TW201920394A - Polarizer protective film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

The purpose of the present invention is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display device which are capable of suppressing warpage of a liquid crystal panel. This polarizer protective polyester film is laminated on one surface of a polarizer, and satisfies conditions (1) and (2) below. (1) In a direction parallel to the transmission axis of the polarizer, the contractile force Ff of the polyester film is 800-9000 N/m, and (2) a ratio (Ff/Fv) of the contractile force Ff of the polyester film in the direction parallel to the transmission axis of the polarizer to the contractile force Fv of the polyester film in a direction parallel to the absorption axis of the polarizer is 2.5 to 12.0.

Description

Polarizer protective film, polarizing plate and liquid crystal display device

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

The demand for liquid crystal display devices is expanding for applications such as liquid crystal televisions and liquid crystal displays for personal computers. Generally, a liquid crystal display device is composed of a liquid crystal cell sandwiching a transparent electrode, a liquid crystal layer, a color filter, and the like with a glass plate, and two polarizing plates provided on both sides thereof, and each polarizing plate is made of two optical films ( For example, a configuration in which a polarizer protective film and a retardation film) sandwich a polarizer (also referred to as a polarizing film).

However, in recent years, as LCD screens have become thinner and larger, and LED backlights have been used as light sources, the thickness of the glass substrate used in liquid crystal panels has become thinner than 0.7 mm, causing display unevenness. The problem requires improvement.

The generation mechanism of display unevenness is believed to be mainly caused by the shrinkage of the polarizer. When the polarizer is placed under high temperature and high humidity, the alignment force is generated due to the loose alignment, and the liquid crystal panel is warped. Swelling on the backlight unit side causes uneven display.

In addition, currently, as described in Patent Documents 1 and 2 below, the thickness of the glass substrate used in the liquid crystal panel is 0.7 mm or more. The shrinkage of this polarizer is suppressed by the high rigidity of the glass, so there is no warping of the liquid crystal panel, and there is no problem of uneven display.

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

For example, when a cycloolefin-based resin is used as a polarizer protective film, the warpage of a liquid crystal panel is not sufficiently improved, and the adhesiveness to be applied to a polarizer is poor, so there is a problem that productivity is lowered.

In addition, in a case where a conventional triacetate (TAC) is used as a polarizer protective film, there is a problem that the liquid crystal panel is warped.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2008-107499

[Patent Document 2] Japanese Patent Laid-Open No. 2009-198666

The present invention is in view of the above problems. The problem-solving 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.

In order to solve the above-mentioned problems, the inventors have found that, in reviewing the causes and the like of the above problems, it has been found that the shrinking force of the polyester film for polarizer protection in a direction parallel to the transmission axis of the polarizer is set to a specific range Can improve the warpage of the LCD panel, based on this knowledge The knowledge has completed the present invention.

As far as details are concerned, the liquid crystal display device usually has a polarizing plate parallel to the long-side direction of the liquid crystal display device in the transmission axis direction of one area layer of the liquid crystal cell such as a polarizer, and becomes the absorption axis direction of the other area layer such as the polarizer A polarizing plate parallel to the long side of the liquid crystal display device. As a result of in-depth review using various commercially available liquid crystal display devices, the inventors found that the essence of the problem lies in the fact that the polarizing plate whose contraction force of the polarizing lens with a large shrinking force becomes the long side of the polarizing plate shrinks, and the shape becomes prone to curl. The problem of factors (curly is generally easy to occur in the long side direction), or the influence caused by the asymmetric composition of the upper and lower polarizers in the liquid crystal panel. The polarizer transmission axis becomes convex on the polarizer side on the long side.

In addition, as a result of an in-depth review, the contraction force in the long-side direction of the polarizer whose polarizer transmission axis becomes the long side can be controlled by the residual strain of the protective film, and it was found that the liquid crystal panel can be controlled by the contraction force. Curl.

Here, a method for measuring the shrinkage force of the polyester film for polarizer protection will be described. Generally, TMA or the like is used for the shrinkage force of the film. The initial length is set under a minimum load at a low temperature state at the start of the test, and the force in the shrinkage direction during temperature rise is measured while maintaining the length of the initial length. However, during the temperature rise process, the free volume of the polymer is generated at the same time as the shrinkage (hereinafter, simply referred to as thermal shrinkage) caused by the recovery of the residual strain accompanying the change in the polymer's conformation. The thermal expansion caused by the increase in the occupied volume due to temperature increase (hereinafter referred to as thermal expansion) is near the glass transition temperature of the polyester film (for example For example, in the temperature range of ~ Tg + 50 ° C), the relationship between thermal contraction and thermal expansion often occurs. Therefore, the film as a whole is inflated, and no contraction force is observed.

As a result of the review, it was clear that even if the shrinkage force was not generated during the TMA heating process, the shrinkage force was generated during the TMA cooling process. The reason is that the strain caused by thermal expansion changes reversibly, so it returns to its original state after heating and cooling, but because it is cooled in a state with a small size corresponding to the amount of heat shrinkage that shrinks during heating, it is cooled during cooling. Generates thermal stress. That is, the strain of thermal stress can be replaced by the thermal shrinkage of a film, and the shrinkage force after cooling can be expressed by the following formula. In addition, the thermal shrinkage ratio in the present invention means a person including a change in the moisture content during heat treatment.

Shrinking force (N / m) = film thickness (mm) × elastic modulus (N / mm ² ) × thermal shrinkage (%) ÷ 100 × 1000

That is, the representative invention is as follows.

Item 1.

A polyester film for polarizer protection is a polyester film for polarizer protection laminated on one side of a polarizer, which meets the following requirements (1) and (2).

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

(2) The ratio of the contraction force F _f of the aforementioned polyester film in a direction parallel to the transmission axis of the polarizer and the contraction force F _v of the aforementioned polyester film in a direction parallel to the absorption axis of the polarizer (F _f / F _v ) is 2.5 or more and 12.0 or less (wherein, the shrinkage force F _v (N / m) is the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ° C. The heat shrinkage of 30 minutes of processing (%) ÷ 100 × 1000. Here, 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 rate is the concentration in the direction parallel to the absorption axis of the polarizer. Thermal shrinkage of ester film.)

Item 2.

The polyester film for polarizer protection as described in item 1 further satisfies the following requirement (3).

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

Item 3.

The polyester film for polarizing lens protection according to item 1 or 2, wherein the polyester film has a retardation of 3000 to 30,000 nm.

Item 4.

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

Item 5.

The polyester film for polarizing lens protection according to any one of items 1 to 4, wherein the polyester film has a surface opposite to the surface of the laminated polarizer, and has a hard coat layer, an anti-reflection layer, a low-reflection layer, Anti-glare layer, or anti-reflective anti-glare layer.

Item 6.

A polyester film for polarizer protection is a polyester film for polarizer protection laminated on one side of a polarizer, which meets the following requirements (1) and (2).

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

(2) the shrinking force F. _MD TD MD shrinkage force of the polyester film and the polyester film F. _TD ratio (F _TD / F _MD) is 2.5 or more 12.0 or less (wherein, contractile force F _MD (N / m) Thickness of polyester film (mm) × modulus of elasticity (N / mm ² ) × 80 ° C. Thermal shrinkage (%) for 30 minutes ÷ 100 × 1000. Here, the modulus of elasticity is polyester film The elastic modulus and thermal shrinkage of MD are the thermal shrinkage of MD of polyester film.)

Item 7.

The polyester film for polarizer protection as described in item 6, which further satisfies the following requirement (3).

(3) The direction in which the thermal shrinkage of the polyester film becomes maximum is substantially parallel to the TD system.

Item 8.

A polarizing plate comprising a polyester film for protecting a polarizer according to any one of items 1 to 7 on at least one area of a polarizer.

Item 9.

A polarizing plate comprising a polyester film for protecting a polarizer as described in any one of items 1 to 7 in an area layer of the polarizer, and having no polyester film on the other side of the polarizer. There are films.

Item 10.

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

Item 11.

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

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

[Form of Implementing Invention]

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

In this specification, the contraction force of the polyester film in a direction parallel to the transmission axis of the polarizer refers to the contraction force of the polyester film in a direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film. meaning.

The thermal shrinkage of the polyester film in a direction parallel to the transmission axis of the polarizer means the thermal 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 a direction parallel to the transmission axis of the polarizer means the elastic modulus of the polyester film in a 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 a direction parallel to the absorption axis of the polarizer means the shrinkage force of the polyester film in a 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 a direction parallel to the absorption axis of the polarizer means the thermal 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 a direction parallel to the absorption axis of the polarizer means the elastic modulus of the polyester film in a 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. The direction parallel to the absorption axis of the polarizer may be simply referred to as the direction of the absorption axis of the polarizer.

The polyester film for polarizing lens protection of the present invention preferably has a substantially parallel relationship between a direction parallel to the transmission axis of the polarizer and a direction in which the thermal shrinkage of the polyester film is maximized. The term “substantially parallel” means that the absolute value of the included angle between the direction of the transmission axis of the polarizer and the direction in which the thermal shrinkage of the polyester film is maximized (hereinafter, simply referred to as the gradient of thermal shrinkage) is 15 degrees or less. The inclination of the heat shrinkage ratio is preferably 12 degrees or less, more preferably 10 degrees or less, even more preferably 8 degrees or less, even more preferably 6 degrees or less, particularly preferably 4 degrees or less, and most preferably 2 degrees or less. . The smaller the slope of the thermal shrinkage ratio, the better, so the lower limit is 0 degrees. If the gradient of the thermal shrinkage of the polyester film is large, the The oblique warpage tends to reduce the effect of reducing the warpage of the liquid crystal panel.

However, the ratio of the contraction force F _f of the polyester film in a direction parallel to the transmission axis of the polarizer and the contraction force F _v of the polyester film in a direction parallel to the absorption axis of the polarizer (F _f / F _v ) 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 of the polyester film is maximized is 40 degrees or less, the warpage of the liquid crystal panel can be reduced. . The angle is preferably 35 degrees or less.

The thermal shrinkage of the polyester film, the gradient of the thermal shrinkage of the polyester film, and the direction in which the thermal shrinkage of the polyester film becomes the largest can be measured by a method used in Examples described later.

Generally, in a liquid crystal display device, two polarizing plates are arranged so as to have a relationship of Cross Nicols. If two polarizers are arranged in a crossed Nicols relationship, light usually cannot pass through the two polarizers. However, due to the shrinkage or warpage of the polarizer, the complete cross-Nicol relationship is disintegrated, which may cause light leakage. From the viewpoint of suppressing light leakage, the direction in which the thermal shrinkage of the polarizer protective film is maximized, and the smaller the angle between the transmission axis of the polarizer, the better.

The polyester film for protecting a polarizer of the present invention preferably has a value of the shrinkage force F _f of the polyester film in a direction parallel to the transmission axis of the polarizer of 800 N / m or more and 9000 N / m or less. When the lower limit value of F _f is less than 800 N / m, there is a possibility that warpage of the liquid crystal panel cannot be sufficiently reduced. In addition, if the upper limit value of F _f exceeds 9000 N / m, there is a possibility that the shrinkage force is too strong and the liquid crystal panel is tilted back in the opposite direction. The preferred range of shrinking force is 900N / m or more and 8000N / m or less, more preferably 1000N / m or more and 8000N / m or less, even more preferably 1100N / m or more and 8000N / m or less, and even more preferably 1200N / m or more. Below 8000N / m. The upper limit is preferably 6000 N / m or less, preferably 5500 N / m or less, and more preferably 4800 N / m or less.

Here, the shrinkage force F _f refers to the shrinkage force of the polyester film in a direction parallel to the transmission axis of the polarizer, and is defined as the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ° C. ． Thermal contraction rate (%) for 30 minutes ÷ 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. In addition, the thermal shrinkage rate is the thermal shrinkage rate of the polyester film in a direction parallel to the transmission axis of the polarizer (thermal shrinkage rate at 80 ° C for 30 minutes).

The shrinkage force of the polyester film in a direction parallel to the absorption axis of the polarizer was set to F _v . The shrinkage force F _v is defined as the thickness of the polyester film (mm) × elastic modulus (N / mm ² ) × 80 ° C. Thermal contraction rate (%) 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 rate is the heat shrinkage rate of the polyester film in a direction parallel to the absorption axis of the polarizer (80 ° C. Heat shrinkage rate under 30-minute treatment).

The polyester film for polarizer protection of the present invention preferably has a 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. When the lower limit value of F _f / F _v is less than 1.0, there is a possibility that warpage of the liquid crystal panel cannot be sufficiently reduced. In addition, when the upper limit value of F _f / F _v exceeds 12.0, thermal deformation in one direction becomes large, and the surface of the polarizer and the surface on which the polyester film for polarizer protection is laminated is the surface laminated on the opposite side. Stress may be applied to the protective film or the retardation film, which may reduce the display quality. In addition, the film forming stability may be reduced and the film may be broken.

Examples of the method for controlling the shrinkage force within the range of the above formula include a method of re-stretching the film 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 a modulus of elasticity of the polyester film in the transmission axis direction of the polarizer of 1000 to 9000 N / mm ² . 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 needs to be highly aligned in the transmission axis direction of the polarizer and improved Degree of crystallization. Therefore, when the elastic modulus of the polyester film in the transmission axis direction of the polarizer exceeds 9000 N / mm ² , the film may be easily cracked. Therefore, the upper limit is preferably 9000 N / mm ² , and more preferably 8000 N. / mm ² , more preferably 7000 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 the film is wound into a roll, which may cause poor planarity. 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 a method employed in Examples described later.

The polyester film for polarizer protection of the present invention is preferably a polyester film in the transmission axis direction of the polarizer at a temperature of 80 ° C. for 30 minutes during heat treatment, preferably 0.10 to 5.0%. 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 thermal shrinkage is lower than 0.10%, that is, 0.01 ~ 0.099% Within the range, it may be difficult to control the thermal shrinkage without variation. In addition, in order to increase the thermal shrinkage rate to more than 5.0%, it is necessary to further reduce the degree of crystallinity or the glass transition temperature, and thus, defects such as poor planarity may occur. The thermal shrinkage can be measured by a method used in Examples described later.

The polyester film for polarizer protection of the present invention preferably has a thickness of 40 to 200 μm, more preferably 40 to 100 μm, and even more preferably 40 to 80 μm. When the thickness of a polyester film is less than 40 micrometers, it will break easily, and it will become easy to become inferior in planarity due to insufficient rigidity. In addition, in the case of thin, it is necessary to correspondingly increase the elastic modulus or thermal shrinkage of the polyester film in the transmission axis direction of the polarizer. However, as mentioned above, each parameter also has an upper limit, so 40 μm is essentially the lower limit. . In addition, when the thickness of the film exceeds 200 μm, the variation of the elastic modulus or thermal shrinkage of the polyester film in the direction of the transmission axis of the polarizer increases correspondingly, which may make it difficult to control it. In addition, the cost Also rose. The thickness of the polyester film can be measured by a method used in Examples described later.

From the viewpoint of suppressing iridescence observed on a screen of a liquid crystal display device, the polyester film for polarizer protection of the present invention preferably has an in-plane retardation amount within a specific range. The lower limit of the in-plane retardation amount is preferably 3,000 nm or more, preferably 5000 nm or more, preferably 6000 nm or more, preferably 7000 nm or more, or more preferably 8000 nm or more. The upper limit of the in-plane retardation amount is preferably 30,000 nm or less, more preferably 18000 nm or less, and even more preferably 15,000 nm or less. In particular, from the viewpoint of thin film formation, the in-plane retardation amount is preferably less than 10,000 nm and 9000 nm or less.

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

In the polyester film for polarizing lens protection of the present invention, the ratio (Re / Rth) of the retardation (Re) in the plane to the retardation (Rth) in the thickness direction is preferably 0.2 or more, preferably 0.3 or more, and more preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more. The larger the ratio (Re / Rth) of the in-plane retardation to the retardation in the thickness direction, the more the isotropy is increased by the effect of birefringence, and it may tend to be difficult to produce a rainbow-like stain caused by an observation angle. . A completely uniaxial (uniaxially symmetric) film has a ratio (Re / Rth) of the retardation amount to the thickness-direction retardation amount of 2.0, so the upper limit of the ratio (Re / Rth) of the retardation amount to the thickness-direction retardation amount is better. Is 2.0. The upper limit of the preferable Re / Rth is 1.2 or less. In addition, the thickness direction retardation means the average of the retardation obtained by multiplying the film thickness d by two birefringences ΔNxz and ΔNyz when the film is viewed from the thickness direction section.

From the viewpoint of further suppressing rainbow-like stains, the NZ coefficient of the polyester film-based polyester film for polarizer protection of the present invention is preferably 2.5 or less, more preferably 2.0 or less, even more preferably 1.8 or less, and even more It is preferably below 1.6. Then, the completely uniaxial (uniaxially symmetric) thin film system has an NZ coefficient of 1.0, so the lower limit of the NZ coefficient is 1.0. However, it is necessary to pay attention to the tendency that the mechanical strength in the direction perpendicular to the alignment direction decreases significantly as the film becomes closer to a completely uniaxial (uniaxially symmetric) film.

The NZ coefficient is represented by | Ny-Nz | / | Ny-Nx |. Here, Ny represents the refractive index in the slow axis direction of the polyester film, and Nx represents the refractive index in the direction orthogonal to the slow axis (in the fast axis direction) Refractive index), Nz represents the refractive index in the thickness direction. The alignment axis of the thin film was determined using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 molecular alignment meter), and the alignment was determined using an Abbe refractometer (NAR-4T manufactured by Atago, measuring wavelength 589 nm) The biaxial refractive index (Ny, Nx, where Ny> Nx) of the axial direction and the direction orthogonal to it, and the refractive index (Nz) of the thickness direction. The value obtained in this way can be substituted into | Ny-Nz | / | Ny-Nx | to obtain the NZ coefficient.

In addition, from the viewpoint of further suppressing rainbow-like stains, the Ny-Nx value of the polyester film-based polyester film of the present invention is preferably 0.05 or more, more preferably 0.07 or more, still more preferably 0.08 or more, and It is more preferably 0.09 or more, and most preferably 0.1 or more. The upper limit is not particularly limited. 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 dibasic acid and a diol can be used.

Examples of the dibasic acid component that can be used for producing a polyester resin include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylphosphonic 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 , Trimethyladipate, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecanedioic acid, and the like.

Examples of the diol component that can be used for producing a polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, and 1,4- Cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2, 2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) fluorene and the like.

Both the dibasic acid component and the diol component constituting the polyester resin can be used singly or in combination of two or more kinds. Examples of suitable polyester resins constituting the polyester film include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples of the diesters include polyethylene terephthalate and polyethylene naphthalate, which may further include other copolymerization components. These resins are excellent in transparency, and also excellent in thermal and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high modulus of elasticity and it is easy to control the thermal shrinkage.

In the case where it is necessary to increase the thermal shrinkage of the polyester film to a high degree, it is desirable to add a copolymerization component to moderately reduce the degree of crystallinity. In addition, since the ratio of elastic strain or permanent strain is high with respect to deformation below or near the glass transition temperature, it is generally difficult to increase the thermal shrinkage rate to a high degree. Therefore, it is also a preferred embodiment to introduce a component having a low glass transition temperature as necessary. Specifically, it is propylene glycol, 1,3- Propanediol, etc.

(Assignment of functional layer)

The polarizing plate using the polyester film for polarizer protection of the present invention is preferably integrated with a glass plate of a liquid crystal cell in a state where the thermal shrinkage of the polyester film remains, and therefore, it is provided with an easy-adhesion layer and hard coating. In the case of functional layers such as anti-glare layer, anti-glare layer, anti-reflection layer, low-reflection layer, anti-reflection layer, anti-reflection anti-glare layer, low-reflection anti-glare layer, and antistatic layer, the drying temperature is set to low, or It is an ideal embodiment to perform the method with a small thermal history such as UV irradiation or electron beam irradiation. In addition, providing these functional layers in the film-forming step of the polyester film can achieve a non-destructive and improved thermal shrinkage rate by integrating the polarizing plate of the present invention and the glass plate of the liquid crystal cell, which is a more desirable embodiment.

Functional layers such as easy adhesion layer, hard coating layer, anti-glare layer, anti-reflective layer, low-reflective layer, anti-low-reflective layer, anti-reflective anti-glare layer, low-reflective anti-glare layer, antistatic layer, etc. The surface opposite to the surface on which the polarizers are laminated is the surface on the opposite side, and it is preferable that the contraction forces F _f and F _v in the state where these functional layers are laminated have the aforementioned conditions.

(Manufacturing method of oriented polyester film)

The polyester film used in the present invention can be produced by a general method for producing a polyester film. For example, a method can be mentioned in which a polyester resin is melted and an extruded non-aligned polyester is extruded into a sheet shape at a temperature higher than the glass transition temperature, after being stretched in a longitudinal direction by a roller speed difference, and then by tentering. The machine was stretched in the transverse direction and heat-treated (heat-fixed). Can be single The axially stretched film may be a biaxially stretched film. It is preferably a uniaxially stretched film that is strongly stretched mainly in the transverse direction or a uniaxially stretched film that is strongly stretched mainly in the longitudinal direction, both of which can be slightly stretched in a direction perpendicular to the main stretching direction. In addition, MD is an abbreviation of Machine Direction, and in this specification, it may be called a film flow direction, a length direction, and a longitudinal direction. The TD is an abbreviation of Transverse Direction, and in this specification, it may be referred to as a width direction and a lateral direction.

The polyester film preferably adjusts the film thickness, elastic modulus, and thermal shrinkage ratio so that the shrinkage force F _f becomes 800 N / m or more and 9000 N / m or less.

(Method for adjusting the elastic modulus of the polyester film)

When the elastic modulus of the polyester film used as the protective film of the polarizer is the same as the MD of the polyester film when the transmission axis direction of the polarizer is the same, if the polyester film is stretched by the currently known method to adjust the MD The modulus of elasticity is sufficient. In the case where the transmission axis direction of the polarizer is consistent with the TD when the polyester film is formed, it is sufficient if the modulus of elasticity of the TD is adjusted by a conventionally known method of stretching the polyester film.

Specifically, when the direction is a stretching direction, the stretching ratio may be set to be high. When the direction is a direction orthogonal to the stretching direction, the stretching ratio may be set to If it is low, then you can.

(Method for adjusting thermal shrinkage of polyester film)

The thermal shrinkage of polyester films used as polarizer protective films In the case where the transmission axis direction of the light mirror is the same as the MD when the polyester film is formed, the thermal shrinkage of the MD can be adjusted by a conventionally known method of stretching the polyester film. The transmission axis direction of the polarizer is When it is the same as TD at the time of polyester film formation, the thermal contraction rate of TD should just be adjusted by the conventionally well-known method of drawing a polyester film.

In the case of adjusting the thermal shrinkage rate of MD of the polyester film, for example, it can be adjusted by the following method: during stretching. In the cooling process after heat fixation, the method of expanding the gap between the clamps that clamp the end in the width direction of the film and the adjacent clamps to stretch in MD; or reducing the gap between the clamps to make them in MD On shrink. In addition, stretching. In the cooling process after heat fixing, when the film is cut or separated from the clamp holding the end in the width direction of the film, the film can be stretched or shrunk in MD by adjusting the force of pulling the film to adjust . In addition, in the off-line step after film formation, when the temperature is raised for the purpose of providing a functional layer or the like, the heat shrinkage rate changes during the temperature rise and cooling process. Therefore, the force for pulling the film can also be adjusted. It is adjusted by stretching or shrinking it in the MD.

In the case of adjusting the thermal shrinkage rate of TD of a polyester film, for example, it can be adjusted by the following method: during stretching. In the cooling process after heat fixing, the method of stretching on the TD by increasing the gap between the clamp that clamps the end in the width direction of the film and the clamp on the opposite side of the width direction, or shrinking it to the TD shrink.

The shrinkage force F _{v is} preferably such that the ratio of the shrinkage force (F _f / F _v ) becomes 1.0 or more and 12.0 or less, and more preferably, it becomes 2.5 or more and 12.0 or less to adjust the elastic modulus and heat of the polyester film. Shrinkage.

(How to adjust the inclination of the shrinking main axis of the polyester film)

The inclination of the shrinking main axis of the polyester film used as the polarizer protective film can be stretched on a polyester film using a tenter in the manner disclosed in PCT / JP2014 / 073451 (WO2015 / 037527). Adjust in the cooling process after heat treatment or offline step after film formation. Specifically, in the cooling step, shrinkage caused by stretching and thermal stress caused by cooling, which are not completely removed in the heat-fixing step, occur upstream due to the balance between the two in the film flow direction. Pulling or pulling toward the downstream side causes the shrinkage spindle to tilt. In order to reduce the inclination of the shrinking main axis, it is necessary to adjust so that the shrinking force (the total of the shrinking force due to stretching and the shrinking force due to cooling) in the film flow direction in the cooling step becomes uniform. In order to achieve uniformity, it is desirable to shrink the film in the direction of film flow in a temperature region where the contraction force is high in the film flow direction, or to stretch in the film flow direction in a temperature region where the contraction force is low in the film flow direction. . A method of shrinking or stretching may be any conventional method. In addition, when the film ends are cut or separated, cutting is performed. Below the temperature range of separation, shrink freely in the width direction, and the heat shrinkage rate below this temperature range becomes smaller, so you need to be careful.

The polarizing plate is formed by laminating the polyester film for protecting a polarizer of the present invention on at least one area 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 another area of the polarizer. Or, from the viewpoint of thinness, it is also preferable that a polarizing plate not having any thin film on another area of the polarizer is used. in In this case, although a film is not layered on another area of the polarizer, a 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 other than the polyester film for polarizer protection or the coating layer of the present invention is laminated on a polarizer, a film other than the polyester film for polarizer protection in a direction parallel to the transmission axis of the polarizer or The shrinkage force of the coating layer and the shrinkage force of the film or coating layer other than the polyester film for polarizer protection in a direction parallel to the absorption axis of the polarizer are preferably F _{f both of the} polyester film for polarizer protection. It is more preferably equal to or less than the F _V value of the polyester film for polarizer protection. In addition, the shrinkage force of films or coating layers other than the polyester film for polarizer protection in a direction parallel to the transmission axis of the polarizer, and other than the polyester film for polarizer protection in a direction parallel to the absorption axis of the polarizer. The shrinkage force of the thin film or coating layer is preferably 250 N / m or less, and more preferably 200 N / m or less. The shrinkage force of a film or a coating layer other than the polyester film for polarizer protection can be measured similarly to the case of a polyester film. That is, it is the thickness (mm) of the film or coating layer × elastic modulus (N / mm ² ) × 80 ° C. Thermal contraction rate (%) for 30 minutes ÷ 100 × 1000.

Industrially, polarizing plates are in the form of roll-to-rolls, which are long strips of polarizers laminated with polarizers and long strips of polyester film for polarizer protection. Then, a polarizer is usually manufactured by stretching in the longitudinal direction, and therefore has an absorption axis in MD and a transmission axis in TD.

Therefore, from the viewpoint of industrially manufacturing a polarizing plate, the polyester film for protecting a polarizer of the present invention is preferably (1) or (2) below.

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

Among them, the shrinkage force F _TD (N / m) is the thickness (mm) of the polyester film × elastic modulus (N / mm ² ) × 80 ° C. Thermal contraction rate (%) for 30 minutes ÷ 100 × 1000. Here, the elastic modulus and the thermal shrinkage rate are the elastic modulus and thermal shrinkage rate of TD of the polyester film, respectively.

(2) The ratio (F _TD / F _MD ) of the shrinkage force F _{TD of the} polyester film _TD and the shrinkage force F _MD of the polyester film MD is preferably 2.5 or more and 12.0 or less.

Among them, the shrinkage force F _MD (N / m) is the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ° C. Thermal contraction rate (%) for 30 minutes ÷ 100 × 1000. Here, the elastic modulus and the thermal shrinkage rate are the elastic modulus and MD thermal shrinkage rate of the MD of the polyester film, respectively.

In addition, in the polyester film for polarizing lens protection of the present invention, it is preferable that the direction in which the thermal shrinkage of the polyester film becomes maximum is substantially parallel to the TD system.

The term “substantially parallel” means that the absolute value of the angle between the direction in which the heat shrinkage of the polyester film is maximized and the angle in the TD direction (the gradient of the heat shrinkage) is 15 degrees or less. The inclination of the heat shrinkage ratio is preferably 12 degrees or less, more preferably 10 degrees or less, even more preferably 8 degrees or less, even more preferably 6 degrees or less, particularly preferably 4 degrees or less, and most preferably 2 degrees or less. . The smaller the slope of the thermal shrinkage ratio, the better, so the lower limit is 0 degrees.

However, in (F _TD / F _MD) is 2.5 or more 12.0 or less than in the case of contractile force F TD MD shrinkage force of the polyester film F _TD and _MD of the polyester film, even if the thermal shrinkage of the polyester film The absolute value of the angle between the maximum direction and TD is 40 ° or less, and it is also possible to reduce the warpage of the liquid crystal panel. The angle is preferably 35 degrees or less.

In addition, when considering the case of industrially manufacturing a polarizing plate in the form of roll-to-roll as described above, F _TD is equivalent to F _f . Therefore, the preferred range of F _TD is the same as the preferred range of F _f . In addition, since F _TD / F _MD is equivalent to F _f / F _v , the preferable ranges of both are the same. "The elastic modulus of the TD of the polyester film" is equivalent to the "elastic modulus of the polyester film in the transmission axis direction of the polarizer", and therefore the preferable ranges are the same. "The thermal shrinkage of TD at 80 ° C and 30 minutes of heat treatment of polyester film" is equivalent to the "thermal shrinkage of polyester film at 80 ° C and 30 minutes of heat treatment of polarizer in the transmission axis direction", so The preferred ranges are the same for both.

The liquid crystal display device includes at least a backlight light source and a liquid crystal cell disposed 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 be the one using 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 preferably a polarizer protective film for the viewing side with the polarizer on the viewing side polarizer as the starting point and / or a polarizer with the polarizer on the light source side for the light source side. The position of the polarizer protects the film.

Generally, the liquid crystal display device is formed in a rectangular shape (the two polarizing plates used in the liquid crystal display device are also rectangular). One of the polarizing plates has a long side parallel to the absorption axis, and the other polarizing plate has a long side. They are arranged parallel to the transmission axis and the absorption axes are in a vertical relationship with each other. Therefore, generally, the long side of the polarizing plate is parallel to the absorption axis. The polarizing plate is used as a viewing-side polarizing plate of a liquid crystal display device, and the polarizing plate having a relationship between the long side of the polarizing plate and the transmission axis is used as a light source-side polarizing plate of the liquid crystal display device. From the viewpoint of suppressing warpage of the liquid crystal panel, it is preferable to use at least the polarizing plate of the present invention as a polarizing plate in which the long side of the polarizing plate has a parallel relationship with the transmission axis. It is also preferable to use both the polarizing plate of the present invention and a polarizing plate having a long side of the polarizing plate having a parallel relationship with the transmission axis, and a polarizing plate having a long side of the polarizing plate having a parallel relationship with the absorption axis.

[Example]

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be implemented by appropriately changing within a range that can meet the gist of the present invention. Those embodiments are also included in Within the technical scope of the present invention.

(1) Contraction force F _f

The shrinkage force F _f of the polyester film is calculated by the following formula. The thickness, elastic modulus, and thermal 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 transmission axis of the polarizer. The thermal shrinkage rate is the thermal shrinkage rate of the polyester film in a direction parallel to the transmission axis of the polarizer.

Shrinkage force F _f (N / m) = thickness of the polyester film (mm) × elastic modulus (N / mm ² ) × 80 ° C. Thermal Shrinkage (%) for 30 minutes ÷ 100 × 1000

(2) Contraction force F _V

The shrinkage force F _V of the polyester film is calculated by the following formula. The thickness, elastic modulus, and thermal 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 thermal shrinkage rate is a thermal shrinkage rate of the polyester film in a direction parallel to the absorption axis of the polarizer.

Shrinking force F _V (N / m) = thickness of the polyester film (mm) × elastic modulus (N / mm ² ) × 80 ° C. Thermal Shrinkage (%) for 30 minutes ÷ 100 × 1000

(3) Film thickness

The thickness (mm) of the polyester film was measured using an electric micrometer (Mintron 1245D, manufactured by Feinpruf, Inc.) under an environment of 25 ° C and 50RH% after standing for 168 hours, and the unit was converted into mm.

(4) Modulus of elasticity of polyester film

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

(5) Thermal shrinkage and gradient of thermal shrinkage of polyester film

A polyester film was allowed to stand at 25 ° C and 50RH% for 168 hours, and then a circle with a diameter of 80 mm was drawn. Using an image size measuring device (ImageMeasure IM6500 manufactured by Keyence Corporation), the circle diameter was measured at 1 ° as Length before processing. Next, heat treatment was performed using a Gear oven set at 80 ° C for 30 minutes, and then, after cooling for 10 minutes in an environment set at room temperature of 25 ° C, the same method as before treatment was performed every 1 °. Evaluation was performed as the treated length. The above-mentioned treatment is performed using a polyester film monomer (polyester film monomer for polarizer protection).

Using the following calculation formulas, the thermal shrinkage was evaluated at various angles.

Heat shrinkage rate = (length before treatment-length after treatment) / length before treatment × 100

With this operation, the thermal shrinkage of the polyester film in the direction parallel to the polarizer transmission axis and the thermal shrinkage of the polyester film in the direction parallel to the polarizer absorption axis were obtained for the polyester film.

In the above, 360 ° evaluation was performed every 1 ° to determine the direction in which the thermal shrinkage ratio becomes the largest, and the absolute value of the angle between the direction and the transmission axis direction of the polarizer was used as the gradient of the thermal shrinkage ratio. The inclination of the thermal shrinkage is defined as a narrow angle from the transmission axis direction of the polarizer, and it is in a range of 0 to 90 °.

(6) Warping of LCD panel

A Keel oven set at 80 ° C will be used in each example. Compare The liquid crystal panel produced in the example was subjected to a heat treatment for 30 minutes, and then, after being cooled for 30 minutes in an environment set to a room temperature of 25 ° C. and 50% RH, the convex side was placed downward on a horizontal surface and measured with a measuring instrument. The height of the four corners is the maximum value as the amount of warpage. The amount of warpage was evaluated in the following manner.

○: 0mm or more and less than 2.0mm

△: 2.0mm or more and 3.0mm or less

×: More than 3.0mm

(7) Refractive index of polyester film

The slow axis direction of the film was determined using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 type molecular alignment meter), and a 4 cm × 2 cm rectangle was cut out so that the slow axis direction became parallel to the long side of the measurement sample. As a measurement sample. For this sample, an orthogonal biaxial refractive index (refractive index in the slow axis direction: Ny, fast axis (in the direction of the slow axis) using an Abbe refractometer (NAR-4T, measurement wavelength: 589 nm) was obtained. Refractive index in the orthogonal direction): Nx) and refractive index (Nz) in the thickness direction. Use these values to find the NZ coefficient.

The retardation is a parameter defined as the product of the anisotropy (△ Nxy = | Nx-Ny |) of the orthogonal biaxial refractive index on the film and the film thickness d (nm) (△ Nxy × d). Optical anisotropy, anisotropy scale. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 molecular alignment meter), the slow axis direction of the film was obtained, and a 4 cm × 2 cm cut was made so that the slow axis direction became parallel to the long side of the sample for measurement. A rectangle is used as a measurement sample. For this sample, an orthogonal biaxial refractive index (refractive index in the slow axis direction: Ny, orthogonal to the slow axis direction) was obtained using an Abbe refractometer (NAR-4T, measuring wavelength: 589 nm). The refractive index in the direction: Nx) and the refractive index (Nz) in the thickness direction. The absolute value (| Nx-Ny |) of the biaxial refractive index difference was used as the anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (Mintron 1245D, manufactured by Feinpruf), and the unit was converted to nm. The retardation (Re) was obtained from the product (ΔNxy × d) of the anisotropy (ΔNxy) of the refractive index and the thickness d (nm) of the thin film.

(8) Delay in thickness direction (Rth)

The retardation in the thickness direction refers to the value obtained by multiplying the film thickness d by the two birefringences ΔNxz (= | Nx-Nz |) and △ Nyz (= | Ny-Nz |) when viewed from the film thickness direction section. The average parameter of the amount of delay. Calculate Nx, Ny, Nz, and film thickness d (nm) by the same method as measuring the retardation, and calculate the average of (△ Nxz × d) and (△ Nyz × d) to determine the retardation in the thickness direction (Rth) .

(Production Example 1-Polyester A)

When the temperature was increased to 200 ° C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added. While stirring, 0.017 parts by mass of antimony trioxide and magnesium acetate tetrahydrate were charged. 0.064 parts by mass and triethylamine 0.16 parts by mass. Next, pressurize and raise the pressure to perform an esterification reaction under the conditions of a gauge pressure of 0.34 MPa and 240 ° C, then return the esterification reactor to normal pressure, and add phosphoric acid by 0.014 mass. Serving. The temperature was further raised to 260 ° C over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Next, after 15 minutes, dispersion treatment was performed using 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, a filtering process using a naslon filter with a 95% cut-off diameter of 5 μm was performed, and the strand was extruded from a nozzle into a strand shape. The filtering process was performed in advance (pore diameter: 1 μm or less) The cooling water is cooled, solidified, and cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl / g, and substantially no inactive particles and internally precipitated particles were contained. (Hereinafter referred to as PET (A).)

(Production Example 2-Polyester B)

The dried ultraviolet absorbent (2,2 '-(1,4-phenylene) bis (4H-3,1-benzo -4-ketone) 10 parts by mass and 90 parts by mass of PET (A) (with an inherent viscosity of 0.62 dl / g) containing no particles, and using a kneading extruder, polyethylene terephthalate containing an ultraviolet absorber was obtained Ester resin (B). (Hereinafter referred to as PET (B).)

(Production Example 3-Preparation of Adhesive Modified Coating Liquid)

The transesterification reaction and the polycondensation reaction are performed by a common method, and 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and isophthalic acid are prepared as a diacid component (relative to the entire diacid component)- Sodium 5-sulfonate 8 mol%, 50 mol of ethylene glycol as a diol component (relative to the entire diol component), and 50 mol of neopentyl glycol. Acid metal salt based copolyester resin. Next, 51.4 parts by mass of water, 38 parts by mass of isopropanol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of the non-ionic surfactant were mixed, and then heated and stirred. Once the temperature reached 77 ° C, the water-dispersible sulfonic acid was added. After 5 parts by mass of the acid metal salt-based copolymerized polyester resin, the resin aqueous dispersion was cooled to normal temperature after continuous stirring until no resin agglomerates, to obtain a uniform water-dispersible copolymerized polyester resin solution having a solid content concentration of 5.0% by mass. After dispersing 3 parts by mass of aggregated silica particles (Sylysia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolymerized polyester resin solution was added with 0.54 parts by mass of Sylysia 310 aqueous dispersion. 20 parts by mass of water was added while stirring to obtain an adhesive modified coating solution.

(Example 1) <Production of Polyester Film 1 for Polarizer Protection>

90 parts by mass of non-particle-containing PET (A) resin pellets and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for a base film intermediate layer were dried under reduced pressure at 135 ° C (1 Torr) After 6 hours, it was supplied to extruder 2 (for intermediate layer II), and PET (A) was dried by a conventional method and supplied to extruder 1 (for outer layer I and outer layer III) at 285 ° C. Under melting. These two polymers were respectively filtered with a filter material of a stainless steel sintered body (with a nominal filtration accuracy of 10 μm and 95% of the particles were retained), and were laminated in two kinds of three-layer converging blocks, extruded into a sheet form from the extrusion port, and then casted using an electrostatic application method. It was wound and solidified on a casting drum having a surface temperature of 30 ° C to produce an unstretched film. At this time, each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer became 10:80:10. Spitting amount.

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

The unstretched film on which the coating layer was formed was guided to a tenter stretcher, and while the end of the film was clamped by a jig, it was guided to a hot air zone at a temperature of 105 ° C. and stretched 4.0 times on TD. Next, heat treatment was performed at a temperature of 180 ° C. for 30 seconds, and then the film cooled to 100 ° C. was stretched by 1.0% in the width direction. Then, the clamps holding both ends of the film cooled to 60 ° C. were placed. It was pulled with a tension of 350 N / m, and a jumbo roll containing a uniaxially oriented PET film with a film thickness of about 80 μm was extracted. The obtained jumbo roll was divided into 3 equal parts to obtain 3 slit rolls. (L (left), C (center), R (right)). A polyester film 1 for polarizer protection was obtained from the slit roll at R. The direction in which the thermal contraction rate of the polyester film 1 series for polarizer protection becomes the largest is 7.0 degrees from TD.

<Creation of liquid crystal panel>

The polyester film 1 for polarizer protection is attached to one side of the polarizer including PVA, iodine, and boric acid so that the transmission axis of the polarizer is parallel to the TD of the polyester film 1 for polarizer protection. In addition, a TAC film (manufactured by Fuji Film Co., Ltd., thickness: 80 μm) was attached to the opposite surface of the polarizer to form a light source-side polarizing plate.

The liquid crystal panel was taken out from a 46-inch IPS-type LCD TV with a glass substrate having a thickness of 0.4 mm and a liquid crystal cell. Peel from LCD panel The light source side polarizing plate is replaced with a transmission axis of the polarizer and the transmission axis direction (parallel to the horizontal direction) of the light source side polarizing plate before peeling. The liquid crystal cell forms a liquid crystal panel.

In addition, the light source side polarizing plate is bonded to the liquid crystal cell so that the polyester film 1 for polarizer protection is a side away from the liquid crystal cell (the side opposite to the liquid crystal cell). In addition, the viewing-side polarizing plate is formed by laminating TAC films on both areas of the polarizer, and attaching the polarizing lens to the liquid crystal cell such that the absorption axis direction of the polarizer becomes parallel to the horizontal direction.

(Example 2) <Production of Polyester Film 2 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 1.5% in the width direction in the film formation of the polyester film 1 for polarizer protection in Example 1, the same operation was performed as the polyester film 1 for polarizer protection. Thus, a polyester film 2 for polarizer protection was obtained. The direction in which the thermal shrinkage of the polyester film 2 series for polarizer protection is the largest is 6.5 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 2 for polarizer protection in Example 1.

(Example 3) <Production of Polyester Film 3 for Polarizer Protection>

Except for forming the polyester film 1 for polarizing lens protection in Example 1, The film cooled to 100 ° C. was stretched to 1.7% in the width direction, and the same operation as in the polyester film 1 for polarizer protection was performed to obtain a polarizer protective film 3. The direction in which the thermal shrinkage of the polyester film 3 series for polarizer protection is maximum is 5.3 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 3 for polarizer protection in Example 1.

(Example 4) <Manufacture of Polyester Film 4 for Polarizer Protection>

Except for forming the polyester film 1 for polarizer protection in Example 1, the film cooled to 100 ° C was made to stretch 2.0% in the width direction, and was stretched 4 times on TD, and then the temperature was 180 ° C. At a time point of 30 seconds before the heat treatment, a polarizer protective film 4 was obtained in the same manner as the polarizer protective polyester film 1 except that the hard coat coating liquid was applied to one side of the polyester film. The direction in which the thermal contraction rate of the polyester film 4 series for polarizer protection is maximized is 4.8 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 4 for polarizer protection in Example 1.

(Example 5) <Production of Polyester Film 5 for Polarizer Protection>

A polyester film 5 for polarizing lens protection was obtained in the same manner as the polyester film 4 for polarizing lens protection except that the thickness of the stretched film was adjusted to 160 μm by adjusting the rotation speed of the casting roll. The direction in which the thermal contraction rate of the polyester film 5 series for polarizer protection is maximum is 4.8 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 5 for polarizer protection in Example 1.

(Example 6) <Production of Polyester Film 6 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 1.5% in the flow direction in the film formation of the polyester film 1 for polarizer protection in Example 1, the same operation was performed as the polyester film 1 for polarizer protection. Thus, a polyester film 6 for polarizer protection was obtained. The direction in which the thermal contraction rate of the polyester film 6 series for polarizer protection is maximized is 9.0 degrees from MD.

<Creation of liquid crystal panel>

Except for the preparation of the light source-side polarizing plate in Example 1, the polyester film 6 for polarizer protection was used instead of the polyester film for polarizer protection, and the MD of the transmission axis of the polarizer and the polyester film 6 for polarizer protection was The light source side polarizing plate was attached in parallel to form a liquid crystal panel, and the same operation as in Example 1 was performed.

(Example 7) <Production of Polyester Film 7 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 1.7% in the flow direction in the film formation of the polyester film 1 for polarizer protection in Example 1, the same operation was performed as the polyester film 1 for polarizer protection. Thus, a polyester film 7 for polarizer protection was obtained. The direction in which the thermal shrinkage of the polyester film 7 series for polarizer protection is the largest is 8.3 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for polarizer protection was replaced with the polyester film 7 for polarizer protection in Example 6.

(Example 8) <Production of Polyester Film 8 for Polarizer Protection>

The film was cooled to 100 ° C. and stretched by 2.0% in the flow direction in the film formation of the polyester film 1 for polarizer protection in Example 1. The same operation was performed as the polyester film 1 for polarizer protection. Thus, a polyester film 8 for polarizer protection was obtained. The direction in which the thermal shrinkage of the 8-series polyester film for polarizer protection becomes the largest is 7.0 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for polarizer protection was replaced with the polyester film 8 for polarizer protection in Example 6.

(Example 9) <Production of Polyester Film 9 for Polarizer Protection>

In addition to adjusting the rotation speed of the casting roll to stretch the film The thickness was set to 160 μm, and the same operation as in the polyester film 8 for polarizer protection was performed to obtain a polyester film 9 for polarizer protection. The direction in which the thermal shrinkage of the 9-series polyester film for polarizing film protection is maximized is 7.0 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for polarizer protection was replaced with the polyester film 9 for polarizer protection in Example 6.

(Example 10) <Manufacture of Polyester Film 10 for Polarizer Protection>

A polarizer protective film 10 was obtained in the same manner as the polyester film 6 for polarizing lens protection except that the stretching on the TD was changed from 4.0 times to 4.0 times on the MD and 1.0 times on the TD. The direction in which the thermal shrinkage of the 10-series polyester film for polarizing film protection is maximized is 8.7 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 6 except that the polyester film 6 for polarizer protection was replaced with the polyester film 10 for polarizer protection in Example 6.

(Example 11) <Production of Polyester Film 11 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 1.7% in the flow direction in the film formation of the polyester film 10 for polarizer protection in Example 10, the same operation was performed as the polyester film 10 for polarizer protection. And get Polyester film 11 for polarizer protection. The direction in which the thermal shrinkage of the 11-series polyester film for polarizer protection becomes the maximum is 7.5 degrees from the MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 10 except that the polyester film 10 for polarizer protection was replaced with the polyester film 11 for polarizer protection in Example 10.

(Example 12) <Production of Polyester Film 12 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 5.0% in the width direction in the film formation of the polyester film 10 for polarizer protection in Example 10, the same operation was performed as the polyester film 10 for polarizer protection. Thus, a polyester film 12 for polarizer protection was obtained. The direction in which the thermal contraction rate of the 12-series polyester film for polarizer protection becomes the largest is 1.8 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 12 for polarizer protection in Example 1.

(Example 13) <Production of Polyester Film 13 for Polarizer Protection>

A polyester film 13 for polarizer protection was obtained in the same manner as the polyester film 4 for polarizer protection, except that the thickness of the stretched film was adjusted to 60 μm by adjusting the rotation speed of the casting roll. The direction in which the thermal shrinkage of the 13-series polyester film for polarizing film protection is maximized is 4.8 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 13 for polarizer protection in Example 1.

(Example 14) <Production of Polyester Film 14 for Polarizer Protection>

A polarizer protective film 14 was obtained in the same manner as the polarizer protective film 3 except that the film was passed through without changing the width of the jig sandwiching both ends of the film in the cooling step after stretching in the width direction by 1.7%. The direction in which the thermal shrinkage of the 14-series polyester film for polarizing film protection is maximized is 33.0 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was fabricated 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 Polarizer Protection>

In addition to adjusting the rotation speed of the casting roll to set the thickness of the stretched film to 200 μm, the film was stretched. In the cooling step after heat fixing, the film is passed through without changing the width of the jig that sandwiches both ends of the film, and a polarizer protective film 15 is obtained in the same manner as the polarizer protective film 1. The direction in which the thermal shrinkage of the 15-series polyester film for polarizing film protection is maximum is 20.0 degrees from MD.

<Creation of liquid crystal panel>

The same procedure as in Example 1 was performed except that the polarizer protective film 1 was replaced with the polarizer protective film 15 and the transmission axis of the polarizer and the MD of the polarizer protective film were bonded to form a light source side polarizer Create a liquid crystal panel.

(Comparative example 2) <Manufacture of Polyester Film 16 for Polarizer Protection>

In addition to stretching. In the cooling step after heat fixing, the process of stretching 1.0% in the width direction is not performed. At 95 ° C, the clamps holding both ends of the film are released, and the polarizer protection is obtained in the same manner as the polarizer protection film 1. Film 16. The direction in which the thermal shrinkage of the 16-series polyester film for polarizing film protection is maximized is 1.0 degree from MD.

<Creation of liquid crystal panel>

The same procedure as in Example 1 was performed except that the polarizer protective film 1 was replaced with the polarizer protective film 16 and the transmission axis of the polarizer and the MD of the polarizer protective film were bonded to form a light source side polarizing plate. Create a liquid crystal panel.

(Comparative example 3) <Production of Polyester Film 17 for Polarizer Protection>

A polyester film 17 for polarizing lens protection was obtained in the same manner as the polyester film 1 for polarizing lens protection except that the thickness of the stretched film was adjusted to 50 μm by adjusting the rotation speed of the casting roll. The direction in which the thermal shrinkage of the 17-series polyester film for polarizing film protection is maximized is 7.0 degrees from TD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 1 except that the polyester film 1 for polarizer protection was replaced with the polyester film 17 for polarizer protection in Example 1.

(Comparative Example 4) <Production of Polyester Film 18 for Polarizer Protection>

A polyester film 18 for polarizing lens protection was obtained in the same manner as the polyester film 11 for polarizing lens protection except that the thickness of the stretched film was adjusted to 160 μm by adjusting the rotation speed of the casting roll. The direction in which the thermal shrinkage of the 18-series polyester film for polarizing film protection becomes the largest is 6.5 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 11 except that the polyester film 11 for polarizer protection was replaced with the polyester film 18 for polarizer protection in Example 11.

(Comparative example 5) <Production of Polyester Film 19 for Polarizer Protection>

Except that the thickness of the stretched film was adjusted to 160 μm by adjusting the rotation speed of the casting roll, in the film formation of the polyester film 1 for polarizer protection in Example 1, the film cooled to 100 ° C. was made to flow. Except for 1.0% stretching in the direction, the same operation as in the polyester film 1 for polarizer protection was performed to obtain a polyester film 19 for polarizer protection. The direction in which the thermal shrinkage of the 19-series polyester film for polarizing film protection is maximized is 11.0 degrees from MD.

<Creation of liquid crystal panel>

Except for the preparation of the light source-side polarizing plate in Example 1, the polyester film 19 for polarizer protection was used instead of the polyester film for polarizer protection, and the transmission axis of the polarizer and the TD of the polyester film 19 for polarizer protection were The light source side polarizing plates were laminated in parallel to form a liquid crystal panel in the same manner as in Example 1.

(Comparative Example 6) <Production of Polyester Film 20 for Polarizer Protection>

A polyester film 20 for polarizing lens protection was obtained in the same manner as the polyester film 19 for polarizing lens protection except that the thickness of the stretched film was adjusted to 80 μm by adjusting the rotation speed of the casting roll. The direction in which the thermal shrinkage of the 20-series polyester film for polarizing film protection becomes the largest is 11.0 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Comparative Example 5 except that the polyester film 19 for polarizer protection was replaced with the polyester film 20 for polarizer protection in Comparative Example 5.

(Comparative Example 7) <Production of Polyester Film 21 for Polarizer Protection>

The polarizer protective film 21 was obtained by operating in the same manner as the polarizer protective film 20. The direction in which the thermal shrinkage of the 20-series polyester film for polarizing film protection becomes the largest is 11.0 degrees from MD.

<Creation of liquid crystal panel>

Except for the preparation of the light source-side polarizing plate of Example 1, a polarizing plate was used. The polyester film 21 for optical lens protection replaces the polyester film 1 for polarizer protection, and the transmission axis of the polarizer and the MD of the polyester film 21 for polarizer protection are bonded in parallel to form a polarizer on the light source side, and A liquid crystal panel was produced in the same manner as in Example 1.

(Comparative Example 8) <Creation of liquid crystal panel>

A liquid crystal panel was fabricated 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 became parallel.

(Comparative Example 9) <Manufacture of Polyester Film 22 for Polarizer Protection>

Except that the thickness of the stretched film was adjusted to 160 μm by adjusting the rotation speed of the casting roll, in the film formation of the polyester film 1 for polarizer protection in Example 1, the film cooled to 100 ° C. was made to flow. Except for 1.0% stretching in the direction, the same operation as in the polyester film 1 for polarizer protection was performed to obtain a polyester film 22 for polarizer protection. The direction in which the thermal contraction rate of the polyester film 22 series for polarizer protection becomes the maximum is 11.0 degrees from MD.

<Creation of liquid crystal panel>

Except for the preparation of the light source-side polarizing plate in Example 1, the polyester film 22 for polarizer protection was used instead of the polyester film 1 for polarizer protection, and the transmission axis of the polarizer and the MD of the polyester film 22 for polarizer protection were used. The light source side polarizing plates were bonded together in a parallel manner to form a liquid crystal panel in the same manner as in Example 1.

(Comparative Example 10) <Production of Polyester Film 23 for Polarizer Protection>

Except that the film cooled to 100 ° C. was stretched by 2.0% in the flow direction in the film formation of the polyester film 10 for polarizer protection in Example 10, the same operation was performed as the polyester film 10 for polarizer protection. Thus, a polyester film 23 for polarizer protection was obtained. The direction in which the thermal shrinkage of the polyester film 23 series for polarizer protection is the largest is 4.5 degrees from MD.

<Creation of liquid crystal panel>

A liquid crystal panel was produced in the same manner as in Example 10, except that the polyester film 10 for polarizer protection was replaced with the polyester film 23 for polarizer protection in Example 10.

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

(Example 1A to Example 5A, Example 13A)

In addition, except that the polarizing plate having the same configuration as the light source-side polarizing plate used in each of Examples 1 to 5, 13 is used as the light source-side polarizing plate and the viewing-side polarizing plate and is used on both sides, When Examples 1 to 5 and 13 were operated in the same manner and evaluated separately, the same results as those of Examples 1 to 5 and 13 in Table 1 above were obtained, and good results were obtained in the evaluation of the warpage of the panel (○ ). Further, 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 polarizer protection became a side away from the liquid crystal cell (the side opposite to the liquid crystal cell).

(Examples 1B to 5B and 13B)

In addition, except that the TAC film was not used as the polarizer protective film on the liquid crystal cell side in Examples 1A to 5A and 13A, the same operations as in Examples 1A to 5A and 13A were performed, and additional In the case of evaluation, similar to Examples 1A to 5A and Example 13A, favorable results (○) were obtained in the evaluation of the warpage of the panel.

[Industrial availability]

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

Claims (11)

A polyester film for polarizer protection is a polyester film for polarizer protection laminated on one side of a polarizer, which meets the following requirements (1) and (2): (1) a direction parallel to the transmission axis of the polarizer The shrinkage force F _f of the polyester film is 800 N / m or more and 9000 N / m or less (where the shrinkage force F _f (N / m) is based on the thickness (mm) of the polyester film × the elastic modulus (N / mm ² ) × 80 ℃. Thermal shrinkage (%) for 30 minutes ÷ 100 × 1000, where the elastic modulus is the elastic modulus of the polyester film in a direction parallel to the transmission axis of the polarizer, and the thermal shrinkage is Thermal shrinkage of the polyester film in a direction parallel to the transmission axis of the polarizer); (2) shrinkage force F _f of the polyester film in a direction parallel to the transmission axis of the polarizer and an absorption axis of the polarizer The ratio (F _f / F _v ) of the shrinking force F _v of the polyester film in the parallel direction is 2.5 or more and 12.0 or less (where the shrinking force F _v (N / m) is the thickness (mm) of the polyester film × Modulus of elasticity (N / mm ² ) × 80 ° C. Thermal shrinkage (%) for 30 minutes ÷ 100 × 1000. Here, the modulus of elasticity is the polyester film in a direction parallel to the absorption axis of the polarizer. Modulus of elasticity Heat shrinkage ratio of the polyester-based heat-shrinkable in a direction parallel to the absorption axis of the polarizer film). For example, the polyester film for polarizer protection of claim 1 further satisfies the following requirements (3): (3) The direction in which the thermal shrinkage of the polyester film becomes maximum and the direction parallel to the transmission axis of the polarizer are approximately Parallel. The polyester film for polarizing lens protection according to claim 1 or 2, wherein the polyester film has a retardation of 3000 to 30,000 nm. The polyester film for polarizing lens protection according to any one of claims 1 to 3, wherein the thickness of the polyester film is 40 to 200 μm. The polyester film for polarizing lens protection according to any one of claims 1 to 4, wherein a surface of the polyester film opposite to the surface of the laminated polarizer is provided with a hard coat layer, an anti-reflection layer, and a low-reflection layer , Anti-glare layer, or anti-reflective anti-glare layer. A polyester film for polarizer protection is a polyester film for polarizer protection laminated on one side of a polarizer, which meets the following requirements (1) and (2): (1) the shrinkage force of the TD of the polyester film F _TD is 800 N / m or more and 9000 N / m or less (wherein, the shrinkage force F _TD (N / m) is the thickness (mm) of the polyester film × elastic modulus (N / mm ² ) × 80 ° C for 30 minutes. Thermal shrinkage (%) ÷ 100 × 1000, where the elastic modulus is the elastic modulus of the TD of the polyester film, and the thermal shrinkage is the thermal shrinkage of the TD of the polyester film); (2) the polyester film the TD and _TD shrinkage force F. F. the polyester film _MD MD than the contractile force (F _TD / F _MD) is 2.5 or more 12.0 or less (wherein, contractile force F _MD (N / m) of the polyester film Thickness (mm) × modulus of elasticity (N / mm ² ) × 80 ° C. Thermal shrinkage (%) for 30 minutes ÷ 100 × 1000. Here, the modulus of elasticity is the modulus of elasticity of MD of the polyester film. The heat shrinkage rate is the heat shrinkage rate of MD of the polyester film). For example, the polyester film for polarizer protection of claim 6 further satisfies the following requirement (3): (3) The direction in which the thermal shrinkage of the polyester film becomes maximum is substantially parallel to the TD system. A polarizing plate, which is laminated on at least one side of a polarizer as in claim 1 The polyester film for polarizer protection according to any one of 7 to 7. A polarizing plate is formed by laminating a polyester film for protecting a polarizer according to any one of claims 1 to 7 on one surface of a polarizer and not including a film on the other surface of the polarizer. For example, the polarizing plate of claim 8 or 9, wherein the polarizing plate has a rectangular shape, and the long side of the polarizing plate is parallel to its transmission axis. A liquid crystal display device is a liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates. At least one of the two polarizing plates is polarized light according to any one of claims 8 to 10. board.