JPWO2019054406A1 - Polarizer protective film, polarizing plate and liquid crystal display - Google Patents

Abstract

An object of the present invention 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. 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 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. (2) The polyester film in the direction parallel to the transmission axis of the polarizer The ratio (Ff / Fv) of the shrinkage force Ff of the polyester film and the shrinkage force Fv 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.

Description

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

  The demand for liquid crystal display devices is expanding for applications such as liquid crystal televisions and liquid crystal displays of personal computers. Normally, a liquid crystal display device includes 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. The optical element (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 television screens have become thinner and larger, and LED backlights have been used as light sources, and glass substrates used for liquid crystal panels have become thinner than 0.7 mm. As a result, a problem that display unevenness occurs occurs, and its improvement is required.
The main cause of display unevenness is that the polarizer shrinks, and when the polarizer is placed under high temperature and high humidity, the shrinkage force in the alignment direction tends to relax. It is considered that the liquid crystal panel warps and bulges toward the backlight unit as a result, resulting in display unevenness.

  Conventionally, as in Patent Documents 1 and 2 below, the thickness of a glass substrate used for a liquid crystal panel is as large as 0.7 mm or more, so that the high rigidity of the glass suppresses the shrinkage of the polarizer. Therefore, the liquid crystal panel did not warp, and display unevenness was not a problem.

Therefore, it has been attempted to improve the warpage of the liquid crystal panel caused when the glass substrate is made thinner than 0.7 mm by using an optical film.
For example, when a cycloolefin-based resin is used as a polarizer protective film, productivity is reduced due to insufficient improvement of warpage of a liquid crystal panel and poor drying of a water paste for bonding to a polarizer. There was a problem of doing.
Further, when conventional triacetyl cellulose (TAC) is used as the polarizer protective film, there is a problem that the liquid crystal panel is warped.

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 that can suppress warpage of a liquid crystal panel.

  The present inventor, in order to solve the above problems, in the process of studying the cause of the above problems, in a direction parallel to the transmission axis of the polarizer, by setting the shrinkage force of the polyester film for protecting the polarizer to a specific range. It has been found that warpage of a liquid crystal panel can be improved, and the present invention has been made based on this finding.

  In detail, the liquid crystal display device, usually, on one surface of the liquid crystal cell, a polarizing plate is laminated so that the transmission axis direction of the polarizer is parallel to the long side direction of the liquid crystal display device, on the other surface, 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 types of commercially available liquid crystal display devices, it was found that a polarizer having a longer absorption axis direction of a polarizer having a large shrinkage force is likely to be curled due to shrinkage of the polarizing plate (curl shape problem). In general, the liquid crystal panel has a polarizer transmission axis of the upper and lower polarizers arranged in crossed Nicols due to the asymmetric configuration of the upper and lower polarizers in the liquid crystal panel. The inventors of the present invention have found that the problem is that the projection becomes convex on the side of the polarizing plate.

Furthermore, as a result of intensive studies, it has been clarified that the contraction force in the long-side direction of the polarizing plate whose polarizer transmission axis is long can be controlled by the residual strain of the protective film. You can control the curl.

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

As a result of the study, it has been clarified that a contraction force is generated in the TMA cooling process even when no contraction force is generated in the TMA heating process. This is because the strain due to thermal expansion is a reversible change and returns to the original state after heating and cooling. Is caused. That is, the distortion of the thermal stress can be replaced by the thermal shrinkage of the film, and the shrinking force after cooling is expressed by the following equation. In addition, the heat shrinkage in the present invention includes a change in moisture content during heat treatment.
Shrinking force (N / m) = film thickness (mm) × elasticity (N / mm ² ) × heat shrinkage (%) ÷ 100 × 1000

That is, a typical present invention is as follows.
Item 1.
A polyester film for protecting a polarizer laminated on one surface of a polarizer, wherein the polyester film satisfies the following requirements (1) and (2).
(1) The polyester film has a shrink force F _f of 800 N / m or more and 9000 N / m or less in a direction parallel to the transmission axis of the polarizer (provided that the shrink force F _f (N / m) of the polyester film is Thickness (mm) × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000, where the elastic modulus is a 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 a direction parallel to the transmission axis of the polarizer.)
(2) The ratio (F _f / F _v ) of the shrinking force F _{f of the} polyester film in a direction parallel to the transmission axis of the polarizer and the shrinking force F _v of the polyester film in a direction parallel to the absorption axis of the polarizer. ) Is 2.5 or more and 12.0 or less (provided that the shrinkage force _Fv (N / m) is the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ° C. for 30 minutes). Heat shrinkage (%) ÷ 100 × 1000, where the elastic modulus is the elastic modulus of the polyester film in a direction parallel to the absorption axis of the polarizer, and the heat shrinkage is equal to the absorption axis of the polarizer. This is the heat shrinkage of the polyester film in the parallel direction.)
Item 2.
Item 4. The polyester film for protecting a polarizer according to Item 1, further satisfying the following requirement (3).
(3) The direction in which the heat shrinkage of the polyester film is maximum and the direction parallel to the transmission axis of the polarizer are substantially parallel.
Item 3. The polyester film for protecting a polarizer according to Item 1 or 2, wherein the polyester film has a retardation of 3,000 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.
Items 1 to 4 having 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 a polarizer according to any one of the above.
Item 6.
A polyester film for protecting a polarizer laminated on one surface of a polarizer, wherein the polyester film satisfies the following requirements (1) and (2).
(1) The polyester film has a TD contraction force F _TD of 800 N / m or more and 9000 N / m or less (provided that the contraction force F _TD (N / m) is the thickness (mm) × elastic modulus (N) of the polyester film. / Mm ² ) × 80 ° C. for 30 minutes, heat shrinkage (%) ÷ 100 × 1000, where the elastic modulus is the TD elastic modulus of the polyester film, and the heat shrinkage is It is the heat shrinkage of TD.)
(2) The ratio (F _TD / F _MD ) of the TD shrink force F _TD of the polyester film to the MD shrink force F _MD of the polyester film is 2.5 or more and 12.0 or less (provided that the shrink force F _MD (N / m) is: polyester film thickness (mm) × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000. Is the MD elastic modulus of the polyester film, and the heat shrinkage is the MD heat shrinkage of the polyester film.)
Item 7.
Item 7. The polyester film for protecting a polarizer according to Item 6, further satisfying the following requirement (3).
(3) TD in which the direction in which the heat shrinkage of the polyester film is maximum is substantially parallel to TD.
Item 7. 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, wherein the polarizer-protecting polyester film according to any one of Items 1 to 7 is laminated on one surface of the polarizer, and the polarizer has no film on the other surface.
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 and a transmission axis thereof are parallel to each other.
Item 11.
A liquid crystal display device including a backlight light 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. Liquid crystal display.

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

The polyester film for protecting a polarizer of the present invention is a polarizer protective film for forming a polarizing plate, which is 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). is there.

In the present specification, the contraction force of the polyester film in the direction parallel to the transmission axis of the polarizer means the contraction 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 of the polyester film in the direction parallel to the transmission axis of the polarizer means the heat shrinkage of the polyester film in a 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 contraction force of the polyester film in the direction parallel to the absorption axis of the polarizer means the contraction 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 of the polyester film in a direction parallel to the absorption axis of the polarizer means the heat shrinkage of the polyester film in a 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 of the polyester film becomes maximum are substantially parallel. The term “substantially parallel” means that the absolute value of the angle between the direction of the transmission axis of the polarizer and the direction in which the heat shrinkage of the polyester film is maximized (hereinafter may be simply referred to as the slope of the heat shrinkage). Allow 15 degrees or less. The gradient of the heat shrinkage is preferably 12 degrees or less, more preferably 10 degrees or less, still more preferably 8 degrees or less, still more preferably 6 degrees or less, and particularly preferably 4 degrees or less. And most preferably 2 degrees or less. Since the smaller the slope of the heat shrinkage ratio is, the more preferable, the lower limit is 0 degree. When the slope of the heat shrinkage 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, in the transmission direction parallel to the axis of the polarizer, the absorption axis parallel to the direction of the contraction force F _f between the polarizer of the polyester film, the ratio of the contractile force F _v of the polyester film (F _f / F _v) is 2 When 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 of the polyester film is maximum is 40 degrees or less, the liquid crystal panel is not more than 0.5. Warpage can be reduced. The angle is preferably less than 35 degrees.
The heat shrinkage of the polyester film, the gradient of the heat shrinkage of the polyester film, and the direction in which the heat shrinkage of the polyester film is maximized can be measured by the method adopted in Examples described later.

  Usually, two polarizing plates are arranged in a liquid crystal display device so as to have a crossed Nicols relationship. When two polarizing plates are arranged in a crossed Nicols relationship, light usually does not pass through the two polarizing plates. However, due to the above-described shrinkage or warpage of the polarizer, the complete cross 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 heat shrinkage of the polarizer protective film is maximized and the transmission axis of the polarizer is small.

Polarizer protective polyester film of the present invention, the transmission axis parallel to the direction of the polarizer, it is desirable that the value of the contractile force F _f of the polyester film is not more than 800 N / m or more 9000 N / m. _If the lower limit of Ff is less than 800 N / m, the warpage of the liquid crystal panel may not be sufficiently reduced. _If the upper limit of Ff exceeds 9000 N / m, the liquid crystal panel may be warped in the opposite direction because the contraction force is too strong. A preferred range of the contraction 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 further more preferably 1200 N / m or less. / 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 shrinking force F _f indicates the shrinking force of the polyester film in a direction parallel to the transmission axis of the polarizer, and the thickness (mm) of the polyester film × elastic modulus (N / mm ² ) × 80 ° C. for 30 minutes The heat shrinkage (%) of the treatment is defined as 100 × 1000.
Here, the elastic modulus is an elastic modulus of the polyester film in a direction parallel to the transmission axis of the polarizer. The heat shrinkage refers to the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer (heat shrinkage in heat treatment at 80 ° C. for 30 minutes).

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

The polyester film for protecting a polarizer of the present invention preferably has an 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, the warpage 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 increases, and the polarizer is laminated on the surface opposite to the surface on which the polyester film for protecting the polarizer is laminated. There is a possibility that stress is applied to the protective film or the retardation film to be produced, and the display quality is degraded. Further, the film formation stability may be reduced and the film may be broken.

As a method of controlling the shrinkage force within the range of the above formula, a method of stretching the film while controlling the winding tension of the film after the completion of the heat treatment step after the film stretching is exemplified.

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 from 1,000 to 9000 N / mm ² . Although the shrinking force of the polyester film can be controlled by the elastic modulus, in order to increase the elastic modulus of the polyester film in the 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 , the polyester film may be easily torn, and the upper limit is preferably 9000 N / mm ² , more preferably 8000 N / mm 2. ² , more preferably 7,000 N / mm ² . On the other hand, when the orientation is low and the degree of crystallinity is low, the film may be deformed due to unevenness of the roll due to uneven thickness when wound on 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, further preferably 1800 N / mm ^2. The elastic modulus can be measured by a method adopted in Examples described later.

The polyester film for protecting a polarizer of the present invention preferably has a heat shrinkage 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 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 is preferably 4.5% or less, more preferably 4.0% or less, still more preferably 3.0% or less, still more preferably 2% or less, and 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 lower the crystallinity and the glass transition temperature, which may cause problems such as poor flatness. The heat shrinkage can be measured by a method adopted in Examples described later.

The polyester film for protecting a polarizer of the present invention preferably has a thickness of 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, the polyester film is liable to crack, and tends to have poor flatness due to insufficient rigidity. When the thickness is thin, it is necessary to increase the elastic modulus or the heat shrinkage of the polyester film in the transmission axis direction of the polarizer accordingly. However, since each parameter has an upper limit as described above, substantially 40 μm Is the lower limit. When the thickness of the film exceeds 200 μm, the variation in the elastic modulus or the heat shrinkage of the polyester film in the transmission axis direction of the polarizer increases accordingly, which may make it difficult to control the polyester film. Also rises. The thickness of the polyester film can be measured by a method adopted in Examples described later.

The polyester film for protecting a polarizer of the present invention preferably has an in-plane retardation in a specific range from the viewpoint of suppressing rainbow spots observed on a 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 the in-plane retardation is preferably 30000 nm or less, more preferably 18000 nm or less, and still more preferably 15000 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 determined by measuring the refractive index and thickness in the biaxial direction, or can be determined by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments). Note that the refractive index can be determined by an Abbe refractometer (measuring 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 retardation in the thickness direction (Rth) of preferably 0.2 or more, and more preferably 0.3 or more. Preferably it is 0.4 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. As the ratio of the in-plane retardation to the thickness direction retardation (Re / Rth) increases, the effect of birefringence increases and the tendency of the occurrence of rainbow-like color spots depending on the observation angle tends to be reduced. In a perfect uniaxial (uniaxially symmetric) film, the ratio of the retardation to the thickness direction retardation (Re / Rth) is 2.0, so that the ratio of the retardation to the thickness direction retardation (Re / Rth) is 2.0. The upper limit is preferably 2.0. The preferred upper limit of Re / Rth is 1.2 or less. The retardation in the thickness direction means an average of retardations obtained by multiplying two birefringences ΔNxz and ΔNyz by the film thickness d when the film is viewed from a cross section in the thickness direction.

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 still more preferably, from the viewpoint of suppressing rainbow-like color spots. It is 1.8 or less, more preferably 1.6 or less. And since a perfect uniaxial (uniaxially symmetric) film has an NZ coefficient of 1.0, 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 decrease significantly as approaching a completely uniaxial (uniaxially symmetric) film.

The NZ coefficient is represented by | Ny-Nz | / | Ny-Nx |, where Ny is the refractive index of the polyester film in the slow axis direction, and Nx is the refractive index in the direction orthogonal to the slow axis (fast axis). Nz represents the refractive index in the thickness direction. The orientation axis of the film is obtained using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments), and the biaxial refractive indexes (Ny, Nx, where Ny> Nx), and the refractive index (Nz) in the thickness direction are determined by an Abbe refractometer (NAR-4T, manufactured by Atago, measurement wavelength: 589 nm). The value thus obtained is 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 still more preferably 0, from the viewpoint of suppressing rainbow-like color spots. 0.08 or more, more preferably 0.09 or more, and most preferably 0.1 or more. There is no particular upper limit, 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 the 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 usable for the production of the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, , 5-Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic 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 Adipine , Pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

Examples of the diol component usable for the production of the polyester resin include, for example, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethyleneglycol, , 3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. No.

As the dicarboxylic acid component and the diol component constituting the polyester resin, one or more kinds can be used. Suitable polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and the like, and more preferably polyethylene terephthalate and polyethylene naphthalate, but these are Further, other copolymer components may be contained. These resins are excellent not only in transparency but also in thermal and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high modulus of elasticity and the control of the heat shrinkage is relatively easy.

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

(Addition of functional layer)
Since the polarizing plate using the polyester film for protecting the polarizer of the present invention is desirably integrated with the glass plate of the liquid crystal cell in a state where the heat shrinkage of the polyester film remains, an easy-adhesion layer, a hard coat layer When providing 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, lower the drying temperature. This is an embodiment in which it is preferable to perform setting or a method with a small heat history such as UV irradiation or electron beam irradiation. In addition, applying these functional layers during the polyester film forming process makes it possible to integrate the polarizing plate of the present invention with the glass plate of the liquid crystal cell without impairing the increased heat shrinkage. Therefore, this is a more desirable embodiment.
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 anti-reflection layer, an anti-reflection anti-glare layer, a low reflection anti-glare layer, and an antistatic layer are made of a polyester film. It is preferable that the layers are laminated on the surface opposite to the surface on which the polarizer is laminated, and that the contraction forces F _f and F _{v satisfy the} above-described conditions in a state where these functional layers are laminated.

(Method for producing oriented polyester film)
The polyester film used in the present invention can be produced according to a general polyester film production method. For example, a polyester resin is melted, and at a temperature higher than the glass transition temperature, the non-oriented polyester extruded and formed into a sheet shape is stretched in the longitudinal direction using a speed difference between rolls, and then stretched in the transverse direction by a tenter. A method of performing a heat treatment (thermal fixation) may be used. The film may be a uniaxially stretched film or a biaxially stretched film. Preferably, it is a uniaxially stretched film mainly stretched strongly in the transverse direction or a uniaxially stretched film 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 of Machine Direction, and may be referred to as a film flow direction, a longitudinal direction, or a longitudinal direction in this specification. Further, TD is an abbreviation of “Transverse Direction”, and may be referred to as a width direction or a lateral direction in this specification.

Polyester film, as contractile force F _f is equal to or less than 800 N / m or more 9000 N / m, it is preferable to adjust the film thickness, elastic modulus and thermal shrinkage.

(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 direction of the polarizer matches the MD of the polyester film when the polyester film is formed. In this case, the elastic modulus of the TD may be adjusted by a conventionally known method for a stretched polyester film.
Specifically, when the direction is the stretching direction, the stretching ratio may be set high, and when the direction is orthogonal to the stretching direction, the stretching ratio may be set low.

(Method of adjusting heat shrinkage of polyester film)
The heat shrinkage of the polyester film used as the polarizer protective film, the heat shrinkage of the MD when the transmission axis direction of the polarizer matches the MD when the polyester film is formed, In the case where the TD coincides with the TD, the thermal shrinkage of the TD may be adjusted by a conventionally known method for a stretched polyester film.

When adjusting the heat shrinkage of MD of the polyester film, for example, in the cooling process after stretching and heat setting, the distance between the clip gripping the film width direction end and the adjacent clip is stretched to MD. This can be adjusted by shrinking the clip interval to MD by reducing the clip interval. Also, in the cooling process after stretching and heat setting, when cutting or separating the film from the clip gripping the film width direction end, the film is stretched or shrunk to MD by adjusting the force for pulling the film. It can be adjusted by the following. When the temperature is raised in the off-line process after film formation for the purpose of providing a functional layer or the like, the heat shrinkage rate changes during the heating / cooling process. It is also possible to make adjustments by making them.

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

The shrinking force _Fv is adjusted so that the ratio of the shrinking force ( _Ff / _Fv ) becomes 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 heat shrinkage.

(How to adjust the inclination of the main axis of shrinkage of polyester film)
As disclosed in PCT / JP2014 / 073451 (WO2015 / 037527), the inclination of the main axis of shrinkage of a polyester film used as a polarizer protective film is determined by a cooling process after stretching and heat treatment of a polyester film by a tenter or film formation. It can be adjusted in a later off-line process. Specifically, in the cooling step, the shrinkage due to stretching and the thermal stress due to cooling that have not been completely removed in the heat setting step are generated, and depending on the balance in the film flow direction, drawing into the upstream side or downstream side. And the contraction main axis tilts. In order to reduce the inclination of the contraction main axis, it is necessary to adjust the contraction force in the film flow direction in the cooling step (total of the contraction force due to stretching and the contraction force due to cooling) to be uniform. In order to make the film uniform, it is desirable that the film be shrunk in the film flow direction in a temperature range where the shrinkage force is high in the film flow direction, or that the film be stretched in the film flow direction in a temperature region where the shrinkage force is low in the film flow direction. As a method for contracting or stretching, a conventionally known method may be used. Also, when cutting or separating the film end, it is necessary to pay attention to the fact that the film shrinks freely in the width direction below the cut / separated temperature range and the heat shrinkage below the temperature range becomes small.

The polarizing plate has the polarizer-protecting polyester film of the present invention 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, or a norbornene film is laminated on the other surface of the polarizer. Alternatively, a polarizing plate having no film 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 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 may be a retardation film formed by coating.
When a film or coating layer other than the polarizer-protecting polyester film of the present invention is laminated on the polarizer, shrinkage of the film or coating layer other than the polarizer-protecting polyester film in a direction parallel to the transmission axis of the polarizer. Force, and in the direction parallel to the absorption axis of the polarizer, the shrinking force of the film and the coating layer other than the polyester film for protecting the polarizer is preferably less than or equal to the value of _Ff of the polyester film for protecting the polarizer. Preferably, the value of _Fv of the polyester film for protecting a polarizer is equal to or less than Fv. Further, in the direction parallel to the transmission axis of the polarizer, the shrinking force of the film and 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 shrinking force of the film or the coating layer is preferably 250 N / m or less, more preferably 200 N / m or less. The shrinkage force of a film or coating layer other than the polarizer-protecting polyester film can be measured in the same manner as in the case of the polyester film. That is, (thickness (mm) of film or coating layer × modulus of elasticity (N / mm ² ) × heat shrinkage (%) of 80 ° C. for 30 minutes ÷ 100 × 1000).

Industrially, a polarizing plate is formed by laminating a long polarizer and a long polyester film for protecting a polarizer via an adhesive in a roll-to-roll manner. And since a polarizer is normally manufactured by extending | stretching in a longitudinal direction, MD has an absorption axis and TD has a transmission axis.

Therefore, from the viewpoint of industrially producing a polarizing plate, the polyester film for protecting a polarizer of the present invention is preferably the following (1) and (2).
(1) The polyester film has a TD contraction force F _TD of 800 N / m or more and 9000 N / m or less.
However, the shrinkage force F _TD (N / m) is the thickness of the polyester film (mm) × elasticity (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000. Here, the elastic modulus and the thermal shrinkage are the TD elastic modulus and the TD thermal shrinkage of the polyester film, respectively.
(2) The ratio (F _TD / F _MD ) of the TD shrink force F _TD of the polyester film to the MD shrink force F _MD of the polyester film 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 (%) at 80 ° C. for 30 minutes ÷ 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.

Moreover, 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 of the polyester film is maximum.
The expression “substantially parallel” allows that the absolute value of the angle (gradient of the heat shrinkage) between the direction in which the heat shrinkage of the polyester film is maximized and the TD direction is 15 degrees or less. The gradient of the heat shrinkage is preferably 12 degrees or less, more preferably 10 degrees or less, still more preferably 8 degrees or less, still more preferably 6 degrees or less, and particularly preferably 4 degrees or less. And most preferably 2 degrees or less. Since the smaller the slope of the heat shrinkage ratio is, the more preferable, the lower limit is 0 degree.
However, when the ratio (F _TD / F _MD ) of the TD shrink force F _TD of the polyester film to the MD shrink force F _MD of the polyester film is 2.5 or more and 12.0 or less, the heat shrinkage of the polyester film is Even when the absolute value of the angle formed by the maximum direction and the TD is 40 degrees or less, the warpage of the liquid crystal panel can be reduced. The angle is preferably less than 35 degrees.

When considering the industrial production of a polarizing plate in the form of a roll-to-roll method as described above, F _TD is equivalent to F _f , so that the preferred range of F _TD and F _f Are preferably the same. Further, since F _TD / F _MD is equivalent to F _f / F _v , the preferred ranges of 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 of both are the same. "Thermal shrinkage of TD at the time of heat treatment of the polyester film at 80 ° C. for 30 minutes" corresponds to "the heat shrinkage of the polyester film at the time of heat treatment of the polyester film at 80 ° C. for 30 minutes in the transmission axis direction of the polarizer". Therefore, both preferred ranges 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 protecting 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, the position of the polarizer protective film on the light source side starting from the polarizer of the viewing side polarizer and / or the polarizer of the light source side polarizing plate starting from the polarizer of the viewing 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 one of the polarizing plates has its long side parallel to the absorption axis and the other has a parallel absorption axis. Are arranged such that their long sides are parallel to the transmission axis and their absorption axes are perpendicular to each other. Usually, a polarizing plate having a relationship 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 of the liquid crystal display device, and a polarizing plate in which the long side of the polarizing plate and the transmission axis are parallel to each other. Are used as a light source side polarizing plate of a liquid crystal display device. At least, the polarizing plate of the present invention is preferably used as a polarizing plate having a parallel relation between the long side of the polarizing plate and the transmission axis, from the viewpoint of suppressing the 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 and a transmission axis parallel to each other and a polarizing plate having a long axis and an absorption axis parallel to each other.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and the present invention is implemented with appropriate modifications within a range that is compatible with the gist of the present invention. And they are all included in the technical scope of the present invention.

(1) Contraction force F _f
The shrink force F _f of the polyester film was calculated from the following equation. The thickness, elastic modulus, and heat shrinkage of the polyester film are measured values described below. The modulus of elasticity is the modulus of elasticity of the polyester film in a direction parallel to the transmission axis of the polarizer. The heat shrinkage is a heat shrinkage of the polyester film in a direction parallel to the transmission axis of the polarizer.
Shrink force F _f (N / m) = thickness (mm) of polyester film × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000

(2) Contraction force _Fv
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 measured values described below. The elastic modulus is an elastic modulus of the polyester film in a direction parallel to the absorption axis of the polarizer. The heat shrinkage is a heat shrinkage of the polyester film in a direction parallel to the absorption axis of the polarizer.
Shrinkage force _Fv (N / m) = thickness (mm) of polyester film × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes 分 100 × 1000

(3) Film Thickness The thickness (mm) of the polyester film was measured using an electric micrometer (Millitron 1245D, manufactured by Fineleuf Co.) after standing for 168 hours in an environment of 25 ° C. and 50 RH%, and the unit was 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%. The evaluation was performed using. Tensile mode, drive frequency is 1 Hz, distance between chucks is 5 mm, and temperature rise rate is 2 ° C./min. Measure the temperature dependence of 25 ° C. to 120 ° C. and average the storage elastic modulus of 30 ° C. to 100 ° C. 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. Note that the above measurement was performed using a polyester film alone (a polyester film alone for protecting a polarizer).

(5) Heat Shrinkage Ratio and Slope of Heat Shrinkage Ratio of Polyester Film The polyester film was allowed to stand in an environment of 25 ° C. and 50 RH% for 168 hours, and then a circle having a diameter of 80 mm was drawn. Using an image measure IM6500), the measurement was made at every 1 °, and the length was measured before processing. Next, a heat treatment is performed for 30 minutes using a gear oven set at 80 ° C., and then, after cooling for 10 minutes in an environment set at room temperature of 25 ° C., an evaluation is performed for each 1 ° in the same manner as before the processing. , After treatment. In addition, the said process was performed with the polyester film simple substance (the polyester film single substance for polarizer protection).

The heat shrinkage rate was evaluated for each angle using the following formula.
Heat shrinkage = (length before processing−length after processing) / length before processing × 100
Thus, for the polyester film, the heat shrinkage of the polyester film in the direction parallel to the polarizer transmission axis and the heat shrinkage of the polyester film in the direction parallel to the polarizer absorption axis were determined.

An evaluation of 360 ° was performed for each 1 ° above, the direction in which the heat shrinkage rate was maximum was specified, and the absolute value of the angle between the 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 is defined by a narrow angle from the direction of the transmission axis of the polarizer, and is in a range of 0 to 90 °.

(6) Warpage of liquid crystal panel
The liquid crystal panel manufactured in each of the examples and comparative examples was subjected to a heat treatment for 30 minutes using a gear oven set at 80 ° C., and then cooled in an environment set at room temperature of 25 ° C. and 50% RH for 30 minutes. It was placed on a horizontal surface with its side down, the height of the four corners was measured with a measure, and the maximum value was taken as the amount of warpage. The amount of warpage was evaluated as follows.
：: 0 mm or more and less than 2.0 mm
Δ: 2.0 mm or more and 3.0 mm or less
×: exceeds 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), and the slow axis direction was the long side of the sample for measurement. A rectangle having a size of 4 cm × 2 cm was cut out so as to be in parallel with the sample, and used as a measurement sample. For this sample, a biaxial refractive index orthogonal to the refractive index (refractive index in the slow axis direction: Ny, a fast axis (refractive index in the direction orthogonal to the slow axis direction): Nx), and a refractive index in the thickness direction (Nx) Nz) was determined using an Abbe refractometer (NAR-4T, manufactured by Atago, measurement wavelength: 589 nm). The NZ coefficient was determined using these values.

The retardation is a parameter defined by a product (の Nxy × d) of anisotropy (△ Nxy = | Nx−Ny |) of the biaxial refractive index on the film and the film thickness d (nm). Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (△ Nxy) was determined by the following method. 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), and 4 cm was set so that the slow axis direction was parallel to the long side of the sample for measurement. A rectangle of 2 cm was cut out and used as a measurement sample. For this sample, the Abbe refraction is the refractive index of two orthogonal axes (the refractive index in the slow axis direction: Ny, the refractive index in the direction orthogonal to the slow axis direction: Nx), and the refractive index (Nz) in the thickness direction. The absolute value of the biaxial refractive index difference (| Nx-Ny |) was determined as the anisotropy of the refractive index (ｘNxy) using a refractometer (NAR-4T, manufactured by Atago Co., Ltd., measurement wavelength: 589 nm). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Fineleuf Co.), and the unit was converted to nm. The retardation (Re) was determined from the product (ΔNxy × d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(8) Thickness direction retardation (Rth)
Thickness direction retardation is defined as multiplying two birefringences △ Nxz (= | Nx-Nz |) and △ Nyz (= | Ny-Nz |) by a film thickness d when viewed from a cross section in the film thickness direction. It is a parameter indicating the average of the retardation obtained by the above. Nx, Ny, Nz and the film thickness d (nm) are obtained in the same manner as the measurement of the retardation, and the average value of (△ Nxz × d) and (△ Nyz × d) is calculated to obtain the retardation in the thickness direction (Rth ).

(Production Example 1-Polyester A)
When the temperature of the esterification reactor reached 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 temperature was increased under pressure to perform a pressure esterification reaction under the conditions of a gauge pressure of 0.34 MPa and 240 ° C. Then, the esterification reactor was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Next, after 15 minutes, a dispersion treatment was performed with a high-pressure disperser. 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 completion of the polycondensation reaction, the mixture is filtered through a NASLON filter having 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 diameter: 1 μm or less). , And cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl / g, and substantially no inert particles and no internally precipitated particles were contained. (Hereinafter abbreviated as PET (A))

(Production Example 2-Polyester B)
10 parts by mass of a dried ultraviolet absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinone-4-one), PET (A) containing no particles (intrinsic viscosity (0.62 dl / g), and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorbent (hereinafter abbreviated as PET (B)).

(Production Example 3-Preparation of Adhesion Modification Coating Solution)
A transesterification reaction and a polycondensation reaction are carried out by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal base-containing copolymerized polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as a glycol component (based on the whole 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 was heated and stirred. After adding 5 parts by mass of the water-dispersible sulfonic acid metal base-containing copolymerized polyester resin and continuing to stir until the resin no longer solidifies, the aqueous resin dispersion is cooled to room temperature to obtain a solid content of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia K.K., Sylysia 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolymerized polyester resin solution was used to disperse thyricia 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 adhesion-modified coating solution.

(Example 1)
<Production 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 an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) as raw materials for a base film intermediate layer, To the extruder 2 (for the intermediate layer II), and the PET (A) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I and the outer layer III), and was melted at 285 ° C. . The two types of polymers are respectively filtered with a stainless steel sintered body filter medium (nominal filtration accuracy: 10 μm, particles cut by 95%), laminated in a two-type three-layer merging block, extruded into a sheet from a die, and extruded. It was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and cooled and solidified to form an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, the above-mentioned adhesion-modified coating solution was applied to both surfaces of the unstretched PET film by a reverse roll method so that the application amount after drying was 0.08 g / m ² , followed by drying at 80 ° C. for 20 seconds. .

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

<Creating a liquid crystal panel>
A polyester film 1 for protecting a polarizer was attached to one side of a polarizer made of PVA, iodine and boric acid such that the transmission axis of the polarizer and the TD of the polyester film 1 for protecting the polarizer were parallel. Further, a TAC film (manufactured by Fuji Film Co., Ltd., thickness: 80 μm) was adhered to the opposite surface of the polarizer to prepare 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 having a thickness of 0.4 mm as a liquid crystal cell. The light source side polarizing plate is peeled off from the liquid crystal panel, and instead, the light source side polarizing plate prepared above is set so that the transmission axis of the polarizer is the transmission axis direction (parallel to the horizontal direction) of the light source side polarizing plate before being peeled off. The liquid crystal cells were bonded via the PSA so as to match each other, and a liquid crystal panel was prepared.
In addition, the light source side polarizing plate was bonded to the liquid crystal cell such that the polarizer-protecting polyester film 1 was on the distal side (opposite side) of the liquid crystal cell. Further, the viewing side polarizing plate was formed by laminating TAC films on both sides of a polarizer, and was bonded to a liquid crystal cell such that the absorption axis direction of the polarizer was parallel to the horizontal direction.

(Example 2)
<Production of polyester film 2 for protecting polarizer>
In the production of the polarizer-protecting polyester film 1 of Example 1, a polarizer-protecting polyester film 1 was produced in the same manner as the polarizer-protecting polyester film 1 except that the film cooled to 100 ° C. was stretched 1.5% in the width direction. Polyester film 2 was obtained. In the polyester film 2 for protecting a polarizer, the direction in which the heat shrinkage ratio was the maximum was 6.5 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 a polarizer was replaced with the polyester film 2 for protecting a polarizer.

(Example 3)
<Production of polyester film 3 for protecting polarizer>
A polarizer protective film was produced in the same manner as the polarizer protective polyester film 1 except that the film cooled to 100 ° C. was stretched 1.7% in the width direction in the production of the polarizer protective polyester film 1 of Example 1. 3 was obtained. In the polyester film 3 for protecting a polarizer, the direction in which the heat shrinkage was the largest 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 a polarizer was replaced with the polyester film 3 for protecting a polarizer.

(Example 4)
<Production of polyester film 4 for protecting polarizer>
In the production of the polyester film 1 for protecting a polarizer in Example 1, the film cooled to 100 ° C. was stretched 2.0% in the width direction, and after 4 times stretching in TD, heat treatment at 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 liquid 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 a polarizer, the direction in which the heat shrinkage was the largest 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 polarizer-protecting polyester film 1 was replaced with the polarizer-protecting polyester film 4.

(Example 5)
<Production of polyester film 5 for protecting polarizer>
A polyester film 5 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 adjusted to 160 μm by adjusting the rotation speed of the casting roll. The direction in which the heat shrinkage ratio of the polyester film 5 for protecting a polarizer was the largest 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 a polarizer was replaced with the polyester film 5 for protecting a polarizer.

(Example 6)
<Production of polyester film 6 for protecting polarizer>
In the production of the polarizer-protecting polyester film 1 of Example 1, a polarizer-protecting polyester film 1 was formed in the same manner as the polarizer-protecting polyester film 1 except that the film cooled to 100 ° C. was stretched by 1.5% in the flow direction. Polyester film 6 was obtained. In the polyester film 6 for protecting a polarizer, the direction in which the heat shrinkage ratio was maximum was 9.0 degrees from MD.
<Creating a liquid crystal panel>
In preparing the light source side polarizing plate of Example 1, the polarizer protecting polyester film 6 was used instead of the polarizer protecting polyester film, and the transmission axis of the polarizer and the MD of the polarizer protecting polyester film 6 were 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 sticking to each other.

(Example 7)
<Production of polyester film 7 for protecting polarizer>
In the production of the polarizer-protecting polyester film 1 of Example 1, a polarizer-protecting polyester film 1 was produced in the same manner as the polarizer-protecting polyester film 1 except that the film cooled to 100 ° C. was stretched 1.7% in the flow direction. Polyester film 7 was obtained. In the polyester film 7 for protecting a polarizer, the direction in which the heat shrinkage ratio was the maximum was 8.3 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared 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 polarizer>
In the production of the polarizer-protecting polyester film 1 of Example 1, a polarizer-protecting polyester film 1 was prepared in the same manner as the polarizer-protecting polyester film 1 except that the film cooled to 100 ° C. was stretched 2.0% in the machine direction. Polyester film 8 was obtained. In the polyester film 8 for protecting a polarizer, the direction in which the heat shrinkage ratio was maximum was 7.0 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 6, except that the polarizer-protecting polyester film 6 was replaced with the polarizer-protecting polyester film 8.

(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 a polarizer, the direction in which the heat shrinkage ratio was the maximum was 7.0 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared 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 was formed in the same manner as the polarizer protective polyester film 6 except that the film was stretched 4.0 times in TD, but was changed to 4.0 times in MD and 1.0 times in TD. 10 was obtained. The direction in which the heat shrinkage ratio of the polyester film 10 for protecting a polarizer was the largest was 8.7 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 6, except that the polarizer-protecting polyester film 6 was changed to the polarizer-protecting polyester film 10.

(Example 11)
<Production of polyester film 11 for protecting polarizer>
In the production of the polarizer-protecting polyester film 10 of Example 10, except that the film cooled to 100 ° C. was stretched 1.7% in the flow direction, the same as the polarizer-protecting polyester film 10 was used. Polyester film 11 was obtained. In the polyester film 11 for protecting a polarizer, the direction in which the heat shrinkage ratio was the 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 a polarizer was replaced with the polyester film 11 for protecting a polarizer.

(Example 12)
<Production of polyester film 12 for protecting polarizer>
In the production of the polarizer-protecting polyester film 10 of Example 10, except that the film cooled to 100 ° C. was stretched by 5.0% in the width direction, the same as the polarizer-protecting polyester film 10 was performed. A polyester film 12 was obtained. In the polyester film 12 for protecting the polarizer, the direction in which the heat shrinkage was the largest was 1.8 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 polarizer-protecting polyester film 1 was replaced with the polarizer-protecting polyester film 12.

(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 adjusted to 60 μm by adjusting the rotation speed of the casting roll. In the polyester film 13 for protecting a polarizer, the direction in which the heat shrinkage was the largest 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 polarizer-protecting polyester film 1 was replaced with the polarizer-protecting polyester film 13.

(Example 14)
<Production of polyester film 14 for protecting polarizer>
In the cooling step after stretching by 1.7% in the width direction, the polarizer protective film 14 was replaced with the polarizer protective film 14 in the same manner as the polarizer protective film 3 except that the film was passed without changing the width of the clips holding both ends of the film. Obtained. The direction in which the heat shrinkage ratio of the polyester film 14 for protecting a polarizer was maximized was 33.0 degrees from TD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 3, except that the polarizer protective film 1 was changed to the polarizer protective film 14.

(Comparative Example 1)
<Production of polyester film 15 for protecting polarizer>
Except that the film thickness after stretching was adjusted to 200 μm by adjusting the rotation speed of the casting roll, and the film was passed without changing the width of the clips holding both ends of the film in the cooling process after stretching and heat setting. Was obtained in the same manner as in the polarizer protective film 1. In the polyester film 15 for protecting a polarizer, the direction in which the heat shrinkage ratio was the maximum was 20.0 degrees from MD.
<Creating a liquid crystal panel>
The examples except that the polarizer protective film 1 was replaced by the polarizer protective film 15 and that the light source side polarizing plate was prepared by laminating so that the transmission axis of the polarizer and the MD of the polarizer protective film were parallel. A liquid crystal panel was prepared in the same manner as in Example 1.

(Comparative Example 2)
<Production of polyester film 16 for protecting polarizer>
In the cooling step after stretching and heat setting, the polarization was performed in the same manner as in the polarizer protective film 1 except that the clips holding both ends of the film were released at 95 ° C. without performing the stretching process by 1.0% in the width direction. A child protection film 16 was obtained. In the polyester film 16 for protecting a polarizer, the direction in which the heat shrinkage ratio was maximum was 1.0 degree from MD.
<Creating a liquid crystal panel>
The examples except that the polarizer protective film 1 was replaced with the polarizer protective film 16 and that the light source side polarizing plate was prepared by laminating so that the transmission axis of the polarizer and the MD of the polarizer protective film were parallel. A liquid crystal panel was prepared in the same manner as in Example 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 a polarizer, the direction in which the heat shrinkage was the largest was 7.0 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 polarizer-protecting polyester film 1 was replaced with the polarizer-protecting polyester film 17.

(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 adjusted to 160 μm by adjusting the rotation speed of the casting roll. The direction in which the heat shrinkage ratio of the polyester film 18 for protecting a polarizer was the largest was 6.5 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared in the same manner as in Example 11, except that the polarizer-protecting polyester film 11 was changed to the polarizer-protecting polyester film 18.

(Comparative Example 5)
<Production of polyester film 19 for protecting polarizer>
The film thickness after stretching was adjusted to 160 μm by adjusting the rotation speed of the casting roll. In the production of the polarizer-protecting polyester film 1 of Example 1, the film cooled to 100 ° C. A polarizer-protecting polyester film 19 was obtained in the same manner as in the polarizer-protecting polyester film 1 except that the film was stretched in%. In the polyester film 19 for protecting a polarizer, the direction in which the heat shrinkage was the largest was 11.0 degrees from MD. <Creating a liquid crystal panel>
In producing the light source side polarizing plate of Example 1, the polarizer protecting polyester film 19 was 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 were 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 sticking to each other.

(Comparative Example 6)
<Production 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 adjusted to 80 μm by adjusting the rotation speed of the casting roll. In the polyester film 20 for protecting a polarizer, the direction in which the heat shrinkage ratio was maximum was 11.0 degrees from MD.
<Creating a liquid crystal panel>
A liquid crystal panel was prepared 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 a polarizer, the direction in which the heat shrinkage ratio was maximum was 11.0 degrees from MD.
<Creating a liquid crystal panel>
In producing the light source side polarizing plate of Example 1, the polarizer protecting polyester film 21 was 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 were parallel. A liquid crystal panel was prepared in the same manner as in Example 1 except that a light source side polarizing plate was prepared by sticking to each other.

(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 bonded 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 adjusted to 160 μm by adjusting the rotation speed of the casting roll. In the production of the polarizer-protecting polyester film 1 of Example 1, the film cooled to 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 film was stretched in%. In the polyester film 22 for protecting a polarizer, the direction in which the heat shrinkage ratio 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, the polarizer protecting polyester film 22 was 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 22 were parallel. A liquid crystal panel was prepared in the same manner as in Example 1 except that a light source side polarizing plate was prepared by sticking to each other.

(Comparative Example 10)
<Production of polyester film 23 for protecting polarizer>
In the production of the polarizer-protecting polyester film 10 of Example 10, except that the film cooled to 100 ° C. was stretched by 2.0% in the flow direction, the same as the polarizer-protecting polyester film 10 was used. A polyester film 23 was obtained. In the polyester film 23 for protecting a polarizer, the direction in which the heat shrinkage ratio was the maximum was 4.5 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 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 warpage of the panel as compared with the polarizing plate of the comparative example.

(Examples 1A to 5A and 13A)
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 for both polarizing plates as the light source side polarizing plate and the viewing side polarizing plate. Also in the case where evaluation was made separately in the same manner as in Examples 5 to 13, good results (に お い て) were obtained in the evaluation of the warpage of the panel, similarly to the results of Examples 1 to 5 and 13 in Table 1 above. The light source side polarizing plate and the viewing side polarizing plate were bonded to the liquid crystal cell such that the polarizer-protecting polyester film was on the distal side (opposite side) of the liquid crystal cell.

(Examples 1B to 5B and 13B)
In Examples 1A to 5A and Example 13A, evaluation was separately performed in the same manner as in Examples 1A to 5A and Example 13A, except that a TAC film was not used as the polarizer protective film on the liquid crystal cell side. In this case, as in Examples 1A to 5A and 13A, good results (（) were obtained in the evaluation of the warpage of the panel.

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

Claims (11)

A polyester film for protecting a polarizer laminated on one surface of a polarizer, wherein the polyester film satisfies the following requirements (1) and (2).
(1) The polyester film has a shrink force F _f of 800 N / m or more and 9000 N / m or less in a direction parallel to the transmission axis of the polarizer (provided that the shrink force F _f (N / m) of the polyester film is Thickness (mm) × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000, where the elastic modulus is a 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 a direction parallel to the transmission axis of the polarizer.)
(2) The ratio (F _f / F _v ) of the shrinking force F _{f of the} polyester film in a direction parallel to the transmission axis of the polarizer and the shrinking force F _v of the polyester film in a direction parallel to the absorption axis of the polarizer. ) Is 2.5 or more and 12.0 or less (provided that the shrinkage force _Fv (N / m) is the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ° C. for 30 minutes). Heat shrinkage (%) ÷ 100 × 1000, where the elastic modulus is the elastic modulus of the polyester film in a direction parallel to the absorption axis of the polarizer, and the heat shrinkage is equal to the absorption axis of the polarizer. This is the heat shrinkage of the polyester film in the parallel direction.) The polyester film for protecting a polarizer according to claim 1, further satisfying the following requirement (3).
(3) The direction in which the heat shrinkage of the polyester film is maximum and the direction parallel to the transmission axis of the polarizer are substantially parallel. 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 any one of claims 1 to 3, wherein the polyester film has a thickness of 40 to 200 µm.   The polyester film has a hard coat layer, an anti-reflection layer, a low reflection layer, an anti-glare layer, or an anti-reflection anti-glare layer on the surface opposite to the surface on which the polarizer is laminated, the anti-glare layer. 4. The polyester film for protecting a polarizer according to any one of 4. A polyester film for protecting a polarizer laminated on one surface of a polarizer, wherein the polyester film satisfies the following requirements (1) and (2).
(1) The polyester film has a TD contraction force F _TD of 800 N / m or more and 9000 N / m or less (provided that the contraction force F _TD (N / m) is the thickness (mm) × elastic modulus (N) of the polyester film. / Mm ² ) × 80 ° C. for 30 minutes, heat shrinkage (%) ÷ 100 × 1000, where the elastic modulus is the TD elastic modulus of the polyester film, and the heat shrinkage is It is the heat shrinkage of TD.)
(2) The ratio (F _TD / F _MD ) of the TD shrink force F _TD of the polyester film to the MD shrink force F _MD of the polyester film is 2.5 or more and 12.0 or less (provided that the shrink force F _MD (N / m) is: polyester film thickness (mm) × elastic modulus (N / mm ² ) × heat shrinkage (%) at 80 ° C. for 30 minutes ÷ 100 × 1000. Is the MD elastic modulus of the polyester film, and the heat shrinkage is the MD heat shrinkage of the polyester film.) The polarizer-protecting polyester film according to claim 6, further satisfying the following requirement (3).
(3) TD is substantially parallel to the direction in which the heat shrinkage of the polyester film is maximum.   A polarizing plate comprising the polarizer protecting polyester film according to any one of claims 1 to 7 laminated on at least one surface of the polarizer.   A polarizing plate, wherein the polarizer-protecting polyester film according to any one of claims 1 to 7 is laminated on one surface of a polarizer, and the polarizer has no film on the other surface. The polarizing plate according to claim 8, wherein the polarizing plate has a rectangular shape, and a long side of the polarizing plate and a transmission axis thereof are parallel to each other. A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates, wherein at least one of the two polarizing plates is the polarizing plate according to claim 8. , Liquid crystal display device.