JP2019091059A - Liquid crystal display device, polarizing plate, and polarizer protection film - Google Patents

Abstract

To provide a polarizer protection film comprising a polyester film capable of suppressing light leakage even when two polarizing plates are disposed in a cross-Nicol arrangement.SOLUTION: A polarizing plate protection film comprising a polyester film is characterized in that an absolute value of a difference between a thermal shrinkage rate in a direction 45 degrees from a machine direction of the film and a thermal shrinkage rate in a direction -45 degrees from the machine direction of the film is 0.4% or less.SELECTED DRAWING: None

Description

  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 (LCD) has a configuration in which a polarizer in which iodine is dyed in polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films, and as a polarizer protective film Usually, triacetyl cellulose (TAC) film is used. In recent years, with the reduction in thickness of LCDs, thinning of polarizing plates has been required. However, if the thickness of the TAC film used as the protective film is made thin for this reason, sufficient mechanical strength can not be obtained, and the problem that the moisture permeability is deteriorated occurs. In addition, TAC films are very expensive, and inexpensive alternative materials are strongly required.

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

  A polyester film is superior in durability to a TAC film, but unlike a TAC film, has birefringence and 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 it is used as a polarizer protective film, rainbow color spots occur when observed from an oblique direction, and the image quality is deteriorated. . Therefore, in the patent documents 1-3, the countermeasure which makes retardation small is made by using co-polyester as polyester.

  Further, Patent Document 4 discloses that rainbow 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 the step of manufacturing the polarizing plate or the step of combining the obtained polarizing plate with a liquid crystal cell. Specifically, the shrinkage rate of the polyester film after non-confining heat treatment at 120 ° C. × 30 minutes is 5% or less in any of the film MD direction (film flow direction) and the TD direction (film width direction) It is disclosed that is preferable.

Japanese Patent Laid-Open No. 2002-116320 JP 2004-219620 A Unexamined-Japanese-Patent No. 2004-205773 WO2011-162198 JP, 2010-277028, A

Although a TAC film has been conventionally used as a polarizer protective film, as described in the background art, a polarizer protective film consisting of a polyester film is attracting attention as a substitute therefor. The polarizing plate has a structure in which a polarizer is sandwiched between two polarizer protective films. Light leaks slightly if two polarizers with at least one of the two polarizer protective films prepared as a polyester film and the two polarizers are placed in a crossed nicols environment The present inventors discovered that there is a new problem that may arise and the visibility may deteriorate. An object of the present invention is to provide a polarizer protective film made of a polyester film capable of suppressing the slight light leakage described above.

As a result of examining the above-mentioned subject day and night, the inventors of the present invention have found that the thermal contraction rate in the 45 ° direction with respect to the film flow direction and the absolute value of the thermal shrinkage rate difference in the −45 ° direction with respect to the film flow direction are 0. If it is a polarizer protective film which consists of a polyester film which is 4% or less, it discovered that the above-mentioned subject could be solved.

The representative invention is as follows.
Item 1.
Polarized 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.
The polarizer protective film of claim 1 or 2, wherein the polyester film has a degree of plane orientation of 0.13 or less.
Item 4.
It has a configuration in which a polarizer protective film is laminated on both sides of a polarizer,
The polarizing plate in which the polarizer protective film of at least one side is the polarizer protective film in any one of claim 1 to 3.
Item 5.
It has a configuration in which a polarizer protective film is laminated on both sides of a polarizer,
One polarizer protective film consists of a triacetyl cellulose film,
4. A 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 comprising a backlight source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum,
The polarizing plate has a configuration 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 are:
Item 4. A liquid crystal display device, which is the polarizer protective film according to any one of items 1 to 3.
Item 7.
The polarizer protective film on the incident light side of the polarizing plate disposed on the incident light side and the polarizer protective film on the outgoing light side of the polarizing plate disposed on the outgoing light side are:
Item 7. The liquid crystal display device according to item 6, which is a polarizer protective film according to any one of items 1 to 3.

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

1. Polarizer Protective Film The polarizer protective film of the present invention is made of a polyester film, and 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 degree direction with respect to the film flow direction Hereinafter, it is preferable that “the thermal contraction rate difference in the oblique direction” or “the thermal contraction rate difference” may be simply referred to as 0.4% or less. The absolute value of the difference in heat shrinkage ratio is preferably 0.3% or less, more preferably 0.2% or less. The lower the heat shrinkage difference value, the better, and the lower limit is 0%. The directions of 45 degrees with respect to the film flow direction and the directions of -45 degrees with respect to the film flow direction are naturally orthogonal to each other. In addition, the thermal contraction rate in the 45 ° direction and the thermal contraction rate in the −45 ° direction with respect to the film flowing direction are preferably 1.0% or less, more preferably 0.8% or less, and 0.6% or less. Is more preferred.

  Usually, in the liquid crystal display device, two polarizing plates are disposed under a crossed Nicol environment. It has been discovered that when two polarizing plates are placed in a crossed nicols environment, light is not normally transmitted, but light may leak depending on the difference in the 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 thereto.

  The polarizing plate is usually produced by bonding a polarizer protective film and a polarizer via an adhesive. In such an adhesion process, the polarizing plate is usually heat-treated at a temperature of 70 ° C. to 120 ° C. for about 10 minutes to 60 minutes. When a film having a large difference in thermal contraction rate in the oblique direction is used as a polarizer protective film, the polyester film warps obliquely during the above-mentioned heat treatment, and a slight warp occurs in the polarizing plate itself in the oblique direction. As a result, the polarization axis is distorted in a slightly oblique direction, and when such two polarizers are placed in a cross nicol environment, the polarization axes of the two polarizers are not placed in a vertical relationship through space. Therefore, a slight light leakage is considered to occur.

  As described in the background art, Patent Document 5 discloses a polarizer protective film made of a polyester film having a thermal shrinkage of 5% or less in both the film flow direction and the film width direction. However, as apparent from the above-mentioned mechanism, even if the thermal contraction rate in the film flow direction and the thermal contraction rate in the film width direction are small, if the thermal contraction rate difference in the oblique direction is large, the oblique direction of the polarizing plate Warpage can not 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 kind in particular of polyester resin is not restrict | limited, Arbitrary polyester resin obtained by condensing dicarboxylic acid and diol can be used.

  Examples of dicarboxylic acid components that can be used for producing polyester resins include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic 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 Adipin , Pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

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

  The dicarboxylic acid component and the diol component constituting the polyester resin may be used alone or in combination of two or more. As a suitable polyester resin which comprises a polyester film, a polyethylene terephthalate, a polypropylene terephthalate, a polybutylene terephthalate, a polyethylene naphthalate etc. are mentioned, for example, Although a polyethylene terephthalate and a polyethylene naphthalate can be mentioned more preferably, these are It may further contain other copolymerizable components. These resins are excellent in transparency and also excellent in thermal and mechanical properties, and retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most preferable material because it has a large intrinsic birefringence and a relatively large retardation can be obtained relatively easily even if the thickness of the film is small.

(Straight direction heat shrinkage difference)
The heat shrinkage rate difference in the oblique direction in the present invention refers to 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 heat treated in water at 85 ° C. for 30 minutes. It is the absolute value of the difference with the thermal contraction rate in the -45 ° direction. Specifically, before and after the above heat treatment, the lengths of the 45 ° direction and the −45 ° direction with respect to the flow direction of the polyester film are measured, and they are compared to determine the thermal contraction rate in each direction. The thermal contraction rate in the 45 ° direction and the thermal contraction rate in the −45 ° direction can be compared to determine the difference between the thermal contraction rates.

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 in a cross nicol relationship, and the maximum light transmittance of light having a wavelength of 550 to 600 nm with respect to the two polarizing plates is measured using a spectrophotometer. it can. In the two polarizing plates, the polarizer and the polyester film used as a polarizer protective film are bonded together such that the polarization axis of the polarizer and the main orientation axis of the polyester film are perpendicular to each other. And, if the maximum light transmittance in the range of the wavelength is 0.02% or less, it can be evaluated that the light leakage is substantially zero.
Hereinafter, from the viewpoint of rainbow mark suppression, the preferable range of the retardation, the Nz coefficient and the plane orientation degree of the polyester film will be described.

(Retardation)
Although the polyester film used for the polarizer protective film used by this invention is not specifically limited, It is preferable to have the retardation of 4000-30000 nm. When 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 ensured. The retardation of the oriented polyester film is preferably 4500 nm or more, next preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, still more preferably 10000 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, no further improvement in visibility can be substantially obtained, and as the retardation increases, the thickness of the film becomes considerably thick, and the handleability as an industrial material decreases. Because there is a risk of

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

(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-mentioned range of retardation. The Nz coefficient can be determined as follows. The orientation axis direction of the film is determined using a molecular orientation meter (MOI-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), and the refractive index in the biaxial direction of the orientation axis direction and the direction orthogonal thereto (ny, nx, However, the refractive index (nz) in the thickness direction is determined by an Abbe refractometer (manufactured by Atago Co., NAR-4T, measurement wavelength: 589 nm). The Nz coefficient can be determined by substituting nx, ny, nz determined in this way into the equation represented by | ny-nz | / | ny-nx |.

  Even when the retardation of the polyester film is 4,000 nm to 30,000 nm, when the Nz coefficient exceeds 1.7, the polyester film is used as a polarizer protective film in both of 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 disposed on the outgoing light side are polyester films), when the liquid crystal display is viewed from an oblique direction Still, depending on the angle, there may be rainbow marks. Therefore, the Nz coefficient is more preferably 1.65 or less, further preferably 1.63 or less. The lower limit value of the Nz coefficient is 1.2. This is because it is technically difficult to obtain a film of less than 1.2. Further, 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 still more preferably 1.45 or more.

(Plane orientation coefficient)
In addition to controlling the retardation value and the Nz coefficient of the polyester film in the above specific range, the pair of polarizing plates can be more reliably ensured by setting the plane orientation degree represented by (nx + ny) / 2-nz to a specific value or less In the case where a polyester film is used as a polarizer protective film in both cases, rainbow marks can be completely eliminated. Here, the values of nx, ny and nz are determined in the same manner as the Nz coefficient. The orientation degree of the oriented polyester film is preferably 0.13 or less, more preferably 0.125 or less, and further preferably 0.12 or less. By setting the plane orientation degree to 0.13 or less, it is possible to more completely eliminate rainbow marks observed by an angle when the liquid crystal display device is observed from an oblique direction. The plane orientation degree is preferably 0.08 or more, more preferably 0.1 or more. If the degree of plane orientation is less than 0.08, the film thickness may fluctuate, and the value of retardation may be nonuniform within the film plane.

(Retardation ratio)
The polyester film has a ratio (Re / Rth) of retardation (Re) to retardation in the thickness direction (Rth) of preferably 0.2 or more, more preferably 0.5 or more, still more preferably 0.6 or more. . The larger the ratio of retardation to retardation in the thickness direction (Re / Rth), the more isotropic the action of birefringence and the less likely the occurrence of rainbow color spots due to the observation angle. The ratio of the retardation to the thickness direction retardation (Re / Rth) is 2 for a perfectly uniaxial (uniaxially symmetric) film. However, as described later, the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced as it approaches a perfect uniaxial (uniaxially symmetric) 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 color spots due to the observation angle, the ratio of the retardation to the thickness direction retardation (Re / Rth) does not have to be 2, but 1.2 or less is sufficient. Further, even if the ratio is 1.0 or less, it is sufficiently possible to satisfy the viewing angle characteristics (180 degrees left and right, about 120 degrees up and down) required for the liquid crystal display device.

(Thickness spots)
In order to suppress the fluctuation of the retardation of the polyester film, it is preferable that the thickness unevenness of the film be small. From this viewpoint, the thickness unevenness of the polyester film is preferably 5% or less, more preferably 4.5% or less, still more preferably 4% or less, particularly preferably 3% or less preferable.

(Film thickness)
Although the thickness in particular of a polyester film is not restrict | limited, Usually, it is 15-300 micrometers, Preferably it is 15-200 micrometers. When the thickness of the film is less than 15 μm, the anisotropy of the mechanical properties of the film becomes remarkable, which may cause tears, tears and the like. The particularly preferred lower limit of thickness is 25 μm. On the other hand, when 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. The particularly preferred upper limit of thickness is 100 μm, which is comparable to that of a general TAC film.

(Light transmittance)
The polyester film preferably has a light transmittance of 20% or less at a wavelength of 380 nm from the viewpoint of suppressing deterioration of the 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. When the light transmittance is 20% or less, it is possible to suppress the deterioration of the optically functional dye by ultraviolet light. The light transmittance is measured by 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. For the ultraviolet absorber used in the present invention, known ultraviolet absorbers can be appropriately selected and used. Specific examples of the UV absorber include organic UV absorbers and inorganic UV absorbers, but organic UV absorbers are preferable from the viewpoint of transparency.

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

  Examples of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers and acrylonitrile-based ultraviolet absorbers include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole [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'-) Tylphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- ( 1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol etc. Examples of cyclic imino ester-based UV absorbers include 2,2 ′-(1 , 4-phenylene) bis (4H-3, 1-benzoxazinone-4-one), 2-methyl-3, 1-benzoxazin-4-one, 2-butyl-3, 1-benzoxazine-4-one On, 2-phenyl-3, 1-benzoxazin-4-one etc. These ultraviolet absorbers may use only 1 type, and may use 2 or more types together.

  When a UV absorber is blended in the polyester film, it is preferable to make the oriented polyester film into a multilayer structure of three or more layers, and to add the UV absorber to a layer other than the outermost layer of the film (that is, an intermediate layer).

(Other ingredients etc.)
It is also a preferred embodiment to contain various additives in the oriented polyester film, as long as the effects of the present invention are not impaired, in addition to the ultraviolet light absorber. Additives include, for example, inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, thermal stabilizers, antioxidants, antigelling agents And surfactants. In addition, in order to achieve high transparency, it is also preferable that the polyester film does not substantially contain particles. The phrase "does not substantially contain particles" means, for example, in the case of inorganic particles, a content which is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less when the inorganic element is quantified by fluorescent X-ray analysis. means.

(Easy adhesion layer)
In the present invention, in order to improve the adhesion to the polarizer, at least one surface of the oriented polyester film has an easily adhesive layer containing at least one of polyester resin, polyurethane resin or polyacrylic resin as a main component. preferable. Here, the "main component" refers to a component that is 50% by mass or more among the solid components constituting the easily bonding layer. The coating solution used to form 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. As these coating solutions, for example, water-soluble or water-dispersible coexistence disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, etc. Examples thereof include polymerized polyester resin solutions, acrylic resin solutions, and polyurethane resin solutions.

The easy adhesion layer can be obtained by applying the coating solution to one side 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 transverse 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 to the resulting polarizer may be insufficient. On the other hand, when the coating amount exceeds 0.2 g / m ² , the blocking resistance may be reduced. When providing an easily bonding layer on both sides of a polyester film, the application amount of the easily bonding layer on both sides may be the same or different, and can be set independently within the above range.

  It is preferable to add particles to the easily adhesive layer in order to impart slipperiness. It is preferable to use particles having an average particle diameter of 2 μm or less. When the average particle size of the particles exceeds 2 μm, the particles are easily detached from the coating layer. The particles to be contained in the easy adhesion layer include, 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 thereof include inorganic particles such as calcium fluoride, and organic polymer particles such as styrene type, acrylic type, melamine type, benzoguanamine type and silicone type particles. These may be added alone to the easily bonding layer, or two or more may be added in combination.

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

  The measurement of the average particle diameter of the above-mentioned particles can be carried out 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 of the smallest particles is 2 to 5 mm, the largest diameter of 300 to 500 particles ( Measure the distance), and let the average value be the average particle size.

  It is also possible to subject the polyester film to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion to the polarizer.

(Functional layer)
Various functional layers, ie, hard coat layer, antiglare layer, antireflective layer, on the side opposite to the side on which the polarizer of the polyester film is disposed, for the purpose of preventing reflection, glare and scratch prevention, etc. It is also a preferable embodiment to provide at least one functional layer selected from the group consisting of a low reflective layer, a low antireflective layer, an antireflective antiglare layer, and an antistatic layer on the surface of the oriented polyester. When providing various functional layers, it is preferable that an oriented polyester film has an easily bonding layer on its surface. At that time, it is preferable to adjust the refractive index of the easily bonding layer so as to be near the geometric mean of the refractive index of the functional layer and the refractive index of the oriented polyester film, from the viewpoint of suppressing interference by reflected light. The refractive index of the easily bonding layer can be adjusted by a known method, and can be easily adjusted, for example, by adding titanium, zirconium, or other metal species to the binder resin.

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

  In order to reduce the absolute value of the difference between the thermal shrinkage in the 45 ° oblique direction with respect to the film flow direction and the thermal shrinkage in the 45 ° oblique direction with respect to the film flow direction, the uniaxial obtained by the above method In the film formation step of the drawn film and the biaxially drawn film, it is preferable to relieve the stress in the oblique direction which is generated in the step of cooling after the heat treatment. For this reason, it is preferable to adjust the relaxation rate and temperature 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 (traveling direction) to an optimum range. It is preferable to control the tension in the film flow direction by adjusting the difference between the tenter clip speed and the take-up roll speed to an appropriate range. After the heat treatment step, it is also preferable to adjust the relaxation rate and the temperature to an appropriate range, and relax by shortening the clip interval in the film flow direction while relaxing in the film width direction. Also preferred is a method of cutting or releasing the film from the tenter clip during the cooling step, and cooling while relaxing the film in the film flow direction and the film width direction. In addition, it is also effective to carry out off-line annealing treatment, for example, at 80 ° C. to 120 ° C., for 10 seconds to 90 minutes, of the roll once taken up.

  The polyester film is longitudinally stretched and transversely stretched, and then subjected to a heat treatment step, the both edges are cut into mill rolls, and slit as required, to obtain slit rolls. Among them, in the range of 33% at both ends of the mill roll (area of 33% from the right end of the film, area of 33% from the left end of the film), the heat shrinkage ratio difference in the oblique direction tends to be high. Therefore, for example, in the case of an off-line annealing process, it is preferable to adjust the temperature and time of the annealing process sufficiently.

  The oriented polyester film having the specific retardation and the Nz coefficient described above can be obtained by adjusting the conditions at the time of film formation (for example, the draw ratio, the draw temperature, the thickness of the film, etc.). For example, the higher the draw ratio, the lower the draw temperature, and the thicker the film, the easier it is to obtain high retardation. On the other hand, as the stretching ratio is lower, the stretching temperature is higher, and as the thickness of the film is thinner, lower retardation is easily obtained.

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

  In order to control retardation in the specific range mentioned above, it is preferable to control the ratio of the longitudinal stretch ratio and the transverse stretch ratio. If the difference between the longitudinal and lateral stretching 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-mentioned specific value, it is preferable to control the ratio of the longitudinal stretching ratio to the lateral stretching ratio, and it is preferable to use a uniaxially stretched film. In order to lower the Nz coefficient, it is also preferable to raise the molecular weight of the polymer and to lower the crystallinity by adding a copolymerization component. Furthermore, in order to control the Nz coefficient of the film within a specific range, it can be carried out by appropriately setting the total stretching ratio and the stretching temperature. For example, the lower the total draw ratio, the higher the drawing temperature, the lower the Nz coefficient can be obtained.

  In order to set the plane orientation degree to the above-mentioned specific value, it is preferable to control the total stretch ratio. If the total stretch ratio is too high, it is not preferable because the degree of plane orientation becomes too high. It is also preferable to control the stretching temperature in order to lower the degree of plane orientation. By increasing the difference between the longitudinal stretching ratio and the transverse stretching ratio, setting the total stretching ratio low, and setting the stretching temperature high, it is possible to make the Nz coefficient and the surface orientation degree equal to or less than a specific value.

  Since the stretching temperature and the stretching ratio greatly affect the thickness unevenness of the film, it is preferable to optimize the film forming conditions also 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 in which the longitudinal thickness unevenness becomes very bad in a certain range of the draw ratio, it is desirable to set film forming conditions when this range is removed.

  The incorporation of the ultraviolet light absorber into the oriented polyester film can be carried out by combining known methods. For example, using a kneading extruder, the dried ultraviolet absorber and the polymer raw material are blended to prepare a master batch in advance, and the film formation is carried out by mixing the predetermined master batch and the polymer raw material at the time of 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 disperse the UV absorber uniformly and to formulate it economically. As a condition for producing a master batch, it is preferable to use a kneading extruder, and extrude the extrusion temperature in the temperature of not less than the melting point of polyester raw material and not more than 290 ° C. in 1 to 15 minutes. At 290 ° C. or higher, the weight loss of the ultraviolet light absorber is large, and the viscosity decrease of the master batch is large. In the extrusion for 1 minute or less, uniform mixing of the UV absorber becomes difficult. At this time, a stabilizer, a color tone modifier, and an antistatic agent may be added as necessary.

  The incorporation of the ultraviolet light absorber into the intermediate layer of the oriented polyester film having a multilayer structure of three or more layers can be carried out in the following manner. Pellets of polyester alone for outer layer, masterbatch containing UV absorber for intermediate layer and polyester pellets are mixed at a predetermined ratio and dried, and then supplied to a known extruder for melt lamination to form slit-like The sheet is extruded from a die and solidified by cooling on a casting roll to form an unstretched film. That is, the film layer constituting both outer layers and the film layer constituting the intermediate layer are laminated by using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square junction), The three-layer sheet is extruded from the die and cooled with a casting roll to make an unstretched film.

  In order to remove foreign substances contained in the raw material polyester which causes optical defects, it is preferable to carry out 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 filtration particle size of the filter medium exceeds 15 μm, removal of foreign matter 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 sandwich both sides of a polarizer made of a polyvinyl alcohol-based film or the like dyed with iodine, and among the two polarizer protective films, It is preferable that at least one of them is a polyester film having a specific heat shrinkage difference in the oblique direction. The polarizer and the polarizer protective film are laminated via an adhesive, and usually heat-treated in the range of 70 ° C. to 120 ° C. for about 10 minutes to 60 minutes to obtain a polarizing plate.

(Arrangement of polarizer protective film)
In the liquid crystal display device of the present invention, the above-mentioned specific polyester film is preferably used as a polarizer protective film for both of a pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate disposed on the incident light side with respect to the liquid crystal and a polarizing plate disposed on the outgoing light side with respect to the liquid crystal. That is, it is preferable that the said polyester film is used for the polarizing plate of both the polarizing plate by the side of incident light, and the polarizing plate by the side of emitted light. The said polyester film should just be used as at least one among the polarizer protective film of 2 sheets which comprises 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 said oriented polyester film is used only for one of two polarizer protective films which comprise a polarizing plate, arbitrary polarizer protective films (for example, TAC film etc.) can be used for the other. When the oriented polyester film is adopted as a polarizer protective film on the liquid crystal cell side of the polarizing plate disposed on the incident light side and a polarizer protective film on the liquid crystal cell side of the polarizing plate disposed on the outgoing light side Since there is a possibility that the properties may be changed, the polarizer protective film at these positions is a polarizer protective film other than the oriented polyester film (such as a TAC film, an acrylic film, a norbornene film, etc.). It is preferable to use a film without birefringence. It is preferable that these films also have a small difference in thermal contraction rate in the oblique direction.

3. Liquid Crystal Display Device In general, a liquid crystal display device has a back surface module, a liquid crystal cell, and a front surface module in order from the side facing the backlight source to the side (viewing side or outgoing light side) displaying an image. The back surface module and the front surface 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, in the rear surface module, the polarizing plate is disposed on the side facing the backlight light source, and in the front surface module, it is disposed on the side on which an image is displayed (viewing side or outgoing light side).

  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 a component. The liquid crystal display device of the present invention may appropriately include other components other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like.

  The configuration of the backlight may be an edge light method using a light guide plate, a reflection plate or the like as a component, or may be a direct method. In the present invention, it is preferable to use a white light source having a continuous broad emission spectrum as a backlight source of the 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 the wavelength range of at least 450 nm to 650 nm, preferably in the visible light range. Examples of the white light source having such a continuous broad emission spectrum can include, but is not limited to, a white LED.

  Examples of white LEDs that can be used in the present invention include 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) etc. are included. As a fluorescent substance, the yellow fluorescent substance of a yttrium aluminum garnet type | system | group, the yellow fluorescent substance of a terbium aluminum garnet type | system | group, etc. can be mentioned, for example. Among white LEDs, a white light emitting diode composed of a light emitting element in which a blue light emitting diode using a compound semiconductor and an yttrium aluminum garnet yellow phosphor are combined has a continuous and wide emission spectrum and luminous efficiency. It is suitable as a back light source of the present invention because it is excellent. Since the white LED consumes less power, the liquid crystal display device of the present invention utilizing it also contributes to energy saving.

  A fluorescent tube such as a cold cathode tube or a hot cathode tube which has conventionally been widely used as a backlight source has a discontinuous emission spectrum in which the emission spectrum has a peak at a specific wavelength. Therefore, since it is difficult to obtain the intended effect of the present invention, it is not preferable as a light source of the liquid crystal display device of the present invention.

  Hereinafter, the present invention will be more specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be implemented with appropriate modifications as long as the gist of the present invention can be adopted. It is possible, and all are included in the technical scope of the present invention.

  The evaluation method of the physical property in an Example is as follows.

(1) Heat shrinkage rate difference in oblique directions The polarizer protective films 1 to 15 (which have been subjected to the off-line annealing treatment and those which have not been subjected to the treatment) to be described later are cut out into squares of 21 cm on each side. It was left in an atmosphere of 65 ° C., 65% RH for 2 hours or more. A circle with a diameter of 20 cm is drawn on this film so that the center is at the center of the film, and the vertical direction (film withdrawal direction) is 0 °, and a straight line passing the center of the circle in 45 ° and -45 ° is drawn. The diameter of each direction was measured. The film was heat-treated in water at 85 ° C. for 30 minutes, wiped off with water adhering to the surface, air-dried, and left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. Thereafter, the length of the straight line drawn in each diameter direction was measured as described above. Then, the length of the diameter before the heat treatment was compared with the length of the diameter after the heat treatment to determine the thermal shrinkage in each direction, and further compare them to determine the absolute value of the difference in the thermal shrinkage. This measurement was performed by sampling at three points in the width direction of the film with the same slit roll, and the average was taken as the heat shrinkage percentage difference. As a result of the measurement, in the case of the off-line annealing treatment, the thermal contraction rate difference is 0.4% or less at each of three points in the same slit roll, and the thermal contraction rates in the 45 degree direction and -45 degree direction It was less than 1.0%.

(2) Light Leakage Evaluation Method A polyester film prepared by laminating a triacetylcellulose film (Fujifilm Co., Ltd., thickness 80 μm) on one side of a polarizer made of a PVA film, and on the other side by a method described later Together. Each film was bonded to a polarizer via an adhesive. Thereafter, heat treatment was performed in an oven at 85 ° C. for 30 minutes to produce a polarizing plate. In addition, it bonded together so that the polarization axis of a polarizer and the main orientation axis of a polyester film might become mutually perpendicular | vertical. The two polarizing plates thus obtained are arranged in crossed nicols so that the polyester film is on the outside of the two polarizers, and the maximum at a wavelength of 550 to 600 nm is obtained using a spectrophotometer V7100 manufactured by JASCO Corporation. The light transmittance was measured.
○: Maximum light transmittance is not more than 0.02% ×: Maximum light transmittance is more than 0.02%

(3) Retardation (Re)
The retardation is a parameter defined by the product (ΔNxy × d) of the anisotropy (ΔNxy = | nx−ny |) of the biaxial refractive index orthogonal to the film and the film thickness d (nm). It is a measure showing optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. The orientation axis direction of the film is determined using a molecular orientation meter (MOI-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), and a rectangle of 4 cm × 2 cm is cut out so that the orientation axis direction becomes a long side, for measurement It was a sample. About this sample, the refractive index (nx, ny) of the biaxial which intersects perpendicularly, and the refractive index (Nz) of thickness direction are measured using an Abbe refractometer (made by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). The absolute value (| nx-ny |) of the difference between the two refractive indexes is taken as the anisotropy of refractive index (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (Filt Luff, Millitron 1245D), and the unit was converted to nm. The retardation (Re) was determined from the product (ΔNxy × d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(4) Nz coefficient The value obtained by | ny-nz | / | ny-nx | However, 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 taken as the degree of plane orientation (ΔP).

(6) Thickness direction retardation (Rth)
The thickness direction retardation is obtained by multiplying the film thickness d by each of two birefringence ΔNxz (= | nx-nz |) and ΔNyz (= | ny-nz |) when viewed from the cross section in the film thickness direction. It is a parameter which shows the average of the retardation obtained. The film thickness d (nm) is determined by the same method as the retardation measurement, and the average value of (ΔNxz × d) and (ΔNyz × d) is calculated to obtain retardation in the thickness direction (Rth) Asked for).

(7) Iridescent observation 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 main axis of the polyester film are perpendicular, and the opposite side Then, a TAC film (Fuji Film Co., Ltd., thickness 80 μm) was attached thereto to prepare a polarizing plate. The obtained polarizing plate was disposed on both sides of the liquid crystal one by one so that each polarizing plate was under the condition of crossed nicols, to produce a liquid crystal display. Each polarizing plate was disposed such that the polyester film was on the opposite side (distal) to the 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 an yttrium aluminum garnet yellow phosphor were combined was used as a light source (Nyspao Chemical, NSPW500CS). It observed visually from the front and the diagonal direction of such a liquid crystal display device, and it was judged as follows about generation | occurrence | production presence or absence of rainbow blotch.
A: There is no occurrence of rainbow marks from any direction.
A ': Very thin rainbow spots are observed depending on the angle when observed from an oblique direction.
B: When observed from an oblique direction, thin rainbow spots are observed depending on the angle.
C: Rainbow spots are observed when observed from an oblique direction.
D: Rainbow spots are observed when viewed from the front and diagonal directions.

(8) Tear strength The tear strength of each film was measured according to JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisaku-sho. The tearing direction was made parallel to the orientation main axis direction of the film and judged as follows. In addition, the measurement of the orientation main axis direction was measured by a molecular alignment meter (MOA-6004 type molecular alignment meter manufactured by Oji Scientific Instruments Co., Ltd.).
○: 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 reached 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. Then, the temperature was raised under pressure and the pressure esterification reaction was carried out under conditions of a gauge pressure of 0.34 MPa and 240 ° C. Then, the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was carried out with a high pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and a polycondensation reaction was performed at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, filtration treatment is carried out with a Naslon filter with a 95% cut diameter of 5 μm, extruded in a strand form from the nozzle, cooled and solidified using cooling water previously subjected to filtration treatment (pore diameter: 1 μm or less). , Cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl / g, and substantially no inert particles and internally precipitated particles were contained. (Hereafter, it is 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-benzoxazinone-4-one), particle-free PET (A) (intrinsic viscosity Mixed 90 parts by mass of 0.62 dl / g, and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter referred to as PET (B)).

Production Example 3 Preparation of Adhesiveness-Modified Coating Solution
The ester exchange reaction and the polycondensation reaction are carried out according to a conventional method, and 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate as a dicarboxylic acid component (relative to the entire dicarboxylic acid component) A water dispersible metal base containing sulfonic acid metal base-containing copolyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol (relative to the total glycol component) as a glycol component was prepared. Next, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of nonionic surfactant, the mixture is heated and stirred to reach 77 ° C. After 5 parts by mass of a water-dispersible metal base containing sulfonic acid metal base-containing copolymerized polyester resin is added and stirring is continued until clumps of the resin disappear, the resin aqueous dispersion is cooled to normal temperature to have a solid content concentration of 5.0% by mass A uniform water dispersible copolymerized polyester resin liquid was obtained. Furthermore, 3 parts by mass of aggregate silica particles (manufactured by Fuji Silysia Co., Ltd., Psylysia 310) are dispersed in 50 parts by mass of water, and then 99.46 parts by mass of the above-mentioned water dispersible copolymerized polyester resin solution are added thereto. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added while stirring to obtain an adhesion modified coating liquid.

(Polarizer protective film 1)
After 90 parts by mass of PET (A) resin pellet containing no particles as a raw material for a base film intermediate layer and 10 parts by mass of PET (B) resin pellet containing an ultraviolet absorber at reduced pressure (1 Torr) at 135 ° C for 6 hours , The extruder 2 (for the intermediate layer II layer), and the PET (A) was dried by an ordinary method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III), respectively, and dissolved at 285 ° C. . The two polymers are respectively filtered with a filter material of a stainless sintered body (nominal filtration accuracy 10 μm particle 95% cut), laminated in a two-kind three-layer merging block, sheeted out from a die, and extruded The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and solidified by cooling to form an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of layer I, layer II, and layer III was 10:80:10.

Next, the above adhesion modifying coating solution was applied to both sides of this unstretched PET film by reverse roll method so that the coating amount after drying was 0.08 g / m ² , and then dried at 80 ° C. for 20 seconds .

  The unstretched film on which the coated layer was formed was guided to a tenter stretching machine, and while holding the end of the film with a clip, it was guided to a hot air zone at a temperature of 125 ° C. and stretched 4.0 times in the width direction. Next, processing was carried out at a temperature of 225 ° C. for 30 seconds while keeping the width stretched in the width direction, and both edge portions were cut and removed to obtain a mill roll consisting of uniaxially oriented PET film with a film thickness of about 50 μm. . The mill roll was divided into three equal parts to obtain three slit rolls (L, C, R). About each slit roll, what carried out the off-line annealing treatment for 5 minutes at 90 degreeC, and two types of what was what carried out the off-line annealing treatment were created.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, a slit roll composed 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. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

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

(Polarizer protective film 4)
In the same manner as in the polarizer protective film 3, the slit roll was stretched 2.0 times in the traveling direction and 4.0 times in the width direction to obtain a slit roll composed of a biaxially oriented PET film having a film thickness of about 50 μm. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 5)
By the method similar to the polarizer protective film 1, the slit roll which consists of uniaxial-oriented PET film with a film thickness of 50 micrometers was obtained, without using PET resin (B) which contains an ultraviolet absorber in the intermediate | middle layer. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 6)
In the same manner as in the polarizer protective film 1, the film was stretched 1.0 times in the traveling direction and 3.5 times in the width direction to obtain a slit roll composed of uniaxially oriented PET film with a film thickness of about 75 μm. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 7)
Using a method similar to that of the polarizer protective film 1, change the thickness of the unstretched film, set the transverse stretching ratio to 3.8 times, set the stretching temperature to 135 ° C., and make a slit roll of uniaxially oriented PET film of about 100 μm thickness Obtained. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 8)
Using a method similar to that of the polarizer protective film 1, a slit roll composed of a uniaxially oriented PET film with a thickness of about 50 μm was obtained, with a transverse draw ratio of 3.8 and a draw temperature of 135 ° C. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 9)
Using a method similar to that of the polarizer protective film 1, a slit roll composed of a uniaxially oriented PET film with a thickness of 50 μm was obtained by setting the transverse stretching ratio to 3.8 times. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 10)
Using a method similar to that of the polarizer protective film 1, a slit roll composed of a uniaxially oriented PET film with a thickness of about 50 μm was obtained, with a transverse draw ratio of 4.2 and a draw temperature of 135 ° C. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 11)
Using a method similar to that of the polarizer protective film 1, the thickness of the unstretched film was changed, and the lateral stretching ratio was changed to 3.8 times to obtain a slit roll composed of a uniaxially oriented PET film having a thickness of 38 μm. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 12)
The slit roll which consists of uniaxially oriented PET film whose thickness is 38 micrometers was obtained by changing the thickness of an unstretched film using the method similar to the polarizer protective film 1. FIG. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

(Polarizer protective film 13)
In the same manner as in the polarizer protective film 3, the slit roll was stretched 1.8 times in the traveling direction and 2.0 times in the width direction to obtain a slit roll composed of a biaxially oriented PET film having a film thickness of about 275 μm. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

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

(Polarizer protective film 15)
The slit roll consisting of a uniaxially oriented PET film with a thickness of about 10 μm was obtained by changing the thickness of the unstretched film using the same method as that of the polarizer protective film 1. Similar to the polarizer protective film 1, two types were prepared: one that was subjected to the offline annealing treatment, and one that was to be subjected to the offline annealing treatment.

  The results of the light leakage evaluation for the polarizer protective films 1 to 15 are shown in Table 1 (samples treated with offline annealing) and Table 2 (samples not treated with 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.

  Moreover, the result of having measured rainbow mark observation and tear strength about the liquid crystal display device produced as mentioned above using the polarizer protective films 1-15 (sample processed by offline annealing) is shown in the following Table 3.

  In Table 3, the polarizer protective film No. 1 7 * shows the case where the polarizer protective film 7 is used as a polarizer protective film and an organic light emitting diode (OLED) is used as a light source. Moreover, in Table 3, the polarizer protective film No. 7 ** shows the case where a polarizer protective film 7 is used as a polarizer protective film and a cold cathode tube is used as a 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 thereof is 1.7 or less, the occurrence of rainbow blotches is significantly suppressed. . Moreover, it was shown that it is possible to suppress generation | occurrence | production of a rainbow mark more effectively by controlling the degree of plane orientation of an oriented polyester film to 0.13 or less in addition to this condition.

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

Claims (1)

The invention described herein.