JP2020091494A - 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, capable of suppressing warpage of a liquid crystal panel.SOLUTION: There is provided a polarizer protective polyester film, which is laminated on one surface of a polarizer and satisfies the following conditions (1) and (2). (1) In a direction parallel to a transmission axis of the polarizer, contractile force Fof the polyester film is 800 N/m or more and 9000 N/m or less. (2) A ratio (F/F) of the contractile force Fof the polyester film in a direction parallel to the transmission axis of the polarizer to the contractile force Fof the polyester film in a direction parallel to an absorption axis of the polarizer is 2.5 or more and 12.0 or less.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 expanding in applications such as liquid crystal televisions and liquid crystal displays for personal computers. Usually, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, and the like are sandwiched between glass plates, and two polarizing plates provided on both sides of the liquid crystal cell. It has a structure in which a child (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 come to be used as a light source, and the thickness of glass substrates used for liquid crystal panels has become thinner than 0.7 mm. Accordingly, a problem that display unevenness occurs occurs, and its improvement is demanded.
The display unevenness is mainly caused by the shrinkage of the polarizer, and when the polarizer is placed under high temperature and high humidity, the shrinkage force tends to be relaxed in the alignment direction in order to relax the alignment. It is believed that the liquid crystal panel warps and swells toward the backlight unit side as a result, resulting in display unevenness.

Note that, conventionally, as in Patent Document 1 and Patent Document 2 below, the thickness of the glass substrate used for the liquid crystal panel is as thick as 0.7 mm or more, so that the high rigidity of the glass suppresses the contraction of the polarizer. Therefore, the liquid crystal panel did not warp, and uneven display did not pose a problem.

Therefore, it has been attempted to improve the warp of the liquid crystal panel, which occurs when the glass substrate is made thinner than 0.7 mm, by using an optical film.
For example, when a cycloolefin resin is used as a polarizer protective film, the improvement of the warp of the liquid crystal panel is insufficient, and the drying property of water glue for adhering to the polarizer is poor, resulting in a decrease in productivity. There was a problem to do.
Further, when conventional triacetyl cellulose (TAC) is used as the polarizer protective film, there is a problem that the liquid crystal panel warps.

JP, 2008-107499, A JP, 2009-198666, A

The present invention has been made in view of the above problems and circumstances, and a problem to be solved is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device capable of suppressing warpage of a liquid crystal panel.

The present inventors, in order to solve the above problems, in the process of examining the cause of the above problems, in the direction parallel to the transmission axis of the polarizer, by setting the shrinkage force of the polarizer protective polyester film to a specific range. The inventors have found that the warp of the liquid crystal panel can be improved, and the present invention has been completed based on this finding.

Specifically, in a liquid crystal display device, usually, a polarizing plate is laminated on one surface of a liquid crystal cell so that the transmission axis direction of a polarizer is parallel to the long side direction of the liquid crystal display device, and on the other surface, Polarizing plates are laminated 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 diligent studies using various commercially available liquid crystal display devices, the problem of a shape factor (curl that a polarizing plate having a large shrinkage force and a polarizing plate whose long side is in the absorption axis direction is likely to be curled) Is generally easy to occur in the long side direction) and due to the asymmetrical configuration of the upper and lower polarizing plates in the liquid crystal panel, the liquid crystal panel has a polarizer transmission axis of the upper and lower polarizing plates arranged in crossed Nicols on the long side The present inventors have found that the essence of the problem is to form a convex on the polarizing plate side.

Furthermore, as a result of diligent studies, it became clear that the shrinkage force in the long side direction of the polarizing plate whose polarizer transmission axis is the long side can be controlled by the residual strain of the protective film. I found that I could control the curl.

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

As a result of the investigation, it has been clarified that the contracting force is generated during the TMA cooling process even when the contracting force is not generated during the TMA temperature rising process. This is because the strain due to thermal expansion is a reversible change, so it returns to its original state after heating and cooling, but since it is cooled in a state in which the dimensions are small by the amount of heat shrinkage contracted during the temperature rise process, thermal stress This is because That is, the strain of thermal stress can be replaced by the thermal shrinkage of the film, and the shrinkage force after cooling is expressed by the following formula. The heat shrinkage ratio in the present invention includes a change in water content during heat treatment.
Shrinkage force (N/m)=film thickness (mm)×elastic modulus (N/mm ² )×heat shrinkage rate (%)÷100×1000

That is, the representative invention is as follows.
Item 1.
A polyester film for protecting a polarizer, which is laminated on one surface of a polarizer, and which 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 (where the shrinkage force F _f (N/m) is Thickness (mm)×elastic modulus (N/mm ² )×thermal shrinkage rate (%) at 80° C. for 30 minutes÷100×1000, where 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 is the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer.
(2) Ratio (F _f /F _v ) of the shrinkage force F _{f of the} polyester film in the direction parallel to the transmission axis of the polarizer and the shrinkage force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer. ) 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×elastic modulus (N/mm ² )×80° C./30 minutes treatment) Thermal shrinkage (%)/100×1000, where 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 absorption axis of the polarizer. This is the heat shrinkage rate of the polyester film in the parallel direction.)
Item 2.
Furthermore, 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 heat shrinkage rate of the polyester film is maximum and the direction parallel to the transmission axis of the polarizer are substantially parallel to each other.
Item 3. The polyester film for protecting a polarizer according to Item 1 or 2, wherein the polyester film has a retardation of 3000 to 30,000 nm.
Item 4.
Item 4. The polyester film for protecting a polarizer according to any one of Items 1 to 3, wherein the polyester film has a thickness of 40 to 200 µm.
Item 5.
Item 1 to 4, which has a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, or an antireflection antiglare layer on the surface of the polyester film opposite to the surface on which the polarizer is laminated. The polyester film for protecting the polarizer according to any one of 1.
Item 6.
A polyester film for protecting a polarizer, which is laminated on one surface of a polarizer, and which satisfies the following requirements (1) and (2).
(1) The shrinkage force F _TD of TD of the polyester film is 800 N/m or more and 9000 N/m or less (where the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film×elastic modulus (N /Mm ² )×80° C./30-minute heat shrinkage (%)÷100×1000, where the elastic modulus is the TD elastic modulus of the polyester film and the thermal shrinkage is the polyester film's TD elastic modulus. It is the thermal shrinkage of TD.)
(2) the ratio of the contractile force _{F MD} in the MD shrinkage force _{F TD} and the polyester film in the TD of the polyester film _{(F TD} / _{F MD)} is 2.5 to 12.0 (where contraction force F _MD (N/m) is the thickness (mm) of the polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of treatment at 80° C. for 30 minutes÷100×1000. Is the MD elastic modulus of the polyester film, and the heat shrinkage is the MD thermal shrinkage of the polyester film.)
Item 7.
Furthermore, the polyester film for protecting a polarizer according to item 6, which further satisfies the following requirement (3).
(3) Item 8 in which TD is substantially parallel to the direction in which the heat shrinkage rate of the polyester film is maximum.
A polarizing plate in which the polyester film for protecting a polarizer according to any one of items 1 to 7 is 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 film is not provided on the other surface of the polarizer.
Item 10.
Item 10. The polarizing plate according to item 8 or 9, wherein the polarizing plate has a rectangular shape, and a long side of the polarizing plate is parallel to a transmission axis thereof.
Item 11.
A liquid crystal display device comprising a backlight light source and a liquid crystal cell arranged 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. Liquid crystal 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 capable of suppressing the warpage of a liquid crystal panel.

The polyester film for protecting a polarizer 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 made of polyvinyl alcohol and a dye) to form a polarizing plate. is there.

In the present 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 surface of the polyester film. Is.
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 surface 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 surface of the polyester film.
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 surface of the polyester film.
The heat shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer means the heat shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one surface 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 surface 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. 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 to each other. The term “substantially parallel” means that the absolute value of the angle formed by 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). Allow less than 15 degrees. The gradient of the heat shrinkage ratio is preferably 12 degrees or less, more preferably 10 degrees or less, further preferably 8 degrees or less, still more preferably 6 degrees or less, and particularly preferably 4 degrees or less. And most preferably twice or less. Since the smaller the gradient of the heat shrinkage is, the more preferable, the lower limit is 0 degree. When the inclination of the heat shrinkage rate of the polyester film is large, the polarizing plate including the polyester film is warped in an oblique direction, and the effect of reducing the warpage of the liquid crystal panel tends to be weakened.
However, the ratio (F _f /F _v ) of the shrinkage force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer and the shrinkage force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer is 2 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 maximum is 40 degrees or less, the liquid crystal panel in the case of 0.5 or more and 12.0 or less. The warp of the can be reduced. The angle is preferably 35 degrees or less.
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 methods adopted in the examples described later.

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 does not normally pass through the two polarizing plates. However, due to the contraction or warpage of the above-described polarizer, there is a possibility that the relationship of complete crossed Nicols may be broken and light leakage may occur. From the viewpoint of suppressing light leakage, it is preferable that the angle formed between the direction in which the heat shrinkage of the polarizer protective film is maximum and the transmission axis of the polarizer is small.

In the polyester film for protecting a polarizer of the present invention, the shrinkage force Ff of the polyester film in the direction parallel to the transmission axis of the polarizer is preferably 800 N/m or more and 9000 N/m or less. _If the lower limit of F _f is less than 800 N/m, the warp of the liquid crystal panel may not be sufficiently reduced. When the upper limit of F _f exceeds 9000 N/m, the contraction force is too strong and the liquid crystal panel may warp in the opposite direction. The range of the preferable contracting 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, further preferably 1100 N/m or more and 8000 N/m or less, and even more preferably 1200 N/m. /M or more and 8000 N/m or less. The upper limit is preferably 6000 N/m or less, 5500 N/m or less, and 4800 N/m or less.

Here, the contraction force F _f refers to the contraction force of the polyester film in the direction parallel to the transmission axis of the polarizer, and is the thickness (mm) of the polyester film×elastic modulus (N/mm ² )×80° C./30 minutes It is defined by the heat shrinkage rate (%)/100×1000 of the treatment.
Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer. The heat shrinkage is the heat shrinkage of the polyester film (heat shrinkage in heat treatment at 80° C. for 30 minutes) in the direction parallel to the transmission axis of the polarizer.

In the absorption axis parallel to the direction of the polarizer, the contractile force of the polyester film and F _v. The shrinkage force F _v is defined by the thickness (mm) of the polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of 80° C./30-minute treatment÷100×1000. Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The heat shrinkage is the heat shrinkage of the polyester film (heat shrinkage in heat treatment at 80° C. for 30 minutes) in the direction parallel to the absorption axis of the polarizer.

The polyester film for protecting a polarizer of the present invention preferably has F _f /F _v of 1.0 or more and 12.0 or less. It is more preferably 2.5 or more and 12.0 or less. _If the lower limit of F _f /F _v is less than 1.0, the warp of the liquid crystal panel may not be sufficiently reduced. When the upper limit of F _f /F _v exceeds 12.0, thermal deformation in one direction becomes large, and the polarizer is laminated on the surface opposite to the surface on which the polyester film for protecting the polarizer is laminated. The protective film or the retardation film to be applied may be stressed, and the display quality may be deteriorated. In addition, the film forming stability may be lowered and the film may be broken.

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

In the polyester film for protecting a polarizer of the present invention, the elastic modulus of the polyester film in the transmission axis direction of the polarizer is preferably 1000 to 9000 N/mm ² . Although the shrinkage 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 transmission axis direction of the polarizer, the polyester film is highly oriented in the transmission axis direction of the polarizer, and, It is necessary to increase the crystallinity. Therefore, when the elastic modulus of the polyester film in the transmission axis direction of the polarizer exceeds 9000 N/mm ² , there is a risk of tearing and the like. Therefore, the upper limit is preferably 9000 N/mm ² , and more preferably 8000 N/mm 2. ² and more preferably 7,000 N/mm ² .
On the other hand, when the orientation is low and the crystallinity is low, the film may be deformed by roll irregularities caused by thickness unevenness when wound on a roll, resulting in poor planarity. Therefore, the lower limit of the elastic modulus is preferably 1000 N / mm ^2, more preferably 1500 N / mm ^2, further preferably 1800 N / mm ^2. The elastic modulus can be measured by the method adopted in Examples described later.

In the polyester film for protecting a polarizer of the present invention, it is preferable that the polyester film has a heat shrinkage rate of 0.10 to 5.0% when 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, 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, further preferably 3.0% or less, further preferably 2% or less, most preferably 1.4% or less. When the heat shrinkage 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 without variation. Further, in order to increase the heat shrinkage ratio to more than 5.0%, it is necessary to further reduce the crystallinity and the glass transition temperature, which may cause defects such as poor planarity. The heat shrinkage rate can be measured by the method adopted in 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 further preferably 40 to 80 μm. When the thickness of the polyester film is less than 40 μm, the polyester film is likely to be cracked, and insufficient rigidity tends to result in poor planarity. In the case of a thin film, it is necessary to increase the elastic modulus or heat shrinkage of the polyester film in the transmission axis direction of the polarizer accordingly. Is the lower limit. Further, when the thickness of the film exceeds 200 μm, the elastic modulus or heat shrinkage of the polyester film in the direction of the transmission axis of the polarizer may vary greatly, which may make it difficult to control the cost. Also rises. The thickness of the polyester film can be measured by the method adopted in Examples described later.

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 rainbow spots observed on the screen of a liquid crystal display device. The lower limit of the 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 in-plane retardation is preferably 30,000 nm or less, more preferably 18,000 nm or less, and further preferably 15,000 nm or less. In particular, from the viewpoint of thinning, the in-plane retardation is preferably less than 10,000 nm and 9000 nm or less.

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

The polarizer protective polyester film of the present invention has a ratio (Re/Rth) of in-plane retardation (Re) to retardation in the thickness direction (Rth) of preferably 0.2 or more, preferably 0.3 or more, It is preferably 0.4 or more, more preferably 0.5 or more, and further preferably 0.6 or more. The larger the ratio (Re/Rth) of the in-plane retardation to the thickness direction retardation, the more isotropic the birefringence action is, and the occurrence of iridescent color spots depending on the observation angle tends to be less likely to occur. Since the ratio (Re/Rth) of the retardation and the thickness direction retardation is 2.0 in a perfect uniaxial (uniaxially symmetric) film, the ratio of the retardation and the thickness direction retardation (Re/Rth) is The upper limit is preferably 2.0. The preferable upper limit of Re/Rth is 1.2 or less. The retardation in the thickness direction means the average of the retardations obtained by multiplying the two birefringences ΔNxz and ΔNyz when the film is viewed from the cross section in the thickness direction by the film thickness d.

In the polyester film for protecting a polarizer of the present invention, the NZ coefficient of the polyester film is preferably 2.5 or less, more preferably 2.0 or less, and further preferably from the viewpoint of further suppressing iridescent color spots. It is 1.8 or less, and more preferably 1.6 or less. Since the NZ coefficient is 1.0 in a perfectly uniaxial (uniaxially symmetric) film, the lower limit of the NZ coefficient is 1.0. However, it should be noted that the mechanical strength in the direction perpendicular to the orientation direction tends to be significantly reduced as the film approaches a completely 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 (fast axis). (Refractive index in the direction), Nz represents the refractive index in the thickness direction. The orientation axis of the film is obtained by using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), and biaxial refractive indices (Ny, Nx, provided in the directions orthogonal to the orientation axis direction). Ny>Nx) and the refractive index (Nz) in the thickness direction are obtained by an Abbe refractometer (NAR-4T, manufactured by Atago Co., measurement wavelength 589 nm).
The value thus obtained can be substituted into |Ny-Nz|/|Ny-Nx| to obtain the NZ coefficient.

Further, in the polyester film of the present invention, the value of Ny-Nx of the polyester film is preferably 0.05 or more, more preferably 0.07 or more, and further preferably 0 from the viewpoint of suppressing more iridescent color spots. 0.08 or more, more preferably 0.09 or more, and most preferably 0.1 or more. The upper limit is not particularly specified, but in the case of a polyethylene terephthalate 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 polyester resin is not particularly limited, and any polyester resin obtained by condensing a dicarboxylic acid and a diol can be used.

Examples of the dicarboxylic acid component that can be used for producing the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 ,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid , Hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyl Examples thereof include adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid and dodecadicarboxylic acid.

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

The dicarboxylic acid component and the diol component constituting the polyester resin may be used either individually or in combination of two or more. Examples of suitable polyester resin constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like. More preferably, polyethylene terephthalate and polyethylene naphthalate can be mentioned. Further, other copolymerization component may be contained. These resins have excellent transparency as well as thermal and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high elastic modulus and the heat shrinkage rate is relatively easy to control.

When it is necessary to increase the heat shrinkage of the polyester film to a high degree, it is desirable to add a copolymerization component to appropriately lower the crystallinity. Further, since the proportion of elastic strain and permanent strain is high with respect to the deformation below the glass transition temperature, it is generally difficult to highly increase the heat shrinkage rate. Therefore, it is also a preferred embodiment to introduce a component having a low glass transition temperature as needed. Specifically, it is propylene glycol, 1,3-propanediol, or the like.

(Provision of functional layer)
The polarizing plate using the polyester film for protecting the polarizer of the present invention is preferably integrated with the glass plate of the liquid crystal cell in the state where the heat shrinkage rate of the polyester film remains, and therefore, an easy-adhesion layer and a hard coat layer. , A functional layer such as an antiglare layer, an antireflection layer, a low reflection layer, a low antireflection layer, an antireflection antiglare layer, a low reflection antiglare layer, and an antistatic layer, the drying temperature should be low. It is a desirable embodiment to perform setting or a method having a small thermal history such as UV irradiation or electron beam irradiation. Further, by providing these functional layers in the film forming process of the polyester film, the polarizing plate of the present invention and the glass plate of the liquid crystal cell can be integrated without impairing the increased heat shrinkage rate. Therefore, this is a more desirable embodiment.
Functional layers such as an easily adhesive layer, a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low antireflection layer, an antireflection antiglare layer, a low reflection antiglare layer, and an antistatic layer are polyester films, It is preferable that the contracting forces F _f and F _v have the above-described conditions when the functional layers are laminated on the surface opposite to the surface on which the polarizer is laminated and the functional layers are laminated.

(Method for producing oriented polyester film)
The polyester film used in the present invention can be manufactured according to a general method for manufacturing a polyester film. For example, a polyester resin is melted, and a non-oriented polyester extruded and molded into a sheet is stretched in the longitudinal direction by utilizing the speed difference of rolls at a temperature of glass transition temperature or higher, and then stretched in the lateral direction by a tenter, A method of performing heat treatment (heat fixing) can be mentioned. 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 the direction perpendicular to the main stretching direction. Note that MD is an abbreviation for Machine Direction, and may be referred to as a film flow direction, a longitudinal direction, and a longitudinal direction in the present specification. TD is an abbreviation for Transverse Direction, and may be referred to as a width direction or a lateral direction in the present specification.

For the polyester film, it is preferable to adjust the film thickness, elastic modulus, and thermal shrinkage so that the shrinkage force F _f is 800 N/m or more and 9000 N/m or less.

(Method of adjusting elastic modulus of polyester film)
The elastic modulus of the polyester film used as the polarizer protective film is the same as the MD of the polyester film when the transmission axis of the polarizer matches the MD of the polyester film when it is formed. In that case, the elastic modulus of TD may be adjusted by a conventionally known method for the stretched polyester film.
Specifically, the stretching ratio may be set high when the direction is the stretching direction, and may be set low when the direction is orthogonal to the stretching direction.

(Method of adjusting heat shrinkage of polyester film)
The heat shrinkage rate of the polyester film used as the polarizer protective film is the heat shrinkage rate of MD when the transmission axis direction of the polarizer matches the MD at the time of film formation of the polyester film. When it coincides with TD, the heat shrinkage ratio of TD may be adjusted by a conventionally known method for the stretched polyester film.

When adjusting the heat shrinkage ratio of MD of the polyester film, for example, in the cooling process after stretching and heat setting, the distance between the clip holding the edge portion in the film width direction and the adjacent clip is expanded to MD. It can be adjusted by contracting the MD or by reducing the clip interval. Further, in the cooling process after stretching and heat setting, when the film is cut or separated from the clip that grips the film width direction end portion, the film drawing force is adjusted to stretch or shrink the film in MD. It can be adjusted by Also, in the offline process after film formation, when the temperature is raised for the purpose of providing a functional layer, etc., the heat shrinkage rate changes during the temperature rising and cooling process. It is also possible to make adjustments.

When adjusting the TD heat shrinkage of the polyester film, for example, in the cooling process after stretching and heat setting, the interval between the clip holding the film width direction end and the clip located on the opposite side in the width direction is set. It can be adjusted by a method of stretching to TD by enlarging or contracting to TD by reducing.

The shrinkage force F _v of the polyester film is set so 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 the thermal shrinkage.

(How to adjust the inclination of the main axis of shrinkage of polyester film)
The inclination of the shrinkage main axis of the polyester film used as the polarizer protective film is, as disclosed in PCT/JP2014/073451 (WO2015/037527), a cooling process after stretching/heat treatment of the polyester film by a tenter, or film formation. It can be adjusted in a later off-line process. Specifically, in the cooling process, shrinkage due to stretching and thermal stress due to cooling, which could not be completely removed in the heat setting process, are generated, and depending on the balance between the two in the film flow direction, drawing in to the upstream side or downstream side The contraction main shaft is tilted. In order to reduce the inclination of the main shrinkage axis, it is necessary to adjust the shrinkage force in the film flow direction in the cooling step (the total of the shrinkage force associated with stretching and the shrinkage force associated with cooling) to be uniform. In order to make the film uniform, it is desirable to shrink in the film flow direction in a temperature range where the shrinkage force is high in the film flow direction, or to stretch in the film flow direction in a temperature range where the shrinkage force is low in the film flow direction. As a method of shrinking or stretching, a conventionally known method may be used. Further, when cutting or separating the film end portion, it should be noted that the film shrinks freely in the width direction below the temperature range where the film is cut and separated, and the heat shrinkage rate below the temperature range decreases.

In the polarizing plate, the polyester film for protecting the polarizer of the present invention is laminated on at least one surface of the polarizer. It is preferable that a film having no birefringence such as a TAC film, an acrylic film, 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 surface of the polarizer is also a preferable embodiment from the viewpoint of thinness. In this case, the film is not laminated on the other surface 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 a coating layer other than the polyester film for protecting the polarizer of the present invention on a polarizer, the shrinkage of the film or the coating layer other than the polyester film for protecting the polarizer in a direction parallel to the transmission axis of the polarizer. The force and the shrinking force of the film or the coating layer other than the polyester film for protecting the polarizer in the direction parallel to the absorption axis of the polarizer are preferably not more than the value of F _f of the polyester film for protecting the polarizer, preferably less than the value of F _v polarizer protective polyester film is preferred. Further, 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 in the direction parallel to the absorption axis of the polarizer, other than the polyester film for protecting the polarizer The shrinkage force of the film or coating layer is preferably 250 N/m or less, and more preferably 200 N/m or less. The shrinkage force of films other than the polyester film for protecting the polarizer and the coating layer can be measured in the same manner as in the case of the polyester film. That is, the thickness (mm) of the film or the coating layer×the elastic modulus (N/mm ² )×the heat shrinkage rate (%) of the treatment at 80° C. for 30 minutes÷100×1000.

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

Therefore, from the viewpoint of industrially manufacturing a polarizing plate, the polyester film for protecting a polarizer of the present invention is preferably the following (1) and (2).
(1) contractile force _{F TD} in the TD of the polyester film is not more than 800 N / m or more 9000 N / m.
However, the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of 80° C./30 minute treatment÷100×1000. Here, the elastic modulus and the heat shrinkage are the TD elastic modulus and the TD heat shrinkage 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 (thickness (mm) of polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of 80° C./30 minutes treatment/100×1000). Here, the elastic modulus and the heat shrinkage are the MD elastic modulus and the MD heat shrinkage of the polyester film, respectively.

Further, in the polyester film for protecting a polarizer of the present invention, it is preferable that TD is substantially parallel to the direction in which the heat shrinkage rate of the polyester film is maximum.
The term “substantially parallel” means that the absolute value of the angle between the direction in which the heat shrinkage of the polyester film is maximum and the TD direction (the slope of the heat shrinkage) is 15 degrees or less. The gradient of the heat shrinkage ratio is preferably 12 degrees or less, more preferably 10 degrees or less, further preferably 8 degrees or less, still more preferably 6 degrees or less, and particularly preferably 4 degrees or less. And most preferably twice or less. Since the smaller the gradient of the heat shrinkage is, the more preferable, the lower limit is 0 degree.
However, when the ratio of the TD shrinkage force F _TD of the polyester film and 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, the warpage of the liquid crystal panel can be reduced. The angle is preferably 35 degrees or less.

When considering industrially manufacturing a polarizing plate in a roll-to-roll format as described above, since F _TD corresponds to F _f , the preferable range of F _TD and F _f The preferred ranges of are the same. Further, since F _TD /F _MD corresponds to F _f /F _v , their preferable ranges 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", both preferable ranges are the same. "The heat shrinkage rate of TD of the polyester film when heat-treated at 80°C for 30 minutes" corresponds to "the heat shrinkage rate of the polyester film when heat-treated at 80°C for 30 minutes in the transmission axis direction of the polarizer". Therefore, the preferable ranges of both are the same.

The liquid crystal display device has at least a backlight light source and a liquid crystal cell arranged between two polarizing plates. At least one of the two polarizing plates is preferably a polarizing plate using the polyester film for protecting a polarizer 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 the polarizer of the present invention is a polarizer protective film on the viewer side starting from the polarizer of the viewer side polarizing plate and/or the position of 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, the liquid crystal display device has a rectangular shape (the two polarizing plates used in the liquid crystal display device are also rectangular), and one polarizing plate has its long side parallel to the absorption axis, and the other polarizing plate. The polarizing plates are arranged such that their long sides are parallel to the transmission axis and their absorption axes are in a vertical relationship with each other. A polarizing plate having a long side of the polarizing plate parallel to the absorption axis is usually used as a viewing side polarizing plate of a liquid crystal display device, and a polarizing plate having the long side of the polarizing plate parallel to the transmission axis. Is used as a light source side polarizing plate of a liquid crystal display device. It is preferable to use the polarizing plate of the present invention as a polarizing plate having a long side of the polarizing plate and a transmission axis parallel to each other from the viewpoint of suppressing warpage of the liquid crystal panel. Further, it is also preferable to use the polarizing plate of the present invention for both a polarizing plate having a long axis of the polarizing plate in a parallel relationship with the transmission axis and a polarizing plate having a long side of the polarizing plate in a parallel relationship with the absorption axis.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples, and is appropriately modified within the scope of the gist of the present invention. It is also possible, 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. The thickness, elastic modulus, and heat shrinkage of the polyester film are the measured values described below. The elastic modulus is the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer. The heat shrinkage is the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer.
Shrinkage force F _f (N/m)=thickness (mm) of polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of treatment at 80° C. for 30 minutes÷100×1000

(2) Contraction force F _v
Contractile force F _v of the polyester film was calculated from the following equation. The thickness, elastic modulus, and heat shrinkage of the polyester film are the measured values described below. The elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The heat shrinkage is the heat shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer.
Contractile force _F v (N / m) = thickness of the polyester film (mm) × modulus (N / mm ²⁾ Thermal shrinkage × 80 ° C. · 30 min treatment (%) ÷ 100 × 1000

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

(4) Elastic Modulus of Polyester Film The elastic modulus of the polyester film is a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments Inc. according to JIS-K7244 (DMS) after standing for 168 hours in an environment of 25° C. and 50 RH%. Was evaluated. Tensile mode, driving frequency is 1 Hz, chuck distance is 5 mm, temperature rising rate is 2° C./min, temperature dependence of 25° C. to 120° C. is measured, and average storage elastic modulus of 30° C. to 100° C. is measured. The elastic modulus was used. Thus, for the polyester film, 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.
In addition, the above-mentioned measurement was performed with a polyester film alone (polyester film for protecting a polarizer alone).

(5) Heat shrinkage rate and gradient of heat shrinkage rate of polyester film After the polyester film was allowed to stand in an environment of 25° C. and 50 RH% for 168 hours, a circle having a diameter of 80 mm was drawn and the diameter of the circle was measured by an image size measuring device (manufactured by KEYENCE). Image measure IM6500) was used to measure every 1° to obtain the length before treatment. Next, heat treatment was performed for 30 minutes using a gear oven set at 80° C., and after that, after cooling for 10 minutes in an environment set at room temperature 25° C., evaluation was performed every 1° by the same method as before treatment. , And the length after processing. The above treatment was performed with a polyester film alone (polyester film for protecting a polarizer alone).

The thermal contraction rate was evaluated for each angle using the following formula.
Heat shrinkage ratio=(length before treatment−length after treatment)/length before treatment×100
Thus, for the polyester film, 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.

In the above, evaluation was performed at 1° intervals of 360°, the direction in which the heat shrinkage rate was the maximum was specified, and the absolute value of the angle between that direction and the transmission axis direction of the polarizer was defined as the slope of the heat shrinkage rate. .. The slope of the heat 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 of the examples and comparative examples were heat-treated for 30 minutes using a gear oven set at 80°C, and then in an environment set at room temperature of 25°C and 50% RH. After cooling for 30 minutes, the convex side was placed on a horizontal plane and the heights of the four corners were measured with a measure, and the maximum value was defined as the amount of warpage. The amount of warpage was evaluated as follows.
◯: 0 mm or more and less than 2.0 mm Δ: 2.0 mm or more and 3.0 mm or less ×: Exceeding 3.0 mm

(7) Refractive index of polyester film The slow axis direction of the film is determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), and the slow axis direction is the measurement sample long side. A 4 cm×2 cm rectangle was cut out so as to be parallel to, and used as a measurement sample. With respect to this sample, the refractive index of two orthogonal axes (refractive index in the slow axis direction: Ny, fast axis (refractive index in the direction orthogonal to the slow axis direction): Nx), and refractive index in the thickness direction ( Nz) was determined by an Abbe refractometer (NAR-4T, manufactured by Atago Co., measurement wavelength 589 nm). The NZ coefficient was determined using these values.

Retardation is a parameter defined by a product (ΔNxy×d) of anisotropy (ΔNxy=|Nx−Ny|) of biaxial refractive indexes on the film and film thickness d (nm). Yes, it is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. The slow axis direction of the film is determined using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), and 4 cm so that the slow axis direction is parallel to the long side of the sample for measurement. A rectangle of ×2 cm was cut out and used as a measurement sample. Regarding this sample, the orthogonal biaxial refractive index (refractive index in the slow axis direction: Ny, refractive index in the direction orthogonal to the slow axis direction: Nx) and the refractive index in the thickness direction (Nz) are Abbe refracted. The absolute value (|Nx-Ny|) of the biaxial refractive index difference was determined by an index meter (NAR-4T, manufactured by ATAGO Co., Ltd., measurement wavelength 589 nm), and the anisotropy of refractive index (ΔNxy) was used. The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D manufactured by Fine Luff Co., Ltd.), and the unit was converted to nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the anisotropy of refractive index (ΔNxy) and the film thickness d (nm).

(8) Thickness direction retardation (Rth)
The thickness direction retardation means two birefringences ΔNxz (=|Nx-Nz|) and ΔNyz (=|Ny-Nz|) multiplied by the film thickness d when viewed from the cross section in the film thickness direction. It is a parameter indicating the average retardation obtained. Nx, Ny, Nz and film thickness d (nm) are obtained by the same method as the measurement of retardation, and the average value of (ΔNxz×d) and (ΔNyz×d) is calculated to calculate the thickness direction retardation (Rth). ) Was asked.

(Production Example 1-Polyester A)
When the temperature of the esterification reaction vessel 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 0.017 parts by mass of antimony trioxide as a catalyst were added while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Next, the pressure was raised and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240° C., the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, the temperature was raised to 260° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, 15 minutes later, a dispersion treatment was performed with a high-pressure disperser, and 15 minutes later, the obtained esterification reaction product was transferred to a polycondensation reaction vessel, and a polycondensation reaction was performed at 280° C. under reduced pressure.

After the completion of the polycondensation reaction, a 95% cut diameter was filtered through a Naslon filter having a diameter of 5 μm, extruded in a strand form from a nozzle, and cooled and solidified with cooling water that had been subjected to a filtering treatment (pore diameter: 1 μm or less) in advance. , Cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl/g, and the inert particles and the internally precipitated particles were substantially not contained. (Hereinafter, abbreviated as PET(A).)

(Production Example 2-Polyester B)
10 parts by mass of dried ultraviolet absorber (2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), PET(A) containing no particles (intrinsic viscosity 0.62 dl/g) was 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-Adjustment of Adhesion Modification Coating Liquid)
Performing an ester exchange reaction and a polycondensation reaction by a conventional method, 46 mol% of terephthalic acid as a dicarboxylic acid component (based on the entire dicarboxylic acid component), 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate, A water-dispersible metal sulfonate-containing copolymer polyester resin having a composition of ethylene glycol 50 mol% and neopentyl glycol 50 mol% as a glycol component (based on the entire glycol component) was prepared. Next, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant, the mixture is heated and stirred, and when it reaches 77° C., the above. After adding 5 parts by mass of a water-dispersible metal sulfonate-containing copolyester resin and continuing stirring until the resin clumps out, the resin aqueous dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolyester resin solution was obtained. Furthermore, after dispersing 3 parts by mass of aggregate silica particles (manufactured by Fuji Silysia Chemical Ltd., Silysia 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolyester resin solution is mixed with Silysia 310. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modification coating liquid.

(Example 1)
<Production of Polarizer-Protecting Polyester Film 1>
After 90 parts by mass of PET(A) resin pellets containing no particles and 10 parts by mass of PET(B) resin pellets containing an ultraviolet absorber as a raw material for the base film intermediate layer were dried under reduced pressure (1 Torr) at 135° C. for 6 hours. , Extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method and fed to Extruder 1 (for outer layer I layer and outer layer III) and melted at 285°C. .. These two types of polymers were respectively filtered with a stainless sintered filter medium (nominal filtration accuracy: 10 μm particles 95% cut), laminated with a type 2 three-layer confluent block, and extruded into a sheet form from a die. The film was wound around a casting drum having a surface temperature of 30° C. and cooled and solidified by using an electrostatically applied casting method to prepare an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Then, the above-mentioned adhesive property modification coating liquid 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 this coating layer was formed was guided to a tenter stretching machine, guided to a hot air zone at a temperature of 105° C. while gripping the end portion of the film with a clip, and stretched to TD 4.0 times. Next, heat treatment is performed at a temperature of 180° C. for 30 seconds, then the film cooled to 100° C. is stretched 1.0% in the width direction, and then a clip that holds both ends of the film cooled to 60° C. To remove the jumbo roll consisting of a uniaxially oriented PET film with a film thickness of about 80 μm, and divide the jumbo roll into three equal parts to obtain three slit rolls (L (left side)). , C (center), R (right side)) were obtained. A polyester film 1 for protecting a polarizer was obtained from a slit roll positioned at R. In the polyester film 1 for protecting a polarizer, the direction in which the heat shrinkage rate was the maximum was 7.0 degrees from TD.

<Creating a liquid crystal panel>
The polyester film 1 for protecting a polarizer was attached to one side of a polarizer composed of PVA, iodine and boric acid 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. Further, a TAC film (manufactured by Fuji Film Co., Ltd., thickness: 80 μm) was attached to the surface opposite to the polarizer to prepare a light source side polarizing plate.

A liquid crystal panel was taken out from a 46-inch size IPS type liquid crystal television using a 0.4 mm-thick glass substrate for the liquid crystal cell. Peel off the polarizing plate on the light source side from the liquid crystal panel, and replace the polarizing plate on the light source side created above with the transmission axis direction of the polarizing plate on the light source side before peeling (parallel to the horizontal direction). A liquid crystal panel was prepared by bonding the liquid crystal cells through PSA so as to match each other.
The polarizing plate on the light source side was attached to the liquid crystal cell so that the polyester film 1 for protecting the polarizer was on the distal side (opposite side) to the liquid crystal cell. Further, the viewing-side polarizing plate was one in which a TAC film was laminated on both surfaces of a polarizer, and was attached to a liquid crystal cell so that the absorption axis direction of the polarizer was parallel to the horizontal direction.

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

(Example 3)
<Production of polyester film 3 for protecting the polarizer>
In the film formation of the polyester film 1 for protecting a polarizer of Example 1, a polarizer protective film was prepared in the same manner as the polyester film for protecting a polarizer 1 except that the film cooled to 100° C. was stretched by 1.7% in the width direction. Got 3. The direction in which the polyester film 3 for protecting the polarizer had the maximum heat shrinkage was 5.3 degrees from TD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared 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 Polyester Film 4 for Protecting Polarizer>
In the film formation of the polyester film 1 for protecting a polarizer of Example 1, the film cooled to 100° C. was stretched by 2.0% in the width direction, and after being stretched 4 times in TD, heat treatment was performed at a temperature of 180° C. for 30 seconds. A polarizer protective film 4 was obtained in the same manner as the polarizer protective polyester film 1 except that the coating solution for the hard coat layer was applied to one surface of the polyester film at the previous time. In the polyester film 4 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 4.8 degrees from TD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 1 except that the polyester film 1 for protecting the polarizer was replaced with the polyester film 4 for protecting the polarizer.

(Example 5)
<Production of Polarizer-Protecting Polyester Film 5>
A polyester film 5 for protecting the polarizer was obtained in the same manner as the polyester film 4 for protecting the polarizer, except that the film thickness after stretching was adjusted to 160 μm by adjusting the rotation speed of the casting roll. In the polyester film 5 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 4.8 degrees from TD.
<Creating a liquid crystal panel>
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)
<Production of Polarizer-Protecting Polyester Film 6>
In the production of the polyester film 1 for protecting a polarizer of Example 1, a film for cooling 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 flow direction. A polyester film 6 was obtained. In the polyester film 6 for protecting the polarizer, the direction in which the heat shrinkage rate was the maximum was 9.0 degrees from MD.
<Creating a liquid crystal panel>
In the production of the light source side polarizing plate of Example 1, the polarizer protecting polyester film 6 was used in place of the polarizer protecting polyester film, and the transmission axis of the polarizer was parallel to the MD of the polarizer protecting polyester film 6. A liquid crystal panel was prepared in the same manner as in Example 1 except that the light source side polarizing plate was prepared by adhering as described above.

(Example 7)
<Production of polyester film 7 for protecting the polarizer>
In the production of the polyester film 1 for protecting a polarizer of Example 1, a film for cooling a polarizer was protected in the same manner as the polyester film 1 for protecting a polarizer, except that the film cooled to 100° C. was stretched by 1.7% in the flow direction. A polyester film 7 was obtained. In the polyester film 7 for protecting the polarizer, the direction in which the heat shrinkage rate became the maximum was 8.3 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 6 except that the polarizer protecting polyester film 6 was replaced with the polarizer protecting polyester film 7.

(Example 8)
<Production of polyester film 8 for protecting the polarizer>
In the film formation of the polyester film 1 for protecting a polarizer of Example 1, the polyester film 1 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 2.0% in the flow direction. A polyester film 8 was obtained. In the polyester film 8 for protecting the polarizer, the direction in which the heat shrinkage rate was the maximum was 7.0 degrees from MD.
<Creating a liquid crystal panel>
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)
<Production of Polyester Film 9 for Protecting Polarizer>
A polyester film 9 for protecting a polarizer was obtained in the same manner as the polyester film 8 for protecting a polarizer, except that the film thickness after stretching was adjusted to 160 μm by adjusting the rotation speed of the casting roll. In the polyester film 9 for protecting the polarizer, the direction in which the heat shrinkage rate was the maximum was 7.0 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 6 except that the polarizer protecting polyester film 6 was replaced with the polarizer protecting polyester film 9.

(Example 10)
<Production of Polyester Film 10 for Protecting Polarizer>
A polarizer protective film in the same manner as the polyester film 6 for protecting a polarizer, except that it was stretched 4.0 times in MD and 4.0 times in TD instead of being stretched 4.0 times in TD. Got 10. In the polyester film 10 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 8.7 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 6 except that the polarizer protecting polyester film 6 was replaced with the polarizer protecting polyester film 10.

(Example 11)
<Production of Polarizer-Protecting Polyester Film 11>
In the production of the polyester film 10 for protecting a polarizer of 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 flow direction. A polyester film 11 was obtained. In the polyester film 11 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 7.5 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 10 except that the polyester film 10 for protecting the polarizer was replaced with the polyester film 11 for protecting the polarizer.

(Example 12)
<Production of Polyester Film 12 for Protecting Polarizer>
In the film formation of the polyester film 10 for protecting a polarizer of 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 5.0% in the width direction. A polyester film 12 was obtained. The direction in which the heat shrinkage rate of the polyester film 12 for protecting the polarizer was maximum was 1.8 degrees from TD.
<Creating a liquid crystal panel>
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 12 for protecting the polarizer.

(Example 13)
<Production 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 60 μm by adjusting the rotation speed of the casting roll. The direction in which the heat shrinkage rate of the polyester film 13 for protecting the polarizer was maximum was 4.8 degrees from TD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared 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)
<Production of Polarizer-Protecting Polyester Film 14>
In the cooling step after stretching 1.7% in the width direction, the polarizer protective film 14 was prepared in the same manner as the polarizer protective film 3 except that the film was passed through without changing the clip width holding both ends of the film. Obtained. The direction in which the heat shrinkage rate of the polyester film 14 for protecting the polarizer was maximum was 33.0 degrees from TD.
<Creating a liquid crystal 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)
<Production of Polyester Film 15 for Protecting Polarizer>
The film thickness after stretching was set to 200 μm by adjusting the rotating speed of the casting roll, and the film was passed through the cooling process after stretching and heat setting without changing the width of the clip holding both ends of the film. A polarizer protective film 15 was obtained in the same manner as the polarizer protective film 1. In the polyester film 15 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 20.0 degrees from MD.
<Creating a liquid crystal 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 prepared by laminating the polarizer protective film in parallel with the transmission axis of the polarizer. A liquid crystal panel was prepared in the same manner as in 1.

(Comparative example 2)
<Production of Polarizer-Protecting Polyester Film 16>
In the cooling step after stretching and heat setting, the polarized light was the same as that of the polarizer protective film 1, except that the clips holding both ends of the film were released at 95° C. without stretching the film in the width direction by 1.0%. The child protection film 16 was obtained. In the polyester film 16 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 1.0 degree from MD.
<Creating a liquid crystal 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 prepared by laminating the polarizer protective film in parallel with the transmission axis of the polarizer. A liquid crystal panel was prepared in the same manner as in 1.

(Comparative example 3)
<Production 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 adjusted to 50 μm by adjusting the rotation speed of the casting roll. In the polyester film 17 for protecting the polarizer, the direction in which the heat shrinkage rate was the maximum was 7.0 degrees from TD.
<Creating a liquid crystal panel>
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)
<Production of Polyester Film 18 for Protecting Polarizer>
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 film thickness after stretching was set to 160 μm by adjusting the rotation speed of the casting roll. The direction in which the heat shrinkage rate of the polyester film 18 for protecting the polarizer was maximum was 6.5 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 11 except that the polarizer protecting polyester film 11 was replaced with the polarizer protecting polyester film 18.

(Comparative example 5)
<Production of Polyester Film 19 for Protecting Polarizer>
The film thickness after stretching was set to 160 μm by adjusting the rotation speed of the casting roll, and in the film formation of the polyester film 1 for protecting the polarizer of Example 1, the film cooled to 100° C. was 1.0 in the flow direction. 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 stretching was performed. The direction in which the polyester film 19 for protecting the polarizer had the maximum heat shrinkage was 11.0 degrees from MD.
<Creating a liquid crystal panel>
In the production of the light source side polarizing plate of Example 1, the polarizer protecting polyester film 19 is used instead of the polarizer protecting polyester film, and the transmission axis of the polarizer and the TD of the polarizer protecting polyester film 19 are parallel to each other. A liquid crystal panel was prepared in the same manner as in Example 1 except that the light source side polarizing plate was prepared by adhering as described above.

(Comparative example 6)
<Production of Polarizer-Protecting Polyester Film 20>
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 adjusted to 80 μm by adjusting the rotation speed of the casting roll. In the polyester film 20 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Comparative Example 5 except that the polarizer protecting polyester film 19 was replaced with the polarizer protecting polyester film 20.

(Comparative Example 7)
<Production 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 polyester film 21 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from MD.
<Creating a liquid crystal panel>
In the production of the light source side polarizing plate of Example 1, a polarizer protecting polyester film 21 is used instead of the polarizer protecting polyester film 1, and the transmission axis of the polarizer and the MD of the polarizer protecting polyester film 21 are parallel. A liquid crystal panel was prepared in the same manner as in Example 1 except that the light source side polarizing plate was prepared by adhering so as to form the light source side polarizing plate.

(Comparative Example 8)
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 1 except that the polarizer protective film 15 was laminated so that the transmission axis of the polarizer and the TD of the polarizer protective film were parallel to each other to prepare a light source side polarizing plate. did.

(Comparative Example 9)
<Production of Polyester Film 22 for Protecting Polarizer>
The film thickness after stretching was set to 160 μm by adjusting the rotation speed of the casting roll, and in the film formation of the polyester film 1 for protecting the polarizer of Example 1, the film cooled to 100° C. was 1.0 in the flow direction. 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 film was stretched in%. In the polyester film 22 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was 11.0 degrees from MD.
<Creating a liquid crystal panel>
In the production of the light source side polarizing plate of Example 1, a polarizer protecting polyester film 22 is used instead of the polarizer protecting polyester film 1, and the transmission axis of the polarizer is parallel to the MD of the polarizer protecting polyester film 22. A liquid crystal panel was prepared in the same manner as in Example 1 except that the light source side polarizing plate was prepared by adhering so as to form the light source side polarizing plate.

<Production of Polyester Film 23 for Protecting Polarizer>
In the production of the polyester film 10 for protecting a polarizer of Example 10, the polyester film for protecting a polarizer 10 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 flow direction. A polyester film 23 was obtained. In the polyester film 23 for protecting the polarizer, the direction in which the heat shrinkage rate was maximum was from MD to 4.5 degrees.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 10 except that the polarizer protecting polyester film 10 was replaced with the polarizer protecting polyester film 23.

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

(Example 1A to Example 5A, Example 13A)
It should be noted that Example 1 was repeated except that a polarizing plate having the same configuration 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. Also in the case of separately evaluating in the same manner as in Examples 5 to 13, similar to the results of Examples 1 to 5 and 13 in Table 1 above, good results (◯) in the warp evaluation of the panel were obtained. The polarizing plate on the light source side and the polarizing plate on the viewing side 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)
In Examples 1A to 5A and 13A, evaluation was separately performed 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. Also in this case, as in Examples 1A to 5A and Example 13A, good results (◯) were obtained in the warp evaluation of the panel.

According to the present invention, it is possible to provide a polarizer protective film, a polarizing plate and a liquid crystal display device capable of suppressing the warpage of a liquid crystal panel.

Claims (11)

A polyester film for protecting a polarizer, which is laminated on one surface of a polarizer, and which 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 (where the shrinkage force F _f (N/m) is Thickness (mm)×elastic modulus (N/mm ² )×thermal shrinkage rate (%) at 80° C. for 30 minutes÷100×1000, where 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 is the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer.
(2) Ratio (F _f /F _v ) of the shrinkage force F _{f of the} polyester film in the direction parallel to the transmission axis of the polarizer and the shrinkage force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer. ) 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×elastic modulus (N/mm ² )×80° C./30 minutes treatment) Thermal shrinkage (%)/100×1000, where 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 absorption axis of the polarizer. This is the heat shrinkage rate of the polyester film in the parallel direction.) Furthermore, the polyester film for protecting a polarizer according to claim 1, which further satisfies the following requirement (3).
(3) The direction in which the heat shrinkage rate of the polyester film is maximum and the direction parallel to the transmission axis of the polarizer are substantially parallel to each other. The polyester film for protecting a polarizer according to claim 1 or 2, wherein the polyester film has a retardation of 3,000 to 30,000 nm. The polyester film for protecting a polarizer according to claim 1, wherein the polyester film has a thickness of 40 to 200 μm. The polyester film 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. 4. The polyester film for protecting a polarizer according to any one of 4 above. A polyester film for protecting a polarizer, which is laminated on one surface of a polarizer, and which satisfies the following requirements (1) and (2).
(1) The shrinkage force F _TD of TD of the polyester film is 800 N/m or more and 9000 N/m or less (where the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film×elastic modulus (N /Mm ² )×80° C./30-minute heat shrinkage (%)÷100×1000, where the elastic modulus is the TD elastic modulus of the polyester film and the thermal shrinkage is the polyester film's TD elastic modulus. It is the thermal shrinkage of TD.)
(2) the ratio of the contractile force _{F MD} in the MD shrinkage force _{F TD} and the polyester film in the TD of the polyester film _{(F TD} / _{F MD)} is 2.5 to 12.0 (where contraction force F _MD (N/m) is the thickness (mm) of the polyester film×elastic modulus (N/mm ² )×heat shrinkage rate (%) of treatment at 80° C. for 30 minutes÷100×1000. Is the MD elastic modulus of the polyester film, and the heat shrinkage is the MD thermal shrinkage of the polyester film.) The polyester film for protecting a polarizer according to claim 6, which further satisfies the following requirement (3).
(3) TD is substantially parallel to the direction in which the heat shrinkage rate of the polyester film is maximum. A polarizing plate comprising the polarizer-protecting polyester film according to claim 1 laminated on at least one surface of the polarizer. A polarizing plate in which the polyester film for protecting a polarizer according to any one of claims 1 to 7 is laminated on one surface of the polarizer, and the film is not provided on the other surface of the polarizer. The polarizing plate according to claim 8 or 9, wherein the polarizing plate has a rectangular shape, and the long side of the polarizing plate is parallel to the transmission axis thereof. A liquid crystal display device comprising a backlight light source and a liquid crystal cell arranged between two polarizing plates, wherein at least one of the two polarizing plates is the polarizing plate according to any one of claims 8 to 10. , Liquid crystal display device.