TW202200685A - Polyester film for protecting polarizer, polarizer, and liquid crystal display device - Google Patents

Abstract

The present invention addresses the problem of providing a polyester film for protecting a polarizer that can suppress warpage of a liquid crystal panel, and also to provide a polarizer and a liquid crystal display device. The problem can be solved by a polyester film for protecting a polarizer that satisfies the following requirements (1) and (2). (1) A TD shrinkage stress F of the polyester film is 8-25 MPa (inclusive). (2) The ratio (F/HS) of the TD shrinkage stress F of the polyester film to a TD heat shrinkage rate HS caused by treatment of the polyester film at 80 DEG C for 30 minutes is 30-60 (MPa/%) (inclusive).

Description

Polyester film for polarizer protection, polarizing plate and liquid crystal display device

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

The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and liquid crystal displays for personal computers. Usually, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched by a glass substrate, and two polarizing plates provided on both sides of the liquid crystal cell; and each polarizing plate uses two polarizing plates. Optical films (eg, polarizer protective film and retardation film) sandwich the polarizer (also called polarizer film).

In recent years, it has been confirmed that liquid crystal panels are warped and display unevenness due to an increase in size and thickness of a liquid crystal television screen. For example, the rigidity varies depending on the thickness of the glass substrate used for the liquid crystal panel, and the liquid crystal panel may warp and display unevenness due to the influence of minute shrinkage of the polarizer. In particular, when the thickness of the glass substrate is made thinner than 0.7 mm due to further thinning of the liquid crystal panel, the occurrence of display unevenness is likely to be a problem, and improvement thereof has been sought.

Patent Document 1 proposes a method of improving the warpage and display unevenness of a liquid crystal panel by setting the shrinkage force of the polarizer protective polyester film laminated on one side of the polarizer to a specific range. [Prior Art Literature] [Patent Literature]

Patent Document 1: WO2019/054406

[Summary of Invention] [The problem to be solved by the invention]

The present inventors discovered that the shrinkage stress of the polyester film for polarizer protection must be increased in order to suppress the warpage of the liquid crystal panel with the increase in size of the liquid crystal panel and the thinning of the glass substrate of the liquid crystal cell. In order to increase the shrinkage stress of the polyester film for polarizer protection, an effective countermeasure is to increase the thermal shrinkage rate by processing at 80°C/30 minutes. When the liquid crystal panel of the polyester film for mirror protection is placed in a high temperature environment for a long time, especially when the liquid crystal panel is large, the liquid crystal panel may warp.

The present invention was made in view of the above-mentioned problems and circumstances, and its main subject is to provide a polarizer-protecting polyester film, a polarizing plate, and a liquid crystal display device capable of suppressing warpage of a liquid crystal panel. In particular, the subject is to provide a polarizer-protecting polyester film, a polarizing plate, and a liquid crystal display device capable of suppressing warpage of the liquid crystal panel even when the liquid crystal panel is left in a high-temperature environment for a long time. [means to solve the problem]

Representative inventions are as follows. Item 1. A polarizer protective polyester film that satisfies the following requirements (1) and (2): (1) The shrinkage stress F of the TD of the aforementioned polyester film is not less than 8 MPa and not more than 25 MPa; (2) The ratio (F/HS) of the shrinkage stress F of the TD of the polyester film to the thermal shrinkage HS of the TD of the polyester film by the treatment at 80°C/30 minutes (F/HS) is 30 (MPa/%) or more 60 (MPa/%) or less. Item 2. The polarizer protective polyester film according to Item 1, which further satisfies the requirements of the following (3): (3) The in-plane retardation (retardation) of the said polyester film is 3000-30000 nm. Item 3. The polarizer protective polyester film according to Item 1 or 2, which further satisfies the requirements of the following (4): (4) The thickness of the said polyester film is 40-200 micrometers. Item 4. The polyester film for protecting polarizers according to any one of Items 1 to 3, wherein the polyester film has a hard coat layer, an anti-resistant coating on the surface opposite to the surface of the polyester film and the surface of the laminated polarizer. Reflective layer, low-reflection layer, anti-glare layer, or anti-reflection and anti-glare layer. Item 5. A polarizing plate comprising the polarizer protective polyester film according to any one of Items 1 to 4 laminated on one surface of a polarizer. Item 6. A polarizing plate, wherein the polarizer protective polyester film according to any one of Items 1 to 4 is laminated on one side of the polarizer, and no film is laminated on the other side of the polarizer. Item 7. A polarizing plate comprising the polarizer protective polyester film according to any one of Items 1 to 4 laminated on one side of the polarizer, and a coating layer laminated on the other side of the polarizer. Item 8. The polarizing plate according to Item 7, wherein the coating layer is a hard coat layer or a retardation film. Item 9. A liquid crystal display device comprising the polarizing plate according to any one of Items 5 to 8. [Effect of invention]

According to the present invention, it is possible to provide a polarizer protective film, a polarizer, and a liquid crystal display device capable of suppressing warpage of a liquid crystal panel. In particular, even when a liquid crystal panel is left in a high temperature environment for a long time, it is possible to provide a polarizer protective polyester film, a polarizer, and a liquid crystal display device capable of suppressing warpage of the liquid crystal panel.

[Form for carrying out the invention]

The polyester film for polarizer protection of the present invention is composed of a polyester film, preferably a polarizer used to be laminated on at least one side of a polarizer (for example, a film composed of polyvinyl alcohol and a pigment) to produce a polarizing plate mirror protective film.

In the polyester film for protecting polarizers of the present invention, the value of shrinkage stress F of the TD of the polyester film is preferably 8 MPa or more and 25 MPa or less. When the lower limit of the shrinkage stress F is made 8 MPa or more, the warpage of the liquid crystal panel can be sufficiently reduced. In addition, if the upper limit of the shrinkage stress F is made 25 MPa or less, the liquid crystal panel can also be prevented from being warped in the opposite direction. Therefore, the shrinkage stress F is preferably within the aforementioned range. The lower limit of the shrinkage stress F is more preferably 10 MPa or more, and still more preferably 12 MPa or more. The upper limit of the shrinkage stress F is more preferably 23 MPa or less, and still more preferably 20 MPa or less. The range of the shrinkage stress F is more preferably 10 MPa or more and 23 MPa or less, and still more preferably 12 MPa or more and 20 MPa or less.

The shrinkage stress Fv in the MD of the polyester film is generally in the case of microstretching, which will be described later, during film formation, and stress also occurs in the MD due to Poisson shrinkage, but it is preferably approximately 1.8 to 2.2 Shrinkage stress around MPa. The shrinkage stress Fv of the MD of the polyester film can be arbitrarily controlled by the tension of the MD.

The shrinkage stress F in TD and the shrinkage stress Fv in MD are measured by TMA (thermomechanical analysis) as detailed in the examples. In addition, TD is an abbreviation for Transverse Direction, and in this specification, it may be referred to as a width direction or a lateral direction. MD is an abbreviation of Machine Direction, and in this specification, it may be referred to as a film flow direction, a longitudinal direction, or a longitudinal direction.

In the polyester film for protecting polarizers of the present invention, from the viewpoint of further reducing the warpage of the liquid crystal panel or suppressing the curling (propeller curling) accompanying twisting, the shrinkage stress F of the TD of the polyester film is the same as The ratio (F/Fv) of the shrinkage stress Fv in the MD of the polyester film is preferably 1.5 or more and 15 or less. The range of the ratio (F/Fv) is more preferably 1.5 or more and 12 or less, more preferably 1.5 or more and 10 or less, and still more preferably 1.5 or more and 8 or less.

The polyester film for protecting polarizers of the present invention is preferably the shrinkage stress F (MPa) of the TD of the polyester film, and the thermal shrinkage HS (%) of the TD caused by the polyester film passing through the treatment at 80° C. for 30 minutes. ) ratio (F/HS) is 30 (MPa/%) or more and 60 (MPa/%) or less. By setting the ratio (F/HS) in the aforementioned range, it becomes possible to suppress the warpage of the liquid crystal panel even when the liquid crystal panel is left in a high temperature environment for a long time. The ratio (F/HS) is more preferably 35 (MPa/%) or more and 55 (MPa/%) or less. In addition, when the upper limit of the ratio (F/HS) is 60 (MPa/%) or less, the film formation stability is improved, and a more stable operation can be performed.

The polyester film for protecting polarizers of the present invention preferably has a thermal shrinkage rate of 0.1-5% in TD caused by the treatment of the polyester film at 80° C. for 30 minutes. The lower limit of the thermal shrinkage rate in TD is preferably 0.1% or more, more preferably 0.15% or more, and most preferably 0.2% or more. The upper limit of the thermal shrinkage rate of TD is preferably 5% or less, 4.5% or less, 4% or less, 3% or less, or 2% or less, more preferably 1.5% or less, still more preferably 1% or less, particularly preferred 0.7% or less, preferably 0.5% or less. When the thermal shrinkage rate of TD is 0.1% or more, it becomes easy to control the thermal shrinkage rate without unevenness. In addition, if the thermal shrinkage rate of TD is 5% or less, the polarizer protective film will not be thermally shrunk in one direction due to the heat of the backlight, and the liquid crystal panel will not be warped.

The thermal contraction rate of TD can be measured by the method used in the Example mentioned later.

Generally, a liquid crystal display device is arranged such that two polarizers are in a crossed Nicol relationship. When two polarizers are arranged using the crossed Nicols relationship, normally, light does not pass through the two polarizers. However, due to the shrinkage or warpage of the polarizer described above, the relationship of the complete crossed Nicols collapses as a result, and there is a possibility of light leakage. From the viewpoint of suppressing light leakage, it is preferable that the angle formed with the transmission axis of the polarizer is small in the direction in which the thermal shrinkage rate of the polarizer protective film becomes the largest.

It is preferable that the thickness of the polyester film for polarizer protection of this invention is 40-200 micrometers. More preferably, it is 40-100 micrometers, More preferably, it is 40-80 micrometers. When the thickness is 40 μm or more, cracks are unlikely to occur, and flatness failure due to insufficient rigidity is also unlikely to occur. In addition, when the thickness is 200 μm or less, the variation of the shrinkage stress in the TD of the film is small, and the cost required to control the shrinkage stress can also be suppressed. The thickness can be measured by the method employed in the examples described later.

The polyester film for protecting a polarizer of the present invention preferably has an in-plane retardation within a specific range from the viewpoint of suppressing rainbow unevenness observed on the screen of a liquid crystal display device. The lower limit of the in-plane hysteresis is preferably 3000 nm or more, 4000 nm or more, 5000 nm or more, 6000 nm or more, 7000 nm or more, or 8000 nm or more. The upper limit of the in-plane hysteresis is preferably 30000 nm or less, more preferably 18000 nm or less, still more preferably 15000 nm or less, and still more preferably 10000 nm or less. In particular, from the viewpoint of thinning, the in-plane retardation is preferably less than 10,000 nm or less than 9,000 nm.

The hysteresis of the polyester film can also 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 apparatus such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). In addition, the refractive index can be obtained by an Abbe's refractomer (measurement wavelength: 589 nm).

The ratio (Re/Rth) of the in-plane retardation (Re) to the thickness direction retardation (Rth) of the polyester film for protecting polarizers of the present invention is preferably 0.2 or more, 0.3 or more, or 0.4 or more, more preferably 0.5 or more , more preferably 0.6 or more. The greater the ratio (Re/Rth) of the above-mentioned in-plane retardation to thickness direction retardation, the more isotropic the birefringence will be, and the more difficult it is to produce rainbow-like color spots depending on the viewing angle. tendency. For a completely uniaxial (uniaxially symmetric) film, the ratio (Re/Rth) of the above-mentioned in-plane retardation to thickness direction retardation becomes 2, and the above-mentioned ratio of in-plane retardation to thickness direction retardation (Re/Rth) is The upper limit is preferably 2. The upper limit of Re/Rth is preferably 1.2 or less. In addition, the retardation in the thickness direction means the average of the values obtained by multiplying the two birefringences ΔNxz and ΔNyz by the film thickness d when the film is viewed in cross section in the thickness direction.

In the polyester film for protecting polarizers of the present invention, the NZ coefficient of the polyester film is preferably 2.5 or less, more preferably 2 or less, further preferably 1.8 or less, and still more preferably, from the viewpoint of further suppressing iridescent unevenness. Preferably it is 1.6 or less. Then, in a completely uniaxial (uniaxially symmetric) thin film, since the NZ coefficient becomes 1, the lower limit of the NZ coefficient is 1. The larger the NZ coefficient, the higher the mechanical strength in the direction perpendicular to the alignment direction tends to be.

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 (the refractive index in the fast axis direction). Refractive index), and Nz represents the refractive index in the thickness direction. The alignment axis of the thin film was obtained using a molecular alignment meter (MOA-6004 type molecular alignment meter, manufactured by Oji Scientific Instruments Co., Ltd.), and was determined by an Abbe refractometer (manufactured by ATAGO, NAR-4T, measurement wavelength: 589 nm). The refractive indices (Ny, Nx, but Ny>Nx) of the biaxial directions in the direction of the alignment axis and the direction perpendicular to it, and the refractive index (Nz) in the thickness direction are obtained. The NZ coefficient can be obtained by substituting the value obtained in this manner into |Ny-Nz|/|Ny-Nx|.

In addition, in the polyester film for protecting polarizers of the present invention, the Ny-Nx value of the polyester film is preferably 0.05 or more, more preferably 0.07 or more, and still more preferably, from the viewpoint of further suppressing iridescence. It is 0.08 or more, more preferably 0.09 or more, and most preferably 0.1 or more. The upper limit of Ny-Nx is not particularly limited, but is preferably about 0.15 in the case of a polyethylene terephthalate-based film.

The polarizer protective polyester film of the present invention can be obtained from any polyester resin. The kind of polyester resin is not particularly limited, and for example, any polyester resin obtained by condensing a dicarboxylic acid component and a diol component can be used.

As a dicarboxylic acid component which can be used for the manufacture of polyester resin, for example, terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalene dicarboxylic acid can be mentioned. Formic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, biphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ethylene dicarboxylic acid, anthracenedicarboxylic 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, nonanedioic acid Diacid, dimer acid, sebacic acid, suberic acid, dodecanedicarboxylic acid, etc.

The diol component that can be used for the production of polyester trees includes, for example, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, and 1,2-cyclohexanediol. Methanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propane diol, 1,4-butanediol, 1,5-pentanediol, 1 , 6-hexanediol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) bismuth, etc.

As for the dicarboxylic acid component and the diol component constituting the polyester resin, one type or two or more types can be used. Examples of suitable polyester resins constituting the polyester film include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. More preferable examples of ethylene terephthalate include polyethylene terephthalate and polyethylene naphthalate, but these may further include other copolymerization components. These resins are excellent in transparency, and are also excellent in thermal properties and mechanical properties. In particular, polyethylene terephthalate is a suitable material because it can achieve a high elastic modulus and is relatively easy to control the thermal shrinkage rate.

When it is necessary to increase the thermal shrinkage rate of the polyester film to a high degree, it is desirable to appropriately lower the crystallinity by adding a copolymerization component. In addition, since the ratio of elastic strain and permanent strain is high for deformation at or 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 having a low glass transition temperature as needed. As a component with a low glass transition temperature, propylene glycol, 1, 3- propanediol, etc. are mentioned specifically,.

The polyester film for polarizer protection may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to obtain good adhesion to the polarizer.

(Improvement of the easy-bonding layer) In order to improve the adhesiveness with functional layers, such as a hard coat layer, and a polarizer, it is preferable to have an easy-adhesion layer on at least one side of a polyester film. Such a polyester film having an easily adhesive layer is also included in the polarizer protective polyester film of the present invention. Preferably, at least one side of the polyester film has at least one selected from the group consisting of polyester resins (including copolyester resins), polyurethane resins, and polyacrylic resins. The easy-bond layer of the main component. Here, the "main component" refers to a component that constitutes 50 mass % or more of the solid components constituting the easily bonding layer. The coating liquid used for the formation of the easily adhesive layer preferably contains at least one selected from the group consisting of water-soluble or water-dispersible copolyester resins, polyacrylic resins, and polyurethane resins 1 type of aqueous coating solution. Examples of such coating liquids include those disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Disclosed are water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, polyurethane resin solutions, and the like.

For the easily bonding layer, for example, the aforementioned coating liquid can be applied to one side or both sides of an unstretched film or a uniaxially stretched film in the longitudinal direction, dried at 100 to 150° C., and further in the transverse direction. obtained by stretching. The coating amount of the final easily bonding layer (coating amount after drying) is preferably managed to be 0.05 to 0.2 g/m ² . When the coating amount is 0.05 g/m ² or more, the obtained adhesiveness to the polarizer is sufficient. On the other hand, when the coating amount is 0.2 g/m ² or less, blocking resistance is improved. When the easy-bonding layers are provided on both sides of the polyester film, the coating amounts of the easily-bonding layers on both sides may be the same or different, and can be independently set within the above-mentioned ranges.

In the easily bonding layer, it is preferable to add particles in order to impart easy slipperiness. As the particles, fine particles having an average particle diameter of 2 μm or less are preferably used. When the average particle diameter of the particles is 2 μm or less, the dropping of the particles can be suppressed. Examples of particles to be contained in the easily bonding layer include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silicon oxide, aluminum oxide, talc, kaolin, clay, calcium phosphate, mica, and hectorite. ), zirconia, tungsten oxide, lithium fluoride, calcium fluoride and other inorganic particles, and styrene-based, acrylic-based, melamine-based, benzoguanamine-based, silicone-based and other organic polymer-based particles, etc. These may be added to the easily bonding layer alone, or may be added in combination of two or more.

In addition, a well-known method can be used for the method of apply|coating a coating liquid. For example, a reverse roll coating method, a gravure coating method, a coincident coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, etc. are mentioned. and the like can be performed alone or in combination.

In addition, the measurement of the average particle diameter of the said particle|grains was performed by the following method. The particles are photographed with a scanning electron microscope (SEM), and the size of the smallest particle is set to a magnification of 2 to 5 mm, and the maximum diameter of 300 to 500 particles (the distance between the two most separated points) is measured. The average value thereof was taken as the average particle diameter.

(The assignment of functional layers) The polarizer protective polyester film of the present invention preferably has a hard coat layer, an anti-glare layer, an anti-reflection layer, a low-reflection layer (including an anti-low-reflection layer and low-reflection anti-glare layer), anti-reflection anti-glare layer, anti-static layer and other functional layers. In the state where these functional layers are laminated on the polyester film, it is preferable that the shrinkage stress F and the ratio (F/HS) have the aforementioned conditions. The polarizing plate using the polyester film for protecting polarizers 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 other words, in an ideal embodiment, the drying temperature is set low, or a method with a small thermal history such as UV irradiation or electron beam irradiation is used. In addition, when these functional layers are provided in the film forming step of the polyester film, it becomes possible to integrate the polarizing plate of the present invention and the glass plate of the liquid crystal cell without impairing the increased thermal shrinkage rate, which is more desirable. implementation form.

(Manufacturing method of polyester film) The polyester film can be produced in accordance with a general polyester film production method. For example, a polyester resin is melted, and the non-oriented polyester that has been extruded into a sheet shape is stretched in the longitudinal direction at a temperature equal to or higher than the glass transition temperature by means of the speed difference of the rolls, and then passed through a tenter. The machine is stretched in the transverse direction and subjected to heat treatment (heat setting). The polyester film can be a uniaxially stretched film or a biaxially stretched film, preferably a uniaxially stretched film that has been strongly stretched mainly in the transverse direction, or a direction perpendicular to the main stretching direction. is slightly stretched.

If the film forming conditions of the polyester film are specifically described, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 130°C, respectively, and particularly preferably 90 to 120°C. The longitudinal stretching ratio is preferably 1 to 3.5 times, particularly preferably 1 to 3 times. Further, the lateral draw ratio is preferably 2.5 to 6 times, particularly preferably 3 to 5.5 times. In order to control the hysteresis within the above-mentioned range, it is preferable to control the ratio of the longitudinal stretch ratio and the transverse stretch ratio. In the subsequent heat treatment (heat setting), the treatment temperature is preferably 100 to 250°C, particularly preferably 180 to 245°C.

Preferably, the film is directed through the stretching/heat-setting zone to a cooling zone lower than the set temperature in the heat-setting zone and microstretched in TD. The shrinkage stress and thermal shrinkage rate of TD can be controlled through the temperature and microstretching ratio during microstretching. The shrinkage stress F in TD tends to increase by increasing the actual temperature of the film during microstretching or by increasing the TD microstretching ratio. In addition, F/HS tends to decrease as the actual temperature of the film becomes lower at the time of microstretching. Since the shrinkage stress F in TD and the ratio (F/HS) of the shrinkage stress F in TD to the thermal shrinkage rate HS in TD (F/HS) are set in the aforementioned preferable ranges, the TD micro-stretching ratio represented by the following formula is preferable For the range of 1.5% to 5%: TD micro-stretching ratio=(TD transverse width after micro-stretching-TD transverse width before micro-stretching)/TD transverse width before micro-stretching. In addition, the actual temperature of the film at the end of the microstretching is preferably about 120°C to 150°C. The actual temperature of the film can be controlled by the entrained heat from the front zone (accompanying flow), or the temperature/wind speed/nozzle configuration of the zone, etc.

In the polarizing plate of the present invention, the polarizer protective polyester film of the present invention is laminated on at least one side of the polarizer. On the other side of the polarizer, a film having no birefringence, such as a laminated TAC film, an acrylic film, and a norbornene film, is preferably provided. Alternatively, from the viewpoint of thinness, a polarizing plate without any thin film laminated on the other side of the polarizer is also preferable. In this case, the film is not laminated on the other side of the polarizer, but the coating layer may be laminated on the polarizer. The coating layer may be a functional layer such as a hard coat layer or a retardation film formed by coating. Furthermore, when a film or coating other than the polarizer protective polyester film of the present invention is laminated on the polarizer, the film other than the polarizer protective polyester film in the direction parallel to the transmission axis of the polarizer Or the shrinkage stress of the coating layer, and the shrinkage stress of the film other than the polarizer protective polyester film or the coating layer in the direction parallel to the absorption axis of the polarizer, are preferably the polarizer protective polyester film. The value of shrinkage stress in TD is less than or equal to the value of shrinkage stress in MD of the polyester film for protecting polarizers, more preferably less than or equal to the value of shrinkage stress in MD.

In addition, the shrinkage force of the film or coating layer other than the polarizer protective polyester film in the direction parallel to the transmission axis of the polarizer, and the polarizer protective polyester in the direction parallel to the absorption axis of the polarizer The shrinkage force of the film or coating layer other than the film is preferably 250 N/m or less, more preferably 200 N/m or less. For films and coating layers other than polyester films for protecting polarizers, the shrinkage force (N/m) in a specific direction of the evaluation object is defined as: the thickness of the film or coating layer (mm) × the elastic modulus in a specific direction ( N/mm ² )×thermal shrinkage rate (%) in a specific direction by treatment at 80° C./30 minutes÷100×1000. In addition, the elastic modulus was evaluated using the dynamic viscoelasticity measuring apparatus (DMS6100) by Seiko Instruments company after standing for 168 hours in the environment of 25 degreeC 50RH% according to JIS-K7244 (DMS). The temperature dependence of 25°C to 120°C was measured under the conditions of tensile mode, driving frequency 1 Hz, distance between chucks 5 mm, and heating rate 2°C/min, and the average storage elastic modulus of 30°C to 100°C was calculated. Set to elastic modulus.

Industrially, the polarizing plate of the present invention is preferably a roll-to-roll (roll-to-roll) lamination of a long polarizer and a long polarizer protective polyester film through an adhesive. Then, the polarizer is usually manufactured by being stretched in the longitudinal direction, and thus has an absorption axis in MD and a transmission axis in TD.

In the polarizing plate of the present invention, the polarizer and the polarizer protective polyester film are preferably laminated so that the transmission axis of the polarizer and the TD of the polarizer protective polyester film are substantially parallel. Here, "substantially parallel" refers to the angle formed between the transmission axis of the polarizer and the TD of the polarizer protective polyester film, preferably 0°±15° or less, more preferably 0°±10° or less, and more preferably It is preferably 0°±8° or less, more preferably 0°±5° or less, particularly preferably 0°±3° or less, and most preferably 0°.

Further, in the polarizing plate of the present invention, the polarizer and the polarizer-protecting polyester film are preferably arranged such that the transmission axis of the polarizer and the slow axis of the polarizer-protecting polyester film are substantially parallel to each other. Laminate. Here, substantially parallel refers to the angle formed by the transmission axis of the polarizer and the slow axis of the polarizer protective polyester film, preferably 0°±15° or less, more preferably 0°±10° or less, and further It is preferably 0°±8° or less, more preferably 0°±5° or less, particularly preferably 0°±3° or less, and most preferably 0°.

The liquid crystal display device of the present invention is not particularly limited as long as it includes the polarizing plate of the present invention, but usually includes at least a backlight source and a liquid crystal cell arranged between two polarizing plates. Preferably, at least one of the two polarizing plates is a polarizing plate of the present invention, that is, a polarizing plate in which the polarizer protective polyester film of the present invention is used as a polarizer protective film. In the liquid crystal display device, both of the two polarizing plates may be polarizing plates of the present invention.

The thickness of the glass substrate which is a constituent member of the liquid crystal cell is preferably 0.7 mm or less, more preferably 0.6 mm or less, still more preferably 0.5 mm or less, and most preferably 0.4 mm or less.

The polarizer protective polyester film of the present invention can be used in any size of liquid crystal display device, but can be used in preferably 42 inches or more, more preferably 46 inches or more, and further preferably 50 inches or more. More preferably, it is a liquid crystal display device of 55 inches or more, and particularly preferably a liquid crystal display device of 60 inches or more.

The polarizer protective polyester film of the present invention is preferably used at the position of the polarizer protective film on the visual recognition side with the polarizer of the polarizer on the visual recognition side as the starting point and/or polarized light of the polarizer on the light source side The mirror is used as the starting point for the position of the polarizer protective film on the light source side.

Usually, the liquid crystal display device is in the shape of a rectangle (the two polarizers used in the liquid crystal display device are also rectangular), one of the polarizers is parallel to the absorption axis, and the other polarizer is The sides are parallel to the transmission axis, and are arranged so that the absorption axes are perpendicular to each other. Then, in general, a polarizing plate having a relationship in which the long side of the polarizing plate is parallel to the absorption axis is used as a polarizing plate on the viewing side of a liquid crystal display device, and a polarizing plate having a relationship in which the long side of the polarizing plate is parallel to the transmission axis is used as a polarizing plate. The plate is a light source side polarizing plate used as a liquid crystal display device. The absorption axis direction of the polarizer with large shrinkage stress is the polarizer of the long side, and there is a problem of the shape factor that curls easily occur due to shrinkage (curl is generally easy to occur in the longitudinal direction), or because of the liquid crystal panel. Due to the influence of the asymmetric structure of the upper and lower polarizers, the liquid crystal panel tends to be convex on the polarizer side where the polarizer transmission axis of the upper and lower polarizers arranged in crossed Nicols becomes the long side. At least, from the viewpoint of suppressing warpage of the liquid crystal panel, it is preferable to use the polarizing plate of the present invention as a polarizing plate having a relationship in which the long side of the polarizing plate is parallel to the transmission axis. In addition, it is also preferable to use the polarizing plate of the present invention for both the polarizing plate having the long side of the polarizing plate parallel to the transmission axis and the polarizing plate having the long side of the polarizing plate parallel to the absorption axis. [Example]

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and may be implemented with appropriate modifications within the scope suitable for the gist of the present invention, and any of these All are included in the technical scope of the present invention.

(1) Shrinkage stress of MD and TD of polyester film After standing for 168 hours in an environment of 25°C/50RH%, the measurement was performed using a thermomechanical analyzer (manufactured by Hitachi High Tech Science, TMA7100). The film sample was set to have a width of 1 mm and a sample length of 15 mm, was sandwiched with a minimum load of 19 mN, and was heated from 30° C. to 260° C. at 5° C./min, and the shrinkage load was measured. From the obtained shrinkage load curve, the maximum shrinkage load occurring up to 80°C to 150°C was divided by the initial cross-sectional area, and used as shrinkage stress (MPa). In addition, when measuring the shrinkage stress of MD, it was set so that the film sample length and MD might become parallel, and when measuring the shrinkage stress of TD, it set so that the film sample length might become parallel with TD.

(2) Thermal shrinkage rate of TD of polyester film After the polyester film was left to stand for 168 hours in an environment of 25°C/50RH%, a circle with a diameter of 80 mm was drawn, and the diameter of the circle was measured every 1° using an image sizer (Image Measure IM6500 manufactured by KEYENCE Corporation), which was used as a treatment. length before. Next, heat treatment was performed for 30 minutes using a Gear oven set at 80° C., and then cooled in an environment set at room temperature of 25° C. for 10 minutes by the same method as before the treatment. The evaluation was performed at 1° and used as the length after treatment. In addition, the said process is performed by the polyester film for polarizer protection individually.

The value of the length before processing in TD and the length after processing was substituted into the following calculation formula, and the thermal shrinkage rate of TD was calculated|required. Thermal shrinkage = (length before treatment - length after treatment) / length before treatment × 100

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

(4) Warpage of the LCD panel The liquid crystal panels produced in the respective Examples/Comparative Examples were heat-treated for 2 hours in a Kiel oven set at 80°C and 5% RH, and then heated at room temperature of 25°C and 50% RH. After the environment was cooled for 30 minutes, the convex side was placed on a horizontal surface, and the heights of the four corners were measured with a measure, and the maximum value was defined as the amount of warpage. The warpage amount was evaluated as follows. In addition, the liquid crystal panel was carried out in a state where the four corners were supported by the corner posts, and the panel was placed horizontally above the corner posts (that is, the panel was in a floating state except for the four corners). Heat treatment and cooling treatment. ○: 0mm or more and less than 1.5mm ×: 1.5mm or more

(5) Warpage of LCD panel after long time/high temperature environment The liquid crystal panels produced in each Example/Comparative Example were subjected to heat treatment for 240 hours in a Kiel oven set at 70°C and 5% RH, and thereafter, were set at room temperature of 25°C and 50% RH. After cooling for 30 minutes in an environment of , the convex side was placed on a horizontal surface, and the height of the four corners was measured with a measuring instrument, and the maximum value was set as the amount of warpage. The warpage amount was evaluated as follows. In addition, the liquid crystal panel was carried out in a state where the four corners were supported by the corner posts, and the panel was placed horizontally above the corner posts (that is, the panel was in a floating state except for the four corners). heat treatment and cooling treatment. ○: 0mm or more and less than 3.0mm ×: 3.0mm or more

(6) Refractive index and in-plane retardation (Re) of polyester film The in-plane retardation is a parameter defined by the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|Nx-Ny|) of the biaxial perpendicular to the film and the thickness d (nm) of the film (ΔNxy×d). isotropic and anisotropic scales. Biaxial refractive index anisotropy (ΔNxy) was obtained by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), the slow axis direction of the film was obtained, and a 4 cm × A 2 cm rectangle was used as a sample for measurement. For this sample, the refractive index of the perpendicular biaxial (refractive index in the slow axis direction: Ny, the refractive index in the direction perpendicular to the slow axis direction: Ny, and Refractive index: Nx), and the refractive index in the thickness direction (Nz), and the absolute value of the biaxial refractive index difference (|Nx-Ny|) was defined as the refractive index anisotropy (ΔNxy). The thickness d (nm) of the thin film was measured using an electric micrometer (Millitron 1245D manufactured by Feinpruf), and the unit was converted into nm. The in-plane retardation (Re) was obtained from the product (ΔNxy×d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the thin film.

(7) Thickness direction hysteresis (Rth) The thickness-direction hysteresis refers to the average of the hysteresis obtained by multiplying the two birefringences ΔNxz (=|Nx-Nz|) and ΔNyz (=|Ny-Nz|) by the film thickness d when viewed from a cross-section in the thickness direction of the film. parameter. Nx, Ny, Nz and the film thickness d (nm) were obtained by the same method as the measurement of the in-plane hysteresis, and the average value of (ΔNxz×d) and (ΔNyz×d) was calculated to obtain the thickness direction hysteresis (Rth).

(Production Example 1 - Polyester A) The temperature of the esterification reaction tank was heated and when it reached 200°C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were fed, and 0.017 parts by mass of antimony trioxide and 0.064 parts by mass of antimony trioxide as catalysts were fed while stirring. Magnesium acetate tetrahydrate, 0.16 parts by mass of triethylamine. Next, after pressurizing and raising the temperature and performing the pressurized esterification reaction under the conditions of a gauge pressure of 0.34 MPa and 240° C., the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, the temperature was raised to 260° C. for 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transported to a polycondensation reaction tank, and a polycondensation reaction was performed under reduced pressure at 280°C.

After the completion of the polycondensation reaction, it was filtered with a NASLON filter with a 95% cut-off diameter of 5 μm, extruded from a nozzle into a strand shape, and cooled with cooling water that had previously been filtered (pore size: 1 μm or less). Allow to cool, solidify, and cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (A) was 0.62 dl/g, and inactive particles and internally precipitated particles were not substantially contained. (Hereinafter abbreviated to PET(A).)

(benzoxazin)-4-酮))、90質量份不含有粒子的PET(A)(固有黏度為0.62dl/g)，並使用混煉擠出機，獲得了含有紫外線吸收劑的聚對苯二甲酸乙二酯樹脂(B)。(以後簡稱為PET(B)。)(Production Example 2-Polyester B) 10 parts by mass of the dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzone) was mixed

(benzoxazin)-4-one)), 90 parts by mass of particle-free PET (A) (intrinsic viscosity: 0.62 dl/g), and a kneading extruder was used to obtain a UV absorber-containing polyethylene terephthalate Ethylene formate resin (B). (Hereinafter abbreviated to PET(B).)

(Production Example 3 - Preparation of Adhesive-Modifying Coating Liquid) Transesterification and polycondensation are carried out by common methods to prepare 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% as dicarboxylic acid components (relative to the whole dicarboxylic acid component) Water-dispersible sulfonic acid containing % sodium isophthalate-5-sulfonate, 50 mol% ethylene glycol and 50 mol% neopentyl glycol as diol components (with respect to the entire diol component) Metal salt 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, heating and stirring were performed, and when the temperature reached 77° C., added 5 parts by mass of the above-mentioned water-dispersible sulfonic acid metal salt group-containing copolyester resin was continuously stirred until the agglomeration of the resin disappeared, and then the aqueous resin dispersion was cooled to room temperature to obtain uniform water with a solid content concentration of 5.0% by mass. Dispersible copolyester resin liquid. 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 Sylysia 310 was added to 99.46 parts by mass of the above-mentioned water-dispersible copolyester resin liquid. To the aqueous dispersion, 20 parts by mass of water was added while stirring to obtain an adhesive modified coating liquid.

(Example 1) <Manufacture of polarizer protective polyester film 1> 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for the intermediate layer of the base film were decompressed at 135° C. for 6 hours After drying (1 Torr), it was supplied to extruder 2 (for the intermediate layer II layer), and the PET (A) was dried by a conventional method and supplied to the extruder 1 (for outer layer I layer and outer layer III layer), respectively, and melted at 285°C. The two kinds of polymers were filtered using stainless steel sintered filter media (nominal filtration accuracy of 10 μm particles was 95% intercepted), and were layered in two kinds of three-layer confluence blocks. The casting method was applied and the film was wound up to a casting drum having a surface temperature of 30° C., and was cooled and solidified to prepare an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the ratio of the thickness of the I layer, the II layer, and the III layer would be 10:80:10.

Next, the adhesive modified coating liquid was applied to both sides of the unstretched PET film by the reverse roll method so that the coating weight after drying was 0.08 g/m ² , and dried at 80° C. for 20 second.

The unstretched film on which the coating layer was formed was guided to a tenter stretching machine, and was guided to a hot air zone with a temperature of 105° C. while holding the end of the film with a clip, and stretched 4.0 times in TD. Next, heat treatment was performed at a temperature of 180°C for 30 seconds, after that, the film was guided to a cooling zone of 120°C, and the film was stretched by 2.5% in the width direction (micro-stretching), and then the film was cooled by releasing the clamps. The clamps at both ends of the film to 60°C were pulled with a tension of 350 N/m, and a jumbo roll composed of a uniaxially oriented PET film with a film thickness of about 80 μm was taken, and the obtained jumbo roll was 3 Three slit rolls (L (left side), C (center), R (right side)) were obtained by equally dividing. The polarizer protective polyester film 1 was obtained from the slit roll at R. When measuring the actual temperature of the film in progress at the end of the 2.5% stretching in the width direction with a non-contact radiation thermometer, it was about 125°C.

<Production of liquid crystal panel> The polarizer protective polyester film 1 was attached to one side of a polarizer composed of PVA, iodine, and boric acid so that the transmission axis of the polarizer was parallel to the TD of the polarizer protective polyester film 1 . Further, 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.

A liquid crystal panel was taken out from a 65-inch size IPS type liquid crystal television having a glass substrate with a thickness of 0.4 mm for a liquid crystal cell. And peel off the light source side polarizer from the liquid crystal panel, and replace it with the light source side polarizer made above, so that the transmission axis of the polarizer is consistent with the transmission axis direction (parallel to the horizontal direction) of the light source side polarizer before peeling off In the method of PSA (pressure sensitive adhesive), it is attached to the liquid crystal cell, and the liquid crystal panel is produced. Furthermore, the polarizing plate on the light source side is bonded to the liquid crystal cell so that the polarizer protective polyester film 1 and the liquid crystal cell are on the far side (opposite side). In addition, the polarizing plate on the visual recognition side is attached to the liquid crystal cell so that the absorption axis direction of the polarizer is parallel to the horizontal direction with the TAC film layered on both areas of the polarizer.

(Example 2) <Manufacture of polarizer protective polyester film 2> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 120° C., and the film was stretched by 3.0% in the width direction. , was carried out in the same manner as the polyester film 1 for protecting a polarizer to obtain a polyester film 2 for protecting a polarizer. <Production of liquid crystal 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 polarizer protective polyester film 3> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 120° C., and the film was stretched by 3.5% in the width direction. , the polyester film 3 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal 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 polarizer protective polyester film 4> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was led to a cooling zone of 120° C., and the film was stretched by 4.0% in the width direction. , the polyester film 4 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal 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 polarizer protective polyester film 5> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180°C for 30 seconds, the film was led to a cooling zone of 120°C, and the film was stretched by 4.5% in the width direction. It carried out similarly to the polyester film 1 for polarizer protection, and obtained the polyester film 5 for polarizer protection. <Production of liquid crystal 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.

(Comparative Example 1) <Manufacture of polarizer protective polyester film 6> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 120° C., and the film was stretched by 5.0% in the width direction. , the polyester film 6 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 6 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Comparative Example 2) <Manufacture of polarizer protective polyester film 7> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 100° C., and the film was stretched by 1.0% in the width direction. , the polyester film 7 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. When measuring the actual temperature of the film in progress at the time of completion of the 1.0% stretching in the width direction with a non-contact radiation thermometer, it was about 115°C. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 7 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Comparative Example 3) <Manufacture of polarizer protective polyester film 8> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was led to a cooling zone of 100° C., and the film was stretched by 1.5% in the width direction. , the polyester film 8 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 8 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Comparative Example 4) <Manufacture of polarizer protective polyester film 9> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 100° C., and the film was stretched by 2.0% in the width direction. , the polyester film 9 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 9 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Comparative Example 5) <Manufacture of the polyester film 10 for polarizer protection> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was guided to a cooling zone of 100° C., and the film was stretched by 2.5% in the width direction. , was carried out in the same manner as the polyester film 1 for protecting a polarizer to obtain a polyester film 10 for protecting a polarizer. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 10 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

(Comparative Example 6) <Manufacture of the polyester film 11 for polarizer protection> In the film formation of the polarizer protective polyester film 1 of Example 1, except that after heat treatment at a temperature of 180° C. for 30 seconds, the film was led to a cooling zone of 100° C., and the film was stretched by 3.5% in the width direction. , the polyester film 11 for protecting a polarizer was obtained in the same manner as the polyester film 1 for protecting a polarizer. <Production of liquid crystal panel> In Example 1, except having replaced the polyester film 1 for polarizer protection with the polyester film 11 for polarizer protection, it carried out similarly to Example 1, and produced the liquid crystal panel.

[Table 1] Polarizer Protective Film Evaluation results Thickness (μm) Cooling zone temperature (℃) Re (nm) Shrinkage stress F in TD direction (MPa) Thermal shrinkage HS (%) in TD direction F/HS (MPa/%) Shrinkage stress in MD direction Fv (MPa) Shrinkage stress ratio F/Fv Warpage of LCD panel (80°C/2 hours) Warpage of LCD panels arranged in long-term/high-temperature environments (70°C/240 hours) Example 1 80 120 8120 8.3 0.21 40 1.97 4.2 ○ ○ Example 2 80 120 8120 12.0 0.25 48 1.91 6.3 ○ ○ Example 3 80 120 8120 15.8 0.30 53 1.98 8.0 ○ ○ Example 4 80 120 8120 19.6 0.34 57 2.06 9.5 ○ ○ Example 5 80 120 8120 23.4 0.39 60 2.06 11.4 ○ ○ Comparative Example 1 80 120 8120 27.2 0.43 63 2.25 12.1 × - Comparative Example 2 80 100 8120 3.7 0.20 19 2.02 1.8 × - Comparative Example 3 80 100 8120 5.5 0.27 twenty one 2.07 2.7 × - Comparative Example 4 80 100 8120 7.3 0.33 twenty two 1.89 3.9 × - Comparative Example 5 80 100 8120 9.1 0.40 twenty three 2.03 4.5 ○ × Comparative Example 6 80 100 8120 12.7 0.54 twenty three 2.08 6.1 ○ ×

From the results shown in Table 1, it was confirmed that the polarizing plate using the polyester film for protecting a polarizer of the present invention can suppress the warpage of the liquid crystal panel compared to the polarizing plate of the comparative example.

In Examples 1 to 5, liquid crystal panels were produced in the same manner, except that the TAC film was not used as the protective film on the liquid crystal cell side of the light source side polarizing plate. The liquid crystal panels of the respective Examples obtained favorable results (○) in any of the evaluations of "warpage of liquid crystal panel" and "warpage of liquid crystal panel after placement in a long-term/high temperature environment". [Possibility of Industrial Use]

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

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Claims (9)

A polarizer protective polyester film, which satisfies the following requirements (1) and (2): (1) The shrinkage stress F of the TD of the polyester film is not less than 8MPa and not more than 25MPa; (2) The ratio (F/HS) of the shrinkage stress F of the TD of the polyester film to the thermal shrinkage HS of the TD of the polyester film by the treatment at 80°C/30 minutes (F/HS) is 30 (MPa/%) or more 60 (MPa/%) or less. As claimed in claim 1, the polarizer protective polyester film further satisfies the requirements of the following (3): (3) The in-plane retardation (retardation) of this polyester film is 3000-30000 nm. As claimed in claim 1 or 2, the polarizer protective polyester film further satisfies the requirements of the following (4): (4) The thickness of the polyester film is 40 to 200 μm. The polyester film for polarizer protection according to any one of claims 1 to 3, wherein the polyester film has a hard coat layer, an anti-reflection layer, and a low-reflection layer on the opposite side to the surface of the laminated polarizer. , anti-glare layer, or anti-reflection anti-glare layer. A polarizing plate, wherein the polarizer protective polyester film according to any one of claims 1 to 4 is laminated on one side of the polarizer. A polarizing plate, which has the polarizer protective polyester film as claimed in any one of claims 1 to 4 laminated on one side of the polarizer, and has no laminated film on the other side of the polarizer. A polarizing plate, one side of the polarizer is laminated with the polarizer protective polyester film as claimed in any one of claims 1 to 4, and the other side of the polarizer is provided with a laminated coating layer. The polarizing plate of claim 7, wherein the coating layer is a hard coat layer or a retardation film. A liquid crystal display device comprising the polarizing plate according to any one of claims 5 to 8.