JP2023143934A - Polarizer protective film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

To provide a polarizer protective film, a polarizing plate, and a liquid crystal display device with which it is possible to suppress the warp of a liquid crystal panel.SOLUTION: Provided is a polyester film for polarizer protection that is laminated on one plane of a polarizer, the polyester film for polarizer protection satisfying the requirements (1) and (2) below. (1) The contractive force Ff of the polyester film in a direction parallel to the transmission axis of the polarizer is 800 N/m to 9000 N/m inclusive; (2) The ratio (Ff/Fv) of the contractive force Ff of the polyester film in a direction parallel to the transmission axis of the polarizer to the contractive force Fv of the polyester film in a direction parallel to the absorption axis of the polarizer is 2.5 to 12.0 inclusive.SELECTED DRAWING: None

Description

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

Demand for liquid crystal display devices is increasing for applications such as liquid crystal displays in liquid crystal televisions and personal computers. Normally, a liquid crystal display device consists of a liquid crystal cell with transparent electrodes, a liquid crystal layer, a color filter, etc. sandwiched between glass plates, and two polarizing plates installed on both sides of the cell. The polarizer (also referred to as a polarizing film) is sandwiched between two optical films (for example, a polarizer protective film and a retardation film).

By the way, in recent years, LCD TV screens have become thinner and larger, and LED backlights have become used as light sources, and the thickness of the glass substrate used in LCD panels has become thinner than 0.7 mm. Along with this, a problem arises in which display unevenness occurs, and an improvement is required.
The main cause of display unevenness is the shrinkage of the polarizer. When the polarizer is placed under high temperature and high humidity, the shrinkage force is generated in the orientation direction as it tries to relax the orientation. It is believed that this causes the liquid crystal panel to warp and bulge toward the backlight unit, resulting in uneven display.

In addition, conventionally, as shown in Patent Document 1 and Patent Document 2 below, the thickness of the glass substrate used in the liquid crystal panel was as thick as 0.7 mm or more, so the shrinkage of the polarizer was suppressed due to the high rigidity of the glass. Therefore, the liquid crystal panel did not warp, and display unevenness did not become a problem.

Therefore, attempts have been made to use optical films to improve the warping of liquid crystal panels that occurs when glass substrates are made thinner than 0.7 mm.
For example, when a cycloolefin resin is used as a polarizer protective film, the warping of the liquid crystal panel is not sufficiently improved, and the water glue used to adhere to the polarizer has poor drying properties.
There was a problem that productivity decreased.
Further, when conventional triacetyl cellulose (TAC) was used as a polarizer protective film, there was a problem that the liquid crystal panel warped.

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

The present invention was made in view of the above problems and circumstances, and an object to be solved is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device that can suppress warping of a liquid crystal panel.

In order to solve the above problem, in the process of investigating the causes of the above problem, the present inventors determined that the shrinkage force of the polyester film for protecting the polarizer in the direction parallel to the transmission axis of the polarizer was within a specific range. , discovered that it is possible to improve the warpage of liquid crystal panels,
Based on this knowledge, we have arrived at the present invention.

Specifically, in a liquid crystal display device, a polarizing plate is usually laminated on one side of a liquid crystal cell so that the transmission axis direction of the polarizer is parallel to the long side direction of the liquid crystal display device, and on the other side, Polarizing plates are stacked so that the absorption axis direction of the polarizer is parallel to the long side of the liquid crystal display device. As a result of intensive studies using various commercially available liquid crystal display devices, we found that the shape factor problem (curl (generally tends to occur in the long side direction) and due to the asymmetric configuration of the upper and lower polarizing plates in the liquid crystal panel, the polarizer transmission axis of the upper and lower polarizing plates arranged in crossed Nicols is aligned with the long side The present inventors have discovered that the essence of the problem is that the polarizing plate becomes convex.

Furthermore, as a result of extensive research, it became clear that the shrinkage force in the long side direction of the polarizing plate, where the polarizer transmission axis is the long side, can be controlled by the residual strain of the protective film, and by this shrinkage force,
It turns out that it is possible to control the curl of the liquid crystal panel.

Here, a method for measuring the shrinkage force of a polyester film for protecting a polarizer will be described. Generally, the shrinkage force of a film is measured by using TMA etc. to set the initial length under a minimal load at a low temperature at the start of the test, and then measuring the force in the shrinkage direction while the temperature is rising while maintaining the initial length. do. However, during the heating process, the polymer shrinks due to recovery of residual strain accompanied by a conformational change (
At the same time, thermal expansion (hereinafter simply referred to as thermal expansion) occurs due to an increase in the free volume and occupied volume of the polymer as the temperature rises, so the glass transition temperature of the polyester film In a temperature range around (for example, about Tg+50°C), the relationship of thermal contraction < thermal expansion is often established, so the film as a whole expands and no contraction force is observed.

As a result of the study, it was revealed that even if no contraction force is generated during the TMA temperature raising process, a contraction force is generated during the TMA cooling process. This is because the strain caused by thermal expansion is a reversible change, so it returns to its original state after heating and cooling. However, because it is cooled in a state where the dimensions are smaller by the amount of thermal contraction caused by the thermal contraction during the heating process, thermal stress is caused during the cooling process. This is because In other words, the distortion of thermal stress can be replaced by the thermal shrinkage rate of the film, and the shrinkage force after cooling is expressed by the following formula. Note that the heat shrinkage rate in the present invention includes the change in moisture content during heat treatment.
Shrinkage force (N/m) = Film thickness (mm) x Elastic modulus (N/mm ² ) x Heat shrinkage rate (%) ÷
100×1000

That is, a typical present invention is as follows.
Item 1.
A polyester film for protecting a polarizer that is laminated on one side of a polarizer and that satisfies 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) of the polyester film is Thickness (mm) x elastic modulus (N/mm ² ) x heat shrinkage rate (%) after treatment at 80°C for 30 minutes ÷ 100 x 1000. Here, the elastic modulus is the direction parallel to the transmission axis of the polarizer. is the elastic modulus of the polyester film, and the heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer.)
(2) The _ratio ( _F
f /F _v ) is 2.5 or more and 12.0 or less (however, the shrinkage force F _v (N/m) is calculated by polyester film thickness (mm) x elastic modulus (N/mm ² ) x 80°C. Heat shrinkage rate (%) after 30 minutes treatment ÷ 100 x 1000. Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer; It is the heat shrinkage rate of polyester film in the direction parallel to the absorption axis of
Item 2.
Item 1. The polyester film for protecting a polarizer according to item 1, which further satisfies the following requirement (3).
(3) Item 3. The direction in which the polyester film has a maximum heat shrinkage rate and the direction parallel to the transmission axis of the polarizer are substantially parallel.
Item 1: The polyester film has a retardation of 3000 to 30000 nm.
Or the polyester film for protecting a polarizer according to 2.
Item 4.
Items 1 to 3, wherein the polyester film has a thickness of 40 to 200 μm.
The polyester film for protecting a polarizer according to any one of the above.
Item 5.
Items 1 to 4, wherein the polyester film has a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, or an antireflection and antiglare layer on the surface opposite to the surface on which the polarizer is laminated. The polyester film for protecting a polarizer according to any one of the above.
Item 6.
A polyester film for protecting a polarizer that is laminated on one side of a polarizer and that satisfies the following requirements (1) and (2).
(1) TD shrinkage force F of the polyester film _TD is 800 N/m or more and 9000 N/m
m or less (however, the shrinkage force F _TD (N/m) is the thickness of the polyester film (mm
) × elastic modulus (N/mm ² ) × heat shrinkage rate (%) of treatment at 80° C. for 30 minutes ÷ 100 × 1000. Here, the elastic modulus is the TD elastic modulus of the polyester film, and the heat shrinkage rate is the TD heat shrinkage rate of the polyester film. )
(2) Shrinkage force F of TD of the polyester film _TD and M of the polyester film
The ratio of shrinkage force F _MD (F _TD /F _MD ) of D is 2.5 or more and 12.0 or less (however, shrinkage force F _MD (N/m) is the thickness (mm) of the polyester film x elastic modulus (N/ ^mm2 )
x Heat shrinkage rate (%) of treatment at 80°C for 30 minutes ÷ 100 x 1000. Here, the elastic modulus is
It is the MD elastic modulus of the polyester film, and the heat shrinkage rate is the MD elastic modulus of the polyester film.
is the heat shrinkage rate. )
Section 7.
Item 6. The polyester film for protecting a polarizer according to item 6, which further satisfies the following requirement (3).
(3) Item 8. TD is approximately parallel to the direction in which the polyester film has a maximum heat shrinkage rate.
A polarizing plate comprising a polarizer protective polyester film according to any one of Items 1 to 7 laminated on at least one surface of the 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 the polarizer, and the other surface of the polarizer does not have a film.
Item 10.
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.
Polarizing plate described in .
Item 11.
A liquid crystal display device comprising a backlight source and a liquid crystal cell disposed between two polarizing plates, wherein at least one of the two polarizing plates is the polarizing plate according to any one of items 8 to 10. LCD display device.

According to the present invention, it is possible to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device that can suppress warping of a liquid crystal panel.

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

In this specification, the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer means 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. It is.
The heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer means the heat shrinkage rate 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 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.
Further, the shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer means the shrinkage 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 heat shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer means the heat shrinkage rate of the polyester film in the direction parallel to the absorption 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 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 simply referred to as the transmission axis direction of the polarizer. Further, the direction parallel to the absorption axis of the polarizer may be simply referred to as the absorption axis direction of the 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 maximum are substantially parallel. Being substantially parallel means that the absolute value of the angle between the transmission axis direction of the polarizer and the direction in which the heat shrinkage rate of the polyester film is maximum (hereinafter sometimes simply referred to as the slope of the heat shrinkage rate) is It is allowed to be below 15 degrees. 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, even more preferably 6 degrees or less, particularly preferably 4 degrees or less. and most preferably 2 degrees or less. Since it is preferable that the slope of the thermal shrinkage rate is as small as possible, the lower limit is 0 degrees. If the slope of the heat shrinkage rate of the polyester film is large, the polarizing plate containing the polyester film will warp in an oblique direction, and the effect of reducing warpage of the liquid crystal panel will tend to weaken.
However, the _ratio (F _{f /} F
_v ) is 2.5 or more and 12.0 or less, 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 maximum is 40 degrees or less. It is also possible to reduce warping of the liquid crystal panel. Said angle is preferably less than or equal to 35 degrees.
The heat shrinkage rate of the polyester film, the slope of the heat shrinkage rate of the polyester film, and the direction in which the heat shrinkage rate of the polyester film is maximum can be measured by the method adopted in the Examples described below.

Usually, in a liquid crystal display device, two polarizing plates are arranged in a crossed nicol relationship. When two polarizing plates are arranged in a crossed nicol relationship, light usually does not pass through the two polarizing plates. However, due to the shrinkage or warping of the polarizer as described above, the perfect crossed Nicol relationship may be broken as a result, and light leakage may occur. From the viewpoint of suppressing light leakage, it is preferable that the angle between the direction in which the polarizer protective film has the maximum thermal shrinkage rate and the transmission axis of the polarizer is small.

In the polyester film for protecting a polarizer of the present invention, it is desirable that the value of the shrinkage force Ff 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. If the lower limit of F _f is less than 800 N/m, there is a possibility that warpage of the liquid crystal panel cannot be sufficiently reduced. Furthermore, if the upper limit of F _f exceeds 9000 N/m, the shrinkage force may be too strong and the liquid crystal panel may warp in the opposite direction. The preferred range of contractile force is 900 N/m or more and 8000 N/m or less, more preferably 1000 N/m or more and 800 N/m or more.
00 N/m or less, more preferably 1100 N/m or more and 8000 N/m or less, even more preferably 1200 N/m or more and 8000 N/m or less. Note that the upper limit is 6
000 N/m or less, 5500 N/m or less, and 4800 N/m or less are preferable.

Here, the shrinkage force F _f refers to the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer, and is calculated by polyester film thickness (mm) x elastic modulus (N/mm ² ) x 80°C.
- Defined as heat shrinkage rate (%) after 30 minutes treatment ÷ 100 x 1000.
Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer. Moreover, the heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer (heat shrinkage rate after heat treatment at 80° C. for 30 minutes).

Let F _v be the shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer.
Shrinkage force _Fv is calculated by polyester film thickness (mm) x elastic modulus (N/mm ² ) x 80°C.
It is defined as heat shrinkage rate (%) after 30 minutes treatment/100×1000. Here, the elastic modulus refers to the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The heat shrinkage rate is the heat shrinkage rate (80℃) of the polyester film in the direction parallel to the absorption axis of the polarizer.
・Heat shrinkage rate after 30 minutes of heat treatment).

It is preferable that the polyester film for protecting a polarizer of the present invention has F _f /F _v of 1.0 or more and 12.0 or less. More preferably, it is 2.5 or more and 12.0 or less. If the lower limit value of F _f /F _v is less than 1.0, there is a possibility that warpage of the liquid crystal panel cannot be sufficiently reduced.
In addition, if the upper limit of F _f /F _v exceeds 12.0, thermal deformation in one direction becomes large, and the polarizer cannot be laminated on the side opposite to the side on which the polyester film for protecting the polarizer is laminated. There is a risk that stress will be applied to the protective film and retardation film, which may deteriorate display quality. Furthermore, the stability of film formation may decrease and breakage may occur.

Examples of a method for controlling the shrinkage force within the range of the above formula include a method of stretching the film again while controlling the winding tension of the film after the heat treatment step after stretching the film is completed.

The polyester film for protecting a polarizer of the present invention preferably has an elastic modulus of 1000 to 9000 N/mm ² in the transmission axis direction of the polarizer. Although the shrinkage force of a polyester film can be controlled by its elastic modulus, in order to increase the elastic modulus of the polyester film in the direction of the transmission axis of the polarizer, the polyester film must be highly oriented in the direction of the transmission axis of the polarizer, and It is necessary to increase the degree of crystallinity. Therefore, if the elastic modulus of the polyester film in the transmission axis direction of the polarizer exceeds 9000 N/mm ² , there is a risk that it will tear easily, so the upper limit is preferably 9000 N/mm ² , more preferably 80 N/mm 2 .
00N/mm ² , more preferably 7000N/mm ² .
On the other hand, if the orientation is low and the degree of crystallinity is low, the film may be deformed due to roll unevenness caused by uneven thickness when wound onto a 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 more preferably 1800N/mm ² . The elastic modulus can be measured by the method adopted in the examples described below.

The polyester film for protecting a polarizer of the present invention preferably has a heat shrinkage rate of 0.10 to 5.0% when the polyester film is heat-treated at 80° C. for 30 minutes in the transmission axis direction of the polarizer. The lower limit of the heat shrinkage rate 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, and 4.
It is more preferably 0% or less, even more preferably 3.0% or less, even more preferably 2% or less, and most preferably 1.4% or less. If the heat shrinkage rate is lower than 0.10%, that is, 0.0
In the range of 1 to 0.099%, it may be difficult to control the heat shrinkage rate without variation. Further, in order to increase the thermal shrinkage rate to more than 5.0%, it is necessary to further lower the degree of crystallinity and the glass transition temperature, which may cause problems such as poor flatness. Thermal shrinkage rate can be measured by the method adopted in the examples described later.

The thickness of the polyester film for protecting a polarizer of the present invention is preferably 40 to 200 μm, more preferably 40 to 100 μm, and still more preferably 40 to 80 μm. When the thickness of the polyester film is less than 40 μm, it tends to be easily broken and to have poor flatness due to insufficient rigidity. In addition, if the film is thin, it is necessary to increase the elastic modulus or thermal shrinkage rate of the polyester film in the transmission axis direction of the polarizer.
Since each parameter has an upper limit as described above, the lower limit is substantially 40 μm. In addition, if the thickness of the film exceeds 200 μm, the variation in the elastic modulus or heat shrinkage rate of the polyester film in the direction of the transmission axis of the polarizer increases accordingly, which may be difficult to control, and may be costly. will also rise. The thickness of the polyester film can be measured by the method employed in the examples described below.

The polyester film for protecting a polarizer of the present invention preferably has an in-plane retardation within a specific range from the viewpoint of suppressing iridescence observed on the screen of a liquid crystal display device. The lower limit of in-plane retardation is 3000 nm or more, 5000 nm or more, 6000 nm or more, and 700 nm or more.
It is preferably 0 nm or more, or 8000 nm or more. The upper limit of the in-plane retardation is preferably 30,000 nm or less, more preferably 18,000 nm or less, even more preferably 15,000 nm or less. In particular, from the perspective of thinning the film, the in-plane retardation is 100
It is preferably less than 000 nm and 9000 nm or less.

The retardation of a polyester film can be determined by measuring the refractive index and thickness in two axial directions, or can be determined using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). Note that the refractive index can be determined using an Abbe refractometer (measurement wavelength: 589 nm).

The polyester film for protecting a polarizer of the present invention has a ratio (Re/Rth) of in-plane retardation (Re) to thickness direction retardation (Rth), preferably 0.2 or more, preferably 0.3 or more, Preferably it is 0.4 or more, more preferably 0.5 or more, still more preferably 0.6 or more. The ratio of the in-plane retardation to the thickness direction retardation (Re/R
th) is larger, the effect of birefringence becomes more isotropic, and it tends to be less likely that rainbow-like color spots will occur depending on the viewing angle. In a completely uniaxial (uniaxially symmetrical) film, the ratio of the above retardation to the thickness direction retardation (Re/Rth) is 2.0, so the ratio of the above retardation to the thickness direction retardation (Re/Rth) is 2.0. The upper limit is preferably 2.0. A preferable upper limit of Re/Rth is 1.2 or less. Note that the thickness direction retardation means the average of the retardations obtained by multiplying the two birefringences ΔNxz and ΔNyz by the film thickness d when the film is viewed from a cross section in the thickness direction.

The polyester film for protecting polarizers of the present invention has the following features from the viewpoint of further suppressing rainbow-like color spots:
The NZ coefficient of the polyester film is preferably 2.5 or less, more preferably 2.
．． It is 0 or less, more preferably 1.8 or less, even more preferably 1.6 or less. Since the NZ coefficient is 1.0 in a completely uniaxial (uniaxially symmetrical) film, the lower limit of the NZ coefficient is 1.0. However, care must be taken because the mechanical strength in the direction perpendicular to the orientation direction tends to decrease significantly as the film approaches a completely uniaxial (uniaxially symmetrical) film.

The NZ coefficient is expressed as |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 perpendicular to the slow axis (fast axis refractive index in the thickness direction), Nz represents the refractive index in the thickness direction. Molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6
The orientation axis of the film was determined using a molecular orientation meter (Model 004), and the refractive index of the two axes in the direction of the orientation axis and the direction orthogonal thereto (Ny, Nx, where Ny>Nx), and the refractive index in the thickness direction (Nz ) is determined using an Abbe refractometer (manufactured by Atago, NAR-4T, measurement wavelength 589 nm).
The NZ coefficient can be obtained by substituting the value thus obtained into |Ny-Nz|/|Ny-Nx|.

Further, in the polyester film of the present invention, from the viewpoint of further suppressing rainbow-like color spots, the value of Ny-Nx of the polyester film is preferably 0.05 or more, more preferably 0.07.
More preferably, it is 0.08 or more, even more preferably 0.09 or more, and most preferably 0.1 or more. The upper limit is not particularly determined, but in the case of polyethylene terephthalate films, 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 polyester resin is not particularly limited, and any polyester resin obtained by condensing dicarboxylic acid and diol can be used.

Examples of dicarboxylic acid components that can be used in the production of polyester resins include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1 , 5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonedicarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid , hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyl Examples include adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

Examples of diol components that can be used in the production of polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol,
, 2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2 -bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and the like.

Both the dicarboxylic acid component and the diol component constituting the polyester resin are one or two types.
More than one species 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 naphthalate. Furthermore, other copolymerization components may be included. These resins have excellent transparency and thermal,
It also has excellent mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high elastic modulus and the heat shrinkage rate can be controlled relatively easily.

When it is necessary to highly increase the heat shrinkage rate of a polyester film, it is desirable to add a copolymer component to appropriately lower the degree of crystallinity. Furthermore, since the rate of elastic strain and permanent strain is high for deformation at or below the glass transition temperature, it is generally difficult to increase the thermal shrinkage rate to a high degree. Therefore, it is also a preferred embodiment to introduce a component with a low glass transition temperature as necessary. Specific examples include propylene glycol and 1,3-propanediol.

(Adding functional layer)
It is desirable that the polarizing plate using the polyester film for polarizer protection of the present invention be integrated with the glass plate of the liquid crystal cell while the heat shrinkage rate of the polyester film remains.
When adding functional layers such as an easy-adhesion layer, a hard coat layer, an anti-glare layer, an anti-reflection layer, a low-reflection layer, a low-reflection anti-glare layer, an anti-reflection anti-glare layer, a low-reflection anti-glare layer, and an antistatic layer. In this embodiment, it is desirable to set the drying temperature low or to use a method with a small thermal history such as UV irradiation or electron beam irradiation. Furthermore, by adding these functional layers during the polyester film forming process, it becomes 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 rate. Therefore, this is a more desirable embodiment.
Functional layers such as easy adhesion layer, hard coat layer, anti-glare layer, anti-reflection layer, low-reflection layer, low-reflection anti-layer, anti-reflection anti-glare layer, low-reflection anti-glare layer, and antistatic layer are made of polyester film. The polarizer is laminated on the surface opposite to the surface on which the polarizer is laminated, and when these functional layers are laminated, the shrinkage force F _f ,
Preferably, F _v has the conditions described above.

(Method for producing oriented polyester film)
The polyester film used in the present invention can be manufactured according to a general polyester film manufacturing method. For example, a polyester resin is melted, unoriented polyester extruded into a sheet, stretched in the longitudinal direction using a speed difference between rolls at a temperature higher than the glass transition temperature, and then stretched in the transverse direction with a tenter. One example is a method of applying heat treatment (heat setting). It may be a uniaxially stretched film or a biaxially stretched film. Preferably, it is a uniaxially stretched film that is strongly stretched mainly in the transverse direction or a uniaxially stretched film that is strongly stretched mainly in the longitudinal direction, and both may be slightly stretched in a direction perpendicular to the main stretching direction. Note that MD is an abbreviation for Machine Direction, and is sometimes referred to as the film flow direction, longitudinal direction, or vertical direction in this specification. Also, TD means Transverse.
It is an abbreviation for Direction, and is sometimes referred to as the width direction or horizontal direction in this specification.

It is preferable to adjust the film thickness, elastic modulus, and heat shrinkage rate of the polyester film 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 polyester film)
The elastic modulus of the polyester film used as a polarizer protective film is the elastic modulus in MD when the polarizer transmission axis direction matches the MD at the time of film formation of the polyester film, and the elastic modulus in MD that matches the TD at the time of film formation of the polyester film. In this case, the elastic modulus of TD may be adjusted by a conventionally known method for stretched polyester films.
Specifically, when the direction is the stretching direction, the stretching ratio may be set high, and when the direction is perpendicular to the stretching direction, the stretching ratio 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 determined by the MD heat shrinkage rate when the transmission axis direction of the polarizer matches the MD when the polyester film was formed, and the MD heat shrinkage rate when the polyester film was formed. If it matches the TD, the heat shrinkage rate of TD may be adjusted by a conventionally known method for stretched polyester films.

When adjusting the MD heat shrinkage rate of a polyester film, for example, in the cooling process after stretching and heat setting, the distance between the clip that grips the edge of the film in the width direction and the adjacent clip can be increased to stretch the polyester film in the MD. This can be adjusted by shrinking the MD by reducing the clip interval. In addition, in the cooling process after stretching and heat setting, when cutting or separating the film from the clips that grip the ends in the film width direction, the film can be stretched or shrunk in the MD by adjusting the force for pulling the film. It is possible to adjust by In addition, in the offline process after film formation, when the temperature is raised for the purpose of adding a functional layer, etc., the thermal shrinkage rate changes during the heating and cooling process, so the force for drawing the film is adjusted to stretch or shrink it in the MD. It is also possible to adjust by

When adjusting the heat shrinkage rate of the TD of a polyester film, for example, in the cooling process after stretching and heat setting, the interval between the clip holding the end of the film in the width direction and the clip located on the opposite side in the width direction may be adjusted. Adjustments can be made by enlarging the film to stretch it in the TD, or by shrinking it to shrink it in the TD.

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

(How to adjust the inclination of the main axis of contraction of polyester film)
The inclination of the principal axis of contraction of the polyester film used as a polarizer protective film is PCT
As disclosed in /JP2014/073451 (WO2015/037527), it is possible to adjust it in the cooling process after stretching and heat treatment of the polyester film with a tenter or in the offline process after film formation. Specifically, in the cooling process, shrinkage due to stretching and thermal stress due to cooling occur, which could not be completely removed in the heat setting process, and depending on the balance between the two in the film flow direction, it may be pulled upstream or downstream. There is a pull to
A phenomenon occurs in which the principal axis of contraction is tilted. In order to reduce the inclination of the main axis of contraction, it is necessary to adjust the contraction force in the film flow direction (the sum of the contraction force associated with stretching and the contraction force associated with cooling) in the cooling process to be uniform. In order to make the film uniform, it is desirable to shrink the film in a temperature range where the shrinkage force is high in the film flow direction, or to stretch the film in the film flow direction in a temperature range where the shrinkage force is low in the film flow direction. Conventionally known methods may be used for shrinking or stretching. In addition, when cutting or separating the ends of the film, care must be taken because the film will shrink freely in the width direction below the cutting/separation temperature range, and the heat shrinkage rate below the temperature range will be small.

In the polarizing plate, the polyester film for protecting a polarizer of the present invention is laminated on at least one surface of the polarizer. On the other side of the polarizer, TAC film, acrylic film,
It is preferable that a film having no birefringence, such as a norbornene film, is laminated. Alternatively, a polarizing plate in which no film is laminated on the other surface of the polarizer is also a preferable embodiment from the viewpoint of thinness. In this case, a film is not laminated on the other side of the polarizer, but a coating layer may be laminated on the polarizer. The coating layer may be a functional layer such as a hard coat layer, or a retardation film formed by coating.
In addition, when laminating a film or coating layer other than the polyester film for polarizer protection of the present invention on a polarizer, shrinkage 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. The shrinkage force of 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 is preferably equal to or less than the value of F _f of the polyester film for protecting the polarizer, and more preferably Preferably, it is less than or equal to the _Fv value of the polyester film for protecting a polarizer. In addition, the shrinkage force of films and coating layers other than the polyester film for protecting the polarizer in a direction parallel to the transmission axis of the polarizer, and the shrinkage force of films other than the polyester film for protecting the polarizer in the direction parallel to the absorption axis of the polarizer. The shrinkage force of the film or coating layer is preferably 250 N/m or less, more preferably 200 N/m or less. The shrinkage force of films and coating layers other than the polyester film for protecting a polarizer can be measured in the same manner as in the case of polyester films. That is, the thickness (mm) of the film or coating layer x
Elastic modulus (N/mm ² ) x heat shrinkage rate (%) of treatment at 80° C. for 30 minutes ÷ 100 x 1000.

Industrially, a polarizing plate is produced by laminating a long polarizer and a long polarizer protective polyester film in a roll-to-roll manner via an adhesive. Since a polarizer is usually manufactured by being stretched in the longitudinal direction, it has an absorption axis in the MD and a transmission axis in the TD.

Therefore, from the viewpoint of manufacturing a polarizing plate industrially, it is preferable that the polyester film for protecting a polarizer of the present invention has the following (1) and (2).
(1) TD shrinkage force F 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 calculated by polyester film thickness (mm) x elastic modulus (N
/mm ² )×Heat shrinkage rate (%) of treatment at 80° C. for 30 minutes ÷ 100×1000. here,
The elastic modulus and the heat shrinkage rate are the TD elastic modulus and the TD heat shrinkage rate of the polyester film, respectively.
(2) The ratio of the TD shrinkage force F _TD of the polyester film to the MD shrinkage force F _MD of the polyester film (F _TD /F _MD ) is preferably 2.5 or more and 12.0 or less.
However, the shrinkage force F _MD (N/m) is calculated by polyester film thickness (mm) x elastic modulus (
N/mm ² )×Heat shrinkage rate (%) of treatment at 80° C. for 30 minutes ÷ 100×1000. Here, the elastic modulus and heat shrinkage rate are the MD elastic modulus and MD heat shrinkage rate of the polyester film, respectively.

Further, in the polyester film for protecting a polarizer of the present invention, it is preferable that the TD is substantially parallel to the direction in which the polyester film has a maximum heat shrinkage rate.
Being substantially parallel allows that the absolute value of the angle between the direction in which the polyester film has the maximum heat shrinkage rate and the TD direction (the slope of the heat shrinkage rate) 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, even more preferably 6 degrees or less, particularly preferably 4 degrees or less. and most preferably 2 degrees or less. Since it is preferable that the slope of the thermal shrinkage rate is as small as possible, the lower limit is 0 degrees.
However, if the ratio of the TD shrinkage force F _TD of the polyester film to the MD shrinkage force F _MD of the polyester film (F _TD /F _MD ) is 2.5 or more and 12.0 or less, the heat shrinkage rate of the polyester film is Even if the absolute value of the angle between the maximum direction and TD is 40 degrees or less,
Warpage of the liquid crystal panel can be reduced. Said angle is preferably less than or equal to 35 degrees.

In addition, when considering the industrial production of polarizing plates in a roll-to-roll format as described above, _FTD corresponds to _Ff , so the preferable range of _FTD and _Ff The preferred ranges of are the same. Furthermore, since F _TD /F _MD corresponds to F _f /F _v , the preferred ranges for both are the same. Since "the TD elastic modulus of the polyester film" corresponds to "the elastic modulus of the polyester film in the transmission axis direction of the polarizer", the preferred ranges for both are the same. "TD heat shrinkage rate of polyester film when heat treated at 80°C for 30 minutes" corresponds to "heat shrinkage rate of polyester film when heat treated at 80°C for 30 minutes in the transmission axis direction of the polarizer" Therefore, the preferred ranges for both are the same.

A liquid crystal display device includes at least a backlight 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 using the polarizer protective polyester film of the present invention as 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 protecting a polarizer of the present invention has the position of the polarizer protective film on the viewing side starting from the polarizer of the viewing side polarizing plate and/or the polarizer protective film on the light source side starting from the polarizer of the light source side polarizing plate. It is preferably used for.

Usually, a liquid crystal display device has a rectangular shape (the two polarizing plates used in the liquid crystal display device are also rectangular), and the long side and absorption axis of one polarizing plate are parallel to each other, and the other polarizing plate has a rectangular shape. The polarizing plates are arranged such that their long sides and transmission axes are parallel, and their absorption axes are perpendicular to each other.
Generally, a polarizing plate in which the long side of the polarizing plate and the absorption axis are parallel to each other is used as a viewing-side polarizing plate in a liquid crystal display device, and a polarizing plate in which the long side of the polarizing plate and the transmission axis are in parallel to each other is used as a polarizing plate on the viewing side of a liquid crystal display device. is used as a polarizing plate on the light source side of a liquid crystal display device. From the viewpoint of suppressing warping of the liquid crystal panel, it is preferable that the polarizing plate of the present invention is used at least as a polarizing plate in which the long side of the polarizing plate and the transmission axis are parallel to each other. Further, it is also preferable to use the polarizing plate of the present invention for both a polarizing plate in which the long side of the polarizing plate has a parallel relation to the transmission axis and a polarizing plate in which the long side of the polarizing plate has a parallel relation to the absorption axis.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the Examples, and can be carried out with appropriate changes within the scope of the spirit of the present invention. It is also possible to do so, and all of them are included in the technical scope of the present invention.

(1) Contraction force F _f
The shrinkage force F _f of the polyester film was calculated from the following formula. Note that the thickness, elastic modulus, and heat shrinkage rate of the polyester film are measured values explained below. Elastic modulus refers to the elastic modulus of the polyester film in a direction parallel to the transmission axis of the polarizer. The heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer.
Shrinkage force F _f (N/m) = Thickness of polyester film (mm) x elastic modulus (N/mm ² )
× Heat shrinkage rate (%) of treatment at 80°C for 30 minutes ÷ 100 × 1000

(2) Contractile force _Fv
The shrinkage force _Fv of the polyester film was calculated from the following formula. Note that the thickness, elastic modulus, and heat shrinkage rate of the polyester film are measured values explained below. Elastic modulus refers to the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer.
Shrinkage force F _v (N/m) = Thickness of polyester film (mm) x Modulus of elasticity (N/mm ² )
× Heat shrinkage rate (%) of treatment at 80°C for 30 minutes ÷ 100 × 1000

(3) Film thickness The thickness (mm) of the polyester film is measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf Co., Ltd.) after standing for 168 hours in an environment of 25°C and 50RH%, and the unit is converted to mm. did.

(4) Elastic modulus of polyester film The elastic modulus of polyester film is JI
Evaluation was performed using a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments Inc. in accordance with S-K7244 (DMS). The temperature dependence from 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 storage modulus from 30°C to 100°C was calculated. It was taken as the elastic modulus. In this manner, 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.
Note that the above measurements were performed using a single polyester film (a single polyester film for protecting a polarizer).

(5) Heat shrinkage rate and slope of heat shrinkage rate of polyester film After the polyester film was left standing in an environment of 25°C and 50RH% for 168 hours, the diameter was 80 m.
Draw a circle of m, and measure the diameter of the circle using an image size measuring device (Image Measure IM6 manufactured by KEYENCE).
500), measurements were taken every 1°, and the length was taken as the length before treatment. Next, heat treatment was performed for 30 minutes using a gear oven set at 80°C, and then at room temperature set at 25°C for 10 minutes.
After cooling for a minute, evaluation was performed at every 1° in the same manner as before treatment, and the length after treatment was determined. Note that the above treatment was performed on a single polyester film (a single polyester film for protecting a polarizer).

Thermal shrinkage rate was evaluated for each angle using the following calculation formula.
Heat shrinkage rate = (length before treatment - length after treatment) / length before treatment x 100
In this way, the heat shrinkage rate of the polyester film in the direction parallel to the polarizer transmission axis and the heat shrinkage rate of the polyester film in the direction parallel to the polarizer absorption axis were determined.

The above evaluation was performed for 360° every 1°, the direction in which the thermal shrinkage rate was maximum was identified, and the absolute value of the angle between that direction and the transmission axis direction of the polarizer was taken as the slope of the thermal contraction rate. . Note that the slope of the thermal shrinkage rate is defined as a narrow angle from the transmission axis direction of the polarizer, and is in the range of 0 to 90°.

(6) Warpage of liquid crystal panel The liquid crystal panels produced in each example and comparative example were heated for 30 minutes using a gear oven set at 80°C.
Heat treatment is performed for 30 minutes, then cooled for 30 minutes in an environment set at room temperature 25 degrees Celsius 50% RH. Place the convex side down on a horizontal surface, measure the height of the four corners with a tape measure, and find the maximum value. It was defined as the amount of warpage. The amount of warpage was evaluated as follows.
○: 0 mm or more, 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 The slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), and the slow axis direction was the long side of the sample for measurement. 4cm parallel to
A rectangle of 2 cm x 2 cm was cut out and used as a sample for measurement. Regarding this sample, the refractive index of two orthogonal axes (refractive index in the slow axis direction: Ny, fast axis (refractive index in the direction perpendicular to the slow axis direction): Nx), and the refractive index in the thickness direction ( Nz) using an Abbe refractometer (manufactured by Atago, NAR-4).
T, measurement wavelength 589 nm). The NZ coefficient was determined using these values.

Retardation is the anisotropy of the refractive index on two orthogonal axes on the film (△Nxy=|Nx
-Ny|) and the film thickness d (nm) (ΔNxy×d), and is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), determine the slow axis direction of the film. A rectangle of 2 cm x 2 cm was cut out and used as a sample for measurement. For this sample, the refractive index of two orthogonal axes (refractive index in the slow axis direction: Ny, refractive index in the direction perpendicular to the slow axis direction: Nx), and the refractive index in the thickness direction (Nz) are Abbe refracted. The absolute value of the refractive index difference between the two axes (
|Nx−Ny|) was defined as the anisotropy of the refractive index (△Nxy). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf Co., Ltd.), and the unit was converted into nm. Product of refractive index anisotropy (△Nxy) and film thickness d (nm) (△
Retardation (Re) was determined from Nxy×d).

(8) Thickness direction retardation (Rth)
Thickness direction retardation refers to two birefringences △N when viewed from a cross section in the film thickness direction.
This is a parameter indicating the average retardation obtained by multiplying xz (=|Nx-Nz|) and ΔNyz (=|Ny-Nz|) by the film thickness d, respectively. Determine Nx, Ny, Nz and film thickness d (nm) using the same method as for retardation measurement, calculate the average value of (△Nxz×d) and (△Nyz×d), and calculate the thickness direction retardation (Rth ) was sought.

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200°C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged, and while stirring, 0.017 parts by mass of antimony trioxide as a catalyst was added. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the pressure and temperature were increased to a gauge pressure of 0.34 MPa and 24
After performing the pressurized esterification reaction at 0°C, the esterification reaction vessel was returned to normal pressure, and phosphoric acid
．． 014 parts by mass were added. Furthermore, the temperature was raised to 260° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, 15 minutes later, a dispersion treatment was performed using a high-pressure dispersion machine, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reactor, and a polycondensation reaction was performed at 280° C. under reduced pressure.

After the polycondensation reaction is complete, it is filtered using a Naslon filter with a 95% cut diameter of 5 μm, extruded into a strand from a nozzle, and cooled and solidified using cooling water that has been previously filtered (pore size: 1 μm or less). , cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g, and contained substantially no inert particles or internally precipitated particles. (Hereafter abbreviated as PET(A).)

(Production Example 2-Polyester B)
10 parts by mass of dried UV absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), particle-free PET (A) (intrinsic viscosity (0.62 dl/g) were mixed and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter abbreviated as PET (B)).

(Production Example 3 - Preparation of adhesion-modifying coating liquid)
Transesterification and polycondensation reactions were carried out in a conventional manner to obtain dicarboxylic acid components (based on the entire dicarboxylic acid component) of 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 5-
A water-dispersible sulfonic acid metal base-containing copolyester resin was prepared having a composition of 8 mol% sodium sulfonatoisophthalate, 50 mol% ethylene glycol (based on the entire glycol component), and 50 mol% neopentyl glycol as glycol components. . Next, water 5
After mixing 1.4 parts by mass, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of nonionic surfactant, the mixture was heated and stirred, and when the temperature reached 77°C, the above water dispersibility After adding 5 parts by mass of a copolyester resin containing a sulfonic acid metal base and continuing stirring until there are no lumps of resin, the aqueous resin dispersion was cooled to room temperature to form uniform water with a solid content concentration of 5.0% by mass. A dispersible copolymerized polyester resin liquid was obtained. Further, after dispersing 3 parts by mass of aggregate silica particles (Sylysia 310, manufactured by Fuji Silicia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolymerized polyester resin liquid was added with 3 parts by mass of Silicia 310. Water dispersion 0
．． 54 parts by mass was added thereto, and 20 parts by mass of water was added while stirring to obtain an adhesion-modifying coating liquid.

(Example 1)
<Manufacture of polyester film 1 for protecting polarizer>
After drying 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 as raw materials for the base film intermediate layer at 135° C. for 6 hours under reduced pressure (1 Torr). , is supplied to extruder 2 (for intermediate layer II), and PET (A
) were dried in a conventional manner and supplied to extruder 1 (for outer layer I and outer layer III), and 28
It was dissolved at 5°C. These two types of polymers are each filtered using a stainless steel sintered filter medium (nominal filtration accuracy: 95% of particles cut out at 10 μm), laminated in a two-type and three-layer confluence block, and extruded in a sheet form from a nozzle. An unstretched film was produced by winding the film around a casting drum with a surface temperature of 30° C. and cooling and solidifying it using an electrostatic casting method. At this time, I layer, II layer,
The discharge amount of each extruder was adjusted so that the thickness ratio of the III layer was 10:80:10.

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

The unstretched film on which the coating layer was formed was introduced into a tenter stretching machine, and while the ends of the film were held with clips, the film was introduced into a hot air zone at a temperature of 105° C. and stretched to 4.0 times in the TD. Next, heat treatment was performed at a temperature of 180°C for 30 seconds, and then the film, which had been cooled to 100°C, was stretched by 1.0% in the width direction, and then the film, which had been cooled to 60°C, was held by clips holding both ends. was opened and pulled under a tension of 350 N/m, a jumbo roll made of uniaxially oriented PET film with a film thickness of about 80 μm was collected, and the resulting jumbo roll was divided into three equal parts.
Three slit rolls (L (left side), C (center), R (right side)) were obtained. A polyester film 1 for protecting a polarizer was obtained from the slit roll located at R. In the polyester film 1 for protecting a polarizer, the direction in which the heat shrinkage rate was maximum was 7.0 degrees from TD.

<Creation of LCD panel>
A polyester film 1 for protecting the polarizer is placed on one side of the polarizer made of PVA, iodine, and boric acid.
was attached so that the transmission axis of the polarizer and the TD of the polyester film 1 for protecting the polarizer were parallel to each other. In addition, on the opposite side of the polarizer, a TAC film (manufactured by Fuji Film Co., Ltd., thickness 80
μm) was attached to create a light source side polarizing plate.

A liquid crystal panel was taken out from a 46-inch IPS type liquid crystal television using a glass substrate with a thickness of 0.4 mm for the liquid crystal cell. Peel off the light source side polarizing plate from the liquid crystal panel, and replace it with the light source side polarizing plate created above so that the transmission axis of the polarizer is the same as the transmission axis direction (parallel to the horizontal direction) of the light source side polarizing plate before peeling off. They were bonded to a liquid crystal cell via PSA so that they matched, and a liquid crystal panel was created.
In addition, the light source side polarizing plate was bonded to the liquid crystal cell so that the polyester film 1 for protecting the polarizer was on the distal side (opposite side) of the liquid crystal cell. The viewing side polarizing plate was made by laminating TAC films on both sides of a polarizer, and was bonded to the liquid crystal cell so that the absorption axis direction of the polarizer was parallel to the horizontal direction.

(Example 2)
<Manufacture of polyester film 2 for protecting polarizer>
In the production of the polyester film 1 for protecting a polarizer in Example 1, a film for protecting a polarizer was prepared in the same manner as the polyester film 1 for protecting a polarizer, except that the film cooled to 100°C was stretched by 1.5% in the width direction. Polyester film 2 was obtained. In the polarizer protective polyester film 2, the direction in which the heat shrinkage rate was maximum was 6.5 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 2 for protecting a polarizer.

(Example 3)
<Manufacture of polyester film 3 for protecting polarizer>
A polarizer protective film was prepared in the same manner as the polyester film 1 for protecting a polarizer, except that the film was cooled to 100° C. and stretched by 1.7% in the width direction in forming the polyester film 1 for protecting a polarizer in Example 1. I got 3. In the polarizer protective polyester film 3, the direction in which the heat shrinkage rate was maximum was 5.3 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 3 for protecting a polarizer.

(Example 4)
<Manufacture of polyester film 4 for protecting polarizer>
In the film formation of the polyester film 1 for protecting a polarizer in Example 1, the film cooled to 100°C was stretched by 2.0% in the width direction, and after being stretched 4 times in the TD, the temperature was 180°C, 30°C.
A polarizer protective film 4 was obtained in the same manner as the polarizer protective polyester film 1 except that a hard coat layer coating liquid was applied to one side of the polyester film before the second heat treatment. The polyester film 4 for protecting a polarizer has a maximum heat shrinkage rate from TD to 4.
．． It was 8 degrees.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 4 for protecting a polarizer.

(Example 5)
<Manufacture of polyester film 5 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 160 μm.
A polyester film 5 for protecting a polarizer was obtained in the same manner as the polyester film 4 for protecting a polarizer except for the following. In the polarizer protective polyester film 5, the direction in which the heat shrinkage rate was maximum was 4.8 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 5 for protecting a polarizer.

(Example 6)
<Manufacture of polyester film 6 for protecting polarizer>
In the film formation of the polyester film 1 for protecting a polarizer in Example 1, except that the film cooled to 100°C was stretched by 1.5% in the machine direction.
A polyester film 6 for protecting a polarizer was obtained in the same manner as above. In the polarizer protective polyester film 6, the direction in which the heat shrinkage rate was maximum was 9.0 degrees from the MD.
<Creation of LCD panel>
In creating the light source side polarizing plate of Example 1, the polyester film 6 for protecting the polarizer was used instead of the polyester film for protecting the polarizer, and the transmission axis of the polarizer and the MD of the polyester film 6 for protecting the polarizer were parallel to each other. A liquid crystal panel was produced in the same manner as in Example 1, except that a light source side polarizing plate was produced by attaching the polarizing plates so that

(Example 7)
<Manufacture of polyester film 7 for protecting polarizer>
In the film formation of the polyester film 1 for protecting a polarizer in Example 1, except that the film cooled to 100°C was stretched by 1.7% in the machine direction.
Polyester film 7 for protecting a polarizer was obtained in the same manner as above. In the polarizer protective polyester film 7, the direction in which the heat shrinkage rate was maximum was 8.3 degrees from the MD.
<Creation of LCD 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 a polarizer was replaced with the polyester film 7 for protecting a polarizer.

(Example 8)
<Manufacture of polyester film 8 for protecting polarizer>
In the film formation of the polyester film 1 for protecting a polarizer in Example 1, except that the film cooled to 100°C was stretched by 2.0% in the machine direction.
Polyester film 8 for protecting a polarizer was obtained in the same manner as above. In the polarizer protective polyester film 8, the direction in which the heat shrinkage rate was maximum was 7.0 degrees from the MD.
<Creation of LCD 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 a polarizer was replaced with the polyester film 8 for protecting a polarizer.

(Example 9)
<Manufacture of polyester film 9 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 160 μm.
A polyester film 9 for protecting a polarizer was obtained in the same manner as the polyester film 8 for protecting a polarizer except for the following. In the polarizer protective polyester film 9, the direction in which the heat shrinkage rate was maximum was 7.0 degrees from the MD.
<Creation of LCD 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 a polarizer was replaced with the polyester film 9 for protecting a polarizer.

(Example 10)
<Manufacture of polyester film 10 for protecting polarizer>
A polarizer protective film was prepared in the same manner as Polyester Film for Polarizer Protection 6, except that the stretching was changed from 4.0 times in TD to 4.0 times in MD and 1.0 times in TD. 1
I got 0. In the polyester film 10 for protecting a polarizer, the direction in which the heat shrinkage rate is maximum is M.
It was 8.7 degrees from D.
<Creation of LCD 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 a polarizer was replaced with the polyester film 10 for protecting a polarizer.

(Example 11)
<Manufacture of polyester film 11 for protecting polarizer>
In forming the polyester film 10 for protecting a polarizer in Example 10, the polyester film 10 for protecting a polarizer was prepared in the same manner as the polyester film 10 for protecting a polarizer, except that the film cooled to 100°C was stretched by 1.7% in the machine direction. A polyester film 11 was obtained. In the polarizer protective polyester film 11, the direction in which the heat shrinkage rate was maximum was 7.5 degrees from the MD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 10, except that the polyester film 10 for protecting a polarizer was replaced with the polyester film 11 for protecting a polarizer.

(Example 12)
<Manufacture of polyester film 12 for protecting polarizer>
In the film formation of the polyester film 10 for protecting a polarizer in Example 10, the polyester film 1 for protecting a polarizer was prepared except that the film cooled to 100°C was stretched by 5.0% in the width direction.
A polyester film 12 for protecting a polarizer was obtained in the same manner as in Example 0. In the polarizer protective polyester film 12, the direction in which the heat shrinkage rate was maximum was 1.8 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 12 for protecting a polarizer.

(Example 13)
<Manufacture of polyester film 13 for protecting polarizer>
A polyester film 13 for protecting a polarizer was obtained in the same manner as the polyester film 4 for protecting a polarizer except that the film thickness after stretching was set to 60 μm by adjusting the rotation speed of the casting roll. In the polarizer protective polyester film 13, the direction in which the heat shrinkage rate was maximum was 4.8 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 13 for protecting a polarizer.

(Example 14)
<Manufacture of polyester film 14 for protecting polarizer>
Polarizer protective film 14 was formed in the same manner as polarizer protective film 3, except that the film was passed through the film without changing the width of the clips holding both ends of the film in the cooling process after being stretched by 1.7% in the width direction. Obtained. In the polarizer protective polyester film 14, the direction in which the heat shrinkage rate was maximum was 33.0 degrees from the TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 3 except that the polarizer protective film 1 was replaced with the polarizer protective film 14.

(Comparative example 1)
<Manufacture of polyester film 15 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 200 μm.
Polarizer protective film 15 was obtained in the same manner as polarizer protective film 1, except that the film was passed through the film without changing the width of the clips holding both ends of the film in the cooling process after stretching and heat setting. . In the polarizer protective polyester film 15, the direction in which the heat shrinkage rate was maximum was 20.0 degrees from the MD.
<Creation of LCD panel>
Example except that the polarizer protective film 1 was replaced with the polarizer protective film 15, and the light source side polarizing plate was created by laminating the polarizer so that the transmission axis of the polarizer and the MD of the polarizer protective film were parallel to each other. A liquid crystal panel was created in the same manner as in 1.

(Comparative example 2)
<Manufacture of polyester film 16 for protecting polarizer>
In the cooling process after stretching and heat setting, polarized light was produced in the same manner as Polarizer Protective Film 1, except that the clips holding both ends of the film were released at 95°C without stretching by 1.0% in the width direction. A child protection film 16 was obtained. In the polarizer protective polyester film 16, the direction in which the heat shrinkage rate was maximum was 1.0 degrees from the MD.
<Creation of LCD panel>
Example except that the polarizer protective film 1 was replaced with the polarizer protective film 16, and the light source side polarizing plate was created by laminating the polarizer so that the transmission axis of the polarizer and the MD of the polarizer protective film were parallel to each other. A liquid crystal panel was created in the same manner as in 1.

(Comparative example 3)
<Manufacture of polyester film 17 for protecting polarizer>
A polyester film 17 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer except that the film thickness after stretching was set to 50 μm by adjusting the rotation speed of the casting roll. In the polarizer protective polyester film 17, the direction in which the heat shrinkage rate was maximum was 7.0 degrees from TD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for protecting a polarizer was replaced with the polyester film 17 for protecting a polarizer.

(Comparative example 4)
<Manufacture of polyester film 18 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 160 μm.
A polyester film 18 for protecting a polarizer was obtained in the same manner as the polyester film 11 for protecting a polarizer except that the polyester film 18 for protecting a polarizer was prepared. In the polarizer protective polyester film 18, the direction in which the heat shrinkage rate was maximum was 6.5 degrees from the MD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 11 except that the polyester film 11 for protecting a polarizer was replaced with the polyester film 18 for protecting a polarizer.

(Comparative example 5)
<Manufacture of polyester film 19 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 160 μm.
In forming the polyester film 1 for protecting a polarizer in Example 1, the temperature was 100°C.
A polyester film 19 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer except that the cooled film was stretched by 1.0% in the machine direction. In the polarizer protective polyester film 19, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from the MD.
<Creation of LCD panel>
In creating the light source side polarizing plate in Example 1, a polyester film 19 for protecting the polarizer was used instead of a polyester film for protecting the polarizer, and the transmission axis of the polarizer and the TD of the polyester film 19 for protecting the polarizer were parallel to each other. A liquid crystal panel was produced in the same manner as in Example 1, except that a light source side polarizing plate was produced by attaching the polarizing plates so that

(Comparative example 6)
<Manufacture of polyester film 20 for protecting polarizer>
A polyester film 20 for protecting a polarizer was obtained in the same manner as the polyester film 19 for protecting a polarizer except that the film thickness after stretching was set to 80 μm by adjusting the rotation speed of the casting roll. In the polarizer protective polyester film 20, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from the MD.
<Creation of LCD panel>
In Comparative Example 5, a liquid crystal panel was produced in the same manner as in Comparative Example 5, except that the polarizer protective polyester film 19 was replaced with a polarizer protective polyester film 20.

(Comparative example 7)
<Manufacture of polyester film 21 for protecting polarizer>
A polarizer protective film 21 was obtained in the same manner as the polarizer protective film 20. In the polarizer protective polyester film 21, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from the MD.
<Creation of LCD panel>
In creating the light source side polarizing plate of Example 1, a polyester film 21 for protecting the polarizer was used instead of the polyester film 1 for protecting the polarizer, and the transmission axis of the polarizer and the MD of the polyester film 21 for protecting the polarizer were parallel to each other. A liquid crystal panel was produced in the same manner as in Example 1, except that a light source side polarizing plate was created by pasting the polarizing plates so that

(Comparative example 8)
<Creation of LCD panel>
A liquid crystal panel was created in the same manner as in Example 1, except that the light source side polarizing plate was created by laminating the polarizer protective film 15 so that the transmission axis of the polarizer and the TD of the polarizer protective film were parallel. did.

(Comparative example 9)
<Manufacture of polyester film 22 for protecting polarizer>
By adjusting the rotation speed of the casting roll, the film thickness after stretching can be adjusted to 160 μm.
In forming the polyester film 1 for protecting a polarizer in Example 1, the temperature was 100°C.
A polyester film 22 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer except that the cooled film was stretched by 1.0% in the machine direction. In the polarizer protective polyester film 22, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from the MD.
<Creation of LCD panel>
In creating the light source side polarizing plate of Example 1, the polyester film 22 for protecting the polarizer was used instead of the polyester film 1 for protecting the polarizer, and the transmission axis of the polarizer and the MD of the polyester film 22 for protecting the polarizer were parallel to each other. A liquid crystal panel was produced in the same manner as in Example 1, except that a light source side polarizing plate was created by pasting the polarizing plates so that

<Manufacture of polyester film 23 for protecting polarizer>
In forming the polyester film 10 for protecting a polarizer in Example 10, a film for protecting a polarizer was prepared in the same manner as the polyester film 10 for protecting a polarizer, except that the film cooled to 100°C was stretched by 2.0% in the machine direction. A polyester film 23 was obtained. In the polarizer protective polyester film 23, the direction in which the heat shrinkage rate was maximum was 4.5 degrees from the MD.
<Creation of LCD panel>
A liquid crystal panel was produced in the same manner as in Example 10, except that the polyester film 10 for protecting a polarizer was replaced with the polyester film 23 for protecting a polarizer.

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

(Example 1A to Example 5A, Example 13A)
In addition, Example 1 except that a polarizing plate having the same structure as the light source side polarizing plate used in each of Examples 1 to 5 and 13 was used as both the light source side polarizing plate and the viewing side polarizing plate. When separately evaluated in the same manner as in Examples 1 to 5 and 13, good results (◯) were obtained in the evaluation of panel warpage, similar to the results of Examples 1 to 5 and 13 in Table 1 above. Note that the light source side polarizing plate and the viewing side polarizing plate were attached to the liquid crystal cell so that the polyester film for protecting the polarizer was on the distal side (opposite side) to the liquid crystal cell.

(Example 1B to Example 5B, Example 13B)
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 in Examples 1A to 5A and 13A.
When separately evaluated in the same manner as in Example 1A to Example 5A and Example 13A, good results (◯) were obtained in the evaluation of panel warpage.

According to the present invention, it is possible to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device that can suppress warping of a liquid crystal panel.

Claims (7)

A polarizer protective polyester film laminated on one side of a polarizer, the polarizer being a polyvinyl alcohol film containing iodine, and meeting the following requirements (1), (2) and (3). A polyester film for protecting polarizers that meets the following requirements.
(1) The shrinkage force F _f of the polyester film for protecting a polarizer 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 , Thickness (mm) of polyester film for protecting polarizer × Elastic modulus (N/mm ² ) × Heat shrinkage rate (%) after treatment at 80°C for 30 minutes ÷ 100 × 1000. Here, the elastic modulus is The elastic modulus of the polyester film for protecting a polarizer in the direction parallel to the transmission axis of the polarizer, and the heat shrinkage rate is the heat shrinkage rate of the polyester film for protecting the polarizer in the direction parallel to the transmission axis of the polarizer. .)
(2) Shrinkage force F _f of the polyester film for protecting a polarizer in a direction parallel to the transmission axis of the polarizer and contraction force F _v of the polyester film for protecting a polarizer in a direction parallel to the absorption axis of the polarizer. The ratio (F _f /F _v ) is 2.5 or more and 12.0 or less (however, the shrinkage force F _v (N/m) is calculated by multiplying the thickness (mm) of the polyester film for protecting the polarizer by the elastic modulus (N /mm ² ) x heat shrinkage rate (%) of treatment at 80°C for 30 minutes ÷ 100 x 1000.Here, the elastic modulus is the elastic modulus of the polyester film for protecting the polarizer in the direction parallel to the absorption axis of the polarizer. It is the elastic modulus, and the heat shrinkage rate is the heat shrinkage rate of the polyester film for protecting the polarizer in the direction parallel to the absorption axis of the polarizer.)
(3) The absolute value of the angle formed by the direction in which the heat shrinkage rate of the polyester film for protecting a polarizer is maximum and the direction parallel to the transmission axis of the polarizer is 15 degrees or less. The polyester film for protecting a polarizer according to claim 1, wherein the polyester film for protecting a polarizer has a thickness of 40 to 200 μm. The polyester film for protecting a polarizer has a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, or an antireflection antiglare layer on the surface opposite to the surface on which the polarizer is laminated. The polyester film for protecting a polarizer according to claim 1. A polarizing plate comprising a polarizer protective polyester film according to claim 1 laminated on at least one surface of the polarizer. A polarizing plate, wherein the polyester film for protecting a polarizer according to claim 1 is laminated on one surface of the polarizer, and the other surface of the polarizer has no film. The polarizing plate according to claim 4 or 5, wherein 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 comprising a backlight source and a liquid crystal cell disposed between two polarizing plates, wherein at least one of the two polarizing plates is the polarizing plate according to claim 5 or 6. Device.