TWI805917B - Polarizing plate and liquid crystal display device - Google Patents

Abstract

Provide polarizers and liquid crystal display devices. A polarizing plate in which a polyester film for protecting a polarizer satisfying the following requirements (1) and (2) is laminated on one side of a polarizer. (1) The shrinkage force F _f of the aforementioned 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; (2) the aforementioned polyester film in a direction parallel to the transmission axis of the polarizer The ratio (F _f /F _v ) of the shrinkage force F _f of the film to the shrinkage force F _v of the polyester film in a direction parallel to the absorption axis of the polarizer is 2.5 to 12.0.

Description

Polarizing plate and liquid crystal display device

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

Liquid crystal display devices are in increasing demand 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, etc. with a glass plate, and two polarizers arranged on both sides thereof, and each polarizer is made of two optical films ( For example, a polarizer protective film and a retardation film) sandwich a polarizer (also called a polarizing film).

However, in recent years, along with thinner and larger LCD TV screens, LED backlights are used as light sources, and glass substrates used in liquid crystal panels are made thinner than 0.7mm, causing display unevenness. question, request to improve the question. The 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, due to the relaxation of the alignment, a shrinkage force is generated in the alignment direction, and the liquid crystal panel is warped as a result. Swells on the backlight unit side, causing display unevenness.

Also, at present, as in the following patent document 1 and patent document 2, the thickness of the glass substrate used in the liquid crystal panel is as thick as 0.7mm or more, so the shrinkage of the polarizer is suppressed by the high rigidity of the glass, so there is no possibility of warping of the liquid crystal panel. In this case, there is no problem of uneven display.

Therefore, an attempt has been made to improve the warpage of the liquid crystal panel that occurs when the glass substrate is made thinner than 0.7 mm by using an optical film. For example, when a cycloolefin-based resin is used as a polarizer protective film, the improvement of the warpage of the liquid crystal panel is not sufficient, and the drying property of the glue for adhering to the polarizer is poor, so that there is a problem that productivity is lowered. Moreover, when using the current triacetyl cellulose (TAC) as a polarizer protective film, there exists a problem that a liquid crystal panel warps. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2008-107499 [Patent Document 2] Japanese Patent Laid-Open No. 2009-198666

[Problem to be solved by the invention]

The present invention is in view of the above problems. The invention has been completed to solve the problem of providing a polarizer protective film, a polarizing plate, and a liquid crystal display device capable of suppressing warping of a liquid crystal panel. [Means to solve the problem]

In order to solve the above-mentioned problems, the inventors of the present invention found in the process of examining the causes of the above-mentioned problems that by setting the shrinkage force of the polyester film for polarizer protection in a direction parallel to the transmission axis of the polarizer within a specific range, The present invention was completed based on the knowledge that warping of liquid crystal panels can be improved.

In terms of details, a liquid crystal display device usually has a polarizing plate in one area of the liquid crystal cell such as a polarizer whose transmission axis direction is parallel to the long side direction of the liquid crystal display device, and on another area layer such as a polarizer whose absorption axis direction is A polarizing plate parallel to the long sides of the liquid crystal display device. As a result of in-depth examination using various commercially available liquid crystal display devices, the present inventors found that the essence of the problem lies in a shape that tends to be curled due to the shrinkage of the polarizing plate whose absorption axis direction is the long side of the polarizer with a large shrinkage force. factor (curl 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 upper and lower polarizers of the liquid crystal panel are configured as crossed polarizers The transmission axis of the polarizer becomes convex on the polarizer side of the long side.

In addition, as a result of in-depth examination, it is clear that the shrinkage force in the longitudinal direction of the polarizer whose transmission axis is the long side can be controlled by the residual strain of the protective film, and it is known that the liquid crystal panel can be controlled by this shrinkage force the curl.

Here, the method of measuring the shrinkage force of the polyester film for polarizer protection is described. Generally, TMA or the like is used for the shrinkage force of the film, and the initial length is set under a very small load at a low temperature at the start of the test, and the force in the shrinking direction during heating is measured at a length that maintains the initial length. However, during the heating process, the free volume of the polymer is generated simultaneously with the shrinkage (hereinafter, abbreviated as heat shrinkage) caused by the recovery of the residual strain accompanying the conformation change of the polymer. Thermal expansion due to increase in occupied volume due to increase in temperature (hereafter abbreviated as thermal expansion), therefore, in the temperature range near the glass transition temperature of the polyester film (for example, ~Tg+50°C or so), there is always a relationship of thermal contraction > thermal expansion , so the film as a whole is inflated, and no shrinkage force is observed.

As a result of the review, it became clear that contraction forces were generated during TMA cooling even when no contraction force was generated during TMA heating. The reason for this is that the strain caused by thermal expansion becomes a reversible change, so it returns to the original state after heating up and cooling down, but since it is cooled in a state of small size corresponding to the amount of thermal contraction during the heating up process, during the cooling process generate thermal stress. That is, the thermal stress strain can be substituted for the thermal shrinkage rate of the film, and the shrinkage force after cooling can be expressed by the following formula. In addition, the heat shrinkage rate in this invention means what includes the moisture content change in heat processing. Shrink force (N/m) = film thickness (mm) × elastic modulus (N/mm ² ) × heat shrinkage rate (%) ÷ 100 × 1000

That is, the representative invention is as follows. Item 1. A polyester film for protecting a polarizer, which is a polyester film for protecting a polarizer laminated on one side of a polarizer, and which satisfies the following requirements (1) and (2). (1) The shrinkage force F _f of the aforementioned polyester film in the direction parallel to the transmission axis of the polarizer is 800 N/m to 9000 N/m (wherein, the shrinkage force F _f (N/m) is the thickness of the polyester film (mm)×Elastic modulus (N/mm ² )×80℃．The heat shrinkage rate after 30 minutes treatment (%)÷100×1000. Here, the elastic modulus is in the direction parallel to the transmission axis of the polarizer The modulus of elasticity of the polyester film, the heat shrinkage rate is the heat shrinkage rate of the polyester film on the direction parallel to the transmission axis of the polarizer.) (2) the aforementioned polyester film on the direction parallel to the transmission axis of the polarizer The ratio (F _f / _{F v ) of the shrinkage force F f of} the aforementioned polyester film in the direction parallel to the absorption axis of the polarizer is 2.5 or more and 12.0 or less (wherein, 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 heat shrinkage (%) ÷ 100 × 1000. Here, the elastic modulus is the same as that of the polarizer 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 thermal shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer.) Item 2. Polarizer protection as in item 1 A polyester film is used which further satisfies the following requirement (3). (3) The direction in which the heat shrinkage rate of the polyester film becomes the largest is substantially parallel to the direction parallel to the transmission axis of the polarizer. Item 3. The polyester film for polarizer protection according to Item 1 or 2, wherein the polyester film has a retardation of 3000 to 30000 nm. Item 4. The polyester film for polarizer protection according to any one of Items 1 to 3, wherein the polyester film has a thickness of 40 to 200 μm. Item 5. The polyester film for polarizer protection according to any one of Items 1 to 4, wherein the polyester film has a hard coat layer, an antireflection layer, a low- A reflective layer, an antiglare layer, or an antireflective antiglare layer. Item 6. A polyester film for protecting a polarizer, which is a polyester film for protecting a polarizer laminated on one side of a polarizer, and which satisfies the following requirements (1) and (2). (1) The shrinkage force F _TD of the TD of the aforementioned polyester film is more than 800N/m and less than 9000N/m (wherein, the shrinkage force F _TD (N/m) is the thickness (mm) of the polyester film × modulus of elasticity (N /mm ² ) × 80°C. Thermal shrinkage rate (%) ÷ 100 × 1000 after 30 minutes of treatment. 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 rate.) (2) The ratio (F _TD /F _MD ) of the shrinkage force F _TD of the TD of the aforementioned polyester film to the shrinkage force F _MD of the MD of the aforementioned polyester film is 2.5 or more and 12.0 or less (wherein, the shrinkage force Thickness (mm) of F _MD (N/m) polyester film × elastic modulus (N/mm ² ) × 80°C. Thermal shrinkage rate (%) after 30 minutes of treatment ÷ 100 × 1000. Here, elastic modulus The modulus of elasticity of the MD of the numerical system polyester film, the heat shrinkage rate of the MD of the polyester film.) Item 7. The polyester film for polarizer protection as item 6, which further satisfies the following requirements (3 ). (3) The direction in which the thermal shrinkage rate of the polyester film becomes the largest is substantially parallel to the TD system. Item 8. A polarizing plate in which the polarizer protective polyester film according to any one of Items 1 to 7 is layered on at least one area 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 layered on one surface of a polarizer, and does not have a film on the other side of the polarizer. Item 10. The polarizing plate according to 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, which is a liquid crystal display device having a backlight source and a liquid crystal cell disposed between two polarizers, at least one of the two polarizers being any one of items 8 to 10 polarizer. [Effect of Invention]

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 warping of a liquid crystal panel.

[Mode for Carrying Out the Invention]

The polarizer protective polyester film of the present invention includes a polyester film, and is a polarizer protective film for laminating on at least one side of a polarizer (for example, a film containing polyvinyl alcohol and a pigment) to form a polarizer.

In this specification, the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer refers to 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. mean. The heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer means the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film. The elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer means the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer laminated on one side of the polyester film. In addition, 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 rate of the polyester film in the direction parallel to the absorption axis of the polarizer means the thermal shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film. The elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer means the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer laminated on one side of the polyester film. The direction parallel to the transmission axis of the polarizer may be simply referred to as the transmission axis direction of the polarizer. In addition, the direction parallel to the absorption axis of the polarizer may be simply referred to as the absorption axis direction of the polarizer.

The polyester film for polarizer 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 rate of the polyester film becomes the largest. 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 becomes the largest (hereinafter, may be simply referred to as the gradient of the thermal shrinkage rate) is 15 degrees or less. The inclination of the thermal shrinkage rate is preferably less than 12 degrees, more preferably less than 10 degrees, more preferably less than 8 degrees, more preferably less than 6 degrees, most preferably less than 4 degrees, and most preferably less than 2 degrees. . The smaller the inclination of the thermal contraction rate, the better, so the lower limit is 0 degrees. When the inclination of the thermal shrinkage rate of a polyester film is large, the oblique curvature of the polarizing plate containing a polyester film will arise, and there exists a tendency for the effect of reducing the curvature of a liquid crystal panel to decline. However, 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 not less than 2.5 and not more than 12.0, 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 becomes the largest is 40 degrees or less, the warpage of the liquid crystal panel can be reduced . The aforementioned angle is preferably 35 degrees or less. The thermal shrinkage rate of the polyester film, the inclination of the thermal shrinkage rate of the polyester film, and the direction in which the thermal shrinkage rate of the polyester film becomes the largest can be measured by the method employed in Examples described later.

Generally, in a liquid crystal display device, two polarizing plates are arranged in a relationship of crossed Nicols. If two polarizing plates are arranged in a crossed Nicols relationship, usually light cannot pass through the two polarizing plates. However, due to shrinkage or warping of the above-mentioned polarizers, the perfect cross-Nicol relationship collapses, and light leakage may occur. From the viewpoint of suppressing light leakage, the smaller the angle between the direction in which the thermal shrinkage rate of the polarizer protective film becomes the largest and the transmission axis of the polarizer, the better.

The polyester film for polarizer protection of the present invention preferably has a shrinkage force F _f value 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 of F _f is less than 800 N/m, there exists a possibility that the curvature of a liquid crystal panel may not fully be reduced. Moreover, when the upper limit of F _f exceeds 9000 N/m, there exists a possibility that a shrinkage force may become too strong and a liquid crystal panel may warp in the reverse direction. The preferred range of shrinkage force is above 900N/m and below 8000N/m, more preferably above 1000N/m and below 8000N/m, more preferably above 1100N/m and below 8000N/m, and more preferably above 1200N/m Below 8000N/m. Moreover, the upper limit is preferably 6000 N/m or less, preferably 5500 N/m or less, more preferably 4800 N/m or less.

Here, the shrinkage force F _f refers to the shrinkage force of the polyester film in the direction parallel to the transmission axis of the polarizer, defined as the thickness of the polyester film (mm) × modulus of elasticity (N/mm ² ) × 80°C ． Heat shrinkage rate (%)÷100×1000 after 30 minutes treatment. Here, the modulus of elasticity is the modulus of elasticity of the polyester film in a direction parallel to the transmission axis of the polarizer. In addition, the heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer (80° C. heat shrinkage rate under 30-minute treatment).

Let the shrinkage force of the polyester film in the direction parallel to the absorption axis of the polarizer be F _v . The shrinkage force F _v is defined as the thickness of polyester film (mm) × modulus of elasticity (N/mm ² ) × 80 ℃. Heat shrinkage rate (%)÷100×1000 after 30 minutes treatment. Here, the modulus of elasticity is the modulus of elasticity 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 the direction parallel to the absorption axis of the polarizer (80°C, heat shrinkage rate under 30-minute treatment).

In the polyester film for polarizer protection of the present invention, the system F _f /F _v is preferably 1.0 or more and 12.0 or less. More preferably, it is not less than 2.5 and not more than 12.0. When the lower limit of F _f /F _v is less than 1.0, there is a possibility that the warpage of the liquid crystal panel cannot be sufficiently reduced. In addition, if the upper limit of F _f /F _v exceeds 12.0, the thermal deformation in one direction will increase, and the polarizer is laminated on the surface opposite to the surface on which the polyester film for polarizer protection is laminated. Stress is applied to the protective film or retardation film, which may lower the display quality. In addition, film forming stability may be lowered to cause breakage.

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

In the polyester film for polarizer protection of the present invention, the elastic modulus of the polyester film in the direction of the transmission axis of the polarizer is preferably 1000-9000 N/mm ² . The shrinkage force of the polyester film can be controlled by the elastic modulus. In order to improve the elastic modulus of the polyester film in the direction of the transmission axis of the polarizer, it is necessary to make the polyester film highly aligned in the direction of the transmission axis of the polarizer, and to increase Crystallinity. Therefore, when the elastic modulus of the polyester film in the transmission axis direction of the polarizer exceeds 9000N/mm ² , there is a risk of cracking, etc., so the upper limit is preferably 9000N/mm ² , more preferably 8000N /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 roll irregularities caused by uneven thickness at the time of winding into a roll, resulting in poor planarity. Therefore, the lower limit of the modulus of elasticity is preferably 1000 N/mm ² , more preferably 1500 N/mm ² , and still more preferably 1800 N/mm ² . The modulus of elasticity can be measured by the method used in Examples described later.

The polyester film for polarizer protection of the present invention preferably has a heat shrinkage rate of 0.10-5.0% when the polyester film is 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 at least 0.10%, more preferably at least 0.15%, most preferably at least 0.20%. The upper limit of the heat shrinkage rate is preferably at most 4.5%, more preferably at most 4.0%, even more preferably at most 3.0%, even more preferably at most 2%, most preferably at most 1.4%. When the heat shrinkage rate 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 rate without variation. In addition, in order to increase the heat shrinkage rate to more than 5.0%, it is necessary to further lower the degree of crystallization or the glass transition temperature, which may cause defects such as poor planarity. The thermal shrinkage rate can be measured by the method adopted in the examples described later.

The thickness of the polyester film for polarizer protection of the present invention is preferably 40-200 μm, more preferably 40-100 μm, and even more preferably 40-80 μm. When the thickness of the polyester film is less than 40 μm, it tends to be easily cracked, and the flatness tends to be poor due to insufficient rigidity. In addition, when it is thin, it is necessary to increase the elastic modulus or thermal shrinkage rate of the polyester film in the direction of the transmission axis of the polarizer accordingly. However, as mentioned above, each parameter also has an upper limit, so 40 μm is actually the lower limit. . In addition, when the thickness of the film exceeds 200 μm, the variation in the elastic modulus or thermal shrinkage rate of the polyester film in the direction of the transmission axis of the polarizer increases accordingly, and its control may become difficult. In addition, the cost also rose. The thickness of the polyester film can be measured by the method employed in the examples described later.

In the polyester film for polarizer protection of the present invention, the in-plane retardation is preferably within a specific range from the viewpoint of suppressing iridescent spots seen on the screen of a liquid crystal display device. The lower limit of the in-plane retardation is preferably at least 3000 nm, preferably at least 5000 nm, preferably at least 6000 nm, preferably at least 7000 nm, or more preferably at least 8000 nm. The upper limit of the in-plane retardation is preferably at most 30000 nm, more preferably at most 18000 nm, still more preferably at most 15000 nm. In particular, from the viewpoint of thinning, the in-plane retardation is preferably less than 10000 nm and not more than 9000 nm.

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

The polarizer protective polyester film of the present invention has a ratio (Re/Rth) of the in-plane retardation (Re) and the retardation (Rth) in the thickness direction (Rth) of preferably 0.2 or more, preferably 0.3 or more, preferably 0.4 or more, more preferably 0.5 or more, still more preferably 0.6 or more. The larger the ratio (Re/Rth) of the above-mentioned in-plane retardation to the thickness direction retardation, the more the effect of birefringence increases the isotropy, and there is a possibility that it becomes difficult to generate rainbow-like color spots due to the viewing angle. tendency. The ratio (Re/Rth) of the above-mentioned retardation to the thickness direction retardation is 2.0 for a completely uniaxial (uniaxially symmetric) film, so the upper limit of the ratio (Re/Rth) of the above retardation to the thickness direction retardation is preferable. is 2.0. A preferable upper limit of Re/Rth is 1.2. In addition, the retardation in the thickness direction means the average of the retardation obtained by multiplying the thickness d of the film by two birefringences ΔNxz and ΔNyz when the film is viewed in cross-section in the thickness direction.

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, still more preferably 1.8 or less, and even more preferably 1.6 or less. Then, the NZ coefficient of a completely uniaxial (uniaxially symmetric) thin film system becomes 1.0, so the lower limit of the NZ coefficient is 1.0. However, since there is a tendency for the mechanical strength in the direction parallel to the alignment direction to significantly decrease as the film approaches a completely uniaxial (uniaxially symmetric) film, care must be taken.

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

In addition, from the viewpoint of further suppressing rainbow-like stains, the value of Ny-Nx of the polyester film-based polyester film of the present invention is preferably at least 0.05, more preferably at least 0.07, still more preferably at least 0.08, and still more preferably at least 0.08. Preferably, it is at least 0.09, most preferably at least 0.1. There is no particular upper limit, but in the case of a polyethylene terephthalate film, the upper limit is preferably about 1.5.

The polyester film of the present invention can be obtained from any polyester resin. The type of polyester resin is not particularly limited, and any polyester resin obtained by condensing a dibasic acid and a diol can be used.

Examples of dibasic acid components that can be used in the production of polyester resins include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl formic acid, diphenoxyethane dicarboxylic acid, diphenyl arginine carboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic 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, trimethyladipic acid, pimelic acid, azelaic acid, Dimer acid, sebacic acid, suberic acid, dodecanedicarboxylic acid, etc.

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-hexanediol, 2, 2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)pyridine, etc.

Both the dibasic acid component and the diol component which comprise a polyester resin can be used 1 type or 2 or more types. As suitable polyester resins constituting the polyester film, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate As diester, etc., more preferable examples include polyethylene terephthalate and polyethylene naphthalate, and these may further contain other copolymerization components. These resins are excellent in transparency, and also excellent in thermal properties and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high modulus of elasticity and it is relatively easy to control the heat shrinkage rate.

When it is necessary to highly increase the heat shrinkage rate of the polyester film, it is desirable to add a copolymerization component to moderately reduce the degree of crystallinity. In addition, since the proportion of elastic strain or permanent strain is high relative to deformation below the glass transition temperature, it is generally difficult to increase the thermal shrinkage rate to a high degree. Therefore, it is also a preferable embodiment to introduce a component with a low glass transition temperature as needed. Specifically, they are propylene glycol, 1,3-propanediol, and the like.

(Provision of Functional Layer) The polarizing plate using the polyester film for polarizer protection of the present invention is ideally integrated with the glass plate of the liquid crystal cell in a state where the thermal shrinkage of the polyester film remains. In the case of functional layers such as easy adhesive layer, hard coat layer, antiglare layer, antireflection layer, low reflection layer, antilow reflection layer, antireflection antiglare layer, low reflection antiglare layer, and antistatic layer, dry It is an ideal embodiment to set the temperature low, or use a 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 integrate the polarizing plate of the present invention and the glass plate of the liquid crystal cell without impairing the improved thermal shrinkage rate, so it is a more preferable embodiment. Easy-to-adhesive layer, hard coat layer, anti-glare layer, anti-reflection layer, low-reflection layer, anti-low-reflection layer, anti-reflection anti-glare layer, low-reflection anti-glare layer, antistatic layer and other functional layers, laminated on polyester film As for the surface opposite to the surface on which the polarizer is laminated, it is preferable that the shrinkage forces F _f and F _v satisfy the aforementioned conditions in the state in which these functional layers are laminated.

(Manufacturing method of aligned polyester film) The polyester film used in this invention can be manufactured according to the manufacturing method of a general polyester film. For example, the method of melting the polyester resin and stretching the non-oriented polyester extruded into a sheet shape in the longitudinal direction at a temperature equal to or higher than the glass transition temperature by using a speed difference of the rolls, and then stretching the non-oriented polyester by a tenter The machine is stretched in the transverse direction and subjected to heat treatment (heat fixing). 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 longitudinal direction, both of which may be slightly stretched in a direction perpendicular to the main stretching direction. In addition, MD is an abbreviation of a machine direction (Machine Direction), and in this specification, it may be called a film flow direction, a longitudinal direction, and a longitudinal direction. In addition, TD is an abbreviation of a transverse direction (Transverse Direction), and in this specification, it may be called a width direction and a transverse direction.

In the polyester film, it is preferable to adjust the film thickness, elastic modulus, and heat shrinkage rate so that the shrinkage force F _f becomes 800 N/m to 9000 N/m.

(Adjustment method of elastic modulus of polyester film) As the modulus of elasticity of the polyester film of the polarizer protective film, under the situation that the MD of the polarizer transmission axis direction system is consistent with the polyester film film, if the present known method of stretching the polyester film is used to adjust the MD The modulus of elasticity is enough. If the direction of the transmission axis of the polarizer is consistent with the TD when the polyester film is formed, it is sufficient to adjust the modulus of elasticity of the TD by a currently known method of stretching the polyester film. Specifically, when the direction is the stretching direction, it is sufficient if the stretching ratio is set high, and when the direction is a direction perpendicular to the stretching direction, if the stretching ratio is set to It's fine if it's low.

(Adjustment method of thermal shrinkage rate of polyester film) The thermal shrinkage rate of the polyester film used as a polarizer protective film, in the case where the transmission axis direction of the polarizer is consistent with the MD of the polyester film when the film is made, if the MD is adjusted by the currently known method of stretching the polyester film If the thermal shrinkage rate of the polarizer is consistent with the TD when the polyester film is made into a film, it is sufficient if the thermal shrinkage rate of the TD is adjusted by the currently known method of stretching the polyester film. .

In the case of adjusting the thermal shrinkage rate of the MD of the polyester film, for example, it can be adjusted by the following method: stretching. In the cooling process after heat setting, the distance between the clips clamping the end of the width direction of the film and the adjacent clips is enlarged to stretch on the MD; Shrink up. In addition, in stretching. When the film is cut or separated from the clamps clamping the ends of the film in the width direction during the cooling process after heat setting, the film can be adjusted by stretching or shrinking the film on the MD by adjusting the pulling force of the film. . In addition, in the offline (off-line) step 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 it is also possible to adjust the pulling force of the film. Adjust it by making it stretch or shrink on the MD.

In the case of adjusting the thermal shrinkage rate of TD of the polyester film, for example, it can be adjusted by the following method: stretching. In the cooling process after heat setting, the gap between the clamps clamping the end of the width direction of the film and the clamps located on the opposite side in the width direction is enlarged, and stretched in TD; or it is stretched in TD by shrinking shrink.

The shrinkage force F _v is preferably adjusted so that the ratio of the shrinkage force (F _f /F _v ) is 1.0 to 12.0, more preferably 2.5 to 12.0, and the elastic modulus and thermal conductivity of the polyester film are adjusted. Shrinkage.

(How to adjust the inclination of the shrinkage axis of the polyester film) The inclination of the main axis of shrinkage of the polyester film used as a polarizer protective film can be stretched using a tenter in the manner disclosed in PCT/JP2014/073451 (WO2015/037527). Adjustment is made during the cooling process after heat treatment, or in an off-line step after film formation. Specifically, the shrinkage accompanying stretching that was not completely removed in the heat-fixing step, and the thermal stress accompanying cooling occurred in the cooling step, and are generated toward the upstream side due to the balance of both in the flow direction of the film. Pulling or pulling toward the downstream side produces the phenomenon that the contraction axis is inclined. In order to reduce the inclination of the main axis of shrinkage, it is necessary to adjust so that the shrinkage force in the flow direction of the film in the cooling step (the sum of the shrinkage force accompanying stretching and the shrinkage force accompanying cooling) becomes uniform. In order to achieve uniformity, it is desirable to shrink it in the film flow direction in a temperature region where the shrinkage force is high in the film flow direction, or to shrink it in the film flow direction in a temperature region where the shrinkage force is low in the film flow direction. stretch. As a method of shrinking or stretching, conventionally known methods may be used. In addition, in the case of cutting or separating the end of the film, cutting. Below the separated temperature range, it is free to shrink in the width direction, and the heat shrinkage ratio below this temperature range becomes small, so care is required.

The polarizing plate is coated with the polarizer protective polyester film of the present invention on at least one surface of the polarizer. It is preferable to layer a non-birefringent film such as a TAC film, an acrylic film, or a norbornene film on the other surface of the polarizer. Or, from the viewpoint of thinness, a polarizing plate without any thin film on the other side of the polarizer is also a preferable aspect. In this case, although a thin film is not layered on the other surface of the polarizer, a coating layer can be laminated on the polarizer. The coating layer may be a functional layer such as a hard coat layer, or a retardation film formed by coating. In addition, in the case of laminating a film or coating layer other than the polyester film for polarizer protection of the present invention on a polarizer, the 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 films other than the polyester film for polarizer protection or the coating layer in a direction parallel to the absorption axis of the polarizer are preferably F _f of the polyester film for polarizer protection. Below the value of , more preferably below the value of F _V of the polyester film for polarizer protection. In addition, the shrinkage force of the film or coating layer other than the polyester film for polarizer protection in the direction parallel to the transmission axis of the polarizer, and the polyester film for polarizer protection in the direction parallel to the absorption axis of the polarizer The shrinkage force of the film or coating layer is preferably below 250N/m, more preferably below 200N/m. The shrinkage force of a film other than a polyester film for polarizer protection or a coating layer can be measured similarly to the case of a polyester film. That is, the thickness of the film or coating layer (mm) × modulus of elasticity (N/mm ² ) × 80 ℃. Heat shrinkage rate (%) ÷ 100×1000 after 30 minutes treatment.

In the industry, the polarizer is rolled to roll (roll-to-roll), through the strips of adhesive laminated polarizers and the strips of polyester film for polarizer protection. Polarizers are then usually fabricated by stretching in the machine direction, thus having an absorption axis in MD and a transmission axis in TD.

Therefore, the polyester film for polarizer protection of the present invention is preferably the following (1) and (2) from the viewpoint of industrial production of polarizing plates. (1) The shrinkage force F _TD of 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 polyester film × modulus of elasticity (N/mm ² ) × 80 ℃. Heat shrinkage rate (%) ÷ 100×1000 after 30 minutes treatment. Here, the modulus of elasticity and the thermal contraction rate are the modulus of elasticity in TD and the rate of thermal contraction in TD of the polyester film, respectively. (2) The ratio (F _TD /F _MD ) of the shrinkage force F _TD in TD of the polyester film to the shrinkage force F _MD in MD of the polyester film is preferably from 2.5 to 12.0. Among them, the shrinkage force F _MD (N/m) is the thickness (mm) of polyester film × modulus of elasticity (N/mm ² ) × 80 ℃. Heat shrinkage rate (%) ÷ 100×1000 after 30 minutes treatment. Here, the modulus of elasticity and the rate of thermal shrinkage are the modulus of elasticity in MD of the polyester film and the rate of thermal contraction in MD, respectively.

In addition, in the polyester film for polarizer protection of the present invention, it is preferable that the direction in which the thermal shrinkage rate of the polyester film becomes the largest is substantially parallel to the TD system. Substantially parallel means that the absolute value of the angle between the direction in which the thermal shrinkage rate of the polyester film is allowed to be the largest and the TD direction (inclination of thermal shrinkage rate) is 15 degrees or less. The inclination of the thermal shrinkage rate is preferably less than 12 degrees, more preferably less than 10 degrees, more preferably less than 8 degrees, more preferably less than 6 degrees, most preferably less than 4 degrees, and most preferably less than 2 degrees. . The smaller the inclination of the thermal contraction rate, the better, so the lower limit is 0 degrees. 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 (F _TD /F _MD ) is 2.5 or more and 12.0 or less, even if the thermal shrinkage rate of the polyester film The absolute value of the included angle between the direction that becomes the largest and TD is 40 degrees or less, and warpage of the liquid crystal panel can also be reduced. The aforementioned angle is preferably 35 degrees or less.

Also, considering the industrial production of polarizing plates by roll-to-roll, etc. as described above, _FTD is equivalent to _Ff , so the preferred range of _FTD is the same as the preferred range of _Ff . 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 TD of the polyester film" is equivalent to the "elastic modulus of the polyester film in the direction of the transmission axis of the polarizer", and therefore the preferred ranges of both are the same. "TD heat shrinkage rate of polyester film at 80°C for 30 minutes heat treatment" is equivalent to "thermal shrinkage rate of polyester film at 80°C for 30 minutes heat treatment in the direction of the transmission axis of the polarizer", therefore The preferred ranges for both are the same.

A liquid crystal display device includes at least a backlight and a liquid crystal cell arranged between two polarizing plates. At least one of the aforementioned two polarizers is preferably a polarizer using the polarizer protective polyester film of the present invention as a polarizer protective film. A liquid crystal display device may use the polarizing plate of the present invention for both of the aforementioned two polarizing plates.

The polyester film for polarizer protection of the present invention is preferably used for the polarizer protective film on the viewing side starting from the polarizer of the polarizing plate on the viewing side and/or used on the light source side starting from the polarizer of the polarizing plate on the light source side position of the polarizer protective film.

Usually, the liquid crystal display device is made into a rectangular shape (the two polarizers used in the liquid crystal display device are also rectangular), one of the polarizers has its long side parallel to the absorption axis, and the other polarizer has its long side Parallel to the transmission axis, they are arranged such that the absorption axes are perpendicular to each other. Therefore, generally, a polarizing plate whose long side is parallel to the absorption axis is used as a viewing side polarizing plate of a liquid crystal display device, and a polarizing plate whose long side is parallel to the transmission axis is used as a liquid crystal display. The light source side polarizing plate of the 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 sides of the polarizing plate are in a parallel relationship to the transmission axis. In addition, it is also preferable to use the polarizing plate of the present invention for both the polarizing plate whose long side is parallel to the transmission axis and the polarizing plate whose long side is parallel to the absorption axis. [Example]

Hereinafter, the present invention will be described in more detail with reference to the examples, but the present invention is not limited by the following examples, and can also be implemented with appropriate changes within the scope that can meet the gist of the present invention, and those implementation modes are also included in within the technical scope of the present invention.

(1) Shrinkage force F _f The shrinkage force F _f of the polyester film is calculated by the following formula. In addition, the thickness, elastic modulus, and thermal contraction rate of a polyester film are measured values demonstrated below. The modulus of elasticity is the modulus of elasticity of the polyester film in the direction parallel to the transmission axis of the polarizer. The heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the transmission axis of the polarizer. Shrink force F _f (N/m) = thickness of polyester film (mm) × modulus of elasticity (N/mm ² ) × 80°C. Heat shrinkage rate after 30 minutes treatment (%)÷100×1000

(2) Shrink force F _V The shrink force F _V of the polyester film is calculated by the following formula. In addition, the thickness, elastic modulus, and thermal contraction rate of a polyester film are measured values demonstrated below. The modulus of elasticity is the modulus of elasticity of the polyester film in the direction parallel to the absorption axis of the polarizer. The heat shrinkage rate is the heat shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer. Shrink force F _V (N/m) = thickness of polyester film (mm) × modulus of elasticity (N/mm ² ) × 80 ℃. Heat shrinkage rate after 30 minutes treatment (%)÷100×1000

(3) Film thickness The thickness (nm) of the polyester film was measured using an electric micrometer (manufactured by Feinpruf, Millitron 1245D) after standing still for 168 hours in an environment of 25° C. and 50 RH%, and the unit was converted into nm.

(4) Elastic modulus of polyester film The elastic modulus of the polyester film was evaluated using a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments in accordance with JIS-K7244 (DMS) after standing still for 168 hours in an environment of 25° C. and 50 RH%. Under the conditions of tensile mode, drive frequency of 1Hz, distance between chucks of 5mm, and heating rate of 2°C/min, the temperature dependence of 25°C to 120°C was measured, and the storage temperature of 30°C to 100°C was measured. The average of the elastic modulus was used as the elastic modulus. In this way, for the polyester film, the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer and the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer were measured. In addition, the above measurement was performed using a polyester film alone (polyester film for polarizer protection alone).

(5) Thermal shrinkage rate of polyester film and gradient of thermal shrinkage rate After the polyester film was left to stand for 168 hours in an environment of 25° C. and 50 RH%, a circle with a diameter of 80 mm was drawn, and the diameter of the circle was measured every 1° using an image size measuring device (ImageMeasure IM6500 manufactured by KEYENCE Co., Ltd.). Length before processing. Heat treatment was performed for 30 minutes in a Gear oven set at 80°C, and then evaluated every 1° by the same method as before treatment after cooling for 10 minutes in an environment set at room temperature 25°C , as the processed length. In addition, the above-mentioned treatment was carried out using a polyester film monomer (a polyester film monomer for polarizer protection).

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

In the above, 360° evaluation was performed every 1°, the direction in which the thermal shrinkage rate became the largest was determined, and the absolute value of the angle between this direction and the transmission axis direction of the polarizer was taken as the inclination of the thermal shrinkage rate. In addition, the inclination of the heat shrinkage rate is defined as a narrow angle (narrow angle) away from the transmission axis direction of the polarizer, and is in the range of 0 to 90°.

(6) Warpage of LCD panel Using a Keel oven set at 80 ° C, will be in each example. The liquid crystal panel produced in the comparative example was heat-treated for 30 minutes, and then cooled for 30 minutes in an environment set at room temperature 25° C. 50% RH, and placed on a horizontal surface with the convex side facing down to measure The heights of four corners were measured, and the maximum value was taken as the amount of warping. The warpage amount was evaluated in the following manner. ○: 0mm or more, less than 2.0mm △: 2.0mm or more and 3.0mm or less ×: more than 3.0mm

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

Retardation refers to the parameter defined as the product (ΔNxy×d) of the anisotropy of the refractive index (ΔNxy=|Nx-Ny|) of the orthogonal biaxial on the film and the film thickness d (nm), which represents the optical Isotropic and anisotropic scales. The biaxial refractive index anisotropy (ΔNxy) was obtained by the following method. The direction of the slow axis of the film was determined using a molecular alignment meter (Molecular Orientation Meter MOA-6004, manufactured by Oji Scientific Instruments Co., Ltd.), and a rectangle of 4 cm x 2 cm was cut out so that the direction of the slow axis became parallel to the long side of the sample for measurement. , as a sample for measurement. For this sample, using an Abbe refractometer (manufactured by Atago Corporation, NAR-4T, measurement wavelength 589nm), the refractive index of the orthogonal biaxial (refractive index in the slow axis direction: Ny, Ny, perpendicular to the slow axis direction) was obtained. The refractive index in the direction: Nx) and the refractive index in the thickness direction (Nz), let the absolute value (|Nx-Ny|) of the above-mentioned biaxial refractive index difference be the anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Feinpruf, Millitron 1245D), and the unit was converted into nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(8) Thickness direction retardation (Rth) Retardation in the thickness direction refers to the retardation obtained by multiplying the film thickness d by the two birefringence ΔNxz (=|Nx-Nz|), ΔNyz (=|Ny-Nz|) when viewed from the film thickness direction section The average parameter of . Nx, Ny, Nz and film thickness d (nm) were obtained in the same manner as the retardation measurement, and the average value of (ΔNxz×d) and (ΔNyz×d) was calculated to obtain thickness direction retardation (Rth).

(Manufacturing example 1-polyester A) When the temperature reaches 200°C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol are added to the reaction kettle for esterification, and 0.017 parts by mass of antimony trioxide and magnesium acetate tetrahydrate are added as catalysts while stirring. 0.064 parts by mass, 0.16 parts by mass of triethylamine. Next, pressurization and temperature raising were performed, and after pressurized esterification reaction was performed on the conditions of gauge pressure 0.34MPa and 240 degreeC, the esterification reactor was returned to normal pressure, and phosphoric acid 0.014 mass part was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and added 0.012 mass parts of trimethyl phosphates. Next, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and 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 polycondensation reaction is completed, filter with a filter made of Naslon with a 95% cut-off diameter of 5 μm, extrude it into a strand from a nozzle, and use a pre-filtered filter (pore size: 1 μm or less) cooling water to cool, solidify, and cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g, and substantially did not contain inert particles and internal precipitated particles. (Hereafter abbreviated as PET(A).)

-4-酮)10質量份、不含有粒子的PET(A)(固有黏度為0.62dl/g) 90質量份混合，使用混練擠出機，得到含有紫外線吸收劑的聚對苯二甲酸乙二酯樹脂(B)。(以下簡記為PET(B)。)(Production Example 2-Polyester B) The dried UV absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzo

-4-ketone) 10 parts by mass and 90 parts by mass of PET (A) (intrinsic viscosity: 0.62dl/g) not containing particles were mixed, and a polyethylene terephthalate containing an ultraviolet absorber was obtained by using a kneading extruder. Ester resin (B). (Hereafter abbreviated as PET(B).)

(Manufacturing Example 3 - Preparation of Adhesive Modification Coating Solution) Utilize common method to carry out transesterification reaction and polycondensation reaction, prepare as dibasic acid component (relative to dibasic acid component whole) terephthalic acid 46 mol %, isophthalic acid 46 mol % and isophthalic acid- Water-dispersible metal salt containing sulfonic acid containing 8 mol% of sodium 5-sulfonate, 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as diol components based copolyester resin. Next, after mixing 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 a nonionic surfactant, heat and stir, and once the temperature reaches 77°C, add the above-mentioned water-dispersible sulfonate-containing 5 parts by mass of acid metal salt-based copolyester resin, and continued stirring until no resin agglomeration, and then cooling the aqueous resin dispersion to room temperature to obtain a uniform water-dispersible copolyester resin solution with a solid content concentration of 5.0% by mass. Further, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Sylysia 310) in 50 parts by mass of water, 0.54 parts by mass of an aqueous dispersion of Sylysia 310 was added to 99.46 parts by mass of the above-mentioned water-dispersible copolyester resin liquid. 20 parts by mass of water was added while stirring to obtain an adhesive modification coating liquid.

(Example 1) 90 parts by mass of PET (A) resin pellets not containing particles and 10 parts by mass of PET (B) resin pellets containing ultraviolet absorbers as raw materials for the intermediate layer of the base film were dried under reduced pressure at 135° C. (1 Torr) After 6 hours, it was supplied to the extruder 2 (for the middle layer II layer). In addition, the PET (A) was dried by a common method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III layer) at 285° C. Melt down. These two kinds of polymers are respectively filtered with stainless steel sintered filter media (nominal filtration precision 10μm particle 95% cut-off), laminated in two kinds of three-layer confluence blocks, extruded into sheets from the extrusion port, and then electrostatically applied casting method It was wound and solidified on a casting drum with a surface temperature of 30° C. to produce an unstretched film. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of I layer, II layer, and III layer might become 10:80:10.

Next, the above-mentioned adhesion-improving coating liquid was coated on both sides of the unstretched PET film by the reverse roll method so that the coating amount after drying was 0.08 g/m ² , and then dried at 80° C. for 20 seconds.

The unstretched film on which the coating layer was formed was led to a tenter stretching machine, and was led to a hot air zone at a temperature of 105° C. while holding the ends of the film with clips, and stretched 4.0 times in 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, and then the clips clamping both ends of the film cooled to 60°C were placed Pull with a tension of 350N/m, extract a jumbo roll containing a uniaxially aligned PET film with a film thickness of about 80 μm, divide the obtained jumbo roll into 3 equal parts, and obtain 3 slit rolls (L(left), C(center), R(right)). The polyester film 1 for polarizer protection was obtained from the slit roll at R. The direction in which the heat shrinkage rate of the polyester film 1 series for polarizer protection becomes the largest is 7.0 degrees away from TD.

>Production of LCD panel> The polarizer protective polyester film 1 was attached to one side of the polarizer containing PVA, iodine, and boric acid so that the transmission axis of the polarizer was parallel to the TD of the polarizer protective polyester film 1 . In addition, a TAC film (manufactured by Fuji Film Co., Ltd., thickness 80 μm) was attached to the opposite surface of the polarizer to prepare a light source side polarizing plate.

The liquid crystal panel was taken out from a 46-inch IPS type liquid crystal television using a glass substrate with a thickness of 0.4 mm for the liquid crystal cell. Peel off the light source side polarizing plate from the liquid crystal panel, and replace it with the light source side polarizing plate prepared above in such a way that the transmission axis of the polarizer coincides with the transmission axis direction (parallel to the horizontal direction) of the light source side polarizing plate before peeling off. The PSA is attached to the liquid crystal cell to make a liquid crystal panel. Moreover, the light source side polarizing plate was bonded to a liquid crystal cell so that the polyester film 1 for polarizer protection may become the side away from a liquid crystal cell (the side opposite to a liquid crystal cell). In addition, the polarizer on the viewing side is laminated with TAC film on both sides of the polarizer, and is attached to the liquid crystal cell so that the absorption axis direction of the polarizer is parallel to the horizontal direction.

(Example 2) >Manufacture of polyester film 2 for polarizer protection> In the film formation of the polyester film 1 for protecting a polarizer in Example 1, the film cooled to 100° C. was stretched 1.5% in the width direction, and the same operation was performed as the polyester film 1 for protecting a polarizer. And the polyester film 2 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 2-series polyester film for polarizer protection becomes the largest is 6.5 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 2 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 3) >Manufacture of polyester film 3 for polarizer protection> In the film formation of the polyester film 1 for protecting polarizers in Example 1, the film cooled to 100° C. was stretched 1.7% in the width direction, and the same operation as the polyester film 1 for protecting polarizers was carried out. Thus, a polarizer protective film 3 was obtained. The direction in which the thermal shrinkage rate of the 3-series polyester film for polarizer protection becomes the largest is 5.3 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 3 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 4) >Manufacture of polyester film 4 for polarizer protection> Except in the film-making of the polyester film 1 for polarizer protection in Example 1, the film cooled to 100° C. was stretched by 2.0% in the width direction, and after being stretched 4 times in TD, it was stretched at a temperature of 180°C. At a point before the heat treatment at ° C. for 30 seconds, the polarizer protective film 4 was obtained in the same manner as the polarizer protective polyester film 1 except that the hard coat coating solution was coated on one side of the polyester film. The direction in which the thermal shrinkage rate of the 4-series polyester film for polarizer protection becomes the largest is 4.8 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 4 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 5) >Manufacture of polyester film 5 for polarizer protection> The polyester film 5 for polarizer protection was obtained similarly to the polyester film 4 for polarizer protection except having adjusted the rotation speed of the casting roll so that the film thickness after stretching might be 160 micrometers. The direction in which the thermal shrinkage rate of the 5-series polyester film for polarizer protection becomes the largest is 4.8 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 5 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 6) >Manufacture of polyester film 6 for polarizer protection> In the film formation of the polyester film 1 for protecting polarizers in Example 1, the film cooled to 100° C. was stretched by 1.5% in the flow direction, and operated in the same manner as the polyester film 1 for protecting polarizers. And the polyester film 6 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 6-series polyester film for polarizer protection becomes the largest is 9.0 degrees from MD. >Production of LCD panel> Except that in the making of the light source side polarizing plate of embodiment 1, the polyester film 6 for polarizer protection is used instead of the polyester film for polarizer protection, and the transmission axis of the polarizer and the MD of the polyester film 6 for polarizer protection become A liquid crystal panel was produced in the same manner as in Example 1, except that it was attached in parallel to form a light source-side polarizing plate.

(Example 7) >Manufacture of polyester film 7 for polarizer protection> In the film-making of the polyester film 1 for protecting polarizers in Example 1, the film cooled to 100° C. was stretched 1.7% in the flow direction, and operated in the same manner as the polyester film 1 for protecting polarizers. And the polyester film 7 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 7-series polyester film for polarizer protection becomes the largest is 8.3 degrees off MD. >Production of LCD panel> In Example 6, except having replaced the polyester film 6 for polarizer protection with the polyester film 7 for polarizer protection, it carried out similarly to Example 6, and produced the liquid crystal panel.

(Embodiment 8) >Manufacture of polyester film 8 for polarizer protection> In the film formation of the polyester film 1 for protecting polarizers in Example 1, the film cooled to 100° C. was stretched 2.0% in the flow direction, and the same operation was performed as the polyester film 1 for protecting polarizers. And the polyester film 8 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 8-series polyester film for polarizer protection becomes the largest is 7.0 degrees from MD. >Production of LCD panel> In Example 6, except having replaced the polyester film 6 for polarizer protection with the polyester film 8 for polarizer protection, it carried out similarly to Example 6, and produced the liquid crystal panel.

(Example 9) >Manufacture of polyester film 9 for polarizer protection> The polyester film 9 for polarizer protection was obtained similarly to the polyester film 8 for polarizer protection except having adjusted the rotational speed of the casting roll so that the film thickness after stretching might be 160 micrometers. The direction in which the thermal shrinkage rate of the 9-series polyester film for polarizer protection becomes the largest is 7.0 degrees from MD. >Production of LCD panel> In Example 6, except having replaced the polyester film 6 for polarizer protection with the polyester film 9 for polarizer protection, it carried out similarly to Example 6, and produced the liquid crystal panel.

(Example 10) >Manufacture of polyester film 10 for polarizer protection> The polarizer protective film 10 was obtained in the same manner as the polyester film 6 for polarizer protection, except that the stretching in TD was changed to 4.0 times in MD and 1.0 times in TD. The direction in which the thermal shrinkage rate of the 10-series polyester film for polarizer protection becomes the largest is 8.7 degrees from MD. >Production of LCD panel> In Example 6, except having replaced the polyester film 6 for polarizer protection with the polyester film 10 for polarizer protection, it carried out similarly to Example 6, and produced the liquid crystal panel.

(Example 11) >Manufacture of polyester film 11 for polarizer protection> In the film formation of the polyester film 10 for protecting polarizers in Example 10, the film cooled to 100° C. was stretched 1.7% in the flow direction, and the same operation was performed as for the polyester film 10 for protecting polarizers. Thus, the polyester film 11 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 11-series polyester film for polarizer protection becomes the largest is 7.5 degrees away from MD. >Production of LCD panel> In Example 10, except having replaced the polyester film 10 for polarizer protection with the polyester film 11 for polarizer protection, it carried out similarly to Example 10, and produced the liquid crystal panel.

(Example 12) >Manufacture of polyester film 12 for polarizer protection> In the film formation of the polyester film 10 for protecting a polarizer in Example 10, the film cooled to 100° C. was stretched by 5.0% in the width direction, and the same operation as the polyester film 10 for protecting a polarizer was carried out. Thus, the polyester film 12 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 12-series polyester film for polarizer protection becomes the largest is 1.8 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 12 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 13) >Manufacture of polyester film 13 for polarizer protection> The polyester film 13 for polarizer protection was obtained similarly to the polyester film 4 for polarizer protection except having adjusted the rotational speed of the casting roll so that the film thickness after stretching might be 60 micrometers. The direction in which the thermal shrinkage rate of the 13-series polyester film for polarizer protection becomes the largest is 4.8 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 13 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Example 14) >Manufacture of polyester film 14 for polarizer protection> The polarizer protective film 14 was obtained in the same manner as the polarizer protective film 3 except that the film was passed without changing the width of the clips clamping both ends of the film in the cooling step after stretching by 1.7% in the width direction. The direction in which the thermal shrinkage rate of the 14-series polyester film for polarizer protection becomes the largest is 33.0 degrees away from TD. >Production of LCD panel> Except having replaced the polarizer protective film 1 with the polarizer protective film 14, it carried out similarly to Example 3, and produced the liquid crystal panel.

(comparative example 1) >Manufacture of polyester film 15 for polarizer protection> In addition to setting the thickness of the stretched film to 200 μm by adjusting the rotation speed of the casting roll, in stretching. In the cooling step after heat setting, the film was passed outside without changing the width of the clips clamping both ends of the film, and the polarizer protective film 15 was obtained in the same manner as the polarizer protective film 1 . The direction in which the thermal shrinkage rate of the 15-series polyester film for polarizer protection becomes the largest is 20.0 degrees away from MD. >Production of LCD panel> Except that the polarizer protective film 1 is replaced by the polarizer protective film 15, and the transmission axis of the polarizer and the MD of the polarizer protective film are bonded together to form a light source side polarizing plate, the same operation as in Example 1 is carried out. Make a liquid crystal panel.

(comparative example 2) >Manufacture of polyester film 16 for polarizer protection> Except stretching. In the cooling step after heat setting, the polarizer is protected in the same way as the polarizer protection film 1, except that the clamps clamping both ends of the film are released at 95°C without stretching 1.0% in the width direction. film16. The direction in which the thermal shrinkage rate of the 16-series polyester film for polarizer protection becomes the largest is 1.0 degrees away from MD. >Production of LCD panel> Except that the polarizer protective film 1 is replaced by the polarizer protective film 16, and the transmission axis of the polarizer and the MD of the polarizer protective film are bonded together to form a light source side polarizing plate, the same operation as in Example 1 is carried out. Make a liquid crystal panel.

(comparative example 3) >Manufacture of polyester film 17 for polarizer protection> The polyester film 17 for polarizer protection was obtained similarly to the polyester film 1 for polarizer protection except having adjusted the rotation speed of the casting roll so that the film thickness after stretching was 50 micrometers. The direction in which the thermal shrinkage rate of the 17-series polyester film for polarizer protection becomes the largest is 7.0 degrees away from TD. >Production of LCD panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 17 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(comparative example 4) >Manufacture of polyester film 18 for polarizer protection> The polyester film 18 for polarizer protection was obtained similarly to the polyester film 11 for polarizer protection except having adjusted the rotation speed of the casting roll so that the film thickness after stretching might be 160 micrometers. The direction in which the thermal shrinkage rate of the 18-series polyester film for polarizer protection becomes the largest is 6.5 degrees away from MD. >Production of LCD panel> In Example 11, except having replaced the polyester film 11 for polarizer protection with the polyester film 18 for polarizer protection, it carried out similarly to Example 11, and produced the liquid crystal panel.

(comparative example 5) >Manufacture of polyester film 19 for polarizer protection> In addition to adjusting the rotation speed of the casting roll to set the thickness of the stretched film to 160 μm, in the film formation of the polarizer protective polyester film 1 in Example 1, the film cooled to 100° C. Except stretching 1.0% in the direction, the polyester film 19 for polarizer protection was obtained similarly to the polyester film 1 for polarizer protection. The direction in which the thermal shrinkage rate of the 19-series polyester film for polarizer protection becomes the largest is 11.0 degrees away from MD. >Production of LCD panel> Except that in the making of the light source side polarizing plate of embodiment 1, the polyester film 19 for polarizer protection is used to replace the polyester film for polarizer protection, and the transmission axis of the polarizer and the TD of the polyester film 19 for polarizer protection become A liquid crystal panel was produced in the same manner as in Example 1, except that they were laminated in parallel to form a light source-side polarizing plate.

(comparative example 6) >Manufacture of polyester film 20 for polarizer protection> The polyester film 20 for polarizer protection was obtained similarly to the polyester film 19 for polarizer protection except having adjusted the rotation speed of the casting roll so that the film thickness after stretching was 80 micrometers. The direction in which the thermal shrinkage rate of the 20-series polyester film for polarizer protection becomes the largest is 11.0 degrees from MD. >Production of LCD panel> In comparative example 5, except having replaced the polyester film 19 for polarizer protection with the polyester film 20 for polarizer protection, it carried out similarly to the comparative example 5, and produced the liquid crystal panel.

(comparative example 7) >Manufacture of polyester film 21 for polarizer protection> The polarizer protective film 21 was obtained in the same manner as the polarizer protective film 20 . The direction in which the thermal shrinkage rate of the 20-series polyester film for polarizer protection becomes the largest is 11.0 degrees from MD. >Production of LCD panel> Except that in the making of the light source side polarizing plate of embodiment 1, the polyester film 21 for polarizer protection is used instead of the polyester film 1 for polarizer protection, and the MD of the polyester film 21 for polarizer protection is determined by the transmission axis of the polarizer. A liquid crystal panel was produced in the same manner as in Example 1, except that the polarizing plate on the light source side was produced by bonding them in parallel.

(comparative example 8) >Production of LCD panel> A liquid crystal panel was produced 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 was parallel to the TD of the polarizer protective film to produce a light source side polarizing plate.

(comparative example 9) >Manufacture of polyester film 22 for polarizer protection> In addition to adjusting the rotation speed of the casting roll to set the thickness of the stretched film to 160 μm, in the film formation of the polarizer protective polyester film 1 in Example 1, the film cooled to 100° C. Except stretching 1.0% in the direction, the polyester film 22 for polarizer protection was obtained similarly to the polyester film 1 for polarizer protection. The direction in which the thermal shrinkage rate of the 22-series polyester film for polarizer protection becomes the largest is 11.0 degrees from MD. >Production of LCD panel> Except that in the making of the light source side polarizing plate of embodiment 1, the polyester film 22 for polarizer protection is used instead of the polyester film 1 for polarizer protection. A liquid crystal panel was produced in the same manner as in Example 1, except that the polarizing plate on the light source side was produced by bonding them in parallel.

(comparative example 10) >Manufacture of polyester film 23 for polarizer protection> In the film formation of the polyester film 10 for protecting polarizers in Example 10, the film cooled to 100° C. was stretched by 2.0% in the flow direction, and the same operation was performed as for the polyester film 10 for protecting polarizers. Thus, a polyester film 23 for polarizer protection was obtained. The direction in which the thermal shrinkage rate of the 23-series polyester film for polarizer protection becomes the largest is 4.5 degrees away from MD. >Production of LCD panel> In Example 10, except having replaced the polyester film 10 for polarizer protection with the polyester film 23 for polarizer protection, it carried out similarly to Example 10, and produced the liquid crystal panel.

[Table 1] Polyester film for polarizer protection Evaluation results Thickness (μm) Re (nm) Elastic modulus of polyester film in the direction of the transmission axis of the polarizer (N/mm ² ) Thermal shrinkage rate of polyester film in the direction of transmission axis of polarizer (%) F _f (N/m) Elastic modulus of the polyester film in the direction of the absorption axis of the polarizer (N/mm ² ) Thermal shrinkage rate of polyester film in the direction of absorption axis of polarizer (%) F _v (N/m) Contraction force ratio (F _f /F _v ) Gradient of heat shrinkage () Warpage of the LCD panel Example 1 80 8120 6000 0.17 816 2000 0.16 256 3.2 7.0 ○ Example 2 80 8120 6000 0.29 1392 2000 0.14 224 6.2 6.5 ○ Example 3 80 8120 6000 0.34 1632 2000 0.14 224 7.3 5.3 ○ Example 4 80 8120 6000 0.43 2064 2000 0.13 208 9.9 4.8 ○ Example 5 160 16240 6000 0.43 4128 2000 0.13 416 9.9 4.8 ○ Example 6 80 8120 2000 0.60 960 6000 0.08 384 2.5 9.0 ○ Example 7 80 8120 2000 0.90 1440 6000 0.07 336 4.3 8.3 ○ Example 8 80 8120 2000 1.30 2080 6000 0.06 288 7.2 7.0 ○ Example 9 160 16240 2000 1.30 4160 6000 0.06 576 7.2 7.0 ○ Example 10 80 8120 6000 0.60 2880 2000 0.33 528 5.5 8.7 ○ Example 11 80 8120 6000 1.00 4800 2000 0.27 432 11.1 7.5 ○ Example 12 80 8120 2000 1.40 2240 6000 0.18 864 2.6 1.8 ○ Example 13 60 6090 6000 0.43 1548 2000 0.13 156 9.9 4.8 ○ Example 14 80 8120 6000 0.34 1632 2000 0.14 224 7.3 33.0 ○ Comparative example 1 200 20300 2000 0.21 840 6000 0.04 480 1.8 20.0 x Comparative example 2 80 8120 2000 0.14 224 6000 0.01 48 4.7 1.0 x Comparative example 3 50 5075 6000 0.17 510 2000 0.16 160 3.2 7.0 x Comparative example 4 160 16240 6000 1.00 9600 2000 0.27 864 11.1 6.5 x Comparative Example 5 160 16240 6000 0.11 1056 2000 0.30 960 1.1 79.0 x Comparative Example 6 80 8120 6000 0.11 528 2000 0.30 480 1.1 79.0 x Comparative Example 7 80 8120 2000 0.30 480 6000 0.11 528 0.9 11.0 x Comparative Example 8 200 20300 6000 0.04 480 2000 0.21 840 0.6 70.0 x Comparative Example 9 160 16240 2000 0.30 960 6000 0.11 1056 0.9 11.0 △ Comparative Example 10 80 8120 6000 1.80 8640 2000 0.17 272 31.8 4.5 △

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 warping of the panel compared with the polarizing plate of the comparative example.

(Example 1A to Example 5A, Example 13A) In addition, except that polarizing plates having the same configuration as the light source-side polarizing plates used in Examples 1 to 5, and 13 were used as the light source-side polarizing plate and viewing-side polarizing plate for both sides of the polarizing plate, and Examples 1 to 5 and 13 were performed in the same manner and evaluated separately, similarly to the results of Examples 1 to 5 and 13 in Table 1 above, good results were obtained in the warpage evaluation of the panel (○ ). Also, the light source side polarizer and the viewing side polarizer were attached to the liquid crystal cell so that the polyester film for polarizer protection was on the side away from the liquid crystal cell (the side opposite to the liquid crystal cell).

(Example 1B to Example 5B, Example 13B) Also, except that in Example 1A to Example 5A and Example 13A, the TAC film was not used as the polarizer protective film on the side of the liquid crystal cell, the same operations were performed as in Example 1A to Example 5A and Example 13A, and additionally Also in the case of evaluation, in the same manner as in Example 1A to Example 5A and Example 13A, favorable results (◯) were obtained in the evaluation of the curvature 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 warping of a liquid crystal panel.

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Claims (11)

A kind of polarizing plate, it is the polarizing plate that laminates on one side of the polarizer and satisfies the following requirements (1) and (2) The polarizer protective polyester film of the polarizer: (1) on the direction parallel to the transmission axis of the polarizer The shrinkage force F _f of the polyester film is more than 800N/m and less than 9000N/m (wherein, the shrinkage force _Ff (N/m) is the thickness (mm) of the polyester film × modulus of elasticity (N/mm ² ) × 80°C. Thermal shrinkage rate (%) ÷ 100×1000 after 30 minutes of treatment. Here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the transmission axis of the polarizer, and the thermal shrinkage rate is related to the polarizer. _The thermal shrinkage rate of the polyester film on the direction parallel to the transmission axis of the polarizer); The ratio (F _f /F _v ) of the shrinkage force F _v of the polyester film in the direction is 2.5 to 12.0 (wherein, the shrinkage force F _v (N/m) is the thickness (mm) of the polyester film × elastic modulus Number (N/mm ² )×80℃．The thermal shrinkage rate after 30 minutes treatment (%)÷100×1000, here, the elastic modulus is the elastic modulus of the polyester film in the direction parallel to the absorption axis of the polarizer The thermal shrinkage rate is the thermal shrinkage rate of the polyester film in the direction parallel to the absorption axis of the polarizer). The polarizing plate according to claim 1, wherein the polyester film further satisfies the following requirement (3): (3) The direction in which the heat shrinkage rate of the polyester film becomes the largest is substantially parallel to the direction parallel to the transmission axis of the polarizer. The polarizing plate according to claim 1, wherein the polyester film has a retardation of 3000-30000 nm. The polarizing plate according to claim 1, wherein the thickness of the polyester film is 40-200 μm. The polarizing plate according to claim 1, wherein the polyester film has a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, or an antireflection and antiglare layer on the side opposite to the laminated polarizer. . The polarizing plate according to any one of claims 1 to 5, which is laminated with a TAC film, an acrylic film, or a norbornene film on the other side of the polarizer. The polarizing plate according to any one of claims 1 to 5, which does not have a film on the other side of the polarizer. The polarizing plate according to any one of claims 1 to 5, wherein a coating layer is laminated on the other side of the polarizer. The polarizing plate according to claim 8, wherein the coating layer is a hard coat layer or a retardation film. The polarizing plate according to any one of claims 1 to 5, wherein the polarizing plate is in the shape of a rectangle, and the long side of the polarizing plate is parallel to its transmission axis. A liquid crystal display device, which is a liquid crystal display device with a backlight source and a liquid crystal cell arranged between two polarizers, at least one of which is polarized according to any one of claims 1 to 10 plate.