KR20200046111A - Polarizer protective film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

The present invention provides a polarizer protective film, a polarizing plate, and a liquid crystal display device capable of suppressing warpage of a liquid crystal panel. A polyester film for protecting a polarizer laminated on one side of a polarizer, and the polyester film for protecting a polarizer satisfying the following requirements (1) and (2): (1) The poly in a direction parallel to the transmission axis of the polarizer The shrinkage force F _f of the ester film is 800 N / m or more and 9000 N / m or less. (2) In the direction parallel to the transmission axis of the polarizer, in the direction parallel to the shrinkage force F _f of the polyester film and the absorption axis of the polarizer. , The ratio (F _f / F _v ) of the shrinkage force F _v of the polyester film is 2.5 or more and 12.0 or less.

Description

Polarizer protective film, polarizing plate, and liquid crystal display device {POLARIZER PROTECTIVE FILM, POLARIZING PLATE, AND LIQUID CRYSTAL DISPLAY DEVICE}

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

The demand for the liquid crystal display device has been expanded for use in liquid crystal TVs, liquid crystal displays of PCs, and the like. Normally, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, or the like is sandwiched between glass plates, and two polarizing plates provided on both sides, and each polarizing plate is a polarizer (also referred to as a polarizing film). Is composed of two optical films (for example, a polarizer protective film and a retardation film).

By the way, in recent years, the thickness of the liquid crystal TV screen has been reduced in size, size, and furthermore, the backlight of the LED is used for the light source, and as a result, the thickness of the glass substrate used in the liquid crystal panel is thinner than 0.7 mm. However, improvement is required.

The main cause of shrinkage of the display unevenness mechanism is caused by the polarizer shrinking, and when the polarizer is placed under high temperature and high humidity, the shrinking force acts in the alignment direction because it attempts to mitigate the alignment, resulting in a liquid crystal panel. It is considered that the display becomes uneven by bending and bulging toward the backlight unit.

In addition, conventionally, since the thickness of the glass substrate used for the liquid crystal panel is thicker than 0.7 mm, as in the following Patent Documents 1 and 2, the shrinkage of the polarizer is suppressed by the high rigidity of the glass. There was no bending of the liquid crystal panel, and display unevenness was not a problem.

Therefore, attempts have been made to improve the warpage of the liquid crystal panel generated when the glass substrate is made thinner than 0.7 mm with an optical film.

For example, when a cycloolefin-based resin is used as the polarizer protective film, improvement in warpage of the liquid crystal panel is insufficient, and there is a problem that productivity decreases because the dryness of the water glue for adhering to the polarizer is poor.

In addition, when a conventional triacetyl cellulose (TAC) is used as the polarizer protective film, there is a problem that the liquid crystal panel is broken.

Japanese Patent Publication No. 2008-107499 Japanese Patent Publication No. 2009-198666

This invention is made | formed in view of the said problem and situation, and the solving subject is to provide the polarizer protective film, polarizing plate, and liquid crystal display device which can suppress curvature of a liquid crystal panel.

In order to solve the above problem, the present inventors, in the process of examining the cause of the problem and the like, by setting the shrinkage force of the polyester film for protecting the polarizer in a specific range in the direction parallel to the transmission axis of the polarizer, the liquid crystal panel It was found that the warpage could be improved, and the present invention was reached based on this knowledge.

In detail, in a liquid crystal display device, a polarizing plate is usually laminated on one surface of a liquid crystal cell so that the direction of the transmission axis of the polarizer is parallel to the long side direction of the liquid crystal display, and on the other surface, the absorption axis of the polarizer The polarizing plates are laminated so that the direction is parallel to the long side of the liquid crystal display. As a result of careful examination using various commercially available liquid crystal display devices, the problem of shape factors that tends to cause curling due to shrinkage of the polarizing plate in which the direction of absorption axis of a polarizer having a large shrinking force becomes a long side (curls generally occur in a long side direction) It is easy to do), or the inventor of the present invention that, due to the influence of the asymmetric configuration of the upper and lower polarizing plates in the liquid crystal panel, the liquid crystal panel is convex toward the polarizing plate side where the polarizer transmission axis of the upper and lower polarizing plates arranged in cross nicol is a long side. Found.

In addition, as a result of careful examination, it became clear that the contraction force in the direction of the long side of the polarizing plate in which the polarizer transmission axis becomes a long side can be controlled by the residual distortion of the protective film. It was found that the control was possible.

Here, a method of measuring the shrinkage force of the polyester film for polarizer protection will be described. In general, the shrinkage force of the film is set using a TMA or the like, the initial length is set to a minimum load at a low temperature state of the start of the test, and the force in the shrinking direction during heating is measured while maintaining the length of the initial length. However, during the temperature increase process, shrinkage due to recovery of residual distortion accompanying the change in polymer composition (hereinafter referred to as thermal contraction only) and thermal expansion (hereinafter referred to as thermal shrinkage) of the polymer by increasing the free volume and occupied volume of the polymer due to the temperature increase Since only thermal expansion occurs), in the temperature range around the glass transition temperature of the polyester film (for example, about -Tg + 50 ° C), the film generally expands due to the fact that it is a relationship of thermal contraction <thermal expansion. , No shrinkage force is observed.

As a result of the examination, it became clear that the shrinkage force occurred in the TMA cooling process even if the shrinkage force did not occur during the TMA heating process. This is because the distortion due to thermal expansion is a reversible change, so it returns to its original state after cooling at elevated temperature, but due to the fact that it is cooled in a state with a small size as the heat shrinkage contracted during the heating process, thermal stress occurs in the cooling process. . That is, the distortion of the thermal stress can be replaced with the thermal contraction rate of the film, and the shrinkage force after cooling is expressed by the following equation. In addition, the thermal contraction rate in this invention contains the change of the moisture content during heat processing.

Shrinkage (N / m) = Film thickness (mm) × Elastic modulus (N / mm) × Heat shrinkage (%) ÷ 100 × 1000

That is, the typical present invention is as follows.

Item 1.

As a polyester film for polarizer protection laminated on one side of a polarizer, the polyester film for polarizer protection satisfying the following requirements (1) and (2):

(1) The shrinkage force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer is 800 N / m or more and 9000 N / m or less (however, the shrinkage force F _f (N / m) is the thickness of the polyester film) (Mm) × elastic modulus (N / mm 2) × 80 ° C., 30 minutes heat shrinkage of treatment (%) ÷ 100 × 1000, where the modulus of elasticity of the polyester film in the direction parallel to the transmission axis of the polarizer Elastic modulus, and heat shrinkage is the heat shrinkage of the polyester film in a direction parallel to the transmission axis of the polarizer.)

(2) The ratio (F _f / F) of the shrinking force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer and the shrinking force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer _v ) is 2.5 or more and 12.0 or less (however, the shrinkage force F _v (N / m) is the thickness (mm) of the polyester film x elastic modulus (N / mm) x heat shrinkage (%) of processing at 80 ° C for 30 minutes ÷ Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer, and the thermal shrinkage is the thermal shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer. to be.).

Item 2.

In addition, the polyester film for polarizer protection according to item 1, which satisfies the following requirement (3):

(3) The direction in which the heat shrinkage rate of the polyester film becomes maximum and the direction parallel to the transmission axis of the polarizer are approximately parallel.

Section 3.

The polyester film for polarizer protection according to item 1 or 2, wherein the polyester film has retardation of 3000 to 30000 nm.

Item 4.

The polyester film for polarizer protection according to any one of items 1 to 3, wherein the thickness of the polyester film is 40 to 200 μm.

Clause 5.

The polarizer according to any one of items 1 to 4, wherein the polyester film has a hard coat layer, an anti-reflection layer, a low-reflection layer, an anti-glare layer, or an anti-reflective anti-glare layer on a surface opposite to the surface on which the polarizer is laminated. Protective polyester film.

Clause 6.

As a polyester film for polarizer protection laminated on one side of a polarizer, the polyester film for polarizer protection satisfying the following requirements (1) and (2):

(1) The shrinkage force F TD of the polyester film _TD is 800 N / m or more and 9000 N / m or less (however, the shrinkage force F _TD (N / m) is the thickness (mm) of the polyester film × elastic modulus (N / mm 2). ) × 80 ° C., 30 minutes heat shrinkage (%) ÷ 100 × 1000, where elastic modulus is the elastic modulus of the TD of the polyester film, and thermal shrinkage is the thermal shrinkage of the TD of the polyester film.)

(2) The ratio (F _TD / F _MD ) of the shrinking force F _TD of the _TD of the polyester film and the shrinking force F _MD of the MD of the polyester film is 2.5 or more and 12.0 or less (however, the shrinking force F _MD (N / m) Is the thickness (mm) of the polyester film x the modulus of elasticity (N / mm) x the heat shrinkage rate (%) ÷ 100 x 1000 at 80 ° C for 30 minutes, where the modulus of elasticity is the modulus of the MD of the polyester film. , The heat shrinkage is the heat shrinkage of MD of the polyester film.).

Section 7.

In addition, the polyester film for polarizer protection according to item 6, which satisfies the following requirement (3):

(3) The direction in which the heat shrinkage rate of the polyester film becomes maximum and the TD are approximately parallel.

Item 8.

A polarizing plate obtained by laminating the polyester film for protecting a polarizer according to any one of items 1 to 7 on at least one surface of a polarizer.

Item 9.

A polarizing plate in which the polyester film for protecting a polarizer according to any one of items 1 to 7 is laminated on one surface of a polarizer, and does not have a film on the other surface of the polarizer.

Item 10.

The polarizing plate according to item 8 or 9, wherein the polarizing plate has a rectangular shape and the long side of the polarizing plate and its transmission axis are parallel.

Clause 11.

A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates, wherein at least one of the two polarizing plates is a polarizing plate according to any one of items 8 to 10.

ADVANTAGE OF THE INVENTION According to this invention, the polarizer protective film, a polarizing plate, and a liquid crystal display device which can suppress curvature of a liquid crystal panel can be provided.

The polyester film for polarizer protection of the present invention is a polarizer protective film made of a polyester film and laminated on at least one surface of a polarizer (for example, a film composed of polyvinyl alcohol and a dye) to form a polarizing plate.

In the present specification, the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer is the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film. Meaning.

The heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer means the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film.

The elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer means that the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film.

In addition, the shrinking force of the polyester film in the direction parallel to the absorption axis of the polarizer means the shrinking force of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film.

The thermal contraction rate of a polyester film in the direction parallel to the absorption axis of a polarizer means the thermal contraction rate of a polyester film in the direction parallel to the absorption axis of a polarizer laminated on one side of a polyester film.

The elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer means the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film.

The direction parallel to the transmission axis of the polarizer may be referred to simply as the transmission axis direction of the polarizer. Moreover, the direction parallel to the absorption axis of a polarizer may be called simply as the absorption axis direction of a polarizer.

In the polyester film for protecting a polarizer of the present invention, it is preferable that the direction parallel to the transmission axis of the polarizer and the direction in which the heat shrinkage rate of the polyester film is maximized are substantially parallel. Almost parallel allows the absolute value of the angle (hereinafter, sometimes referred to simply as the slope of the thermal contraction rate) of the angle formed by the direction of the polarizer's transmission axis and the direction in which the thermal contraction rate of the polyester film is maximized to be 15 degrees or less.

The slope of the thermal contraction rate is preferably 12 degrees or less, more preferably 10 degrees or less, even more preferably 8 degrees or less, still more preferably 6 degrees or less, particularly preferably 4 degrees or less , Most preferably 2 degrees or less. The smaller the slope of the thermal contraction rate, the lower the limit is 0 degrees from a preferable point. When the slope of the thermal contraction rate of the polyester film is large, the warp in the oblique direction of the polarizing plate containing the polyester film occurs, and the effect of reducing the warpage of the liquid crystal panel tends to fade.

However, the ratio (F _f / F _v ) of the shrinking force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer and the shrinking force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer In the case of 2.5 or more and 12.0 or less, even if the absolute value of the angle between the direction parallel to the transmission axis of the polarizer and the direction in which the heat shrinkage rate of the polyester film is maximized is 40 degrees or less, the warpage of the liquid crystal panel can be reduced. The angle is preferably 35 degrees or less.

The heat shrinkage ratio of the polyester film, the slope of the heat shrinkage ratio of the polyester film, and the direction in which the heat shrinkage ratio of the polyester film is maximized can be measured by the method employed in the Examples described later.

Usually, in a liquid crystal display device, two polarizing plates are arrange | positioned so that it may become a cross nicol relationship. When two polarizing plates are arranged in a cross-Nicol relationship, light does not normally pass through the two polarizing plates. However, due to the shrinkage or warpage of the polarizer described above, as a result, the relationship of the complete cross nicotine is broken and light leakage may occur. From the viewpoint of suppressing light leakage, the direction in which the heat shrinkage rate of the polarizer protective film is maximized and the angle formed by the transmission axis of the polarizer is preferably smaller.

It is preferable that the value of the shrinking force F _f of a polyester film in the direction parallel to the transmission axis of a polarizer is 800 N / m or more and 9000 N / m or less in the polyester film for polarizer protection of this invention. When the lower limit of F _f is less than 800 N / m, there is a fear that the warpage of the liquid crystal panel cannot be sufficiently reduced. Moreover, when the upper limit of F _f exceeds 9000 N / m, the contraction force is too strong, and there is a fear that the liquid crystal panel may curl in the reverse direction. The preferred range of shrinkage force is 900 N / m or more and 8000 N / m or less, more preferably 1000 N / m or more and 8000 N / m or less, more preferably 1100 N / m or more and 8000 N / m or less, even more preferably 1200 N / m It is 8000 N / m or less. Moreover, it is preferable that an upper limit is 6000 N / m or less, 5500 N / m or less, and 4800 N / m or less.

Here, the shrinkage force F _f indicates the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer, and the thickness (mm) of the polyester film (modulus of elasticity (N / mm)) of 80 ° C. for 30 minutes It is defined as the heat shrinkage rate (%) ÷ 100 × 1000.

Here, the elastic modulus refers to the elastic modulus of the polyester film in a direction parallel to the transmission axis of the polarizer. In addition, the thermal contraction rate refers to the thermal contraction rate of the polyester film in the direction parallel to the transmission axis of the polarizer (thermal contraction rate at 80 ° C and 30 minute heat treatment).

The contraction force of the polyester film in the direction parallel to the absorption axis of the polarizer is called F _v . The shrinkage force F _v is defined as the thickness (mm) of the polyester film x the elastic modulus (N / mm 2) x 80 占 폚, and the heat shrinkage rate (%) ÷ 100 x 1000 for 30 minutes. Here, the elastic modulus means the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The thermal contraction rate refers to the thermal contraction rate of the polyester film in the direction parallel to the absorption axis of the polarizer (thermal contraction rate at 80 ° C. and 30 minute heat treatment).

It is preferable that F _f / F _v is 1.0 or more and 12.0 or less of the polyester film for polarizer protection of this invention. More preferably, it is 2.5 or more and 12.0 or less. When the lower limit of F _f / F _v is less than 1.0, there is a fear that the warpage of the liquid crystal panel cannot be sufficiently reduced. Moreover, when the upper limit of F _f / F _v exceeds 12.0, thermal deformation in one direction becomes large, and stress is applied to a protective film or a retardation film that is laminated on a surface opposite to the surface of the polarizer and the polyester film for protecting the polarizer. This is applied, and there is a fear that display quality may deteriorate. Moreover, film forming stability may fall and may rupture.

As a method of controlling the shrinkage force within the range of the above formula, after the heat treatment step after the film stretching is completed, a method of stretching again while controlling the winding tension of the film may be mentioned.

The polyester film for polarizer protection of the present invention preferably has an elastic modulus of 1000 to 9000 N / mm 2 of the polyester film in the direction of the transmission axis of the polarizer. Although the shrinking force of the polyester film can be controlled by the elastic modulus, in order to increase the elastic modulus of the polyester film in the transmissive axis direction of the polarizer, it is necessary to highly align the polyester film in the transmissive axis direction of the polarizer and also increase the crystallinity. have. Therefore, when the elastic modulus of the polyester film in the direction of the transmissive axis of the polarizer exceeds 9000 N / mm 2, there is a concern that it is liable to tear, so the upper limit is preferably 9000 N / mm 2, more preferably 8000 N / mm 2 And more preferably 7000 N / mm 2. On the other hand, when the orientation is low and the crystallinity is low, there is a fear that the film is deformed due to unevenness of the roll due to thickness variation when wound up on the roll, resulting in poor flatness. Therefore, the lower limit of the elastic modulus is preferably 1000 N / mm 2, more preferably 1500 N / mm 2, and even more preferably 1800 N / mm 2. The modulus of elasticity can be measured by the method employed in Examples described later.

It is preferable that the heat shrinkage rate of the polyester film for polarizer protection of this invention at 80 degreeC and 30 minute heat treatment of a polyester film in the direction of the transmission axis of a polarizer is 0.10 to 5.0%. The lower limit of the heat shrinkage ratio is preferably 0.10% or more, more preferably 0.15% or more, and most preferably 0.20% or more. The upper limit of the heat shrinkage rate is preferably 4.5% or less, more preferably 4.0% or less, still more preferably 3.0% or less, even more preferably 2% or less, and most preferably 1.4% or less. When the heat shrinkage rate is lower than 0.10%, that is, in the range of 0.01 to 0.099%, it may be difficult to control the heat shrinkage rate without unevenness. Further, in order to increase the heat shrinkage ratio to more than 5.0%, it is necessary to further lower the crystallinity and the glass transition temperature, which may cause problems such as poor flatness. The heat shrinkage rate can be measured by the method employed in Examples described later.

It is preferable that the thickness of the polyester film for polarizer protection of this invention is 40-200 micrometers, More preferably, it is 40-100 micrometers, More preferably, it is 40-80 micrometers. When the thickness of the polyester film is less than 40 μm, it tends to be fragile, and also tends to be poor in planarity due to insufficient rigidity. Moreover, when it is thin, it is necessary to increase the elasticity modulus or thermal contraction rate of the polyester film in the transmissive axis direction of the polarizer accordingly, but since each parameter has an upper limit as described above, the practically 40 µm is the lower limit. Moreover, when the thickness of a film exceeds 200 micrometers, the nonuniformity of the elastic modulus or thermal contraction rate of a polyester film in the transmissive axis direction of a polarizer becomes large accordingly, there exists a possibility that control may become difficult, and cost also rises. The thickness of the polyester film can be measured by the method employed in Examples described later.

It is preferable that the in-plane retardation exists in a specific range from the viewpoint of suppressing the rainbow stain observed on the screen of a liquid crystal display device of the polyester film for polarizer protection of this invention. The lower limit of in-plane retardation is preferably 3000 nm or more, 5000 nm or more, 6000 nm or more, 7000 nm or more, or 8000 nm or more. The upper limit of the in-plane retardation is preferably 30000 nm or less, more preferably 18000 nm or less, still more preferably 15000 nm or less. In particular, from the viewpoint of thinning, in-plane retardation is preferably less than 10000 nm and 9000 nm or less.

The retardation of the polyester film can also be obtained by measuring the refractive index and thickness in the biaxial direction, or by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). In addition, the refractive index can be determined with an Abbe's refractive index meter (measurement wavelength 589 nm).

In the polyester film for protecting a polarizer of the present invention, the ratio (Re / Rth) of in-plane retardation (Re) and retardation (Rth) in the thickness direction is preferably 0.2 or more, preferably 0.3 or more, preferably 0.4 Above, it is more preferably 0.5 or more, and still more preferably 0.6 or more. The larger the ratio (Re / Rth) of the in-plane retardation and the thickness-direction retardation, the more birefringent action is to increase the isotropy, which tends to make it difficult to generate rainbow-colored stains depending on the viewing angle. In a complete uniaxial (single-axis symmetry) film, the ratio (Re / Rth) of the retardation and the thickness direction retardation is 2.0, so the upper limit of the ratio (Re / Rth) of the retardation and the thickness direction retardation is 2.0 is preferred. The preferred upper limit of Re / Rth is 1.2 or less. In addition, the thickness direction retardation means the average of the retardation obtained by multiplying the film thickness d by two birefringence (DELTA) Nxz and (DELTA) Nyz when the film is viewed from the thickness direction cross section.

The polyester film for polarizer protection of the present invention has a NZ coefficient of preferably 2.5 or less, more preferably 2.0 or less, still more preferably 1.8 or less, even more preferably from the viewpoint of further suppressing rainbow-colored stains. It is 1.6 or less. In addition, since the NZ coefficient is 1.0 in a complete uniaxial (single axis symmetry) film, the lower limit of the NZ coefficient is 1.0. However, care should be taken as the mechanical strength in the direction perpendicular to the orientation tends to decrease remarkably as it approaches the complete uniaxial (uniaxially symmetric) film.

The NZ coefficient is represented by | Ny-Nz | / | Ny-Nx |, where Ny is the refractive index in the slow axis direction of the polyester film, and Nx is the refractive index in the direction orthogonal to the slow axis (true) The refractive index in the axial direction) and Nz represent the refractive index in the thickness direction. The orientation axis of the film is obtained using a molecular orientation system (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation system), and the refractive index of two axes (Ny, Nx, but Ny in the direction perpendicular to the orientation axis direction) > Nx), and the refractive index (Nz) in the thickness direction is determined by an Abbe's refractive index meter (manufactured by Atago, NAR-4T, measurement wavelength: 589 nm). The NZ coefficient can be obtained by substituting the value thus obtained for | Ny-Nz | / | Ny-Nx |.

Moreover, the polyester film of this invention WHEREIN: From a viewpoint which suppresses a rainbow color stain more, the value of Ny-Nx of a polyester film is preferably 0.05 or more, More preferably, it is 0.07 or more, More preferably, it is 0.08. Above, even more preferably 0.09 or more, and most preferably 0.1 or more. Although the upper limit is not particularly determined, in the case of a polyethylene terephthalate-based film, the upper limit is preferably about 1.5.

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

Examples of the dicarboxylic acid component usable in the production of the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-naphthalene Dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3 -Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2 -Dimethyl glutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecanedicarboxylic acid and the like.

Diol components that can be used in the production of polyester resins include, for example, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and deca Methylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxy And phenyl) sulfones.

As the dicarboxylic acid component and the diol component constituting the polyester resin, either one or two or more of them can be used. Suitable polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and more preferably polyethylene terephthalate and polyethylene. Although naphthalate is mentioned, these may further contain other copolymerization components. These resins are excellent in transparency and excellent in thermal and mechanical properties. In particular, polyethylene terephthalate is a suitable material in that it can achieve a high modulus of elasticity and control heat shrinkage is relatively easy.

When it is necessary to increase the thermal contraction rate of a polyester film highly, it is preferable to add a copolymerization component to appropriately lower the crystallinity. Moreover, since the ratio of elastic distortion or permanent distortion is high for deformations below the glass transition temperature, it is generally difficult to increase the thermal contraction rate to a high level. Therefore, it is also a preferable embodiment to introduce a component having a low glass transition temperature as necessary. Specifically, it is propylene glycol, 1,3-propanediol, and the like.

(Grant of functional layer)

Since the polarizing plate using the polyester film for protecting a polarizer of the present invention is preferably integrated with a glass plate of a liquid crystal cell in a state in which the thermal contraction rate of the polyester film remains, an easily bonding layer, a hard coat layer, an anti-glare layer When a functional layer such as an antireflection layer, a low antireflection layer, a low antireflection layer, an antireflection antiglare layer, a low antireflection antiglare layer, and an antistatic layer is provided, the drying temperature is set low or heat such as UV irradiation or electron beam irradiation is applied. It is a preferred embodiment to perform in a method with a small history. Moreover, providing these functional layers during the film forming process of the polyester film is a more preferable embodiment because it is possible to integrate the polarizing plate of the present invention and the glass plate of the liquid crystal cell without impairing the increased heat shrinkage.

Functional layers such as an easy-adhesive layer, hard coat layer, anti-glare layer, anti-reflection layer, low-reflection layer, anti-reflection layer, anti-reflection anti-glare layer, low-reflection anti-glare layer, anti-static layer, and the other side of the polyester film is laminated It is preferable that the shrinking forces F _f and F _v have the above-described conditions in a state where they are laminated on the opposite side and these functional layers are laminated.

(Method for producing oriented polyester film)

The polyester film used in this invention can be manufactured according to the manufacturing method of a general polyester film. For example, the non-oriented polyester formed by melting the polyester resin and extruding into a sheet form is stretched in the longitudinal direction using a difference in the speed of the roll at a temperature equal to or higher than the glass transition temperature, followed by a tenter. A method of stretching in the horizontal direction and performing heat treatment (heat fixation) can be given. It may be a uniaxially stretched film or a biaxially stretched film. Preferably, it is mainly a uniaxially stretched film that is strongly stretched in the horizontal direction or a uniaxially stretched film that is mainly strongly stretched in the vertical direction, and both may be slightly stretched in a direction perpendicular to the main stretching direction. In addition, MD is an abbreviation of Machine Direction, and in this specification, it may be called a film flow direction, a longitudinal direction, and a vertical direction. In addition, TD is an abbreviation of Transverse Direction, and may be called a width direction and a horizontal direction in this specification.

In the polyester film, it is preferable to adjust the film thickness, modulus of elasticity, and heat shrinkage so that the shrinkage force F _f is 800 N / m or more and 9000 N / m or less.

(How to adjust the elastic modulus of the polyester film)

The elastic modulus of the polyester film used as the polarizer protective film is TD when the polarizer transmission axis direction coincides with MD at the time of film formation of the polyester film and TD at the time of film formation of the polyester film. The elastic modulus of may be adjusted by a conventionally known method of a stretched polyester film.

Specifically, if the direction is the stretching direction, the stretching magnification is high, and when the direction is the direction perpendicular to the stretching direction, the stretching magnification may be set low.

(How to adjust the heat shrinkage rate of polyester film)

The heat shrinkage rate of the polyester film used as a polarizer protective film is the same as the heat shrinkage rate of MD when the direction of the transmission axis of the polarizer coincides with the MD at the time of film formation of the polyester film and the TD at the time of film formation of the polyester film. In that case, the thermal contraction rate of TD may be adjusted by a conventionally known method of a stretched polyester film.

When adjusting the thermal contraction rate of MD of a polyester film, for example, in the cooling process after extending | stretching and heat fixation, the space | interval of the clip which is holding the edge part of the film width direction and the clip adjacent to it is fixed. It can adjust by extending | stretching to MD by expanding, or contracting to MD by reducing the clip interval. In the cooling process after stretching and heat fixing, when the film is cut or separated from the clip gripping the end portion in the width direction of the film, the film is stretched or contracted to MD by adjusting the force of pulling the film. It is possible to adjust it. In the offline process after film formation, when the temperature is increased for the purpose of providing a functional layer or the like, since the heat shrinkage rate changes during the temperature-cooling process, it is also possible to adjust the force of drawing the film by stretching or shrinking with MD. .

When adjusting the heat shrinkage rate of the TD of the polyester film, for example, in the cooling process after stretching and heat fixing, the gap between the clip gripping the edge in the film width direction and the clip located on the opposite side in the width direction is enlarged. It can be adjusted by stretching to TD by doing or shrinking to TD by shrinking.

It is preferable to adjust the elastic modulus and the heat shrinkage rate of a polyester film so that the contraction force F _v may be a ratio (F _f / F _v ) of a contraction force of 1.0 or more and 12.0 or less, more preferably 2.5 or more and 12.0 or less.

(How to adjust the tilt of the shrinkage axis of the polyester film)

The slope of the shrinkage axis of the polyester film used as the polarizer protective film, as disclosed in PCT / JP2014 / 073451 (WO2015 / 037527), is a cooling process after stretching and heat treatment by a tenter of the polyester film, or after film formation. It is possible to adjust in an offline process. Specifically, in the cooling process, shrinkage with stretching and thermal stress with cooling are generated due to stretching that could not be completely removed in the heat setting process, and are drawn upstream according to the balance of both in the film flow direction (引入) or the attraction to the downstream side occurs, causing a phenomenon that the main axis of the contraction is inclined. In order to reduce the inclination of the shrinkage main axis, it is necessary to adjust so that the shrinking force in the film flow direction in the cooling process (the sum of the shrinking force with stretching and the shrinking force with cooling) becomes uniform. In order to make it uniform, it is preferable to contract in the film flow direction in the film flow direction at a temperature region with high shrinkage force or in the film flow direction in the film flow direction with a low shrinkage force. The method of shrinking or stretching may be a conventionally known method. In addition, when cutting or separating the end of the film, care must be taken in that the heat shrinkage ratio below the temperature range is reduced by shrinking freely in the width direction below the cut and separated temperature range.

As for the polarizing plate, the polyester film for polarizer protection of this invention is laminated | stacked on at least one surface of a polarizer. It is preferable that a film having no birefringence such as a TAC film, an acrylic film or a norbornene film is laminated on the other surface of the polarizer. Alternatively, a polarizing plate in which no film is laminated on the other side of the polarizer is also a preferred aspect from the viewpoint of thinness. In this case, the film is not laminated on the other side of the polarizer, but the coating layer may be laminated on the polarizer. As the coating layer, a functional layer such as a hard coat layer may be used, or a retardation film formed by coating may be used.

In addition, when a film or a coating layer other than the polyester film for polarizer protection of the present invention is laminated on the polarizer, the shrinkage force of the film or coating layer other than the polyester film for polarizer protection in the direction parallel to the transmission axis of the polarizer, and the polarizer In the direction parallel to the absorption axis of the film, the shrinkage force of the film or the coating layer other than the polyester film for polarizer protection is preferably equal to or less than the value of F _f of the polyester film for polarizer protection, and more preferably the poly for polarizer protection The value of F _v of the ester film or less is preferred. In addition, in the direction parallel to the transmission axis of the polarizer, the shrinkage force of the film or the coating layer other than the polyester film for protecting the polarizer, and the film or coating layer other than the polyester film for protecting the polarizer in the direction parallel to the absorption axis of the polarizer The shrinkage force of is preferably 250 N / m or less, and more preferably 200 N / m or less. The shrinkage force of the film or coating layer other than the polyester film for polarizer protection can be measured similarly to the case of a polyester film. That is, the thickness (mm) of the film or coating layer (modulus of elasticity (N / mm 2) × 80 ° C., the heat shrinkage ratio (%) ÷ 100 × 1000 for 30 minutes treatment).

Industrially, a polarizing plate is laminated | stacked the elongate thing of a polarizer and the elongate thing of the polyester film for polarizer protection via an adhesive in the form of roll-to-roll. In addition, since the polarizer is usually stretched and produced in the vertical direction, it has an absorption axis in MD and a transmission axis in TD.

Therefore, from the viewpoint of industrially producing a polarizing plate, it is preferable that the polyester films for polarizer protection of the present invention are (1) and (2) below.

(1) The shrinkage force F _TD of the TD of the polyester film is 800 N / m or more and 9000 N / m or less.

However, the shrinkage force F _TD (N / m) is the thickness (mm) of the polyester film x the modulus of elasticity (N / mm2) x 80 占 폚, and the heat shrinkage rate (%) of a 30 minute treatment (100) 占 100 x 1000. Here, the elastic modulus and the thermal shrinkage are the elastic modulus of TD of the polyester film and the thermal shrinkage of TD, respectively.

(2) It is preferable that the ratio (F _TD / F _MD ) of the shrinking force F _TD of the TD of the polyester film and the shrinking force F _MD of the MD of the polyester film is 2.5 or more and 12.0 or less.

However, the shrinkage force F _MD (N / m) is the thickness (mm) of the polyester film x the modulus of elasticity (N / mm2) x 80 deg. Here, the elastic modulus and the thermal shrinkage are respectively the elastic modulus of MD of the polyester film and the thermal shrinkage of MD.

Moreover, in the polyester film for polarizer protection of this invention, it is preferable that the direction in which the thermal contraction rate of a polyester film becomes maximum and TD are substantially parallel.

The approximately parallel allows the absolute value (the slope of the heat shrinkage rate) of the angle between the direction where the heat shrinkage rate of the polyester film is maximized and the TD direction is 15 degrees or less. The slope of the thermal contraction rate is preferably 12 degrees or less, more preferably 10 degrees or less, even more preferably 8 degrees or less, still more preferably 6 degrees or less, particularly preferably 4 degrees or less , Most preferably 2 degrees or less. The smaller the slope of the thermal contraction rate, the lower the limit is 0 degrees from a preferable point.

However, when the ratio (F _TD / F _MD ) of the shrinkage force F _TD of the TD of the polyester film and the shrinkage force F _MD of the MD of the polyester film is 2.5 or more and 12.0 or less, the heat shrinkage ratio of the polyester film is the maximum and Even if the absolute value of the angle formed by the TD is 40 degrees or less, the warpage of the liquid crystal panel can be reduced. The angle is preferably 35 degrees or less.

In addition, when considering industrially manufacturing a polarizing plate in the form of roll-to-roll or the like as described above, since F _TD corresponds to F _f , the preferred range of F _{TD and} the preferred range of F _f are the same. Moreover, since F _TD / F _MD corresponds to F _f / F _v , the preferable ranges of both are the same. Since the "elastic modulus of TD of the polyester film" corresponds to the "elastic modulus of the polyester film in the direction of the transmissive axis of the polarizer", both of the preferred ranges are the same. Since the "thermal shrinkage of TD at 80 ° C for 30 minutes of heat treatment of a polyester film" corresponds to "thermal shrinkage at 80 ° C of a polyester film for 30 minutes of heat treatment at a transmissive axis direction of a polarizer", The preferred ranges of both are the same.

The liquid crystal display device has at least a backlight light source and a liquid crystal cell disposed between two polarizing plates. It is preferable that at least one of the two polarizing plates is a polarizing plate in which the polyester film for protecting a polarizer of the present invention is a polarizer protective film. In the liquid crystal display device, both of the two polarizing plates may use the polarizing plate of the present invention.

The polyester film for polarizer protection of the present invention is positioned at the position of the polarizer protective film on the light source side using the polarizer protective film on the viewer side and / or the polarizer on the light source side polarizer as a starting point with the polarizer of the viewer side polarizing plate as a starting point. It is preferably used.

Normally, the liquid crystal display device has a rectangular shape (two polarizing plates used in a liquid crystal display device are also rectangular), and one polarizing plate has a parallel side and an absorption axis thereof, and the other polarizing plate has a long side and a transmission axis. These are parallel and arranged so that the absorption axes are perpendicular to each other. In addition, a polarizing plate having a parallel relationship between a long side and an absorption axis of a polarizing plate is usually used as a viewing side polarizing plate of a liquid crystal display, and a polarizing plate having a long relationship between a long side and a transmission axis of a polarizing plate is a light source side of a liquid crystal display device. It is used as a polarizing plate. At least, it is preferable from the viewpoint of suppressing the warpage of the liquid crystal panel that the polarizing plate of the present invention is used as a polarizing plate having a parallel relationship between a long side and a transmission axis of the polarizing plate. Moreover, it is also preferable to use the polarizing plate of this invention for both the polarizing plate which has a parallel relationship of a long side and a transmission axis of a polarizing plate, and the polarizing plate which has a parallel relationship of a long side and an absorption axis of a polarizing plate.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples, and may be carried out by appropriately changing it within a range suitable for the gist of the present invention. And all of them are included in the technical scope of the present invention.

(1) Shrinkage force F _f

The shrinkage force F _f of the polyester film was calculated by the following formula. In addition, the thickness, elasticity modulus, and thermal contraction rate of a polyester film are measurement values demonstrated below. The modulus of elasticity refers to the modulus of elasticity of the polyester film in a direction parallel to the transmission axis of the polarizer. The thermal contraction rate refers to the thermal contraction rate of the polyester film in a direction parallel to the transmission axis of the polarizer.

Shrinkage force F _f (N / m) = thickness of polyester film (mm) × modulus of elasticity (N / mm) × 80 ° C. and heat shrinkage at 30 minutes (%) ÷ 100 × 1000

(2) Shrinkage force F _v

The shrinkage force F _v of the polyester film was calculated by the following formula. In addition, the thickness, elasticity modulus, and thermal contraction rate of a polyester film are measurement values demonstrated below. The modulus of elasticity refers to the modulus of elasticity of the polyester film in a direction parallel to the absorption axis of the polarizer. The thermal contraction rate refers to the thermal contraction rate of the polyester film in a direction parallel to the absorption axis of the polarizer.

Shrinkage force F _v (N / m) = thickness of polyester film (mm) × modulus (N / mm) × 80 ° C. and heat shrinkage at 30 minutes (%) ÷ 100 × 1000

(3) Film thickness

The thickness (mm) of the polyester film was measured using an electric micrometer (Minetron 1245D manufactured by FineLoop Co., Ltd.) after standing for 168 hours in an environment of 50RH% at 25 ° C, and the unit was converted to mm. .

(4) Elastic modulus of polyester film

The elastic modulus of the polyester film was evaluated using a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments in accordance with JIS-K7244 (DMS) after standing for 168 hours in an environment of 25 ° C and 50RH%. The temperature dependence of 25 ° C to 120 ° C was measured under the conditions of tensile mode, driving frequency of 1 Hz, distance between chucks of 5 mm, and heating rate of 2 ° C / min, and the average of the storage modulus of 30 ° C to 100 ° C was taken as the elastic modulus. . In this way, the elastic modulus of the polyester film in the direction parallel to the polarizer transmission axis and the elastic modulus of the polyester film in the direction parallel to the polarizer absorption axis were measured for the polyester film. In addition, the said measurement was performed with the polyester film single substance (a single polyester film for polarizer protection).

(5) Heat shrinkage and slope of heat shrinkage of polyester film

After the polyester film was left for 168 hours in an environment of 50 RH% at 25 ° C., a circle of 80 mm in diameter was drawn, and the diameter of the circle was measured every 1 ° using an image dimension measuring device (image measurer IM6500 manufactured by KEYENCE), and the length before treatment. I made it. Next, heat treatment is performed for 30 minutes using a gear oven set at 80 ° C, and then cooled for 10 minutes in an environment set at room temperature of 25 ° C, and then evaluated every 1 ° in the same manner as before treatment. Length. In addition, the said process was performed with the polyester film simple substance (polyester film single body for polarizer protection).

The heat shrinkage rate was evaluated for each angle using the following calculation formula.

Heat shrinkage ratio = (length before treatment-length after treatment) / length before treatment x 100

In this way, the heat shrinkage of the polyester film in the direction parallel to the polarizer transmission axis and the heat shrinkage of the polyester film in the direction parallel to the polarizer absorption axis were determined for the polyester film.

In the above, 360 ° was evaluated every 1 °, and the direction in which the heat shrinkage ratio was maximized was specified, and the absolute value of the angle between the direction and the transmission axis direction of the polarizer was taken as the slope of the heat shrinkage rate. In addition, the slope of the thermal contraction rate is defined as a narrow angle from the direction of the transmission axis of the polarizer, and is in the range of 0 to 90 °.

(6) bending of the liquid crystal panel

The liquid crystal panel produced in each of Examples and Comparative Examples was subjected to heat treatment for 30 minutes using a gear oven set at 80 ° C, and then cooled for 30 minutes in an environment set at room temperature 25 ° C 50% RH, and then convex. Was placed on a horizontal surface, the height of the four corners was measured with a measure, and the maximum value was taken as the amount of warpage. The amount of warpage was evaluated as follows.

○: 0 mm or more and less than 2.0 mm

△: 2.0 mm or more, 3.0 mm or less

×: more than 3.0 mm

(7) Refractive index of polyester film

Using a molecular orientation system (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation system), the direction of the slow axis of the film was determined, and the length of the slow axis was parallel to the long side of the sample for measurement. The rectangle was cut out and used as a sample for measurement. For this sample, the refractive index of the two axes orthogonal (refractive index in the ground axis direction: Ny, the true axis (refractive index in the direction perpendicular to the ground axis direction): Nx), and the refractive index (Nz) in the thickness direction were determined by the Abbe refractometer (Atta It was calculated | required by the yarn manufacture, NAR-4T, measurement wavelength 589nm). NZ coefficients were determined using these values.

Retardation is a parameter defined by the product of orthogonal biaxial refractive index (ΔNxy = | Nx-Ny |) and film thickness d (nm) (△ Nxy × d) on the film, and shows optical isotropy and anisotropy. It is a measure. The anisotropy (ΔNxy) of the biaxial refractive index was determined by the following method. Using a molecular orientation system (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation system), the direction of the slow axis of the film was determined, and the length of the slow axis was parallel to the long side of the sample for measurement. The rectangle was cut out and used as a sample for measurement. For this sample, an Abbe refractometer (manufactured by Atago, NAR) was used to measure the refractive index of the two axes orthogonal (the refractive index in the ground axis direction: Ny, the refractive index in the direction perpendicular to the slow axis direction: Nx), and the refractive index (Nz) in the thickness direction. -4T, measurement wavelength 589nm), and the absolute value (| Nx-Ny |) of the refractive index difference between the two axes was defined as anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (manufactured by FineLoop, Millitron 1245D), and the unit was converted to nm. The retardation (Re) was calculated | required from the product ((triangle | delta) Nxyxd) of the anisotropy ((triangle | delta) Nxy) of refractive index and the film thickness d (nm).

(8) Thickness direction retardation (Rth)

The thickness direction retardation is the average of the retardation obtained by multiplying the film thickness d by two birefringences ΔNxz (= | Nx-Nz |) and ΔNyz (= | Ny-Nz |) when viewed from the cross section in the film thickness direction. Is a parameter indicating Nx, Ny, Nz and film thickness d (nm) were obtained in the same manner as the measurement of retardation, and the average values of (ΔNxz × d) and (△ Nyz × d) were calculated to calculate the thickness direction retardation (Rth). I got it.

(Production Example 1-Polyester A)

When the temperature of the esterification reaction tube was raised to reach 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added, and 0.017 parts by mass of antimony trioxide as a catalyst while stirring, and magnesium acetate tetrahydrate were added. 0.064 parts by mass and 0.16 parts by mass of triethylamine were added. Subsequently, the pressure was elevated to carry out a pressure esterification reaction under conditions of gauge pressure of 0.34 MPa and 240 ° C, and then the esterification reaction tube was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Moreover, it heated up to 260 degreeC over 15 minutes, and 0.012 mass parts of trimethyl phosphate was added. Subsequently, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tube, and polycondensation reaction was carried out under reduced pressure at 280 ° C.

After completion of the polycondensation reaction, filtration is performed with a filter made by Naslon, which has a 95% cut diameter of 5 µm, extruded from the nozzle into a strand, and cooled using cooling water that has been previously subjected to filtration treatment (hole diameter: 1 µm or less). , 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 internally precipitated particles (hereinafter abbreviated as PET (A)).

(Production Example 2-Polyester B)

10 parts by mass of the dried ultraviolet absorbent (2,2 '-(1,4-phenylene) bis (4H-3,1-benzooxazin-4-one), PET (A) containing no particles (unique viscosity (0.62dl / g) 90 parts by mass was mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder. (Hereinafter abbreviated as PET (B)).

(Production Example 3-Preparation of adhesive modified coating liquid)

Transesterification and polycondensation reactions were carried out by a conventional method, and as a dicarboxylic acid component (relative to the entire dicarboxylic acid component), 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 5-sulfonatoisophthalate 8 A water-dispersible sulfonic acid metal base-containing copolymer polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as a mol% and glycol component (relative to the entire glycol component) 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 nonionic surfactant were mixed, stirred with heating, and reached 77 ° C., and the water-dispersible sulfonic acid After adding 5 parts by weight of the metal base-containing copolymer polyester resin, stirring was continued until the lump of the resin disappeared, and then the resin aqueous dispersion was cooled to room temperature to obtain a uniform water-dispersible copolymer polyester resin solution having a solid content concentration of 5.0 mass%. Got In addition, after dispersing 3 parts by mass of aggregated silica particles (Filixia Co., Ltd., Silisia 310) in 50 parts by mass of water, 0.54 parts of water dispersion of Silisia 310 in 99.46 parts by mass of the water-dispersible copolymer polyester resin solution. 20 parts by mass of water was added while stirring, and an adhesive-modified coating solution was obtained.

(Example 1)

<Production of the polarizer protective polyester film 1>

As a raw material for an intermediate layer of a base film, 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing ultraviolet absorbers were dried under reduced pressure at 135 ° C for 6 hours (1 Torr). Then, it was supplied to extruder 2 (for the middle layer II layer), and PET (A) was dried by a conventional method, and then supplied to extruder 1 (for the outer layer I layer and the outer layer III layer), respectively, and dissolved at 285 ° C. Each of these two polymers was filtered with a filter medium (nominal filtration accuracy of 10 µm particles, 95% cut) of a stainless sintered body, and laminated with two types of three-layer confluence blocks to form a sheet from custody. After extruding as, it was wound on a casting drum having a surface temperature of 30 ° C. and solidified by cooling using an electrostatically applied casting method to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the ratio of the thicknesses of the I layer, the II layer, and the III layer was 10:80:10.

Subsequently, the adhesive-modified coating solution was applied on both surfaces of this unstretched PET film by a reverse roll method so that the applied amount after drying was 0.08 g / m 2, and then dried at 80 ° C. for 20 seconds.

The unstretched film on which this coating layer was formed was guided to a tenter stretching machine, and the end of the film was gripped with a clip, guided to a hot-air zone at a temperature of 105 ° C, and stretched 4.0 times with TD. Next, heat treatment is performed at a temperature of 180 ° C. for 30 seconds, and then the film cooled to 100 ° C. is stretched by 1.0% in the width direction, and then a clip holding both ends of the film cooled to 60 ° C. is opened. And then withdrawn at a tension of 350 N / m, a jumbo roll made of a uniaxially oriented PET film having a film thickness of about 80 µm was collected, and the obtained jumbo roll was divided into three equal parts, and three slit rolls (L (left), C (center) ), R (right)). The polarizer protective polyester film 1 was obtained from the slit roll located at R. In the polyester film 1 for polarizer protection, the direction in which the heat shrinkage ratio is maximum was 7.0 degrees from TD.

<Preparation of liquid crystal panel>

The polarizer protective polyester film 1 was attached to one side of the polarizer made of PVA, iodine and boric acid so that the transmission axis of the polarizer and the TD of the polarizer protective polyester film 1 were parallel. Moreover, a TAC film (Fujifilm Co., Ltd. product, thickness of 80 µm) was attached to the opposite side of the polarizer to prepare a light source side polarizing plate.

A liquid crystal panel was taken out from a 46-inch IPS IPS liquid crystal TV using a 0.4 mm thick glass substrate for a liquid crystal cell. Remove the light source side polarizing plate from the liquid crystal panel, and instead, replace the light source side polarizing plate created above so that the transmission axis of the polarizer coincides with the transmission axis direction (parallel to the horizontal direction) of the light source side polarizing plate before being removed. A liquid crystal panel was created by interposing and attaching to a liquid crystal cell.

In addition, the light source-side polarizing plate was pasted to the liquid crystal cell so that the polarizer protective polyester film 1 was distal to the liquid crystal cell (opposite side). Moreover, the TAC film was laminated | stacked on both surfaces of a polarizer on the viewer side, and was attached to the liquid crystal cell so that the absorption axis direction of a polarizer was parallel to a horizontal direction.

(Example 2)

<Preparation of polarizer protective polyester film 2>

In the film formation of the polyester film 1 for polarizer protection of Example 1, the film cooled to 100 degreeC was made like the polyester film 1 for polarizer protection except having made 1.5% stretch in the width direction, and the polyester film 2 for polarizer protection was obtained. In the polyester film 2 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 6.5 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, the liquid crystal panel was produced like Example 1 except having replaced the polarizer protective polyester film 1 with the polarizer protective polyester film 2.

(Example 3)

<Preparation of polarizer protective polyester film 3>

In the film forming of the polyester film 1 for protecting polarizers of Example 1, the polarizer protective film 3 was obtained like the polarizer protective polyester film 1 except that the film cooled to 100 degreeC was made 1.7% stretch in the width direction. In the polyester film 3 for polarizer protection, the direction in which the heat shrinkage ratio was maximized was 5.3 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, a liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting the polarizer was replaced with the polyester film 3 for protecting the polarizer.

(Example 4)

<Production of the polarizer protective polyester film 4>

In the film forming of the polyester film 1 for polarizer protection of Example 1, the film cooled to 100 ° C. was stretched by 2.0% in the width direction, poly was stretched at a temperature of 180 ° C. for 30 seconds after heat treatment by TD for 4 times, and poly A polarizer protective film 4 was obtained in the same manner as in the polyester film 1 for polarizer protection, except that a hard coat layer coating solution was applied to one side of the ester film. In the polyester film 4 for polarizer protection, the direction in which the heat shrinkage ratio became maximum was 4.8 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, the liquid crystal panel was produced like Example 1 except having replaced the polarizer protective polyester film 1 with the polarizer protective polyester film 4.

(Example 5)

<Preparation of polarizer protective polyester film 5>

By adjusting the rotation speed of the casting roll, a polyester film 5 for polarizer protection was obtained in the same manner as the polyester film 4 for polarizer protection, except that the film thickness after stretching was 160 μm. In the polyester film 5 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 4.8 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, a liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting the polarizer was replaced with the polyester film 5 for protecting the polarizer.

(Example 6)

<Preparation of polarizer protective polyester film 6>

In the film formation of the polyester film 1 for polarizer protection of Example 1, the film cooled to 100 degreeC was made similar to the polyester film 1 for polarizer protection except having made 1.5% stretch in the flow direction, and the polyester film 6 for polarizer protection was obtained. In the polyester film 6 for polarizer protection, the direction in which the heat shrinkage ratio became maximum was 9.0 degrees from MD.

<Preparation of liquid crystal panel>

In the preparation of the polarizing plate on the light source side of Example 1, instead of the polyester film for protecting the polarizer, the polyester film 6 for protecting the polarizer was used, and the transmission axis of the polarizer and the MD of the polyester film 6 for protecting the polarizer were attached so as to be parallel. A liquid crystal panel was produced in the same manner as in Example 1 except that the polarizing plate was prepared.

(Example 7)

<Preparation of polarizer protective polyester film 7>

In the film formation of the polyester film 1 for polarizer protection of Example 1, the film cooled to 100 degreeC was made similar to the polyester film 1 for polarizer protection except having made it 1.7% stretch in the flow direction, and the polyester film 7 for polarizer protection was obtained. In the polyester film 7 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 8.3 degrees from MD.

<Preparation of liquid crystal panel>

In Example 6, a liquid crystal panel was produced in the same manner as in Example 6, except that the polarizer protective polyester film 6 was replaced with the polarizer protective polyester film 7.

(Example 8)

<Preparation of polarizer protective polyester film 8>

In the film formation of the polyester film 1 for polarizer protection of Example 1, the film cooled to 100 degreeC was made like the polyester film 1 for polarizer protection except having made it 2.0% stretch in the flow direction, and the polyester film 8 for polarizer protection was obtained. In the polyester film 8 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 7.0 degrees from MD.

<Preparation of liquid crystal panel>

In Example 6, a liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for protecting the polarizer was replaced with the polyester film 8 for protecting the polarizer.

(Example 9)

<Preparation of polarizer protective polyester film 9>

By adjusting the rotational speed of the casting roll, a polyester film for polarizer protection 9 was obtained in the same manner as the polyester film for polarizer protection 8 except that the film thickness after stretching was 160 μm. In the polyester film 9 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 7.0 degrees from MD.

<Preparation of liquid crystal panel>

In Example 6, a liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for protecting the polarizer was replaced with the polyester film 9 for protecting the polarizer.

(Example 10)

<Production of the polarizer protective polyester film 10>

A polarizer protective film 10 was obtained in the same manner as in the polyester film 6 for polarizer protection, except that the thing that was stretched 4.0 times in TD was changed to 4.0 times in MD and 1.0 times in TD. In the polyester film 10 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 8.7 degrees from MD.

<Preparation of liquid crystal panel>

In Example 6, a liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for protecting the polarizer was replaced with the polyester film 10 for protecting the polarizer.

(Example 11)

<Production of polyester film 11 for polarizer protection>

In the film forming of the polyester film 10 for protecting polarizers of Example 10, a polyester film 11 for polarizer protections was obtained in the same manner as the polyester film 10 for polarizer protections except that the film cooled to 100 ° C was stretched 1.7% in the flow direction. In the polyester film 11 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 7.5 degrees from MD.

<Preparation of liquid crystal panel>

In Example 10, a liquid crystal panel was produced in the same manner as in Example 10, except that the polarizer protective polyester film 10 was replaced with the polarizer protective polyester film 11.

(Example 12)

<Preparation of polarizer protective polyester film 12>

In the film forming of the polyester film 10 for protecting polarizers of Example 10, the polarizer protective polyester film 12 was obtained in the same manner as the polarizer protective polyester film 10 except that the film cooled to 100 ° C was stretched 5.0% in the width direction. In the polyester film 12 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 1.8 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, a liquid crystal panel was produced in the same manner as in Example 1 except that the polarizer protective polyester film 1 was replaced with the polarizer protective polyester film 12.

(Example 13)

<Production of the polarizer protective polyester film 13>

By adjusting the rotation speed of the casting roll, a polyester film 13 for polarizer protection was obtained in the same manner as the polyester film 4 for polarizer protection, except that the film thickness after stretching was 60 µm. In the polyester film 13 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 4.8 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, a liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting the polarizer was replaced with the polyester film 13 for protecting the polarizer.

(Example 14)

<Preparation of polarizer protective polyester film 14>

In the cooling step after stretching by 1.7% in the width direction, the polarizer protective film 14 was obtained in the same manner as the polarizer protective film 3 except that the clip width holding both ends of the film was changed without changing. In the polyester film 14 for polarizer protection, the direction in which the heat shrinkage ratio was maximized was 33.0 degrees from TD.

<Preparation of liquid crystal panel>

The liquid crystal panel was produced like Example 3 except having replaced the polarizer protective film 1 with the polarizer protective film 14.

(Comparative Example 1)

<Production of the polarizer protective polyester film 15>

By adjusting the rotational speed of the casting roll, the film thickness after stretching was set to 200 µm, similar to that of the polarizer protective film 1, except that the film width at both ends of the film was kept unchanged in the cooling step after stretching and heat fixing. Thereby, a polarizer protective film 15 was obtained. In the polyester film 15 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 20.0 degrees from MD.

<Preparation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1, except that the polarizer protective film 1 was replaced with the polarizer protective film 15, and the transmission axis of the polarizer and the MD of the polarizer protective film were parallel to each other to prepare a polarizing plate on the light source side.

(Comparative Example 2)

<Production of the polarizer protective polyester film 16>

In the cooling step after stretching and heat fixation, the polarizer protective film 16 was obtained in the same manner as the polarizer protective film 1, except that the clip holding both ends of the film was released at 95 ° C without stretching treatment in the width direction at 1.0%. . In the polyester film 16 for polarizer protection, the direction in which the heat shrinkage ratio became maximum was 1.0 degrees from MD.

<Preparation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1, except that the polarizer protective film 1 was replaced with the polarizer protective film 16, and the transmission axis of the polarizer and the MD of the polarizer protective film were parallel to each other to prepare a light source side polarizing plate.

(Comparative Example 3)

<Production of the polarizer protective polyester film 17>

By adjusting the rotation speed of the casting roll, a polyester film for polarizer protection 17 was obtained in the same manner as in the polyester film for polarizer protection except that the film thickness after stretching was 50 μm. The direction in which the heat shrinkage ratio was the maximum in the polyester film 17 for polarizer protection was 7.0 degrees from TD.

<Preparation of liquid crystal panel>

In Example 1, a liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting the polarizer was replaced with the polyester film 17 for protecting the polarizer.

(Comparative Example 4)

<Preparation of polarizer protective polyester film 18>

By adjusting the rotation speed of the casting roll, a polyester film for polarizer protection 18 was obtained in the same manner as the polyester film for polarizer protection 11 except that the film thickness after stretching was 160 μm. In the polyester film 18 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 6.5 degrees from MD.

<Preparation of liquid crystal panel>

In Example 11, the liquid crystal panel was produced like Example 11 except having replaced the polarizer protective polyester film 11 with the polarizer protective polyester film 18.

(Comparative Example 5)

<Production of the polarizer protective polyester film 19>

By adjusting the rotational speed of the casting roll, the film thickness after stretching was set to 160 μm, in the film forming of the polyester film 1 for polarizer protection in Example 1, the film cooled to 100 ° C. was drawn at 1.0% in the flow direction. A polyester film for polarizer protection 19 was obtained in the same manner as in the polyester film for polarizer protection except 1. The direction in which the heat shrinkage ratio was the maximum in the polyester film 19 for polarizer protection was 11.0 degrees from MD.

<Preparation of liquid crystal panel>

In the preparation of the light source-side polarizing plate of Example 1, instead of the polarizer protective polyester film, the polarizer protective polyester film 19 was used, and the transmission axis of the polarizer and the TD of the polarizer protective polyester film 19 were attached in parallel to the light source side. A liquid crystal panel was produced in the same manner as in Example 1 except that the polarizing plate was prepared.

(Comparative Example 6)

<Preparation of polarizer protective polyester film 20>

By adjusting the rotational speed of the casting roll, a polarizer protective polyester film 20 was obtained in the same manner as the polarizer protective polyester film 19 except that the film thickness after stretching was 80 μm. In the polyester film 20 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 11.0 degrees from MD.

<Preparation of liquid crystal panel>

In Comparative Example 5, a liquid crystal panel was prepared in the same manner as in Comparative Example 5, except that the polarizer protective polyester film 19 was replaced with the polarizer protective polyester film 20.

(Comparative Example 7)

<Production of the polarizer protective polyester film 21>

A polarizer protective film 21 was obtained in the same manner as the polarizer protective film 20. In the polyester film 21 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 11.0 degrees from MD.

<Preparation of liquid crystal panel>

In the preparation of the light-source-side polarizing plate of Example 1, instead of the polarizer protective polyester film 1, the polarizer protective polyester film 21 was used, and the transmission axis of the polarizer and the MD of the polarizer protective polyester film 21 were attached so as to be parallel to the light source A liquid crystal panel was produced in the same manner as in Example 1 except that the side polarizing plate was prepared.

(Comparative Example 8)

<Preparation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1, except that the polarizer protective film 15 was pasted so that the transmission axis of the polarizer and the TD of the polarizer protective film were parallel to prepare a light source side polarizing plate.

(Comparative Example 9)

<Preparation of polarizer protective polyester film 22>

By adjusting the rotational speed of the casting roll, the film thickness after stretching was set to 160 μm, in the film forming of the polyester film 1 for polarizer protection in Example 1, the film cooled to 100 ° C. was drawn at 1.0% in the flow direction. Except for the polarizer protective polyester film 1, a polarizer protective polyester film 22 was obtained. In the polyester film 22 for polarizer protection, the direction in which the heat shrinkage ratio becomes maximum was 11.0 degrees from MD.

<Preparation of liquid crystal panel>

In the preparation of the light-source-side polarizing plate of Example 1, instead of the polarizer protective polyester film 1, the polarizer protective polyester film 22 was used, and the transmission axis of the polarizer and the MD of the polarizer protective polyester film 22 were attached so as to be parallel to the light source A liquid crystal panel was produced in the same manner as in Example 1 except that the side polarizing plate was prepared.

(Comparative Example 10)

<Production of the polarizer protective polyester film 23>

In the film forming of the polyester film 10 for polarizer protection of Example 10, the polarizer protective polyester film 23 was obtained in the same manner as the polyester film 10 for polarizer protection except that the film cooled to 100 ° C. was stretched by 2.0% in the flow direction. In the polyester film 23 for polarizer protection, the direction in which the heat shrinkage ratio became maximum was 4.5 degrees from MD.

<Preparation of liquid crystal panel>

In Example 10, the liquid crystal panel was produced like Example 10 except having replaced the polarizer protective polyester film 10 with the polarizer protective polyester film 23.

[Table 1]

From the results shown in Table 1, it was recognized that the polarizing plate using the polarizer protective film according to the present invention can suppress the warpage of the panel compared to the polarizing plate of the comparative example.

(Examples 1A to 5A and 13A)

In addition, the same procedure as in Examples 1 to 5 and 13 was performed except that the polarizing plates having the same configuration as the light source side polarizing plates used in the respective examples of Examples 1 to 5 and 13 were used for both polarizing plates as the light source side polarizing plate and the viewing side polarizing plate. When evaluated separately, as in the results of Examples 1 to 5 and 13 in Table 1 above, good results (○) were obtained in the evaluation of the warpage of the panel. In addition, the light source side polarizing plate and the viewing side polarizing plate were pasted to the liquid crystal cell so that the polarizer protective polyester film was distal to the liquid crystal cell (opposite side).

(Examples 1B to 5B and 13B)

Examples 1A to 5A and 13A were also evaluated separately in the same manner as in Examples 1A to 5A and 13A, except that the TAC film was not used as the polarizer protective film on the liquid crystal cell side. Like Examples 1A to 5A and 13A, good results (○) were obtained in the evaluation of the warpage of the panel.

ADVANTAGE OF THE INVENTION According to this invention, the polarizer protective film, a polarizing plate, and a liquid crystal display device which can suppress curvature of a liquid crystal panel can be provided.

Claims (11)

A polarizing plate in which a polarizer protective polyester film that satisfies the following requirements (1) and (2) is laminated on one side of the polarizer:
(1) The shrinkage force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer is 800 N / m or more and 9000 N / m or less (however, the shrinkage force F _f (N / m) is the thickness of the polyester film) (Mm) × elastic modulus (N / mm 2) × 80 ° C., 30 minutes heat shrinkage of treatment (%) ÷ 100 × 1000, where the modulus of elasticity of the polyester film in the direction parallel to the transmission axis of the polarizer Elastic modulus, and heat shrinkage is the heat shrinkage of the polyester film in a direction parallel to the transmission axis of the polarizer.)
(2) The ratio (F _f / F) of the shrinking force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer and the shrinking force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer _v ) is 2.5 or more and 12.0 or less (however, shrinkage force F _v (N / m) is the thickness (mm) of the polyester film x modulus of elasticity (N / mm) x heat shrinkage of the treatment at 80 ° C for 30 minutes (%) ÷ Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer, and the thermal shrinkage is the thermal shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer. to be.). According to claim 1,
A polarizing plate in which the polyester film further satisfies the following requirement (3):
(3) The direction in which the heat shrinkage rate of the polyester film becomes maximum and the direction parallel to the transmission axis of the polarizer are approximately parallel. The method of claim 1 or 2,
A polarizing plate in which the polyester film has a retardation of 3000 to 30000 nm. The method according to any one of claims 1 to 3,
The polarizing plate, characterized in that the thickness of the polyester film is 40 ~ 200㎛. The method according to any one of claims 1 to 4,
The polarizing plate which has a hard-coat layer, an anti-reflection layer, a low-reflection layer, an anti-glare layer, or an anti-reflection anti-glare layer on the surface of the polyester film on the side opposite to the surface on which the polarizer is laminated. The method according to any one of claims 1 to 5,
A polarizing plate in which a TAC film, an acrylic film, or a norbornene film is laminated on the other side of the polarizer. The method according to any one of claims 1 to 5,
A polarizing plate having no film on the other side of the polarizer. The method according to any one of claims 1 to 5,
A polarizing plate in which a coating layer is laminated on the other side of the polarizer. The method of claim 8,
The coating layer is a hard coat layer or a retardation film polarizing plate. The method according to any one of claims 1 to 9,
The polarizing plate has a rectangular shape, and the long side of the polarizing plate and its transmission axis are parallel. A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates, wherein at least one of the two polarizing plates is a polarizing plate according to any one of claims 1 to 10.