KR20160053955A - Liquid crystal display device, polarization 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 it is made of a polyester film having an absolute value of a slope of a heat shrinkage ratio with respect to a film flow direction or a width direction of 15 degrees or less.

Description

[0001] The present invention relates to a liquid crystal display device, a polarization 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.

The polarizing plate used in the liquid crystal display (LCD) is generally constituted by sandwiching a polarizer in which iodine is dyed in polyvinyl alcohol (PVA) or the like between two polarizer protective films. As the polarizer protective film, triacetyl cellulose (TAC) . 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 used as a polarizer protective film, irregular color unevenness occurs when observed in an oblique direction, and 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 constant retardation as a polarizer protective film.

Patent Document 5 discloses that the polarizer protective film has good dimensional stability because it passes through many heat treatment processes such as a process of producing a polarizing plate or a process of combining the obtained polarizing plate with a liquid crystal cell. Specifically, the polarizer protective film is preferably subjected to heat treatment at 120 ° C for 30 minutes It is disclosed that the shrinkage percentage of the polyester film is preferably 5% or less in both the MD and TD directions of the film.

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 described above, the polyester film used as the polarizer protective film has been improved in many aspects, but the present inventors have found that there is room for further improvement. That is, the inventors of the present invention have found that when a polarizing plate employing a modified polyester film as a polarizer protective film is disposed so as to be in a relationship of crossed nicol with another polarizing plate, a slight light leakage occurs and visibility deteriorates I found the existence of one task. Accordingly, it is an object of the present invention to provide a polarizer protective film comprising a polyester film capable of suppressing the above-mentioned slight light leakage.

The inventors of the present invention have conducted intensive studies in order to solve the above problems. As a result, they have found that the angle formed by the direction in which the heat shrinkage rate of the polyester film is maximized and the flow direction or width direction of the polyester film The inclination in the direction in which the heat shrinkage rate with respect to the width direction is the maximum) is 15 degrees or less. On the basis of this knowledge, further examination is repeated to provide the following representative invention.

Section 1.

Wherein the absolute value of the angle formed by the film flow direction or the width direction and the direction in which the heat shrinkage rate of the film becomes maximum is 15 degrees 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.

Wherein the polarizer protective film described in any one of items 1 to 3 is laminated on one side of the polarizer.

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,

Wherein at least one of the polarizer protective film of the polarizing plate disposed on the side of the incident light and the polarizer protective film of the polarizing plate disposed on the side of the emerging light are the polarizer protective film according to any one of items 1 to 3.

Item 7.

Side polarizer protective film of the polarizing plate disposed on the side of the incident light and the polarizing plate protective film of the polarizing plate disposed on the side of the emerging light are the polarizing protective films according to any one of items 1 to 3, Device.

Section 8.

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,

Wherein the polarizing plate is the polarizing plate described in Item 5.

According to the present invention, when two polarizing plates are arranged in a cross-Nicol relationship, a slight amount of light leakage that has occurred in the past can be suppressed. Further, according to a preferred embodiment, it is possible to provide a liquid crystal display device which is suitable for thinning, does not cause rainbow stains, is less deteriorated in visibility due to the light leakage, and has excellent visibility.

Fig. 1 shows an example of a result of measuring the heat shrinkage ratio of the film at 360 deg. In this example, the angle at which the heat shrinkage rate becomes maximum is about 15 degrees.
FIG. 2 is a diagram in which an angle is plotted on the X-axis and a heat shrinkage rate is plotted on the Y-axis in order to obtain an angle at which the heat shrinkage rate becomes maximum at an interval of 1 degree or more from the heat shrinkage rate measured at intervals of 5 degrees.
3 is a diagram schematically showing intervals of clips used in the method 1 for reducing the slope of heat shrinkage.
4 shows the relationship between the distance in the longitudinal direction of the tenter and the temperature of the tenter which can be used in the method 4 for reducing the slope of the heat shrinkage rate.

1. Polarizer protective film

The polarizer protective film of the present invention is a polyester film and has an absolute value of a slope in a direction in which a heat shrinkage rate with respect to the flow direction or width direction of the film is maximized (hereinafter also referred to as a slope of a heat shrinkage rate) Or less. The absolute value of the slope of the heat shrinkage percentage is preferably 12 degrees or less, more preferably 10 degrees or less, still more preferably 8 degrees or less, further preferably 6 degrees or less, particularly preferably 4 Or less, and most preferably 2 degrees or less. The smaller the absolute value of the slope of the heat shrinkage ratio is, the better, and the lower limit is 0 degree.

The exact mechanism by which the above-mentioned slight light leakage occurs is not clarified, but it can be thought as follows. Normally, two polarizing plates are disposed in the liquid crystal display device so that they are in a cross-Nicol relationship. When two polarizing plates are arranged in a cross-Nicol relationship, normal light does not pass through two polarizing plates. However, when the polarizer protective film is shrunk by the heat treatment, a slight shrinkage or inversion occurs also in the polarizer, resulting in the complete cross-Nicol relationship being broken, resulting in light leakage. In this principle, the light leakage becomes remarkable when the direction in which the heat shrinkage rate of the polarizer protective film is largest is in the film flow direction or in the oblique direction with respect to the film width direction. In addition, the polarizer protective film flow direction is usually parallel or perpendicular to the polarization axis of the polarizer.

Patent Document 5 discloses a polarizer protective film made of a polyester film having a heat shrinkage of 5% or less both in the MD and TD directions. However, as is apparent from the above-described mechanism, when the direction in which the heat shrinkage rate is maximum is inclined with respect to the film flow direction or the film width direction even though the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction are small, (Sam) The problem occurs.

Patent Document 5 also discloses that the angle between the in-plane slow axis in the in-plane in-plane direction and the direction of the film TD and the deviation therebetween are reduced to prevent color separation and color unevenness of the liquid crystal display. However, since the direction of the in-plane slow axis and the slope of the heat shrinkage ratio are not necessarily parallel to each other, even if the in-plane slow axis is controlled, the problem of leakage of the polarized light occurs.

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.

(Heat shrinkage ratio)

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

The polyester film was cut into a square shape of 21 cm at one side and left in an atmosphere of 23 캜 and 65% RH for 2 hours or more. A circle having a diameter of 80 mm centered on the center thereof was placed on the polyester film, and the flow direction of the film was set at 0 degree using a two-dimensional image measuring device (e.g., MITUTOYO QUICK IMAGE) . Here, when the film flow direction is 0 degree and the film is viewed from the top surface in the tenter, the clockwise direction (right rotation) is positive angle, and the counterclockwise direction (left rotation) is negative angle. Measured in the range of -90 degrees to 85 degrees, the diameter in all directions can be measured.

Then, the polyester film was heat-treated in water at 85 캜 for 30 minutes, then the water adhering to the film surface was wiped off, allowed to stand in an atmosphere at 23 캜 and 65% RH for 2 hours or more. Thereafter, the diameters of the circles are measured at intervals of 5 degrees in the same manner as described above. The heat shrinkage ratio in each direction can be obtained by the following equation, assuming that the diameter before heat treatment is L ₀ and the diameter in the tangential direction after heat treatment is L.

Heat shrinkage percentage (%) = ((L ₀ -L) / L ₀ ) × 100

If the heat shrinkage percentage measured 360 degrees at intervals of 5 degrees is displayed in a graph, for example, as shown in Fig. 1, the center of the circle has a heat shrinkage rate of 0%, and the heat shrinkage rate increases as the distance from the center of the circle increases. Also, the circumference indicates an angle obtained by zero degree of the film flow direction. Thus, 90 degrees is parallel to the film width direction.

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

(Slope of heat shrinkage rate)

As described above, the heat shrinkage rate is measured at an interval of 5 degrees. The direction in which the heat shrinkage rate becomes maximum can be obtained with accuracy of 1 degree in the following order. That is, the measurement result of the heat shrinkage ratio (the result of the heat shrinkage ratio in the range of -90 degrees to 85 degrees) is plotted as an angle at which the film flow direction is 0 degree, and the axis of abscissa is the heat shrinkage rate at the angle. At this time, values of -180 degrees to -95 degrees and 90 degrees to 175 degrees are also interpolated (a heat shrinkage ratio of -90 degrees corresponds to a heat shrinkage ratio of 90 degrees, and a heat shrinkage ratio of 0 degrees corresponds to a heat shrinkage ratio of -180 degrees). Next, an approximation curve connecting the respective plots is drawn, and the direction in which the heat shrinkage rate becomes the maximum is read at an accuracy of 1, and this is defined as?. And -90 degrees??? 90 degrees.

When the direction? In which the heat shrinkage rate is maximum is in the range of -45 to 45 degrees, the value is taken as the slope of the heat shrinkage rate. When the direction of the maximum heat shrinkage is in the range of 45 degrees or more and -45 degrees or less, it is interpreted that the film is inclined with respect to the film width direction, , 90 degrees + alpha (when? Is less than -45 degrees) is defined as the slope of the heat shrinkage ratio. When the difference between the maximum value and the minimum value of the heat shrinkage rate is 0.1% or less, the heat shrinkage rate is almost the same in all directions and the slope of the heat shrinkage rate is regarded as 0 because there is no slope in the heat shrinkage rate.

(Light leakage evaluation method)

In the light leakage, two polarizing plates are arranged in a cross-Nicol relationship, and the maximum transmittance of light having a wavelength of 550 nm to 600 nm is measured. The light transmittance can be measured by using any spectrophotometer. The maximum transmittance to be measured is preferably not more than 0.02%, more preferably not more than 0.015%.

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

(Retardation)

The polyester film used for the polarizer protective film preferably has a retardation of 4,000 to 30,000 nm. When the retardation is 4,000 nm or more, iridescence unevenness that may occur when the liquid crystal display device is viewed in the oblique direction is suppressed, and good visibility can be ensured. The preferred retardation of the polyester film is 4,500 nm or more, more preferably 5,000 nm or more, still more preferably 6,000 nm or more, even more preferably 8,000 nm or more, and still more preferably 10,000 nm or more. Here, the range of 4,000 to 30,000 nm means that the lower limit value includes 4,000 nm and the upper limit value includes 30,000 nm, but the range not including the upper limit value is also assumed.

The upper limit of the retardation of the polyester film is not particularly limited, but is, for example, 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 Because.

The retardation value of the oriented polyester film can be obtained by the following procedure. The orientation axis direction of the film is obtained by using a molecular orientation system (for example, MOA-6004 type molecular alignment system, manufactured by Oji Measurement Instruments Co., Ltd.). The index of refraction ny in the orientation axis direction and the index of refraction nx in the direction perpendicular to the orientation axis direction within the film plane are measured at a measurement wavelength of 589 nm. The absolute value (| ny-nx |) of the difference (anisotropy) of the refractive indexes in the biaxial directions is obtained, and the retardation value is obtained by multiplying the absolute value (| ny-nx |) by the thickness of the film. The retardation of the film can be measured using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Measurement Instruments Co., Ltd.). The refractive index of the film can be measured using a commercially available measuring device such as Abbe's refractometer (NAR-4T manufactured by Atago).

(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. (Ny, nx, where ny> nx (ny, nx), which is the direction of the orientation axis and the direction orthogonal to the orientation axis, is obtained by using the molecular alignment system (MOA-6004 type molecular alignment system manufactured by Oji Instruments Co., And a refractive index (nz) in the thickness direction are determined by an Abbe's refractive index meter (NAR-4T manufactured by Atago KK, measurement wavelength: 589 nm). The Nz coefficient can be obtained by substituting the obtained nx, ny, and nz into an expression represented by | ny-nz | / | ny-nx |.

When the polyester film is used as a polarizer protective film on both of the pair of polarizing plates (for example, when the retardation of the polyester film is in the range of 4,000 nm to 30,000 nm, the incident light side When the polarizer protective film and the polarizer protective film on the outgoing light side of the polarizing plate disposed 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. The Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less from the viewpoint of suppressing the occurrence of such rainbow stains. 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 setting the plane orientation coefficient represented by (nx + ny) / 2-nz to be not more than a specific value, It is possible to eliminate rainbow stains in the case of using a polyester film as a polarizer protective film. Here, the values of nx, ny, and nz can be obtained 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 planar orientation degree to 0.13 or less, it is possible to completely eliminate rainbow stains observed along the angle 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. If the degree of planar orientation is less than 0.08, the thickness of the film may fluctuate and the value of the retardation may become uneven in the film surface.

(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 (Re / Rth) between the retardation and the retardation in the thickness direction (Rth), the greater the isotropic action of the birefringence is, and the less irregularly visible irregularity is less likely to occur. In 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. (Re / Rth) of the retardation in the thickness direction does not need to be 2, and it is sufficient that the retardation and the retardation in the thickness direction do not have to be 1.2 or less in order to completely suppress the generation of color irregularity in the rainbow shape according to the observation angle. 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. The thickness variation of the film can be measured in the following order. The film is cut into a 40 mm width in the TD direction on the film roll. The cut samples are continuously measured in the TD direction by an Anrits production contact continuous thickness meter (feed rate: 1.5 m / min, sampling period: 100 ms), and the average value, the maximum value and the minimum value are obtained. The thickness deviation was taken as the absolute value of the value calculated by the following equation.

 Thickness deviation = ((maximum value of measurement result) - (minimum value of measurement result) / (average value of measurement result) x 100 (%)

(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 preferred from the viewpoint of transparency.

Examples of the organic ultraviolet absorber include benzotriazole-based, benzophenone-based, cyclic imino ester-based, and any combination thereof, but are not particularly limited. From the viewpoint of durability, a benzotriazole-based or cyclic imino ester-based is 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'-hydroxy-5'- (methacryloyloxypropyl) ) Phenyl] -2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'4,4'-tetrahydroxybenzophenone, 2,4- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2 Methyl-6- (tert-butyl) phenol, 2,2'-methylenebis (4- (1,1,3,3- (2H-benzotriazole-2-yl) phenol, etc. Examples of the cyclic imino ester-based ultraviolet absorber include 2,2 '- (1,4-phenylene) Bis (4H-3,1-benzoxazinone-4-one), 2-methyl- 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazin-4-one, etc. These ultraviolet absorbers Or two or more of them 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 such coating liquids include water-soluble organic solvents such as those disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, Or a 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 longitudinal uniaxially stretched film, then 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. The average particle size of the fine particles is preferably 2 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 average particle size of the particles was measured by scanning electron microscopy (SEM), and the maximum diameter of the particles (the distance between the two most distant points) was 300 to 500 at a magnification of 2 to 5 mm. , And calculating the average value thereof.

The coating liquid can be applied by a known method. For example, a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, and a pipe doctor method. These methods can be carried out singly or in combination.

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

(Functional layer)

The surface of the polyester film opposite to the side on which the polarizer is disposed is provided with various functional layers 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, 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 polyester film)

The polyester film used as the polarizer protective film 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 molded 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 then stretched in the transverse direction And heat treatment is carried out. The film may be a uniaxially stretched film or a biaxially stretched film.

(Reduction of slope of heat shrinkage rate)

Means for controlling the absolute value of the slope in the direction in which the heat shrinkage rate with respect to the film flow direction or the width direction is maximized to 15 degrees or less is not particularly limited, but it is preferable to pay attention to the following points. That is, in the cooling section after the heat treatment process in the tenter, the shrinkage stress accompanying the stretching and the thermal stress accompanying the cooling, which could not be completely removed by heat fixation, exist. Since the film at the end portion is constrained by the clip, while the film at the middle portion is relatively stretchable, there is a tendency to distribute the stress in the film flow direction and the width direction in the cooling section. These are the main causes and cause a slope of heat shrinkage. In view of such circumstances, specific means for reducing the slope of the heat shrinkage ratio are exemplified below.

(Method 1 for reducing the slope of heat shrinkage)

It is possible to narrow the clip interval in the film flow direction in the cooling section after fixing the heat, to make the stress in the film flow direction in the tenter cooling section uniform, and to reduce the slope of the heat shrinkage rate. Therefore, in order to reduce the slope of the heat shrinkage ratio, it is preferable to appropriately adjust the temperature range for narrowing the clip interval. The film thickness of the film at the left end (when the film is viewed from the top) with respect to the flow direction has a slope of the heat shrinkage ratio in the positive direction (right side The end becomes larger in the negative direction). In addition, when the temperature is too low, the amount of heat shrinkage of the film is too small, resulting in poor flatness. By setting the temperature at which the clip interval is narrowed in an appropriate range, the stress in the flow direction in the tenter cooling section can be made uniform, and the slope of the heat shrinkage rate can be reduced.

In order to reduce the slope of the heat shrinkage rate, it is also important to reduce the clip interval in the film flow direction. Is not particularly limited because it varies depending on the film composition and film production conditions, but the relaxation rate is preferably 0.01 to 3%, more preferably 0.05 to 1.5%. When the relaxation rate is excessively high, the film is not completely shrunk, resulting in poor flatness. When the relaxation rate is too low, the effect of reducing the slope of the heat shrinkage rate is lowered. Here, the relaxation rate can be calculated by the following equation using the center-to-center distance of the clip as shown in Fig.

(Distance between clip before mitigation) - (Distance between clips after mitigation) / (Distance between clips before mitigation)) x 100 (%)

 When the heat shrinkage ratio in the width direction is excessively high, the slope of the heat shrinkage ratio tends to become large. For this reason, it is more preferable to adjust the tenter rail pattern so as to appropriately adjust the relaxation rate and the temperature at which the clip interval is narrowed in the film width direction. In this manner, the temperature range and the relaxation rate for narrowing the clip interval in the film flow direction are set to an appropriate range, and if necessary, the tenter rail pattern is appropriately adjusted so that the shrinkage ratio in the width direction does not become too large, The stress can be made uniform and the slope of the heat shrinkage rate can be reduced.

(Method 2 for reducing the slope of heat shrinkage)

The film end portion can be separated from the clip in the cooling section after the heat is fixed and released from the constraint by the clip so that the stress in the width direction in the tenter cooling section can be made uniform. Further, by adjusting the tension of the winding process to an appropriate value, the stress in the flow direction in the tenter cooling section can be made uniform. By thus making the stress in the flow direction in the tenter cooling section uniform, it is possible to reduce the slope of the heat shrinkage rate.

A method of separating the film end from the clip is not particularly limited, but a conventionally known method may be used. Specifically, a method of cutting the film from the clip and a method of opening the clip may be mentioned. The method of cutting the film from the clip is optional, and examples thereof include cutting with a shearing blade or fusing with a laser. It is also possible to carry out these methods in combination. When the film is cut from the clip, it is preferable that the film is cut at a position close to the clip at both ends of the film.

The film temperature at the time of separating the film end from the clip is preferably 50 ° C to 300 ° C. The higher the film temperature, the more difficult it is to maintain the flatness of the film. Further, when the film temperature is too low with respect to the glass transition temperature Tg of the film, the slope of the heat shrinkage rate becomes difficult to be reduced. Therefore, it is preferable to cut off the film from the clip at a temperature higher than (glass transition temperature Tg-20 ° C) and lower than (melting point Tm-10 ° C). Here, the film temperature is a value measured by a radiation thermometer.

When separating the end of the film from the clip, it is preferable to appropriately adjust the tension in the winding step. The appropriate tensile force is not particularly limited, since it varies depending on the film composition, thickness and film production conditions, but is preferably 0.01 to 3 kg / mm 2, more preferably 0.1 to 2 kg / mm 2. When the tension is excessively high, the slope of the heat shrinkage rate of the film at the left end with respect to the flow direction becomes large in the positive direction (the right end becomes large in the negative direction). When the tension is too low, the slope of the heat shrinkage rate of the film at the left end with respect to the flow direction increases in the negative direction (the right end becomes larger in the positive direction). However, these tendencies are when the angles are evaluated based on the flow direction, and when the width direction is taken as a reference, the positive tends to be opposite.

When the heat shrinkage ratio in the width direction is excessively high, the slope of the heat shrinkage ratio becomes large. Therefore, it is preferable to adjust the rail pattern before separating the film end from the clip to adjust the relaxation rate and the temperature at which the clip interval is narrowed in the film width direction as described above. By setting the tension to an appropriate range in this way, the stress in the flow direction in the tenter cooling section can be made uniform, and the slope of the heat shrinkage rate can be reduced.

(Method 3 for reducing slope of heat shrinkage)

It is possible to reduce the slope of the heat shrinkage rate by setting the film temperature at the outlet of the tenter to be higher than the predetermined temperature (i.e., the glass transition temperature Tg-20 DEG C) and lower than the predetermined temperature (melting point Tm-70 DEG C) . In this case, since the effect depends on the room temperature, it is preferable to control the room temperature.

(Method of reducing slope of heat shrinkage ratio 4)

The inclination of the heat shrinkage rate can be reduced by adjusting the temperature setting of the cooling step after fixing the tenter heat. For example, as shown in FIG. 4, it is preferable to set the heat fixing temperature to the tenter outlet temperature so as to be -15 / X to -100 / X (占 폚 / m) along the longitudinal direction of the tenter. Where X is the width of the tenter outlet (m). Therefore, for example, when the width of the tenter outlet is 2 m, it is preferable to lower the temperature within the range of -7.5 캜 to -50 캜 for every 1 m in the longitudinal direction of the tenter. Since the temperature represents the temperature per tenter outlet width, this is referred to below as the temperature setting per unit width.

 Further, it is preferable that the temperature of the outlet of the tenter is set to be generally equal to or less than Tg. When the temperature setting per unit width is -100 / X (° C / m) or less in the longitudinal direction, the slope of the heat shrinkage rate is not preferable because the slope of the heat shrinkage rate exceeds 15 degrees. Though it can be sufficiently reduced, it is not desirable because investment in tenter equipment becomes excessive.

(Method 5 for reducing the slope of heat shrinkage)

Even a film having a slope of heat shrinkage can be subjected to off-line annealing at a temperature of, for example, 80 DEG C to 120 DEG C for 10 seconds to 90 minutes to reduce the slope of the heat shrinkage rate. In the case of the offline annealing process, it is preferable to adequately control the temperature and time of the annealing process. It is also preferable to perform the in-line annealing process between the conventionally known tenter outlet and the wound roll. Also in this case, it is preferable to sufficiently secure the temperature and time of the annealing treatment in the same manner as the off-line annealing treatment, and it is more preferable to use the air canola from the viewpoint of heat treatment efficiency and planarity maintenance.

Any one of these reduction methods 1 to 5 may be performed alone or in combination. By these methods, the slope of the heat shrinkage ratio can be 15 degrees or less.

The polyester film is subjected to longitudinal stretching and transverse stretching, followed by a heat treatment step, and both edge portions are cut to form a mill roll, and if necessary, the polyester film is slit roll. Both edges are preferably in the range of 1% to 10%, more preferably in the range of 1% to 5% at both ends of the film, with the entire width of the film being 100% in length. The term " both ends " as used herein is the same as both ends of the film before cutting as described for the abatement method 2. Among these, the absolute value of the slope of the heat shrinkage percentage in this region is preferably controlled to 15 degrees or less because the absolute value of the slope of the heat shrinkage ratio tends to become large particularly when the mill roll is divided into three equal parts.

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, and more preferably 90 to 140 占 폚. The longitudinal stretching magnification is preferably 1.0 to 3.5 times, more preferably 1.0 to 3.0 times. The transverse draw ratio is preferably 2.5 to 6.0 times, more preferably 3.0 to 5.5 times.

In order to control the retardation 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 to increase the retardation. The temperature of the subsequent heat treatment is preferably 100 to 250 占 폚, more 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. In order to lower the Nz coefficient, it is also preferable to increase the molecular weight of the polymer and to add a copolymerization component to lower the crystallinity. 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 adjust the degree of planar orientation to the above-mentioned specific value, it is preferable to control the total drawing magnification. If the total stretching ratio is too high, the degree of planar orientation becomes too high, which is not preferable. It is also preferable to control the stretching temperature 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 great 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, there is a case where the longitudinal thickness deviation becomes worse. Since the vertical thickness deviation has a region where the draw ratio is extremely poor in a certain range, it is preferable to set the film formation conditions at a point outside this range.

The combination of the ultraviolet absorber with the oriented polyester film can be carried out by combining known methods. For example, a master batch may be prepared in advance by blending a polymer raw material with an ultraviolet absorber dried by using a kneading extruder, and the raw material may be blended by a predetermined master batch and a 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 formulate it economically. 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 ° C for 1 to 15 minutes. Above 290 占 폚, the weight loss of the ultraviolet absorber is large, and the viscosity drop of the master batch becomes large. It is difficult to uniformly mix the ultraviolet absorber in extrusion of one minute or less. 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 polyester as the outer layer alone and the master batch containing the ultraviolet absorber as the middle layer and the polyester pellets 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 unstretched film. That is, a film layer constituting the both outer layers and a film layer constituting the 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 rectangular confluent portion) The sheet of the layer is extruded and cooled in 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 raw material polyester which causes optical defects. The filtration particle size (initial filtration efficiency: 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. 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.

1. Polarizer

The polarizing plate has a structure in which both sides of a polarizer made of a polyvinyl alcohol film dyed with iodine or the like are sandwiched between two polarizer protective films and at least one of the two polarizer protective films has an absolute value of a slope of a heat shrinkage percentage Lt; RTI ID = 0.0 > polyester < / RTI > In one embodiment, the polarizer preferably has a structure in which a polarizer protective film is laminated on one side of the polarizer. The polarizer and the polarizer protective film are laminated through an adhesive, and can be generally subjected to a heat treatment for 10 minutes to 60 minutes at a temperature of 70 to 120 ° C to obtain a polarizing plate.

(Arrangement of Polarizer Protective Film)

In the liquid crystal display device, it is preferable that the specific polyester film is used as both polarizer protective films of a pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate arranged on the incident light side with respect to the liquid crystal and a polarizing plate arranged on the emerging light side with respect to the liquid crystal. That is, the polyester film is preferably used for both polarizers of the incident-light-side polarizer and the emergent-light-side polarizer. The polyester film may be laminated on at least one surface of the polarizer constituting each polarizing plate.

In a preferred embodiment, the polyester film is used as an incident-light-side polarizer protective film of the incident-light-side polarizer, and is also used as a polarizer protective film of an emergent-light-side polarizer. When the oriented polyester film is laminated on only one side of the polarizer constituting the polarizing plate, it is possible not to use any polarizer protective film (for example, TAC film) or the polarizer protective film on the other side . When the polyester film is used as the polarizer protective film on the liquid crystal cell side (i.e., the incident light side) 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, It is preferable to use a polarizer protective film (such as a TAC film, an acrylic film, or a birefringent film typified by a norbornene-based film) other than the above-mentioned polyester film as the polarizer protective film at these positions . It is also preferable that the absolute value of the slope of the heat shrinkage ratio of these films is small.

2. Liquid crystal display

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

(Backlight source)

The liquid crystal display device includes at least a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates as a constituent member. 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 an edge light system using a light guide plate or a reflective plate as a constituent member, or may be a direct lower type system. The backlight source is preferably a white light source having a continuous broad emission spectrum. Here, the continuous broad emission spectrum means an emission spectrum in which there is no wavelength at which the intensity of light is zero in a wavelength region of at least 450 nm to 650 nm, preferably in a visible light region. The white light source having such a continuous broad emission spectrum includes, 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 fluorescent material, and the like. Among the white LEDs, the white light emitting diode comprising a light emitting element made of a combination of a blue light emitting diode using a compound semiconductor and a yttrium aluminum garnet yellow phosphor has a continuous wide emission spectrum and also has excellent luminous efficiency, It is suitable as a 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 effect of suppressing rainbow stains, and therefore, it is not preferable as a 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.

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

(1) Heat shrinkage and its slope

The polyester film cut out from each cut portion of the slit roll was cut into a square shape of 21 cm on each side and allowed to stand in an atmosphere of 23 ° C and 65% RH for 2 hours or more. A circle having a diameter of 80 mm centered on the center of the polyester film was measured, and the diameter of the film was measured at intervals of 5 degrees using a two-dimensional image measuring device (QUICK IMAGE manufactured by MITUTOYO) at a flow rate of 0 degree. Here, the film flow direction was set to 0 degree, and the clockwise direction (right rotation) was set to a positive angle and the counterclockwise direction (left rotation) was set to a negative angle on the film surface. Since the diameter was measured, it was measured in all directions with measurements ranging from -90 to 85 degrees. Then, the polyester film was heat-treated at 85 ° C for 30 minutes in water, then the water adhering to the surface of the film was wiped off, allowed to stand in air at 23 ° C and 65% RH for 2 hours or more. Thereafter, the diameters of the circles were measured at intervals of 5 degrees in the same manner as described above. The heat shrinkage ratio in each direction was calculated by the following equation, assuming that the diameter before heat treatment is L ₀ and the diameter after heat treatment is L in the same direction.

Heat shrinkage percentage (%) = ((L ₀ -L) / L ₀ ) × 100

(Maximum value of heat shrinkage rate)

The maximum value of the heat shrinkage rate in all directions is defined as the maximum heat shrinkage rate. (Three points at the center and both ends) in the film width direction with respect to each of the slit rolls L, C, and R. The average values of the three maximum heat shrinkage ratios are shown in Table 1 as the maximum values of the heat shrinkage ratios . Also, in this embodiment, the maximum heat shrinkage rate at any of the center and both ends of the slit roll was 5% or less.

(Reading of the maximum direction (?) Of the heat shrinkage rate)

The slope of the heat shrinkage rate was measured as follows from the result of calculating the heat shrinkage rate in all directions. As shown in Fig. 2, the obtained measurement values (-90 to 85 degrees) were plotted as an axis of abscissa and an axis of ordinate as a heat shrinkage rate corresponding to the angle, and values of -180 degrees to -95 degrees and 90 degrees to 175 degrees were interpolated. (A heat shrinkage ratio of -90 degrees corresponds to a heat shrinkage ratio of 90 degrees, and a heat shrinkage ratio of 0 degrees corresponds to a heat shrinkage ratio of -180 degrees). Next, an approximate curve connecting the plots is drawn, 1, and defined as α. However, -90 degrees??? 90 degrees.

(Slope of heat shrinkage rate)

When the direction? In which the heat shrinkage rate is the maximum is in the range of -45 to 45 degrees, the value is defined as the slope of the heat shrinkage rate. When the direction of the maximum heat shrinkage is in the range of 45 degrees or more and -45 degrees or less, it is interpreted that the film is inclined with respect to the film width direction instead of the film flow direction. , 90 ° + α (when α is -45 ° or less) was defined as the slope of the heat shrinkage ratio. The above measurement was carried out in the same manner by sampling three points (three points at the center and both ends) in the film width direction with respect to each of the slit rolls L, C, and R. The average of the absolute values of the slopes of the three heat shrinkage ratios The slope is shown in Table 1. Also, in this embodiment, the absolute value of the slope of the heat shrinkage ratio at the center and both ends is 15 degrees or less.

(2) Light leakage evaluation method

A triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., thickness 80 탆) 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. The adhesive was applied to the polarizing plate by heating in an oven at 85 DEG C for 30 minutes. And the polarizing axis of the polarizer and the main alignment axis of the polyester film were perpendicular to each other. Two polarizing plates thus obtained were arranged by Cross Nicole. At this time, two polarizing plates were arranged so that each of the polyester films was located outside the polarizer. Then, the maximum light transmittance of light having a wavelength of 550 nm to 600 nm transmitted through the two polarizing plates was measured using a spectrophotometer V7100 manufactured by JASCO. The measurement results were evaluated as follows.

○: The maximum light transmittance is 0.02% or less

X: 0.02% or more in the maximum light transmittance

(3) Retardation (Re)

The retardation is a parameter defined by a product (DELTA Nxy x d) of anisotropy (DELTA Nxy = | nx-ny |) of a biaxial orthogonal refractive index on a film and a film thickness d (nm) to be. 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 (manufactured by Pahrung Paste, MITORON 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (DELTA Nxyxd) of the anisotropy (DELTA Nxy) of the refractive index and the film thickness d (nm).

(4) Nz coefficient

The value obtained from | 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 determined as the planar orientation degree (DELTA P).

(6) Thickness direction retardation (Rth)

The retardation in the thickness direction means the retardation obtained by multiplying the birefringence ΔNxz (= | nx-nz |) and ΔNyz (= | ny-nz | . Nx, ny, and nz and the film thickness d (nm) were obtained in the same manner as in the measurement of the retardation, and the average value of (DELTA Nxzxd) and (DELTA Nyzxd) was calculated to calculate the thickness direction retardation (Rth) 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 (manufactured by Fuji Film Co., Thickness: 80 占 퐉) was attached to the polarizing plate. The resulting polarizing plate was arranged so that each polarizing plate was in a Cross-Nicol relationship, one on each side of the liquid crystal between which the liquid crystal was interposed. Each polarizing plate was disposed such 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, 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). The presence or absence of rainbow stains was visually observed in the front and oblique directions of the liquid crystal display device as described below.

A: Rainbow stains do not occur in any direction.

A ': When observed in the oblique direction, an extremely light rainbow stain is observed depending on the angle.

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

C: Rainbow stain is observed when observed in the oblique direction.

D: Rainbow stains are 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 Co., Ltd. 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)

86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added while the temperature of the esterification reaction tube was elevated to 200 ° C, 0.017 parts by mass of antimony trioxide, 0.064 parts by mass of magnesium acetate tetrahydrate, 0.164 parts by mass of triethylamine Mass part was added. Subsequently, pressure elevation was carried out, and a pressure esterification reaction was carried out under the conditions of gauge pressure 0.34 MPa and 240 deg. C, and then the esterification reaction tube was returned to normal pressure and 0.014 mass part 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 tube and subjected to a polycondensation reaction under reduced pressure at 280 ° C.

After completion of the polycondensation reaction, filtration was performed with a Naslon-made filter having a 95% cut diameter of 5 탆, extruded from a nozzle into a strand shape, and cooled using cooling water previously subjected to filtration treatment (pore diameter: 1 탆 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)

Ester exchange reaction and polycondensation reaction were carried out in a usual manner to obtain 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol of 5-sulfonatoisophthalic acid as a dicarboxylic acid component (relative to the entire dicarboxylic acid component) , And 50% by mole of ethylene glycol and 50% by mole of neopentyl glycol as glycol components (relative to the entire glycol component). Subsequently, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosol and 0.06 parts by mass of a nonionic surfactant were mixed and heated and stirred. When the temperature reached 77 占 폚, And 5 parts by mass of a base-containing copolymerized polyester resin was added to the mixture to continue the stirring until the lump of the resin disappeared. Thereafter, the resin aqueous dispersion was cooled to room temperature to obtain a homogeneous water dispersible copolymer polyester resin liquid 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 탆 particle size 95% cut) of a stainless steel sintered body, laminated with a two-kind three-layer confluence block, extruded into a sheet form from the indentation and then subjected to electrostatic casting 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 modified coating liquid was applied on both sides of the unstretched PET film so as to have a coating amount after drying of 0.08 g / m 2 by a reverse roll method, and then dried at 80 ° C for 20 seconds.

The unstretched film having the coated layer formed thereon was introduced into a tenter stretching machine, and an end portion of the film was guided to a hot air zone at a temperature of 125 캜 while gripping with a clip, and stretched 4.0 times in the width direction. Next, the film was processed at a temperature of 225 DEG C for 30 seconds while maintaining the stretched width in the width direction. Thereafter, the film cooled to 130 DEG C was cut at a position of 2% from both ends with a shearing blade to produce a tension of 0.5 kg / And both edge portions 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). In the film flow direction, the slit roll located on the left side is labeled L, the slit roll located on the right side is labeled R, and the center is labeled C.

(Polarizer protective film 2)

Three slit rolls (L, C, and R) made of a uniaxially oriented PET film were 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 about 100 탆.

(Polarizer Protective Film 3)

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

(Polarizer Protective Film 4)

The unstretched film produced in the same manner as in the polarizer protective film 1 was heated to 105 DEG C using a heated roll group and an infrared heater and then stretched twice in the running direction with a group of rolls having a peripheral speed, 1, the film was cooled to 140 DEG C at a stretching ratio of 0.65 kg / mm < 2 > at a position of 2% from both ends with a shearing blade, and the thickness of the non- And three slit rolls (L, C, R) made of a biaxially oriented PET film having a film thickness of about 50 mu m were obtained.

(Polarizer protective film 5)

And three slit rolls (L, C, and B) made of a uniaxially oriented PET film were produced in the same manner as in the case of the polarizer protective film 1 except that the method of separating the film from the clip was changed to a method of opening the clip in a method of cutting with a shearing blade. R).

(Polarizer protective film 6)

Three slit rolls (L, C, and R) were formed by uniaxially oriented PET films having a film thickness of about 75 mu m by stretching 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. [

(Polarizer protective film 7)

The thickness of the unstretched film was changed using the same method as in the case of the polarizer protective film 1, and three slit rolls (L (mm)) of a uniaxially oriented PET film having a thickness of about 100 탆 and a transverse stretching magnification of 3.8 times and a stretching temperature of 135 캜 , C, R).

(Polarizer protective film 8)

Three slit rolls (L, C, and R) consisting of a uniaxially oriented PET film having a thickness of about 50 탆 were obtained at a transverse stretching magnification of 3.8 times and a stretching temperature of 135 캜 by the same method as that of the polarizer protective film 1.

(Polarizer protective film 9)

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

(Polarizer protective film 10)

Three slit rolls (L, C, and R) consisting of a uniaxially oriented PET film having a thickness of about 50 mu m were obtained at a transverse stretching magnification of 4.2 times and a stretching temperature of 135 DEG C by the same method as that of the polarizer protective film 1. [

(Polarizer protective film 11)

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

(Polarizer protective film 12)

Three slit rolls (L, C, and R) consisting of a uniaxially oriented PET film were obtained in the same manner as in the case of the polarizer protective film 10 except that the heat-setting was not cut to the shearing blade.

(Polarizer protective film 13)

The biaxially oriented PET film having a film thickness of about 275 탆 was 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 4 and with a winding tension of 0.2 kg / To obtain three slit rolls (L, C, R).

(Polarizer protective film 14)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while maintaining a width of 0.2 mm and a width of 0.2% in a flow direction in a temperature range of 90 캜 to 70 캜 to obtain three Slit rolls (L, C, R) were obtained.

(Polarizer protective film 15)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while maintaining a width of 0.1 탆 and a width of 0.1% in a flow direction in a temperature range of 90 캜 to 70 캜 to obtain a film having a thickness of about 75 탆, Slit rolls (L, C, R) were obtained.

(Polarizer protective film 16)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while keeping the width of the film, and narrowed the interval of 0.2% in the flow direction in the temperature range of 110 캜 to 70 캜 to obtain three pieces of uniaxially oriented PET film having a film thickness of about 75 탆 Slit rolls (L, C, R) were obtained.

(Polarizer protective film 17)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while keeping the width of the film, and narrowed the intervals of 0.4% in the flow direction in the temperature range of 150 캜 to 100 캜 to form three Slit rolls (L, C, R) were obtained.

(Polarizer protective film 18)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while maintaining a width of -55 캜 / m per unit width to obtain three slit rolls (L, C, R).

(Polarizer protective film 19)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, Treated at a temperature of 225 캜 for 30 seconds while maintaining a width of -35 캜 / m per unit width to obtain three slit rolls (L, C, R).

(Polarizer protective film 20)

An unstretched film prepared in the same manner as in the case of the polarizer protective film 1 was introduced into a tenter stretching machine, and the end of the film was guided to a hot air zone at a temperature of 125 캜 while gripping the ends thereof with a clip, stretched 3.5 times in the width direction, And maintained at a temperature of 225 캜 for 30 seconds and cooled at a temperature setting of -120 캜 / m per unit width to obtain three slit rolls (L, C, R).

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

In Table 1, " film " means the above polarizer protective film.

The results of measuring the iridescent blur and tear strength of the liquid crystal display device manufactured using the polarizer protective films 1 to 20 as described above are shown in Table 2 below.

From the results shown in Table 1, it has been shown that when the absolute value of the slope of the heat shrinkage ratio is 15 degrees or less, slight light leakage can be suppressed in the case where two polarizing plates are disposed so as to have a cross-Nicol relationship. In addition, the maximum values of the heat shrinkage ratios of the polarizer protective films 1 to 20 were all less than 1%.

From the results shown in Table 2, 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, the occurrence of rainbow stains was markedly suppressed. In addition to this condition, it has been shown that the degree of planar orientation of the oriented polyester film can be controlled to 0.13 or less, whereby the occurrence of rainbow stains can be suppressed more effectively.

According to the present invention, there is provided a polarizer protective film comprising a polyester film suitable for obtaining a liquid crystal display device in which generation of slight light leakage is suppressed when two polarizing plates are disposed so as to be in a cross-Nicol relationship can do. Therefore, the industrial applicability of the present invention is very high.

Claims (8)

Wherein an absolute value of a slope in a direction in which a heat shrinkage rate with respect to a film flow direction or a width direction is maximized is 15 degrees 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. Wherein the polarizer protective film according to any one of claims 1 to 3 is laminated on one side of the polarizer. 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. 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,
Wherein the polarizing plate is the polarizing plate according to claim 5.

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