WO2022024492A1 - Polyester film for polarizer protection and polarizing plate comprising said polyester film - Google Patents

Abstract

The present invention provides a polyester film for polarizer protection, which is capable of contributing to the improvement of the durability of a polarizing plate in a humidified environment, while using a common polyester resin as a resin material.　A polyester film for polarizer protection according to the present invention is configured such that if the temperature and the humidity are raised from the initial state at 25°C at 10% RH to the high-temperature high-humidity state at 85°C at 85% RH at constant rates for 50 minutes, the dimensional change rate A (%) in a first direction and the dimensional change rate B (%) in a second direction that is perpendicular to the first direction satisfy the formulae (1) to (3) described below.　(1): -110 × A + 101 × B ≤ 130 (2): -1 ≤ A ≤ 1 (3): -1 ≤ B ≤ 1

Description

A polyester film for protecting a stator and a polarizing plate containing the polyester film.

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

In an image display device (for example, a liquid crystal display device or an organic EL display device), a polarizing plate is often arranged on at least one side of a display cell due to the image forming method. In recent years, image display devices have tended to have more diversified functions and uses, and are required to be able to withstand use in harsher environments, and one of them is required to be able to withstand use in humid environments. Has been done. The polarizing plate generally has a structure in which a polarizing element is sandwiched between two protective films, and as the protective film, triacetyl cellulose, an acrylic resin, a cycloolefin resin and the like are widely used.

In order to improve the durability (particularly, moisture resistance) of the polarizing plate, it is common to take measures to improve the durability from the characteristic aspect of the resin material forming the protective film. However, there is a problem that it takes a lot of time and cost to improve the characteristics of the resin material.

Japanese Unexamined Patent Publication No. 8-271733

The present invention has been made to solve the above-mentioned conventional problems, and the main object thereof is polarization which can contribute to the improvement of the humidification durability of the polarizing plate while using a general polyester resin as the resin material. The purpose is to provide a polyester film for child protection.

The polyester film for protecting a polarizing element of the present invention is the first when the temperature and humidity are raised at a constant rate in 50 minutes from the initial condition of 25 ° C. and 10% RH to the high temperature and high humidity condition of 85 ° C. and 85% RH. The dimensional change rate A (%) in the direction of 1 and the dimensional change rate B (%) in the second direction orthogonal to the first direction satisfy the following equations (1) to (3).
-110 x A + 101 x B ≤ 130 ... (1)
-1 ≤ A ≤ 1 ... (2)
-1 ≤ B ≤ 1 ... (3)
In one embodiment, the polarizing element protective polyester film is formed from polyethylene terephthalate and / or modified polyethylene terephthalate.
In one embodiment, the modified polyethylene terephthalate comprises a building block derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid.
In one embodiment, the polyester film for protecting a polarizing element has a thickness of 80 μm or less.
According to another aspect of the invention, a polarizing plate is provided. In one embodiment, the polarizing plate includes a polarizing element and a polyester film for protecting the polarizing element arranged on one side of the polarizing element, the thickness of the polarizing element is 20 μm or less.
In one embodiment, the polarizing plate further includes an easy-adhesion layer arranged on the polarizing element side of the polyester film for protecting a polarizing element.
In one embodiment, the easy-adhesion layer contains fine particles.
In one embodiment, the refractive index of the easy-adhesion layer is 1.55 or less.
In one embodiment, the surface on the polarizing element side of the polyester film for protecting the polarizing element is a surface-treated surface.
In one embodiment, the surface treatment is a corona treatment or a plasma treatment.

According to the present invention, it is possible to provide a polyester film for protecting a stator that can contribute to the improvement of the humidification durability of the polarizing plate while using a general polyester resin as the resin material.

It is a schematic sectional drawing of the polarizing plate by one Embodiment of this invention. FIG. 3 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 polyester film for protecting a extruder of the present invention (hereinafter, also simply referred to as a polyester film) has a temperature and humidity of 50 minutes from an initial condition of 25 ° C. 10% RH to a high temperature and high humidity condition of 85 ° C. 85% RH. The dimensional change rate A (%) in the first direction and the dimensional change rate B (%) in the second direction orthogonal to the first direction when the film is increased at a constant velocity in the following equation (1). ~ (3) is satisfied.
-110 x A + 101 x B ≤ 130 ... (1)
-1 ≤ A ≤ 1 ... (2)
-1 ≤ B ≤ 1 ... (3)
The dimensional change rate can be obtained by the formula {(dimension (length) in high temperature humidification condition-dimension (length) in initial condition} / dimension in initial condition} × 100.

In the present invention, when the dimensional change rate satisfies the above relationship, it is possible to obtain a polyester film capable of improving the humidification durability of the polarizing element when used for protecting the polarizing element. The dimensional change rate can be controlled mainly by adjusting the film forming conditions when producing the polyester film. The film forming conditions include 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, and MD / TD direction after stretching. The mitigation rate of The stretching temperature, stretching ratio and stretching speed can be appropriately adjusted for each MD / TD. It is a book that a polarizing element protective film that exhibits the effect of imparting humidification durability was obtained by adjusting the film forming conditions using polyester, which is a general resin, without relying on optimizing the characteristics of the resin material itself. It is a great achievement of the invention. In the present invention, using polyester as a material is advantageous in that a polarizing element protective film can be obtained at low cost and that mechanical properties (for example, elastic modulus) can be easily controlled by stretching. In one embodiment, the first direction corresponds to the transport direction (MD) when producing the polyester film. Further, the second direction may correspond to a TD orthogonal to the MD.

In one embodiment, the dimensional change rate A and the dimensional change rate B satisfy the following formula (1a).
-70 x A + 101 x B ≤ 90 ... (1a)
If the dimensional change rate satisfies such a relationship, the above-mentioned effect of the present invention becomes more remarkable.

In one embodiment, the dimensional change rate A and the dimensional change rate B satisfy the following formula (1b), and more preferably the following formula (1b').
-110 x A + 101 x B ≤ 108 ... (1b)
-110 x A + 101 x B ≤ 84 ... (1b')
If the dimensional change rate satisfies such a relationship, the above-mentioned effect of the present invention becomes more remarkable.

In one embodiment, the dimensional change rate A (%) in the first direction is −0.8% to 1%, preferably −0.65% to 0.8%, more preferably. Is -0.6% to 0.7%. In one embodiment, the dimensional change rate B (%) in the second direction is -1% to 0.8%, preferably -0.8% to 0.65%, more preferably. Is -0.7% to 0.6%.

The polyester film has a crystallinity of preferably 30% or more, more preferably 40% or more, still more preferably 50% or more, as measured by differential scanning calorimetry (DSC). 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 polarizing element protective film can be obtained.

The thickness of the polyester film is preferably 80 μm or less, more preferably 10 μm to 80 μm, and further preferably 20 μm to 50 μm.

The total light transmittance of the polyester film is preferably 80% or more, more preferably 85% or more, further 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 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 acid, aliphatic dicarboxylic acid, and alicyclic dicarboxylic acid. 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 and fumaric acid. Examples thereof include maleic acid, itaconic acid, thiodipropionic acid and diglycolic acid. 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-norbornandicarboxylic acid. Examples include acids and adamantandicarboxylic acids. The carboxylic acid component may be a derivative such as an ester, chloride or acid anhydride, for example, dimethyl 1,4-cyclohexanedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylic acid, dimethyl isophthalate, dimethyl terephthalate. And contains diphenyl terephthalate. The carboxylic acid component may be used alone or in combination of two or more.

Typical examples of the polyol component are dihydric alcohols. 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, and 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. Be done. Examples of the alicyclic diol include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecanedimethanol, adamantandiol, 2,2,4. , 4-Tetramethyl-1,3-cyclobutanediol. Examples of the aromatic diol include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-(2-norbornenilidene) diphenol, 4,4'-dihydroxybiphenol, o-, Included are m- and p-dihydroxybenzene, 4,4'-isopropyridenephenol, 4,4'-isopropyridenebis (2,6-cyclochlorophenol) 2,5-naphthalenediol and p-xylenediol. The polyol component may be used alone or in combination of two or more.

As the polyester resin, polyethylene terephthalate and / or modified polyethylene terephthalate is preferably used, and polyethylene terephthalate is more preferably used. By using these resins, it is possible to obtain a polyester film having excellent mechanical properties and easy control of dimensional change. Polyethylene terephthalate and modified polyethylene terephthalate may be blended and used.

Examples of the modified polyethylene terephthalate include modified polyethylene terephthalate containing a structural 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 mol% with respect to the total of all polymer repeating units.

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, a polyester film with an easy-adhesion layer is provided. The easy-adhesion layer contains, for example, a water-based polyurethane and an oxazoline-based cross-linking agent. Details of the easy-adhesion layer are described in, for example, Japanese Patent Application Laid-Open No. 2010-55062. The entire description of the publication is incorporated herein by reference.

In one embodiment, the easy-adhesion layer contains any suitable 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 inorganic oxides such as silica, titania, alumina, and zirconia, 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-based resin, fluorine-based resin, (meth) acrylic-based resin, and the like. Among these, silica is preferable.

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

The thickness of the easy-adhesion 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 easily adhesive layer that does not easily impair the optical characteristics of other members when applied to an image display device.

In one embodiment, the refractive index of the easy-adhesion layer is preferably 1.55 or less, more preferably 1.5 or less. Within such a range, it is possible to obtain a polyester film with an easily adhesive layer that does not easily impair the optical characteristics of other members when applied to an image display device.

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

In one embodiment, at least one surface of the polyester film may be a surface-treated surface. As the surface treatment, any appropriate treatment may be adopted. For example, corona treatment, plasma treatment and the like can be mentioned.

(Manufacturing method of polyester film)
The polyester film can be obtained through a molding step of molding a film-forming material (resin composition) containing the polyester-based resin into a film, and a stretching step of stretching the molded film. Preferably, the stretching step comprises a preheat treatment of the film performed prior to film stretching and a heat treatment performed after film stretching. Further, after the film is stretched, a relaxation treatment may be performed in which the film is shrunk in the width direction while the film is held by the tenter. In one embodiment, the polyester film is provided in a long shape (or a shape cut out from a long body).

The film-forming material may contain an additive or a solvent in addition to the polyester-based resin. As the additive, any suitable additive may be adopted depending on the purpose. Specific examples of additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, antioxidants, UV absorbers, leveling agents, thixotropic agents, antistatic agents, conductive materials, and flame retardants. Can be mentioned. The number, type, combination, addition amount and the like of the additives can be appropriately set according to the purpose.

As a method for forming a film from a film forming material, any appropriate molding processing method can be adopted. Specific examples include a compression molding method, a transfer molding method, an injection molding method, an extrusion molding method, a blow molding method, a powder molding method, an FRP molding method, a cast coating method (for example, a casting method), a calendar molding method, and a hot press. The law etc. can be mentioned. Extrusion molding method or cast coating method is preferable. This is because the smoothness of the obtained film can be enhanced and good optical uniformity can be obtained.

The film stretching method may be uniaxial stretching or biaxial stretching.

In one embodiment, uniaxial stretching is adopted as the stretching method of the film, and the film is stretched in the length direction (MD) of the film.

The biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. 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.

In one embodiment, sequential biaxial stretching is adopted as the stretching method of the film. It is preferable to perform MD stretching after TD stretching to obtain the polyester film. By doing so, it is possible to mitigate the influence of Boeing that occurs during TD stretching, and to make the angle between the first direction (MD) and the slow axis of the polyester film an appropriate value. ..

The stretching temperature is preferably Tg + 5 ° C. to Tg + 50 ° C., more preferably Tg + 5 ° C. to Tg + 30 ° C., and even more preferably Tg + 10 ° C. to Tg + 20 ° C. with respect to the glass transition temperature (Tg) of the film. By stretching at such a temperature, a polyester film in which the direction of the slow phase axis and the linear expansion coefficient are controlled in a well-balanced manner can be obtained. In addition, a polyester film having excellent transparency can be obtained.

The draw ratio in MD is preferably 1.1 times to 8 times, more preferably 2.5 times to 6.5 times, still more preferably 3 times to 6 times, and particularly preferably 3 times to 3 times. It is 5 times. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range.

The draw ratio in TD is preferably 1.1 times to 11 times, more preferably 2.5 times to 6.5 times, still more preferably 3 times to 6 times, and particularly preferably 3 times to 3 times. It is 5 times. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range.

The ratio of the stretching ratio in TD to the stretching ratio in MD (MD stretching ratio / TD stretching ratio) is preferably more than 0.1 and 7 or less, more preferably 0.2 to 5, and even more preferably 0. It is .3 to 4, more preferably 0.4 to 3, particularly preferably 0.5 to 2, and most preferably 0.6 to 1.7. Within such a range, the relationship between the dimensional change rate in the first direction (MD) and the dimensional change rate in the second direction (TD) is kept within a desired range, and the polyester has an excellent effect of imparting humidification durability. You can get the film.

The stretching speed in MD is preferably 5% / sec to 100% / sec, more preferably 8% / sec to 80% / sec, and further preferably 8% / sec to 60% / sec. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range.

The stretching speed in TD is preferably 5% / sec to 100% / sec, more preferably 8% / sec to 80% / sec, and further preferably 8% / sec to 60% / sec. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range.

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 10 seconds to 100 seconds, more preferably 15 seconds to 80 seconds. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range.

The temperature of the heat treatment is preferably 100 ° C. to 250 ° C., more preferably 120 ° C. to 200 ° C., and even more preferably 130 ° C. to 180 ° C. Within such a range, it is possible to obtain a polyester film having an excellent effect of imparting humidification durability while keeping the dimensional change rate within a desired range. The heat treatment time is preferably 2 seconds to 50 seconds, more preferably 5 seconds to 40 seconds, still more preferably 8 seconds to 30 seconds. Within such a range, a polyester film having excellent transparency, good crystallinity, and excellent durability can be obtained.

In one embodiment, the relaxation treatment is performed after the film is stretched (after the heat treatment when the heat treatment is performed). The relaxation treatment is a treatment in which the film is shrunk in the width direction while being held by the tenter. The temperature during the relaxation treatment is preferably 80 ° C. to 210 ° C., more preferably 90 ° C. to 200 ° C. In one embodiment, the temperature during the relaxation treatment is preferably 80 ° C. to 150 ° C., more preferably 90 ° C. to 140 ° C. In another embodiment, the temperature during the relaxation treatment is preferably 150 ° C. to 210 ° C., more preferably 160 ° C. to 200 ° C. Within such a temperature range, the resin constituting the polyester film can be crystallized. The shrinkage rate in the relaxation treatment is preferably more than 0% and 5% or less, and more preferably 0.5% to 3%.

B. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 includes a polarizing element 10 and a polyester film 20 arranged on one side of the polarizing element 10. As the polyester film 20, the polyester film of the present invention described in Section A above is used. Any suitable alternative polarizing element protective film may be placed on the other side of the polarizing element, and the polarizing element protective film may not be placed. In one embodiment, the polarizing element 10 and the polyester film 20 (or another polarizing element protective film) are laminated via an adhesive layer 30. When the polyester film 20 has a surface-treated surface (for example, a corona-treated surface, a plasma-treated surface), it is preferable that the surface of the polyester film 20 on the polarizing element 10 side is the surface-treated surface.

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

As the polarizing element, any appropriate polarizing element can be adopted. For example, the resin film forming the polarizing element may be a single-layer resin film or a laminated body having two or more layers.

Specific examples of the polarizing element composed of a single-layer resin film include a hydrophilic polymer film such as a polyvinyl alcohol (PVA) -based film, a partially formalized PVA-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. Examples thereof include those which have been dyed and stretched with a bicolor substance such as iodine and a bicolor dye, and polyene-based oriented films such as a dehydrated product of PVA and a dehydrogenated product of polyvinyl chloride. Preferably, since the PVA-based film is excellent in optical properties, a polarizing element obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used.

The dyeing with iodine is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or may be performed while dyeing. Further, it may be dyed after being stretched. If necessary, the PVA-based film is subjected to a swelling treatment, a crosslinking treatment, a cleaning treatment, a drying treatment and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, it is possible not only to clean the dirt and blocking inhibitor on the surface of the PVA-based film, but also to swell the PVA-based film to prevent uneven dyeing. Can be prevented.

Specific examples of the polarizing element obtained by 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 polarizing element obtained by using a laminate with a PVA-based resin layer coated and formed on a base material. The polarizing element obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed 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 it. It is produced by forming a PVA-based resin layer on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer a stator. obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further comprise, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. The obtained resin base material / polarizing element laminate may be used as it is (that is, the resin base material may be used as a protective layer for the polarizing element), and the resin base material is peeled off from the resin base material / polarizing element laminate. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of the method for producing such a polarizing element are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

The thickness of the polarizing element is, for example, 1 μm to 80 μm. In one embodiment, the thickness of the polarizing element is preferably 20 μm or less, more preferably 3 μm to 15 μm. The polyester film of the present invention has a large polarizing element protection effect, and can effectively prevent cracks in the polarizing element, for example. Therefore, it is possible to use a thin polarizing element even in a harsh environment such as a high temperature and a large temperature change.

The polarizing element and the polarizing element protective film (polyester film) can be laminated via any suitable adhesive layer. Preferably, the adhesive layer is formed from an adhesive composition containing a polyvinyl alcohol-based resin.

In one embodiment, the absorption axis direction of the polarizing element and the first direction (typically MD) of the polyester film are substantially parallel. If the polarizing plate is configured so that the absorption axis of the polarizing element and the first direction of the polyester film are substantially parallel to each other, the polyester film and the polarizing element can be synchronized and preferably change in shape. As a result, cracking of the stator is prevented. The slow axis angle of the polyester film is preferably such that the angle formed by the absorption axis direction of the polarizing element is the same, and the angle formed by the two axes is preferably 0 ° ± 10 °, more preferably 0 ° ± 7 °. Yes, more preferably 0 ° ± 5 °. Within such a range, a polyester film with less occurrence of rainbow unevenness when applied to an image display device can be obtained. The slow phase axis angle is an angle when the roll flow direction is 0 °.

FIG. 2 is a schematic cross-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 polarizing element 10 side of the polyester film 20. In one embodiment, the polyester film A with an easy-adhesion layer is arranged on the polarizing element 10 so that the easy-adhesion layer 40 is on the side of the polarizing element 10. As the easy-adhesion layer, the easy-adhesion layer described in the above item A can be adopted. When the polyester film 20 has a surface-treated surface (for example, a corona-treated surface and a plasma-treated surface), it is preferable that the surface of the polyester film 20 on the decoder 10 side (easy-adhesion layer 40 side) is the surface-treated surface.

C. Image display device The above 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 adopts a configuration well known in the industry, detailed description thereof will be omitted.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic in the examples is as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Dimensional change rate For the polyester films used in the examples and comparative examples, strip-shaped samples having MD (first direction) in the longitudinal direction and strip-shaped samples having TD (second direction) in the longitudinal direction were prepared. Got ready. The dimensional change rate of the sample was measured using a thermomechanical analyzer (TMA) (manufactured by NETZSCH, trade name "TMA4000SE").
In this evaluation, the short side of the film was cut with a width of 4 mm, and the sample was mounted with a gap of about 20 mm between the chucks. After stabilizing at 25 ° C. and 10% RH as an initial condition, the temperature and humidity were raised at a constant velocity so as to reach 85 ° C. and 85% RH in 50 minutes. The dimensional change at the time when the temperature reached 85 ° C. and 85% RH was defined as the dimensional change rate of the film. It should be noted that the case where the numerical value changes in the positive direction indicates expansion and the case where the numerical value changes in the negative direction indicates contraction with respect to the initial stage.

(2) Humidification durability The surface of the polarizing plate obtained in Examples and Comparative Examples on the opposite side of the polyester film and the non-alkali glass are bonded to each other via an adhesive to obtain an evaluation sample. rice field. The degree of polarization (initial degree of polarization) of the evaluation sample was measured using an ultraviolet-visible near-infrared spectrophotometer (manufactured by JASCO Corporation, trade name "V7100", with VAP-7070 automatic polarizing film measuring device). Then, it was put into a constant temperature and humidity constant device of 85 ° C. and 85% RH for 1000 hours. Then, after returning the evaluation sample to room temperature, the degree of polarization (degree of polarization after humidification) of the evaluation sample was measured in the same manner as above. Humidification durability was evaluated according to the following criteria from the amount of change in the degree of polarization after humidification with respect to the degree of initial polarization.
◎ The amount of change in the degree of polarization after the humidification test with respect to the initial degree of polarization is 1% or less 〇 The amount of change in the degree of polarization after the humidification test with respect to the initial degree of polarization is less than 10% × The amount of change in the degree of polarization after the humidification test with respect to the initial degree of polarization Is 10% or more

[Production Example 1] Preparation of Polarizer As a base material, an amorphous isophthalic acid copolymer polyethylene terephthalate (IPA copolymer PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75 ° C. Was used. One side of the substrate 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. %, Degree of polymerization of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z200") is applied at a ratio of 9: 1 and dried at 25 ° C. to a thickness of 11 μm. A PVA-based resin layer was formed to prepare a laminated body.
The obtained laminate was uniaxially stretched at the free end in the vertical direction (longitudinal direction) 2.0 times between rolls having different peripheral speeds in an oven at 120 ° C. (aerial auxiliary stretching).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, 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 parts 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 immersed in the obtained iodine aqueous solution for 60 seconds (dyeing treatment). ..
Then, it was immersed in a cross-linked bath having a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, the laminate is immersed in an aqueous solution of boric acid having a liquid temperature of 70 ° C. (an aqueous solution obtained by blending 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water). However, uniaxial stretching was performed between rolls having different peripheral speeds so that the total stretching ratio was 5.5 times in the longitudinal direction (longitudinal direction) (underwater stretching).
Then, the laminate is immersed in a washing bath at 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), and has a peelable substrate. Obtained a stator.

[Production Example 2] Production of polyester film A Polyester resin (polyester terephthalate, manufactured by Bell Polyester Products, Inc., IV value 0.75 dl / g (phenol: 1,1,2,2, -tetrachloroethane = 6: 4 mixed solvent solution) After vacuum drying the concentration 0.4 g / dl) at 100 ° C for 10 hours, a single-screw extruder (manufactured by Toyo Seiki Co., Ltd., screw diameter 25 mm, cylinder set temperature: 280 ° C), T-die (width 500 mm, set temperature: An amorphous polyester resin film having a thickness of 200 μm was prepared using a film forming apparatus equipped with a chill roll (set temperature: 50 ° C.) and a winder.
The obtained amorphous polyester resin film was biaxially stretched by a stretching machine KAROIV manufactured by Bruckner to obtain a polyester film A (thickness: 20 μm). The draw ratio was 3.1 times in the length direction (MD) and 3.9 times in the width direction (TD). The MD stretching temperature was 95 ° C., the TD stretching temperature was 110 ° C., and the stretching speed was 30% / sec for both MD and TD. In addition, after the stretching treatment, heat treatment was performed at 180 ° C. for 10 seconds while maintaining the dimensions, and then a relaxation treatment was performed in which the width of the tenter was narrowed while the film was held by the tenter to shrink the film by 1% in the width direction. ..

[Manufacturing Example 3] Production of polyester film B Except that the draw ratio was set to 3 times in the length direction (MD) and 3.7 times in the width direction (TD), and the shrinkage rate during the relaxation treatment was set to 2%. Obtained a polyester film B (thickness: 24 μm) in the same manner as in Production Example 2.

[Production Example 4] Production of polyester film C The draw ratio was set to 3.2 times in the length direction (MD) and 3.8 times in the width direction (TD), and the shrinkage rate during the relaxation treatment was set to 2%. A polyester film C (thickness: 20 μm) was obtained in the same manner as in Production Example 2.

[Manufacturing Example 5] Production of Polyester Film D The stretch ratio was 3.3 times in the length direction (MD) and 3.7 times in the width direction (TD), and the shrinkage rate during the relaxation treatment was 2%. A polyester film D (thickness: 20 μm) was obtained in the same manner as in Production Example 2.

[Manufacturing Example 6] Production of Polyester Film E The stretching ratio was set to 3.4 times in the length direction (MD) and 3.6 times in the width direction (TD), the TD stretching temperature was set to 115 ° C, and relaxation was achieved. A polyester film E (thickness: 22 μm) was obtained in the same manner as in Production Example 2 except that the shrinkage rate during the treatment was 3%.

[Manufacturing Example 7] Production of Polyester Film F The stretching ratio was 3.4 times in the length direction (MD) and 3.6 times in the width direction (TD), the MD stretching temperature was 90 ° C, and the TD stretching temperature was set. Polyester film F (thickness: 22 μm) in the same manner as in Production Example 2, except that the temperature was 120 ° C., the heat treatment temperature after stretching was 160 ° C., and the shrinkage rate during the relaxation treatment was 3%. Got

[Manufacturing Example 8] Production of Polyester Film G The stretching ratio was 3.3 times in the length direction (MD) and 3.6 times in the width direction (TD), the MD stretching temperature was 90 ° C, and the TD stretching temperature was set. Polyester film G (thickness: 23 μm) in the same manner as in Production Example 2, except that the temperature was 120 ° C., the heat treatment temperature after stretching was 140 ° C., and the shrinkage rate during the relaxation treatment was 3%. Got

[Example 1]
The polyester film A manufactured in Production Example 2 is corona-treated, and the product name "Superflex 210R" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. is 15.2 wt% and the product name "WS-700" manufactured by Nippon Catalyst Co., Ltd. is 2.7 wt%. After drying, the aqueous solution in which% was dissolved was applied so that the film thickness became 300 μm, and dried at 80 ° C. for 1 minute to obtain a polyester film A with an easy-adhesion layer.
The polyester film with an easy-adhesion layer was attached to the surface of the polarizing element with a substrate obtained in Production Example 1 via a UV curable adhesive. Specifically, the curable adhesive was coated so as to have a total thickness of about 1.0 μm, and bonded using a roll machine. Then, UV light was irradiated from the polyester film A side to cure the adhesive. Then, the substrate was peeled off from the PVA-based resin layer to obtain a polarizing plate (polarizer (transmittance 42.3%, thickness 5 μm) / protective film (polyester film)). The polyester film A and the polarizing element were laminated so that the MD direction of the polyester film A and the absorption axis direction of the polarizing element were substantially parallel to each other.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). 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 produced in Production Example 3 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). The results are shown in Table 1.

[Example 3]
A polarizing plate was obtained in the same manner as in Example 1 except that the polyester film C produced in Production Example 4 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). 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 D produced in Production Example 5 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). 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 E produced in Production Example 6 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). 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 F produced in Production Example 7 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). 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 G produced in Production Example 8 was used instead of the polyester film A produced in Production Example 2.
The obtained polarizing plate was subjected to the above evaluations (1) and (2). The results are shown in Table 1.

10 Polarizer 20 Polyester film 30 Adhesive layer 40 Easy adhesive layer 100, 200 Polarizing plate

Claims (11)

1. The dimensional change rate A (%) in the first direction when the temperature and humidity are increased at a constant rate in 50 minutes from the initial condition of 25 ° C. 10% RH to the high temperature and high humidity condition of 85 ° C. 85% RH. , A polyester film for protecting a transducer in which the dimensional change rate B (%) in the second direction orthogonal to the first direction satisfies the following formulas (1) to (3).
   -110 x A + 101 x B ≤ 130 ... (1)
   -1 ≤ A ≤ 1 ... (2)
   -1 ≤ B ≤ 1 ... (3)
2. The polyester film for protecting a polarizing element according to claim 1, which is formed from polyethylene terephthalate and / or modified polyethylene terephthalate. It was
3. The polyester film for protecting a polarizing element according to claim 2, wherein the modified polyethylene terephthalate contains a structural unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid.
4. The polyester film for protecting a polarizing element according to any one of claims 1 to 3, which has a thickness of 80 μm or less.
5. A polarizing plate comprising a polarizing element and a polyester film for protecting the polarizing element according to any one of claims 1 to 4, which is arranged on one side of the polarizing element.
6. The polarizing plate according to claim 5, wherein the polarizing element has a thickness of 20 μm or less.
7. The polarizing plate according to claim 5 or 6, further comprising an easy-adhesion layer arranged on the polarizing element side of the polarizing element protection polyester film.
8. The polarizing plate according to claim 7, wherein the easily adhesive layer contains fine particles.
9. The polarizing plate according to any one of claims 5 to 8, wherein the refractive index of the easy-adhesion layer is 1.55 or less.
10. The polarizing plate according to any one of claims 5 to 9, wherein the surface on the polarizing element side of the polyester film for protecting the polarizing element is a surface-treated surface.
11. The polarizing plate according to claim 10, wherein the surface treatment is a corona treatment or a plasma treatment.
    

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