JP7288878B2 - Polarizer protective film, polarizing plate and liquid crystal display device - Google Patents

Description

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

Demand for liquid crystal display devices is increasing for applications such as liquid crystal televisions and liquid crystal displays for personal computers. Normally, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides of the cell. It has a structure in which a film (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, liquid crystal television screens have become thinner and larger, and LED backlights have come to be used as light sources. Along with this, there arises a problem that display unevenness occurs, and there is a demand for its improvement.
The main cause of the display unevenness is the contraction of the polarizer. When the polarizer is placed under high temperature and high humidity conditions, the shrinkage force is generated in the orientation direction in order to relax the orientation. As a result, the liquid crystal panel warps and bulges toward the backlight unit, which is thought to cause display unevenness.

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

Therefore, attempts have been made to improve the warp of the liquid crystal panel that occurs when the thickness of the glass substrate is less than 0.7 mm, using an optical film.
For example, when a cycloolefin resin is used as a polarizer protective film, the improvement in the warpage of the liquid crystal panel is insufficient, and the water paste used to adhere to the polarizer has poor drying properties, resulting in a decrease in productivity. There was a problem of
Moreover, when conventional triacetyl cellulose (TAC) is used as a 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 an object thereof is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device capable of suppressing warping of liquid crystal panels.

In order to solve the above problems, the present inventors, in the process of examining the causes of the above problems, found that the shrinkage force of the polyester film for protecting the polarizer in the direction parallel to the transmission axis of the polarizer is set to a specific range. , and found that the warp of the liquid crystal panel can be improved, and based on this knowledge, the present invention was achieved.

Specifically, the liquid crystal display device is generally formed by laminating a polarizing plate on one surface of a liquid crystal cell so that the transmission axis direction of the polarizer is parallel to the long side direction of the liquid crystal display device, and on the other surface, The polarizing plates are laminated such 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 there is a shape factor problem (curl generally tends to occur in the long side direction) and the asymmetric configuration of the upper and lower polarizing plates in the liquid crystal panel. The inventors of the present invention have found that the essence of the problem is the convexity on the polarizing plate side.

Furthermore, as a result of intensive studies, it became clear that the shrinkage force in the long-side direction of the polarizing plate, in which the transmission axis of the polarizer is the long side, can be controlled by the residual strain of the protective film. It was found that the curl of the tape can be controlled.

Here, a method for measuring the shrinkage force of the polyester film for protecting the polarizer will be described. In general, the shrinkage force of a film is measured by using a TMA or the like, setting the initial length with a minimal load at the start of the test at a low temperature, and measuring the force in the shrinkage direction while the temperature is rising while maintaining the initial length. do. However, in the process of temperature rise, the contraction due to the recovery of the residual strain accompanying the conformational change of the polymer (hereinafter simply referred to as thermal contraction), and at the same time, the thermal expansion due to the increase in the free volume and occupied volume of the polymer due to the temperature rise ( hereinafter, simply referred to as thermal expansion) occurs, so in the temperature range near the glass transition temperature of the polyester film (for example, about Tg + 50 ° C.), the relationship is often thermal contraction < thermal expansion, so the film as a whole It expands and no contractile force is observed.

As a result of the investigation, it was found that even if the shrinkage force was not generated during the TMA heating process, the shrinkage force was generated during the TMA cooling 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. This is because In other words, the strain of thermal stress can be replaced with the thermal shrinkage rate of the film, and the shrinkage force after cooling is expressed by the following formula. In addition, the heat shrinkage rate in the present invention includes a change in moisture content during heat treatment.
Shrinkage force (N/m) = film thickness (mm) x elastic modulus (N/mm ² ) x heat shrinkage rate (%)/100 x 1000

That is, the representative present invention is as follows.
Section 1.
A polarizer-protecting polyester film that is laminated on one side of a polarizer and that satisfies the following requirements (1) and (2).
(1) The shrinkage force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer is 800 N/m or more and 9000 N/m or less (however, the shrinkage force F _f (N/m) is the Thickness (mm) × elastic modulus (N/mm ² ) × thermal shrinkage (%) after 30 minutes treatment at 80°C / 100 × 1000. Here, the elastic modulus is the direction parallel to the transmission axis of the polarizer. , is the elastic modulus of the polyester film, and the heat shrinkage is the heat shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer.)
(2) The ratio of the shrinkage force F _f of the polyester film in the direction parallel to the transmission axis of the polarizer to the shrinkage force F _v of the polyester film in the direction parallel to the absorption axis of the polarizer (F _f /F _v ) is 2.5 or more and 12.0 or less (however, the shrinkage force F _v (N/m) is the thickness of the polyester film (mm) × elastic modulus (N/mm ² ) × 80 ° C. · 30 minutes of treatment Thermal shrinkage rate (%) ÷ 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, and the thermal shrinkage rate is the absorption axis of the polarizer. It is the heat shrinkage rate of the polyester film in the parallel direction.)
Section 2.
Item 1. The polyester film for protecting a polarizer according to Item 1, which further satisfies the following requirement (3). (3) The direction in which the thermal shrinkage of the polyester film is maximized is substantially parallel to the direction parallel to the transmission axis of the polarizer.
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 30000 nm.
Section 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, wherein 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. The polyester film for protecting a polarizer according to any one of .
Item 6.
A polarizer-protecting polyester film that is laminated on one side of a polarizer and that satisfies the following requirements (1) and (2).
(1) The shrinkage force F _TD of the TD of the polyester film is 800 N/m or more and 9000 N/m or less (however, the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film x the elastic modulus (N /mm ² ) × Thermal shrinkage rate (%) after 30 minutes treatment at 80°C / 100 × 1000. Here, the elastic modulus is the TD elastic modulus of the polyester film, and the thermal shrinkage ratio is the polyester film's TD elastic modulus. It is the thermal shrinkage rate of TD.)
(2) The ratio of the shrinkage force F _TD in the TD of the polyester film to the shrinkage force F _MD in the MD of the polyester film ( _FTD / _FMD ) is 2.5 or more and 12.0 or less (provided that the shrinkage force F _MD (N/m) is polyester film thickness (mm)×elastic modulus (N/mm ² )×heat shrinkage (%) after 30-minute treatment at 80° C./100×1000, where elastic modulus is 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 6. The polyester film for protecting a polarizer according to Item 6, which further satisfies the following requirement (3). (3) Item 8. TD is substantially parallel to the direction in which the thermal shrinkage of the polyester film is maximized.
A polarizing plate comprising a polarizer and the polyester film for protecting a polarizer according to any one of Items 1 to 7 laminated on at least one surface of the polarizer.
Item 9.
A polarizing plate in which the polyester film for protecting a polarizer according to any one of Items 1 to 7 is laminated on one surface of a polarizer and the other surface of the polarizer does not have a film.
Item 10.
Item 10. The polarizing plate according to item 8 or 9, wherein the polarizing plate has a rectangular shape, and the long sides of the polarizing plate are parallel to the transmission axis thereof.
Item 11.
A liquid crystal display device having a backlight 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.

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 polarizer-protecting polyester film of the present invention is a polarizer-protecting 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. be.

In this specification, the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer means the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film. is.
The thermal shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer means the thermal shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film.
The elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer means 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.
The shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer means the shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film.
The thermal shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer means the thermal shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film.
The elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer means the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film.
The direction parallel to the transmission axis of the polarizer may be simply referred to as the transmission axis direction of the polarizer. Also, 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 polarizer-protecting polyester film of the present invention, it is preferable that the direction parallel to the transmission axis of the polarizer and the direction in which the thermal shrinkage of the polyester film is maximized are substantially parallel to each other. The term “substantially parallel” means that the absolute value of the angle between the transmission axis direction of the polarizer and the direction in which the thermal shrinkage rate of the polyester film is maximized (hereinafter sometimes simply referred to as the slope of the thermal shrinkage rate) is 15 degrees or less is allowed. The slope of the thermal shrinkage rate 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. The lower limit is 0 degrees because the smaller the slope of the thermal shrinkage rate, the better. If the inclination of the heat shrinkage rate of the polyester film is large, the polarizing plate including the polyester film warps in an oblique direction, and the effect of reducing the warp of the liquid crystal panel tends to diminish.
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 .5 or more and 12.0 or less, even if the absolute value of the angle between the direction parallel to the transmission axis of the polarizer and the direction in which the thermal shrinkage rate of the polyester film is maximized is 40 degrees or less, the liquid crystal panel warpage can be reduced. Said angle is preferably less than or equal to 35 degrees.
The heat shrinkage rate of the polyester film, the slope of the heat shrinkage rate of the polyester film, and the direction in which the heat shrinkage rate of the polyester film is maximized can be measured by the method employed in the examples described later.

Normally, two polarizing plates are arranged in a crossed Nicols relationship in a liquid crystal display device. When two polarizers are arranged in a crossed Nicols relationship, no light normally passes through the two polarizers. However, the contraction or warpage of the polarizer described above may result in a loss of the perfect crossed Nicols relationship, resulting in light leakage. From the viewpoint of suppressing light leakage, it is preferable that the angle formed between the direction in which the thermal shrinkage rate of the polarizer protective film is maximized and the transmission axis of the polarizer is small.

The polyester film for protecting a polarizer of the present invention preferably has a shrinkage force Ff of 800 N/m or more and 9000 N/m or less in the direction parallel to the transmission axis of the polarizer. If the lower limit of _Ff is less than 800 N/m, it may not be possible to sufficiently reduce the warpage of the liquid crystal panel. Further, when the upper limit of _Ff exceeds 9000 N/m, the shrinkage force is too strong and the liquid crystal panel may warp in the opposite direction. The range of contractile force is preferably 900 N/m or more and 8000 N/m or less, more preferably 1000 N/m or more and 8000 N/m or less, still more preferably 1100 N/m or more and 8000 N/m or less, and still more preferably 1200 N. /m or more and 8000 N/m or less. In addition, the upper limit is preferably 6000 N/m or less, 5500 N/m or less, and 4800 N/m or less.

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

Let _Fv be the shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer. The shrinkage force _Fv is defined by the following formula: polyester film thickness (mm)×elastic modulus (N/mm ² )×heat shrinkage rate (%) after treatment at 80° C. for 30 minutes/100×1000. Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. The thermal shrinkage rate is the thermal shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer (thermal shrinkage rate in heat treatment at 80° C. for 30 minutes).

The polyester film for protecting a polarizer of the present invention preferably has a 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, it may not be possible to sufficiently reduce the warpage of the liquid crystal panel. In addition, when the upper limit of F _f /F _v exceeds 12.0, the 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. Stress is applied to the protective film and retardation film that are applied, and the display quality may deteriorate. In addition, film-forming stability may decrease and the film may break.

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

The polyester film for protecting a polarizer of the present invention preferably has an elastic modulus of 1000 to 9000 N/mm ² in the transmission axis direction of the polarizer. Although the shrinkage force of 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 degree of crystallinity. Therefore, if the elastic modulus of the polyester film in the transmission axis direction of the polarizer exceeds 9000 N/mm ² , the upper limit is preferably 9000 N/mm ² , more preferably 8000 N/mm, because there is a risk that it may be easily torn. ² , more preferably 7000 N/mm ² .
On the other hand, if the orientation is low and the degree of crystallinity is low, the film may be deformed due to unevenness of the roll caused by thickness unevenness 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 and even more preferably 1800 N/mm ² . The elastic modulus can be measured by the method adopted in the examples described later.

The polyester film for protecting a polarizer of the present invention preferably has a heat shrinkage rate of 0.10 to 5.0% when heat-treated at 80° C. for 30 minutes in the direction of the transmission axis of the polarizer. The lower limit of the heat shrinkage rate is preferably 0.10% or more, more preferably 0.15% or more, and most preferably 0.20% or more. The upper limit of the heat shrinkage rate is preferably 4.5% or less, more preferably 4.0% or less, even more preferably 3.0% or less, even 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 thermal shrinkage rate to more than 5.0%, it is necessary to further decrease the degree of crystallinity and the glass transition temperature, which may cause defects such as poor flatness. The thermal shrinkage rate can be measured by the 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, still more preferably 40 to 80 μm. When the thickness of the polyester film is less than 40 μm, it tends to crack easily and tends to have poor flatness due to insufficient rigidity. In addition, if the film is thin, it is necessary to increase the elastic modulus or thermal shrinkage of the polyester film in the transmission axis direction of the polarizer. is the lower bound. In addition, when the thickness of the film exceeds 200 μm, the variation in the elastic modulus or thermal shrinkage of the polyester film in the transmission axis direction of the polarizer increases accordingly, which may make it difficult to control. also rises. The thickness of the polyester film can be measured by the method employed in the 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 iridescence observed on the screen of a liquid crystal display device. The lower limit of in-plane retardation is preferably 3000 nm or more, 5000 nm or more, 6000 nm or more, 7000 nm or more, or 8000 nm or more. The upper limit of the in-plane retardation is preferably 30000 nm or less, more preferably 18000 nm or less, still more preferably 15000 nm or less. In particular, from the viewpoint of thinning, the in-plane retardation is preferably less than 10000 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 directions, or can be determined 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 polyester film for protecting a polarizer of the present invention has a ratio (Re/Rth) of in-plane retardation (Re) to thickness direction retardation (Rth) 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 still more preferably 0.6 or more. As the ratio of the in-plane retardation to the thickness direction retardation (Re/Rth) increases, the birefringence action becomes more isotropic, and rainbow-like color spots tend to be less likely to occur depending on the viewing angle. Since the ratio of the retardation to the thickness direction retardation (Re/Rth) is 2.0 in a perfect uniaxial (uniaxially symmetric) film, the ratio of the retardation to the thickness direction retardation (Re/Rth) The upper limit is preferably 2.0. A preferable upper limit of Re/Rth is 1.2 or less. The thickness direction retardation means the average retardation obtained by multiplying the two birefringences ΔNxz and ΔNyz when the film is viewed from the thickness direction section by the film thickness d.

In the polarizer-protecting polyester film 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 2.0 or less, 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 symmetrical) 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 decrease significantly as the film approaches a perfect uniaxial (uniaxially symmetrical) 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 perpendicular to the slow axis (fast axis direction), and 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 Keisoku Co., Ltd.), and the biaxial refractive indices (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 Co., Ltd., measuring wavelength 589 nm). The NZ coefficient can be obtained by substituting the value obtained in this way for |Ny-Nz|/|Ny-Nx|.

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 greater, even more preferably 0.09 or greater, and most preferably 0.1 or greater. The upper limit is not particularly defined, but in the case of 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 dicarboxylic acid components that can be used in the production of polyester resins 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 adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecadicarboxylic acid and the like.

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

One type or two or more types can be used for each of the dicarboxylic acid component and the diol component that constitute the polyester resin. Suitable polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and more preferably polyethylene terephthalate and polyethylene naphthalate. Furthermore, other copolymer components may be included. These resins are excellent in transparency as well as in thermal and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high elastic modulus and its thermal shrinkage can be relatively easily controlled.

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

(Addition of functional layer)
Since it is desirable that the polarizing plate using the polyester film for protecting a polarizer of the present invention is integrated with the glass plate of the liquid crystal cell while the heat shrinkage of the polyester film remains, the easy-adhesion layer and the hard coat layer are provided. , Anti-glare layer, anti-reflection layer, low reflection layer, low anti-reflection layer, anti-reflection anti-glare layer, low reflection anti-glare layer, and anti-static layer When applying a functional layer, the drying temperature is lowered. In this embodiment, it is preferable to set the temperature, or to use a method with a small thermal history such as UV irradiation or electron beam irradiation. Further, by providing these functional layers during the process of forming a polyester film, it becomes possible to integrate the polarizing plate of the present invention and the glass plate of the liquid crystal cell without impairing the increased thermal shrinkage rate. Therefore, it is a more desirable embodiment.
Functional layers such as easy adhesion layer, hard coat layer, antiglare layer, antireflection layer, low reflection layer, low antireflection layer, antireflection antiglare layer, low reflection antiglare layer, antistatic layer, etc. It is preferable that the functional layers are laminated on the surface opposite to the surface on which the polarizer is laminated, and that the contractile forces F _f and F _v satisfy the conditions described above in the state in which 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 a non-oriented polyester extruded into a sheet is stretched in the longitudinal direction using the speed difference between rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction with a tenter, A method of applying heat treatment (heat setting) can be mentioned. It may be a uniaxially stretched film or a biaxially stretched film. Preferably, it is a uniaxially stretched film strongly stretched mainly in the transverse direction or a uniaxially stretched film strongly stretched mainly in the machine direction, both of which may be slightly stretched in the direction perpendicular to the main stretching direction. In addition, MD is an abbreviation for Machine Direction, and in this specification, it may be referred to as the film flow direction, the longitudinal direction, and the vertical direction. Also, TD is an abbreviation for Transverse Direction, and is sometimes referred to as the width direction and the lateral direction in this specification.

It is preferable to adjust the film thickness, elastic modulus and heat shrinkage of the polyester film so that the shrinkage force _Ff is 800 N/m or more and 9000 N/m or less.

(Method for adjusting elastic modulus of polyester film)
Regarding the elastic modulus of the polyester film used as the polarizer protective film, when the direction of the transmission axis of the polarizer coincides with the MD during film formation of the polyester film, the elastic modulus of MD coincides with the TD during film formation of the polyester film. In that case, the elastic modulus of the TD may be adjusted by a conventionally known method for stretched polyester films.
Specifically, when the direction is the stretching direction, the stretching ratio may be set high, and when the direction is the direction perpendicular to the stretching direction, the stretching ratio may be set low.

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

When adjusting the MD heat shrinkage rate of the polyester film, for example, in the cooling process after stretching and heat setting, the distance between the clip holding the end of the film in the width direction and the adjacent clip is expanded to stretch the film in the MD. It can be adjusted by shrinking the MD by reducing the clip interval. Further, in the cooling process after stretching and heat setting, when cutting or separating the film from the clip that grips the end of the film in the width direction, the film is stretched or shrunk in MD by adjusting the force to pull the film. It is possible to adjust by Also, in the offline process after film formation, when the temperature is raised for the purpose of imparting a functional layer, etc., the thermal shrinkage rate changes during the heating and cooling process, so the force to pull the film is adjusted to stretch or shrink in MD. It is also possible to adjust by

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

The shrinkage force _Fv is such that the shrinkage force ratio (F _f /F _v ) is 1.0 or more and 12.0 or less, more preferably 2.5 or more and 12.0 or less. It is preferable to adjust the elastic modulus and thermal shrinkage.

(Method for adjusting the inclination of the main shrinkage axis of the polyester film)
As disclosed in PCT/JP2014/073451 (WO2015/037527), the inclination of the shrinkage principal axis of the polyester film used as the polarizer protective film is determined by the cooling process after stretching and heat treatment of the polyester film by a tenter or the film formation. Adjustments can be made in a later off-line step. Specifically, in the cooling process, shrinkage due to stretching and thermal stress due to cooling, which could not be removed in the heat setting process, are generated. A phenomenon occurs in which the principal axis of contraction is tilted. In order to reduce the inclination of the main axis of shrinkage, it is necessary to adjust the shrinkage force in the direction of film flow (the sum of the shrinkage force associated with stretching and the shrinkage force associated with cooling) in the cooling process so as to be uniform. For uniformity, it is desirable to shrink the film in the machine direction in a temperature range where the shrinkage force is high in the film machine direction, or to stretch the film in the film machine direction in a temperature range where the shrinkage force is low in the film machine direction. A conventionally known method may be used for shrinking or stretching. Also, when cutting or separating the ends of the film, it should be noted that the film shrinks freely in the width direction below the cutting/separating temperature range, and the thermal shrinkage rate becomes smaller below this temperature range.

In the polarizing plate, the polyester film for protecting a polarizer of the present invention is laminated on at least one surface of a polarizer. It is preferable that a non-birefringent film such as a TAC film, acrylic film, or 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, no film is 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.
When a film or coating layer other than the polyester film for protecting the polarizer of the present invention is laminated on the polarizer, the film or coating layer other than the polyester film for protecting the polarizer shrinks in the direction parallel to the transmission axis of the polarizer. The force and the shrinkage force of the film other than the polarizer-protecting polyester film and the coating layer in the direction parallel to the absorption axis of the polarizer are both preferably the F _f value of the polarizer-protecting polyester film or less, and more It is preferably not more than the _Fv value of the polyester film for protecting the polarizer. In addition, the shrinkage force of films other than the polarizer-protecting polyester film and the coating layer in the direction parallel to the transmission axis of the polarizer, and the shrinkage force of the coating layer other than the polarizer-protecting polyester film in the direction parallel to the absorption axis of the polarizer. The shrinkage force of the film or coating layer is preferably 250 N/m or less, more preferably 200 N/m or less. The shrinkage force of films 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, thickness (mm) of film or coating layer×elastic modulus (N/mm ² )×heat shrinkage rate (%) after treatment at 80° C. for 30 minutes/100×1000.

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

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

In the polyester film for protecting a polarizer of the present invention, it is preferable that the direction in which the thermal shrinkage of the polyester film is maximized and the TD are substantially parallel.
“Substantially parallel” means that the absolute value of the angle (slope of thermal shrinkage) between the direction in which the thermal shrinkage of the polyester film is maximized and the TD direction is allowed to be 15 degrees or less. The slope of the thermal shrinkage rate 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. The lower limit is 0 degrees because the smaller the slope of the thermal shrinkage rate, the better.
However, when the ratio of the shrinkage force F _TD of the TD of the polyester film to the shrinkage force F _MD of the MD of the polyester film ( _FTD / _FMD ) is 2.5 or more and 12.0 or less, the heat shrinkage 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 warp of the liquid crystal panel can be reduced. Said angle is preferably less than or equal to 35 degrees.

As described above, considering the industrial production of polarizing plates in a roll- _to -roll format _or the like, F _TD corresponds to F _f . are the same. Also, since F _TD /F _MD corresponds to F _f /F _v , the preferred ranges of both are the same. Since "the elastic modulus of the TD of the polyester film" corresponds to "the elastic modulus of the polyester film in the transmission axis direction of the polarizer", the preferred ranges for both are the same. "80 ° C. of the polyester film, the thermal shrinkage rate of TD when heat-treated for 30 minutes", "80 ° C. of the polyester film in the transmission axis direction of the polarizer, the heat shrinkage rate of 30 minutes heat treatment of the polyester film". , the preferred ranges for both are the same.

A liquid crystal display device has at least a backlight 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 polarizer protection of the present invention as a polarizer protective film. The liquid crystal display device may use the polarizing plate of the present invention for both of the two polarizing plates.

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

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

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by the following examples, and can be carried out with appropriate modifications within the scope of the gist of the present invention. Both 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 measured values described below. Elastic modulus refers to the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer. Thermal shrinkage refers to the thermal shrinkage of the polyester film in the direction parallel to the transmission axis of the polarizer.
Shrinkage force F _f (N/m) = polyester film thickness (mm) x elastic modulus (N/mm ² ) x heat shrinkage rate (%) after treatment at 80°C for 30 minutes/100 x 1000

(2) contractile force F _v
The shrinkage force _Fv of the polyester film was calculated from the following formula. The thickness, elastic modulus, and heat shrinkage of the polyester film are measured values described below. Elastic modulus refers to the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer. Thermal shrinkage refers to the thermal shrinkage of the polyester film in the direction parallel to the absorption axis of the polarizer.
Shrinkage force F _v (N/m) = polyester film thickness (mm) x elastic modulus (N/mm ² ) x thermal shrinkage rate (%) after 30 minutes treatment at 80°C/100 x 1000

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

(4) Elastic modulus of polyester film The elastic modulus of the polyester film is determined by 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 used for evaluation. Under the conditions of tension mode, drive frequency of 1 Hz, distance between chucks of 5 mm, and temperature increase rate of 2° C./min, the temperature dependence was measured from 25° C. to 120° C., and the average storage modulus from 30° C. to 100° C. was calculated. The modulus of elasticity. Thus, 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.
The above measurements were performed on a polyester film alone (polarizer-protecting polyester film alone).

(5) Heat shrinkage rate of polyester film and slope of heat shrinkage After the polyester film was left to stand in an environment of 25 ° C. 50 RH% for 168 hours, draw a circle with a diameter of 80 mm and measure the diameter of the circle with an image size measuring instrument (manufactured by KEYENCE Using an image measure (IM6500), the length was measured every 1° and taken as the length before treatment. Next, 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 25°C, evaluation is performed every 1° in the same manner as before treatment. , the length after treatment. The above treatment was performed on the polyester film alone (polarizer-protecting polyester film alone).

The thermal shrinkage rate was evaluated for each angle using the following formula.
Heat shrinkage = (length before treatment - length after treatment) / length before treatment x 100
Thus, regarding the polyester film, the thermal shrinkage rate of the polyester film in the direction parallel to the polarizer transmission axis and the thermal shrinkage rate of the polyester film in the direction parallel to the polarizer absorption axis were obtained.

360 ° evaluation is performed for each 1 ° above, the direction in which the thermal shrinkage rate is maximized is specified, and the absolute value of the angle formed by that direction and the transmission axis direction of the polarizer is taken as the slope of the thermal shrinkage rate. . The slope of the thermal shrinkage rate is defined as a narrow angle from the transmission axis direction of the polarizer, and ranges from 0 to 90°.

(6) Warp of liquid crystal panel The liquid crystal panel produced in each example and comparative example was heat-treated for 30 minutes using a gear oven set at 80 ° C., and then in an environment set at room temperature 25 ° C. 50% RH. After cooling for 30 minutes, it was placed on a horizontal surface with the convex side down, the height of the four corners was measured with a tape measure, and the maximum value was taken as the amount of warpage. The amount of warpage was evaluated as follows.
○: 0 mm or more and less than 2.0 mm △: 2.0 mm or more and 3.0 mm or less ×: more than 3.0 mm

(7) Refractive index of polyester film Using a molecular orienter (manufactured by Oji Keisoku Co., Ltd., MOA-6004 type molecular orienter), the slow axis direction of the film is determined, and the slow axis direction is the long side of the sample for measurement. A rectangle of 4 cm x 2 cm was cut out so as to be parallel to , and used as a measurement sample. For this sample, the refractive index in the orthogonal biaxial direction (refractive index in the slow axis direction: Ny, fast axis (refractive index in the direction perpendicular to the slow axis direction): Nx), and the refractive index in the thickness direction ( Nz) was determined by an Abbe refractometer (NAR-4T manufactured by Atago Co., measuring wavelength 589 nm). These values were used to determine the NZ coefficient.

Retardation is a parameter defined by the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|Nx−Ny|) on the film and the film thickness d (nm). It is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was obtained by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd.), the slow axis direction of the film was determined, and the slow axis direction was 4 cm so that it was parallel to the long side of the sample for measurement. A 2 cm x 2 cm rectangle was cut out and used as a measurement sample. For this sample, the refractive index in the biaxial direction perpendicular to each other (refractive index in the slow axis direction: Ny, refractive index in the direction perpendicular to the slow axis direction: Nx) and the refractive index in the thickness direction (Nz) were measured by the Abbe refractor. The absolute value of the biaxial refractive index difference (|Nx−Ny|) was defined as the anisotropy of the refractive index (ΔNxy) by using an index meter (NAR-4T, manufactured by Atago Co., measuring wavelength: 589 nm). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf Co.) and converted into nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

(8) Thickness direction retardation (Rth)
The retardation in the thickness direction is obtained by multiplying the two birefringences ΔNxz (=|Nx−Nz|) and ΔNyz (=|Ny−Nz|) when viewed from the cross section in the thickness direction of the film by the film thickness d. is a parameter that indicates the average retardation obtained by Nx, Ny, Nz and film thickness d (nm) are obtained in the same manner as in the measurement of retardation, and the average value of (ΔNxz × d) and (ΔNyz × d) is calculated to obtain the thickness direction retardation (Rth ).

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged, and 0.017 parts by mass of antimony trioxide as a catalyst was added while stirring. 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 carry out a pressure esterification reaction under conditions of a gauge pressure of 0.34 MPa and 240° C., after which the pressure in the esterification reactor 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. After 15 minutes, dispersion treatment was performed with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reactor, and polycondensation reaction was performed at 280°C under reduced pressure.

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

(Production Example 2-Polyester B)
10 parts by weight of dried UV absorber (2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), particle-free PET (A) (intrinsic viscosity is 0.62 dl/g), 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-Adhesion-improving coating liquid preparation)
A transesterification reaction and a polycondensation reaction were carried out by a conventional method to obtain 46 mol % of terephthalic acid, 46 mol % of isophthalic acid and 8 mol % of sodium 5-sulfonatoisophthalate as dicarboxylic acid components (relative to the total dicarboxylic acid components). A water-dispersible sulfonic acid metal base-containing copolymer polyester resin was prepared having a composition of 50 mol % ethylene glycol and 50 mol % neopentyl glycol as the glycol component (relative to the total glycol component). Next, 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 are mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal group-containing copolymerized polyester resin and continuing to stir until the lumps of the resin disappear, the resin aqueous dispersion was cooled to room temperature and the solid content concentration was 5.0% by mass. A homogeneous water-dispersible copolyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Silysia 310) in 50 parts by mass of water, Silysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added while stirring to obtain an adhesion-improving coating liquid.

(Example 1)
<Production of Polyester Film 1 for Polarizer Protection>
After drying under reduced pressure (1 Torr) at 135° C. for 6 hours, 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 raw materials for the base film intermediate layer. , supplied to extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method, supplied to extruder 1 (for outer layer I layer and outer layer III), and melted at 285 ° C. . These two types of polymers are each filtered with a stainless sintered filter material (nominal filtration accuracy: 10 μm, 95% cut of particles), laminated in a two-type, three-layer confluence block, extruded in a sheet form from a nozzle, An unstretched film was produced by winding the film around a casting drum having a surface temperature of 30° C. and solidifying it by cooling using an electrostatic casting method. At this time, the discharge rate 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 adhesion-improving coating solution was applied to both sides of the 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 having the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, was guided to a hot air zone at a temperature of 105° C. and stretched 4.0 times in TD. Next, heat treatment is performed at a temperature of 180 ° C. for 30 seconds, then the film cooled to 100 ° C. is stretched by 1.0% in the width direction, and then the clip holding both ends of the film cooled to 60 ° C. is released and taken up with a tension of 350 N / m, a jumbo roll made of a uniaxially oriented PET film with a film thickness of about 80 μm is collected, the obtained jumbo roll is divided into three equal parts, and three slit rolls (L (left side) , C (middle), R (right)). A polyester film 1 for protecting a polarizer was obtained from a slit roll positioned at R. In the polarizer-protecting polyester film 1, the direction in which the thermal shrinkage rate was maximized was 7.0 degrees from TD.

<Creating a liquid crystal panel>
A polarizer-protecting polyester film 1 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 polarizer-protecting polyester film 1 were parallel. A TAC film (manufactured by Fuji Film Co., Ltd., thickness 80 μm) was adhered to the opposite side of the polarizer to prepare a light source side polarizing plate.

A liquid crystal panel was taken out from a 46-inch size IPS type liquid crystal television using a glass substrate with a thickness of 0.4 mm for the liquid crystal cell. Remove the light source side polarizing plate from the liquid crystal panel, and replace the light source side polarizing plate prepared above so that the transmission axis of the polarizer is the same as the transmission axis direction of the light source side polarizing plate before peeling (parallel to the horizontal direction). A liquid crystal panel was produced by laminating to a liquid crystal cell through PSA so as to match.
The light source-side polarizing plate was attached to the liquid crystal cell so that the polarizer-protecting polyester film 1 was on the distal side (opposite side) of the liquid crystal cell. Also, the viewing-side polarizing plate was a polarizer with TAC films laminated on both sides thereof, and was attached to the liquid crystal cell so 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 formation of the polarizer-protecting polyester film 1 of Example 1, the 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 by 1.5% in the width direction. A polyester film 2 was obtained. In the polarizer-protecting polyester film 2, the direction in which the thermal shrinkage rate was maximized 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 polarizer>
A polarizer protective film was produced in the same manner as the polarizer protective polyester film 1 in Example 1, except that the film cooled to 100° C. was stretched by 1.7% in the width direction. got 3. In the polarizer-protecting polyester film 3, the direction in which the thermal shrinkage rate is maximized was 5.3 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 3 for protecting the polarizer.

(Example 4)
<Production of Polyester Film 4 for Polarizer Protection>
In the film formation of the polarizer-protecting polyester film 1 of Example 1, the film cooled to 100 ° C. was stretched 2.0% in the width direction, and the temperature was 180 ° C. for 30 seconds after stretching 4 times in TD. A polarizer protective film 4 was obtained in the same manner as the polarizer protective polyester film 1 except that the hard coat layer coating solution was applied to one side of the polyester film at the previous point. In the polarizer-protecting polyester film 4, the direction in which the thermal shrinkage rate was maximized 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 4 for protecting the polarizer.

(Example 5)
<Production of polyester film 5 for protecting polarizer>
A polarizer-protecting polyester film 5 was obtained in the same manner as the polarizer-protecting polyester film 4 except that the film thickness after stretching was adjusted to 160 μm by adjusting the rotation speed of the casting roll. In the polarizer-protecting polyester film 5, the direction in which the thermal shrinkage rate was maximized 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 polyester film 6 for protecting polarizer>
In the film formation of the polarizer-protecting polyester film 1 of Example 1, the 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 by 1.5% in the machine direction. A polyester film 6 was obtained. In the polarizer-protecting polyester film 6, the direction in which the heat shrinkage ratio is maximized was 9.0 degrees from the MD.
<Creating a liquid crystal panel>
In the preparation of 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 produced in the same manner as in Example 1, except that the light source side polarizing plate was produced by sticking so as to be aligned.

(Example 7)
<Production of polyester film 7 for protecting polarizer>
In the film formation of the polarizer-protecting polyester film 1 of Example 1, the 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 by 1.7% in the machine direction. A polyester film 7 was obtained. In the polarizer-protecting polyester film 7, the direction in which the thermal shrinkage rate is maximized was 8.3 degrees from the 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 in Example 6.

(Example 8)
<Production of polyester film 8 for protecting polarizer>
In the film formation of the polarizer-protecting polyester film 1 of Example 1, the 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 by 2.0% in the machine direction. A polyester film 8 was obtained. In the polarizer-protecting polyester film 8, the direction in which the heat shrinkage ratio is maximized was 7.0 degrees from the 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 8 in Example 6.

(Example 9)
<Production of polyester film 9 for protecting polarizer>
A polarizer-protecting polyester film 9 was obtained in the same manner as the polarizer-protecting polyester film 8 except that the film thickness after stretching was adjusted to 160 μm by adjusting the rotation speed of the casting rolls. In the polarizer-protecting polyester film 9, the direction in which the heat shrinkage ratio is maximized was 7.0 degrees from the 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 9 for protecting the polarizer.

(Example 10)
<Production of polyester film 10 for protecting polarizer>
A polarizer protective film was prepared in the same manner as the polarizer protective polyester film 6, except that the TD was stretched 4.0 times, but the MD was stretched 4.0 times and the TD was stretched 1.0 times. Got 10. In the polarizer-protecting polyester film 10, the direction in which the thermal shrinkage rate was maximized was 8.7 degrees from the 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 10 for protecting the polarizer.

(Example 11)
<Production of polyester film 11 for protecting polarizer>
In the formation of the polarizer-protecting polyester film 10 of Example 10, the polarizer-protecting polyester film 10 was prepared in the same manner as the polarizer-protecting polyester film 10 except that the film cooled to 100 ° C. was stretched by 1.7% in the machine direction. A polyester film 11 was obtained. In the polarizer-protecting polyester film 11, the direction in which the heat shrinkage ratio is maximized was 7.5 degrees from the MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 10, except that the polarizer-protecting polyester film 10 was replaced with the polarizer-protecting polyester film 11 in Example 10.

(Example 12)
<Production of polyester film 12 for protecting polarizer>
In the formation of the polarizer-protecting polyester film 10 of Example 10, the polarizer-protecting polyester film 10 was prepared in the same manner as the polarizer-protecting polyester film 10 except that the film cooled to 100 ° C. was stretched by 5.0% in the width direction. A polyester film 12 was obtained. In the polarizer-protecting polyester film 12, the direction in which the thermal shrinkage rate was maximized 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 polarizer-protecting polyester film 13 was obtained in the same manner as the polarizer-protecting polyester film 4, except that the film thickness after stretching was adjusted to 60 μm by adjusting the rotation speed of the casting rolls. In the polarizer-protecting polyester film 13, the direction in which the thermal shrinkage rate is maximized 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 13 for protecting the polarizer.

(Example 14)
<Production of polyester film 14 for protecting polarizer>
In the cooling process after stretching 1.7% in the width direction, the polarizer protective film 14 was formed in the same manner as the polarizer protective film 3 except that the film was passed without changing the width of the clips that hold both ends of the film. Obtained. In the polarizer-protecting polyester film 14, the direction in which the heat shrinkage ratio is maximized 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>
Except that the thickness of the film after stretching was adjusted to 200 μm by adjusting the rotation speed of the casting rolls, and the film was passed without changing the width of the clips that hold both ends of the film in the cooling process after stretching and heat setting. obtained a polarizer protective film 15 in the same manner as the polarizer protective film 1. In the polarizer-protecting polyester film 15, the direction in which the thermal shrinkage rate is maximized was 20.0 degrees from the MD.
<Creating a liquid crystal panel>
Except that the polarizer protective film 1 was replaced with the polarizer protective film 15 and that the light source side polarizing plate was prepared by laminating the polarizer 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 1.

(Comparative example 2)
<Production of polyester film 16 for protecting polarizer>
In the cooling process after stretching and heat setting, the film was not stretched by 1.0% in the width direction, and the clips holding both ends of the film were released at 95 ° C. The same polarized light as in the polarizer protective film 1 A child protective film 16 was obtained. In the polarizer-protecting polyester film 16, the direction in which the thermal shrinkage rate was maximized was 1.0 degrees from the MD.
<Creating a liquid crystal panel>
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 the polarizer 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 1.

(Comparative Example 3)
<Production of polyester film 17 for protecting polarizer>
A polarizer-protecting polyester film 17 was obtained in the same manner as the polarizer-protecting polyester film 1 except that the film thickness after stretching was adjusted to 50 μm by adjusting the rotation speed of the casting roll. In the polarizer-protecting polyester film 17, the direction in which the thermal shrinkage rate is maximized 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 polarizer-protecting polyester film 18 was obtained in the same manner as the polarizer-protecting polyester film 11 except that the film thickness after stretching was 160 μm by adjusting the rotation speed of the casting roll. In the polarizer-protecting polyester film 18, the direction in which the thermal shrinkage rate is maximized was 6.5 degrees from the MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 11, except that the polyester film 11 for protecting the polarizer was replaced with the polyester film 18 for protecting the polarizer.

(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 rolls, and in the film formation of the polarizer-protecting polyester film 1 of Example 1, the film cooled to 100 ° C. was 1.0 in the machine direction. A polarizer-protecting polyester film 19 was obtained in the same manner as the polarizer-protecting polyester film 1, except that the film was stretched by %. In the polarizer-protecting polyester film 19, the direction in which the thermal shrinkage rate was maximized was 11.0 degrees from the MD.
<Creating a liquid crystal panel>
In the preparation of 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 produced in the same manner as in Example 1, except that the light source side polarizing plate was produced by sticking so as to be aligned.

(Comparative Example 6)
<Production of polyester film 20 for protecting polarizer>
A polarizer-protecting polyester film 20 was obtained in the same manner as the polarizer-protecting polyester film 19 except that the film thickness after stretching was 80 μm by adjusting the rotation speed of the casting roll. In the polarizer-protecting polyester film 20, the direction in which the thermal shrinkage rate was maximized was 11.0 degrees from the 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 in Comparative Example 5 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 polarizer-protecting polyester film 21, the direction in which the thermal shrinkage rate is maximized was 11.0 degrees from the MD.
<Creating a liquid crystal panel>
In the preparation of 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 produced in the same manner as in Example 1, except that the light source side polarizing plate was produced by sticking so as to form a liquid crystal panel.

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

(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 rolls, and in the film formation of the polarizer-protecting polyester film 1 of Example 1, the film cooled to 100 ° C. was 1.0 in the machine 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 by %. In the polarizer-protecting polyester film 22, the direction in which the thermal shrinkage rate was maximized was 11.0 degrees from the MD.
<Creating a liquid crystal panel>
In the preparation 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 produced in the same manner as in Example 1, except that the light source side polarizing plate was produced by sticking so as to form a liquid crystal panel.

(Comparative Example 10)
<Production of polyester film 23 for protecting polarizer>
In the formation of the polarizer-protecting polyester film 10 of Example 10, the polarizer-protecting polyester film 10 was prepared in the same manner as the polarizer-protecting polyester film 10 except that the film cooled to 100 ° C. was stretched by 2.0% in the machine direction. A polyester film 23 was obtained. In the polarizer-protecting polyester film 23, the direction in which the thermal shrinkage rate is maximized is 4.5 degrees from the MD.
<Creating a liquid crystal panel>
A liquid crystal panel was produced in the same manner as in Example 10, except that the polyester film 10 for protecting the polarizer was replaced with the polyester film 23 for protecting the polarizer.

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

(Examples 1A to 5A, Example 13A)
In Example 1, 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 viewer side polarizing plate. 1 to 5 and 13, similarly to the results of Examples 1 to 5 and 13 in Table 1, good results (◯) were obtained in the evaluation of panel warpage. The light source side polarizing plate and the viewing side polarizing plate were attached to the liquid crystal cell so that the polyester film for protecting the polarizer was on the far side (opposite side) of the liquid crystal cell.

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

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 (10)

A method for producing a polarizing plate by laminating a polarizer-protecting polyester film that satisfies the following requirements (1), (2), and (3) on one surface of a polarizer,
The polyester film is stretched in TD and stretched again in TD in the cooling process after heat setting,
The polyester film is a polyethylene terephthalate film,
The polarizer is a polyvinyl alcohol film containing iodine,
The method for producing the polarizing plate, wherein the transmission axis of the polarizer and the TD of the polyester film are parallel.
(1) The shrinkage force F _TD of the TD of the polyester film is 800 N/m or more and 9000 N/m or less (however, the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film x the elastic modulus (N /mm ² ) × Thermal shrinkage rate (%) after 30 minutes treatment at 80°C / 100 × 1000. Here, the elastic modulus is the TD elastic modulus of the polyester film, and the thermal shrinkage ratio is the polyester film's TD elastic modulus. It is the thermal shrinkage rate of TD.)
(2) The ratio of the shrinkage force F _TD in the TD of the polyester film to the shrinkage force F _MD in the MD of the polyester film ( _FTD / _FMD ) is 2.5 or more and 12.0 or less (provided that the shrinkage force F _MD (N/m) is polyester film thickness (mm)×elastic modulus (N/mm ² )×heat shrinkage (%) after 30-minute treatment at 80° C./100×1000, where elastic modulus is is the MD elastic modulus of the polyester film, and the heat shrinkage is the MD heat shrinkage of the polyester film.)
(3) The absolute value of the angle between the direction in which the thermal shrinkage rate of the polyester film is maximized and TD is 15 degrees or less. 2. The method for producing a polarizing plate according to claim 1 , wherein the polyester film has a retardation of 3000-30000 nm. 3. The method for producing a polarizing plate according to claim 1, wherein the polyester film has a thickness of 40 to 200 μm. Claims 1 to 1, wherein 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 method for producing a polarizing plate according to any one of 3 . 5. The method for producing a polarizing plate according to any one of claims 1 to 4 , wherein a TAC film, an acrylic film, or a norbornene film is laminated on the other surface of the polarizer. 5. The method for producing a polarizing plate according to claim 1 , wherein the other surface of the polarizer has no film. 5. The method for producing a polarizing plate according to any one of claims 1 to 4 , wherein a coating layer is laminated on the other surface of the polarizer. 8. The method for producing a polarizing plate according to claim 7 , wherein the coating layer is a hard coat layer or a retardation film. 9. The method for producing a polarizing plate according to claim 1, wherein the polarizing plate has a rectangular shape and the long sides of the polarizing plate are parallel to the transmission axis thereof. A method for manufacturing a liquid crystal display device having a backlight source and a liquid crystal cell arranged between two polarizing plates, wherein at least one of the two polarizing plates is the polarized light according to any one of claims 1 to 8 . A method for manufacturing the liquid crystal display device, wherein the liquid crystal display device is manufactured by a method for manufacturing a plate.