JP2020126217A - Polyester film and polarizing plate comprising the same - Google Patents

Abstract

To provide a polyester film which causes little rainbow irregularity when used for image display devices and may contribute to durability improvement of polarizing plates.SOLUTION: A polyester film of the present invention has an in-plane retardation Re(590) of 100 nm or less, and a linear expansion coefficient in a range of 0/°C to 4.0×10/°C in a first direction. According to one embodiment, an absolute value of a difference between the linear expansion coefficient in the first direction and a linear expansion coefficient in a second direction perpendicular to the first direction is 1.0×10/°C or less.SELECTED DRAWING: None

Description

The present invention relates to a polyester film and a polarizing plate including the polyester film.

In image display devices (for example, liquid crystal display devices and organic EL display devices), a polarizing plate is often arranged on at least one side of a display cell due to its image forming method. 2. Description of the Related Art In recent years, image display devices have tended to further diversify their functions and applications, and are required to withstand use in more harsh environments. A polarizing plate generally has a structure in which a polarizer is sandwiched between two protective films, and as the protective film, triacetyl cellulose, acrylic resin, cycloolefin resin, etc. are widely used. On the other hand, from the viewpoint of durability as described above, a polyester film such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) having excellent mechanical properties, chemical resistance, and moisture barrier properties is used as a polarizer protective film. It has been proposed (for example, Patent Document 1). However, while the polyester film has excellent mechanical properties, it has birefringence, which may cause deterioration of visibility such as rainbow unevenness. In particular, with the recent trend toward higher brightness and higher color purity of image display devices, such a problem of rainbow unevenness becomes remarkable.

On the other hand, a polarizing plate constituted by using a protective film formed of triacetyl cellulose, an acrylic resin or a cycloolefin resin which has been frequently used, has cracks in the polarizer due to temperature change. There is. In recent years, thinning of the polarizer has been required along with the thinning of the image display device, while the number of image display devices expected to be used under high temperature is increasing, the polarizing plate having excellent durability without cracks in the polarizer. Plates are strongly desired.

Japanese Unexamined Patent Publication No. 8-271733

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to reduce the occurrence of rainbow unevenness when applied to an image display device, and may contribute to improving the durability of a polarizing plate. To provide a polyester film.

The polyester film of the present invention has an in-plane retardation Re(590) of 100 nm or less and a linear expansion coefficient in the first direction of 0/°C to 4.0×10 ^-5 /°C.
In one embodiment, the absolute value of the difference between the coefficient of linear expansion in the first direction and the coefficient of linear expansion in the second direction orthogonal to the first direction is 1.0×10 ⁻⁵ / It is below ℃.
In one embodiment, the polyester film has an orientation function (f) of 0.01 to 0.24.
In one embodiment, the polyester film is formed from polyethylene terephthalate and/or modified polyethylene terephthalate.
In one embodiment, the modified polyethylene terephthalate comprises a structural unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid.
In one embodiment, the polyester film has a crystallinity of 30% or more by DSC measurement.
According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate includes a polarizer and the polyester film arranged on one side of the polarizer.
In one embodiment, the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction, and the polyester film The absolute value of the difference between the linear expansion coefficient in the second direction orthogonal to the first direction and the linear expansion coefficient in the direction parallel to the second direction of the polarizer is both 3.5×10 ^−5. /°C or lower.
In one embodiment, the thickness of the above-mentioned light polarizer is 20 micrometers or less.
In one embodiment, the polarizing plate further includes an easy-adhesion layer arranged on the polarizer side of the polyester film.
In one embodiment, the easy-adhesion layer contains fine particles.
In one embodiment, the thickness of the easily adhesive layer is 0.35 μm or less.
In one embodiment, the easy-adhesion layer has a refractive index of 1.55 or less.

According to the present invention, the in-plane retardation is 100 nm or less, and the coefficient of linear expansion in a predetermined direction is 0/°C to 4.0×10 ⁻⁵ /°C. It is possible to provide a polyester film that is less likely to generate and contribute to improving the durability of the polarizing plate.

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Polyester Film The in-plane retardation Re(590) of the polyester film is 100 nm or less. In the present invention, by setting the in-plane retardation Re in such a range, it is possible to obtain a polyester film with less rainbow unevenness when applied to an image display device. The in-plane retardation Re(590) of the polyester film is preferably 80 nm or less, more preferably 60 nm or less, and further preferably 55 nm or less. Within such a range, the above effect becomes more remarkable. The in-plane retardation Re(590) is preferably as small as possible, and the lower limit is ideally 0 nm, and may be 1 nm, for example. The in-plane retardation Re(λ) is the in-plane retardation of the film measured with light having a wavelength of λ nm at 23°C. Therefore, Re(590) is the in-plane retardation of the film measured with light having a wavelength of 590 nm. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d(nm) is the thickness of the film. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), and ny is the refractive index in the in-plane direction orthogonal to the slow axis.

The linear expansion coefficient of the polyester film in the first direction is 0/°C to 4.0×10 ^-5 /°C. Within such a range, it is possible to obtain a polyester film that can be laminated on a polarizer to effectively protect the polarizer and prevent cracking of the polarizer. The linear expansion coefficient in a first direction of the polyester film is preferably ^{0.2 × 10 -5 /℃~4.0×10 -5 / ℃} , more preferably 1.0 × ^{10 -5} / ℃ to 4.0 a × ^{10 -5} / ℃, still more preferably ^{1.5 × 10 -5 /℃~4.0×10 -5 / ℃} , particularly preferably 2.0 × ^{10 -5} / ℃ an ~4.0 × ^{10 -5} / ℃, and most preferably ^{2.5 × 10 -5 /℃~3.8×10 -5 / ℃} . Within such a range, the above effect becomes more remarkable. In one embodiment, the above-mentioned 1st direction is equivalent to a conveyance direction (MD) at the time of manufacturing a polyester film. The linear expansion coefficient can be determined by TMA measurement according to JIS K 7197.

In the present invention, when the in-plane retardation Re(590) and the linear expansion coefficient in the first direction are within the above ranges, the occurrence of rainbow unevenness when applied to an image display device is small, and the polarizing plate It is possible to provide a polyester film that can contribute to improvement of durability (prevention of crack generation). More specifically, the polyester film may be a stretched film obtained through a stretching step, and by appropriately adjusting the manufacturing conditions in the stretching step, the in-plane retardation Re(590) and the first direction may be adjusted. The linear expansion coefficient can be controlled in a well-balanced manner, and as a result, a polyester film having excellent properties as a polarizer protective film can be obtained from the viewpoint of rainbow unevenness and durability as described above. Such an excellent polyester film can be obtained because, in addition to the linear expansion coefficient of the polyester film, the crystallinity (crystallinity, orientation) of the polyester resin is well adjusted by optimizing the production conditions. Is thought to be a cause. As the above-mentioned production conditions, stretching conditions (stretching temperature, stretching ratio, stretching speed, MD/TD stretching order), preheating temperature before stretching, heat treatment temperature after stretching, heat treatment time after stretching, MD/TD direction after stretching The relaxation rate and the like. Focusing on the optimization of these various manufacturing conditions, the in-plane retardation Re(590) and the linear expansion coefficient in the first direction could be controlled in a well-balanced manner, which is one of the great achievements of the present invention. The stretching temperature, the stretching ratio and the stretching speed can be appropriately adjusted for each MD/TD. In addition, TD is a direction orthogonal to the transport direction (MD) when manufacturing a polyester film.

The linear expansion coefficient of the polyester film in the second direction orthogonal to the first direction is preferably 0/° C. to 4.0×10 ⁻⁵ /° C., more preferably 1.0×10 ^−5. /℃～4.0×10 was ^-5 / ° C., more preferably from ^{1.5 × 10 -5 /℃~4.0×10 -5 / ℃} , particularly preferably 2.0 × ^{10 -5} a /℃~4.0×10 ^-5 / ℃, and most preferably ^{2.5 × 10 -5 /℃~3.8×10 -5 / ℃} . In one embodiment, the second direction corresponds to TD. The linear expansion coefficient in the second direction can also be controlled by the production conditions of the polyester film (in particular, the stretching conditions and the heat treatment conditions).

The absolute value of the difference between the linear expansion coefficient in the first direction and the linear expansion coefficient in the second direction of the polyester film is preferably 1.0×10 ⁻⁵ /° C. or less, more preferably 0.7. ×10 ⁻⁵ /° C. or less. Within such a range, the effect of preventing cracking of the polarizer becomes remarkable.

The polyester film has a crystallinity measured by differential scanning calorimetry (DSC) of preferably 30% or more, more preferably 40% or more, and further preferably 50% or more. The upper limit of the crystallinity is, for example, 70%. Within such a range, a polyester film having excellent heat resistance and mechanical properties and suitable as a polarizer protective film can be obtained.

In the above polyester film, it is preferable that the arrangement of the crystal parts is uniform in the plane. For example, it is preferable that the polyester film is adjusted so that the amount of crystal parts in the first direction is the same as that in the second direction orthogonal to the first direction. By adjusting in this way, it is possible to obtain a polyester film having a small in-plane retardation and hardly causing rainbow unevenness. The arrangement of the crystal parts can be adjusted by the stretching conditions during the production of the polyester film. The arrangement of crystal parts can be evaluated by the crystal orientation degree measured by X-ray diffractometry (XRD).

The orientation function (f) of the polyester film is preferably 0.01 to 0.24, more preferably 0.05 to 0.20. The orientation function represents the orientation of crystals in the first direction of the polyester film (for example, the transport direction (MD) when manufacturing the polyester film), and if f=1, complete orientation in the first direction, If f=0, it is random, and if f=-0.5, it is completely oriented in the second direction orthogonal to the first direction. Provided is a polyester film having an orientation function (f) in the above range, which is particularly less likely to cause rainbow unevenness when applied to an image display device, and which can contribute to improving the durability of a polarizing plate (preventing the occurrence of cracks). can do. The orientation function (f) is obtained by, for example, an attenuated total reflection (ATR) measurement using a Fourier transform infrared spectrophotometer (FT-IR) and polarized light as the measurement light. Specifically, the measurement light (polarized light) vibrates in a direction parallel to the polyester film sample surface, and the measurement light (polarized light) vibrates in a direction orthogonal to the polyester film sample surface. It is calculated according to the following equation using the intensity I of 1340 cm ⁻¹ (crystal peak) of the obtained spectrum. Here, the intensity I, as a reference peak to 1410 cm ^-1, the value of 1340cm ^-1 / 1410cm -1.
f=(3<cos ² θ>−1)/2
_{= [(R-1) (} R 0 +2)] / [(R + 2) (R 0 -1)]
=(1-D)/[c(2D+1)]
=-2x(1-D)/(2D+1)
However,
c=(3 cos ² β-1)/2
β=90 deg
θ: Angle of molecular chain with respect to stretching direction β: Transition dipole moment with respect to molecular chain axis (β=0)
R ₀ =2cot ² β
1/R=D=(I//)/(I⊥)
I⊥: Absorption intensity when measured in a state where the vibration direction of the measurement light (polarized light) is orthogonal to the polyester film sample surface I//: In the state where the vibration direction of the measurement light (polarized light) is parallel to the polyester film sample surface Absorption intensity when measured

The thickness of the polyester film may be an appropriate thickness depending on the purpose and desired in-plane retardation. The thickness of the retardation film is typically 10 μm to 100 μm, preferably 20 μm to 80 μm, and more preferably 20 μm to 50 μm.

The total light transmittance of the polyester film is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 95% or more. The haze of the polyester film is preferably 1.0% or less, more preferably 0.7% or less, still more preferably 0.5% or less, and particularly preferably 0.3% or less.

The water vapor permeability of the polyester film is preferably 100 g/m ² ·24 hr or less, more preferably 50 g/m ² ·24 hr or less, and further preferably 15 g/m ² ·24 hr or less. Within such a range, a polarizing plate excellent in durability and moisture resistance can be obtained.

The polyester film of the present invention is formed of a polyester resin. The polyester resin can be obtained by condensation polymerization of a carboxylic acid component and a polyol component.

Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalic acid, diphenic acid, 4,4'-oxybenzoic acid and 2,5-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, zebacic acid, fumaric acid, Maleic acid, itaconic acid, thiodipropionic acid, diglycolic acid may be mentioned. Examples of the alicyclic dicarboxylic acid include 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and 2,5-norbornanedicarboxylic acid. Examples thereof include acids and adamantane dicarboxylic acids. The carboxylic acid component may be a derivative such as an ester, a chloride or an acid anhydride, and examples thereof include dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 2,6-naphthalene dicarboxylate, dimethyl isophthalate and dimethyl terephthalate. And diphenyl terephthalate. The carboxylic acid components may be used alone or in combination of two or more.

As the polyol component, a dihydric alcohol is typically mentioned. Examples of the dihydric alcohol include aliphatic diols, alicyclic diols, and aromatic diols. Examples of the aliphatic diol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2, 2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3- Examples include butadiol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol. To be Examples of the alicyclic diol include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecanedimethanol, adamantanediol, 2,2,4. , 4-tetramethyl-1,3-cyclobutanediol. Examples of the aromatic diol include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-(2-norbornylidene)diphenol, 4,4'-dihydroxybiphenol, o-, Mention may be made of m- and p-dihydroxybenzene, 4,4'-isopropylidenephenol, 4,4'-isopropylidenebis(2,6-cyclolophenol)2,5-naphthalenediol and p-xylenediol. The polyol component may be used alone or in combination of two or more kinds.

As the polyester resin, polyethylene terephthalate and/or modified polyethylene terephthalate is preferably used, and more preferably polyethylene terephthalate is used. By using these resins, it is possible to obtain a polyester film which is excellent in mechanical properties and has less rainbow unevenness. Polyethylene terephthalate and modified polyethylene terephthalate may be blended and used.

Examples of the modified polyethylene terephthalate include modified polyethylene terephthalate containing a constitutional unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid. The proportion of diethylene glycol in the polyol component is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 3 mol% or less. The proportion of 1,4-butanediol in the polyol component is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 3 mol% or less. The proportion of 1,3-propanediol in the polyol component is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 3 mol% or less. The proportion of isophthalic acid in the carboxylic acid component is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 8 mol% or less. Within such a range, a polyester film having good crystallinity can be obtained. The mol% described above is the mol% based on the total of all repeating units of the polymer.

The weight average molecular weight of the polyester resin is preferably 10,000 to 100,000, more preferably 20,000 to 75,000. With such a weight average molecular weight, a film that is easy to handle during molding and has excellent mechanical strength can be obtained. The weight average molecular weight can be measured by GPC (solvent: THF).

In one embodiment, an easy-adhesion layer-attached polyester film is provided. The easy-adhesion layer contains, for example, a water-based polyurethane and an oxazoline-based crosslinking agent. Details of the easy-adhesion layer are described in, for example, JP 2010-55062A. The entire disclosure of this publication is incorporated herein by reference.

In one embodiment, the easy-adhesion layer contains any appropriate fine particles. By forming the easy-adhesion layer containing fine particles, blocking that occurs during winding can be effectively suppressed. The fine particles may be inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include silica, titania, alumina, zirconia and other inorganic oxides, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate and the like. Can be mentioned. Examples of the organic fine particles include silicone resins, fluorine resins, (meth)acrylic resins, and the like. Of these, silica is preferable.

The particle size (number average primary particle size) of the fine particles is preferably 10 to 200 nm, more preferably 20 to 60 nm.

The thickness of the easily adhesive layer is preferably 2 μm or less, more preferably 1 μm or less, and further preferably 0.35 μm or less. Within such a range, it is possible to obtain a polyester film with an easy-adhesion layer that is unlikely to impair the optical properties of other members when applied to an image display device.

In one embodiment, the easy-adhesion layer has a refractive index of preferably 1.45 to 1.60. Within such a range, it is possible to obtain a polyester film with an easy-adhesion layer that is unlikely to impair the optical properties of other members when applied to an image display device. In one embodiment, the easy-adhesion layer has a refractive index of 1.54 or more.

In one embodiment, the polyester film may include an antiblock layer on at least one side thereof. As the structure of the anti-block layer, the structure of the easy-adhesion layer described above can be adopted. Preferably, the antiblock layer contains the fine particles.

(Method for producing polyester film)
The polyester film can be obtained through a molding step of molding a film-forming material (resin composition) containing the polyester resin into a film and a stretching step of stretching the molded film. Preferably, the stretching step includes a pre-heat treatment of the film performed before the film stretching and a heat treatment performed after the film stretching. In one embodiment, the polyester film is provided in an elongated shape (or a shape cut out from an elongated body).

The film-forming material may contain an additive and a solvent in addition to the polyester resin. Any appropriate additive can be adopted as the additive depending on the purpose. Specific examples of the additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, antioxidants, ultraviolet absorbers, leveling agents, thixotropic agents, antistatic agents, conductive materials, flame retardants. Is mentioned. The number, type, combination, addition amount, etc. of the additives can be appropriately set according to the purpose.

As a method for forming a film from the film-forming material, any suitable molding method can be adopted. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (for example, casting method), calender molding method, heat press. Law etc. are mentioned. An extrusion molding method or a cast coating method is preferable. This is because the smoothness of the obtained film can be increased and good optical uniformity can be obtained.

The stretching method of the film is typically biaxial stretching, and more specifically, sequential biaxial stretching or simultaneous biaxial stretching. Preferably, simultaneous biaxial stretching is adopted. If the film is stretched by simultaneous biaxial stretching, the in-plane retardation Re(590) and the linear expansion coefficient are controlled in a well-balanced manner, and a polyester film in which rainbow unevenness is particularly small can be obtained. Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter stretching machine. Therefore, the stretching direction of the film is typically the length direction (MD) and the width direction (TD) of the film.

The stretching temperature is preferably Tg+5° C. to Tg+50° C. with respect to the glass transition temperature (Tg) of the film, more preferably Tg+5° C. to Tg+30° C., and further preferably Tg+5° C. to Tg+10° C. By stretching at such a temperature, it is possible to obtain a polyester film in which the in-plane retardation Re (590) and the linear expansion coefficient are well controlled. Moreover, a polyester film having excellent transparency can be obtained.

The stretching ratio in MD is preferably 1.1 times to 5 times, more preferably 1.1 times to 4 times, further preferably 1.5 times to 3.5 times, and particularly preferably 2 times. It is more than double and 3.2 times or less. Within such a range, a polyester film having good crystallinity can be obtained while keeping the in-plane retardation within a desired range.

The draw ratio in TD is preferably 1.1 times to 5 times, more preferably 1.1 times to 4 times, further preferably 1.5 times to 3.5 times, and particularly preferably 2 times. It is more than 3.2 times and 3.2 times or less. Within such a range, a polyester film having good crystallinity can be obtained while keeping the in-plane retardation within a desired range.

The ratio of the draw ratio in MD to the draw ratio in TD (TD draw ratio/MD draw ratio) is preferably 0.7 to 1.5, more preferably 0.8 to 1.2, and further preferably. Is 0.9 to 1. Within such a range, it is possible to obtain a polyester film in which the occurrence of rainbow unevenness is particularly small.

The stretching speed in MD is preferably 5%/sec to 400%/sec, more preferably 5%/sec to 150%/sec, further preferably 8%/sec to 150%/sec, It is more preferably 8%/sec to 100%/sec, particularly preferably 8%/sec to 80%/sec, and most preferably 8%/sec to 60%/sec. Within such a range, a polyester film having excellent optical properties and good crystallinity can be obtained.

The stretching speed in TD is preferably 5%/sec to 150%/sec, more preferably 5%/sec to 100%/sec, and further preferably 8%/sec to 100%/sec, It is particularly preferably 8%/sec to 80%/sec, and most preferably 8%/sec to 60%/sec. Within such a range, a polyester film having excellent optical properties and good crystallinity can be obtained.

The temperature of the preheat treatment is preferably 80°C to 150°C, more preferably 90°C to 130°C. The preheat treatment time is preferably 5 seconds to 100 seconds, more preferably 10 seconds to 100 seconds, and further preferably 15 seconds to 80 seconds. Within such a range, a polyester film having excellent optical properties and good crystallinity can be obtained.

The temperature of the heat treatment is preferably 100°C to 250°C, more preferably 120°C to 200°C, and further preferably 130°C to 180°C. Within such a range, it is possible to obtain a polyester film having excellent transparency and good crystallinity. The heat treatment time is preferably 1 second to 50 seconds, more preferably 2 seconds to 50 seconds, further preferably 2 seconds to 40 seconds, particularly preferably 5 seconds to 40 seconds, and most preferably Is 8 to 30 seconds. Within such a range, it is possible to obtain a polyester film having excellent transparency and good crystallinity.

B. Polarizing Plate FIG. 1 is a schematic sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 includes a polarizer 10 and a polyester film 20 arranged on one side of the polarizer 10. As the polyester film 20, the polyester film of the present invention described in the above section A is used. Any other suitable polarizer protective film may be arranged on the other side of the polarizer, and the polarizer protective film may not be arranged. In one embodiment, the polarizer 10 and the polyester film 20 (or another polarizer protective film) are laminated via the adhesive layer 30.

In one embodiment, the polarizing plate may be applied to the image display device so that the side on which the polyester film is arranged is the viewing side. When the polarizing plate is applied to a liquid crystal display device, the polarizing plate including a polyester film may be arranged on the viewing side or the back side of the liquid crystal cell.

Any appropriate polarizer can be adopted as the polarizer. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of the polarizer composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) film, partially formalized PVA film, and ethylene/vinyl acetate copolymer partially saponified film. Examples thereof include polyene oriented films such as those that have been subjected to dyeing treatment and stretching treatment with a dichroic substance such as iodine or a dichroic dye, and dehydrated PVA products and dehydrochlorinated polyvinyl chloride products. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because it has excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the PVA film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment or may be performed while dyeing. Further, it may be stretched and then dyed. If necessary, the PVA-based film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment and the like. For example, by dipping the PVA-based film in water and washing it before dyeing, not only can the stains on the surface of the PVA-based film and the anti-blocking agent be washed, but also the PVA-based film can be swollen to prevent uneven dyeing. Can be prevented.

Specific examples of the polarizer obtained using the laminate include a laminate of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin. Examples thereof include a polarizer obtained by using a laminate with a PVA-based resin layer formed by coating on a base material. A polarizer obtained using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the solution. A PVA-based resin layer is formed thereon to obtain a laminate of a resin base material and a PVA-based resin layer; and the PVA-based resin layer is used as a polarizer by stretching and dyeing the laminate. obtain. In the present embodiment, the stretching typically includes dipping the laminate in a boric acid aqueous solution and stretching. Further, the stretching may further include optionally stretching the laminate in air at a high temperature (for example, 95°C or higher) before stretching in the aqueous boric acid solution. The resin base material/polarizer laminate thus obtained may be used as it is (that is, the resin base material may be used as a protective layer of the polarizer), and the resin base material is peeled from the resin base material/polarizer laminate. However, any appropriate protective layer depending on the purpose may be laminated on the peeled surface and used. The details of the method for manufacturing such a polarizer are described in, for example, JP 2012-73580 A. The entire disclosure of this publication is incorporated herein by reference.

The thickness of the polarizer is, for example, 1 μm to 80 μm. In one embodiment, the thickness of the polarizer is preferably 20 μm or less, more preferably 3 μm to 15 μm. By using the polyester film of the present invention, cracking of the polarizer can be effectively prevented, so that a thin polarizer can be used even in a severe environment such as high temperature and large temperature change.

The polarizer and the polarizer protective film (polyester film) may be laminated via any appropriate adhesive layer. Preferably, the adhesive layer is formed from an adhesive composition containing a polyvinyl alcohol resin.

In the above polarizing plate, the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction is preferably 3.5×10 ^{−. 5} /° C. or less, more preferably 3.3×10 ⁻⁵ /° C. or less, and further preferably 3.0×10 ⁻⁵ /° C. or less. Within such a range, cracking of the polarizer can be prevented even under a severe environment such as high temperature and large temperature change. The lower limit of the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction is preferably as small as possible. ^It can be ^-5 /°C.

In the above polarizing plate, the absolute value of the difference between the linear expansion coefficient of the polyester film in the second direction (the direction orthogonal to the first direction) and the linear expansion coefficient of the polarizer in the direction parallel to the second direction. Is preferably 3.5×10 ⁻⁵ /° C. or lower, more preferably 3.3×10 ⁻⁵ /° C. or lower, further preferably 3.0×10 ⁻⁵ /° C. or lower, and particularly preferably It is preferably 2.5×10 ⁻⁵ /° C. or less. Within such a range, cracking of the polarizer can be prevented even under a severe environment such as high temperature and large temperature change. The lower limit of the absolute value of the difference between the linear expansion coefficient of the polyester film in the second direction and the linear expansion coefficient of the polarizer in the direction parallel to the second direction is preferably as small as possible. ^It can be ^-5 /°C.

In one embodiment, the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction, and the second expansion coefficient of the polyester film. The absolute value of the difference between the linear expansion coefficient in the direction (direction orthogonal to the first direction) and the linear expansion coefficient in the direction parallel to the second direction of the polarizer is both 3.5×10 ^−5. /° C. or less (preferably 3.3×10 ⁻⁵ /° C. or less). Within such a range, cracking of the polarizer can be prevented even in a severe environment such as high temperature and large temperature change.

FIG. 2 is a schematic sectional view of a polarizing plate according to another embodiment of the present invention. The polarizing plate 200 further includes an easy-adhesion layer 40 arranged on the polarizer 10 side of the polyester film 20. In one embodiment, the polyester film A with an easily adhesive layer is arranged on the polarizer 10 such that the easily adhesive layer 40 is on the polarizer 10 side. As the easy-adhesion layer, the easy-adhesion layer described in the above section A can be adopted.

C. Image Display Device The polarizing plate can be applied to an image display device. Typical examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Since the image display device has a configuration well known in the industry, detailed description thereof will be omitted.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. The method of measuring each characteristic in the examples is as follows. In the examples, “parts” and “%” are based on weight unless otherwise specified.

(1) In-plane retardation Re(590)
The polyester films used in Examples and Comparative Examples were cut into a length of 5 cm and a width of 5 cm to obtain measurement samples. The in-plane retardation of the measurement sample was measured using a product name “Axoscan” manufactured by Axometrics. The measurement wavelength was 590 nm and the measurement temperature was 23°C.
(2) Coefficient of linear expansion The coefficient of linear expansion of the polyester film and the polarizer was determined to be 10°C/min from 30°C to 150°C using a thermomechanical analyzer "TMA7100" manufactured by Hitachi High-Tech Science Co., Ltd. based on JIS K 7197. The temperature was raised at a rate of and the amount of deformation of the test film at each temperature was measured. And the linear expansion coefficient of the said film was calculated|required from the deformation amount in the temperature range of 30 degreeC-70 degreeC. The case where the film size increases (expands) as the temperature rises is positive (plus), and the case where the film size decreases (shrinks) as the temperature rises is negative (minus).
For the polyester film, the linear expansion coefficients of MD (first direction) and TD (second direction) were measured. The polarizer measured the linear expansion coefficient of the polarizing plate in the direction parallel to the MD and in the direction parallel to the TD.
(3) Crystallinity The crystallinity of the polyester films used in Examples and Comparative Examples was measured by differential scanning calorimetry (DSC). The calorific value and the heat of fusion observed during the temperature rising of the sample to 300° C. at 10° C./min were calculated, and the crystallinity was calculated by the following formula. The calorific value and the heat of fusion were measured by using TA Instruments Q-2000.
Crystallinity (%)=(calorific value of heat obtained by measurement−calorific value of calorific value)/100% crystallinity Heat of fusion of polyethylene terephthalate (119 mJ/mg)×100
(4) Orientation function of polyester film (f)
For the orientation function (f) of the polyester film, a Fourier transform infrared spectrophotometer (manufactured by PerkinElmer, trade name "Frontier FT IR") is used, and polarized light is used as a measurement light, and attenuated total reflection spectroscopy (ATR) is used. It was determined by measurement.
Specifically, the measurement light (polarized light) vibrates in a direction parallel to the polyester film sample surface, and the measurement light (polarized light) vibrates in a direction orthogonal to the polyester film sample surface. It is calculated according to the following equation using the intensity I of 1340 cm ⁻¹ (crystal peak) of the obtained spectrum. Here, the intensity I, as a reference peak to 1410 cm ^-1, the value of 1340cm ^-1 / 1410cm -1.
f=(3<cos ² θ>−1)/2
_{= [(R-1) (} R 0 +2)] / [(R + 2) (R 0 -1)]
=(1-D)/[c(2D+1)]
=-2x(1-D)/(2D+1)
However,
c=(3 cos ² β-1)/2
β=90 deg
θ: Angle of molecular chain with respect to stretching direction β: Transition dipole moment with respect to molecular chain axis (β=0)
R ₀ =2cot ² β
1/R=D=(I//)/(I⊥)
I⊥: Absorption intensity when measured with the vibration direction of the measurement light (polarized light) orthogonal to the polyester film sample plane I//: With the vibration direction of the measurement light (polarized light) parallel to the polyester film sample plane Absorption intensity at the time of measurement (5) Nijimura The liquid crystal cell was taken out from the liquid crystal TV "45UH7500" manufactured by LGD, and the polarizing plate on the backlight side was peeled off. The polarizing plate obtained in each of the examples and comparative examples was attached to the surface of the liquid crystal TV from which the polarizing plate was peeled off with an adhesive agent so that the absorption axis of the polarizer was on the short side of the liquid crystal TV. It was The liquid crystal cell in which the polarizing plates obtained in Examples and Comparative Examples were stuck together was installed again, and the TV was lit in white display.
The lit liquid crystal TV was visually checked in all directions at a polar angle of 60° to observe the presence or absence of rainbow unevenness. The following criteria were evaluated.
○: No rainbow unevenness was observed
△: slight rainbow unevenness was observed
X: Rainbow unevenness was remarkably recognized (6) Dimensional change The polyester films used in Examples and Comparative Examples were cut into 100 mm x 100 mm. The size of the cut film was accurately measured using a CNC image measuring device Quick Vision (QV606) manufactured by Mitutoyo. Then, after placing in a heating oven at 100° C. for 24 hours, the film was taken out, the dimensions were accurately measured again, and the change in dimensions was obtained.
(7) Crack test (heat shock acceleration test)
The polarizing plates obtained in the examples and comparative examples were evaluated using a thermal shock tester (made by ESPEC).
The polarizing plates obtained in Examples and Comparative Examples were cut into a width of 50 mm and a length of 150 mm. At that time, the sample in which the absorption axis direction of the polarizer is parallel to the lateral direction (short side) of the polarizing plate after cutting, and the transmission axis direction of the polarizer is parallel to the lateral direction (short side) of the polarizing plate after cutting. And a sample to be manufactured. A surface of the polarizing plate on which the protective film (polyester film) was not laminated and a non-alkali glass having a thickness of 0.5 mm were bonded together via an acrylic pressure-sensitive adhesive to prepare a sample.
The obtained sample was put in the test area of the thermal shock tester, and the temperature in the test area was lowered to −40° C. over 30 minutes from room temperature. Then, after raising the temperature in the test area to 85° C. over 30 minutes, the temperature was lowered again to −40° C. over 30 minutes. The step of raising the temperature from -40°C to 85°C and lowering it again to -40°C is set as one cycle, and after repeating 100 cycles and 200 cycles, the laminated body is taken out, and the presence or absence of cracks is visually confirmed, The following criteria were evaluated.
◯: No crack was observed even after repeating 200 cycles.
B: No crack was observed after 100 cycles were repeated, but cracks were generated after 200 cycles were repeated.
X: A crack had occurred after repeating 100 cycles.

[Production Example 1] Production of polyester film A Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, IV value: 0.75 dl/g (phenol: 1,1,2,2-tetrachloroethane = 6:4 mixed solvent) Solution concentration 0.4 g/dl)) was vacuum dried at 100° C. for 10 hours, and then a single screw extruder (manufactured by Toyo Seiki Co., screw diameter 25 mm, cylinder set temperature: 280° C.), T-die (width) An amorphous polyester resin film having a thickness of 200 μm was produced by using a film forming apparatus equipped with 500 mm, setting temperature: 280° C., chill roll (setting temperature: 50° C.), and a winder.
The obtained amorphous polyester-based resin film was simultaneously biaxially stretched by a Bruckner stretching machine KAROIV to obtain a polyester film A (in-plane phase Re(590): 89 nm, thickness: 22 μm). The stretching ratio was 3 times in the length direction (MD) and 3 times in the width direction (TD). The stretching temperature was 90° C., and the stretching rate was 10%/sec for both MD and TD. Further, after the stretching treatment, heat treatment was performed at 140° C. for 10 seconds while maintaining the dimensions.

[Production Example 2] Production of Polyester Film B Polyester film B (in-plane phase Re(590): 41 nm, thickness, in the same manner as in Production Example 1 except that the stretching speed was 50%/sec for both MD and TD. : 22 μm) was obtained.

[Production Example 3] Production of polyester film C Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, isophthalic acid modification amount: 2.5 mol% (mol number relative to the total of all polymer repeating units), diethylene glycol modification amount: 1.0 mol % (Mol number relative to the total of all polymer repeating units), IV value: 0.77 dl/g (phenol: 1,1,2,2-tetrachloroethane=6:4 mixed solvent, solution concentration 0.4 g/dl) Measurement)) under vacuum drying at 100° C. for 10 hours, and then a single screw extruder (manufactured by Toyo Seiki Co., Ltd., screw diameter 25 mm, cylinder setting temperature: 280° C.), T die (width 500 mm, setting temperature: 280° C.), An amorphous polyester resin film having a thickness of 200 μm was produced by using a film forming apparatus equipped with a chill roll (set temperature: 50° C.) and a winder.
The obtained amorphous polyester-based resin film was subjected to simultaneous biaxial stretching with a Bruckner stretching machine KAROIV to obtain a polyester film C (in-plane phase Re(590): 52 nm, thickness: 22 μm). The stretching ratio was 3 times in the length direction (MD) and 3 times in the width direction (TD). The stretching temperature was 85° C., and the stretching speed was 50%/sec for both MD and TD. After the stretching treatment, heat treatment was performed at 180° C. for 10 seconds while maintaining the dimensions.

[Production Example 4] Production of Polyester Film D The stretching ratio was 2.5 times in the length direction (MD), 2.5 times in the width direction (TD), and the stretching speed was 30%/sec in both MD and TD. A polyester film D (in-plane phase Re(590): 68 nm, thickness: 35 μm) was obtained in the same manner as in Production Example 1 except for the above.

[Production Example 5] Production of polyester film E except that the stretching ratio was 4 times in the length direction (MD), 4 times in the width direction (TD), and the stretching speed was 100%/sec for both MD and TD. A polyester film D (in-plane phase Re(590): 51 nm, thickness: 20 μm) was obtained in the same manner as in Example 1.

[Production Example 6] Production of Polyester Film F Polyester film F (in-plane phase Re(590): 114 nm, thickness) was produced in the same manner as in Production Example 1 except that the stretching speed was 2%/sec for both MD and TD. : 25 μm) was obtained.

[Production Example 7] Production of Polyester Film G A polyester film G( An in-plane phase Re (590): 54 nm, thickness: 50 μm) was obtained.

[Production Example 8] Production of polyester film H Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, isophthalic acid modification amount: 6.8 mol% (mol number relative to the total of all polymer repeating units), diethylene glycol modification amount: 1.0 mol % (Mol number based on the total of all polymer repeating units), IV value 0.85 dl/g (phenol: 1,1,2,2,-tetrachloroethane=6:4 mixed solvent, measurement at solution concentration 0.4 g/dl) After vacuum drying at 100° C. for 10 hours, a single screw extruder (manufactured by Toyo Seiki Co., screw diameter 25 mm, cylinder setting temperature: 280° C.), T die (width 500 mm, setting temperature: 280° C.), chill roll ( An amorphous polyester resin film having a thickness of 200 μm was produced by using a film forming apparatus equipped with a set temperature: 50° C.) and a winder.
The obtained amorphous polyester-based resin film was simultaneously biaxially stretched with a Bruckner stretching machine KAROIV to obtain a polyester film H (in-plane phase Re(590): 110 nm, thickness: 22 μm). The stretching ratio was 3 times in the length direction (MD) and 3 times in the width direction (TD). The stretching temperature was 90° C., and the stretching rate was 10%/sec for both MD and TD. Further, after the stretching treatment, heat treatment was performed at 140° C. for 10 seconds while maintaining the dimensions.

[Production Example 9] Production of polyester film I Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, isophthalic acid modification amount: 2.5 mol% (mol number relative to the total of all polymer repeating units), diethylene glycol modification amount: 1.0 mol % (Mol number relative to the total of all polymer repeating units), IV value: 0.77 dl/g (phenol: 1,1,2,2-tetrachloroethane=6:4 mixed solvent, solution concentration 0.4 g/dl) After vacuum drying (measurement) at 100° C. for 10 hours, a single-screw extruder (manufactured by Toyo Seiki Co., screw diameter 25 mm, cylinder setting temperature: 280° C.), T die (width 500 mm, setting temperature: 280° C.), chill roll A polyester film I (in-plane phase Re(590): 17 nm, thickness: 50 μm) having a thickness of 50 μm was produced using a film forming apparatus equipped with (setting temperature: 50° C.) and a winder.

[Production Example 10] Production of Polarizer A A long roll of a polyvinyl alcohol (PVA)-based resin film (manufactured by Kuraray, product name "PE3000") having a thickness of 30 µm is 5.9 times in the longitudinal direction by a roll stretching machine. While uniaxially stretching in the longitudinal direction as described above, swelling, dyeing, crosslinking and washing treatments were simultaneously performed, and finally a drying treatment was performed to prepare a polarizer A having a thickness of 12 μm.
Specifically, the swelling treatment was carried out by stretching 2.2 times while treating with pure water at 20°C. Next, the dyeing treatment is performed in an aqueous solution at 30° C. in which the weight ratio of iodine to potassium iodide is 1:7, the iodine concentration of which is adjusted so that the obtained polarizer has a single transmittance of 45.0%. However, it was stretched 1.4 times. Further, the cross-linking treatment employs a two-step cross-linking treatment, and the first-step cross-linking treatment was carried out in an aqueous solution in which boric acid and potassium iodide were dissolved at 40° C. and stretched 1.2 times. The boric acid content and the potassium iodide content of the aqueous solution in the first-stage crosslinking treatment were 5.0% by weight and 3.0% by weight, respectively. The second-stage cross-linking treatment was carried out in an aqueous solution in which boric acid and potassium iodide were dissolved at 65° C. and stretched 1.6 times. The boric acid content of the aqueous solution for the second-stage cross-linking treatment was 4.3% by weight, and the potassium iodide content was 5.0% by weight. The washing treatment was performed with a 20° C. potassium iodide aqueous solution. The potassium iodide content of the aqueous solution for washing treatment was set to 2.6% by weight. Finally, the drying treatment was performed at 70° C. for 5 minutes to obtain Polarizer A.

[Example 1]
As the base material, an elongated isophthalic acid-copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75° C. was used. One side of the base material is corona-treated, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl modification degree 4.6) are applied to the corona-treated surface. %, saponification degree of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer (registered trademark) Z200") at a ratio of 9:1 was applied and dried at 25°C. Then, a PVA-based resin layer having a thickness of 11 μm was formed to produce a laminate.
The obtained laminate was uniaxially stretched by 2.0 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 120°C (in-air auxiliary stretching).
Then, the laminated body was immersed in an insolubilizing bath having a liquid temperature of 30° C. (boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Then, the polarizing plate was immersed in a dyeing bath having a liquid temperature of 30° C. while adjusting the iodine concentration and the immersion time so that the polarizing plate had a predetermined transmittance. In this example, 0.2 part by weight of iodine was mixed with 100 parts by weight of water, and 1.5 parts by weight of potassium iodide was mixed, and the resultant was immersed for 60 seconds in an aqueous iodine solution (dyeing treatment). ..
Then, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 30° C. (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water). (Crosslinking treatment).
Then, the laminate was immersed in an aqueous boric acid solution having a liquid temperature of 70° C. (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with 100 parts by weight of water). On the other hand, uniaxial stretching was performed between rolls having different peripheral speeds in the longitudinal direction (longitudinal direction) such that the total stretching ratio was 5.5 (underwater stretching).
After that, the laminate was immersed in a cleaning bath having a liquid temperature of 30° C. (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Further, the polyester film A produced in Production Example 1 was subjected to corona treatment, and the product name “Superflex 210R” made by Daiichi Kogyo Seiyaku Co., Ltd. 15.2 wt% and the product name “WS-700” made by Nippon Shokubai Co., Ltd. 2. An aqueous solution in which 7 wt% was dissolved was applied after drying so that the film thickness would be 300 μm, and dried at 80° C. for 1 minute to obtain a polyester film A with an easily adhesive layer.
A PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosephimmer (registered trademark) Z-200”, resin concentration: 3% by weight) is applied to the surface of the PVA-based resin layer of the above laminate, The polyester film A with the easy-adhesion layer was attached. The obtained laminate was heated in an oven maintained at 60°C for 5 minutes. Then, the substrate was peeled from the PVA-based resin layer to obtain a polarizing plate (polarizer B (transmittance 42.3%, thickness 5 μm)/protective film (polyester film)). The polyester film A and the polarizer B were laminated such that the MD direction of the polyester film A and the absorption axis direction of the polarizer were substantially parallel to each other.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Example 2]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film B obtained in Production Example 2 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Example 3]
A PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer (registered trademark) Z-200”, resin concentration: 3% by weight) was applied to one surface of the polarizer A obtained in Production Example 10. Then, the polyester film B obtained in Production Example 2 was laminated. The obtained laminate was heated for 5 minutes in an oven maintained at 60°C to obtain a polarizing plate.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Example 4]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film C obtained in Production Example 3 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Example 5]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film D produced in Production Example 4 was used instead of the polyester film A produced in Production Example 1. The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Example 6]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film E obtained in Production Example 5 was used instead of the polyester film A produced in Production Example 1. The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 1]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film F obtained in Production Example 6 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 2]
A polarizing plate was obtained in the same manner as in Example 3 except that the polyester film F obtained in Production Example 6 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 3]
A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film G obtained in Production Example 7 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 4]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film H obtained in Production Example 8 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 5]
Instead of the polyester film A produced in Production Example 1, a polyester film J (manufactured by Toyobo Co., Ltd., trade name "Cosmo Shine A4100", in-plane phase Re(590): 7800 nm, thickness: 75 μm) was used, A polarizing plate was obtained in the same manner as in Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 6]
A polyester film K (manufactured by Mitsubishi Chemical Corporation, trade name “T100-J25”, in-plane phase Re(590): 525 nm, thickness: 25 μm) was used instead of the polyester film A manufactured in Production Example 1. A polarizing plate was obtained in the same manner as in Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

[Comparative Example 7]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film I obtained in Production Example 9 was used instead of the polyester film A produced in Production Example 1.
The obtained polarizing plate was subjected to the above evaluations (2) to (7). The results are shown in Table 1.

10 Polarizer 20 Polyester Film 30 Adhesive Layer 40 Easy Adhesive Layer 100, 200 Polarizing Plate

Claims (13)

The in-plane retardation Re(590) is 100 nm or less,
The linear expansion coefficient in the first direction is 0/° C. to 4.0×10 ⁻⁵ /° C.,
Polyester film. The absolute value of the difference between the linear expansion coefficient in the first direction and the linear expansion coefficient in the second direction orthogonal to the first direction is 1.0×10 ⁻⁵ /° C. or less. 1. The polyester film according to 1. The polyester film according to claim 1 or 2, which has an orientation function (f) of 0.01 to 0.24. The polyester film according to claim 1, wherein the polyester film is formed of polyethylene terephthalate and/or modified polyethylene terephthalate. The polyester film according to claim 4, wherein the modified polyethylene terephthalate contains a constitutional unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid. The polyester film according to claim 1, which has a crystallinity of 30% or more as measured by DSC. A polarizing plate comprising a polarizer and the polyester film according to claim 1, which is disposed on one side of the polarizer. The absolute value of the difference between the coefficient of linear expansion of the polyester film in the first direction and the coefficient of linear expansion of the polarizer in a direction parallel to the first direction, and orthogonal to the first direction of the polyester film The absolute value of the difference between the linear expansion coefficient in the second direction and the linear expansion coefficient of the polarizer in the direction parallel to the second direction is both 3.5×10 ⁻⁵ /° C. or less. Item 7. A polarizing plate according to item 7. The polarizing plate according to claim 8, wherein the polarizer has a thickness of 20 μm or less. The polarizing plate according to claim 7, further comprising an easy-adhesion layer arranged on the polarizer side of the polyester film. The polarizing plate according to claim 10, wherein the easy-adhesion layer contains fine particles. The polarizing plate according to claim 10 or 11, wherein the easily adhesive layer has a thickness of 0.35 µm or less. The polarizing plate according to claim 10, wherein the easy-adhesion layer has a refractive index of 1.55 or less.

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