KR20160007548A - Liquid crystal display device, polarizing plate, and polarizer protective film - Google Patents

Abstract

It is an object of the present invention to provide a polarizer protective film comprising a polyester film capable of suppressing light leakage even when two polarizing plates are disposed under a cross-nicol environment.
In order to solve the above problems, the polarizer protective film of the present invention is 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% A polarizer protective film made of a polyester film.

Description

[0001] The present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film,

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

A polarizing plate used in a liquid crystal display (LCD) is generally constituted by sandwiching a polarizer obtained by dyeing iodine to polyvinyl alcohol (PVA) or the like between two polarizer protective films. As the polarizer protective film, triacetylcellulose ( TAC) films have been used. In recent years, along with the thinning of LCDs, a thin polarizing plate has been required. However, if the thickness of the TAC film used as the protective film is reduced, sufficient mechanical strength can not be obtained and the moisture permeability is deteriorated. In addition, TAC films are very expensive, and inexpensive alternative materials are strongly demanded.

In order to make the polarizing plate thinner, it has been proposed to use a polyester film instead of the TAC film so as to maintain high durability even when the polarizer protective film is thin (Patent Documents 1 to 3).

The polyester film has excellent durability as compared with the TAC film, but has birefringence unlike the TAC film. Therefore, when the polyester film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical deformation. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when it is used as a polarizer protective film, irregular color irregularity occurs when observed in an oblique direction, and the image quality is deteriorated. For this reason, in Patent Documents 1 to 3, a countermeasure for reducing the retardation is made by using a co-polyester as a polyester.

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

In Patent Document 5, since the polarizer protective film passes through many heat processing steps such as a process of producing a polarizing plate or a process of combining the obtained polarizing plate with a liquid crystal cell, in order to have good dimensional stability, specifically, after the heat treatment at 120 ° C for 30 minutes It is preferable that the shrinkage percentage of the polyester film is preferably 5% or less in both the film MD direction (film flow direction) and the TD direction (film width direction).

Japanese Patent Application Laid-Open No. 2002-116320 Japanese Patent Application Laid-Open No. 2004-219620 Japanese Patent Application Laid-Open No. 2004-205773 WO2011-162198 Japanese Patent Application Laid-Open No. 2010-277028

As the polarizer protective film, a TAC film has been conventionally used, but as described in the background art, a polarizer protective film made of a polyester film has attracted attention as an alternative. The polarizing plate has a structure in which a polarizer is sandwiched between two polarizer protective films. When two polarizing plates each having at least one of two polarizer protective films as a polyester film are prepared and two polarizing plates are arranged so as to be in a cross-nicol environment, slight light leakage occurs and visibility deteriorates The present inventors have found that there is a new problem that there is a case where the above-mentioned problems occur. It is an object of the present invention to provide a polarizer protective film made of a polyester film capable of suppressing the above-mentioned slight light leakage.

The inventors of the present invention have conducted a study on the above problems on a day and a night. As a result, they have found that a polyester film having an absolute value of a difference between a heat shrinkage ratio in the direction of 45 degrees with respect to the film flow direction and a heat shrinkage rate in the- The present invention has been made to solve the above problems.

The present invention is as follows.

Section 1.

Wherein an absolute value of a difference between a heat shrinkage ratio in the 45-degree direction with respect to the film flow direction and a heat shrinkage ratio in the -45-degree direction with respect to the film flow direction is 0.4% or less.

Section 2.

The polarizer protective film according to item 1, wherein the retardation of the polyester film is 4,000 to 30,000 nm and the Nz coefficient is 1.7 or less.

Section 3.

The polarizer protective film according to item 1 or 2, wherein the polyester film has a planar orientation degree of 0.13 or less.

Section 4.

A polarizer protective film is laminated on both sides of the polarizer,

Wherein at least one polarizer protective film on one side is the polarizer protective film according to any one of items 1 to 3.

Item 5.

A polarizer protective film is laminated on both sides of the polarizer,

One polarizer protective film is made of triacetylcellulose film,

And the other polarizer protective film is the polarizer protective film according to any one of items 1 to 3. [

Section 6.

A backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,

Wherein the backlight source is a white light source having a continuous emission spectrum,

The polarizer includes a polarizer protective film laminated on both sides of the polarizer,

At least one of the polarizer protective film of the polarizing plate disposed on the incident light side and the polarizer protective film of the polarizing plate disposed on the emerging light side

A liquid crystal display device as defined in any one of items 1 to 3, which is a polarizer protective film.

Item 7.

The incident-light-side polarizer protective film of the polarizing plate disposed on the side of the incident light and the polarizing plate protective film of the emerging-side polarizing plate of the polarizing plate disposed on the emerging-

Item 6. The liquid crystal display device according to item 6, which is the polarizer-protective film according to any one of items 1 to 3.

According to the present invention, there is provided a polarizer protective film and a polarizing plate comprising a polyester film suitable for obtaining a liquid crystal display device in which generation of slight light leakage is suppressed and excellent visibility is obtained when two polarizing plates are disposed under a cross-Nicol environment . According to the present invention, there is provided a liquid crystal display device in which light leakage is suppressed and which is excellent in visibility.

1. Polarizer protective film

The polarizer protective film of the present invention is made of a polyester film and has an 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 Heat shrinkage difference difference " or " heat shrinkage difference difference ") is preferably 0.4% or less. The absolute value of the difference in the heat shrinkage percentage is preferably 0.3% or less, and more preferably 0.2% or less. The smaller the value of the difference in heat shrinkage percentage is, the better the lower limit is 0%. The direction of 45 degrees with respect to the film flow direction and the direction of -45 degrees with respect to the film flow direction are of course perpendicular to each other. Further, the heat shrinkage rate in the direction of 45 degrees and the heat shrinkage rate in the -45 degrees direction with respect to the film flow direction are preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.6% or less.

In general, two polarizing plates are disposed in a cross-nicol environment in a liquid crystal display device. When two polarizing plates are placed under a cross-nicol environment, light is not normally passed through, but it has been found that light may leak depending on the difference in heat shrinkage ratio in the oblique direction of the polarizer protective film. The mechanism is considered as follows, but the present invention is not limited thereto.

The polarizer is usually manufactured by bonding a polarizer protective film and a polarizer through an adhesive. In such a bonding step, the polarizing plate is usually heat-treated at a temperature in the range of 70 ° C to 120 ° C for 10 minutes to 60 minutes. When a film having a large difference in heat shrinkage ratio in the oblique direction is used as the polarizer protective film, the polyester film is warped at the time of the above-mentioned heat treatment, and minute deflection occurs in the polarizing plate itself in the oblique direction. As a result, if the polarizing axes are slightly deformed in the oblique direction and the two polarizing plates are arranged under the Cross-Nicol environment, the light axes of the two polarizing plates are not arranged in a vertical relationship via the space, do.

As described in the background art, Patent Document 5 discloses a polarizer protective film made of a polyester film having a heat shrinkage of 5% or less in both the film flow direction and the film width direction. However, even if the heat shrinkage ratio in the film flow direction and the heat shrinkage ratio in the width direction of the film are small, the difference in the heat shrinkage ratio in the oblique direction is large, as is clear from the above-mentioned mechanism, the deflection in the oblique direction of the polarizer can not be suppressed.

The polyester film used in the polarizer protective film of the present invention can be obtained from any polyester resin. The kind of the polyester resin is not particularly limited, and any polyester resin obtained by condensing a dicarboxylic acid with a 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-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4- Naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenylcarboxylic acid, diphenoxyethane dicarboxylic acid, diphenylsulfonic acid, anthracene dicarboxylic acid, 1,3-cyclopentane Dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethyl malonic acid, But are not limited to, ethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, Carboxylic acid and the like.

Examples of the diol component usable in the production of the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol Propane diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis (4-hydroxyphenyl) propane, bis Sulfone, and the like.

The dicarboxylic acid component and the diol component constituting the polyester resin may be used alone or in combination of two or more. Examples of suitable polyester resins constituting the polyester film include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and more preferably polyethylene terephthalate, polyethylene naphthalate , Which may further contain other copolymerization components. These resins have excellent transparency and excellent thermal and mechanical properties, so that retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and thus a relatively large retardation can be obtained even if the thickness of the film is thin.

(Difference in heat shrinkage ratio in the oblique direction)

The difference in heat shrinkage ratio in the oblique direction in the present invention means that the heat shrinkage rate in the 45 ° direction with respect to the film flow direction when the polyester film is heat-treated at 85 ° C for 30 minutes in water and the heat shrinkage rate in the -45 ° direction Refers to the absolute value of the difference in heat shrinkage ratio. Specifically, the lengths of the polyester film in the directions of 45 ° and -45 ° with respect to the flow direction of the polyester film were measured before and after the heat treatment, and the heat shrinkage rate in each direction was determined by comparing them. The difference in heat shrinkage ratio can be obtained by comparing the heat shrinkage ratios in the? Direction.

The presence or absence of the light emission can be measured by the measurement method described in the following embodiments. That is, two polarizing plates are arranged so as to be in a cross-Nicol relationship, and the maximum light transmittance of the two polarizing plates of light having a wavelength of 550 to 600 nm can be measured using a spectrophotometer. The polarizer and the polyester film used as the polarizer protective film in the two polarizing plates are bonded so that the polarizing axis of the polarizer and the main alignment axis of the polyester film are perpendicular to each other. If the maximum light transmittance in the wavelength range is 0.02% or less, it can be estimated that there is substantially no light leakage.

A preferable range of the retardation, the Nz coefficient, and the degree of planar orientation of the polyester film will be described below from the viewpoint of suppressing rainbow stains.

(Retardation)

The polyester film used for the polarizer protective film used in the present invention is not particularly limited, but it is preferable that the polyester film has a retardation of 4,000 to 30,000 nm. When the retardation is 4,000 nm or more, the interference color can be suppressed when viewing the liquid crystal display device in the oblique direction, and good visibility can be secured. The preferred retardation of the oriented polyester film is 4,500 nm or more, preferably 5,000 nm or more, more preferably 6,000 nm or more, still more preferably 8,000 nm or more, still more preferably 10,000 nm or more.

The upper limit of the retardation of the polyester film is preferably 30,000 nm. Even when a polyester film having a retardation higher than that is used, the effect of further improving the visibility is not substantially obtained, and the thickness of the film becomes considerably thick along with the increase of the retardation, which may lower the handling property as an industrial material to be.

The retardation value of the oriented polyester film can be obtained by measuring the refractive index and the thickness in the biaxial direction according to a known method. It is also possible to perform measurement using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Measurement Instruments Co., Ltd.). The retardation at 589 nm, which is the wavelength of the sodium D line, is measured in any measurement method.

(Nz coefficient)

In addition to the range of retardation described above, the polyester film used for the polarizer protective film preferably has an Nz coefficient represented by | ny-nz | / | ny-nx | of 1.7 or less. The Nz coefficient can be obtained as follows. The orientation axis direction of the film was determined using a molecular orientation system (MOA-6004 type molecular alignment system, manufactured by Oji Measurement Instruments Co., Ltd.), and the refractive indexes (ny, nx, ny> nx ) And a refractive index (nz) in the thickness direction are determined by Abbe's refractive index meter (NAR-4T manufactured by Atago Co., measurement wavelength: 589 nm). The Nz coefficient can be obtained by substituting nx, ny, and nz thus obtained into an expression represented by | ny-nz | / | ny-nx |.

When the retardation of the polyester film is in the range of 4,000 nm to 30,000 nm and the Nz coefficient exceeds 1.7, when the polyester film is used as a polarizer protective film on both of the pair of polarizers (for example, the incident light side When the polarizer protective film and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side are polyester films), irregular unevenness may still occur depending on the angle when the liquid crystal display device is observed in the oblique direction. Therefore, the Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less. The lower limit 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 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 the Nz coefficient of the polyester film to the above specific range, by making the degree of planarization represented by (nx + ny) / 2-nz to be not more than a specific value, It is possible to completely eliminate rainbow stains when a polyester film is used. Here, the values of nx, ny, and nz are obtained in the same manner as the Nz coefficient. The degree of planar 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 planar orientation degree to 0.13 or less, rainbow stains observed along the angle can be completely eliminated when the liquid crystal display device is observed in the oblique direction. The degree of planar orientation is preferably 0.08 or more, and more preferably 0.1 or more. When the degree of planar orientation is less than 0.08, the film thickness may fluctuate and the retardation value may become uneven in the film plane.

(Retardation ratio)

The ratio (Re / Rth) of the retardation (Re) to the thickness direction retardation (Rth) of the polyester film is preferably 0.2 or more, more preferably 0.5 or more, further preferably 0.6 or more. The larger the ratio of retardation to retardation in the thickness direction (Re / Rth) is, the more the action of birefringence increases the isotropy and the irregular color irregularity in the irregular shape depending on the observation angle hardly occurs. In the case of a complete uniaxial (uniaxial) film, the ratio of retardation to thickness direction retardation (Re / Rth) is 2. However, as described below, the mechanical strength in the direction orthogonal to the alignment direction is remarkably lowered as the film becomes closer to the complete uniaxial (uniaxial) film.

Accordingly, the upper limit of the ratio (Re / Rth) between the retardation and the retardation in the thickness direction is preferably 1.2 or less, and more preferably 1 or less. In order to completely suppress the occurrence of color irregularity of the iridescence shape according 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 sufficiently possible to satisfy the viewing angle characteristics (about 180 degrees in the left and right direction, about 120 degrees in the vertical direction) required for the liquid crystal display device.

(Thickness deviation)

In order to suppress the fluctuation of the retardation of the polyester film, it is preferable that the thickness deviation of the film is small. From this viewpoint, the thickness variation 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.

(Film thickness)

The thickness of the polyester film is not particularly limited, but is usually 15 to 300 占 퐉, preferably 15 to 200 占 퐉. When the film thickness is less than 15 탆, the anisotropy of mechanical properties of the film becomes remarkable, which may cause tearing, cracking, and the like. A particularly preferable lower limit of the thickness is 25 占 퐉. On the other hand, if the upper limit of the thickness of the polarizer protective film is more than 300 m, the thickness of the polarizing plate becomes too thick, which is not preferable. From the standpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 占 퐉. An upper limit of a particularly preferable thickness is 100 mu m which is equivalent to that of a general TAC film.

(Light transmittance)

It is preferable that the polyester film has a light transmittance of not more than 20% at a wavelength of 380 nm from the viewpoint of suppressing deterioration of an optically 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, particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration due to ultraviolet rays of the optically functional dye can be suppressed. The light transmittance is measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, 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 kind, concentration and film thickness of the ultraviolet absorber to be incorporated. A known ultraviolet absorber can be suitably selected and used for the ultraviolet absorber to be used in the present invention. Specific ultraviolet absorbers include an organic ultraviolet absorber and an inorganic ultraviolet absorber, but an organic ultraviolet absorber is preferable from the viewpoint of transparency.

Examples of the organic ultraviolet absorber include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as they are in the range of absorbance as defined by the present invention. However, from the viewpoint of durability, benzotriazole-based cyclic imino ester-based ones are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays of respective wavelengths can be simultaneously absorbed, so that the ultraviolet absorption effect can be further improved.

Examples of the benzophenone-based ultraviolet absorber, benzotriazole-based ultraviolet absorber and acrylonitrile-based ultraviolet absorber include 2- [2'-hydroxy-5 '- (methacryloyloxymethyl) phenyl] -2H- Sol, 2- [2'-hydroxy-5'- (methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2'- ) Phenyl] -2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 2,4-di (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, Methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- (1,1,3,3 -Tetramethylbutyl) -6- (2H-benzotriazole-2-yl) phenol, etc. The cyclic imino ester-based ultraviolet absorber includes, for example, 2,2 '- (1,4- ) Bis (4H-3,1-benzoxazinone-4-one), 2-methyl- 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazin-4-one, etc. The ultraviolet absorbers include 1 The species may be used alone or two or more species may be used in combination.

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

(Other components, etc.)

In the oriented polyester film, it is also preferable to add various additives in addition to the ultraviolet absorber within the range not hindering the effect of the present invention. Examples of the additive include inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, antigelling agents and surfactants. In order to exhibit high transparency, it is also preferable that the polyester film contains substantially no particles. The phrase " substantially not containing particles " means, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescent X-ray analysis, it is 50 ppm or less, preferably 10 ppm or less, By weight.

(The adhesive layer)

In the present invention, in order to improve the adhesiveness with the polarizer, it is preferable that the oriented polyester film has this adhesive layer containing at least one kind of polyester resin, polyurethane resin or polyacrylic resin as a main component on at least one side. Here, the " main component " refers to a component that accounts for 50 mass% or more of the solid components constituting the adhesive layer. The coating liquid used for forming the adhesive layer is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymer polyester resin, an acrylic resin and a polyurethane resin. Examples of the coating liquids include those disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, etc. A water-soluble or water-dispersible copolymer polyester resin solution, an acrylic resin solution and a polyurethane resin solution.

This adhesive layer can be obtained by applying the coating liquid on 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 further stretching in the transverse direction. The final application amount of the adhesive layer is preferably 0.05 to 0.2 g / m 2. If the coating amount is less than 0.05 g / m < 2 >, the adhesion to the obtained polarizer may become insufficient. On the other hand, if the applied amount exceeds 0.2 g / m < 2 >, the blocking resistance may be lowered. When the adhesive layer is provided on both sides of the polyester film, the application amount of the adhesive layer on both sides may be the same or different and can be independently set within the above range.

It is preferable to add particles to the adhesive layer to impart releasability thereto. It is preferable to use particles having an average particle size of 2 mu m or less. If the average particle diameter of the particles exceeds 2 탆, the particles tend to fall off from the coating layer. Examples of the particles to be contained in the adhesive layer include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, Calcium, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based ones. These may be added to the adhesive layer alone, or two or more of them may be added in combination.

The coating liquid can be applied by a known method. For example, a reverse roll coating method, a gravure coating method, a kiss-coat method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method and a pipe doctor method. Or in combination.

The average particle diameter of the particles can be measured by the following method. The particles were photographed with a scanning electron microscope (SEM) to measure the maximum diameter (the distance between the two most distant points) of 300 to 500 particles at a magnification of 2 to 5 mm in the size of one smallest particle, The average value is taken as the average particle diameter.

The polyester film may be subjected to a corona treatment, a coating treatment, a flame treatment, or the like in order to improve the adhesiveness to the polarizer.

(Functional layer)

The functional layer such as a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection prevention layer, and an antireflection layer for the purpose of preventing, inhibiting, or suppressing scratches on the side opposite to the side on which the polarizer of the polyester film is disposed. It is also preferable to provide at least one functional layer selected from the group consisting of an antiglare layer and an antistatic layer on the surface of the oriented polyester. When the various functional layers are provided, the oriented polyester film preferably has this adhesive layer on its surface. It is preferable to adjust the refractive index of the adhesive layer so as to be close to 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 the interference by the reflected light. The refractive index of the adhesive layer can be adjusted by a known method. For example, the binder resin can be easily adjusted by containing titanium, zirconium or other metal species.

(Production method of oriented polyester film)

The oriented polyester film as the protective film of the present invention can be produced by a general method for producing a polyester film. For example, after a polyester resin is melted and extruded in a sheet form, the unoriented polyester formed is stretched in the longitudinal direction at a temperature equal to or higher than the glass transition temperature using the speed difference of the roll, And heat treatment is carried out. The film may be a uniaxially stretched film or a biaxially stretched film.

In order to reduce the absolute value of the difference between the heat shrinkage ratio in the direction of the oblique 45 degrees with respect to the film flow direction and the heat shrinkage rate in the direction of -45 degrees with respect to the film flow direction, the monoaxially stretched film and biaxially oriented film It is preferable to relax the stress in the oblique direction generated in the step of cooling after the heat treatment. For this reason, it is preferable to adjust the relax rate and the temperature in a suitable range after the heat treatment process to relax in the film width direction. It is also preferable to adjust the tension in the film flow direction (running direction) to an optimum range. It is preferable to control the tension in the film flow direction by adjusting the speed of the tenter clip and the speed difference between the suction rolls in an appropriate range. It is also preferable to relax the film by adjusting the relax rate and the temperature within a suitable range after the heat treatment process so as to relax in the film width direction while reducing the clip interval in the film flow direction. It is also preferable to cool or cut the film from the tenter clip during the cooling process while cooling the film in the film flow direction and the film width direction. It is also effective to carry out offline annealing at a temperature of, for example, 80 DEG C to 120 DEG C for 10 seconds to 90 minutes.

The polyester film is subjected to longitudinal drawing and transverse drawing, followed by a heat treatment step to cut both edge portions into a mill roll, and if necessary, a slit roll can be obtained by slitting. Of these, the range of 33% at both ends of the mill roll (33% region from the right end of the film, 33% from the left end of the film) tends to have a particularly high heat shrinkage difference in the oblique direction. Therefore, for example, in the case of the off-line annealing process, it is preferable to adjust the temperature and time of the annealing process to a sufficient level.

The above-mentioned oriented polyester film having the specific retardation and Nz coefficient can be obtained by controlling the condition (for example, stretching magnification, stretching temperature, film thickness, etc.) at the time of film formation. For example, the higher the stretching magnification, the lower the stretching temperature, and the thicker the film, the higher the retardation is likely to be obtained. On the other hand, the lower the stretch ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation is likely to be obtained.

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

In order to control the retardation to the above-mentioned specific range, it is preferable to control the ratio of the longitudinal stretching ratio and the lateral stretching ratio. If the difference between the longitudinal and transverse 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 to be low in order to increase the retardation. The temperature of the subsequent heat treatment is preferably 100 to 250 占 폚, particularly preferably 180 to 245 占 폚.

In order to set the Nz coefficient to the specific value described above, it is preferable to control the ratio of the longitudinal stretching magnification and the lateral stretching magnification, and it is preferable that the uniaxially stretched film is used. Further, in order to lower the Nz coefficient, it is also desirable to increase the molecular weight of the polymer and to lower the crystallinity by adding a copolymerization component. Further, in order to control the Nz coefficient of the film to a specific range, it is possible to set by appropriately setting the total stretching magnification and the stretching temperature. For example, the lower the total draw ratio and the higher the draw temperature, the lower the Nz coefficient can be obtained.

In order to set the degree of planar orientation to the specific value described above, it is preferable to control the total drawing magnification. An excessively high total stretching ratio is undesirable because the degree of planar orientation becomes excessively high. It is also preferable to control the stretching temperature in order to lower the degree of planar orientation. The Nz coefficient and the degree of planar orientation can be set to a specific value or less by increasing the difference between the longitudinal drawing magnification and the lateral drawing magnification, setting the total drawing magnification to a low value, and setting the drawing temperature to a high value.

Since the stretching temperature and stretching magnification have a large influence on the thickness variation of the film, it is preferable to optimize the film formation conditions from the viewpoint of the thickness deviation. In particular, when the longitudinal stretching magnification is lowered in order to increase the retardation, the longitudinal thickness deviation may be deteriorated. It is preferable to set the film forming conditions at a point outside this range because the vertical thickness deviation has a region which is extremely deteriorated in a certain range of the draw magnification.

The combination of the ultraviolet absorber with the oriented polyester film can be carried out by combining known methods. For example, the ultraviolet absorber dried by using a kneading extruder may be blended with the polymer raw material to prepare a master batch in advance, and the raw material may be blended with the predetermined master batch and the polymer raw material at the time of film formation.

The concentration of the ultraviolet absorber in the master batch is preferably 5 to 30% by mass in order to uniformly disperse the ultraviolet absorber and to economically blend it. As a condition for producing the master batch, it is preferable to use a kneading extruder and extrude at a temperature of not lower than the melting point of the polyester raw material and not more than 290 캜 for 1 to 15 minutes. When the temperature is higher than 290 占 폚, the weight loss of the ultraviolet absorber is large and the viscosity of the masterbatch decreases. In the case of extrusion of 1 minute or less, uniform mixing of the ultraviolet absorbent becomes difficult. At this time, a stabilizer, a color tone adjusting agent and an antistatic agent may be added as necessary.

The combination of the ultraviolet absorber to the intermediate layer of the oriented polyester film having a multilayer structure of three or more layers can be carried out by the following procedure. The master batch containing the polyester pellets as the outer layer, the master batch containing the ultraviolet absorbent for the intermediate layer and the pellets of the polyester were mixed and dried at a predetermined ratio and then supplied to a known extruder for melt lamination, And cooled and solidified on a casting roll to produce an unoriented film. That is, a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated by using two or more extruders, a three-layer manifold or a confluence block (for example, a confluence block having a confluent confluent portion) Is extruded and cooled with a casting roll to form an unstretched film.

It is preferable to perform high-precision filtration at the time of melt extrusion in the production process of the oriented polyester film in order to remove foreign matters contained in the polyester of the raw material causing optical defects. The filtration particle size (initial filtration efficiency: 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. If the filter particle size of the filter material exceeds 15 μm, the removal of foreign matter of 20 μm or more tends to be insufficient.

2. Polarizer

The polarizing plate of the present invention is constituted such that both sides of a polarizer made of iodine dyed polyvinyl alcohol film or the like are sandwiched between two polarizer protective films and at least one of the two polarizer protective films has a difference in heat shrinkage rate in the oblique direction It is preferable that it is a specific polyester film. The polarizer and the polarizer protective film are laminated via an adhesive, and the polarizer is obtained by heat-treating the film at a temperature in the range of 70 ° C to 120 ° C for 10 minutes to 60 minutes.

(Arrangement of Polarizer Protective Film)

In the case of the liquid crystal display device of the present invention, it is preferable that the specific polyester film is used as a polarizer protective film on both sides 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 emerging light side with respect to the liquid crystal. That is, the polyester film is preferably used for both the polarizing plate on the incident light side and the polarizing plate on both sides of the polarizing plate on the outgoing light side. The polyester film may be used as at least one of the two polarizer protective films constituting each polarizing plate.

In a preferred embodiment, the oriented polyester film is used as an incident-light-side polarizer protective film of an incident-light-side polarizer and also as an emergent-side polarizer protective film of an emergent-side polarizer. When the oriented polyester film is used on only one of the two polarizer protective films constituting the polarizing plate, an optional polarizer protective film (for example, TAC film) may be used on the other side. When the oriented polyester film is used as the liquid crystal cell side polarizer protective film of the liquid crystal cell side polarizer protective film of the polarizing plate disposed on the incident light side and the polarizing plate disposed on the emergent light side, there is a possibility of changing the polarization characteristics of the liquid crystal cell, It is preferable to use a polarizer protective film (for example, a TAC film, an acrylic film, or a birefringence-free film typified by a norbornene-based film) other than the oriented polyester film. These films preferably have a small difference in heat shrinkage ratio in the oblique direction.

3. Liquid crystal display

In general, a liquid crystal display device has a rear module, a liquid crystal cell, and a front module in the order from the side facing the backlight source to the side displaying the image (on the viewer side or the outgoing side). The back module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface thereof, and a polarizing plate disposed on the opposite side thereof. Here, the polarizing plate is disposed on the side facing the backlight light source in the case of the rear module, and on the side (on the viewer side or the outgoing light side) where the image is displayed in the case of the front module.

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

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

The white LED that can be used in the present invention includes a white light emitting element and an organic light emitting diode (OLED), which emit white light by combining a phosphor type, that is, a blue light using a compound semiconductor or a light emitting diode and a phosphor emitting ultraviolet light, . Examples of the fluorescent material include yttrium, aluminum, garnet yellow fluorescent material, terbium, aluminum, garnet yellow fluorescent material, and the like. Among the white LEDs, the white light emitting diode comprising a light emitting element comprising a combination of a blue light emitting diode using a compound semiconductor and a yttrium aluminum garnet yellow phosphor is continuous and has a wide emission spectrum and excellent luminous efficiency. And is suitable as a backlight light source. Since the white LED has low power consumption, the liquid crystal display device using the white LED contributes to energy saving.

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

Example

The present invention will now be described in more detail with reference to the following examples, but it should be understood that the present invention is not limited to the following examples but can be carried out by appropriately changing the scope of the present invention. It is included in the technical scope.

A method of evaluating physical properties in the examples is as follows.

(1) difference in heat shrinkage rate in the oblique direction

Polarizer protective films 1 to 15 to be described later (those subjected to off-line annealing and those not subjected to the same treatment) were cut into squares of 21 cm on each side, and left in an atmosphere of 23 ° C and 65% RH for 2 hours or more. A straight line passing through the center of the circle in the direction of 45 ° and -45 ° was drawn on the film so that the center of the circle having a diameter of 20 cm was the center of the film and the longitudinal direction (film drawing direction) was 0 °, Direction was measured. The film was subjected to heat treatment at 85 캜 for 30 minutes in water, then the water adhering to the surface was wiped off, allowed to stand for at least 2 hours in an atmosphere of 23 캜 and 65% RH after air drying. Thereafter, the length of the straight line in each radial direction was measured as described above. Then, the length of the diameter before the heat treatment and the length of the diameter after the heat treatment were compared, and the heat shrinkage ratios in the respective directions were obtained. Further, the absolute value of the difference in the heat shrinkage ratios was calculated by comparing them. This measurement was performed by sampling three points in the width direction of the film with the same slit roll, and the average was taken as the heat shrinkage difference. As a result of the measurement, the difference in heat shrinkage rate was 0.4% or less in each of the three points in the same slit roll and the heat shrinkage rate in the 45 ° direction and the -45 ° direction was 1.0% or less.

(2) Light leakage evaluation method

A triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., thickness 80 占 퐉) was attached to one side of a polarizer made of a PVA film, and a polyester film produced by a method described later was attached to the other side. Each film was bonded to a polarizer through an adhesive. Thereafter, it was heat-treated in an oven at 85 캜 for 30 minutes to prepare a polarizing plate. And the polarizing axis of the polarizer and the main alignment axis of the polyester film were perpendicular to each other. The two polarizing plates thus obtained were placed in Cross Nicole so that the polyester film was located outside the two polarizers, and the maximum light transmittance at a wavelength of 550 to 600 nm was measured using a spectrophotometer V7100 manufactured by Jasco Corporation.

○: The maximum light transmittance is 0.02% or less

X: The maximum light transmittance exceeds 0.02%

(3) Retardation (Re)

The retardation is a parameter defined by a product (DELTA Nxy x d) of anisotropy (DELTA Nxy = | nx-ny |) of orthogonal biaxial films on a film and a film thickness d (nm), and optical anisotropy and anisotropy It is a scale to indicate. The anisotropy (? Nxy) of the biaxial refractive index was obtained by the following method. The orientation axis direction of the film was determined using a molecular alignment system (MOA-6004 type molecular alignment system, manufactured by Oji Measurement Instruments Co., Ltd.), and a rectangle of 4 cm x 2 cm was cut out so that the orientation axis direction was long . The birefringence index (nx, ny) and the refractive index (Nz) in the thickness direction orthogonal to the sample were measured using Abbe's refractive index meter (NAR-4T manufactured by Atago KK, measurement wavelength 589 nm) (| Nx-ny |) of the difference between the refractive index and the refractive index is defined as anisotropy (? Nxy) of the refractive index. The thickness (d) (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Pahrung Paste Co., Ltd.) and the unit was converted to nm. The retardation (Re) was determined from the product (Nxy x d) of the anisotropy (? Nxy) of the refractive index and the thickness (d) (nm) of the film.

(4) Nz coefficient

The value obtained by | ny-nz | / | ny-nx | is defined as an Nz coefficient. However, values of ny and nx were selected so that ny> nx.

(5) Plane orientation degree (P)

(nx + ny) / 2-nz was defined as the planar orientation degree (DELTA P).

(6) Thickness direction retardation (Rth)

The thickness direction retardation is a retardation value obtained by multiplying the birefringence ΔNxz (= | nx-nz |) and ΔNyz (= | ny-nz |) by the film thickness (d) It is a parameter representing the average. (Nxz d) and (DELTA Nyz d) are calculated in the same manner as in the measurement of the retardation, and the thickness direction retardation (Rth) is calculated by calculating the average value of (DELTA Nxz x d) Respectively.

(7) Rainbow spot observation

A polyester film produced by a method described later on one side of a polarizer made of PVA and iodine was stuck to the polarizing axis of the polarizer so that the alignment main axis of the polyester film was perpendicular to the polarizer and a TAC film ) Having a thickness of 80 占 퐉) was attached thereto to prepare a polarizing plate. The obtained polarizing plate was disposed on both sides of the liquid crystal between the two polarizing plates so that each polarizing plate was under the condition of Cross-Nicol, thereby producing a liquid crystal display device. Each of the polarizing plates was disposed so that the polyester film was located on the opposite side (remote position) to the liquid crystal. As a light source of the liquid crystal display device, a white LED comprising a blue light emitting diode and a light emitting element in combination with a yttrium aluminum garnet yellow phosphor was used as a light source (Nichia Chemical, NSPW500CS). This liquid crystal display was visually observed in the front and oblique directions, and the presence or absence of rainbow stains was determined as follows.

A: Rainbow stains do not occur in any direction.

A ': A very light rainbow stain was observed depending on the angle when observed in the oblique direction.

B: When viewed from the oblique direction, a slight rainbow stain is observed depending on the angle.

C: Irregular stain was observed when observed in oblique direction.

D: Irregular stain was observed when observed in the front direction and the oblique direction.

(8) Tear strength

The tear strength of each film was measured according to JIS P-8116 using an Elmendorf tearing tester manufactured by Toyo Seiki Seisakusho. The tearing direction was determined so as to be in parallel with the main axis direction of the film, and it was judged as follows. The direction of the principal axis of alignment was measured by a molecular alignment system (MOA-6004 type molecular alignment system, manufactured by Oji Measurement Instruments Co., Ltd.).

?: Tensile strength of not less than 50 mN

X: Tearing strength less than 50 mN

(Production Example 1-Polyester A)

After the temperature of the esterification reaction vessel was elevated to 200 ° C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added. While stirring, 0.017 part by mass of antimony trioxide, 0.064 part by mass of magnesium acetate tetrahydrate, Mass part was added. Subsequently, the mixture was subjected to pressure-esterification at a gauge pressure of 0.34 MPa and at a temperature of 240 캜, and then the esterification reaction vessel was returned to normal pressure and 0.014 parts by mass of phosphoric acid was added. The temperature was further raised to 260 DEG C over 15 minutes and 0.012 parts by mass of trimethyl phosphate was added. Subsequently, after 15 minutes, dispersion treatment was carried out with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and a polycondensation reaction under reduced pressure was carried out at 280 ° C.

After completion of the polycondensation reaction, filtration treatment was carried out with a nylon filter having a 95% cut diameter of 5 占 퐉, extruded from the nozzle in the form of a strand, and cooling treatment was carried out using filtration treatment (pore diameter: 1 占 퐉 or less) , And solidified and cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g, and substantially no inert particles and no internal precipitated particles (hereinafter abbreviated as PET (A)).

(Production Example 2-Polyester B)

10 parts by mass of a dried ultraviolet absorber (2,2 '- (1,4-phenylene) bis (4H-3,1-benzoxazinone-4-one), PET (A) Of 0.62 dl / g) were mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained by using a kneading extruder (hereinafter abbreviated as PET (B)).

(Preparation Example 3-Preparation of Adhesive Modifying Coating Solution)

The transesterification reaction and the polycondensation reaction were carried out by a conventional method to obtain a copolymer of 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 5 mol% of sodium 5-sulfonatoisophthalate (relative to the entire dicarboxylic acid component) as the dicarboxylic acid component 8 mol%, as a glycol component, 50 mol% of ethylene glycol (relative to the entire glycol component) and 50 mol% of neopentyl glycol was prepared. Subsequently, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve and 0.06 parts by mass of a nonionic surfactant were mixed and heated and stirred to reach 77 ° C. And 5 parts by mass of a copolymerized polyester resin having a solids content of 5.0% by mass were added and stirred until the mass of the resin disappeared. Thereafter, the resin aqueous dispersion was cooled to room temperature to obtain a homogeneous water dispersible copolymer polyester resin solution having a solid content concentration of 5.0% by mass. Further, 3 parts by mass of agglomerated silica particles (Silysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water. Then, 99.46 parts by mass of the water-dispersible copolymerized polyester resin solution was added with 0.54 And 20 parts by mass of water was added with stirring to obtain an adhesive modified coating liquid.

(Polarizer Protective Film 1)

90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing ultraviolet absorber were dried under reduced pressure (1 Torr) at 135 占 폚 for 6 hours as raw materials for the base film intermediate layer raw material, (For the intermediate layer (layer II)), and the PET (A) was dried by a common method and supplied to the extruder 1 (for the outer layer (layer I) and outer layer 285 < [deg.] ≫ C. These two kinds of polymers were each filtered with a filter material (nominal filtration accuracy 10 μm particle size 95% cut) of a stainless steel sintered body, laminated with a two-kind three-layer confluence block, extruded from the indentation into a sheet shape, And the film was wound around a casting drum having a surface temperature of 30 DEG C and cooled and solidified to form an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of layer I, layer II, and layer III was 10:80:10.

Subsequently, the adhesive modifying coating liquid was applied on both sides of the unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m < 2 >, followed by drying at 80 DEG C for 20 seconds.

The unstretched film having the coating layer formed thereon was introduced into a tenter stretching machine, and the end of the film was guided to a hot wind zone having a temperature of 125 캜 while grasping an end of the film with a clip, and stretched 4.0 times in the width direction. Then, while the stretched width in the width direction was maintained, the film was processed at a temperature of 225 DEG C for 30 seconds, and both edges were cut off to obtain a mill roll comprising a uniaxially oriented PET film having a film thickness of about 50 mu m. This mill roll was divided into three to obtain three slit rolls (L, C, and R). Two kinds of slit rolls were prepared: those which were subjected to off-line annealing at 90 占 폚 for 5 minutes and those that were not subjected to off-line annealing.

(Polarizer protective film 2)

A slit roll made of a uniaxially oriented PET film was obtained in the same manner as in the case of the polarizer protective film 1 except that the thickness of the unstretched film was changed to a thickness of about 100 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer Protective Film 3)

The unstretched film produced in the same manner as in the polarizer protective film 1 was heated to 105 DEG C by using a heated roll group and an infrared heater and then stretched 1.5 times in the running direction with a roll having a peripheral speed, And stretched 4.0 times in the width direction in the same manner to obtain a slit roll of a biaxially oriented PET film having a film thickness of about 50 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer Protective Film 4)

Stretched 2.0 times in the running direction and 4.0 times in the width direction in the same manner as in the polarizer protective film 3 to obtain a slit roll of a biaxially oriented PET film having a film thickness of about 50 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 5)

A slit roll made of a uniaxially oriented PET film having a film thickness of 50 占 퐉 was obtained without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer in the same manner as the polarizer protective film 1. [ Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 6)

Stretched 1.0 times in the running direction and 3.5 times in the width direction in the same manner as in the polarizer protective film 1 to obtain a slit roll of a monoaxially oriented PET film having a film thickness of about 75 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 7)

Using the same method as that of the polarizer protective film 1, the thickness of the unstretched film was changed to obtain a slit roll comprising a uniaxially oriented PET film having a thickness of about 100 탆 at a transverse stretching magnification of 3.8 times and a stretching temperature of 135 캜. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 8)

Using the same method as that of the polarizer protective film 1, a slit roll made of a uniaxially oriented PET film having a transverse stretching magnification of 3.8 times and a stretching temperature of 135 占 폚 and having a thickness of about 50 占 퐉 was obtained. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 9)

A slit roll made of a uniaxially oriented PET film having a thickness of 50 mu m was obtained by setting the transverse stretching magnification to 3.8 times using the same method as that of the polarizer protective film 1. [ Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 10)

Using the same method as that of the polarizer protective film 1, a slit roll made of a monoaxially oriented PET film having a transverse stretching magnification of 4.2 times and a stretching temperature of 135 캜 and having a thickness of about 50 탆 was obtained. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 11)

The thickness of the unstretched film was changed using the same method as that of the polarizer protective film 1 and the transverse stretching magnification was changed to 3.8 times to obtain a slit roll of a uniaxially oriented PET film having a thickness of 38 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 12)

By using the same method as that of the polarizer protective film 1, the thickness of the unstretched film was changed to obtain a slit roll of a uniaxially oriented PET film having a thickness of 38 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 13)

Stretched 1.8 times in the running direction and 2.0 times in the width direction in the same manner as in the polarizer protective film 3 to obtain a slit roll of a biaxially oriented PET film having a film thickness of about 275 占 퐉. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 14)

Stretched 3.6 times in the running direction and 4.0 times in the width direction in the same manner as the polarizer protective film 3 to obtain a slit roll of a biaxially oriented PET film having a film thickness of about 38 mu m. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

(Polarizer protective film 15)

By changing the thickness of the unstretched film by using the same method as that of the polarizer protective film 1, a slit roll made of a uniaxially oriented PET film having a thickness of about 10 mu m was obtained. Two types of films were prepared, one of which was subjected to off-line annealing in the same manner as the polarizer protective film 1, and one of which was not subjected to off-line annealing.

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

The results of measurement of iridescent blotting and tearing strength of the liquid crystal display device manufactured as described above using the polarizer protective films 1 to 15 (sample processed by offline annealing) are shown in Table 3 below.

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

From the results shown in Table 3, it was shown that when the retardation of the oriented polyester film was 4,000 or more and the Nz coefficient thereof was 1.7 or less, occurrence of rainbow stains was remarkably suppressed. In addition to these conditions, it has been shown that the degree of planar orientation of the oriented polyester film can be controlled to be 0.13 or less, whereby the occurrence of rainbow stains can be suppressed more effectively.

According to the present invention, it is possible to provide a polarizer protective film comprising a polyester film suitable for obtaining a liquid crystal display device in which generation of a slight light leakage is suppressed when two polarizing plates are disposed under a cross-nicol environment. Therefore, the industrial applicability of the present invention is very high.

Claims (7)

Wherein an absolute value of a difference between a heat shrinkage ratio in the 45-degree direction with respect to the film flow direction and a heat shrinkage ratio in the -45-degree direction with respect to the film flow direction is 0.4% or less. The method according to claim 1,
Wherein the retardation of the polyester film is 4,000 to 30,000 nm and the Nz coefficient is 1.7 or less. 3. The method according to claim 1 or 2,
Wherein the polyester film has a planar orientation degree of 0.13 or less. A polarizer protective film is laminated on both sides of the polarizer,
Wherein at least one polarizer protective film on one side is the polarizer protective film according to any one of claims 1 to 3. A polarizer protective film is laminated on both sides of the polarizer,
One polarizer protective film is made of triacetylcellulose film,
And the other polarizer protective film is the polarizer protective film according to any one of claims 1 to 3. A backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
Wherein the backlight source is a white light source having a continuous emission spectrum,
The polarizer includes a polarizer protective film laminated on both sides of the polarizer,
At least one of the polarizer protective film of the polarizing plate disposed on the incident light side and the polarizer protective film of the polarizing plate disposed on the emerging light side
A liquid crystal display device which is the polarizer protective film according to any one of claims 1 to 3. The method according to claim 6,
The incident-light-side polarizer protective film of the polarizing plate disposed on the side of the incident light and the polarizing plate protective film of the emerging-side polarizing plate of the polarizing plate disposed on the emerging-
A liquid crystal display device which is the polarizer protective film according to any one of claims 1 to 3.