WO2015037527A1

WO2015037527A1 - Liquid crystal display device, polarization plate, and polarizer protective film

Info

Publication number: WO2015037527A1
Application number: PCT/JP2014/073451
Authority: WO
Inventors: 敦史藤田; 村田　浩一; 向山　幸伸; 佐々木　靖
Original assignee: 東洋紡株式会社
Priority date: 2013-09-10
Filing date: 2014-09-05
Publication date: 2015-03-19
Also published as: CN105531610A; TWI675226B; KR20230015521A; JPWO2015037527A1; KR20210116714A; TW201531748A; KR20160053955A; JP2020115211A; KR102491441B1; JP2022105524A; JP2024045417A; JP2018185535A; CN105531610B

Abstract

Provided is a polarizer protective film comprising a polyester film which is capable of inhibiting the leakage of light, even in cases when two polarization plates are disposed in a crossed Nicols state. This polarizer protective film comprises a polyester film. The absolute value of the gradient of the thermal shrinkage of said polyester film in a film flow direction or width direction is not more than 15˚.

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 treatment steps such as a step of producing a polarizing plate or a step of combining the obtained polarizing plate with a liquid crystal cell. Specifically, it is disclosed that the shrinkage rate of the polyester film after non-restraining heat treatment at 120 ° C. for 30 minutes is preferably 5% or less in both the film MD direction and the TD direction.

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

As described above, the polyester film used as the polarizer protective film has been improved from various viewpoints, but the present inventors have found that there is room for further improvement. That is, the present inventors, when a polarizing plate adopting a polyester film improved so far as a polarizer protective film is arranged so as to have a crossed Nicols relationship with another polarizing plate, We discovered the existence of a new problem that leakage may occur and visibility may deteriorate. Then, this invention makes it a 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 intensive studies to solve the above problems, the present inventors have found that an angle formed by the direction in which the thermal shrinkage rate of the polyester film is maximum and the flow direction or width direction of the polyester film (that is, the film flow). It has been found that the above problem can be solved by controlling the absolute value of the inclination of the direction in which the heat shrinkage rate is maximum with respect to the direction or the film width direction to be 15 degrees or less. Based on such knowledge, further studies are made and the following inventions are provided.
Item 1.
The polarizer protective film which is a polyester film whose absolute value of the angle | corner which the film flow direction or the width direction and the direction in which the thermal contraction rate of a film becomes the maximum is 15 degrees or less.
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.
A polarizing plate in which the polarizer protective film according to any one of Items 1 to 3 is laminated on one side of the polarizer.
Item 6.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
Item 4. The polarizer according to any one of Items 1 to 3, wherein at least one of the polarizer protective films of the polarizing plate arranged on the incident light side and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side are A liquid crystal display device which is a protective film.
Item 7.
Item 4. The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side are described in any one of Items 1 to 3. Item 7. A liquid crystal display device according to Item 6, which is a polarizer protective film.
Item 8.
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;
6. A liquid crystal display device, wherein the polarizing plate is the polarizing plate according to item 5.

According to the present invention, when two polarizing plates are arranged in a crossed Nicols relationship, it is possible to suppress slight light leakage that has conventionally occurred. In addition, according to a preferred embodiment, the liquid crystal display device has excellent visibility, which is suitable for thinning, not only causing rainbow spots, but also reducing the deterioration of visibility due to leakage of the light. Can be provided.

FIG. 1 shows an example of the result of measuring the heat shrinkage rate of a film by 360 degrees at intervals of 5 degrees with the film flow direction being 0 degree. In this example, each maximum heat shrinkage is about 15 degrees. FIG. 2 shows the angle as the X axis and the heat shrinkage rate as the Y axis in order to obtain the angle at which the heat shrinkage rate is maximized with an accuracy of 1 degree interval or more from the heat shrinkage rate measured at intervals of 5 degrees. FIG. FIG. 3 schematically shows the interval between the clips used in the method 1 for reducing the inclination of the heat shrinkage rate. FIG. 4 shows the relationship between the distance in the longitudinal direction of the tenter and the tenter temperature that can be used in the method 4 for reducing the inclination of the thermal shrinkage rate.

1. Polarizer Protective Film The polarizer protective film of the present invention is a polyester film, and is referred to as an inclination in a direction in which the thermal shrinkage rate with respect to the flow direction or width direction of the film is maximized (hereinafter simply referred to as an inclination of the thermal shrinkage rate). Is preferably 15 degrees or less. The absolute value of the slope of the heat shrinkage rate is preferably 12 degrees or less, more preferably 10 degrees or less, still more preferably 8 degrees or less, still more preferably 6 degrees or less, particularly preferably. 4 degrees or less, most preferably 2 degrees or less. Since the absolute value of the slope of the heat shrinkage rate is preferably as small as possible, the lower limit is 0 degree.

The exact mechanism of the slight light leakage described above has not been elucidated, but is thought to be as follows. Usually, in a liquid crystal display device, two polarizing plates are arranged so as to have a crossed Nicols relationship. When two polarizing plates are arranged in a crossed Nicols relationship, light usually does not pass through the two polarizing plates. However, when the polarizer protective film is shrunk by heat treatment, the polarizer is also shrunk or warped slightly, and as a result, the complete crossed Nicols relationship is broken and light leaks. From such a principle, light leakage becomes significant when the direction in which the thermal contraction rate of the polarizer protective film is the largest is oblique to the film flow direction or the film width direction. In addition, the polarizer protective film flow direction is usually parallel or perpendicular to the polarization axis of the polarizer.

Patent Document 5 discloses a polarizer protective film made of a polyester film having a thermal shrinkage rate of 5% or less in both the MD direction and the TD direction. However, as is clear from the mechanism described above, the direction in which the thermal contraction rate is maximum is inclined with respect to the film flow direction or the film width direction even if the thermal contraction rate in the MD direction and the thermal contraction rate in the TD direction are small. If so, the problem of leakage of polarized light occurs.

Patent Document 5 also discloses that the angle formed by the in-plane slow axis and the film TD direction and the variation thereof are reduced at both ends of the film, thereby preventing the color shift and color spot of the liquid crystal display. However, since the in-plane slow axis direction of the film and the inclination of the thermal contraction rate are not always parallel, the problem of leakage of polarized light occurs even if the film has a controlled in-film slow axis.

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.

(Heat shrinkage)
The thermal shrinkage rate of the polyester film is preferably 5% or less in all directions. The thermal shrinkage rate in all directions of the polyester film is measured as follows.

A polyester film is cut into a square shape with a side of 21 cm and left in an atmosphere of 23 ° C. and 65% RH for 2 hours or longer. On this polyester film, draw a circle with a diameter of 80mm centered on the center, and use a two-dimensional image measuring machine (for example, QUICK IMAGE made by MITUTOYO) to set the diameter in 5 degree intervals with the film flow direction as 0 degree. taking measurement. Here, assuming that the film flow direction is 0 degree, when the film is viewed from above in the tenter, the clockwise direction (clockwise) is a positive angle and the counterclockwise direction (counterclockwise) is a negative angle. If measured in the range of -90 degrees to 85 degrees, the diameter in all directions can be measured.

Next, the polyester film is heat-treated at 85 ° C. for 30 minutes in water, then the moisture adhering to the film surface is wiped off, air-dried, and then left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. Thereafter, the diameter of the circle is measured at intervals of 5 degrees as described above. The diameter before heat treatment is Lo, the diameter in the same direction after heat treatment is L, and the heat shrinkage rate in each direction is determined according to the following formula.

Thermal contraction rate (%) = ((L ₀ -L) / L ₀ ) × 100

When the heat shrinkage rate measured 360 degrees at intervals of 5 degrees is displayed in a graph, for example, it is as shown in FIG. In FIG. 1, the center of the circle has a heat shrinkage rate of 0%, and the heat shrinkage rate increases as the distance from the center of the circle increases. The circumference indicates an angle with the film flow direction being 0 degree. Therefore, 90 degrees is parallel to the film width direction.

The maximum value of the heat shrinkage rate obtained by the above measuring method is preferably 5% or less, more preferably 3% or less, still more preferably 1% or less, and most preferably 0.5% or less. . The lower limit of the heat shrinkage rate is not particularly limited, but is 0.01% or more, for example.

(Slope of heat shrinkage)
As described above, the thermal contraction rate is measured at intervals of 5 degrees, and the direction in which the thermal contraction rate is maximized is obtained with an accuracy of 1 degree according to the following procedure. That is, the measurement result of the heat shrinkage rate (result of the heat shrinkage rate in the range of −90 ° to 85 °) is an angle with the horizontal axis as the film flow direction as shown in FIG. Plot as shrinkage. At this time, values of -180 degrees to -95 degrees and 90 degrees to 175 degrees are also interpolated (a thermal contraction rate of -90 degrees corresponds to a thermal contraction ratio of 90 degrees, and a thermal contraction ratio of 0 degrees is -180 degrees). Corresponding to the degree of heat shrinkage). Next, an approximate curve connecting the plots is drawn, and the direction in which the thermal contraction rate is maximized is read with an accuracy of 1 degree, and this is defined as α. Note that −90 degrees ≦ α ≦ 90 degrees.

When the direction α in which the heat shrinkage rate is maximum is in the range of −45 ° to 45 °, the value is defined as the slope of the heat shrinkage rate. Further, when the direction α in which the thermal contraction rate is maximum is 45 degrees or more and −45 degrees or less, it is understood that the direction is inclined with respect to the film width direction, not the film flow direction, and α−90 degrees (α is 90 ° + α (when α is −45 ° or less) and the inclination of the heat shrinkage rate. When the difference between the maximum value and the minimum value of the heat shrinkage rate is 0.1% or less, the heat shrinkage rate is almost equal in all directions, and there is no inclination in the heat shrinkage rate. It is considered.

(Light leakage evaluation method)
For light leakage, two polarizing plates are arranged in a crossed Nicols relationship, and the maximum transmittance of light having a wavelength of 550 nm to 600 nm passing through them is measured. The light transmittance can be measured using any spectrophotometer. The maximum transmittance to be measured is preferably 0.02% or less, more preferably 0.015% or less.

Next, the retardation of the polyester film, the Nz coefficient, and the degree of plane orientation will be described from the viewpoint of suppressing iridoplasm.

(Retardation)
The polyester film used for the polarizer protective film preferably has a retardation of 4000 to 30000 nm. If the retardation is 4000 nm or more, rainbow spots that may occur when the liquid crystal display device is observed from an oblique direction are suppressed, and good visibility can be ensured. The preferable retardation of the polyester film is 4500 nm or more, more preferably 5000 nm or more, still more preferably 6000 nm or more, still more preferably 8000 nm or more, and still more preferably 10,000 nm or more. Here, 4000 to 30000 nm means that 4000 nm is included as the lower limit value and 30000 nm is included as the upper limit value, but a range not including it is also assumed.

The upper limit of the retardation of the polyester film is not particularly limited, but is, for example, 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 is obtained by the following procedure. The orientation axis direction of the film is determined using a molecular orientation meter (for example, MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments). The refractive index (ny) in the orientation axis direction and the refractive index (nx) in the direction orthogonal to the orientation axis direction in the film plane are measured at a measurement wavelength of 589 nm. The absolute value (| ny−nx |) of the difference (anisotropy) of the refractive index in these biaxial directions is obtained, and the retardation value is obtained by multiplying it by the thickness of the film. The retardation of the film can be measured using a commercially available automatic birefringence measuring apparatus such as KOBRA-21ADH (Oji Scientific Instruments). The refractive index of the film can be measured using a commercially available measuring instrument such as an Abbe refractometer (NAGO-4T, manufactured by Atago Co., Ltd.).

(Nz coefficient)
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 in addition to the above-described retardation range. . 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 if the retardation of the polyester film is 4000 nm to 30000 nm, if the Nz coefficient exceeds 1.7, when the polyester film is used as a polarizer protective film in both the pair of polarizing plates (for example, arranged 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, rainbow spots may occur depending on the angle. The Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less, from the viewpoint of suppressing the occurrence of such rainbow spots. 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 within the above specific range, the plane orientation coefficient represented by (nx + ny) / 2-nz is made to be not more than the specific value, thereby ensuring a pair of polarizing plates In both cases, rainbow spots can be eliminated 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 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 thickness direction retardation (Rth) (Re / Rth) is larger, the birefringence action is more isotropic, and the occurrence of iridescent color spots due to the observation angle is less likely to occur. In a complete uniaxial (uniaxial symmetry) film, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2. However, as will be described later, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered as the film approaches a complete uniaxial (uniaxial symmetry) film. Therefore, the upper limit of the ratio of retardation in the thickness direction (Re / Rth) is preferably 1.2 or less, more preferably 1 or less. In order to completely suppress the occurrence of rainbow-like color spots due to the observation angle, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) does not need 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.

(Thick spots)
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. The thickness unevenness of the film can be measured by the following procedure. A film is cut into a width of 40 mm from the film roll in the TD direction. The cut sample is continuously measured with an Anritsu contact-type continuous thickness meter (feeding speed: 1.5 m / min, sampling cycle: 100 ms) to determine the average value, maximum value, and minimum value. The thickness unevenness was an absolute value of a value calculated by the following formula.
Thickness unevenness = ((maximum value of measurement result) − (minimum value of measurement result)) / (average value of measurement result) × 100 (%)

(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 and concentration of the ultraviolet absorber to be blended and the thickness of the film. As the ultraviolet absorber used in the present invention, a known ultraviolet absorber can be appropriately selected and used. Specific examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency.

Examples of the organic ultraviolet absorber include, but are not limited to, benzotriazole, benzophenone, and cyclic imino ester, and any combination thereof. From the viewpoint of durability, a benzotoazole system or a cyclic imino ester system is 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 adhesion to the polarizer, it is preferable to have 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 polyester film. . 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 solutions include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying 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. The average particle size of the fine particles is preferably 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 average particle size of the particles is determined by taking a photograph of the particles with a scanning electron microscope (SEM), the maximum size of 300 to 500 particles (magnification so that the size of one smallest particle is 2 to 5 mm) The distance between the two most distant points) is measured, and the average value can be calculated.

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 polyester film can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion with 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.

(Production method of polyester film)
The polyester film used as the polarizer protective film 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.

(Reduced slope of thermal shrinkage)
The means for controlling the absolute value of the inclination in the direction in which the thermal contraction rate with respect to the film flow direction or the width direction is maximum is not particularly limited, but it is preferable to pay attention to the following points. That is, in the cooling section after the heat treatment step in the tenter, there are contraction stress accompanying stretching and thermal stress accompanying cooling that could not be removed by heat fixation. Further, since the film at the end is restrained by the clip, the film at the center is relatively stretchable, and therefore there is a bias in the distribution of stress in the film flow direction and the width direction in the cooling section. These are the main causes and the inclination of the heat shrinkage rate occurs. Based on such circumstances, specific means for reducing the inclination of the heat shrinkage rate will be exemplified below.

(Method 1 for reducing the slope of thermal shrinkage)
In the cooling section after heat setting, the clip interval is narrowed in the film flow direction, the stress in the film flow direction in the tenter cooling section can be made uniform, and the inclination of the heat shrinkage rate can be reduced. Therefore, in order to reduce the inclination of the heat shrinkage rate, it is preferable to appropriately adjust the temperature zone in which the clip interval is narrowed. Since it varies depending on the film composition and film production conditions, it is not particularly limited, but when the temperature is too high, the film at the left end (when the film is viewed from above) with respect to the flow direction has a positive direction of thermal shrinkage. (The right end increases in the negative direction). On the other hand, when the temperature is too low, the amount of heat shrinkage of the film is too small, and the flatness becomes poor. Thus, by setting the temperature for narrowing the clip interval to an appropriate range, the stress in the flow direction in the tenter cooling section can be made uniform, and the inclination of the thermal contraction rate can be reduced.

In order to reduce the inclination of the thermal shrinkage rate, the relaxation rate that narrows the clip interval in the film flow direction is also important. Since it differs depending on the film composition and film production conditions, it is not particularly limited, but the relaxation rate is preferably 0.01 to 3%, more preferably 0.05 to 1.5%. When the relaxation rate is too high, the film is not completely shrunk and the flatness is poor, which is not preferable. Moreover, when the relaxation rate is too low, the effect of reducing the slope of the heat shrinkage rate is reduced. Here, the relaxation rate can be calculated by the following equation using the distance between the centers of the clips as shown in FIG.
Relaxation rate = (((distance between clips before relaxation) − (distance between clips after relaxation)) / (distance between clips before relaxation)) × 100 (%)
When the heat shrinkage rate in the width direction is too high, the inclination of the heat shrinkage rate tends to increase. Therefore, it is more preferable to adjust the tenter rail pattern and appropriately adjust the relaxation rate and temperature for narrowing the clip interval in the film width direction. In this way, set the temperature zone and the relaxation rate to narrow the clip interval in the film flow direction to an appropriate range, and properly adjust the tenter rail pattern so that the shrinkage rate in the width direction does not become too large. By adjusting, the stress in the flow direction in the tenter cooling section can be made uniform, and the inclination of the heat shrinkage rate can be reduced.

(Method 2 for reducing the slope of the heat shrinkage rate)
In the cooling section after heat setting, the film end can be separated from the clip and released from restraint by the clip, and the stress in the width direction in the tenter cooling section can be made uniform. Moreover, the stress of the flow direction in a tenter cooling area can be made uniform by adjusting the tension | tensile_strength of a winding process to an appropriate value. Thus, the inclination of the heat shrinkage rate can be reduced by making the stress in the flow direction uniform in the tenter cooling section.

The method for separating the film edge from the clip is not particularly limited, but a conventionally known method may be used. Specific examples include a method of cutting a film from a clip and a method of opening a clip. The method of cutting the film from the grip is arbitrary, and examples thereof include cutting using a shear blade or fusing using a laser. A combination of these methods can also be carried out. When cutting a film from a clip, it is desirable to carry out at a position close to the clip at both ends of the film.

The film temperature when separating the film edge from the clip is desirably 50 ° C to 300 ° C. The higher the film temperature with respect to the melting point Tm of the film, the more difficult it is to maintain the flatness of the film. Also, when the film temperature is too low with respect to the glass transition temperature Tg of the film, the slope of the heat shrinkage rate is reduced. It becomes difficult. Therefore, it is desirable to cut and separate the film from the clip at a temperature higher than (glass transition temperature Tg−20 ° C.) and lower than (melting point Tm−10 ° C.). The film temperature here is a value measured by a radiation thermometer.

When separating the film end from the clip, it is preferable to appropriately adjust the tension in the winding process. The appropriate tension varies depending on the film composition, thickness, and film production conditions, and is not particularly limited, but is preferably 0.01 to 3 kg / mm ² , more preferably 0.1 to 2 kg / mm ² . If the tension is too high, the film at the left end with respect to the flow direction has a larger thermal contraction rate in the positive direction (the right end increases in the negative direction). On the other hand, if the tension is too low, the film at the left end with respect to the flow direction has a larger thermal contraction rate in the negative direction (the right end increases in the positive direction). However, these tendencies are when the angle is evaluated based on the flow direction, and when the width direction is used as a reference, the positive and negative tendencies are reversed.

If the heat shrinkage rate in the width direction is too high, the slope of the heat shrinkage rate becomes large. Therefore, it is preferable to adjust the rail pattern before separating the film end from the clip, and to adjust the relaxation rate and temperature for narrowing the clip interval in the film width direction as described above. In this way, by setting the tension within an appropriate range, the stress in the flow direction in the tenter cooling section can be made uniform, and the inclination of the thermal contraction rate can be reduced.

(Method 3 for reducing the slope of the heat shrinkage rate)
In the same way as the reduction method 2, the film temperature at the exit of the tenter is higher than a predetermined temperature (that is, the glass transition temperature Tg-20 ° C.) and lower than the predetermined temperature (melting point Tm-70 ° C.). The shrinkage of the shrinkage rate can be reduced. In this case, since the effect depends on the room temperature, it is desirable to control the room temperature.

(Method 4 for reducing the slope of the heat shrinkage rate)
The inclination of the heat shrinkage rate can also be reduced by adjusting the temperature setting of the cooling process after the tenter heat setting. For example, as shown in FIG. 4, it is preferable to set the heat fixing temperature to the tenter outlet temperature to be −15 / X to −100 / X (° C./m) along the longitudinal direction of the tenter. Here, X represents the tenter outlet width (m). Therefore, for example, when the tenter outlet width is 2 m, it is preferable to lower the temperature in a range of −7.5 ° C. to −50 ° C. every time 1 m is advanced in the tenter longitudinal direction. Since the temperature indicates the temperature per tenter outlet width, this is hereinafter referred to as temperature setting per unit width.

Also, the tenter outlet temperature is usually preferably set to Tg or lower. When the temperature setting per unit width is -100 / X (° C / m) or less in the longitudinal direction, the inclination of the heat shrinkage rate exceeds 15 degrees, which is not preferable. When the temperature setting is -15 / X (° C / m) or more Although the inclination of the heat shrinkage rate can be sufficiently reduced, it is not preferable because the tenter equipment investment becomes excessive.

(Method 5 for reducing the slope of the heat shrinkage rate)
Even with a film having a thermal contraction rate, the roll once wound is subjected to, for example, an offline annealing treatment at 80 ° C. to 120 ° C. for 10 seconds to 90 minutes, so that the thermal contraction rate can be reduced. In the case of off-line annealing treatment, it is preferable to adjust the temperature and time of annealing treatment sufficiently. It is also desirable to perform in-line annealing between the conventionally known tenter outlet and the take-up roll. In this case as well, it is preferable to ensure a sufficient temperature and time for the annealing treatment as in the above-described offline annealing treatment, and the use of an air can roll is more desirable in terms of heat treatment efficiency and flatness maintenance.

These reduction methods 1 to 5 may be carried out by any one method or in combination. By these methods, the inclination of the heat shrinkage rate can be made 15 degrees or less.

The polyester film is subjected to a heat treatment step after being longitudinally stretched and laterally stretched, and both edges are cut into mill rolls and slits as necessary to form slit rolls. The term “both edges” means that the length of the entire width of the film is 100%, preferably from 1% to 10%, more preferably from 1% to 5% from both ends of the film. In addition, the both ends here are the same as the both ends of the film before cutting demonstrated about the said reduction method 2. FIG. Among these, the area on both sides when the mill roll is divided into three equal parts tends to have a particularly large absolute value of the inclination of the heat shrinkage rate, so the absolute value of the inclination of the heat shrinkage rate of this area is 15 degrees or less. It is preferable to control. *

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, more preferably 90 to 140 ° C. The longitudinal draw ratio is preferably 1.0 to 3.5 times, more preferably 1.0 to 3.0 times. The transverse draw ratio is preferably 2.5 to 6.0 times, more 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, more 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 reduce the Nz coefficient, it is also preferable to add a copolymer component in order to increase the molecular weight of the polymer and to decrease the crystallinity. Furthermore, in order to control the Nz coefficient of the film within a specific range, the total stretching ratio and the stretching temperature can be appropriately set. For example, the lower the total draw ratio and the higher the drawing temperature, the lower the Nz coefficient can be obtained.

In order to set the 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.

1. Polarizing plate The polarizing plate has a configuration in which a polarizer made of a polyvinyl alcohol film dyed with iodine is sandwiched between two polarizer protective films, and at least one of the two polarizer protective films is It is preferable that the absolute value of the inclination of the heat shrinkage rate is a polyester film in a specific range. Moreover, in one Embodiment, it is preferable that a polarizing plate is the structure by which the polarizer protective film was laminated | stacked on one surface of the polarizer. 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, 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 laminated | stacked on the at least one surface of the polarizer which comprises each polarizing plate.

In a preferred embodiment, the polyester film is used as a polarizer protective film on the incident light side of the polarizing plate on the incident light side, and used as a polarizer protective film on the outgoing light side of the polarizing plate on the outgoing light side. Is done. When the oriented polyester film is laminated only on one surface of the polarizer constituting the polarizing plate, an arbitrary polarizer protective film (for example, a TAC film) is used on the other surface, or the polarizer. It is possible not to provide a protective film. The 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 (that is, incident light side) of the polarizing plate arranged on the outgoing light side. Then, since there is a possibility of changing the polarization characteristics of the liquid crystal cell, the polarizer protective film at these positions may be a polarizer protective film other than the 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 as represented. These films also preferably have a small absolute value of the slope of the heat shrinkage rate.

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

(Backlight light source)
The liquid crystal display device 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. The backlight light source is preferably a white light source having a continuous broad emission spectrum. 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 effect of suppressing rainbow spots, 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 physical property evaluation methods in the examples are as follows.
(1) Thermal contraction rate and inclination The polyester film cut out from each cut-out part of the slit roll was cut into a square shape with a side of 21 cm and left for 2 hours or more in an atmosphere of 23 ° C. and 65% RH. A circle with a diameter of 80 mm centered on the center of the polyester film was drawn, and the diameter was measured at 5 intervals with the flow direction of the film as 0 degree using a two-dimensional image measuring machine (QUICK IMAGE manufactured by MITUTOYO). Here, the film flow direction was set to 0 degree, and on the upper surface of the film, clockwise (rightward) was set as a positive angle, and counterclockwise (leftward) was set as a negative angle. Since the diameter was measured, it was measured in all directions in the range of -90 to 85 degrees. Next, the polyester film was heat-treated at 85 ° C. for 30 minutes in water, and then moisture adhering to the film surface was wiped off and air-dried, and then left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. Thereafter, the diameter of the circle was measured at intervals of 5 degrees as described above. The diameter before heat treatment was Lo, the diameter in the same direction after heat treatment was L, and the heat shrinkage rate in each direction was determined according to the following formula.

Thermal contraction rate (%) = ((L ₀ -L) / L ₀ ) × 100

(Maximum heat shrinkage)
The maximum value among the heat shrinkage rates in all directions is defined as the maximum heat shrinkage rate. Each slit roll (L, C, R) was sampled at three points in the film width direction (center, three points at both ends) and evaluated in the same manner, and the average value of the three maximum heat shrinkage rates was determined as the maximum heat shrinkage rate. Values are listed in Table 1. In this example, the maximum heat shrinkage rate of each slit roll was 5% or less at the center and at the three ends.

(Reading the maximum direction of heat shrinkage (α))
From the result of obtaining the heat shrinkage rate in all directions, the slope of the heat shrinkage rate was measured as follows. As shown in FIG. 2, the measured values (−90 ° to 85 °) are plotted with the horizontal axis representing the angle and the vertical axis representing the heat shrinkage corresponding to the angle, −180 ° to −95 °, 90 ° to The value of 175 degrees was interpolated. (The thermal contraction rate of -90 degrees corresponds to the thermal contraction ratio of 90 degrees, and the thermal contraction ratio of 0 degrees corresponds to the thermal contraction ratio of -180 degrees.) Next, draw an approximate curve connecting the plots The direction with the highest rate was read with an accuracy of 1 degree and defined as α. However, −90 degrees ≦ α ≦ 90 degrees.

(Slope of heat shrinkage)
When the direction α in which the heat shrinkage rate is maximum is in the range of −45 ° to 45 °, the value is defined as the slope of the heat shrinkage rate. Further, when the direction α in which the heat shrinkage rate is maximum is 45 degrees or more and −45 degrees or less, it is understood that the film is inclined with respect to the film width direction, not the film flow direction, and α−90 degrees (α 90 ° + α (when α is −45 ° or less) and the inclination of the heat shrinkage rate. The above measurement was similarly performed for each slit roll (L, C, R) by sampling three points in the film width direction (center, three points at both ends), and calculating the average of the absolute values of the slopes of the three heat shrinkage rates. The slope of thermal shrinkage is shown in Table 1. In this example, the absolute value of the inclination of the heat shrinkage rate was 15 degrees or less at the three points at the center and both ends.

(2) Light Leakage Evaluation Method A triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., thickness 80 μm) is bonded to one side of a polarizer made of PVA film, and a polyester film produced by the method described later on the other side. Pasted together. Adhesives were used for pasting and heat treatment was performed in an oven at 85 ° C. for 30 minutes to produce a 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 arranged in crossed Nicols. At this time, the two polarizing plates were arranged such that the respective polyester films were positioned outside the polarizer. Then, using a spectrophotometer V7100 manufactured by JASCO, the maximum light transmittance of light having a wavelength of 550 nm to 600 nm that was transmitted through the two polarizing plates was measured. The measurement results were evaluated as follows.
○: Maximum light transmittance is 0.02% or less ×: Maximum light transmittance is 0.02% or more

(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 Fuji Film Co., Ltd., thickness: 80 μm) was attached to the plate to create 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 relationship 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, and the film was 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, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds and then cooled to 130 ° C. with a shear blade at 2% from both ends. The film was wound with a tension of 5 kg / mm ² and both edges were cut and removed to obtain a mill roll made of a uniaxially oriented PET film having a film thickness of about 50 μm. This mill roll was divided into three equal parts to obtain three slit rolls (L, C, R). In addition, the slit roll located on the left with respect to the film flow direction was L, the slit roll located on the right was R, and the center was C.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained in the same manner as the polarizer protective film 1 except that the thickness was about 100 μm.

(Polarizer protective film 3)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained in the same manner as the polarizer protective film 1 except that it was not cut with a shear blade after heat setting.

(Polarizer protective film 4)
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 stretched twice in the traveling direction by a roll group having a difference in peripheral speed. After that, the film was stretched 4.0 times in the width direction in the same manner as the polarizer protective film 1, and then the film cooled to 140 ° C. was cut with a shear blade at a position of 2% from both ends, and 0.65 kg / Three slit rolls (L, C, R) made of a biaxially oriented PET film having a film thickness of about 50 μm were obtained by winding with a tension of mm ² and adjusting the thickness of the unstretched film.

(Polarizer protective film 5)
As a method of separating the film from the clip, three slit rolls made of a uniaxially oriented PET film (L, L) in the same manner as the polarizer protective film 1 except that the method of cutting with a shear blade is changed to the method of opening the clip. C, R).

(Polarizer protective film 6)
Three slit rolls (L, C) made of a uniaxially oriented PET film having a film thickness of about 75 μm, stretched 1.0 times in the running direction and 3.5 times in the width direction in the same manner as the polarizer protective film 1 , R).

(Polarizer protective film 7)
Using the same method as for the polarizer protective film 1, the thickness of the unstretched film was changed, the lateral stretch ratio was 3.8 times, the stretch temperature was 135 ° C., and three uniaxially oriented PET films with a thickness of about 100 μm were used. Slit rolls (L, C, R) were obtained.

(Polarizer protective film 8)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film with a thickness of about 50 μm, using the same method as the polarizer protective film 1, with a lateral stretching ratio of 3.8 times, a stretching temperature of 135 ° C. Got.

(Polarizer protective film 9)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained in the same manner as the polarizer protective film 8 except that it was not cut with a shear blade after heat setting.

(Polarizer protective film 10)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film with a thickness of about 50 μm, using the same method as the polarizer protective film 1, with a lateral stretch ratio of 4.2 times, a stretch temperature of 135 ° C. Got.

(Polarizer protective film 11)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained in the same manner as the polarizer protective film 10 except that the winding tension after cutting with a shear blade was 0.2 kg / mm ² . .

(Polarizer protective film 12)
Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained in the same manner as the polarizer protective film 10 except that it was not cut with a shear blade after heat setting.

(Polarizer protective film 13)
A film which is stretched 1.8 times in the running direction and 2.0 times in the width direction in the same manner as the polarizer protective film 4, and the winding tension after cutting with a shear blade is 0.2 kg / mm ² Three slit rolls (L, C, R) made of a biaxially oriented PET film having a thickness of about 275 μm were obtained.

(Polarizer protective film 14)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was processed at a temperature of 225 ° C. for 30 seconds, and the clip interval was narrowed by 0.2% in the flow direction in the temperature range of 90 ° C. to 70 ° C. Three slit rolls (L, C, R) made of a uniaxially oriented PET film having a film thickness of about 75 μm were obtained.

(Polarizer protective film 15)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was processed at a temperature of 225 ° C. for 30 seconds, and the clip interval was narrowed by 0.1% in the flow direction in the temperature range of 90 ° C. to 70 ° C. Three slit rolls (L, C, R) made of a uniaxially oriented PET film having a film thickness of about 75 μm were obtained.

(Polarizer protective film 16)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was processed at a temperature of 225 ° C. for 30 seconds, and the clip interval was narrowed by 0.2% in the flow direction in the temperature range of 110 ° C. to 70 ° C. Three slit rolls (L, C, R) made of a uniaxially oriented PET film having a film thickness of about 75 μm were obtained.

(Polarizer protective film 17)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Next, while maintaining the width stretched in the width direction, the film was processed at a temperature of 225 ° C. for 30 seconds, and the clip interval was narrowed by 0.4% in the flow direction in the temperature range of 150 ° C. to 100 ° C. Three slit rolls (L, C, R) made of a uniaxially oriented PET film having a film thickness of about 75 μm were obtained.

(Polarizer protective film 18)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Then, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds, cooled at a temperature setting of −55 ° C./m per unit width, and a film thickness of about 75 μm Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained.

(Polarizer protective film 19)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Then, while maintaining the width stretched in the width direction, the film was processed at a temperature of 225 ° C. for 30 seconds, cooled at a temperature setting of −35 ° C./m per unit width, and a film thickness of about 75 μm Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained.

(Polarizer protective film 20)
An unstretched film produced by the same method as that for the polarizer protective film 1 is guided to a tenter stretching machine and guided to a hot air zone having a temperature of 125 ° C. while gripping the end of the film with a clip, and 3.5 times in the width direction. Then, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds, cooled at a temperature setting of −120 ° C./m per unit width, and a film thickness of about 75 μm Three slit rolls (L, C, R) made of a uniaxially oriented PET film were obtained.

Table 1 shows the absolute value of the inclination of the heat shrinkage rate, the maximum value of the heat shrinkage rate, and the results of light leakage evaluation for the polarizer protective films 1 to 20.

In Table 1, “film” means the above polarizer protective film.

Further, Table 2 below shows the results of rainbow-eye observation and tear strength measurement of the liquid crystal display devices manufactured as described above using the polarizer protective films 1 to 20.

From the results shown in Table 1, if the absolute value of the slope of the heat shrinkage rate is 15 degrees or less, slight light leakage is suppressed when the two polarizing plates are arranged in a crossed Nicols relationship. It was shown that you can. Further, the maximum value of the heat shrinkage rate of each of the polarizer protective films 1 to 20 was less than 1%.

From the results shown in Table 2, 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 so as to have a crossed Nicols relationship, slight light leakage is suppressed and suitable for obtaining a liquid crystal display device having excellent visibility. It is possible to provide a polarizer protective film made of a polyester film. Therefore, the industrial applicability of the present invention is extremely high.

Claims

The polarizer protective film which consists of a polyester film whose absolute value of the inclination of the direction where the thermal contraction rate with respect to a film flow direction or the width direction becomes the maximum is 15 degrees or less.
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.
The polarizer protective film of Claim 1 or 2 whose surface orientation degree of a polyester film is 0.13 or less.
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.
A polarizing plate in which the polarizer protective film according to any one of claims 1 to 3 is laminated on one side of the polarizer.
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 disposed on the incident light side, and at least one of the polarizer protective films of the polarizing plate disposed on the outgoing light side,
A liquid crystal display device which is the polarizer protective film according to any one of claims 1 to 3.
The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side,
The liquid crystal display device according to claim 6, which is the polarizer protective film according to any one of claims 1 to 3.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
A liquid crystal display device, wherein the polarizing plate is the polarizing plate according to claim 5.