WO2014185322A1 - Liquid crystal display device, polarizing plate, and polarizer protective film - Google Patents

Abstract

Provided is a polarizer protective film comprising a polyester film which is capable of suppressing the leakage of light even in cases in which two polarizers are disposed in a crossed Nicols state. A polarizer protective film which comprises a polyester film and is characterized in that the absolute value of the difference between the thermal shrinkage at a direction 45 degrees from the film flow direction and the thermal shrinkage at a direction -45 degrees from the film flow direction is no higher than 0.4%.

Description

Liquid crystal display device, polarizing plate and polarizer protective film

The present invention relates to a polarizer protective film used for a polarizing plate in a liquid crystal display device.

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

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

The polyester film is superior to the TAC film in durability, but unlike the TAC film, 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, Patent Documents 1 to 3 take measures to reduce retardation by using a copolyester as the polyester.

Patent Document 4 discloses that a rainbow-like color unevenness can be solved by using a white light emitting diode as a backlight light source and further using an oriented polyester film having a certain retardation as a polarizer protective film. .

In Patent Document 5, the polarizer protective film has good dimensional stability because it passes through many heat-receiving steps such as a step of producing a polarizing plate or a step of combining the obtained polarizing plate with a liquid crystal cell. Therefore, specifically, the shrinkage rate of the polyester film after non-restraining heat treatment at 120 ° C. for 30 minutes is 5% or less in both the film MD direction (film flow direction) and the TD direction (film width direction). It is disclosed that it is preferable.

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A WO2011-162198 JP 2010-277028 A

As the polarizer protective film, a TAC film has been conventionally used. However, as described in the background art, a polarizer protective film made of a polyester film has attracted attention as an alternative. The polarizing plate has a structure in which a polarizer is sandwiched between two polarizer protective films. When two polarizing plates made of polyester film of at least one of the two polarizer protective films are prepared and arranged so that the two polarizing plates are in a crossed Nicols environment, there is a slight light leakage. The present inventors have discovered that there is a new problem that may occur and visibility may deteriorate. This invention makes it one subject to provide the polarizer protective film which consists of a polyester film which can suppress the above-mentioned slight light leakage.

As a result of studying the above problems day and night, the present inventors have found that the absolute value of the difference between the heat shrinkage rate in the 45 ° direction with respect to the film flow direction and the −45 ° direction heat shrinkage rate with respect to the film flow direction is 0. It has been found that the above problem can be solved by a polarizer protective film made of a polyester film that is 4% or less.

The representative present invention is as follows.
Item 1.
Polarized light comprising a polyester film, characterized in that the absolute value of the difference between the heat shrinkage rate in the 45 ° direction with respect to the film flow direction and the heat shrinkage rate in the −45 ° direction with respect to the film flow direction is 0.4% or less. Child protective film.
Item 2.
Item 2. The polarizer protective film according to Item 1, wherein the retardation of the polyester film is 4000 to 30000 nm, and the Nz coefficient is 1.7 or less.
Item 3.
Item 3. The polarizer protective film according to Item 1 or 2, wherein the plane orientation degree of the polyester film is 0.13 or less.
Item 4.
Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
4. The polarizing plate, wherein the polarizer protective film on at least one side is the polarizer protective film according to any one of Items 1 to 3.
Item 5.
Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
One polarizer protective film consists of a triacetyl cellulose film,
4. The polarizing plate, wherein the other polarizer protective film is the polarizer protective film according to any one of Items 1 to 3.
Item 6.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
At least one of the polarizer protective films of the polarizing plate arranged on the incident light side, and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side,
Item 4. A liquid crystal display device, which is the polarizer protective film according to any one of Items 1 to 3.
Item 7.
A polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and a polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side,
Item 6. The liquid crystal display device according to item 6, which is the polarizer protective film according to any one of items 1 to 3.

According to the present invention, when two polarizing plates are arranged in a crossed Nicol environment, the occurrence of slight light leakage is suppressed, and a polyester film suitable for obtaining a liquid crystal display device having excellent visibility. The polarizer protective film which consists of, and a polarizing plate can be provided. In addition, according to the present invention, a liquid crystal display device in which light leakage is suppressed and excellent in visibility is provided.

1. Polarizer Protective Film The polarizer protective film of the present invention comprises a polyester film, and is the absolute value of the difference between the heat shrinkage rate in the 45 ° direction with respect to the film flow direction and the −45 ° direction heat shrinkage rate with respect to the film flow direction. Hereinafter, the “difference in heat shrinkage in the oblique direction” or “difference in heat shrinkage” may be simply referred to as 0.4% or less. The absolute value of the difference in the heat shrinkage rate is preferably 0.3% or less, more preferably 0.2% or less. Since the smaller the value of the difference in heat shrinkage rate is, the lower limit is 0%. The direction of 45 degrees with respect to the film flow direction and the direction of −45 degrees with respect to the film flow direction are naturally orthogonal to each other. In addition, the heat shrinkage rate in the 45 ° direction and the heat shrinkage rate in the −45 ° direction with respect to the film flow direction are both preferably 1.0% or less, more preferably 0.8% or less, and 0.6% or less. Is more preferable.

Usually, in a liquid crystal display device, two polarizing plates are arranged in a crossed Nicols environment. When two polarizing plates are arranged in a crossed Nicols environment, light is not normally transmitted, but it has been discovered that light may leak depending on the difference in thermal contraction rate in the oblique direction of the polarizer protective film. The mechanism is considered as follows, but the present invention is not limited to this.

A polarizing plate is usually produced by adhering a polarizer protective film and a polarizer via an adhesive. In such an adhesion step, the polarizing plate is usually heat-treated in the range of 70 ° C. to 120 ° C. for 10 minutes to 60 minutes. When a film having a large difference in thermal contraction rate in the oblique direction is used as the polarizer protective film, the polyester film warps obliquely during the above-described heat treatment, and the polarizing plate itself undergoes a slight warp in the oblique direction. As a result, the polarization axis is slightly distorted in the oblique direction, and when such two polarizing plates are arranged in a crossed Nicol environment, the polarizing axes of the two polarizing plates are not arranged in a vertical relationship through the space. Therefore, it is considered that slight light leakage occurs.

As described in the background art, Patent Document 5 discloses a polarizer protective film made of a polyester film having a heat shrinkage rate of 5% or less in both the film flow direction and the film width direction. However, as is clear from the mechanism described above, even if the thermal shrinkage rate in the film flow direction and the thermal shrinkage rate in the film width direction are small, if the thermal shrinkage rate difference in the oblique direction is large, the oblique direction of the polarizing plate Warpage cannot be suppressed and light leakage may occur.

The polyester film used for the polarizer protective film of the present invention can be obtained from any polyester resin. The type of the polyester resin is not particularly limited, and any polyester resin obtained by condensing dicarboxylic acid and diol can be used.

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

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

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

(Differential heat shrinkage difference)
The difference in heat shrinkage rate in the oblique direction in the present invention is the heat shrinkage rate in the 45 ° direction with respect to the film flow direction and the film flow direction when the polyester film is heated in water at 85 ° C. for 30 minutes. It is the absolute value of the difference from the thermal shrinkage rate in the -45 ° direction. Specifically, before and after the heat treatment, the length in the 45 ° direction and the −45 ° direction is measured with respect to the flow direction of the polyester film, and the heat shrinkage rate in each direction is obtained by comparing them. The difference in heat shrinkage can be obtained by comparing the heat shrinkage in the 45 ° direction with the heat shrinkage in the −45 ° direction.

The presence or absence of light leakage can be measured according to the measurement method shown in the examples described later. That is, two polarizing plates are arranged so as to have a crossed Nicol relationship, and a maximum light transmittance of the light having a wavelength of 550 to 600 nm with respect to the two polarizing plates can be measured using a spectrophotometer. it can. In the two polarizing plates, the polarizer and the polyester film used as the polarizer protective film are bonded so that the polarization axis of the polarizer and the main alignment axis of the polyester film are perpendicular to each other. And if the maximum light transmittance in the said wavelength range is 0.02% or less, it can be evaluated that there is substantially no light leakage.
Hereinafter, from the viewpoint of suppressing irises, preferable ranges for the retardation, Nz coefficient, and plane orientation of the polyester film will be described.

(Retardation)
The polyester film used for the polarizer protective film used in the present invention is not particularly limited, but preferably has a retardation of 4000 to 30000 nm. If the retardation is 4000 nm or more, the interference color can be suppressed when the liquid crystal display device is observed from an oblique direction, and good visibility can be secured. The preferred retardation of the oriented polyester film is 4500 nm or more, then preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, and even more preferably 10,000 nm or more.

The upper limit of the retardation of the polyester film is preferably 30000 nm. Even if a polyester film having a retardation higher than that is used, the effect of improving the visibility is not substantially obtained, and as the retardation increases, the thickness of the film is considerably increased, and the handling property as an industrial material is lowered. Because there is a risk of doing.

The retardation value of the oriented polyester film can be determined by measuring the biaxial refractive index and thickness according to a known method. Further, for example, measurement can be performed using a commercially available automatic birefringence measuring apparatus such as KOBRA-21ADH (Oji Scientific Instruments). In any measurement method, the retardation at 589 nm, which is the wavelength of the sodium D line, is measured.

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

Even when the retardation of the polyester film is 4000 nm to 30000 nm, when the Nz coefficient exceeds 1.7, the polyester film is used as a polarizer protective film in both the pair of polarizing plates (for example, disposed on the incident light side). When the polarizer protective film on the incident light side of the polarizing plate and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side are polyester films), when the liquid crystal display device is observed from an oblique direction Still, depending on the angle, there is a risk of rainbow spots. Therefore, the Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less. The lower limit value of the Nz coefficient is 1.2. This is because it is difficult in terms of manufacturing technology to obtain a film of less than 1.2. In order to maintain the mechanical strength of the film, the lower limit value of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and further preferably 1.45 or more.

(Plane orientation coefficient)
In addition to controlling the retardation value and Nz coefficient of the polyester film to the above specific range, the plane orientation degree represented by (nx + ny) / 2-nz is made to be not more than the specific value, so that a pair of polarizing plates is more reliably In both cases, it is possible to completely eliminate rainbow spots when a polyester film is used as a polarizer protective film. Here, the values of nx, ny, and nz are obtained by the same method as for the Nz coefficient. The degree of plane orientation of the oriented polyester film is preferably 0.13 or less, more preferably 0.125 or less, and still more preferably 0.12 or less. By setting the degree of plane orientation to 0.13 or less, it is possible to more completely eliminate rainbow spots observed depending on the angle when the liquid crystal display device is observed from an oblique direction. The plane orientation degree is preferably 0.08 or more, and more preferably 0.1 or more. If the degree of plane orientation is less than 0.08, the film thickness varies, and the retardation value may be non-uniform in the film plane.

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

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

(Thickness unevenness)
In order to suppress fluctuations in the retardation of the polyester film, it is preferable that the thickness unevenness of the film is small. In this respect, the thickness unevenness of the polyester film is preferably 5% or less, more preferably 4.5% or less, still more preferably 4% or less, and particularly preferably 3% or less. preferable.

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

(Light transmittance)
The polyester film desirably has a light transmittance of 20% or less at a wavelength of 380 nm from the viewpoint of suppressing deterioration of an optical functional dye such as iodine dye contained in the polarizer. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the optical functional dye can be prevented from being deteriorated by ultraviolet rays. The light transmittance is measured in a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, a spectrophotometer V-7100 manufactured by JASCO Corporation).

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

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

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

When blending a UV absorber with a polyester film, it is preferable that the oriented polyester film has a multilayer structure of three or more layers, and the UV absorber is added to a layer other than the outermost layer of the film (that is, an intermediate layer).

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

(Easily adhesive layer)
In the present invention, in order to improve the adhesiveness with the polarizer, it has an easy-adhesion layer mainly composed of at least one of a polyester resin, a polyurethane resin or a polyacrylic resin on at least one side of the oriented polyester film. preferable. 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 is preferably an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating liquids 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 the coating solution on one or both sides of an unstretched film or a uniaxially stretched film in the longitudinal direction, drying at 100 to 150 ° C., and stretching in the lateral direction. 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 less than 0.05 g / m ² , the adhesion with the resulting polarizer may be insufficient. On the other hand, when the coating amount exceeds 0.2 g / m ² , blocking resistance may be lowered. When providing an easily bonding layer on both surfaces of a polyester film, the application quantity of an easily bonding layer on both surfaces may be the same or different, and can be independently set within the above range.

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 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.

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

The average particle diameter of the above particles can be 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 subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion to the polarizer.

(Functional layer)
Various functional layers, i.e., hard coat layer, antiglare layer, antireflection layer, for the purpose of preventing reflection, glare suppression, scratch control, etc., on the surface opposite to the surface on which the polarizer of the polyester film is disposed, It is also preferable to provide one or more functional layers selected from the group consisting of a low reflection layer, a low antireflection layer, an antireflection antiglare layer, and an antistatic layer on the oriented polyester surface. When providing various functional layers, the oriented polyester film preferably has an easy adhesion layer on the surface thereof. At that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the functional layer and the refractive index of the oriented polyester film. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

(Method for producing oriented polyester film)
The oriented polyester film that is the protective film of the present invention can be manufactured according to a general method for manufacturing a polyester film. For example, the polyester resin is melted and the non-oriented polyester extruded and formed into a sheet shape is stretched in the longitudinal direction by utilizing the speed difference of the roll at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. The method of performing heat processing is mentioned. A uniaxially stretched film or a biaxially stretched film may be used.

In order to reduce the absolute value of the difference between the heat shrinkage rate in the direction of 45 degrees oblique to the film flow direction and the heat shrinkage rate in the direction of −45 degrees oblique to the film flow direction, the uniaxial obtained by the above method is used. In the film forming process of the stretched film and the biaxially stretched film, it is preferable to relieve the stress in the oblique direction generated in the cooling process after the heat treatment. For this reason, it is preferable that the relaxation rate and temperature are adjusted to an appropriate range after the heat treatment step to relax in the film width direction. Furthermore, it is preferable to adjust the tension in the film flow direction (running direction) to an optimum range. It is preferable to control the tension in the film flow direction by adjusting the difference between the speed of the tenter clip and the speed of the take-up roll within an appropriate range. Further, after the heat treatment step, it is also preferable to relax by adjusting the relaxation rate and temperature to an appropriate range and relaxing the clip interval in the film flow direction while relaxing in the film width direction. In addition, a method of cutting or releasing the film from the tenter clip during the cooling step and cooling the film while relaxing in the film flow direction and the film width direction is also preferable. It is also effective to perform an off-line annealing treatment on the roll once wound, for example, at 80 ° C. to 120 ° C. for 10 seconds to 90 minutes.

After the polyester film has been stretched in the longitudinal and transverse directions, it is possible to obtain a slit roll by cutting both edges into a mill roll through a heat treatment step and slitting as necessary. Of these, the range of 33% at both ends of the mill roll (33% from the right end of the film and 33% from the left end of the film) tends to have a particularly high difference in thermal shrinkage in the oblique direction. Therefore, for example, in the case of off-line annealing, it is preferable to adjust the temperature and time of the annealing process to be sufficiently secured.

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

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

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

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

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

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

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

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

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

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

2. Polarizing plate The polarizing plate of the present invention has a configuration in which two polarizer protective films are sandwiched between both sides of a polarizer composed of a polyvinyl alcohol film or the like dyed with iodine. Of the two polarizer protective films, It is preferable that at least one of the polyester films has a specific difference in heat shrinkage rate in the oblique direction. The polarizer and the polarizer protective film are laminated via an adhesive, and are usually heat-treated in the range of 70 ° C. to 120 ° C. for 10 minutes to 60 minutes to obtain a polarizing plate.

(Polarizer protective film arrangement)
In the liquid crystal display device of the present invention, the specific polyester film is preferably used as a polarizer protective film for both of the pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate disposed on the incident light side with respect to the liquid crystal and a polarizing plate disposed on the outgoing light side with respect to the liquid crystal. That is, the polyester film is preferably used for both the incident light side polarizing plate and the outgoing light side polarizing plate. The said polyester film should just be used as at least one among the two polarizer protective films which comprise each polarizing plate.

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

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

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

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

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

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

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

The evaluation method of physical properties in the examples is as follows.

(1) Difference in heat shrinkage rate in oblique direction Polarizer protective films 1 to 15 described later (those subjected to offline annealing treatment and those not subjected to the same treatment) were cut into square shapes with sides of 21 cm, It was left for 2 hours or more in an atmosphere of 65 ° C. and 65% RH. On this film, draw a circle with a diameter of 20 cm so that its center is the center of the film, and draw a straight line passing through the center of the circle in the 45 ° and -45 ° directions, with the vertical direction (film drawing direction) being 0 °. The diameter in each direction was measured. This film was heat-treated at 85 ° C. for 30 minutes in water, then wiped off the moisture adhering to the surface, air-dried, and left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. Then, the length of the straight line drawn in each diameter direction as described above was measured. And the length of the diameter before heat processing was compared with the length of the diameter after heat processing, the heat contraction rate in each direction was calculated | required, and also they were compared, and the absolute value of the difference of heat contraction rate was calculated | required. This measurement was performed by sampling three points in the width direction of the film with the same slit roll, and the average was defined as the difference in thermal shrinkage. As a result of the measurement, the heat-shrinkage difference in the 45 ° direction and the −45 ° direction is not more than 0.4% at the three points in the same slit roll when offline annealing is performed. It was 1.0% or less.

(2) Light Leakage Evaluation Method A polyester film prepared by a method described later on the other surface of a polarizer made of a PVA film, which is bonded to a triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., thickness 80 μm). Are pasted together. Each film was bonded to a polarizer via an adhesive. Then, it heated at 85 degreeC for 30 minute (s) in oven, and manufactured the polarizing plate. In addition, it bonded so that the polarizing axis of a polarizer and the main orientation axis | shaft of a polyester film might become mutually perpendicular | vertical. The two polarizing plates thus obtained were placed in a crossed Nicol state so that the polyester film was outside the two polarizers, and the maximum at a wavelength of 550 to 600 nm was measured using a spectrophotometer V7100 manufactured by JASCO Corporation. The light transmittance was measured.
○: Maximum light transmittance is 0.02% or less ×: Maximum light transmittance exceeds 0.02%

(3) 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, a measure of 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.), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes the long side, for measurement A sample was used. For this sample, the biaxial refractive index (nx, ny) perpendicular to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The absolute value (| nx−ny |) of the difference between the biaxial refractive indexes was defined as the refractive index anisotropy (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (ΔNxy × d) of refractive index anisotropy (ΔNxy) and film thickness d (nm).

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

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

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

(7) Observation of rainbow spots A polyester film prepared by the method described later is attached to one side of a polarizer made of PVA and iodine so that the polarization axis of the polarizer and the orientation axis of the polyester film are perpendicular to each other, and the opposite surface A TAC film (manufactured by FUJIFILM Corporation, thickness 80 μm) was attached to the substrate to prepare a polarizing plate. The obtained polarizing plate was placed on both sides of the liquid crystal so that each polarizing plate was in a crossed Nicols condition to produce a liquid crystal display device. Each polarizing plate was arrange | positioned so that the said polyester film might be on the opposite side (distal) from a liquid crystal. As a light source of the liquid crystal display device, a white LED composed of a light emitting element in which a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor were combined was used as a light source (Nichia Chemical, NSPW500CS). The liquid crystal display device was visually observed from the front and oblique directions, and the presence or absence of rainbow spots was determined as follows.
A: No iridescence from any direction.
A ′: When observed from an oblique direction, very thin rainbow spots are observed depending on the angle.
B: When observed from an oblique direction, a thin iridescence is observed depending on the angle.
C: When observed from an oblique direction, rainbow spots are observed.
D: When observed from the front direction and the oblique direction, rainbow spots are observed.

(8) Tear Strength Using a Toyo Seiki Seisakusho Elmendorf Tear Tester, the tear strength of each film was measured according to JIS P-8116. The tearing direction was performed so as to be parallel to the orientation main axis direction of the film, and was determined as follows. The measurement in the orientation main axis direction was performed with a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments).
○: Tear strength is 50 mN or more ×: Tear strength is less than 50 mN

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

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

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

(Production Example 3-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 whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal group-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol (relative to the entire glycol component) was prepared as a glycol component. Next, 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 a conventional method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III) and dissolved at 285 ° C. . After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, 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 was formed was guided to a tenter stretching machine, guided to a hot air zone at a temperature of 125 ° C. while being gripped by a clip, and stretched 4.0 times in the width direction. Next, a mill roll made of a uniaxially oriented PET film having a film thickness of about 50 μm was obtained by processing at a temperature of 225 ° C. for 30 seconds while keeping the width stretched in the width direction, and cutting and removing both edges. . This mill roll was divided into three equal parts to obtain three slit rolls (L, C, R). For each slit roll, two types were prepared: one that had been subjected to an offline annealing treatment at 90 ° C. for 5 minutes, and one that wanted to be subjected to the offline annealing treatment.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, a slit roll made of a uniaxially oriented PET film was obtained in the same manner as the polarizer protective film 1 except that the thickness was about 100 μm. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 3)
An unstretched film produced by the same method as that for the polarizer protective film 1 is heated to 105 ° C. using a heated roll group and an infrared heater, and then 1.5 rolls in the traveling direction with a roll group having a difference in peripheral speed. After being double-stretched, the film was stretched 4.0 times in the width direction in the same manner as for the polarizer protective film 1 to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 50 μm. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 4)
By a method similar to that for the polarizer protective film 3, the slit roll made of a biaxially oriented PET film having a film thickness of about 50 μm was stretched 2.0 times in the running direction and 4.0 times in the width direction. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 5)
A slit roll made of a uniaxially oriented PET film having a film thickness of 50 μm was obtained in the same manner as in the polarizer protective film 1 without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 6)
In the same manner as for the polarizer protective film 1, the film was stretched 1.0 times in the running direction and 3.5 times in the width direction to obtain a slit roll made of a uniaxially oriented PET film having a film thickness of about 75 μm. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 7)
A slit roll made of a uniaxially oriented PET film having a thickness of about 100 μm is used by changing the thickness of the unstretched film using the same method as that for the polarizer protective film 1, setting the transverse stretch ratio to 3.8 times, and the stretching temperature to 135 ° C. Obtained. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 8)
A slit roll made of a uniaxially oriented PET film having a thickness of about 50 μm was obtained using the same method as for the polarizer protective film 1 with a lateral stretching ratio of 3.8 times and a stretching temperature of 135 ° C. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 9)
A slit roll made of a uniaxially oriented PET film having a thickness of 50 μm was obtained using the same method as for the polarizer protective film 1 with a lateral stretch ratio of 3.8 times. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 10)
A slit roll made of a uniaxially oriented PET film having a thickness of about 50 μm was obtained using the same method as for the polarizer protective film 1 with a transverse draw ratio of 4.2 times and a draw temperature of 135 ° C. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 11)
A slit roll made of a uniaxially oriented PET film having a thickness of 38 μm was obtained by changing the thickness of the unstretched film and changing the lateral stretch ratio to 3.8 times using the same method as for the polarizer protective film 1. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 12)
A slit roll made of a uniaxially oriented PET film having a thickness of 38 μm was obtained by changing the thickness of the unstretched film using the same method as for the polarizer protective film 1. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 13)
By a method similar to that for the polarizer protective film 3, the film was stretched 1.8 times in the running direction and 2.0 times in the width direction to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 275 μm. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 14)
In the same manner as the polarizer protective film 3, the film was stretched 3.6 times in the running direction and 4.0 times in the width direction to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 38 μm. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

(Polarizer protective film 15)
A slit roll made of a uniaxially oriented PET film having a thickness of about 10 μm was obtained by changing the thickness of the unstretched film using the same method as for the polarizer protective film 1. Two types were prepared, one that was subjected to an offline annealing treatment similar to the polarizer protective film 1 and one that was desired to be subjected to the offline annealing treatment.

The results of light leakage evaluation for the polarizer protective films 1 to 15 are shown in Table 1 (samples treated by offline annealing) and Table 2 (samples not treated by offline annealing). In Tables 1 and 2, the L position means the left end, the C position means the center, and the R position means the right end.

In addition, Table 3 below shows the results of rainbow-eye observation and tear strength measurement of the liquid crystal display device manufactured as described above using the polarizer protective films 1 to 15 (samples processed by off-line annealing).

In Table 3, polarizer protective film No. 7 * shows the case where the polarizer protective film 7 is used as the polarizer protective film and the organic light emitting diode (OLED) is used as the light source. In Table 3, the polarizer protective film No. 7 ** shows the case where the polarizer protective film 7 is used as the polarizer protective film and the cold cathode tube is used as the light source.

From the results shown in Table 3, it was shown that when the retardation of the oriented polyester film is 4000 or more and the Nz coefficient is 1.7 or less, the generation of rainbow spots is remarkably suppressed. . In addition to this condition, it has been shown that by controlling the degree of plane orientation of the oriented polyester film to 0.13 or less, it is possible to more effectively suppress the occurrence of rainbow spots.

According to the present invention, when two polarizing plates are arranged in a crossed Nicol environment, the occurrence of slight light leakage is suppressed, and a polyester film suitable for obtaining a liquid crystal display device having excellent visibility. The polarizer protective film which consists of can be provided. Therefore, the industrial applicability of the present invention is extremely high.

Claims (7)

1. Polarized light comprising a polyester film, characterized in that the absolute value of the difference between the heat shrinkage rate in the 45 ° direction with respect to the film flow direction and the heat shrinkage rate in the −45 ° direction with respect to the film flow direction is 0.4% or less. Child protective film.
2. The polarizer protective film according to claim 1, wherein the retardation of the polyester film is 4000 to 30000 nm, and the Nz coefficient is 1.7 or less.
3. The polarizer protective film of Claim 1 or 2 whose surface orientation degree of a polyester film is 0.13 or less.
4. Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
   The polarizing plate, wherein the polarizer protective film on at least one side is the polarizer protective film according to any one of claims 1 to 3.
5. Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
   One polarizer protective film consists of a triacetyl cellulose film,
   A polarizing plate, wherein the other polarizer protective film is the polarizer protective film according to any one of claims 1 to 3.
6. A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
   The backlight source is a white light source having a continuous emission spectrum;
   The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
   At least one of the polarizer protective films of the polarizing plate arranged on the incident light side, and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side,
   A liquid crystal display device which is the polarizer protective film according to any one of claims 1 to 3.
7. A polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and a polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side,
   The liquid crystal display device according to claim 6, which is the polarizer protective film according to any one of claims 1 to 3.