TW202030239A - Polyester film, and polarizing plate comprising polyester film - Google Patents

Abstract

Provided is a polyester film with which little rainbow unevenness occurs when applied to an image display device and which can contribute to improving the durability of a polarizing plate. A polyester film, according to the present invention, has a linear expansion coefficient in a first direction of not more than 3.5*10-5/DEG C, a linear expansion coefficient in a second direction that is orthogonal to the first direction of not more than 3.5*10-5/DEG C, and has a slow axis in a direction that is -5 DEG to 5 DEG relative to the first direction.

Description

Polyester film and polarizing plate containing the polyester film

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

Background of the invention

In image display devices (such as liquid crystal display devices, organic EL display devices), in most cases, a polarizing plate is arranged on at least one side of the display unit due to the image forming method. In recent years, there has been a trend toward more diversified functions and uses of image display devices, and there is an increasing demand for being able to withstand use in more severe environments. The polarizing plate generally has a structure in which a polarizer is sandwiched between two protective films, and the protective film is widely used with triacetyl cellulose, acrylic resin, cycloolefin resin, etc. On the other hand, from the viewpoint of durability as mentioned above, for example, there have been proposals to use mechanical properties and chemical resistance such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). A polyester film excellent in flexibility and moisture barrier properties is used as a polarizer protective film (for example, Patent Document 1). However, although polyester films have excellent mechanical properties, relatively they have birefringence and become a cause of deterioration in visibility such as rainbow lines. In particular, with the increase in brightness and color purity of image display devices in recent years, this kind of rainbow pattern problem has become prominent.

On the other hand, a polarizing plate made of a protective film made of triacetyl cellulose, acrylic resin, or cycloolefin resin, which is commonly used in the past, may crack in the polarizer due to temperature changes. In recent years, with the thinning of image display devices, thinner polarizers have been required. On the other hand, the number of image display devices that are preset to be used at high temperatures has greatly increased. Among them, there is an urgent need for the durability of the polarizers without cracks. Excellent polarizing plate.

Prior art literature Patent literature Patent Document 1: Japanese Patent Application Laid-Open No. 8-271733

Summary of the invention Problems to be solved by the invention The present invention was made to solve the above-mentioned conventional problems, and its main purpose is to provide a polyester film that produces less rainbow patterns when applied to an image display device and can contribute to improving the durability of a polarizing plate.

Means to Solve the Problem The polyester film of the present invention has a linear expansion coefficient of 3.5×10 ^-5 /°C or less in the first direction, and a linear expansion coefficient of 3.5× in a second direction perpendicular to the first direction. 10 ^-5 /℃ or less, and has a slow axis in the direction of -5°~5° with respect to the first direction. In one embodiment, the crystallinity of the polyester film measured by DSC is 30% or more. According to another aspect of the present invention, a polarizing plate can be provided. The polarizing plate includes a polarizing member and a polyester film such as claim 1 or 2 arranged on one side of the polarizing member. In one embodiment, the thickness of the above-mentioned polarizer is 20 μm or less. In one embodiment, the polarizing plate further includes an easy-adhesive layer, and the easy-adhesive layer is arranged on the polarizer side of the polyester film. In one embodiment, the easily bonding layer contains fine particles. In one embodiment, the thickness of the easily bonding layer is 0.35 µm or less. In one embodiment, the refractive index of the easily bonding layer is 1.55 or less.

Invention effect According to the present invention, it is possible to provide a polyester film which, by selectively reducing the linear expansion coefficient in a predetermined direction, can reduce the occurrence of rainbow patterns when combined with a polarizer, and can help to improve the polarizing plate The durability.

The form used to implement the invention The preferred embodiments of the present invention are described below, but the present invention is not limited by these embodiments.

A. Polyester film The linear expansion coefficient of the polyester film of the present invention in the first direction is 3.5×10 ^-5 /℃ or less, and the linear expansion coefficient in the second direction perpendicular to the first direction is 3.5×10 Below ^-5 /℃. If a polyester film with such a linear expansion coefficient is used, it can be laminated on the polarizer to effectively protect the polarizer and at the same time prevent the polarizer from cracking. In more detail, if the polyester film of the present invention is used as a polarizer protective film and laminated on a polarizer to form a polarizing plate, the polyester film can be used to suppress the dimensional change of the polarizer (such as dimensional change due to heat) ). As a result, if the polyester film of the present invention is used, it is possible to obtain a polarizing plate that can prevent cracks in the polarizer and has excellent durability even under severe environments such as high temperature and large temperature changes. In one embodiment, the above-mentioned first direction corresponds to the conveying direction (MD) when producing a polyester film. In addition, the above-mentioned second direction may correspond to TD perpendicular to MD. The coefficient of linear expansion can be determined by TMA measurement in accordance with JIS K 7197. In addition, the expression "slightly parallel" includes the case where the angle formed by the two directions is 0°±10°, and it is preferably 0°±7°, and more preferably 0°±5°.

The polyester film of the present invention has a slow axis in a direction of -5° to 5° with respect to the first direction. If it is in the above range, a polyester film with less rainbow patterns can be produced when combined with a polarizer. In more detail, as described above, when the polarizer and the polyester film are laminated so that the absorption axis of the polarizer is slightly parallel to the first direction to form a polarizer, rainbow stripes can be effectively prevented.

The angle between the first direction and the slow axis is preferably -3°~3°, more preferably -1°~1°, particularly preferably -0.5°~0.5°, and most preferably 0°. If it is within the range, the above-mentioned effect becomes more significant.

The linear expansion coefficient of the polyester film in the first direction is preferably 3.0×10 ^-5 /°C or less, preferably 2.5×10 ^-5 /°C or less, more preferably 1.5×10 ^-5 /°C or less, especially It is 1.3×10 ^-5 /℃ or less. If it is within the range, the above-mentioned effect becomes more significant. The linear expansion coefficient of the polyester film in the first direction is as small as possible, and its lower limit is, for example, 0.3×10 ^-5 /℃ (preferably 0.1×10 ^-5 /℃, and preferably 0×10 ^-5 / ℃).

The linear expansion coefficient of the above-mentioned polyester film in the second direction is preferably 3.4×10 ^-5 /°C or less, and more preferably 2.3×10 ^-5 /°C or less. If it is within the range, the above-mentioned effect becomes more significant. The linear expansion coefficient of the polyester film in the first direction is as small as possible. The lower limit is, for example, 1×10 ^-5 /℃ (preferably 0.5×10 ^-5 /℃, and preferably 0.3×10 ^-5 / ℃).

Representatively, the aforementioned polyester film may be a stretched film obtained through a stretching step. By appropriately adjusting the manufacturing conditions in the stretching step, the linear expansion coefficients in the first and second directions (and the in-plane phase difference Re (590) described later) can be well controlled. As a result, the rainbow A polyester film with excellent characteristics from the standpoint of grain and durability is used as a polarizer protective film. The above manufacturing conditions can include elongation conditions (extension temperature, extension ratio, extension speed, MD/TD extension sequence), preheat temperature before extension, heat treatment temperature after extension, heat treatment time after extension, MD/TD after extension The relaxation rate of the direction, etc. Extension temperature, extension ratio and extension speed can be adjusted appropriately according to MD/TD.

The in-plane retardation Re (590) of the polyester film is, for example, greater than 0 nm and 10000 nm or less. In addition, the in-plane retardation Re(λ) is the in-plane retardation of the film measured at 23°C with light of wavelength λnm. Therefore, Re (590) is the in-plane retardation of the film measured by light with a wavelength of 590 nm. Re(λ) is obtained by using the formula: Re(λ)=(nx-ny)×d when the film thickness is d(nm). Here, nx is the refractive index in the direction in which the refractive index in the plane is the maximum (ie, the slow axis direction), and ny is the refractive index in the direction perpendicular to the slow axis in the plane.

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

The thickness of the above polyester film is typically 10µm~100µm, preferably 20µm~80µm, and more preferably 20µm~50µm.

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

The moisture permeability of the polyester film is preferably 100g/m ² ·24hr or less, more preferably 50g/m ² ·24hr or less, and more preferably 15g/m ² ·24hr or less. If it is within the above range, a polarizing plate having excellent durability and moisture resistance can be produced.

The polyester film of the present invention is formed of 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 aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalenedicarboxylic acid, biphthalic acid, 4,4'-oxybenzoic acid, 2,5 -Naphthalene dicarboxylic acid. Aliphatic dicarboxylic acids include, for example, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid Acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, thiodipropionic acid, glycolic acid. The alicyclic dicarboxylic acid may include, for example, 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexane dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 2 , 5-Norbornane dicarboxylic acid, adamantane dicarboxylic acid. The carboxylic acid component can also be derivatives such as esters, chlorides, and acid anhydrides, including, for example, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 2,6-naphthalate, and dimethyl isophthalate. Esters, dimethyl terephthalate and diphenyl terephthalate. The carboxylic acid component may be used alone or in combination of two or more kinds.

As for the polyol component, diols are representatively mentioned. Examples of diols include aliphatic diols, alicyclic diols, and aromatic diols. Aliphatic diols include, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexyl-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-butadiene, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanedione, 3-methyl-1,5-pentadiene Alcohol, 2,2,4-trimethyl-1,6-hexanediol. The cycloaliphatic diols include, for example, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycerin, tricyclodecanedimethanol, diamond Alkanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Aromatic diols include, for example, 4,4'-thiodiol, 4,4'-methylene diol, 4,4'-(2-norbornanyl) diol, 4,4'-diphenol Hydroxy bisphenol, o/m/p-dihydroxybenzene, 4,4'-isopropylidene phenol, 4,4'-isopropylidene bis(2,6-cyclophenyl) 2,5-naphthalenediol And p-xylene glycol. The polyol component may be used alone or in combination of two or more kinds.

The polyester resin is preferably polyethylene terephthalate and/or modified polyethylene terephthalate, and more preferably polyethylene terephthalate. If these resins are used, a polyester film with good mechanical properties and less rainbow patterns can be produced. Polyethylene terephthalate and modified polyethylene terephthalate can be blended and used.

Examples of the modified polyethylene terephthalate include modified polyethylene terephthalate containing structural units derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid Diester. The ratio of diethylene glycol in the polyol component should be more than 0 mol% and less than 10 mol%, more preferably more than 0 mol% and less than 3 mol%. The ratio of 1,4-butanediol in the polyol component is preferably greater than 0 mol% and less than 10 mol%, more preferably greater than 0 mol% and less than 3 mol%. The ratio of 1,3-propanediol in the polyol component should preferably exceed 0 mol% and be below 10 mol%, and more preferably be more than 0 mol% and below 3 mol%. The ratio of isophthalic acid in the carboxylic acid component is preferably greater than 0 mol% and less than 10 mol%, more preferably greater than 0 mol% and less than 8 mol%. If it is within the above range, a polyester film with good crystallinity can be obtained. In addition, the molar% described above is the molar% relative to the total of the total repeating units of the polymer.

The weight average molecular weight of the polyester resin is preferably 10,000 to 100,000, preferably 20,000 to 75,000. If it is such a weight average molecular weight, handling at the time of forming is easy, and a film having excellent mechanical strength can be obtained. The weight average molecular weight can be measured by GPC (solvent: THF).

In one embodiment, a polyester film with an adhesive layer is provided. The easy bonding layer contains, for example, an aqueous polyurethane and an azoline-based crosslinking agent. The details of the easy bonding layer are described in, for example, Japanese Patent Laid-Open No. 2010-55062. In this specification, the entire description of the gazette is used as a reference.

In one embodiment, the easily bonding layer contains arbitrary and appropriate fine particles. By forming an easy-to-adhesive layer containing fine particles, it can effectively inhibit adhesion during winding. The above-mentioned fine particles may be inorganic fine particles or organic fine particles. Inorganic particles include inorganic oxides such as silica, titania, alumina, zirconia, calcium carbonate, talc, clay, calcined kaolinite, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, and silicon Magnesium acid, calcium phosphate, etc. Examples of organic fine particles include silicone resins, fluorine resins, and (meth)acrylic resins. Among these, silicon dioxide is suitable.

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

The thickness of the aforementioned easy-to-bond layer is preferably 2 µm or less, more preferably 1 µm or less, and more preferably 0.35 µm or less. If it is in the above range, a polyester film with an easy-to-adhesion layer that is not easy to hinder the optical properties of other members when applied to an image display device can be produced.

In one embodiment, the refractive index of the easily bonding layer is preferably 1.45 to 1.60. If it is in the above range, a polyester film with an easy-to-adhesion layer that is not easy to hinder the optical properties of other members when applied to an image display device can be produced. In one embodiment, the refractive index of the easily bonding layer is 1.54 or more.

In one embodiment, the polyester film is provided with an anti-blocking layer on at least one side thereof. The composition of the anti-blocking layer can adopt the composition of the easy bonding layer described above. Ideally, the anti-caking layer contains the above-mentioned fine particles.

(Method of manufacturing polyester film) The polyester film can be obtained through the following steps: a forming step of forming a film-forming material (resin composition) containing the polyester resin into a film; and a step of extending the formed film. The stretching step preferably includes: pre-heat treatment of the film before stretching and heat treatment after the stretching of the film. In one embodiment, the polyester film is provided in a long strip (or a shape cut from a long strip).

In addition to the above-mentioned polyester resin, the film forming material may contain additives or a solvent. Additives can use arbitrary and appropriate additives according to the purpose. Specific examples of additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, anti-aging agents, ultraviolet absorbers, leveling agents, thixotropic agents, antistatic agents, conductive agents, flame retardants Agent. The number, type, combination, amount of additives, etc. can be appropriately set according to the purpose.

As the method of forming a thin film from a thin film forming material, an arbitrary and appropriate forming processing method can be adopted. Specific examples include compression molding methods, transfer molding methods, injection molding methods, extrusion molding methods, blow molding methods, powder molding methods, FRP molding methods, casting coating methods (such as flow casting methods), and calender molding methods. , Hot pressing method, etc. The extrusion method or casting coating method is suitable. The cover can improve the smoothness of the obtained film and obtain good optical uniformity.

The stretching method of the film can be uniaxial stretching or biaxial stretching.

In one embodiment, the stretching method of the above-mentioned film may adopt uniaxial stretching and extend along the length direction (MD) of the above-mentioned film.

The biaxial extension can be a sequential biaxial extension or a synchronous biaxial extension. Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter stretching machine. Therefore, the extension direction of the film is typically the length direction (MD) and the width direction (TD) of the film.

In one embodiment, the stretching method of the above-mentioned film may adopt successive biaxial stretching. It is better to perform MD stretching after TD stretching to obtain the above polyester film. In this way, the influence of bowing generated during TD stretching can be alleviated, and the angle formed between the first direction (MD) of the polyester film and the slow axis can be set to an appropriate value.

The stretching temperature should be Tg+5℃~Tg+50℃ relative to the glass transition temperature (Tg) of the film, and Tg+5℃~Tg+30℃ is better, and Tg+6℃~Tg+10℃ is better. Stretching at such a temperature, a polyester film with balanced control of the slow axis direction and linear expansion coefficient can be obtained. It can also produce polyester film with good transparency.

The extension ratio of MD is preferably 1 to 7 times, preferably 2.5 to 6.5 times, more preferably 3 to 6 times. If it is within the above range, a polyester film with a linear expansion coefficient falling within a desired range while having good crystallinity and excellent durability can be obtained.

The extension ratio of TD is preferably 1 to 7 times, preferably 1.2 to 4 times, and more preferably 1.5 to 3.5 times. If it is within the above range, a polyester film with a linear expansion coefficient falling within a desired range while having good crystallinity and excellent durability can be obtained.

The ratio of TD extension ratio to MD extension ratio (MD extension ratio/TD extension ratio) is preferably 1~4, more preferably 1~2. If it is in the above range, a polyester film with extremely few rainbow patterns can be produced. Furthermore, if the obtained polyester film is used, it is possible to prevent cracks in the polarizer and obtain a polarizing plate with excellent durability.

The extension speed of MD is preferably 5%/sec～100%/sec, more preferably 8%/sec～80%/sec, and more preferably 8%/sec～60%/sec. If it is within the above range, a polyester film having excellent optical properties, good crystallinity, and excellent durability can be obtained.

The extension speed of TD should be 5%/sec~100%/sec, more preferably 8%/sec~80%/sec, and more preferably 8%/sec~60%/sec. If it is within the above range, a polyester film having excellent optical properties, good crystallinity, and excellent durability can be obtained.

The temperature of the pre-heat treatment should be 80℃~150℃, more preferably 90℃~130℃. In addition, the preheat treatment time is preferably 10 seconds to 100 seconds, and more preferably 15 seconds to 80 seconds. If it is within the above range, a polyester film having excellent optical properties, good crystallinity, and excellent durability can be obtained.

The heat treatment temperature should be 100°C~250°C, more preferably 120°C~200°C, and more preferably 130°C~180°C. Within the above range, a polyester film having excellent transparency, good crystallinity, and excellent durability can be obtained. The heat treatment time is preferably 2 seconds to 50 seconds, preferably 5 seconds to 40 seconds, and more preferably 8 seconds to 30 seconds. Within the above range, a polyester film having excellent transparency, good crystallinity, and excellent durability can be obtained.

B. Polarizing plate Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes a polarizing member 10 and a polyester film 20 arranged on one side of the polarizing member 10. As the polyester film 20, the polyester film of the present invention described in the above item A can be used. Arbitrary and appropriate another polarizer protective film can be arranged on the other side of the polarizer, or no polarizer protective film can be arranged. In one embodiment, the polarizer 10 and the polyester film 20 (or another polarizer protective film) are laminated through the adhesive layer 30.

In one embodiment, the polarizing plate may be applied to an image display device in such a way that the side on which the polyester film is disposed is the visual side. In addition, when the above-mentioned polarizing plate is applied to a liquid crystal display device, the polarizing plate provided with a polyester film can be arranged on the viewing side of the liquid crystal cell or on the back side.

The polarizing member can be any and appropriate polarizing member. 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 polarizers composed of a single-layer resin film include polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, ethylene and vinyl acetate using dichroic substances such as iodine or dichroic dyes. Hydrophilic polymer films such as ester copolymer partially saponified films are dyed and stretched, and polyene-based oriented films such as dehydrated PVA or dehydrated polyvinyl chloride. From the viewpoint of excellent optical properties, it is preferable to use a polarizer obtained by dyeing a PVA-based film with iodine and performing uniaxial stretching.

The above-mentioned dyeing with iodine can be performed, for example, by immersing a PVA-based film in an iodine aqueous solution. The stretching ratio of the above uniaxial stretching is preferably 3~7 times. The extension can be carried out after the dyeing treatment or at the same time as the dyeing. Also, it can be dyed after stretching. PVA-based films can be subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, etc. according to demand. For example, immersing a PVA-based film in water for washing before dyeing can not only clean the dirt and anti-blocking agent on the surface of the PVA-based film, but also swell the PVA-based film to prevent uneven dyeing.

Specific examples of polarizers obtained by using a laminate include a laminate of a resin substrate and a PVA resin layer (PVA resin film) laminated on the resin substrate, or a laminate formed using a resin substrate and coating The polarizer obtained by the laminate of the PVA-based resin layer of the resin substrate. The polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate can be produced by, for example, the following procedure: Coating the PVA-based resin solution on the resin substrate and making This is dried to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; the laminate is extended and dyed to form the PVA-based resin layer into a polarizer. In this embodiment, the stretching means includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, if necessary, stretching may further include stretching the laminate in the air at a high temperature (for example, 95° C. or higher) before stretching in a boric acid aqueous solution. The obtained resin substrate/polarizer laminate can be used directly (that is, the resin substrate can be used as the protective layer of the polarizer), or the resin substrate can be peeled from the resin substrate/polarizer laminate and the peeled area An arbitrary and appropriate protective layer for the purpose is used later. The details of the manufacturing method of the polarizer are described in, for example, Japanese Patent Laid-Open No. 2012-73580. In this specification, the entire description of the gazette is used as a 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. If the polyester film of the present invention is used, the polarizer can be effectively prevented from cracking, so even in severe environments such as high temperature and large temperature changes, thin polarizers can be used.

The polarizer and the polarizer protective film (polyester film) can be laminated through an arbitrary and appropriate adhesive layer. Ideally, the adhesive layer is formed of an adhesive composition containing polyvinyl alcohol-based resin.

The direction of the absorption axis of the polarizer is preferably slightly parallel to the first direction (representing MD) or the second direction (representing TD) of the polyester film, and preferably slightly parallel to the first direction (representing MD) . With such a structure, the polyester film and the polarizing member will be in the same tune and can undergo an ideal shape change. As a result, cracks of the polarizing member are prevented.

The more consistent the angle between the slow axis angle of the polyester film and the direction of the absorption axis of the polarizer, the better. The angle formed by the two axes is preferably 0°±10°, preferably 0°±7°, and more preferably 0° ±5°. If it is in the above range, a polyester film with less rainbow patterns can be produced when applied to an image display device. In addition, the slow axis angle is the angle when the flow direction of the roller is set to 0°.

In the above-mentioned 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 2.0×10 ^-5 /℃ or less , Preferably below 1.5×10 ^-5 /℃, more preferably below 1.0×10 ^-5 /℃. If it is within this range, even in severe environments such as high temperature and large temperature changes, the polarizer can still be prevented from cracking. 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 the smaller the better, for example, it can be 0.1×10 ^-5 /℃ .

In the above-mentioned polarizing plate, the absolute value of the difference between the linear expansion coefficient of the polyester film in the second direction (the direction perpendicular to the first direction) and the linear expansion coefficient of the polarizer in the direction parallel to the second direction is preferable It is below 2.0×10 ^-5 /℃, preferably below 1.5×10 ^-5 /℃, and more preferably below 1.0×10 ^-5 /℃. If it is within this range, even in severe environments such as high temperature and large temperature changes, the polarizer can still be prevented from cracking. 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, the smaller the better, for example, it can be 0.1×10 ^-5 /℃ .

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 in the second direction ( The absolute value of the difference between the coefficient of linear expansion in the direction perpendicular to the first direction and the coefficient of linear expansion in the direction parallel to the second direction of the polarizer is both 2.0×10 ^-5 /℃ or less (preferably 1.0 ×10 ^-5 /℃ below). If it is within this range, the polarizer can still be prevented from cracking even in severe environments such as high temperature and large temperature changes.

Fig. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention. The polarizing plate 200 includes an easy-to-bond layer 40 which is arranged on the polarizer 10 side of the polyester film 20. In one embodiment, the polyester film A with an easy-adhesive layer is arranged on the polarizer 10 so that the easy-adhesive layer 40 is on the side of the polarizer 10. The easy adhesion layer can be the easy adhesion layer described in item A above.

C. Image display device The above-mentioned polarizing plate can be applied to an image display device. Representative examples of image display devices include liquid crystal display devices and organic electroluminescence (EL) display devices. The image display device can adopt a structure well known in the industry, so detailed description is omitted.

Example Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measurement methods of each characteristic in the examples are as follows. In addition, as long as there is no special note, "parts" and "%" in the examples are based on weight.

(1) Orientation angle (showing direction of slow axis) The central part of the polyester film obtained in the Example and the comparative example was cut into a square with a width of 50 mm and a length of 50 mm so that one side was parallel to the width direction of the film, and a sample was prepared. This sample was measured using a Muller matrix polarizer (manufactured by Axometrics, trade name "Axoscan"), and the orientation angle θ at a wavelength of 550 nm and 23°C was measured. In addition, the orientation angle θ is measured with the sample placed in parallel on the measurement table. (2) Linear expansion coefficient The coefficient of linear expansion of polyester film and polarizer is measured according to JIS K 7197, using a thermomechanical analyzer "TMA7000" manufactured by Hitachi High-Tech Co., Ltd., at a rate of 10°C/min from 30°C to 150°C. The amount of deformation of the film at various temperatures. Then, the linear expansion coefficient of the film is calculated from the amount of deformation in the temperature range of 30°C to 70°C. In addition, as the temperature rises, the film size becomes larger (expands), it is positive (plus sign); as the temperature rises, the film size becomes smaller (shrink), it becomes negative (minus sign). The MD (first direction) and TD (second direction) coefficients of linear expansion were measured for polyester films. The polarizer measures the linear expansion coefficient in the direction parallel to the MD and the direction parallel to the TD in the polarizer. (3) Crystallinity Differential scanning calorimetry (DSC) was used to measure the crystallinity of the polyester films used in the examples and comparative examples. Obtain the observed exothermic heat and heat of fusion during the temperature increase at 10°C/min to 300°C, and obtain the crystallinity according to the following formula. In addition, the measurement of heat release and heat of fusion was performed using Q-2000 manufactured by TA instruments. Crystallinity (%) = (measured heat of fusion-measured heat of exotherm) / crystallinity 100% polyethylene terephthalate's heat of fusion (119mJ/mg) × 100 (4) Rainbow pattern Take out the LCD unit from the LCD TV "45UH7500" made by LGD, and peel off the polarizing plate on the backlight side. In such a way that the absorption axis of the polarizer becomes the short side of the liquid crystal TV, the polarizing plates obtained in the examples and the comparative examples are bonded to the surface of the liquid crystal TV with the polarizing plate removed through an adhesive. After re-installing the liquid crystal cell on which the polarizing plate obtained in the embodiment and the comparative example have been laminated, the TV is lit with a white screen. At the polar angle of 60° of the lit LCD TV, perform all-round visual confirmation to observe whether there are rainbow patterns. The evaluation is based on the following benchmarks. ○: No rainbow pattern is observed △: Some rainbow patterns are observed ×: Rainbow patterns are clearly observed (5) Size change The polyester films used in the examples and the comparative examples were cut into 100mm×100mm. Then, put it in a heating oven at 100°C for 24 hours, take out the film and measure the size accurately again, confirm the size with an iron ruler, and obtain the change in size. Then visually confirm the state of the sample and evaluate it according to the following criteria. ○: No significant shrinkage above 1mm ×: There is shrinkage or deformation of 1mm or more (6) Crack test (thermal shock accelerated test) The polarizing plates produced in the examples and comparative examples were evaluated using a thermal shock tester (manufactured by ESPEC). The polarizing plates obtained in the Examples and Comparative Examples were cut into 50 mm width x 150 mm length. At this time, make the following samples: the absorption axis of the polarizer is parallel to the transverse direction (short side) of the polarizing plate after cutting; and the transmission axis of the polarizer is the same as that of the cut polarizer. The specimen with the transverse direction (short side) parallel. Laminate the non-protective film (polyester film) of the polarizing plate and 0.5mm thick non-alkaline glass through acrylic adhesive to make a sample. Put the obtained sample into the test area of the thermal shock tester, and cool the test area from room temperature to -40°C in 30 minutes. Then, the temperature in the test area was raised to 85°C in 30 minutes, and then the temperature was lowered to -40°C in 30 minutes. The step of raising the temperature from -40°C to 85°C and then lowering the temperature to -40°C is set as 1 cycle. After 100 cycles and 200 cycles are repeated, the laminate is taken out and visually confirmed for cracks, and evaluated according to the following criteria . ⊚: No cracks were observed even after 300 cycles. ○: No cracks were observed after repeated 200 cycles, but cracks were generated after repeated 300 cycles. △: No cracks were observed after 100 cycles, but cracks occurred after 200 cycles. ×: Cracks occurred after 100 cycles were repeated.

[Production Example 1] Production of Polarizer A The base material is an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100µm) with a water absorption rate of 0.75% and a Tg of 75°C. Apply corona treatment on one side of the substrate, and coat the corona treated surface at 25°C with a ratio of 9:1 containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and ethyl acetate Aqueous solution of modified PVA (polymerization degree 1200, acetyl acetyl modification degree 4.6%, saponification degree 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") and then dried, A PVA-based resin layer with a thickness of 11 µm is formed to produce a laminate. In an oven at 120°C, the resulting laminate was uniaxially stretched to 2.0 times in the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds (air-assisted stretch). Next, the layered body was immersed in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30°C for 30 seconds (insolubilization treatment). Next, while immersing in a dyeing bath with a liquid temperature of 30°C, the iodine concentration and immersion time were adjusted so that the polarizing plate had a predetermined transmittance. In this example, it was immersed in an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water for 60 seconds (dyeing treatment). Next, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30°C for 30 seconds (crosslinking treatment). Then, while immersing the layered body in an aqueous solution of boric acid at 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 respect to 100 parts by weight of water), rolls with different peripheral speeds The tube is stretched uniaxially (underwater stretch) in the longitudinal direction (long side direction) so that the total stretch magnification becomes 5.5 times. Then, the laminate was immersed in a washing bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water with a liquid temperature of 30°C) (washing treatment) to obtain a polarizer A with a peelable substrate.

[Production Example 2] Production of Polarizer B A polarizer B with a peelable substrate was produced in the same manner as in Production Example 1, except that the stretching ratio of the underwater stretching was set to 4.6 times.

[Production example 3] Production of polyester film A Modified polyester resin (polyethylene terephthalate, manufactured by Dabell Polyester Products Co., Ltd., isophthalic acid to 2.5 mol% (the number of moles relative to the total polymer repeating unit), and diethylene glycol to mass ：1.0mol% (the number of moles relative to the total repeating units of the polymer), IV value 0.77dl/g (phenol: 1,1,2,2-tetrachloroethane=6:4 mixed solvent solution concentration 0.4g /dl) After vacuum drying at 100°C for 10 hours, use a uniaxial extruder (manufactured by Toyo Seiki Co., Ltd., screw diameter 25mm, cylinder set temperature: 280°C), T mold (width 500mm, set temperature: 280 ℃), cooling roll (set temperature: 50℃), and the film forming device of the coiler to produce an amorphous polyester resin film with a thickness of 200µm. The obtained amorphous polyester resin film was stretched synchronously biaxially using the stretcher KAROIV manufactured by Brückner Co., to obtain a polyester film A (slow axis angle with respect to the longitudinal direction: -0.5°, in-plane retardation Re( 590): thickness 80nm, thickness: 17µm). The stretch magnification was set to 4 times in the longitudinal direction (MD) and 3 times in the width direction (TD). The extension temperature is set to 90℃, and the extension speed is set to 30%/sec for both MD and TD. In addition, after the stretching treatment, while maintaining the size, a heat treatment was performed at 180°C for 10 seconds.

[Production Example 4] Production of polyester film I Polyester resin (polyethylene terephthalate, manufactured by Daejong Polyester Products Co., Ltd., IV value 0.75dl/g (phenol: 1,1,2,2-tetrachloroethane = 6:4 mixed solvent solution concentration 0.4g/dl) After vacuum drying at 100°C for 10 hours, use a single-axis extruder (manufactured by Toyo Seiki Co., Ltd., screw diameter length 25mm, cylinder set temperature: 280°C), T mold (width 500mm, set temperature : 280°C), cooling roll (set temperature: 50°C), and film-making device of the coiler to produce an amorphous polyester resin film with a thickness of 200µm. The obtained amorphous polyester resin film was stretched synchronously biaxially using the stretching machine KAROIV manufactured by Brückner Co., to obtain a polyester film I (the slow axis angle with respect to the longitudinal direction: -2.5°, the in-plane retardation Re( 590): 271nm, thickness: 22µm). The stretch magnification is 3 times in the longitudinal direction (MD) and 3 times in the width direction (TD). The extension temperature is set to 90℃, and the extension speed is set to 2%/sec for both MD and TD. In addition, after the stretching treatment, while maintaining the size, a heat treatment was performed at 140°C for 10 seconds.

[Production Example 5] Production of polyester film II Set the stretching ratio to 2 times in the length direction (MD) and 2 times in the width direction (TD), set the stretching speed to both MD and TD at 2%/sec, and heat treatment at 140°C for 10 seconds after the stretching treatment Except for this, a polyester film II (slow axis angle with respect to the longitudinal direction: -11.9°, in-plane phase Re (590): 54 nm, thickness: 50 µm) was produced in the same manner as in Production Example 4 except for this.

[Production Example 6] Production of polyester film III Set the extension ratio to 6 times in the length direction (MD) and 1 time in the width direction (TD) by using the fixed end extension, set the extension speed to both MD and TD at 2%/sec, and heat treatment at 140°C after the extension treatment For 10 seconds, except for this, a polyester film III was produced in the same manner as in Production Example 4 (slow axis angle with respect to the longitudinal direction: -0.6°, in-plane retardation Re(590): 2823 nm, thickness: 41 µm).

[Production Example 7] Production of polyester film IV Modified polyester resin (polyethylene terephthalate, manufactured by Dabell Polyester Products Co., Ltd., isophthalic acid to 2.5 mol% (the number of moles relative to the total polymer repeating unit), and diethylene glycol to mass ：1.0mol% (the number of moles relative to the total repeating units of the polymer), IV value 0.77dl/g (phenol: 1,1,2,2-tetrachloroethane=6:4 mixed solvent solution concentration 0.4g /dl) After vacuum drying at 100°C for 10 hours, use a uniaxial extruder (manufactured by Toyo Seiki Co., Ltd., screw diameter 25mm, cylinder set temperature: 280°C), T mold (width 500mm, set temperature: 280 ℃), cooling roll (set temperature: 50℃), and the film forming device of the coiler, to produce an amorphous polyester resin film with a thickness of 100µm. The obtained amorphous polyester-based resin film was stretched simultaneously biaxially with the stretcher KAROIV manufactured by Brückner, to prepare a polyester film IV (the slow axis angle with respect to the longitudinal direction: -0.9°, the in-plane retardation Re( 590): thickness of 3191nm, thickness: 38μm). The stretch magnification is set to 7 times in the length direction (MD) and 1 time in the width direction (TD) with the fixed end extended. The extension temperature is set to 90℃, and the extension speed is set to 10%/sec for both MD and TD. In addition, after the stretching treatment, while maintaining the size, a heat treatment was performed at 140°C for 10 seconds.

[Production Example 8] Production of polyester film V A polyester film V was produced in the same manner as in Production Example 7 except that the film thickness was set to 50 µm and no stretching was performed (the slow axis angle with respect to the longitudinal direction: 3.0°, the in-plane retardation Re(590): 17 nm , Thickness: 50µm).

[Production Example 9] Production of polyester film VI Modified polyester resin (polyethylene terephthalate, manufactured by Dabell Polyester Products Co., Ltd., isophthalic acid to 2.5 mol% (the number of moles relative to the total polymer repeating units), IV value 0.77dl/g (Phenol: 1,1,2,2-tetrachloroethane = 6:4 mixed solvent solution concentration 0.4g/dl) After vacuum drying at 100°C for 10 hours, use a uniaxial extruder (manufactured by Toyo Seiki Co., Ltd.) , Spiral diameter and length 25mm, cylinder set temperature: 280℃), T mold (width 500mm, set temperature: 280°C), cooling roll (set temperature: 50°C) and film forming device of the coiler to produce the thickness 170µm amorphous polyester resin film. The film was uniaxially stretched to 2.0 times in the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds in an oven at 120°C. Next, after immersing in water at a liquid temperature of 30°C for 120 seconds, while immersed in water at a liquid temperature of 73°C, the total stretch ratio becomes 5.5 times in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds. Method for uniaxial extension (underwater extension). The obtained stretched film was heat-treated at 90°C for 10 seconds using a stretcher KAROIV manufactured by Brückner, to obtain a polyester film VI (slow axis angle with respect to the longitudinal direction: -0.2°, in-plane phase Re(590): 3243nm , Thickness: 35µm).

[Production Example 10] Production of polyester film VII A stretched film was produced in the same manner as in Production Example 9. The obtained stretched film was heat-treated at 90°C for 10 seconds using a stretcher KAROIV manufactured by Brückner Co., and then heat-treated at 140°C for 10 seconds to obtain a polyester film VII (slow axis angle with respect to the longitudinal direction: -0.4 °, in-plane phase Re(590): 4052nm, thickness: 35µm).

[Example 1] Corona treatment was performed on the polyester film A produced in Production Example 3, and 15.2wt% of the product name "SUPERFLEX 210R" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd. and 2.7wt% of the product name "WS-700" manufactured by Nippon Shokubai Co., Ltd. were dissolved. % Aqueous solution is applied in a way that the film thickness becomes 300µm after drying and dried at 80°C for 1 minute to form an easy-adhesive layer, and a polyester film A with an easy-adhesive layer is obtained. Coat the surface of the polarizer of the polarizer with substrate prepared in Manufacturing Example 1 with a PVA-based resin aqueous solution (manufactured by Nippon Gosei Chemical Industry Co., Ltd., trade name "GOHSEFIMER (registered trademark) Z-200", resin concentration: 3 weight) %), and attach the above-mentioned polyester film with easy adhesion layer. The resulting 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 (transmittance 42.3%, thickness 5 µm)/protective film (polyester film)). In addition, the polyester film A and the polarizer are laminated so that the MD direction of the polyester film A and the absorption axis direction of the polarizer are slightly parallel. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Example 2] A polarizing plate was produced in the same manner as in Example 1, except that the polarizer obtained in Production Example 2 was used instead of the polarizer with a substrate obtained in Production Example 1. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 1] The polyester film I obtained in Production Example 4 was used instead of the polyester film A obtained in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1 except that the polyester film I was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 2] The polyester film II produced in Production Example 5 was used instead of the polyester film A produced in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1, except that the polyester film II produced in Production Example 5 was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 3] The polyester film III produced in Production Example 6 was used instead of the polyester film A produced in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1 except that the polyester film III was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 4] The polyester film IV produced in Production Example 7 was used instead of the polyester film A produced in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1, except that the polyester film IV produced in Production Example 7 was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 5] Use polyester film a (manufactured by Toyobo Co., Ltd., trade name "COSMOSHINE A4100", slow axis angle with respect to the longitudinal direction: 90°, in-plane retardation Re(590): 7800nm, thickness: 75µm) instead of manufacturing example 3 A polarizing plate was produced in the same manner as in Example 1 except for the obtained polyester film A. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 6] Use polyester film b (manufactured by Mitsubishi Chemical Co., trade name "T100-J25", slow axis angle with respect to the longitudinal direction: 27°, in-plane retardation Re(590): 525 nm, thickness: 25 µm) instead of manufacturing Except for the polyester film A produced in Example 3, a polarizing plate was produced in the same manner as in Example 1. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 7] The polyester film V produced in Production Example 8 was used instead of the polyester film A produced in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1, except that the polyester film V produced in Production Example 8 was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 8] The polyester film VI obtained in Production Example 9 was used instead of the polyester film A obtained in Production Example 3, and a polarizing plate was produced in the same manner as in Example 1 except that the polyester film VI was used. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 9] A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film VII obtained in Production Example 10 was used instead of the polyester film A produced in Production Example 3. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 10] A polarizing plate was produced in the same manner as in Comparative Example 1, except that the polarizer obtained in Production Example 2 was used instead of the polarizer with a substrate obtained in Production Example 1. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 11] A polarizing plate was produced in the same manner as in Comparative Example 3 except that the polarizer obtained in Production Example 2 was used instead of the polarizer with a substrate obtained in Production Example 1. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Comparative Example 12] A polarizing plate was produced in the same manner as in Comparative Example 8, except that the polarizer obtained in Production Example 2 was used instead of the polarizer with a substrate obtained in Production Example 1. The prepared polarizing plate was used for the above evaluation (1)~(6). The results are shown in Table 1.

[Table 1]

10: Polarizing parts 20: polyester film 30: Adhesive layer 40: Easy bonding layer 100, 200: Polarizing plate A: Polyester film with easy bonding layer

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention.

(no)

Claims (8)

A polyester film whose linear expansion coefficient in the first direction is 3.5×10 ^-5 /℃ or less, and the linear expansion coefficient in the second direction perpendicular to the first direction is 3.5×10 ^-5 /℃ or less , And has a slow axis in the direction of -5°~5° with respect to the first direction. Such as the polyester film of claim 1, the crystallinity measured by DSC is 30% or more. A polarizing plate is provided with a polarizing member and a polyester film such as claim 1 or 2 arranged on one side of the polarizing member. Such as the polarizing plate of claim 3, wherein the thickness of the aforementioned polarizing element is 20 µm or less. For example, the polarizing plate of claim 3 or 4, which further includes an easy-adhesive layer disposed on the polarizer side of the polyester film. The polarizing plate of claim 5, wherein the easily bonding layer contains fine particles. Such as the polarizing plate of claim 5 or 6, wherein the thickness of the aforementioned easy bonding layer is 0.35 µm or less. The polarizing plate according to any one of claims 5 to 7, wherein the refractive index of the easily bonding layer is 1.55 or less.

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