-03-29
Publication date: 2018-10-04
Also published as: JP2022132306A; TW201839476A; JPWO2018181653A1; JP2022132305A; JP7143842B2; CN110383122B; JP7327594B2; KR20190128653A; TWI770153B; JP2023171426A; CN110383122A; CN114966913A; KR102303171B1

Abstract

A polarizer protection film including a polyester film, wherein the slow axis direction of the polyester film is approximately parallel to an MD direction, the in-plane birefringence ΔNxy of the polyester film is 0.06-0.20 inclusive, and the following (A) or (B) is satisfied: (A) the refractive index of the fast axis direction of the polyester film is 1.580-1.630 inclusive; and (B) the smaller value out of tear strengths by a right angle tear method in the slow axis direction and the fast axis direction of the polyester film is 250 N/mm or more.

Description

Polarizer protective film, polarizing plate, and image display device

The present invention relates to a polarizer protective film, a polarizing plate, an image display device such as a liquid crystal display device and an organic EL display. Specifically, the present invention relates to a polarizer protective film, a polarizing plate, and an image display device (liquid crystal display device, organic EL display, etc.) that have good visibility and are suitable for thinning.

A polarizing plate used in a liquid crystal display (LCD) usually has a configuration in which a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films. As the film, a triacetyl cellulose (TAC) film is usually used. In recent years, with the thinning and cost reduction 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.

The polyester film is superior to the TAC film in durability, but unlike the TAC film, it has birefringence. Therefore, when it 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 document 1, the countermeasure against a rainbow-like color spot is made | formed by controlling the in-plane retardation of a polyester film to a specific range.

WO2011-162198

However, in the market, there is a demand for further thinning of image display devices such as liquid crystal display devices, and when the thickness of the polarizer protective film is reduced, the retardation is sufficient to sufficiently suppress rainbow-like color spots. It was difficult to secure. Furthermore, since the mechanical strength required for processing becomes insufficient due to the thin film, it may be difficult to meet the demand for thinning the film.

An object of the present invention in one embodiment is to cope with the thinning of an image display device such as a liquid crystal display device or an organic EL display (that is, has sufficient mechanical strength) and is visually recognized by a rainbow-like color spot. It is providing the polarizer protective film, polarizing plate, and image display apparatus (a liquid crystal display device, an organic EL display, etc.) by which deterioration of property was suppressed.

The representative present invention is as follows.
Term A1.
A polarizer protective film including a polyester film,
The slow axis direction of the polyester film is substantially parallel to the MD direction,
In-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.20 or less,
The refractive index in the fast axis direction of the polyester film is 1.580 or more and 1.630 or less,
Polarizer protective film.
Term A2.
The polarizer protective film according to Item A1, wherein the smaller value of the tear strength by the right-angled tearing method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.
Term A3.
The polarizer protective film according to Item A1 or A2, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less.
Term A4.
The polarizer protective film according to any one of Items A1 to A3, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less.
Term A5.
The polarizer protective film according to any one of Items A1 to A4, wherein the polyester film has a thickness of 25 to 60 μm.
Term A6.
The polarizer protective film according to any one of Items A1 to A5, wherein an angle formed by the slow axis direction of the polyester film and the MD direction is within 3 degrees.
Term A7.
The polarizer protective film according to any one of Items A1 to A6, wherein the elastic modulus in the MD direction of the polyester film is 3000 MPa or more.
Term A8.
A polarizing plate comprising the polarizer protective film according to any one of Items A1 to A7 laminated on at least one surface of the polarizer.
Term A9.
A polarizing plate in which the polarizer protective film according to any one of Items A1 to A7 is laminated on one side of the polarizer and the film is not laminated on the other side of the polarizer.
Term A10.
A polarizing plate in which the polarizer protective film according to any one of Items A1 to A7 is laminated on one side of the polarizer, and a quarter-wave plate is laminated on the other side of the polarizer.
Term A11.
An image display device comprising the polarizing plate according to any one of Items A8 to A10.
Term A12.
A liquid crystal display device comprising the polarizing plate according to item A8 or A9.
Term A13.
An organic EL display comprising the polarizing plate according to any one of Items A8 to A10.
Term A14.
A QLED display comprising the polarizing plate according to any one of Items A8 to A10.

Term B1.
A polarizer protective film including a polyester film,
The slow axis direction of the polyester film is substantially parallel to the MD direction,
The in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.2 or less,
The smaller value of the tear strength by the right-angled tearing method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.
Polarizer protective film.
Term B2.
The polarizer protective film according to Item B1, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less.
Term B3.
The polarizer protective film according to Item B1 or B2, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less.
Term B4.
The polarizer protective film according to any one of Items B1 to B3, wherein the polyester film has a thickness of 25 to 60 μm.
Term B5.
The polarizer protective film according to any one of Items B1 to B4, wherein an angle formed between the slow axis direction of the polyester film and the MD direction is within 3 degrees.
Term B6.
The polarizer protective film according to any one of Items B1 to B5, wherein the elastic modulus in the MD direction of the polyester film is 3000 MPa or more.
Term B7.
A polarizing plate in which the polarizer protective film according to any one of Items B1 to B6 is laminated on at least one surface of the polarizer.
Term B8.
A polarizing plate in which the polarizer protective film according to any one of Items B1 to B6 is laminated on one side of the polarizer, and the film is not laminated on the other side of the polarizer.
Term B9.
A polarizing plate in which the polarizer protective film according to any one of Items B1 to B6 is laminated on one side of the polarizer and a quarter-wave plate is laminated on the other side of the polarizer.
Term B10.
An image display device comprising the polarizing plate according to any one of Items B7 to B9.
Term B11.
A liquid crystal display device comprising the polarizing plate according to item B7 or B8.
Term B12.
An organic EL display comprising the polarizing plate according to any one of Items B7 to B9.
Term B13.
A QLED display comprising the polarizing plate according to any one of Items B7 to B9.

Term C1.
A polarizer protective film including a polyester film,
The slow axis direction of the polyester film is substantially parallel to the MD direction,
The in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.2 or less,
The polyester film has a thickness of 15 to 60 μm.
Polarizer protective film.
Term C2.
The polarizer protective film according to Item C1, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less.
Term C3.
The polarizer protective film according to Item C1 or C2, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less.
Term C4.
The polarizer protective film according to any one of Items C1 to C3, wherein an angle formed between the slow axis direction of the polyester film and the MD direction is 3 degrees or less.
Term C5.
The polarizer protective film according to any one of Items C1 to C4, wherein the elastic modulus in the MD direction of the polyester film is 3000 MPa or more.
Term C6.
A polarizing plate in which the polarizer protective film according to any one of Items C1 to C5 is laminated on at least one surface of the polarizer.
Term C7.
A polarizing plate in which the polarizer protective film according to any one of Items C1 to C5 is laminated on one side of the polarizer, and the film is not laminated on the other side of the polarizer.
Term C8.
A polarizing plate in which the polarizer protective film according to any one of Items C1 to C5 is laminated on one side of the polarizer, and a quarter-wave plate is laminated on the other side of the polarizer.
Term C9.
An image display device comprising the polarizing plate according to any one of Items C6 to C8.
Term C10.
A liquid crystal display device comprising the polarizing plate according to item C6 or C7.
Term C11.
An organic EL display comprising the polarizing plate according to any one of Items C6 to C8.
Term C12.
A QLED display comprising the polarizing plate according to any one of Items C6 to C8.

The polarizer protective film, polarizing plate and image display device (liquid crystal display device, organic EL display, etc.) of the present invention are excellent in that rainbow-like color spots (hereinafter the same as rainbow spots) are suppressed at any observation angle. High visibility can be secured. In addition, the polarizing plate and the polarizer protective film of the present invention have mechanical strength suitable for thinning, and can ensure good processing characteristics. According to the present invention, it is possible to provide a polarizer protective film, a polarizing plate, and an image display device in which deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is thinned.

1. Polarizer Protective Film In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, and the slow axis direction of the polyester film is substantially parallel to the MD direction, and the polyester film In-plane birefringence ΔNxy is 0.06 or more and 0.20 or less, and the refractive index in the fast axis direction of the polyester film is 1.580 or more and 1.630 or less.

In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, the slow axis direction of the polyester film being substantially parallel to the MD direction, Refraction ΔNxy is 0.06 or more and 0.2 or less, and the smaller value of the tear strength of the polyester film by the right-angled tearing method in the slow axis direction and the fast axis direction is 250 N / mm or more.

In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, the slow axis direction of the polyester film being substantially parallel to the MD direction, Refraction ΔNxy is 0.06 or more and 0.20 or less, and the thickness of the polyester film is 15 to 60 μm. The problem in this embodiment is to provide a polarizer protective film in which deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is thinned, and a thin polarizing plate and an image display device ( A liquid crystal display device, an organic EL display, etc.).

The slow axis of the polyester film used as the polarizer protective film of the present invention is preferably substantially parallel to the MD direction (traveling direction during film formation) from the viewpoint of suppressing iridescent color spots. Here, being substantially parallel means that the angle formed by the slow axis direction of the polyester film and the MD direction (traveling direction during film formation) is preferably within 10 degrees, more preferably within 7 degrees, and even more preferably It means within 5 degrees, particularly preferably within 3 degrees, most preferably within 2 degrees.

The direction of the slow axis can be determined using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments).

In the present specification, the MD direction is a traveling direction during film formation, and may be referred to as a longitudinal direction. The TD direction is the width direction during film formation, and may be referred to as the horizontal direction.

When industrially producing an image display device (liquid crystal display device, organic EL display, etc.) using a polarizing plate using a polyester film as a polarizer protective film, the direction of the absorption axis of the polarizer and the slow axis of the polyester film Are usually arranged perpendicular to each other. This is due to the following circumstances. The polyvinyl alcohol film which is a polarizer is manufactured by MD uniaxial stretching. Therefore, the polyvinyl alcohol film used as a polarizer is usually a long film in the stretching direction and has an absorption axis in the MD direction. On the other hand, since the polyester film as the protective film is usually produced by MD stretching and then TD stretching in many cases, the orientation main axis direction (slow axis direction) of the polyester film is the TD direction. From the viewpoint of production efficiency, these films are usually bonded together by roll-to-roll so that their longitudinal directions are parallel to each other, whereby a polarizing plate is produced. Then, the slow axis of the polyester film and the absorption axis of the polarizer are usually perpendicular.

On the other hand, in the present invention, the orientation main axis direction (slow axis direction) of the polyester film is preferably the MD direction. Such a polyester film can be obtained by strongly stretching the polyester film in the MD direction. When a polarizing plate is produced by laminating this polyester film and a polarizer produced by MD uniaxial stretching by roll-to-roll so that the longitudinal direction is parallel, the absorption axis of the polarizer and the slow axis of the polyester film The directions are parallel. In the case where the polarizer is laminated with the absorption axis of the polarizer and the slow axis of the polyester film being parallel, the polarizer is laminated with the absorption axis of the polarizer and the slow axis of the polyester film being perpendicular. It has been found that the effect of suppressing iridolysis is better than the case. In order to efficiently produce a polarizing plate excellent in the effect of suppressing rainbow spots by an industrially advantageous roll-to-roll method, the polyester film is strongly stretched in the MD direction, and the relationship between the MD direction and the slow axis direction is substantially parallel. It is preferable to use the polyester film which has.

The in-plane birefringence ΔNxy of the polyester film used for the polarizer protective film of the present invention is preferably 0.06 or more and 0.2 or less, more preferably 0.07 or more and 0.19 or less, and further preferably 0.08 or more and 0. .18 or less. When ΔNxy is less than 0.06, rainbow-like color spots are easily observed when observed from an oblique direction. Further, in the case where ΔNxy is larger than 0.2, iridescent color spots are not generated, but since it approaches perfect uniaxiality (uniaxial symmetry), the mechanical strength in the direction parallel to the orientation direction is significantly reduced. The in-plane birefringence ΔNxy is an absolute value of the difference between the refractive index (nx) in the slow axis direction and the refractive index (ny) in the fast axis direction. The measurement wavelength of the refractive index is 589 nm.

In one embodiment, the refractive index (ny) in the fast axis direction of the polyester film having a relationship in which the slow axis direction is substantially parallel to the MD direction used in the polarizer protective film of the present invention is preferably 1.58 or more. It is 1.63 or less, More preferably, it is 1.584 or more and 1.625 or less, More preferably, it is 1.588 or more and 1.62 or less. When the refractive index (ny) in the fast axis direction is less than 1.58, it approaches perfect uniaxiality (uniaxial symmetry), so that the mechanical strength (tear strength) in the direction parallel to the orientation direction is significantly reduced. Further, when the refractive index (ny) in the fast axis direction exceeds 1.63, rainbow-like color spots are easily observed when observed from an oblique direction.

The smaller value of the tear strength by the right-angled tearing method in the slow axis direction and the fast axis direction of the polyester film used for the polarizer protective film of the present invention is preferably 250 N / mm or more, more preferably 280 N / mm. As mentioned above, More preferably, it is 300 N / mm or more. In a film having a high ΔNxy value, the tear strength value in the slow axis direction tends to be smaller than in the fast axis direction. Conventionally, since the mechanical strength required for processing is insufficient due to the reduced thickness of the film, it has been difficult to meet the demand for thinning, but the slow axis direction and the fast axis direction of the film If the smaller value of the tear strength by the right-angled tearing method is 250 N / mm or more, the above problem can be solved. If it is less than 250 N / mm, the film is easily torn, and the stability at the time of film formation and processing decreases. On the other hand, the higher the tear strength, the greater the stability during film formation and processing, but the biaxiality (biaxial symmetry) increases and rainbow-like color spots occur. It is preferable to increase the tear strength within a range in which no occurrence occurs, and in practice, it is preferably 500 N / mm or less.
The tear strength is measured according to a right-angled tear method (JIS K-7128-3) to determine the tear strength (N / mm) per film thickness.

The NZ coefficient of the polyester film used for the polarizer protective film of the present invention is preferably 1.5 or more and 2.5 or less, more preferably 1.6 or more and 2.3 or less, and further preferably 1.7 or more and 2.1 or less. It is. As the NZ coefficient is smaller, rainbow-like color spots due to the observation angle are less likely to occur. In a perfect uniaxial (uniaxial symmetry) film, the NZ coefficient is 1.0, but as it approaches the perfect uniaxial (uniaxial symmetry) film, the mechanical strength in the direction parallel to the orientation direction tends to decrease. .

NZ coefficient can be obtained as follows. Using a molecular orientation meter (Oji Keiki Co., Ltd., MOA-6004 type molecular orientation meter), the orientation principal axis direction (slow axis direction) of the film is obtained, and the orientation principal axis direction and the direction perpendicular to this (fast axis direction) ) Of biaxial refractive index (refractive index nx in the slow axis direction, refractive index ny in the fast axis direction, nx> ny), and refractive index (nz) in the thickness direction (Abago Refractometer) Manufactured, 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 | nx−nz | / | nx−ny |. The measurement wavelength of the refractive index is 589 nm.

From the viewpoint of further reducing rainbow spots, the polyester film used for the polarizer protective film preferably has a retardation of 1500 nm or more and 30000 nm or less. The lower limit of retardation is preferably 2500 nm, and the next lower limit is preferably 3000 nm.

On the other hand, the upper limit of retardation is 30000 nm. Even if a polyester film having a retardation of more than that is used, it is not only possible to substantially improve the visibility, but also because the film thickness becomes considerably thick and the handling property as an industrial material is reduced, it is preferable. Absent. In one embodiment, the preferable upper limit of retardation is 8000 nm, the more preferable upper limit is 6000 nm, the still more preferable upper limit is 5500 nm, and the particularly preferable upper limit is 5000 nm.

The birefringence can be obtained by measuring the refractive index in the biaxial direction, or can be obtained by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments). The measurement wavelength of the refractive index is 589 nm.

The elastic modulus in the MD direction of the polyester film used for the polarizer protective film of the present invention is preferably 3000 MPa or more. In recent years, with the thinning of LCDs, the thinning of members has progressed. Under such circumstances, with the thinning of the glass substrate used in the liquid crystal panel, the problem of warpage of the liquid crystal panel due to the contraction of the polarizing plate has become apparent. The contraction of the polarizing plate is caused by the contraction of the PVA film that is the polarizer (mainly the contraction in the absorption axis direction), and the contraction of the polarizer is preferably controlled by the rigidity of the protective film. If the elastic modulus in the running direction of the protective film is 3000 MPa or more, a sufficient control force can be exerted on the contraction of the polarizer to prevent the liquid crystal panel from warping. May become apparent. A preferable lower limit value of the elastic modulus in the MD direction is 3500 MPa, a more preferable lower limit value is 4000 MPa, and a further preferable lower limit value is 4500 MPa.

The polyester used in the polarizer protective film of the present invention may be polyethylene terephthalate or polyethylene naphthalate, but may contain other copolymer components. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the in-plane birefringence can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and can easily obtain a large in-plane birefringence.

Also, for the purpose of suppressing deterioration of optical functional dyes such as iodine dyes, it is desirable that the polarizer protective film of the present invention has a light transmittance of 20% or less at a wavelength of 380 nm. 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 transmittance in the present invention 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).

In order to reduce the transmittance at a wavelength of 380 nm of the polarizer protective film of the present invention to 20% or less, it is desirable to appropriately adjust the type, concentration and thickness of the ultraviolet absorber. The ultraviolet absorber used in the present invention is a known substance. 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, cyclic imino ester, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. However, from the viewpoint of durability, benzotriazole type and cyclic imino ester type 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'-methylphenyl) 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-benzoxazin-4-one, 2-phenyl -3,4-benzoxazin-4-one, etc., but is not particularly limited thereto.

In addition to the ultraviolet absorber, it is also preferable to include various additives other than the catalyst 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. Moreover, in order to show high transparency, it is also preferable that a polyester film does not contain a particle | grain substantially. “Substantially free of particles” means, for example, in the case of inorganic particles, a content that is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less when inorganic elements are quantified by fluorescent X-ray analysis. means.

In the polarizer protective film of the present invention, it is also preferable to apply various hard coats on the surface for the purpose of preventing reflection, suppressing glare, and suppressing scratches.

Furthermore, in the present invention, the polyester film can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion to the polarizer and various hard coat layers.

In the present invention, in order to improve the adhesion to the polarizer, at least one surface of the film of the present invention has an easy-adhesion layer mainly composed of at least one of a polyester resin, a polyurethane resin or a polyacrylic resin. Is preferred. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating solution used for forming the easy-adhesion layer of the present invention is preferably an aqueous coating solution containing at least one of water-soluble or water-dispersible copolymerized polyester resin, acrylic resin, and polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying a coating solution to at least one of the film surfaces and drying at 100 to 150 ° C. in an arbitrary step during the production process of the polyester film. The final coating amount of the easy adhesion layer is preferably controlled to 0.05 to 0.2 g / m ² . If the coating amount is significantly less than 0.05 g / m ² , adhesion with the resulting polarizer may be insufficient. On the other hand, if the coating amount significantly 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.

It is preferable to add particles to the easy-adhesion layer in order to impart slipperiness. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles significantly 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 alone to the easy-adhesion layer, or may be added in combination of two or more.

Further, as a method for applying the coating solution, a known method can be used. For example, 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, etc. can be mentioned. Or it can carry out in combination.

The average particle size of the above particles is measured by 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 polyester film can be manufactured according to a general polyester film manufacturing method. For example, there is a method in which a polyester resin is melted, and a non-oriented polyester extruded and formed into a sheet is stretched in the longitudinal direction and the transverse direction at a temperature equal to or higher than the glass transition temperature and subjected to heat treatment.

The 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, it may be observed from directly above the film surface. Although rainbow-like color spots are not seen, caution is necessary because 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 display screen is observed from a specific oblique direction, a point where the retardation is zero may be generated, and a rainbow-like color spot is generated concentrically around the 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 parallel to the orientation direction is significantly reduced. The present invention has biaxiality (biaxial symmetry) 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 the display screen. It is preferable.

The film forming conditions of the polyester film of the present invention may be sequential biaxial stretching or simultaneous biaxial stretching. However, in general sequential biaxial stretching, since the longitudinal stretching is roll stretching, the film is easily scratched. Therefore, from the viewpoint of preventing scratches during stretching, simultaneous biaxial stretching without using a roll is preferred. The film forming conditions will be specifically described. The longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 150 ° C., particularly preferably 90 to 140 ° C. The longitudinal draw ratio is preferably 5.5 to 7.5 times, more preferably 6.0 times to 7.0 times, and particularly preferably 6.5 times to 7.0 times. Further, the transverse draw ratio is preferably 1.5 to 3.0 times, particularly preferably 1.8 to 2.8 times. In order to control the slow axis direction, ΔNxy, the refractive index value in the fast axis direction, the NZ coefficient, and the tear strength within the above ranges, it is preferable to control the respective ratios 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 ΔNxy, which is not preferable. Also, setting the stretching temperature low is a preferable measure for increasing ΔNxy.

In order to set the refractive index value in the fast axis direction to the above range and increase the tear strength, the biaxiality should be moderately biaxial under the condition that ΔNxy satisfies the range specified in the present application rather than a complete uniaxial film. Is preferably given. In the subsequent heat treatment, the treatment temperature is preferably from 100 to 250 ° C., particularly preferably from 180 to 245 ° C.

As described above, in order to control the ΔNxy and NZ coefficients to a specific range, it can be performed by appropriately setting the draw ratio and the draw temperature. For example, it becomes easier to obtain higher ΔNxy as the stretching ratio is higher and the stretching temperature is lower. Conversely, the lower the draw ratio and the higher the draw temperature, the easier it is to obtain a lower ΔNxy. In addition to controlling ΔNxy and NZ coefficients, it is preferable to set final film forming conditions in consideration of physical properties necessary for processing.

The thickness of the polyester film used as the polarizer protective film of the present invention is arbitrary, but is preferably in the range of 15 to 200 μm, more preferably in the range of 15 to 150 μm. In a film having a thickness of less than 15 μm, the mechanical properties of the film are remarkably lowered, and the film tends to be torn, torn, etc., and the utility as an industrial material tends to be remarkably lowered. The lower limit of the preferred thickness is 25 μm, the more preferred lower limit is 30 μm, and the still more preferred lower limit is 35 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 200 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 150 μm, the more preferable upper limit of the thickness is 80 μm, the more preferable upper limit of the thickness is 60 μm, and the further preferable upper limit of the thickness is 55 μm. The upper limit of the more preferable thickness is 50 μm, and the upper limit of the more preferable thickness is 45 μm. In the above thickness range, in order to control the ΔNxy, NZ coefficient and tear strength within the range of the present invention, the polyester used as the film substrate is preferably polyethylene terephthalate.

In addition, as a method of blending the ultraviolet absorber with the polyester film in the present invention, a known method can be used in combination. For example, a preliminarily kneaded extruder is used to blend the dried ultraviolet absorber and the polymer raw material. A master batch can be prepared and blended by, for example, a method of mixing the predetermined master batch and a polymer raw material during film formation.

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

In the present invention, it is preferable that the film has a multilayer structure of at least three layers, and an ultraviolet absorber is added to the intermediate layer of the film. A film having a three-layer structure containing an ultraviolet absorber in the intermediate layer can be specifically produced as follows. 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 the present invention, it is preferable to perform high-precision filtration during melt extrusion in order to remove foreign substances contained in the raw material polyester, which cause optical defects. 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 significantly exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

2. Polarizing plate The polarizing plate has a configuration in which a polarizer protective film is laminated on at least one surface of a polarizer in which iodine is dyed on PVA or the like. In the polarizing plate of the present invention, the polarizer protective film of the present invention having the specific polyester film described above is preferably used as at least one of the polarizer protective films constituting the polarizing plate. As a preferred embodiment, the polarizer protective film of the present invention having the above-described specific polyester film is laminated on one side of the polarizer, and a TAC film, norbornene film, acrylic film, etc. on the other side of the polarizer. A polarizer protective film or an optical compensation film having no birefringence is laminated. As another preferred embodiment, the polarizer protective film of the present invention including the specific polyester film described above is laminated on one side of the polarizer, and the film is laminated on the other side of the polarizer. No (the film on the other side of the polarizer is not attached to the polarizer as a single unit). In another preferred embodiment described above, a coating layer (a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a moisture resistant layer (organic matter) is provided on the surface opposite to the surface on which the specific polyester film of the polarizer is laminated. Or a layer combining these functions) may be provided.

As described above, the polarizing plate of the present invention is laminated in such a manner that the absorption axis of the polarizer and the slow axis of the polyester film are substantially parallel from the viewpoint of suppressing rainbow spots and suppressing the warpage of the liquid crystal panel. It is preferable. Here, “substantially parallel” intends to allow a slight deviation. The angle formed by the absorption axis of the polarizer and the slow axis of the polyester film is preferably within 10 degrees, more preferably within 7 degrees, even more preferably within 5 degrees, particularly preferably within 3 degrees, and most preferably 2 degrees. Within degrees.

3. Image display device The image display device includes a liquid crystal display device, an organic EL display, a QLED display, or the like that includes a polarizing plate inside the image display device.

4). 2. Liquid Crystal Display Device Generally, a liquid crystal panel includes 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). 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 arranged on the side facing the backlight light source in the rear module, and is arranged on the side (viewing side) displaying the image in the front module.

The liquid crystal display device includes at least a backlight light source and a liquid crystal cell disposed between two polarizing plates. Moreover, you may have suitably other structures other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film etc. suitably.

The arrangement of the polarizer protective film of the present invention having a specific polyester film is not particularly limited. However, the polarizer protective film is arranged on the incident light side (light source side), the liquid crystal cell, and the outgoing light side (viewing side). In the case of a liquid crystal display device provided with a polarizing plate, the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and / or the polarized light on the outgoing light side of the polarizing plate arranged on the outgoing light side The child protective film is preferably the polarizer protective film of the present invention having the specific polyester film. A particularly preferable embodiment is an embodiment in which the polarizer protective film on the incident light side of the polarizing plate disposed on the incident light side is the specific polyester film. When the polyester film is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed. Since it is not preferable to use the polarizer protective film of the present invention at a place where polarization characteristics are required, it is preferably used as a protective film for a polarizing plate at such a specific position.

The configuration of the backlight may be an edge light method using a light guide plate or a reflection plate as a constituent member, or a direct type.

It is preferable to use a white light emitting diode (white LED) as the backlight source of the liquid crystal display device. In the present invention, the white LED is an element that emits white by combining a phosphor with a phosphor system, that is, a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor. Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. In particular, white light-emitting diodes, which are composed 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 are also efficient in light emission. Excellent. Here, the continuous emission spectrum means that there is no wavelength at which the light intensity becomes zero at least in the visible light region. In addition, since the white LED with low power consumption can be widely used by the method of the present invention, it is possible to achieve an energy saving effect.

The backlight source is a white light source having a peak top of the emission spectrum in each wavelength region of 400 nm or more and less than 495 nm (B region), 495 nm or more and less than 600 nm (G region), and 600 nm or more and 780 nm or less (R region). Is also preferable. For example, a white light source using quantum dot technology, a phosphor type white LED light source using a phosphor and a blue LED each having an emission peak in the R (red) and G (green) regions by excitation light, and a three-wavelength method White LED light source, white LED light source combining red laser, and other white LED light source using blue LED and fluoride phosphor (also referred to as “KSF”) whose composition formula is K ₂ SiF ₆ : Mn ⁴⁺ Etc. These white light sources are attracting attention as a backlight light source for liquid crystal display devices that support a wide color gamut, and all of them use a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor that have been used in the past. Compared to a light source composed of a white light emitting diode composed of a combined light emitting element, the half width of the peak is narrow. When using a backlight light source composed of these white light sources, compared to a backlight light source composed of a white light emitting diode composed of a light emitting element combining a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor, When a polarizer protective film that is a constituent member of a polarizing plate is used as a polyester film having retardation, rainbow spots tend to occur. However, if the polarizer protective film of the present invention is used, the rainbow spots are significantly increased. Can be suppressed.

5. Organic EL Display and QLED Display As the organic EL element, an organic EL element known in the technical field can be appropriately selected and used. Use of the organic EL element is preferable in terms of wide viewing angle, high contrast, and high-speed response. An organic EL element is typically a light emitter (organic electroluminescent light emitter) having a structure in which an anode as a transparent electrode, an organic light emitting layer, and a cathode as a metal electrode are laminated in this order on a transparent substrate. is there. The organic EL cell emits light by recombination of holes injected from the anode and electrons injected from the cathode in the organic light emitting layer when a voltage is applied between the anode and the cathode. To do.

Any transparent substrate can be adopted as the transparent substrate. For example, the transparent substrate can be selected from the group consisting of a glass substrate, a ceramic substrate, a semiconductor substrate, a metal substrate, and a plastic substrate. Specific examples of the plastic substrate include conventionally used transparent resin films. The transparent substrate may be provided with a surface treatment layer as necessary. Examples of the surface treatment layer include a moisture permeation prevention layer, a gas barrier layer, a hard coat layer, an undercoat layer, and the like.

Examples of the material constituting the anode and the cathode include metals, metal oxides, alloys, electrically conductive compounds, and mixtures thereof. More specific materials constituting the anode include conductive transparent materials such as gold, silver, chromium, nickel, copper iodide, indium tin oxide (ITO), tin oxide, and zinc oxide. More specific materials constituting the cathode include magnesium, aluminum, indium, lithium, sodium, cesium, silver, magnesium-silver alloy, magnesium-indium alloy, and lithium-aluminum alloy. *

The thickness of the anode and the cathode can be arbitrarily set according to the materials constituting the anode and the cathode. The thickness of the anode can be appropriately set, for example, in the range of 10 nm to 200 nm, preferably 10 nm to 100 nm. The thickness of the cathode is, for example, 10 nm to 1000 nm, and can be appropriately set from the range of 10 nm to 200 nm.

The organic light emitting layer is a layer having a function of emitting light by providing a recombination field of holes and electrons when a voltage is applied. The organic light emitting layer contains an organic light emitting material and may have a single layer structure or a laminated structure of two or more layers. In the case of a laminated structure, each layer may emit light with different emission colors. The thickness of the organic light emitting layer is arbitrary, and can be appropriately set within a range of 3 nm to 3 μm, for example.

The organic light emitting material used for the organic light emitting layer can be appropriately selected from arbitrary light emitting materials. Specifically, olefin-based light emitting materials such as 4,4 ′-(2,2-diphenylvinyl) biphenyl; 9,10-di (2-naphthyl) anthracene, 9,10-bis (3,5-diphenylphenyl) ) Anthracene, 9,10-bis (9,9-dimethylfluorenyl) anthracene, 9,10- (4- (2,2-diphenylvinyl) phenyl) anthracene, 9,10′-bis (2-biphenylyl) -9,9'-bisanthracene, 9,10,9 ', 10'-tetraphenyl-2,2'-bianthryl, 1,4-bis (9-phenyl-10-anthracene) benzene and other anthracene-based luminescent materials Spiro-based luminescent materials such as 2,7,2 ′, 7′-tetrakis (2,2-diphenylvinyl) spirobifluorene; 4,4′-dicarbazolbiphenyl, 1,3 Can be appropriately selected from the group consisting of pyrene based light emitting material such as 1,3,5-tri pin renin benzene; carbazole luminescent material such as di-carbazolyl benzene.

The organic EL element includes a sealing member formed so as to cover the organic EL element in order to block the organic EL element including the anode, the organic light emitting layer, and the cathode on the base material from the outside air. Also good. By providing the sealing member, it is possible to prevent deterioration of the light emitting characteristics of the organic light emitting layer due to moisture and oxygen in the outside air.

The organic EL element may further include an arbitrary member (for example, a hole injection layer, a hole transport layer, an electron injection layer, and / or an electron transport layer) at any appropriate position.

When using an organic EL cell as the image display cell, it is preferable to have a polarizing plate on the viewing side. Since the thickness of the organic light emitting layer is as thin as about 10 nm, external light is reflected by the metal electrode and is emitted again to the viewing side, and when viewed from the outside, the display surface of the organic EL display device may look like a mirror surface. is there. In order to shield such specular reflection of external light, it is preferable to provide a polarizing plate on the viewing side of the organic EL cell, and further provide a quarter wavelength plate between the organic EL cell and the polarizing plate. . As a polarizing plate, the polarizing plate mentioned above can be used, and it is preferable that the polarizer protective film which consists of a polyester film of this invention is laminated | stacked on the visual recognition side of a polarizer. Moreover, the aspect which laminates | stacks a quarter wavelength plate on a polarizer instead of the protective film by the side of the organic EL element of a polarizer is also preferable. By constructing a circularly polarizing plate by combining these viewing side polarizing plates and quarter-wave plates, external light reflected by the metal electrode of the organic EL cell is shielded by the circularly polarizing plate. A reduction in the visibility of the device can be suppressed. Also. A half-wave plate or the like may be further laminated on the organic EL element side or the polarizer side of the quarter-wave plate. Preferably, a half-wave plate or the like is laminated on the organic EL element side of the quarter-wave plate with an inclination to each other's optical axis, and disclosed in JP-A-10-68816 and JP-A-2017-97379. Has been.

Also, the QLED display is similar to the organic EL in that it uses the fact that the quantum dots themselves emit light when electricity is applied, and is attracting attention as a next-generation display.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. These are all included in the technical scope of the present invention. In addition, the evaluation method of the physical property in the following examples is as follows.

(1) Evaluation of slow axis direction of film The evaluation of the slow axis direction of the film was measured with a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments).

(2) ΔNxy and retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | nx−ny |) on the film and the film thickness d (nm). Yes, it is a scale showing optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), determine the slow axis direction of the film, 4 cm so that the slow axis direction is parallel to the long side of the measurement sample. A rectangle of × 2 cm was cut out and used as a measurement sample. About this sample, the biaxial refractive index orthogonal (refractive index in the slow axis direction: nx, the refractive index in the direction perpendicular to the slow axis direction in the plane (that is, the refractive index in the fast axis direction): ny), The refractive index (nz) in the thickness direction is obtained by an Abbe refractometer (Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm), and the absolute value (| nx−ny |) of the biaxial refractive index difference is refracted. Anisotropy of rate (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).

(3) NZ coefficient The values of nx, ny, and nz measured by the Abbe refractometer in (2) were substituted for | nx-nz | / | nx-ny | to obtain the NZ coefficient.

(4) Elastic modulus The elastic modulus of the polyester film was measured by using a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments Inc. according to JIS-K7244 (DMS) after standing for 168 hours in an environment of 25 ° C. and 50% RH. Evaluation was performed. The temperature dependence of 25 ° C to 120 ° C was measured under the conditions of tensile mode, driving frequency 1 Hz, distance between chucks 5 mm, and heating rate 2 ° C / min. The average storage elastic modulus at 30 ° C to 100 ° C was taken as the elastic modulus. did. The measurement was performed in the MD direction.

(5-1) Iris observation (liquid crystal display)
Roll-to-roll of a polarizer roll made of iodine and polyvinyl alcohol film produced by uniaxial stretching in the MD direction and a PET film roll of polarizer protective films 1 to 9 described later so that the MD directions are parallel to each other We pasted together. Further, a TAC film roll (manufactured by FUJIFILM Co., Ltd., thickness 40 μm) is similarly bonded to the other surface of the polarizer by roll-to-roll, and polarized light comprising PET film / polarizer / TAC film. A board was created. The obtained polarizing plate is used as a light source (Nichia Chemical Co., NSPW500CS), a light emitting element combining a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor. The polarizing plate on the incident light side was installed so that the polyester film was on the light source side, and the polarizing plate on the outgoing light side was installed on the viewing side so that the polyester film was on the viewing side. Visual observation was performed from the front side and the oblique direction of the polarizing plate of the liquid crystal display device, and the presence or absence of the occurrence of iridescence was determined as follows.

○: No iridium is observed from any direction.
Δ: When observed from an oblique direction, a thin rainbow spot can be observed depending on the angle.
X: When observing from an oblique direction, rainbow spots can be clearly observed.

(5-2) Iridescent observation (organic EL display)
Roll-to-roll of a polarizer roll made of iodine and polyvinyl alcohol film produced by uniaxial stretching in the MD direction and a PET film roll of polarizer protective films 1 to 9 described later so that the MD directions are parallel to each other We pasted together. In addition, a quarter wave plate roll was similarly bonded to the other surface of the polarizer using a roll-to-roll process to create a polarizing plate made of PET film / polarizer / (1/4 wave plate). . The circularly polarizing plate (the circularly polarizing plate disposed on the viewing side from the organic EL element) was removed from the commercially available organic EL display (LG EL organic EL television C6P 55 inch), and the polarized light obtained above was used instead. The plate was placed in an organic EL display so that the PET film was placed on the viewing side. The organic EL was visually observed from the front and oblique directions of the display, and the presence or absence of rainbow spots was determined as follows.

(6) Warpage Evaluation of Liquid Crystal Panel A polarizer roll made of iodine and a polyvinyl alcohol film manufactured by uniaxial stretching in the MD direction and a PET film roll of a polarizer protective film described later are parallel to each other in the MD direction. As shown in FIG. Further, a TAC film roll (manufactured by FUJIFILM Co., Ltd., thickness 40 μm) is similarly bonded to the other surface of the polarizer by roll-to-roll, and polarized light comprising PET film / polarizer / TAC film. A board was created. Next, a glass plate having a width of 125 mm, a length of 220 mm, and a thickness of 0.4 mm, and the polarizing plate having the same size as the crossed Nicols on both sides of the glass plate (one polarizing plate has an absorption axis parallel to the width direction, One polarizing plate was bonded using PSA so that the absorption axis was parallel to the length direction. At this time, polarizers having the same contraction force were used for the upper and lower polarizing plates. Moreover, the polarizer protective film of this invention is bonded together so that it may be arrange | positioned on the outer side. Next, heat treatment is performed for 30 minutes using a gear oven set at 100 ° C., and after cooling for 10 minutes in an environment set at a room temperature of 25 ° C., the heights of the four corners are measured with a measure to obtain the maximum value. I read. Moreover, the measured value made 5 mm or less into the favorable range.

(7) Tear strength Using a Shimadzu autograph (AG-X plus), the tear strength (N / mm) per film thickness was measured for each film according to the right-angled tear method (JIS K-7128-3). did. The tear strength is measured in two directions parallel to and perpendicular to the orientation direction (slow axis) of the film (ie, the slow axis direction and the fast axis direction), and the smaller value is expressed as the tear strength. 1. In addition, the measurement in the orientation main axis direction (slow axis direction) was performed with a molecular orientation meter (manufactured by Oji Scientific Instruments, MOA-6004 type molecular orientation meter).

(8) Film-forming property Starting 1 hour after the start of film-forming, the number of breaks for 1 hour was compared, and the film-forming property was determined as follows.

○: The number of breaks is less than 3 △: The number of breaks is 3 or more and less than 6 x: The number of breaks is 6 or more

(9) Scratch Evaluation Method Scratches with a maximum height Sz of 0.6 μm or more measured by a laser microscope (OLS4100, manufactured by Olympus Corporation) after inspecting the film one hour after the start of film formation with a defect inspection apparatus The number of these was determined as follows.

○: The number of scratches is less than 3 / m ² Δ: The number of scratches is 3 / m ² or more and less than 6 / m ² ×: The number of scratches is 6 / m ² or more

(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. Subsequently, the pressure was raised and the esterification reaction was performed under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., and then the esterification reaction vessel 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-Adjustment of Adhesive Modification Coating Solution)
A transesterification reaction and a polycondensation reaction were carried out by a conventional method, and as a dicarboxylic acid component (based on the total dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol as a glycol component (based on the entire glycol component) was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of a nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin solution was mixed with 99.46 parts by mass of the silicia 310. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modified coating solution.

(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 an ordinary 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, after applying the adhesive property-modifying coating solution on the both sides of this unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m ² , the coating was dried at 80 ° C. for 20 seconds. .

The unstretched film on which this coating layer has been formed is guided to a simultaneous biaxial stretching machine, and the end of the film is held by a clip, guided to a hot air zone at a temperature of 125 ° C., 6.5 times in the running direction and 2 in the width direction. .2 stretched. Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds to obtain a biaxially oriented PET film having a film thickness of about 40 μm. This was wound into a roll and used as a film roll (film roll having a film length in the MD direction of 500 m). The slow axis of the obtained film was within 3 ° from the running direction. This was designated as a polarizer protective film 1.

(Polarizer protective film 2)
A biaxially oriented PET film having a film thickness of about 40 μm is obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film is changed and stretched 6.0 times in the running direction and 2.2 times in the width direction. It was. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 3 ° from the running direction. This was designated as a polarizer protective film 2.

(Polarizer protective film 3)
An unstretched film is made in the same manner as the polarizer protective film 1, and is heated to 105 ° C. using a heated roll group and an infrared heater in a sequential biaxial stretching machine, and then in a traveling direction with a roll group having a difference in peripheral speed. Then, the film was drawn into a hot air zone having a temperature of 125 ° C. and stretched 2.2 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 to obtain a biaxially oriented PET film having a film thickness of about 40 μm. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 5 ° from the running direction. This was designated as a polarizer protective film 3.

(Polarizer protective film 4)
A uniaxially oriented PET film having a film thickness of about 40 μm was obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film was changed and the film was stretched 1.0 times in the running direction and 4.0 times in the width direction. . This was wound up into a roll to obtain a film roll. The slow axis of the obtained film was within 4 ° from the width direction. This was designated as a polarizer protective film 4. Since the slow axis of the polarizer protective film 4 was the width direction, a thin rainbow-like color spot was observed depending on the angle when observed from an oblique direction. In addition, the tear strength was low and it was easily torn. For example, when the polarizer protective film 4 was bonded to the polarizer and a polarizing plate was produced by roll-to-roll, it was often cracked in the width direction as compared with other films.

(Polarizer protective film 5)
The thickness of the unstretched film was changed, heated to 105 ° C using a heated roll group and an infrared heater, and then stretched 4.0 times in the running direction with a roll group having a difference in peripheral speed, and then the temperature was 125 ° C. It led to the hot air zone and extended | stretched 1.0 time in the width direction. Next, the film was processed at a temperature of 225 ° C. for 30 seconds while maintaining the width stretched in the width direction, to obtain a uniaxially oriented PET film having a film thickness of about 40 μm. This was wound up into a roll to obtain a film roll. The slow axis of the obtained film was within 8 ° from the running direction. This was designated as a polarizer protective film 5. In the polarizer protective film 5, no rainbow-like color spots were observed, but the tear strength was low and the film was easily torn.

(Polarizer protective film 6)
A biaxially oriented PET film having a film thickness of about 40 μm is obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film is changed and stretched 4.5 times in the running direction and 2.4 times in the width direction. It was. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 8 ° from the running direction. Since the obtained film had a low ΔNxy, rainbow-like color spots were observed when observed from an oblique direction.

(Polarizer protective film 7)
Change the thickness of the unstretched film, heat to 105 ° C using a group of rolls heated sequentially by a biaxial stretching machine and an infrared heater, and then stretch 2.2 times in the running direction with a group of rolls with a difference in peripheral speed Then, it was led to a hot air zone having a temperature of 125 ° C. and stretched 5.5 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 to obtain a biaxially oriented PET film having a film thickness of about 40 μm. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 6 ° from the width direction. Since the slow axis direction of the obtained film was the width direction, iridescent color spots were observed when observed from an oblique direction.

(Polarizer protective film 8)
A biaxially oriented PET film having a film thickness of about 40 μm is obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film is changed and the film is stretched 6.0 times in the running direction and 1.5 times in the width direction. It was. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 3 ° from the running direction. This was designated as a polarizer protective film 8.

(Polarizer protective film 9)
A biaxially oriented PET film having a film thickness of about 40 μm is obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film is changed and stretched 6.5 times in the running direction and 2.7 times in the width direction. It was. This was wound up into a roll to obtain a film roll (film roll having a length in the MD direction of 500 m). The slow axis of the obtained film was within 3 ° from the running direction. This was designated as a polarizer protective film 9.

Table 1 below shows the results of measurement of rainbow spot observation and tear strength of the polarizer protective films 1 to 9.

As shown in Table 1, when rainbow spots were observed using the polarizer protective films 1 to 3, 5, 8, and 9, the rainbow spots were observed when observed from either the front or oblique directions. There wasn't. On the other hand, about the polarizer protective film 4, when observed from the diagonal, the thin rainbow was observed partially. Further, the polarizer protective film 5 had no tear, but had low tear strength and unstable film formation. In addition, when the polarizer protective films 6 and 7 were observed from an oblique direction, clear rainbow spots were observed. In addition, in the item (5-1) Iridescent observation described above, a polarizing plate made of a PET film / polarizer obtained by laminating only a PET film without laminating a TAC film on the polarizer was used in the same manner. When a liquid crystal display device was manufactured and rainbow spots were observed in the same manner, the same results as the rainbow spot observation results shown in Table 1 were obtained. Further, when the warpage of the liquid crystal panel was evaluated by the method described in (6) above using the polarizer protective films 1 to 3, 5, 8, and 9, the measured value was 5 mm or less, and all were good. It was a result.

By using the polarizer protective film, polarizing plate and image display device (liquid crystal display device, organic EL display, etc.) of the present invention, the LCD can be made thinner and less expensive without reducing visibility due to iridescent color spots. The industrial applicability is extremely high.

Claims

A polarizer protective film including a polyester film,
The slow axis direction of the polyester film is substantially parallel to the MD direction,
In-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.20 or less,
Furthermore, a polarizer protective film satisfying the following (A) or (B):
(A) The refractive index in the fast axis direction of the polyester film is 1.580 or more and 1.630 or less;
(B) The smaller value of the tear strength by the right-angled tearing method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.
The polarizer protective film of Claim 1 whose refractive index of the fast axis direction of the said polyester film is 1.580 or more and 1.630 or less.
The polarizer protective film according to claim 1 or 2, wherein the smaller value of the tear strength by the right-angled tearing method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.
The polarizer protective film according to any one of claims 1 to 3, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less.
The polarizer protective film according to claim 1, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less.
6. The polarizer protective film according to claim 1, wherein the polyester film has a thickness of 25 to 60 μm.
The polarizer protective film according to any one of claims 1 to 6, wherein an angle formed by the slow axis direction of the polyester film and the MD direction is within 3 degrees.
The polarizer protective film according to any one of claims 1 to 7, wherein the elastic modulus in the MD direction of the polyester film is 3000 MPa or more.
A polarizing plate in which the polarizer protective film according to any one of claims 1 to 8 is laminated on at least one surface of the polarizer.
A polarizing plate in which the polarizer protective film according to any one of claims 1 to 8 is laminated on one side of the polarizer and the film is not laminated on the other side of the polarizer.
A polarizing plate in which the polarizer protective film according to any one of claims 1 to 8 is laminated on one surface of a polarizer and a quarter-wave plate is laminated on the other surface of the polarizer.
An image display device comprising the polarizing plate according to any one of claims 9 to 11.
A liquid crystal display device comprising the polarizing plate according to claim 9.
An organic EL display comprising the polarizing plate according to any one of claims 9 to 11.
A QLED display comprising the polarizing plate according to any one of claims 9 to 11.