JPWO2018181653A1 - Polarizer protective film, polarizing plate and image display device - Google Patents

Abstract

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 0.20 or less, Furthermore, a polarizer protective film that satisfies the following (A) or (B): (A) the polyester film has a refractive index in the fast axis direction of 1.580 or more and 1.630 or less; (B) the polyester film The smaller one of the tear strengths obtained by the right-angled tearing method in the slow axis direction and the fast axis direction is 250 N / mm or more.

Description

  The present invention relates to a polarizer protective film, a polarizing plate, and an image display device such as a liquid crystal display device and an organic EL display. More specifically, the present invention relates to a polarizer protective film, a polarizing plate, and an image display device (a liquid crystal display device, an organic EL display, and the like) having good visibility and suitable for thinning.

  A polarizing plate used in a liquid crystal display device (LCD) usually has a configuration in which a polarizer obtained by dyeing iodine into polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films. Usually, a triacetyl cellulose (TAC) film is used as the film. In recent years, as LCDs have become thinner and costs have been reduced, it has been required to make polarizing plates thinner. However, if the thickness of the TAC film used as a protective film is reduced, sufficient mechanical strength cannot be obtained, and moisture permeability deteriorates. Also, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

  Polyester films are more durable than TAC films, but have birefringence, unlike TAC films. Therefore, when they are used as polarizer protective films, there is a problem that image quality is reduced due to optical distortion. That is, since a polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, a rainbow-like color spot occurs when observed from an oblique direction, and the image quality deteriorates. . Therefore, in Patent Document 1, a measure against rainbow-like color spots is taken by controlling the in-plane retardation of the polyester film to a specific range.

WO2011-162198

  However, in the market, there is a demand for a thinner image display device such as a liquid crystal display device, and when the thickness of the polarizer protective film is reduced, retardation sufficient to sufficiently suppress rainbow-like color spots is required. It was difficult to secure. Furthermore, since the mechanical strength required for processing is insufficient due to the reduction in the thickness of the film, it has been sometimes difficult to respond to the demand for thinning.

  An object of the present invention in one embodiment is to be able to cope with a reduction in the thickness of an image display device such as a liquid crystal display device or an organic EL display (that is, to have sufficient mechanical strength), and to visually recognize the rainbow-like color spot. An object of the present invention is to provide a polarizer protective film, a polarizing plate, and an image display device (a liquid crystal display device, an organic EL display, and the like) in which deterioration of properties is suppressed.

The 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,
The in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.20 or less,
The fast axis direction refractive index of the polyester film is 1.580 or more and 1.630 or less.
Polarizer protection film.
Term A2.
The polarizer protective film according to item A1, wherein the smaller one of the tear strengths of the polyester film in the slow axis direction and the fast axis direction obtained by the perpendicular tearing method is 250 N / mm or more.
Term A3.
The polarizer protective film according to item A1 or A2, wherein the NZ coefficient of the polyester film is 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 from 1500 nm to 30000 nm.
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 the angle between the slow axis direction and the MD direction of the polyester film 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 in which the polarizer protective film according to any one of Items A1 to A7 is 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 surface of the polarizer, and the film is not laminated on the other surface 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 surface of the polarizer, and a 波長 wavelength plate is laminated on the other surface 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 including the polarizing plate according to any one of Items A8 to A10.
Term A14.
A QLED display including 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 one of the tear strengths of the polyester film by the perpendicular tearing method in the slow axis direction and the fast axis direction is 250 N / mm or more,
Polarizer protection film.
Term B2.
The polarizer protective film according to item B1, wherein the NZ coefficient of the polyester film is 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 from 1500 nm to 30000 nm.
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 the angle between the slow axis direction and the MD direction of the polyester film is within 3 degrees.
Term B6.
The polarizer protective film according to any one of Items B1 to B5, wherein the MD modulus 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 surface of the polarizer, and the film is not laminated on the other surface 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 surface of the polarizer, and a 波長 wavelength plate is laminated on the other surface 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 including 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 thickness of the polyester film is 15 to 60 μm,
Polarizer protection film.
Term C2.
The polarizer protective film according to item C1, wherein the NZ coefficient of the polyester film is 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 the angle between the slow axis direction and the MD direction of the polyester film is within 3 degrees.
Term C5.
The polarizer protective film according to any one of Items C1 to C4, wherein the MD modulus 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 surface of the polarizer, and the film is not laminated on the other surface 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 surface of the polarizer, and a 波長 wavelength plate is laminated on the other surface 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 including 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, the polarizing plate, and the image display device (such as a liquid crystal display device and an organic EL display) of the present invention have good rainbow-like color spots (hereinafter, the same as rainbow spots) at any viewing angle. High visibility can be ensured. Further, 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 the deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is made thin.

1. Polarizer protective film In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, wherein the slow axis direction of the polyester film is substantially parallel to the MD direction, the polyester film Has an in-plane birefringence ΔNxy of 0.06 or more and 0.20 or less, and a refractive index in the fast axis direction of the polyester film of 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, wherein the slow axis direction of the polyester film is substantially parallel to the MD direction, and the in-plane copy of the polyester film. The refraction ΔNxy is 0.06 or more and 0.2 or less, and the smaller one of the tear strengths of the polyester film in the slow axis direction and the fast axis direction obtained by the perpendicular tearing method 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, wherein the slow axis direction of the polyester film is substantially parallel to the MD direction, and the in-plane copy of the polyester film. The refraction ΔNxy is 0.06 or more and 0.20 or less, and the thickness of the polyester film is 15 to 60 μm. A problem in this embodiment is to provide a polarizer protective film in which the deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is thinned, and a polarizing plate and an image display device ( Liquid crystal display device, 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 (running direction during film formation) from the viewpoint of suppressing rainbow-like color spots. Here, being substantially parallel means that the angle between the slow axis direction of the polyester film and the MD direction (running 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 (manufactured by Oji Scientific Instruments, MOA-6004 type molecular orientation meter).

  In the present specification, the MD direction is a running direction during film formation, and may be referred to as a vertical direction. Further, the TD direction is a width direction at the time of film formation, and may be referred to as a lateral direction.

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

  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 is obtained by strongly stretching the polyester film in the MD direction. When a polarizing plate is manufactured by laminating the polyester film and a polarizer manufactured by uniaxially stretching the MD 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 are determined. The directions are parallel. The present inventors, when laminated in a state where the absorption axis of the polarizer and the slow axis of the polyester film were parallel, was laminated in a state where the absorption axis of the polarizer and the slow axis of the polyester film were perpendicular. It was found that the iris suppression effect was superior to that of the case. In order to efficiently produce a polarizing plate excellent in rainbow spot suppression effect by an industrially advantageous roll-to-roll method, a 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 a polyester film having the same.

  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 more preferably 0.08 or more and 0 or less. .18 or less. When ΔNxy is less than 0.06, a rainbow-like color spot is easily observed when obliquely observed. In the case of a film having ΔNxy of more than 0.2, rainbow-like color spots do not occur, but since the film approaches full uniaxiality (uniaxial symmetry), the mechanical strength in a direction parallel to the orientation direction is significantly reduced. The in-plane birefringence ΔNxy is the 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 used in the polarizer protective film of the present invention and having a slow axis direction substantially parallel to the MD direction is preferably 1.58 or more. It is 1.63 or less, more preferably 1.584 or more and 1.625 or less, and still more preferably 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. In a film having a refractive index (ny) of more than 1.63 in the fast axis direction, a rainbow-like color spot tends to be easily observed when obliquely observed.

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

  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 still more 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. The NZ coefficient is 1.0 in a perfect uniaxial (uniaxially symmetric) film, but the mechanical strength in a direction parallel to the orientation direction tends to decrease as the film approaches a perfect uniaxial (uniaxially symmetric) film. .

  The NZ coefficient can be obtained as follows. The orientation main axis direction (slow axis direction) of the film is determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments), and the orientation main axis direction and the direction orthogonal to this (fast axis direction) ), The refractive index nx in the slow axis direction, the refractive index ny in the fast axis direction ny, where nx> ny, and the refractive index (nz) in the thickness direction are measured by an Abbe refractometer (Atago Co., Ltd.). Manufactured by NAR-4T, measurement wavelength: 589 nm). The NZ coefficients can be obtained by substituting the 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 iridescence, 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 the retardation is preferably 2500 nm, and the next preferred lower limit is 3000 nm.

  On the other hand, the upper limit of the retardation is 30,000 nm. Even if a polyester film having a further retardation is used, not only the effect of further improving the visibility is not substantially obtained, but also the thickness of the film becomes considerably thick, and the handleability as an industrial material is deteriorated. Absent. In one embodiment, a preferable upper limit of the retardation is 8000 nm, a more preferable upper limit is 6000 nm, a further preferable upper limit is 5500 nm, and a particularly preferable upper limit is 5000 nm.

  The birefringence can be determined by measuring the refractive index in the biaxial direction, or 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 thickness of members has been reduced. Under such circumstances, with the thinning of the glass substrate used for the liquid crystal panel, the problem of the warpage of the liquid crystal panel due to the shrinkage of the polarizing plate has become apparent. The shrinkage of the polarizing plate is caused by the shrinkage of the PVA film as the polarizer (mainly the shrinkage in the absorption axis direction), and the shrinkage 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, sufficient control force acts on the shrinkage of the polarizer to prevent the liquid crystal panel from warping. However, if the elastic modulus is significantly lower than 3000 MPa, the liquid crystal panel warps. May become apparent. A preferred lower limit of the elastic modulus in the MD direction is 3500 MPa, a more preferred lower limit is 4000 MPa, and a still more preferred lower limit is 4500 MPa.

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

  For the purpose of suppressing the deterioration of the optical functional dye such as the iodine dye, the polarizer protective film of the present invention desirably has a light transmittance at a wavelength of 380 nm of 20% or less. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optical functional dye due to ultraviolet rays can be suppressed. 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 make the transmittance at a wavelength of 380 nm of the polarizer protective film of the present invention 20% or less, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber and the thickness of the film. 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 a benzotriazole type, a benzophenone type, a cyclic imino ester type and the like, and a combination thereof, but are not particularly limited as long as the absorbance is within the range specified by the present invention. However, from the viewpoint of durability, benzotriazoles and cyclic iminoesters are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be simultaneously absorbed, so that the ultraviolet absorbing effect can be further improved.

  Examples of the benzophenone-based UV absorber, benzotriazole-based UV absorber, and acrylonitrile-based UV absorber include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole and 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 Lorobenzotriazole, 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 the cyclic iminoester ultraviolet absorber include 2,2 ′-(1,4-phenylene) bis ( 4H-3,1-benzoxazinone-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3 , 1-benzoxazin-4-one, etc., but are not particularly limited thereto.

  It is also a preferable embodiment that various additives other than the catalyst are contained in addition to the ultraviolet absorber as long as the effects of the present invention are not impaired. As additives, for example, inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, anti-gelling agents And surfactants. It is also preferable that the polyester film contains substantially no particles in order to exhibit high transparency. The phrase "do not substantially contain particles" means, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescent X-ray analysis, the content is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less. means.

  In the polarizer protective film of the present invention, it is also a preferable embodiment that various hard coats are applied to the surface for the purpose of preventing reflection, suppressing glare, and suppressing scratches.

  Further, in the present invention, the polyester film may be subjected to a corona treatment, a coating treatment, a flame treatment or the like 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, the film of the present invention has, on at least one surface thereof, an easy-adhesion layer containing at least one of polyester resin, polyurethane resin and polyacryl resin as a main component. 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 liquid used for forming the easily adhesive layer of the present invention is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin and a polyurethane resin. These coating liquids include, for example, water-soluble or water-dispersible compounds disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying the coating liquid to at least one of the film surfaces and drying the applied liquid at 100 to 150 ° C. in any step of the polyester film manufacturing step. It is preferable to control the final coating amount of the easy-adhesion layer to 0.05 to 0.2 g / m ² . When the coating amount is significantly lower than 0.05 g / m ² , the adhesiveness to the obtained polarizer may be insufficient. On the other hand, if the coating amount exceeds 0.2 g / m ² , the blocking resistance may decrease. When the easy-adhesion layers are provided on both surfaces of the polyester film, the application amount of the easy-adhesion layers 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 easily adhesive layer in order to impart lubricity. It is preferable to use particles having an average particle diameter of 2 μm or less. When the average particle diameter of the particles is significantly larger than 2 μm, the particles easily fall off the coating layer. Examples of the particles contained in the easy-adhesion layer include 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 two or more of them may be added in combination.

  In addition, as a method of applying the coating liquid, a known method can be used. For example, a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, and the like, and these methods can be used alone. Alternatively, they can be performed in combination.

  The average particle size of the above particles is measured by the following method. The particles are photographed with a scanning electron microscope (SEM) and the maximum diameter of 300 to 500 particles (between the two most distant points) at a magnification such that the size of one smallest particle is 2 to 5 mm Distance), and the average value is defined as the average particle size.

  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 a longitudinal direction and a transverse direction at a temperature equal to or higher than a 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, even when observed from directly above the film surface. Although rainbow-like color spots are not seen, attention must be paid to the fact that rainbow-like color spots may be observed when obliquely observed.

  This phenomenon occurs because the biaxially stretched film is formed of a refractive index ellipsoid having different refractive indices in the running direction, the width direction, and the 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 looks like a perfect circle. Accordingly, when the display screen is observed from a specific oblique direction, a point where the retardation becomes zero may occur, and a rainbow-like color spot may be formed concentrically around the point. If the angle from directly above the film surface (in the normal direction) to a position at which a rainbow-like color spot is seen is θ, this angle θ increases as the birefringence in the film surface increases, and the rainbow-like color increases. The spots are less visible. Since the angle θ tends to be small in a biaxially stretched film, a uniaxially stretched film is preferable because a rainbow-like color spot is less likely to be seen.

  However, a completely uniaxial (uniaxially symmetric) 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 in which rainbow-like color spots are not substantially generated or in a range in which a rainbow-like color spot is not generated in a viewing angle range required for a display screen. Is preferred.

  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, longitudinal stretching is roll stretching, so that the film is easily scratched. Therefore, from the viewpoint of preventing scratches during stretching, simultaneous biaxial stretching without a roll is more preferable. Explaining the film forming conditions specifically, the longitudinal stretching temperature and the transverse stretching temperature are preferably from 80 to 150 ° C, particularly preferably from 90 to 140 ° C. The longitudinal stretching ratio is preferably 5.5 to 7.5 times, more preferably 6.0 to 7.0 times, and particularly preferably 6.5 to 7.0 times. Further, the transverse stretching ratio is preferably 1.5 to 3.0 times, and particularly preferably 1.8 to 2.8 times. In order to control the direction of the slow axis, ΔNxy, the value of the refractive index in the direction of the fast axis, the NZ coefficient and the tear strength within the above ranges, it is preferable to control each of the longitudinal stretching ratio and the transverse stretching ratio. . If the difference between the longitudinal and transverse stretching ratios is too small, it is difficult to increase ΔNxy, which is not preferable. Setting the stretching temperature low is also a preferable measure for increasing ΔNxy.

  In order to set the value of the refractive index in the fast axis direction to the above-mentioned range, and to increase the tear strength, it is preferable that the ΔNxy is appropriately biaxial under the condition that ΔNxy satisfies the range specified in the present application, rather than a perfect uniaxial film. Is preferably provided. In the subsequent heat treatment, the treatment temperature is preferably from 100 to 250C, particularly preferably from 180 to 245C.

  As described above, the ΔNxy and NZ coefficients can be controlled to specific ranges by appropriately setting the stretching ratio and the stretching temperature. For example, the higher the draw ratio and the lower the drawing temperature, the easier it is to obtain a high ΔNxy. Conversely, the lower the draw ratio and the higher the drawing temperature, the easier it is to obtain a low ΔNxy. In addition to the control of the ΔNxy and NZ coefficients, it is preferable to set final film forming conditions in consideration of physical properties and the like required for processing.

  The thickness of the polyester film used as the polarizer protective film of the present invention is optional, but is preferably in the range of 15 to 200 μm, and more preferably in the range of 15 to 150 μm. When the thickness of the film is less than 15 μm, the mechanical properties of the film are remarkably reduced, and the film tends to be torn or broken, and the practicality as an industrial material tends to be significantly reduced. A preferred lower limit of the thickness is 25 μm, a more preferred lower limit is 30 μm, and a 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 large, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 150 μm, more preferably the upper limit of the thickness is 80 μm, more preferably the upper limit of the thickness is 60 μm, more preferably the upper limit of the thickness is 55 μm, The more preferable upper limit of the thickness is 50 μm, and the more preferable upper limit of the thickness is 45 μm. In order to control the ΔNxy, the NZ coefficient and the tear strength within the range of the present invention even in the above thickness range, polyethylene talephthalate is suitable for the polyester used as the film substrate.

  In addition, as a method of blending the ultraviolet absorber into the polyester film in the present invention, a known method may be used in combination.For example, using a kneading extruder, the dried ultraviolet absorber is blended with the polymer raw material. A masterbatch can be prepared and blended by a method of mixing the masterbatch and a polymer material at the time of 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 to mix it economically. It is preferable to use a kneading extruder as a condition for preparing a master batch, and to extrude at a temperature of from the melting point of the polyester raw material to 290 ° C. for 1 to 15 minutes. At 290 ° C. or higher, the amount of the ultraviolet absorber is greatly reduced, and the viscosity of the master batch is greatly reduced. If the extrusion temperature is 1 minute or less, it becomes difficult to uniformly mix the ultraviolet absorber. At this time, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added as needed.

  In the present invention, it is preferable that the film has a multilayer structure of at least three or more 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, a master batch containing an ultraviolet absorbent and polyester pellets for the intermediate layer are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder to form a slit. The sheet is extruded from a die into a sheet and cooled and solidified on a casting roll to form 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, The three-layer sheet is extruded from a die and cooled by a casting roll to make an unstretched film. In the present invention, it is preferable to perform high-precision filtration at the time of melt extrusion in order to remove foreign matter contained in the raw material polyester, which causes optical defects. The filtration 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 is significantly larger than 15 μm, the removal of foreign substances 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 obtained by dyeing PVA with iodine. In the polarizing plate of the present invention, it is preferable to use the polarizer protective film of the present invention having the above-mentioned specific polyester film 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 specific polyester film described above is laminated on one surface of the polarizer, and the other surface of the polarizer is a TAC film, a norbornene film, an acrylic film, or the like. Of a polarizer protective film or optical compensation film having no birefringence. In another preferred embodiment, the polarizer protective film of the present invention including the specific polyester film described above is laminated on one surface of the polarizer, and the film is laminated on the other surface of the polarizer. No (a separate film as a single unit is not attached to the polarizer on the other side of the polarizer). 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 material)) is formed on the surface of the polarizer opposite to the surface on which the specific polyester film is laminated. Or a layer made of an inorganic material) or a layer combining these functions).

  As described above, the polarizing plate of the present invention is laminated such that the absorption axis of the polarizer and the slow axis of the polyester film are substantially parallel to each other, from the viewpoint of suppressing iris, and from the viewpoint of suppressing the warpage of the liquid crystal panel. Preferably. Here, “substantially parallel” is intended to allow a slight deviation. The angle between 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 within 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, and the like including a polarizing plate inside the image display device.

4. 2. Description of the Related Art In general, a liquid crystal panel includes a rear module, a liquid crystal cell, and a front module in order from a side facing a backlight light source to a side displaying an image (viewing side). The rear module and the front module generally include 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 displaying the image (viewing side) in the front module.

  The liquid crystal display device has at least a backlight light source and a liquid crystal cell disposed between two polarizing plates as constituent members. Further, other configurations such as a color filter, a lens film, a diffusion sheet, an antireflection film, and the like may be appropriately provided.

  The arrangement of the polarizer protective film of the present invention having a specific polyester film is not particularly limited, but the polarizing plate disposed on the incident light side (light source side), the liquid crystal cell, and disposed on the output light side (viewing side). In the case of a liquid crystal display device having a polarizing plate disposed on the incident light side, the polarizer protective film on the incident light side of the polarizing plate disposed on the incident light side and / or the polarized light on the output light side of the polarizing plate disposed on the output light side. The polarizer protective film is preferably the polarizer protective film of the present invention having the specific polyester film. A particularly preferred 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 in a place where polarization characteristics are required, it is preferable to use the polarizer protective film of such a specific position as a protective film.

  The configuration of the backlight may be an edge light type 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 a backlight light source of the liquid crystal display device. In the present invention, a white LED is an element that emits white light by combining a phosphor and a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor. Examples of the phosphor include a yttrium-aluminum-garnet-based yellow phosphor and a terbium-aluminum-garnet-based yellow phosphor. Above all, white light-emitting diodes, which consist of light-emitting elements that combine a blue light-emitting diode using a compound semiconductor and a yttrium-aluminum-garnet-based yellow phosphor, have a continuous and broad emission spectrum and also have a high luminous efficiency. Excellent. Here, that the emission spectrum is continuous means that there is no wavelength at which light intensity becomes zero at least in a visible light region. In addition, the method of the present invention makes it possible to widely use white LEDs with low power consumption, so that an effect of energy saving can be achieved.

As a backlight light source, a white light source having a peak top of an 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 preferred. For example, a white light source using a quantum dot technology, a phosphor type white LED light source using a phosphor having emission peaks in R (red) and G (green) regions by excitation light and a blue LED, respectively, and a three-wavelength type. White LED light source, a white LED light source combining a red laser, and a white LED light source using a blue phosphor and a fluoride phosphor (also referred to as “KSF”) having a composition formula of K ₂ SiF ₆ : Mn ⁴⁺ And the like. These white light sources have been attracting attention as backlight light sources for liquid crystal display devices that support a wide color gamut, and each of them uses a blue light-emitting diode and a yttrium-aluminum-garnet-based yellow phosphor that have been conventionally used. The half width of the peak is narrower than that of the light source composed of the white light emitting diode composed of the combined light emitting elements. When a backlight light source composed of these white light sources is used, compared with a backlight light source composed of a white light emitting diode composed of a light emitting element in which a blue light emitting diode and a yttrium aluminum garnet-based yellow phosphor are combined, When using a polyester film having retardation with a polarizer protective film that is a component of a polarizing plate, there was a problem that rainbow spots tended to occur, but if the polarizer protective film of the present invention, the rainbow spots were significantly increased. Can be suppressed.

5. Organic EL Display and QLED Display As the organic EL element, an organic EL element known in the art can be appropriately selected and used. The use of an organic EL element is preferable in terms of a wide viewing angle, high contrast, and high-speed response. The organic EL element is typically a luminous body (organic electroluminescent luminous body) having a structure in which an anode as a transparent electrode, an organic luminescent 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 when a voltage is applied between the anode and the cathode so that holes (holes) injected from the anode and electrons injected from the cathode recombine in the organic light emitting layer. I 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. As a specific plastic substrate, a transparent resin film conventionally used can be mentioned. The transparent substrate may be provided with a surface treatment layer as needed. 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.

  Materials constituting the anode and the cathode include metals, metal oxides, alloys, electrically conductive compounds, and mixtures thereof. More specific materials for forming 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 for forming the cathode include magnesium, aluminum, indium, lithium, sodium, cesium, silver, a magnesium-silver alloy, a magnesium-indium alloy, and a lithium-aluminum alloy.

  The thicknesses 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 within a range of preferably 10 nm to 200 nm.

  The organic light-emitting layer is a layer having a function of providing a field of recombination of holes and electrons when a voltage is applied to emit light. 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 of a different emission color. The thickness of the organic light-emitting layer is arbitrary, and can be set as appropriate, for example, in the range of 3 nm to 3 μm.

  The organic light emitting material used for the organic light emitting layer can be appropriately selected from any light emitting material. Specifically, olefin-based light-emitting materials such as 4,4 '-(2,2-diphenylvinyl) biphenyl; 9,10-di (2-naphthyl) anthracene, and 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) Anthracene-based light-emitting materials such as -9,9'-bisanthracene, 9,10,9 ', 10'-tetraphenyl-2,2'-bianthryl and 1,4-bis (9-phenyl-10-anthracene) benzene A spiro-based luminescent material such as 2,7,2 ', 7'-tetrakis (2,2-diphenylvinyl) spirobifluorene; 4,4'-dicarbazolbiphenyl; It 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 to cover the organic EL element in order to shield the organic EL element composed of the anode, the organic light emitting layer, and the cathode on the base material from the outside air. Is 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 any 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 an organic EL cell is used as an 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 emitted to the viewing side again, 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 block 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 波長 wavelength plate between the organic EL cell and the polarizing plate. . As the polarizing plate, the above-mentioned polarizing plate can be used, and it is preferable that a polarizer protective film made of the polyester film of the present invention is laminated on the viewing side of the polarizer. Also, an embodiment in which a quarter-wave plate is laminated on the polarizer instead of the protective film on the organic EL element side of the polarizer is preferable. By forming a circular polarizer by combining these viewing-side polarizers and a 波長 wavelength plate, external light specularly reflected by the metal electrode of the organic EL cell is blocked by the circular polarizer, so that image display is performed. A decrease in visibility of the device can be suppressed. Also. A 波長 wavelength plate or the like may be further laminated on the organic EL element side or the polarizer side of the 波長 wavelength plate. Preferably, a 波長 wavelength plate or the like is laminated on the organic EL element side of the 波長 wavelength plate with the optical axis inclined with respect to each other, and is disclosed in JP-A-10-68816 and JP-A-2017-97379. Have been.

  QLED displays are similar to organic EL in that quantum dots emit light by themselves when electricity is applied, and are attracting attention as next-generation displays.

  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 carried out with appropriate modifications within a range that is compatible with the purpose of the present invention. It is also possible, and they 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 the slow axis direction of the 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)
The retardation is a parameter defined by a product (の Nxy × d) of anisotropy (△ Nxy = | nx−ny |) of a biaxial refractive index on a film and a film thickness d (nm). Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (△ Nxy) was determined by the following method. The slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments), and 4 cm was set so that the slow axis direction was parallel to the long side of the sample for measurement. A rectangle of 2 cm was cut out and used as a measurement sample. With respect to this sample, a biaxial refractive index perpendicular to the refractive index (refractive index in the slow axis direction: nx, a refractive index in a direction perpendicular to the slow axis direction in the plane (that is, a refractive index in the fast axis direction): ny), And the refractive index (nz) in the thickness direction is determined with an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., measurement wavelength: 589 nm), and the absolute value (| nx-ny |) of the biaxial refractive index difference is refracted. Rate anisotropy (△ Nxy). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Fineleuf Co.), and the unit was converted to nm. The retardation (Re) was determined from the product (ΔNxy × d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

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

(4) Elastic Modulus The elastic modulus of the polyester film was measured 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. The evaluation was carried out. The temperature dependence of 25 ° C to 120 ° C was measured under the conditions of a tensile mode, a driving frequency of 1 Hz, a distance between chucks of 5 mm, and a heating rate of 2 ° C / min. did. The measurement was performed in the MD direction.

(5-1) Iridescent observation (liquid crystal display device)
A roll of a polarizer made of iodine and a polyvinyl alcohol film manufactured by uniaxially stretching in the MD direction, and a PET film roll of a polarizer protective film 1 to 9 described below are roll-to-roll so that the MD directions are parallel to each other. And pasted together. A TAC film roll (manufactured by FUJIFILM Corporation, thickness: 40 μm) is similarly adhered to the other surface of the polarizer by a roll-to-roll method, and a polarizing film composed of PET film / polarizer / TAC film is formed. A board was created. The obtained polarizing plate is used as a light source (Nichia Chemical Co., NSPW500CS) with a white LED composed of a light emitting element in which a blue light emitting diode and an yttrium aluminum garnet yellow phosphor are combined. On the emission side, the polarizing plate on the incident light side was installed such that the polyester film was on the light source side, and the polarizing plate on the outgoing light side was installed such that the polyester film was on the viewing side. Visual observation was made from the front and oblique directions of the polarizing plate of the liquid crystal display device, and the presence or absence of rainbow spots was determined as follows.

: No iris is observed even when observed from any direction.
Δ: When observed from an oblique direction, a thin rainbow spot can be observed depending on the angle.
×: A clear rainbow spot can be observed when observed from an oblique direction.

(5-2) Rainbow spot observation (organic EL display)
A roll of a polarizer made of iodine and a polyvinyl alcohol film manufactured by uniaxially stretching in the MD direction, and a PET film roll of a polarizer protective film 1 to 9 described below are roll-to-roll so that the MD directions are parallel to each other. And pasted together. In addition, a roll of a 波長 wavelength plate was similarly adhered to the other surface of the polarizer by roll-to-roll, to prepare a polarizing plate composed of PET film / polarizer / (１ wavelength plate). . The circularly polarizing plate (a circularly polarizing plate disposed on the viewing side from the organic EL element) was removed from a commercially available organic EL display (organic EL television C6P 55 inches manufactured by LG), and the polarized light obtained as described above was used instead. The plate was placed in the organic EL display such 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.

: No iris is observed even when observed from any direction.
Δ: When observed from an oblique direction, a thin rainbow spot can be observed depending on the angle.
×: A clear rainbow spot can be observed when observed from an oblique direction.

(6) Evaluation of warpage of liquid crystal panel A roll of a polarizer made of iodine and a polyvinyl alcohol film manufactured by uniaxially stretching in the MD direction and a PET film roll of a polarizer protective film described later are parallel in the MD direction. Roll-to-roll. A TAC film roll (manufactured by FUJIFILM Corporation, thickness: 40 μm) is similarly adhered to the other surface of the polarizer by a roll-to-roll method, and a polarizing film composed of PET film / polarizer / TAC film is formed. A board was created. Next, the above polarizing plate of the same size is placed on both sides of a glass plate having a width of 125 mm, a length of 220 mm, and a thickness of 0.4 mm in a cross-Nicol relationship (the absorption axis of one of the polarizing plates is 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. Further, the polarizer protective film of the present invention is attached so as to be disposed on the outside. Next, heat treatment was performed for 30 minutes using a gear oven set at 100 ° C., and after cooling for 10 minutes in an environment set at room temperature of 25 ° C., the height of the four corners was measured with a measure, and the maximum value was measured. Was read. Also, a measured value of 5 mm or less was regarded as a good range.

(7) Tear strength Using an autograph (AG-X plus) manufactured by Shimadzu Corporation, the tear strength per film thickness (N / mm) was measured for each film according to the right-angled tearing method (JIS K-7128-3). did. The tear strength was measured in two directions parallel to and perpendicular to the orientation main axis (slow axis) of the film (that is, two directions of the slow axis direction and the fast axis direction), and the smaller value was expressed as the tear strength. No. 1. In addition, the measurement of the orientation main axis direction (slow axis direction) was measured with a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments).

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

: Number of breaks is less than 3 times △: Number of breaks is 3 or more and less than 6 times ×: Number of breaks is 6 or more times

(9) Evaluation method for scratches The film one hour after the start of film formation is inspected with a defect inspection apparatus, and the maximum height Sz of the scratches measured by a laser microscope (OLS4100, manufactured by Olympus Corporation) is 0.6 μm or more. Was determined as follows.

○: The number of flaws is less than 3 / ^{m 2} △: number of scratches is three / ^{m 2} or more 6 / ^{m 2} less ×: number of scratches is six / ^{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 while stirring, 0.017 parts by mass of antimony trioxide was used as a catalyst. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the temperature was increased under pressure to carry out a pressure esterification reaction under the conditions of a gauge pressure of 0.34 MPa and 240 ° C. Then, the esterification reactor was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Next, after 15 minutes, a dispersion treatment was performed with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reactor, and a polycondensation reaction was performed at 280 ° C. under reduced pressure.

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

(Production Example 2-Polyester B)
10 parts by mass of a dried ultraviolet absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinone-4-one), PET (A) containing no particles (intrinsic viscosity (0.62 dl / g), and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorbent (hereinafter abbreviated as PET (B)).

(Production Example 3-Preparation of Adhesion Modification Coating Solution)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component, 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate are used. A water-dispersible sulfonic acid metal base-containing copolymerized polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as a glycol component (based on the whole glycol component) was prepared. Next, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant, the mixture was heated and stirred. After adding 5 parts by mass of the water-dispersible sulfonic acid metal base-containing copolymerized polyester resin and continuing to stir until the resin no longer solidifies, the aqueous resin dispersion is cooled to room temperature to obtain a solid content 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 (manufactured by Fuji Silysia K.K., Sylysia 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolymerized polyester resin solution was used to disperse thyricia 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 adhesion-modified coating solution.

(Polarizer protective film 1)
After drying 90 parts by mass of PET (A) resin pellets containing no particles 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) as raw materials for a base film intermediate layer, To the extruder 2 (for the intermediate layer II layer), and dried PET (A) by an ordinary method, and then supplied to the extruder 1 (for the outer layer I and the outer layer III) to be melted at 285 ° C. . The two types of polymers are respectively filtered with a stainless steel sintered body filter medium (nominal filtration accuracy: 10 μm, particles cut by 95%), laminated in a two-type three-layer merging block, extruded into a sheet from a die, and extruded. It was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and cooled and solidified to form 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, the above-mentioned adhesion-modified coating solution was applied to both surfaces of the unstretched PET film by a reverse roll method so that the application amount after drying was 0.08 g / m ² , followed by drying at 80 ° C. for 20 seconds. .

  The unstretched film having the coating layer formed thereon is guided to a simultaneous biaxial stretching machine, and while holding the end of the film with a clip, guided to a hot air zone at a temperature of 125 ° C., 6.5 times in the running direction and 2 times in the width direction. Stretched 2 times. 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 to form a film roll (a 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 polarizer protective film 1.

(Polarizer protective film 2)
A biaxially 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 stretched 6.0 times in the running direction and 2.2 times in the width direction. Was. This was wound up in a roll shape to obtain a film roll (a 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 polarizer protective film 2.

(Polarizer protective film 3)
An unstretched film is made in the same manner as the polarizer protective film 1, and heated to 105 ° C. by using a heated roll group and an infrared heater by a sequential biaxial stretching machine, and then the running direction is changed by a roll group having a peripheral speed difference. After stretching 6.5 times, the film was guided to a hot air zone at 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 in a roll shape to obtain a film roll (a 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 in a roll to form 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 is in 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 to produce a roll-to-roll polarizing plate, the film was more likely to break in the width direction than 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 peripheral speed difference. It was led to a hot air zone and stretched 1.0 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 uniaxially oriented PET film having a film thickness of about 40 μm. This was wound up in a roll to form 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. Although no rainbow-like color spot was observed on the polarizer protective film 5, 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 was obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film was changed and stretched 4.5 times in the running direction and 2.4 times in the width direction. Was. This was wound up in a roll shape to obtain a film roll (a 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, a rainbow-like color spot was observed when observed from an oblique direction.

(Polarizer protective film 7)
The thickness of the unstretched film was changed, and heated to 105 ° C. using a roll group heated by a biaxial stretching machine and an infrared heater, and then stretched 2.2 times in the running direction by a roll group having a peripheral speed difference. After that, it was led to a hot air zone at 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 in a roll shape to obtain a film roll (a 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, a rainbow-like color spot was observed when observed from an oblique direction.

(Polarizer protective film 8)
A biaxially 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 6.0 times in the running direction and 1.5 times in the width direction. Was. This was wound up in a roll shape to obtain a film roll (a 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 protection film 9)
A biaxially 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 6.5 times in the running direction and 2.7 times in the width direction. Was. This was wound up in a roll shape to obtain a film roll (a 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 used as a polarizer protective film 9.

  The results obtained by observing the rainbow spots and measuring the tear strength of the polarizer protective films 1 to 9 are shown in Table 1 below.

  As shown in Table 1, when rainbow dots were observed using the films of the polarizer protective films 1 to 3, 5, 8, and 9, rainbow dots were observed even when viewed from any of the front and oblique directions. Did not. On the other hand, as for the polarizer protective film 4, a thin rainbow spot was observed partially when observed obliquely. Further, in the polarizer protective film 5, although no rainbow spot was observed, the tear strength was low and the film formation was unstable. In addition, clear rainbow spots were observed on the polarizer protective films 6 and 7 when obliquely observed. In the above item (5-1), iridescence observation, the same procedure was performed except that a polarizing plate composed of a PET film / polarizer was used in which only a PET film was laminated without a TAC film laminated on the polarizer. When a liquid crystal display device was manufactured and iris observation was performed in the same manner, the same result as the iris observation result shown in Table 1 was obtained. Further, when the warpage of the liquid crystal panel was evaluated by the method described in the above (6) 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, the polarizing plate, and the image display device (such as a liquid crystal display device and an organic EL display) of the present invention, it is possible to reduce the thickness of the LCD and reduce the cost without lowering the visibility due to rainbow-like color spots. And industrial applicability is extremely high.

Claims (15)

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 0.20 or less,
Further, a polarizer protective film satisfying the following (A) or (B):
(A) the polyester film has a refractive index in the fast axis direction of 1.580 or more and 1.630 or less;
(B) The smaller one of the tear strengths of the polyester film in the slow axis direction and the fast axis direction obtained by the perpendicular tearing method is 250 N / mm or more. The polarizer protective film according to claim 1, wherein the polyester film has a refractive index in a fast axis direction of 1.580 or more and 1.630 or less. 3. The polarizer protective film according to claim 1, wherein the smaller one of the tear strengths of the polyester film in the slow axis direction and the fast axis direction obtained by the perpendicular tearing method is 250 N / mm or more. 4. The polarizer protective film according to any one of claims 1 to 3, wherein the NZ coefficient of the polyester film is 1.5 or more and 2.5 or less. The polarizer protective film according to any one of claims 1 to 4, wherein the retardation of the polyester film is from 1500 nm to 30000 nm. The polarizer protective film according to any one of claims 1 to 5, 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 the angle between the slow axis direction and the MD direction of the polyester film 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 a polarizer. A polarizing plate, wherein the polarizer protective film according to claim 1 is laminated on one surface of a polarizer, and the film is not laminated on the other surface of the polarizer. A polarizing plate comprising the polarizer protective film according to any one of claims 1 to 8 laminated on one surface of the polarizer, and a 板 wavelength plate laminated on the other surface of the polarizer. An image display device comprising the polarizing plate according to claim 9. A liquid crystal display device comprising the polarizing plate according to claim 9. An organic EL display comprising the polarizing plate according to claim 9. A QLED display comprising the polarizing plate according to claim 9.