TW201333551A - Liquid crystal display device, polarizing plate and polarizer protection film - Google Patents

Abstract

The present invention provides a polarizer protection film, wherein the adhesive property between the polyester film and polarizer or polyvinyl alcohol-based resin layer such as adhesive applied on the polarizer is excellent, and it may correspond to thinning of liquid crystal display device; further, aggravation of the visibility by rainbow color spot does not produce. The polarizer protection film is a polarizer protection film having coating layer on at least one side of polyester film, which is characterized in that said polyester film has retardation of 3000-30000nm, said coating layer comprises polyvinyl alcohol-based resin and polyester-based resin, the surface of said coating layer has nano-phase-separated structure comprising a phase of polyvinyl alcohol-based resin cohesion and a phase of polyester resin cohesion, and area ratio of polyvinyl alcohol phase is 30% and more and less than 90%.

Description

Liquid crystal display device, polarizing plate and polarizer protective film

The present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film. Specifically, the liquid crystal display device, the polarizing plate, and the polarizer protective film are suitable for thinning.

A polarizing plate used in a liquid crystal display device (LCD) is usually formed by sandwiching two polarizing mirror protective films to form a polarizing lens coated with iodine such as polyvinyl alcohol (PVA), and is generally used as a polarizing mirror protective film. Ethylene cellulose (TAC) film. In recent years, with the thinning of LCDs, thinning of polarizing plates is required. However, when the thickness of the TAC film used as the protective film is reduced, sufficient mechanical strength cannot be obtained, and the moisture permeability is high, and the polarizer is easily deteriorated. Also, TAC films are very expensive and strongly demand cheap alternative materials.

Therefore, in order to reduce the thickness of the polarizing plate, it has been proposed as a polarizer protective film, and it is possible to maintain high durability even when the thickness is thin, and a polyester film is used instead of the TAC film (Patent Documents 1 to 3).

The triacetone cellulose film used as a polarizer protective film has an alkali treatment or the like on the surface and has an extremely high affinity with a hydrophilic adhesive. Therefore, the protective film formed of the triacetyl cellulose film has a very high adhesion to the polarizer coated with the hydrophilic adhesive. However, the adhesiveness of the polyester film to the hydrophilic adhesive is insufficient, and particularly when the polyester film having an alignment property by the stretching treatment is used, the tendency is changed remarkably. Therefore, in order to improve the adhesion to the polarizer or the hydrophilic adhesive applied to the polarizer, it is proposed to provide an easy-adhesion layer on the polyester film (Patent Documents 4 to 7).

Prior technical literature Patent literature

Patent Document 1 JP-A-2002-116320

Patent Document 2, JP-A-2004-219620

Patent Document 3, JP-A-2004-205773

Patent Document 4 Japanese Patent Publication No. 8-271733

Patent Document 5 Japanese Patent Publication No. 8-271734

Patent Document 6 JP-A-2009-157361

Patent Document 7 Unexamined 2011-8170

The polyester film is superior in durability to the TAC film, but unlike the TAC film, it has birefringence, and when used as a polarizer protective film, there is a problem that image quality is lowered due to optical distortion. In other words, since the polyester film having birefringence has a predetermined optical anisotropy (hysteresis value), when viewed as a polarizing mirror protective film, when viewed from an oblique direction, a rainbow-like color unevenness occurs and the image quality is lowered. Therefore, in Patent Documents 1 to 3, measures for reducing the hysteresis value are performed by using a copolymerized polyester as the polyester. However, even in this case, the rainbow-like stain cannot be completely eliminated.

Further, the polyester film has a low affinity for water, and a polyester film having an aromatic dicarboxylic acid as a dicarboxylic acid component tends to be particularly remarkable. Further, the polyester film having crystal orientation due to stretching has a lower affinity with water. On the other hand, a polarizer or an adhesive applied to a polarizer is generally made of a polyvinyl alcohol-based resin and has a high hydrophilicity. Sex. Due to such a difference in properties, the polyester film has low affinity with a polarizer or a polyvinyl alcohol-based adhesive, and it is difficult to strongly adhere the two. Therefore, even in the polyester film having an easy-adhesion layer disclosed in Patent Documents 1 to 3 and 5, sufficient adhesion has not been obtained as compared with the triacetyl cellulose film. Therefore, when a polarizing plate using a conventional polyester film as a protective film is used as a display member for a long period of time, bulging or peeling easily occurs between the protective film and the polarizing mirror due to the moisture content in the polarizing mirror. The change in polarization characteristics is degraded, and the visibility such as blanking is deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polyvinyl alcohol-based resin layer such as a film and a polarizer or an adhesive applied to a polarizer, which is excellent in adhesion to a liquid crystal display device. The liquid crystal display device and the polarizer protective film which are not deteriorated in visibility due to rainbow-like color spots are not formed.

The inventors of the present invention conducted an intensive review of the mechanism for generating a rainbow-colored stain that occurs when a polyester film is used as a polarizer protective film. As a result, it was found that the rainbow-like color ray was caused by the hysteresis value of the polyester film and the luminescence spectrum of the backlight source. In other words, when a light source having a continuous and wide luminescence spectrum is used as the backlight source, it is possible to suppress deterioration of visibility due to rainbow-like color spots if it is a polyester film having a hysteresis value of a specific range. .

In addition, the inventors of the present invention have obtained a polyester resin having high affinity with a polyester film and affinity with a polyvinyl alcohol-based resin layer in a polyester film which is excellent in adhesion to a polarizer. The idea of a layer containing a polyvinyl alcohol-based resin. However, the inventors found that only groups In the case of the components, the function of adhering the polyester film to the polyvinyl alcohol-based resin layer by each component is not sufficiently exhibited. Therefore, the present inventors have conducted research on the day and night, and as a result, it has been found that in the above-described concept, the polyester resin is formed on the surface of the coating layer by controlling the existence state of the binder resin in the coating layer provided on the surface of the polyester film. The phase in which the agglomerated phase and the phase in which the polyvinyl alcohol-based resin is agglomerated form a nanophase-separated structure, and the adhesion to the polarizer can be further effectively exerted.

In order to achieve the above-mentioned problems, the inventors of the present invention have intensively reviewed and found that a combination of a specific backlight source and a polyester film having a specific hysteresis value and a nano phase separation structure on the surface of the coating layer can be solved. The above problems achieve the completion of the present invention.

The present invention represented by the following is (1) to (12).

(1) A polarizer protective film which is a polarizer protective film having a coating layer on at least one surface of a polyester film, wherein the polyester film has a hysteresis value of 3,000 to 30,000 nm, and the coating layer contains a polyvinyl alcohol resin and a poly The ester-based resin has a nanophase-separated structure formed by a phase in which a phase in which a polyvinyl alcohol-based resin is agglomerated and a phase in which a polyester-based resin is agglomerated, and an area ratio of the polyvinyl alcohol phase is 30% or more and less than 99%. .

(2) The polarizer protective film according to (1), wherein the polyvinyl alcohol-based resin has a degree of saponification of 95% or less.

(3) The polarizer protective film according to (1) or (2), wherein the polyester resin has a glass transition temperature of 25 ° C or higher.

(4) The polarizer protective film according to any one of (1), wherein the coating layer contains a crosslinking agent.

(5) The polarizer protective film according to (4), wherein the crosslinking agent is a melamine-based crosslinking agent and/or an isocyanate-based crosslinking agent.

(6) The polarizer protective film according to any one of (1) to (5), wherein a mass ratio of a polyvinyl alcohol resin (PVA) and a polyester resin (PEs) contained in the coating layer is Satisfy the following formula: 0.2 ≦ PVA / PEs ≦ 1.25.

(7) The polarizer protective film according to any one of (1) to (6), wherein a ratio (Re/Rth) of a hysteresis value to a thickness direction hysteresis value of the polyester film is 0.2 or more and 1.2 or less.

(8) The polarizer protective film according to any one of (1), wherein the polyester film is composed of at least three layers, and a layer other than the outermost layer contains an ultraviolet absorber and a light of 380 nm. The penetration rate is 20% or less.

(9) The polarizer protective film according to any one of (1) to (8), wherein the surface of the polyester film opposite to the surface having the coating layer has a surface selected from a hard coat layer and an antiglare layer. One or more layers of the group consisting of an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an antistatic layer.

(10) A polarizing plate in which a polarizer protective film according to any one of (1) to (9) is laminated on at least one surface of a polarizing mirror.

(11) A liquid crystal display device comprising a backlight source and a liquid crystal cell disposed between two polarizing plates, wherein a white light source having a continuous light emission spectrum is used as the backlight source, and the two polarized lights are used At least one of the plates is a polarizing plate as described in (10).

(12) The liquid crystal display device according to (11), wherein the polarizer protective film disposed on the light-emitting side of the polarizing plate on the light-emitting side is a polarizer protective film described in (1) to (9).

The polarizer protective film of the present invention is excellent in adhesion between a polarizer protective film and a polarizer represented by a polyvinyl alcohol-based resin layer or an adhesive applied thereto. Therefore, the polarizing plate using the polarizer protective film of the present invention is less likely to swell or peel off between the protective film and the polarizer, and it is less likely to cause a decrease in polarization characteristics due to a change in the moisture content in the polarizer. Therefore, the liquid crystal display device using the polarizing plate of the present invention is capable of reducing the deterioration of visibility such as white space due to a decrease in temporal characteristics in a conventional polarizing plate. Further, the liquid crystal display device produced by using the polarizer protective film of the present invention has good visibility without significant rainbow-like color spots even when the display is observed from any observation angle.

It is not bound by the theory, but it is considered that the polarizer protective film of the present invention forms a phase agglomerated by a polyester resin on the surface of the coating layer (hereinafter referred to as "PEs phase" as well as the excellent adhesion to the polarizer). a nanophase-separated structure formed by a phase in which a polyvinyl alcohol-based resin is agglomerated (hereinafter referred to as "PVA phase" as appropriate), and exhibits a strength due to a PVA phase and a polarizer or an adhesive provided thereon. Adhesive.

Form of implementing the invention (liquid crystal display device)

Generally, the liquid crystal panel has a rear module, a liquid crystal cell, and a front module in order from the backlight source side to the side of the display image (the visibility side or the emission side). The rear module and the front module are generally made of a transparent substrate, a transparent conductive film formed on the surface of the liquid crystal cell side, and a configuration It is composed of a polarizing plate on the opposite side. Here, the polarizing plate is disposed on the backlight source side in the rear module, and is disposed on the side of the display image (the visibility side or the emission side) in the front module.

In the liquid crystal display device of the present invention, at least a backlight source and a liquid crystal cell disposed between the two polarizing plates are used as constituent members. Further, other configurations than these may be suitably employed, such as a color filter, a lens film, a diffusion sheet, an antireflection film, and the like.

The configuration of the backlight source may be an edge light method using a light guide plate, a reflection plate or the like as a constituent member, or may be a direct-down type, and is preferably a white light source having a continuous and wide emission spectrum. Here, the continuous and wide-range luminescence spectrum means an luminescence spectrum which does not exist in a wavelength range of at least 450 nm to 650 nm, preferably in the range of visible light, in which the intensity of light becomes zero. As a white light source having such a continuous and wide emission spectrum, for example, a white light-emitting diode (white LED) can be cited. In the white LED, a phosphor is used, that is, a blue component or a phosphor is emitted by using a combination of a blue light of a compound semiconductor or a light emitting diode and a phosphor which emits ultraviolet light, or an organic light emitting diode (Organic) Light-emitting diode: OLED). Among the white LEDs, a blue light-emitting diode using a compound semiconductor is combined with germanium. aluminum. A white light-emitting diode made of a light-emitting element of a garnet-based yellow phosphor is suitable as a backlight source of the present invention because of its continuous and wide emission spectrum and excellent luminous efficiency. It is also effective in energy saving by using a white LED with a smaller power consumption to be equal to the light source.

Conventionally, a fluorescent tube such as a cold cathode tube or a hot cathode tube which is widely used as a backlight source has a discontinuous emission spectrum having a peak of an emission spectrum at a specific wavelength, and thus it is difficult to obtain the effects of the present invention as described above.

The polarizing plate has a configuration in which two sides of a polarizing mirror in which iodine is dyed with PVA or the like is sandwiched by two polarizing film protective films. In the present invention, at least one of polarizing film protective films constituting the polarizing plate can be used. A polyester film having a specific range of hysteresis values.

As a mechanism for suppressing the occurrence of a rainbow-like color spot by the above-described aspect, it is considered as follows.

When a polyester film having birefringence is disposed on one side of the polarizer, the linear polarized light emitted from the polarizer is turbulent when passing through the polyester film. The hysteresis value of the product of the transmitted light system in the birefringence and thickness of the polyester film shows a characteristic dry color. Therefore, when a discontinuous luminescence spectrum such as a cold cathode tube or a hot cathode tube is used as a light source, different penetration light intensities are displayed due to the wavelength, and a rainbow-like color spot is generated (refer to the 15th Microoptics conference pre-collection, Items 30~31).

Conventionally, as a backlight source of a liquid crystal display device, a fluorescent tube such as a cold cathode tube or a hot cathode tube is used. The spectral distribution of a fluorescent lamp such as a cold cathode tube or a hot cathode tube exhibits an emission spectrum having a plurality of peaks, and the discontinuous emission spectrum is combined to obtain a white light source. Such a light having a discontinuous spectrum exhibits different transmitted light intensities due to wavelength when penetrating a film having a high hysteresis value. Therefore, it is considered that only a specific wavelength becomes strongly penetrated, and a rainbow-like color spot occurs.

With respect to this, in the white light-emitting diode, a continuous and wide emission spectrum is usually obtained in a wavelength range of at least 450 nm to 650 nm, preferably in the visible light range. Moreover, since the dry ray spectrum caused by the penetrating light passing through the birefringent body is in the shape of an envelope, by controlling the hysteresis value of the polyester film, light having a similar luminescence spectrum to the light source can be obtained. Spectrum. Thus, it is considered that the envelope shape of the dry ochre spectrum due to the luminescence spectrum of the light source and the penetrating light penetrating the birefringent body is similar, and no rainbow-like color spots occur, and the visibility is remarkably improved.

Based on the above principle, it is considered that in the present invention, by using a white light-emitting diode having a broad spectrum of light emission to the light source, the envelope shape of the spectrum of the transmitted light is approximated to the light source with only a relatively simple configuration. The luminescence spectrum, as a result, can suppress rainbow spots on the liquid crystal display.

In order to achieve the above effects, the polyester film used for the polarizer protective film preferably has a hysteresis value of 3,000 to 30,000 nm. When the hysteresis value is less than 3,000 nm, when it is used as a polarizer protective film, since it exhibits a strong dry bleed when viewed from the oblique direction, the envelope shape is different from the luminescence spectrum of the light source, and good visibility cannot be ensured. The lower limit of the preferred hysteresis value is 4,500 nm or more, and more preferably 6,000 nm or more, more preferably 8000 nm or more, and still more preferably 10,000 nm or more.

On the other hand, the upper limit of the hysteresis value is 30000 nm. When a polyester film having a hysteresis value exceeding this is used, not only the effect of improving the visibility is substantially not obtained, but also the thickness of the film is considerably thick, which is unfavorable because of the workability as an industrial material.

Further, the hysteresis value of the present invention can be obtained by measuring the refractive index and the thickness in the two-axis direction, and can also be obtained by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). Got it. In the present specification, the so-called hysteresis value means the hysteresis value in the plane.

In the present invention, at least one of the polarizer protective films is characterized by having a polarizer protective film having the above specific hysteresis value. Have this specific late The arrangement of the hysteresis protective film of the hysteresis is not particularly limited, and is preferably a polarizer protective film disposed on the incident light side of the polarizing plate on the incident light side of the liquid crystal display device, or a polarizing plate disposed on the light emitting side. The polarizer protective film on the light side is emitted. A particularly preferable aspect is a polarizer protective film disposed on the light-emitting side of the polarizing plate on the light-emitting side as a polyester film having the specific hysteresis value. When the polyester film is disposed at a position other than the above, the polarizing characteristics of the liquid crystal cell may be changed.

The polarizing plate of the present invention is characterized in that it has a configuration in which two polarizing mirror protective films are sandwiched between two sides of a polarizing plate coated with iodine such as polyvinyl alcohol (PVA), and the polarizing film protective film has the above-mentioned characteristics. A polarizing plate protective film with a specific hysteresis value. In the other polarizer protective film, a film having no birefringence such as a TAC film or an acrylic film or a norbornene-based film is preferably used.

The polarizing lens is, for example, a dichroic material containing iodine or the like in a polyvinyl alcohol-based film. The polarizer protective film is bonded to the polarizer directly or via the adhesive layer. However, from the viewpoint of improving the adhesion, it is preferred to bond it via an adhesive. In this case, the coating layer constituting the polarizer protective film of the present invention is preferably disposed on the surface in contact with the polarizer or the adhesive layer. In order to adhere the polyester film of the present invention, as a preferred polarizer, for example, a polyvinyl alcohol film is dyed. Adsorption of iodine or dichroic material, one-axis extension in aqueous boric acid solution, maintaining the extended state, and washing. Dry polarized lens. The stretching ratio of one axis extension is usually about 4 to 8 times. As a polyvinyl alcohol-based film, polyvinyl alcohol is suitable, and it is possible to use "Kuraray Vinylon" [made by KURARAY], "Tohcello Vinylon" [TOHCELLO (share) system," "Nikko Vinylon" [Japan A commercial product such as a chemical (share) system. Examples of the dichroic material include iodine, a disazo compound, and a polymethine dye.

The adhesive applied to the polarizer is preferably a water-based one, that is, a person who dissolves in water or disperses an adhesive component in water from the viewpoint of thinning the adhesive layer. For example, a polyvinyl alcohol-based resin, a urethane resin, or the like is used as a main component, and a composition such as an isocyanate compound or an epoxy compound is blended as needed in order to improve the adhesion. The thickness of the adhesive layer is preferably 10 μm or less, more preferably 5 μm or less, still more preferably 3 μm or less.

When a polyvinyl alcohol-based resin is used as a main component of the adhesive, in addition to partially saponified polyvinyl alcohol or fully saponified polyvinyl alcohol, for example, a carboxyl group-modified polyvinyl alcohol, an ethyl acetate-modified polyvinyl alcohol, or a hydroxyl group can be used. A modified polyvinyl alcohol-based resin of a methyl-modified polyvinyl alcohol or an amine-modified polyvinyl alcohol. The concentration of the polyvinyl alcohol-based resin in the adhesive is preferably from 1 to 10% by mass, more preferably from 2 to 7% by mass.

The polarizing plate used in the present invention is preferably provided with various functional layers on the surface of the polyester film for the purpose of preventing writing or glare suppression, damage suppression, etc., for example, selected from a hard coat layer, an antiglare layer, and an antireflection layer. One or more layers of the group consisting of a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an antistatic layer. Such a functional layer can be provided on the surface of the polarizer protective film of the present invention on the side opposite to the surface on which the coating layer is provided. When the various functional layers are provided, the alignment polyester film preferably has an easy-adhesion layer on its surface. In this case, from the viewpoint of suppressing dryness due to reflected light, it is preferred to adjust the refractive index of the easy-adhesion layer to the vicinity of the multiplication and average of the refractive index of the functional layer and the refractive index of the polyester film. Easy to stick The adjustment of the refractive index of the layer can be carried out by a well-known method, for example, by containing titanium or zirconium, other metal species in the binder resin.

(Polyester film)

The polyester film used as the polarizer protective film of the present invention can be obtained by condensing a dicarboxylic acid and a diol. Examples of the dicarboxylic acid component which can be used in the production of the polyester film include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid. Acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylic acid, diphenoxy ethane dicarboxylic acid, diphenyl hydrazine carboxylic acid, hydrazine dicarboxylic acid, 1, 3-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclopentanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, two Methylmalonic acid, succinic acid, 3,3-diethyl succinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethylhexyl Diacid, pimelic acid, sebacic acid, dimer acid, sebacic acid, suberic acid, dodecane dicarboxylic acid, and the like.

Examples of the diol component which can be used in the production of the polyester film include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclopentane dimethanol, and 1,4-. Cyclopentane dimethanol, decamethyl glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis (4) -Hydroxyphenyl)propane, bis(4-hydroxyphenyl)anthracene, and the like.

One type or two or more types of the dicarboxylic acid component and the diol component which are constituting the polyester film can be used. Specific examples of the polyester resin constituting the polyester film include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Etc., preferably polyethylene terephthalate or polyethylene naphthalate. Such trees The grease is excellent in transparency and excellent in heat and mechanical properties, and the hysteresis value can be easily controlled by stretching processing. In particular, polyethylene terephthalate is a most suitable material because of its large intrinsic birefringence and easy to obtain a large hysteresis value even if the thickness of the film is thin.

In order to suppress deterioration of an optical functional dye such as iodine dye, the film of the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is particularly preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optical functional pigment due to ultraviolet rays can be suppressed. Further, the transmittance in the present invention is measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type). When the ultraviolet absorber is blended in the polyester film, the polyester film is preferably composed of three or more layers, and the ultraviolet absorber is blended in a layer other than the outermost layer (i.e., the intermediate layer).

When the transmittance of the film of the present invention at a wavelength of 380 nm is 20% or less, a coating liquid containing an ultraviolet absorber can be applied to the surface of the film by adding an ultraviolet absorber to the film, and the type of the ultraviolet absorber can be appropriately adjusted. The concentration, the thickness of the film, and the like are achieved. The ultraviolet absorber used in the present invention is a well-known substance. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber. From the viewpoint of transparency, an organic ultraviolet absorber is preferred. The organic ultraviolet absorber is exemplified by a benzotriazole type, a diphenyl ketone type, a cyclic imidate type, and the like, and is not particularly limited as long as it is within the range of the predetermined absorbance of the present invention. However, from the viewpoint of durability, it is particularly preferably a benzotriazole-based or cyclic imido ester-based system. When two or more kinds of ultraviolet absorbers are used in combination, the ultraviolet absorbing effect can be further improved by absorbing ultraviolet rays of respective wavelengths at the same time.

Examples of the diphenylketone-based ultraviolet absorber, the benzotriazole-based ultraviolet absorber, and the acrylonitrile-based ultraviolet absorber include 2-[2'-hydroxy-5'-(methacryloxymethylmethyl). Phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-(methacryloxyethyl)phenyl]-2H-benzotriazole, 2-[2'- Hydroxy-5'-(methacryloxypropyl)phenyl]-2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxydiphenyl ketone, 2, 2',4,4'-tetrahydroxydiphenyl ketone, 2,4-di-t-butyl-6-(5-chlorobenzotriazol-2-yl)phenol, 2-(2'-hydroxy- 3'-Tertibutyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl- 6-(t-butyl)phenol, 2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2- Phenyl, etc. Examples of the cyclic imine ester-based ultraviolet absorber include 2,2'-(1,4-phenylene)bis(4H-3,1-benzo). 4-keto), 2-methyl-3,1-benzo 4-ketone, 2-butyl-3,1-benzo 4-ketone, 2-phenyl-3,1-benzo 4-ketone and the like. However, it is not particularly limited by these.

Further, in addition to the ultraviolet absorber, a variety of additives are also preferred insofar as the effects of the present invention are not impaired. Examples of the additive include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, and anti-gelation. Agent, surfactant, etc. Further, in order to achieve high transparency, it is preferred that the polyester film contains substantially no particles. The term "substantially free of particles" means that, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescent X-ray analysis, the weight is 50 ppm or less, preferably 10 ppm or less, and particularly preferably the content below the detection limit.

The polarizer protective film of the present invention contains a polyester layer on at least one side of the polyester film in order to improve adhesion to a polarizing mirror or a polyvinyl alcohol-based resin layer such as a water-based adhesive provided on one or both sides thereof. An easy-adhesion layer (coating layer) made of a resin composition of the resin (A) and the polyvinyl alcohol-based resin (B). The coating layer is provided on at least one side of the polyester film or on both sides. On the other hand, a heterogeneous resin coating layer may be provided, and the above functional layer may be provided on the coating layer.

The polyester resin (A) is used to obtain adhesion to the base film, and the polyvinyl alcohol resin (B) is used to obtain a polarizer. The adhesion of the water-based adhesive makes it possible to coexist with the adhesion of these two layers.

(covering layer)

In the present invention, the coating layer contains a polyvinyl alcohol resin and a polyester resin as a binder resin, and the surface of the coating layer has a phase in which a phase in which a polyvinyl alcohol resin is agglomerated (PVA phase) and a polyester resin are condensed. The phase separation structure formed by (PEs phase). In addition, in the present invention, the coating layer containing a polyvinyl alcohol-based resin and a polyester-based resin means a resin layer formed by using a polyvinyl alcohol-based resin and a polyester-based resin as a raw material component. Similarly, when the coating layer contains a component other than the resin (for example, a crosslinking agent), it means a coating layer formed by using the resin and other components (for example, a crosslinking agent) as a raw material.

The nanophase separation structure on the surface of the coating layer means two types of nano phase (or region) of the PVA phase and the PEs phase which are clearly distinguished by the detection of the surface of the coating layer using the scanning probe microscope described later. It is present on the surface of the coating. The PVA phase is a phase in which a polyvinyl alcohol-based resin is agglomerated as described above. Therefore, the PVA phase is mainly composed of Although it is composed of a polyvinyl alcohol-based resin, it can be distinguished from PEs by a scanning probe microscope, and may contain other components (for example, a crosslinking agent or a trace amount of PEs) which are mixed with the coating layer. ). Similarly, the so-called PEs are phases in which a polyester resin is agglomerated. Therefore, the PEs phase is mainly composed of a polyester resin, but it can be distinguished from the PVA by a scanning probe microscope, and other components constituting the coating layer (for example, a crosslinking agent or a trace amount of PVA) can be used. Mix exists.

The size and shape of the PVA phase and the PEs phase are not particularly limited as long as they satisfy the surface fraction of the PVA phase to be described later, and can be recognized as a structure of the nanophase separation structure in the technical field. Specific examples of the nano phase separation structure include a sea-island structure, a core-shell structure, and a laminated structure (laminated structure) in which the phases are regularly arranged.

When the nano-separation structure in which the surface of the coating layer is an island structure is formed, either of the PVA phase and the PEs phase can form a phase corresponding to the island. As shown in Fig. 1, the island structure can be in the form of an independent "island" and can also be a continuous "island". The size of the island structure is not particularly limited, and for example, an island structure having a width in the short axis direction of at most 20 nm and 500 nm or less and a length in the long axis direction exceeding 50 nm is dominant. By having such a nanometer-sized dispersion structure, the properties of the two resins can be appropriately coexisted.

The core-shell structure of one of the nanophase separation structures is, for example, a structure in which a PVA phase surrounds the periphery of the PEs phase and a PEs phase surrounds it. In any case, when the surface of the coating layer is measured by a scanning probe microscope, the phase recognized by the aggregate of the polyvinyl alcohol-based resin and the phase recognized by the aggregate of the polyester resin are not significantly biased. Decentralized Among them, it is preferable from the viewpoint of exerting excellent adhesion. In the surface of the coating layer having the nano phase separation structure as described above, the area ratio of the PVA phase defined by the following formula is preferably 30% or more and less than 99%.

PVA phase surface fraction (%) = (area of PVA phase / measured area) × 100

The area of the PVA phase is measured by a phase measurement mode of a scanning probe microscope to be described later. In this case, the polyvinyl alcohol phase is, for example, a dark phase in a phase image. The measurement area is not particularly limited, but may be, for example, 1 μm × 1 μm.

The PVA surface fraction is preferably from 30 to 99%. When less than 30%, the surface fraction of the PEs phase in the surface of the coating layer is relatively large, for the polarizer. The adhesion of the water-based adhesive is lowered. On the other hand, when the PVA surface fraction is 99% or more, the adhesion to the polyester film (substrate) may be lowered. The lower limit of the PVA surface fraction of the surface of the coating layer is preferably 30%, particularly preferably 35%, more preferably 40%. On the other hand, the upper limit of the PVA surface fraction is preferably 99%, particularly preferably 95%, more preferably 90%.

The PVA surface fraction of the nanophase separation structure can be measured by the paper weight method or the image analysis method described in the examples below.

The reason why the adhesion is improved by the above-described nano-separation structure is considered as follows. The polyvinyl alcohol-based resin is rich in hydrophilicity, and the polyester-based resin is rich in hydrophobicity. Therefore, only the two resins are mixed. When the coating is applied, the two resins are completely separated, and sufficient adhesion cannot be exhibited. On the other hand, although the two resins can be forcibly mixed by a surfactant or the like, in this case, sufficient adhesion cannot be exhibited due to the deterioration of the properties of the two resins. With respect to this, the two resins are formed into a nano phase separation structure, and a PVA phase having a predetermined ratio is present on the surface of the coating layer, so that it can be efficiently exhibited at the same time. Due to the adhesion of the PVA resin to the polarizer or the adhesive disposed thereon, and the adhesion of the PEs resin to the polyester film.

The nanophase separation structure on the surface of the coating layer can be measured and confirmed by a phase measurement mode (phase mode) of a scanning probe microscope (SPM). The phase mode is a surface morphology observation and a simultaneous phase delay measurement mode in a normal power mode (DFM mode; when SPM is manufactured by SII NANO TECHNOLOGY).

A phase separation structure in which a coating layer is measured by a phase measurement mode (phase mode) of a scanning probe microscope (SPM) will be described. In the phase mode, the phase delay of the cantilever vibration when the DFM is operated is detected. In the DFM operation, the probe is controlled in such a way that the vibration amplitude of the resonant cantilever becomes constant. The distance between the samples was measured and the shape was measured. Here, when the signal for vibrating the bimorph (piezoelectric element) that vibrates the cantilever is referred to as an "input signal", in the phase measurement mode, the "input signal" is detected simultaneously with the vibration amplitude. That is, the phase delay of the effective cantilever vibration signal. The phase delay is sensitive to the influence of surface physical properties, and the softer the surface of the sample is delayed. By visualizing the magnitude of the phase delay, the distribution of surface physical properties (referred to as phase image, phase, etc.) can be observed. By using the phase measurement mode of the scanning probe microscope (SPM), it is possible to measure the phase separation structure and confirmation of the presence of a plurality of resin phases having different physical properties on the surface.

The evaluation of the phase separation structure of the coating layer may be carried out in other modes such as a frictional force measurement mode or a viscoelasticity measurement mode, as long as it is a surface physical property distribution evaluation mode of the scanning probe microscope. Observation of the most sensible phase separation structure mode. Further, in the phase measurement mode, not only the phase delay can be detected by the difference in the viscoelasticity of the coating layer, but also the phase retardation can be detected by the difference in surface physical properties such as the magnitude of the adsorption force.

The coating layer of the present invention has a nano phase separation structure, and a polarizing mirror or an aqueous adhesive, in particular, a polyvinyl alcohol-based polarizer or an aqueous adhesive, exhibits high adhesion equivalent to or higher than that of triacetyl cellulose. Specifically, in the adhesion test shown in the examples to be described later, the residual area of the coating layer after peeling once is preferably 90% or more, particularly preferably 95% or more, more preferably 100%, after 5 consecutive peelings. The residual area is preferably 75% or more, more preferably 85% or more, more preferably 95% or more, and the residual area after 10 consecutive peeling is preferably 50% or more, particularly preferably 80% or more, more preferably 90%. More preferably, the above is 93% or more, and particularly preferably 95% or more.

The phase separation structure as described above can be controlled by controlling the resin concentration, the resin type, and drying as will be described later. Heating conditions, etc. are obtained.

Hereinafter, each composition of the coating layer will be described in detail.

(polyvinyl alcohol resin)

The polyvinyl alcohol-based resin to be used as a component of the coating layer is not particularly limited as long as it is a polyvinyl alcohol-based resin. In a specific example thereof, a polyvinyl alcohol which is obtained by saponifying polyvinyl acetate, a derivative thereof, and a saponified product of a copolymer of a monomer copolymerizable with vinyl acetate, and a polyvinyl alcohol Modified polyvinyl alcohol, such as hydroformylation, urethane, etherification, grafting, and phosphation. Examples of the monomer include unsaturated carboxylic acids such as maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, and (meth)acrylic acid, and esters thereof; α-olefins such as ethylene and propylene; (methyl)allylsulfonic acid (sodium), sodium sulfonate (monoalkyl maleate), Sodium disulfonate alkyl maleate, N-methylol acrylamide, acrylamide alkyl sulfonate alkali salt, N-vinyl pyrrolidone, N-vinyl pyrrolidone derivative, and the like. These polyvinyl alcohol-based resins may be used alone or in combination of two or more.

The polyvinyl alcohol-based resin to be used in the present invention may, for example, be a vinyl alcohol-vinyl acetate copolymer, a vinyl alcohol-vinyl butyral copolymer or an ethylene-vinyl alcohol copolymer. It is a vinyl alcohol-vinyl acetate copolymer or an ethylene-vinyl alcohol copolymer. The degree of polymerization of the polyvinyl alcohol-based resin is not particularly limited, but the degree of polymerization is preferably 3,000 or less from the viewpoint of the viscosity of the coating liquid.

The copolymerization ratio of vinyl alcohol is expressed by the degree of saponification. The degree of saponification of the polyvinyl alcohol-based resin of the present invention is not particularly limited as long as it exhibits excellent adhesion, but is preferably 60 mol% or more. The upper limit of the degree of saponification of the polyvinyl alcohol-based resin is preferably 95 mol% or less, more preferably 85 mol% or less. The degree of saponification is preferably 65 mol% or more and 83 mol% or less, more preferably 68 mol% or more and 80 mol%, more preferably 70 mol% or more and less than 80 mol%, and more preferably 71 mol%. % or more of 78% by mole or less, particularly preferably 73% by mole or more and 75 % by mole or less. When the degree of saponification of the polyvinyl alcohol-based resin is at least the above lower limit, it has an adhesive property suitable for an aqueous adhesive or a polarizer, and can be suitably phase-separated from the polyester resin. When the degree of saponification of the polyvinyl alcohol-based resin is not more than the above upper limit (or less than), a nano phase separation structure can be formed more suitably with the polyester resin. The degree of saponification of the vinyl alcohol-based resin can be determined by the amount of alkali consumption required for hydrolysis of a copolymerization unit such as vinyl acetate or by composition analysis by NMR.

The content of the polyvinyl alcohol-based resin is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and still more preferably 20% by mass or more and 50% by mass or less. When the content of the polyvinyl alcohol-based resin is at least the above lower limit, the PVA surface fraction becomes higher, and the polarizer is used. The adhesiveness of the aqueous resin is suitable. On the other hand, if it is less than or equal to the above upper limit, it is suitable for adhesion to a polyester film substrate.

(Polyester resin)

The polyester resin used for the coating layer of the present invention is a copolymer obtained by polycondensation of a dicarboxylic acid component and a diol component, and as the dicarboxylic acid component and the diol component, a polymer used as the substrate can be used. The composition of the ester film.

From the viewpoint of improving the adhesion to the polyester film substrate, it is preferred to use the same or similar structure as the dicarboxylic acid component in the polyester film. The dicarboxylic acid component of the nature is a dicarboxylic acid component of the polyester resin. Therefore, for example, when an aromatic dicarboxylic acid is used as the dicarboxylic acid component of the polyester film, it is preferred to use an aromatic dicarboxylic acid as the dicarboxylic acid component of the polyester resin. As such an aromatic dicarboxylic acid component, terephthalic acid and isophthalic acid are preferable. For example, the other dicarboxylic acid component may be copolymerized by adding another aromatic dicarboxylic acid in a range of 10 mol% or less.

The glass transition temperature of the polyester resin is preferably 25 ° C or more, more preferably 30 ° C or more, and still more preferably 35 ° C or more from the viewpoint of blocking resistance. Further, the upper limit of the glass transition temperature is preferably 110 ° C or lower, more preferably 100 ° C or lower, and still more preferably 90 ° C or lower. When the upper limit of the glass transition temperature is the above or lower, it is easy to form a phase by heat treatment which will be described later. from. The glass transition temperature of the polyester resin can be controlled by introducing a copolymerization component, particularly a branched diol component, as will be described later.

The diol component of the polyester resin is preferably composed of ethylene glycol and a branched diol. It is considered that by having a branched structure, stress relaxation of the coating layer is facilitated, and adhesion can be suitably achieved. Examples of the diol component branched as described above include 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, and 2-methyl-2- Butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-positive -1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1 , 3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol Wait.

The lower limit of the molar ratio of the branched diol component is preferably 10 mol%, particularly preferably 20 mol%, based on the total diol component. On the other hand, the upper limit is preferably 80% by mole, more preferably 70% by mole, and particularly preferably 60% by mole.

Further, diethylene glycol, propylene glycol, butanediol, hexanediol or 1,4-cyclopentane dimethanol may be used in combination as needed.

In the polyester resin used as a component of the coating layer in the present invention, a water-soluble or water-dispersible resin is preferably used from the viewpoint of forming a structure in which a phase separation from a polyvinyl alcohol-based resin is suitable. In order to make the polyester resin water-soluble or water-dispersible, it is preferred to copolymerize a compound containing a hydrophilic group such as a sulfonate group or a carboxylate group. In view of the fact that the acid value of the polyester resin is kept low, and the hydrophilicity is imparted while controlling the reactivity with the crosslinking agent, the dicarboxylic acid component having a sulfonate group is bonded. suitable. Examples of the dicarboxylic acid component having a sulfonate group include sulfophthalic acid, 5-sulfoisophthalic acid, 4-sulfonaphthalene isophthalic acid-2,7-dicarboxylic acid, and 5-(4-sulfophenoxy)isophthalic acid or an alkali metal salt thereof, of which 5-sulfoisophthalic acid is preferred.

The dicarboxylic acid component having a sulfonate group is preferably from 1 to 15 mol%, more preferably from 1.5 to 12 mol%, more preferably from 2 to 10 mol%, based on the dicarboxylic acid component of the polyester resin. . When the dicarboxylic acid component having a sulfonate group is at least the above lower limit, it is suitable for water solubility or water dispersion of the polyester resin. Further, when the dicarboxylic acid component having a sulfonate group is at most the above upper limit, it is suitable for adhesion to a polyester film substrate.

When a crosslinking agent is used in combination as described later, it is preferred that the carboxylic acid group of the reactive group of the polyester resin and the crosslinking agent is small from the viewpoint of forming a suitable phase separation structure. It is considered that by reducing the carboxyl group reactive with the crosslinking agent, the reactivity with the crosslinking agent is lowered, and as a result, it is incompletely mixed with the polyvinyl alcohol-based resin, and the crosslinked polyvinyl alcohol-based resin can be used. The phase separation structure is suitably maintained. From such a viewpoint, the acid value of the polyester resin is preferably 20 KOHmg/g or less, more preferably 15 KOHmg/g or less, still more preferably 10 KOHmg/g or less, still more preferably 8 KOHmg/g or less, particularly preferably 5 KOHmg / g or less. The acid value of the polyester resin can be theoretically determined from the results of component analysis such as titration or NMR described later.

In order to control the acid value of the polyester resin in the above range, it is preferred to reduce the amount of introduction of the carboxylate group for water-solubilization or water-dispersion, or to use a hydrophilic group other than the carboxylate group, or to reduce The carboxylic acid terminal concentration of the polyester resin. As a method of reducing the concentration of the carboxylic acid terminal of the polyester resin, a polyester resin having a terminal end group modified with a carboxylic acid terminal group is preferably used. Or a polyester resin having a large number average molecular weight of a polyester resin. Therefore, the number average molecular weight of the polyester resin is preferably 5,000 or more, more preferably 6,000 or more, still more preferably 10,000 or more. Further, it is preferable to use a polyester resin as a constituent component to reduce the content of three or more acid components.

The content of the polyester resin in the coating layer is preferably 40% by mass or more and 90% by mass or less, more preferably 45% by mass or more and 85% by mass or less, and still more preferably 50% by mass or more and 80% by mass or less. When the content of the polyester resin is at least the above lower limit, it is suitable for adhesion to a polyester film substrate, and if it is at most the above upper limit, it is suitable for adhesion to a polarizing mirror or a water-based adhesive provided thereon.

(crosslinking agent)

A more suitable nanophase separation structure can be formed by using a crosslinking agent in combination with the coating layer. It is considered that this is because the hydroxyl groups of the polyvinyl alcohol-based resin are cross-linked to each other, and the polyvinyl alcohol-based resin is easily aggregated, and as a result, a suitable separation structure is formed.

The crosslinking agent is not particularly limited as long as it has crosslinkability with a hydroxyl group, and examples thereof include a melamine system, an isocyanate system, and a carbonization system. A compound such as an oxazoline system or an epoxy group. From the viewpoint of the stability of the coating liquid over time, it is preferably a melamine-based, an isocyanate-based or a carbonized secondary system. An oxazoline compound. Further, the crosslinking agent is preferably a melamine-based compound or an isocyanate-based compound which is suitably subjected to a crosslinking reaction with a hydroxyl group of a polyvinyl alcohol-based resin. It is considered that this is because the melamine-based compound or the isocyanate-based compound reacts with the hydroxyl group with respect to the carbodiimide cross-linking agent and the carboxyl group. Therefore, the polyvinyl alcohol-based resin having a hydroxyl group as a functional group is suitable for topography. Trade union structure. Further, when a melamine-based compound or an isocyanate compound is used, the polyvinyl alcohol in the coating layer is suitably formed into a crosslinked structure, and the surface on the opposite side of the polyester film is easily moved, and the surface fraction of PVA is further increased to form a suitable one. Island structure. Among them, an isocyanate compound is particularly preferably used from the viewpoint of a suitable crosslinking reaction with a hydroxyl group of a polyvinyl alcohol-based resin and excellent transparency. Further, in order to promote the crosslinking reaction, a catalyst or the like may be suitably used as needed.

As the isocyanate compound, a low molecular or high molecular diisocyanate or a trivalent or higher polyisocyanate can be used. For example, examples of the isocyanate compound include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and 2,4'-diphenylmethane diisocyanate. 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, phenyl diisocyanate, tetramethyl dimethyl diisocyanate, 4, 4'- Phenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenyl Aromatic diisocyanates such as methane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate An aromatic aliphatic diisocyanate such as benzodimethyl diisocyanate, isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate or 1,3-bis(isocyanatemethyl)cyclopentane. Aliphatic diisocyanates such as alicyclic diisocyanates, hexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate, and the like Of trimer acid ester compound. Furthermore, the excess amount of these isocyanate compounds is made with ethylene glycol and propylene. Low molecular weight active hydrogen compounds such as diol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, or polyester polyols, polyether polyols, polyfluorenes A polymer-containing terminal isocyanate group-containing compound obtained by reacting a polymer active hydrogen compound such as an amine.

As the crosslinking agent used in the present invention, a blocked isocyanate compound is also preferred. By adding a blocked isocyanate compound, the temporal stability of the coating liquid can be more suitably improved.

The blocked isocyanate compound can be prepared by subjecting the above isocyanate compound and a blocking agent to an addition reaction by a conventional method. Examples of the isocyanate blocking agent include phenols such as phenol, cresol, xylenol, resorcin, nitrophenol, and chlorophenol; thiophenes such as thiophene and methylthiophene; Anthraquinones such as ethyl ketoxime and cyclohexanone oxime, alcohols such as methanol, ethanol, propanol and butanol, halogen-substituted alcohols such as 2-chloroethanol and 1,3-dichloro-2-propanol Tertiary alcohols such as tert-butanol and third pentanol, ε-caprolactam, δ-valeroinamide, γ-butyrolactam, β-propyl decylamine, etc. Active methylene compounds such as amines, aromatic amines, quinones, ethyl acetonide, acetamidine acetate, ethyl malonate, thiols, imines, ureas, diaryls Compounds, sodium hydrogen sulfite, and the like.

Examples of the melamine compound include a melamine compound substituted with a substituent -(CH2)nOR (wherein n is an integer of 1 to 3, and R is an alkyl group having 1 to 4 carbon atoms), and R in the above formula is preferred. Is a methyl group. The number of the above substituents in one melamine structure is preferably from 3 to 6. As a specific example of the melamine compound, Sumitomo Chemical Co., Ltd. M-3, MK, M-6, M-100, MC, etc. of the Sumitex resin series, or Methyl melamine resin MW-22, MX-706, MX-042, etc. manufactured by Chemical Co., Ltd. and Chemical Co., Ltd.

It is also possible to use a melamine compound and an epoxy compound together or An oxazoline compound, an epoxy compound at the time, The content of the oxazoline-based compound is preferably less than 10% by weight, particularly preferably less than 5% by weight, more preferably less than 2% by weight, particularly preferably less than 1% by weight. Epoxy compound or When the content of the oxazoline-based compound is more than the above upper limit, the PVA surface fraction cannot be kept high by the ratio of the polyester to the polyvinyl alcohol in the coating layer, and the adhesion may be poor.

Further, an isocyanate compound and an epoxy compound may be used in combination or An oxazoline compound, an epoxy compound at the time, The content of the oxazoline-based compound is preferably less than 10% by weight, particularly preferably less than 5% by weight, more preferably less than 2% by weight, particularly preferably less than 1% by weight. Epoxy compound or When the content of the oxazoline-based compound is more than the above upper limit, the PVA surface fraction cannot be kept high by the ratio of the polyester to the polyvinyl alcohol in the coating layer, and the adhesion may be poor.

The content of the crosslinking agent is preferably 2% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and still more preferably 8% by mass or more and 30% by mass or less. When the content of the crosslinking agent is at least the above lower limit, it is suitable for crosslinking formation of a polyvinyl alcohol-based resin, and when it is at most the above upper limit, it is suitable for exhibiting an adhesive effect by a binder resin.

The mixing ratio (B)/(A) of the polyester resin (A) and the polyvinyl alcohol resin (B) is preferably 0.2 to 1.25 by mass ratio, more preferably 0.25 to 1, more preferably 0.25 to 0.5. Very good is 0.25~0.45. (B) / (A) if the above lower limit The above is suitable for adhesion to a polyester film substrate, and if it is below the above upper limit, it is suitable for a polarizer. Adhesion of water-based resin.

The mixing ratio of the polyester resin (A) and the polyvinyl alcohol resin (B) to the crosslinking agent (C) ((A) + (B)) / (C) is preferably 2 to 50 by mass ratio, especially Good for 5~40, better for 8~30. When (A)+(B))/(C) is at least the above lower limit, it is suitable to exhibit an adhesive effect by the binder resin component, and if it is at most the above upper limit, it is suitable for the adhesion effect by phase separation.

(additive)

In the coating layer constituting the polarizer protective film of the present invention, well-known additives such as a surfactant, an antioxidant, a catalyst, a heat stabilizer, a weathering stabilizer, and the like may be added to the extent that the effects of the present invention are not impaired. Ultraviolet absorbers, organic slip agents, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, and the like.

In the present invention, in order to further improve the anti-blocking property of the coating layer, it is also preferred to add particles to the coating layer. In the present invention, the particles contained in the coating layer are, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, vermiculite, alumina, talc, kaolin, clay, or the like, or a mixture thereof. Other general inorganic particles, such as inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, and the like, or styrene, acrylic, melamine, Organic polymer particles such as benzoguanamine or anthrone.

The average particle diameter of the particles in the coating layer (the average particle diameter based on the number of measurements by SEM, the same applies hereinafter) is preferably 0.04 to 2.0 μm, more preferably 0.1 to 1.0 μm. If the average particle diameter of the inert particles is less than 0.04 μm, The formation of irregularities on the surface of the film is insufficient, and the slidability or the take-up property of the film is lowered rationally, and the workability at the time of bonding is lowered. On the other hand, when it exceeds 2.0 μm, it is easy to cause the particles to fall off. The concentration of the particles in the coating layer is preferably from 1 to 20% by mass, more preferably from 5 to 15% by mass, based on the solid content.

In the present invention, the thickness of the coating layer can be suitably set in the range of 0.01 to 2 μm, but in order to achieve both workability and adhesion, it is preferably in the range of 0.03 to 0.25 μm, particularly preferably 0.05 to 0.25 μm, more preferably 0.05. ~0.2μm.

When the thickness of the coating layer is less than 0.03 μm, the adhesiveness is insufficient. If the thickness of the coating layer exceeds 0.25 μm, adhesion may occur.

(Method for producing polyester film)

As a method for producing a polyester film, the most common production method is a method in which a polyester resin is melted and extruded into a sheet shape, and the formed unaligned polyester is at a temperature higher than a glass transition temperature, and the speed difference between the rolls is used. After the longitudinal extension, the heat treatment is applied by stretching in the transverse direction by a tenter.

The polyester film of the present invention may be a one-axis stretch film or a biaxially stretched film, but when a biaxially stretched film is used as the polarizer protective film, no rainbow is observed even when viewed from directly above the film face. The color spots, but when viewed from the oblique direction, there will be a situation in which a rainbow-like color spot is observed, so care must be taken.

This phenomenon is because the biaxially stretched film is composed of a refractive index ellipsoid having a different refractive index in the traveling direction, the width direction, and the thickness direction, and the hysteresis value becomes zero due to the light penetration direction inside the film (refraction) The rate ellipsoid presents a true circle) the direction exists. Therefore, if it is specific When the liquid crystal display screen is observed in the direction, there is a case where the hysteresis value becomes zero, and the rainbow-like color spots appear concentrically around the point. Further, if the angle from the directly above (normal direction) of the film surface to the position where the rainbow-colored stain is seen is regarded as θ, the larger the angle of the birefringence in the plane of the film is, the more difficult it is. I saw a rainbow-like stain. Since the angle θ tends to be small in the biaxially stretched film, it is preferable that the one-axis stretch film is difficult to see a rainbow-like color spot.

However, in the completely monoaxial (1-axis symmetry) film, the mechanical strength in the direction orthogonal to the alignment direction is remarkably lowered. The present invention preferably has a biaxial property (2-axis symmetry) in a range in which a rainbow-like color patch does not substantially occur or a rainbow-colored color patch does not occur in a viewing angle range required for a liquid crystal display screen.

As an index for judging the viewing difficulty of the rainbow-like color patch, there is a method of evaluating the difference between the hysteresis value (in-plane hysteresis value) and the thickness direction hysteresis value (Rth). The phase difference in the thickness direction means an average of the phase differences obtained by multiplying the two birefringences ΔNxz and ΔNyz from the cross section of the film thickness direction by the respective film thicknesses d. The smaller the difference between the in-plane hysteresis value and the thickness direction hysteresis value, the more the effect of the birefringence caused by the observation angle is increased isotropic, so the change in the hysteresis value due to the observation angle is smaller. Therefore, it is difficult to determine the rainbow-like color unevenness caused by the observation angle.

The ratio (Re/Rth) of the hysteresis value to the thickness direction retardation value of the polyester film of the present invention is preferably 0.200 or more, more preferably 0.500 or more, still more preferably 0.600 or more. The larger the ratio (Re/Rth) of the hysteresis value to the hysteresis value in the thickness direction, the more the effect of birefringence is increased, and the occurrence of rainbow-like color spots due to the observation angle is less likely to occur. Therefore, on a complete axis In the (one-axis symmetry) film, the ratio (Re/Rth) of the hysteresis value to the thickness direction hysteresis value was 2.0. However, as described above, as the near-complete one-axis (1-axis symmetry) film is approached, the mechanical strength in the direction orthogonal to the alignment direction is remarkably lowered.

On the other hand, the ratio (Re/Rth) of the hysteresis value to the thickness direction hysteresis value of the polyester film of the present invention is preferably 1.2 or less, more preferably 1.0 or less. In order to completely suppress the occurrence of rainbow-like color spots due to the observation angle, the ratio (Re/Rth) of the hysteresis value to the phase difference in the thickness direction is not necessarily 2.0, and 1.2 or less is sufficient. Moreover, even if the ratio is 1.0 or less, the viewing angle characteristics required by the liquid crystal display device (180 degrees left and right, about 120 degrees above and below) can be sufficiently satisfied.

When the film forming conditions of the present invention are specifically described, the longitudinal stretching temperature and the lateral stretching temperature are preferably 80 to 130 ° C, particularly preferably 90 to 120 ° C. The longitudinal stretching ratio is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times. Further, the lateral stretching ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. In order to control the hysteresis value within the above range, it is preferable to control the ratio of the longitudinal stretching ratio to the lateral stretching ratio. If the difference between the vertical and horizontal stretching ratios is too small, it is difficult to produce a hysteresis value difference. Also, setting a low extension temperature is also a better correspondence for increasing the hysteresis value. In the subsequent heat treatment, the treatment temperature is preferably from 140 to 240 ° C, particularly preferably from 180 to 240 ° C.

The coating layer can be provided after the film is manufactured or in the manufacturing step. In particular, from the viewpoint of productivity, it is preferred to apply a coating liquid at any stage of the film production step, that is, at least one side of the PET film which is not stretched or stretched, to form a coating layer.

Any method known in the art can be used for applying the coating liquid to a PET film. For example, a reverse roll coating method, a gravure coating method, a kiss coating method, a die coating method, a roll brush method, a spray coating method, an air knife coating method, a wire rod coating method, and a tube scraping method are mentioned. , impregnation coating method, curtain coating method, and the like. These methods can be applied individually or in combination.

In the present invention, the thickness of the finally obtained coating layer is preferably from 0.04 to 0.33 g/m ² . When the amount is less than 0.04 g/m ² , the adhesiveness is lowered, and when it is thicker than 0.33 g/m ² , the adhesion and the sliding property are lowered.

After the application of the coating liquid, it is preferred to carry out drying in a drying oven. The temperature of the dry air blown on the coated surface is preferably 80 ° C or more and less than 150 ° C. Further, the wind speed is preferably 30 m/sec or more. Further, a more preferable drying temperature is 100 ° C or more and less than 150 ° C. In the drying furnace described above, it is preferred to dry the coating film at a temperature of 80 ° C or more and less than 150 ° C immediately after cooling the laminated film having the coating layer to a temperature near room temperature. By the drying step, the fluidity of the coating liquid can be lowered, and the phase separation structure can be suitably carried out.

In the method for producing a laminated polyester film of the present invention, it is preferred to carry out a heat setting treatment at 140 ° C or higher. In the heat setting treatment step, a suitable phase separation state can be formed by temporarily increasing the flow state of the binder in the coating layer. The reason for this is considered to be that, by increasing the flow state of the binder, the polyester resin having a large hydrophobic group and the polyvinyl alcohol resin having a hydrophilic base are separately agglomerated by themselves to form a suitable phase separation state. Further, the crosslinking reaction of the crosslinking agent proceeds, and the phase separation state can be accelerated as one cause. The temperature of each heat setting zone in the heat setting treatment step, although depending on the constituent tree of the thermoplastic resin film of the substrate There are some differences in the type of fat, but it can be suitably set in the temperature range of 140 to 240 ° C, particularly preferably 180 to 240 ° C.

When the maximum temperature of the heat setting treatment step is less than 140 ° C, the fluidity of the binder resin is insufficient, and it is difficult to form a nano phase separation structure in the coating layer. Furthermore, it is not preferable because the heat shrinkage rate of the obtained laminated film becomes large.

The time required from the temperature at which the phase separation of the coating layer starts significantly to the highest temperature at which the heat setting treatment is reached is preferably 3 seconds or more and less than 20 seconds, particularly preferably 4 seconds or more and less than 15 seconds.

In order to control the variation of the hysteresis value, the thickness unevenness of the film is preferably small.

The elongation temperature and the stretching ratio have a large influence on the thickness unevenness of the film, and it is necessary to optimize the film forming conditions from the viewpoint of thickness unevenness. In particular, when the longitudinal stretching ratio is lowered in order to generate a hysteresis value difference, the value of the longitudinal thickness unevenness becomes high. Since the value of the longitudinal thickness unevenness is a region which is extremely high in a certain range of the stretching ratio, it is preferable to set the film forming conditions outside the range.

The thickness unevenness of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and particularly preferably 3.0% or less. The thickness unevenness of the film can be measured by any means, but for example, a continuous strip sample (length 3 m) can be collected in the flow direction of the film, and an electronic micrometer (Militron 1240) made of Seiko-Em can be used. In the measuring machine, the thickness of 100 points was measured at a pitch of 1 cm, and the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness were determined, and the thickness unevenness (%) was calculated by the following formula.

Uneven thickness (%) = ((dmax-dmin) / d) × 100

As described above, the hysteresis value of the film can be controlled to a specific range by appropriately setting the stretching ratio, the stretching temperature, and the thickness of the film. For example, the higher the difference in stretch ratio between the longitudinal extension and the lateral extension, the lower the extension temperature, and the thicker the thickness of the film, the easier it is to obtain a high hysteresis value. Conversely, the lower the difference in stretch ratio between the longitudinal extension and the transverse extension, the higher the extension temperature, and the thinner the thickness of the film, the easier it is to obtain a low hysteresis value. Further, the higher the extension temperature, the lower the total stretching ratio, and the easier it is to obtain a film having a low ratio of hysteresis value to retardation value (Re/Rth). Conversely, the lower the extension temperature, the higher the total stretching ratio, and the easier it is to obtain a film having a higher retardation value (Re/Rth) in the thickness direction. The final film condition is set in addition to the physical properties required for processing in addition to the control of the hysteresis value.

The thickness of the polyester film of the present invention is arbitrary, but it is preferably in the range of 15 to 300 μm, more preferably in the range of 15 to 200 μm. Even in the case of a film having a thickness of less than 15 μm, a hysteresis value of 3000 nm or more can be obtained in principle. However, in this case, the anisotropy of the mechanical properties of the film is remarkable, and cracking, breakage, and the like are likely to occur, and the practicality as an industrial material is remarkably lowered. The lower limit of the particularly preferable thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes too thick. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. The upper limit of the particularly preferable thickness is 100 μm which is equivalent to that of a general TAC film. In the above thickness range, in order to also control the hysteresis value within the scope of the present invention, the polyester used as the film substrate is preferably polyethylene terephthalate.

Further, as a method of blending the ultraviolet absorber in the polyester film of the present invention, it can be used in combination with a well-known method, for example, a kneading extruder can be used in advance, and a dried ultraviolet absorber and a polymer raw material can be blended. The master batch is prepared and blended by a method of mixing the specified master batch with a polymer material at the time of film formation. The addition weight of the ultraviolet absorber added to the film is preferably from 0.3 to 1.5%, more preferably from 0.4 to 1.0%.

At this time, the concentration of the ultraviolet absorber of the master batch is preferably 5 to 30% by mass in order to uniformly disperse the ultraviolet absorber and economically blend. As a condition for preparing the master batch, it is preferred to use a kneading extruder, and the extrusion temperature is not less than the melting point of the polyester raw material and 290 ° C or lower, and is extruded at 1 to 15 minutes. At 290 ° C or higher, the amount of reduction of the ultraviolet absorber is large, and the viscosity of the master batch is lowered. When the residence time is 1 minute or less, the uniform mixing of the ultraviolet absorber becomes difficult. At this time, a stabilizer, a color tone adjuster, and an antistatic agent may be added as needed.

Further, in the present invention, it is preferred that the film has a multilayer structure of at least three or more layers, and an ultraviolet absorber is added to the intermediate layer of the film. The intermediate layer contains a film of a three-layer structure of an ultraviolet absorber, and specifically, it can be produced as follows. The pellet of the polyester used as the outer layer, the masterbatch containing the ultraviolet absorber as the intermediate layer, and the pellet of the polyester are mixed at a predetermined ratio, dried, and then supplied to a known extruder for a molten laminate. The slit-shaped die was extruded into a sheet shape, and cooled and solidified on a casting roll to prepare an unstretched film. In other words, two or more extruders, three layers of channels, or a junction block (for example, a junction block having a square junction) are used to laminate the film layers constituting the two outer layers and the film layer constituting the intermediate layer. Press out the 3 layers and cool on the casting roll to make the unstretched thin membrane. Further, in the present invention, in order to remove foreign matter contained in the polyester of the raw material which is a cause of optical defects, it is preferred to perform high-precision filtration at the time of melt extrusion. The filter particle size (initial filtration efficiency: 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filtered particle size of the filter medium exceeds 15 μm, the removal of foreign matter of 20 μm or more is likely to be insufficient.

Example

The present invention will be more specifically described by the following examples, but the present invention is not limited by the following examples, and may be appropriately modified and implemented within the scope of the invention. The technical scope of the invention. In addition, the evaluation method of the physical property in the following examples is as follows.

(1) PVA surface fraction (1-1) Evaluation of phase separation structure

The evaluation of the phase separation structure of the coating layer was carried out in a phase measurement mode (phase mode) using a scanning probe microscope (manufactured by SII NANO TECHNOLOGY, NaNoNavi system/SPA300). In the phase image, the larger the phase retardation, the brighter the performance, and the smaller the phase retardation, the darker the performance. A small phase delay means that the hard or adsorption force is small compared to the others. In the coating layer of the easily-adhesive polyester film of the present invention, the dark phase is the polyvinyl alcohol layer β, and the bright phase is the polyester layer α.

The principle of measurement of the phase measurement mode in the scanning probe microscope is described in the website of SII NANO TECHNOLOGY Co., Ltd. (http://www.siint.com/products/spm/tec_mode/l_pm.html).

The cantilever used for the measurement mainly uses DF3 (spring constant: about 1.6 N/m), and new products are often used in order to prevent the sensitivity and resolution of the probe from being lowered. The scanner uses the FS-20A. Further, the observation system has a resolution of 512 × 512 pixels or more, and the observation field of view is 1 μm × 1 μm. The measurement parameters such as the amplitude attenuation rate of the cantilever, the scanning speed, and the scanning frequency at the time of measurement are linearly scanned, and an observable condition which has the highest sensitivity and good resolution is set.

The obtained phase mode image (bit image format, 512 × 512 pixels) was read by the image processing software (Photoshop version 7.0 made by Adobe), and displayed on the display so that the image size was 205 mm × 205 mm. Next, a black line is drawn at the boundary between the bright phase and the dark phase by a pencil tool (main diameter: 3px) of the same software to make the boundary of the two phases clear. Further, using the coating tool of the same software, the dark phase is painted black, and the bright phase is painted white to be binarized.

(1-2) Determination of PVA surface fraction (1-2-1) paper weight method

The measurement of the PVA surface fraction was measured by the following procedure.

The phase mode image obtained by the above method (1-1) is stored as a digital image in the form of a bit map. Next, the image was printed on a printer (made by Xerox, Docucentre Color a250) and printed on A4 paper. The output image (200 mm × 200 mm) was visually confirmed in a bright room under illumination of 500 lux, and the boundary between the bright phase and the dark phase in the image was made clear by a 4B pencil. At this time, since the dark portion having a diameter of 0.1 μm or less which exists in the bright phase is confirmed to be a particle contained in the coating layer which is biased by the bright phase, the boundary line is not drawn. It is considered to be contained in the bright phase. Then, using a cutter to cut and divide on the boundary line between the bright phase and the dark phase, the quality of the paper of the clear phase (polyester phase α) and the dark phase (polyvinyl alcohol phase β) is determined, and the mass is obtained in units of %. The ratio of the mass of the dark phase (polyvinyl alcohol phase β) relative to the total mass of the paper of the bright phase and the dark phase. This measurement operation was carried out on the measurement samples collected from the five different positions, and the average value was taken as the PVA surface fraction. In addition, the case where phase separation does not occur is described as ×.

Further, in addition to the paper weight method described above, the PVA surface fraction can also be measured by the following image analysis method.

(1-2-2) Image analysis method

The binarized image is represented by the same software, with luminance (black and white) as the horizontal axis and degrees as the vertical axis, and the histogram is displayed to obtain the area ratio of the black portion. This measurement operation was carried out on the measurement samples collected from the five different positions, and the average value was taken as the PVA surface fraction. In addition, the case where phase separation does not occur is described as ×.

(2) Glass transition temperature

According to JIS K7121, a differential scanning calorimeter (manufactured by SEIKO INSTRUMENTS, DSC6200) was used, and 10 mg of the resin sample was heated at 20 ° C/min in a temperature range of 25 to 300 ° C, and the glass transition starting temperature was obtained from the DSC curve. Make the glass transfer temperature.

(3) Number average molecular weight

0.03 g of the resin was dissolved in 10 ml of tetrahydrofuran, using a GPC-LALLS apparatus low-angle light scattering photometer LS-8000 (manufactured by Tosoh Corporation, tetrahydrofuran solvent, reference: polystyrene), using a column temperature of 30 ° C, flow rate A column of 1 ml/min (shodex KF-802, 804, 806 manufactured by Showa Denko Co., Ltd.) was used to measure the number average molecular weight.

(4) Resin composition

The resin was dissolved in heavy chloroform, and subjected to ¹ H-NMR analysis using a nuclear magnetic resonance analyzer (NMR) Gemini-200 manufactured by VARIAN Co., Ltd., and the molar ratio of each composition was determined from the integral ratio.

(5) Acid price

1 g (solid content) of the sample was dissolved in 30 ml of chloroform or dimethylformamide, and phenolphthalein was used as an indicator, and titrated with a 0.1 N potassium hydroxide ethanol solution to obtain a required amount of the carboxyl group per 1 g of the neutralized sample. The amount of KOH (mg) is taken as the acid value.

(6) Degree of saponification

According to JIS-K6726, the residual acetic acid group (% by mole) of the polyvinyl alcohol resin was quantified using sodium hydroxide, and the value thereof was defined as the degree of saponification (% by mole). The same sample was measured three times, and the average value thereof was used as the degree of saponification (% by mole).

(7) PVA adhesion

On the surface of the coating layer of the laminated polyester film, a polyvinyl alcohol aqueous solution (PVA117 manufactured by KURARAY) adjusted to a solid concentration of 5 mass% was applied by a wire rod so that the thickness of the dried polyvinyl alcohol resin layer was 2 μm. Dry at 70 ° C for 5 minutes. In the aqueous solution of polyvinyl alcohol, a red dye which is judged to be easy to be used is used. The prepared evaluation target film was adhered to a glass plate having a thickness of 5 mm to which a double-sided tape was attached, and the opposite side of the surface of the laminated film on which the evaluation target was formed with the polyvinyl alcohol resin layer was attached to the double-sided tape. . Next, using a cutter rail having a gap of 2 mm, a 100-square-shaped blade wound that penetrates the polyvinyl alcohol layer and reaches the base film is generated. Next, attach an adhesive tape (Cellotape (registered trademark) CT-24, manufactured by NIKIBAN Co., Ltd.; 24 mm wide) to 100 A square shaped knife wound surface. When the adhesive is pressed with an eraser to press the air remaining on the interface so as to be completely adhered, the adhesive tape is strongly and vertically peeled off once, five times, and ten times. The number of squares in which the polyvinyl alcohol resin layer was not peeled off was counted as PVA adhesion. That is, when the PVA layer is not peeled off at all, the PVA adhesion rate is 100, and when the PVA layer is completely peeled off, the PVA adhesion rate is regarded as 0. Furthermore, the partial peeling of one square is also included in the number of peeled off.

(8) PVA coating properties

On the surface of the coating layer of the laminated polyester film, a polyvinyl alcohol aqueous solution (PVA117 manufactured by KURARAY) adjusted to a solid concentration of 5 mass% was applied by a wire rod so that the thickness of the dried polyvinyl alcohol resin layer was 2 μm. The coating condition of the polyvinyl alcohol resin layer after drying at 70 ° C for 5 minutes was evaluated by the following criteria.

◎: There is no cissing in the entire coating, and it can be beautifully coated.

○: There is no shrinkage in almost all of the applied, and it can be beautifully coated.

△: Shrinkage occurred in a part of the coating.

×: Shrinkage occurred in almost all of the applied.

(9) Hysteresis value (Re)

The parameter defined by the product of the anisotropy (ΔNxy=| Nx-Ny |) of the orthogonal biaxial refractive index on the film and the film thickness d (nm) (ΔNxy × d) is optical The scale of isotropic and anisotropic. The anisotropy (ΔNxy) of the refractive index of the two axes is obtained by the following method. Use two polarizing plates to determine the direction of the alignment axis of the film to match A rectangle of 4 cm × 2 cm was cut out in the direction of the axis, and used as a sample for measurement. For this sample, the two-axis refractive index (Nx, Ny) and the refractive index (Nz) in the thickness direction were obtained by an Abbe refractometer (NAR-4T manufactured by ATAGO Co., Ltd.), and the above two-axis refraction was obtained. The absolute value of the rate difference (|Nx-Ny |) is taken as the anisotropy of the refractive index (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (Militron 1245D, manufactured by FEINPRUF Co., Ltd.), and the unit was converted into nm. The hysteresis value (Re) is obtained from the product of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film (ΔNxy × d).

(10) Thickness direction hysteresis value (Rth)

It is an average of hysteresis values obtained by multiplying two birefringences ΔNxz (=| Nx-Nz |) and ΔNyz (=| Ny-Nz |) when the film thickness direction cross-section is obtained by the film thickness d. parameter. The Nx, Ny, and Nz and the film thickness d (nm) were obtained by the same method as the measurement of the hysteresis value, and the average values of (ΔNxz × d) and (ΔNyz × d) were calculated to obtain the thickness direction hysteresis value. (Rth).

(11) Light transmittance at a wavelength of 380 nm

Using a spectrophotometer (U-3500 model manufactured by Hitachi, Ltd.), the light transmittance of the wavelength range of 300 to 500 nm was measured using an air layer as a standard, and the light transmittance at a wavelength of 380 nm was obtained.

(12) Rainbow spot observation

On the side of the polarizer made of PVA and iodine, the polyester film produced by the procedure described later is attached so that the absorption axis of the polarizing film is perpendicular to the alignment main axis of the film, and the TAC film is attached to the opposite side. (Fuji FILM Co., Ltd., thickness 80 μm), and made a polarizing plate. Polyester The film becomes a visually recognizable side, and the obtained polarizing plate is disposed in combination with a blue light emitting diode and a crucible. aluminum. A white LED formed by a light-emitting element of a garnet-based yellow phosphor is used as a light source (Nissan Chemical NSPW500CS) liquid crystal display device (having a liquid crystal cell and a polarizing plate having two TAC films on the incident light side as a polarizer protective film) ) on the light side. The front side and the oblique direction of the polarizing plate of the liquid crystal display device were visually observed, and the occurrence of rainbow spots was judged as follows.

◎: No rainbow spots occurred in either direction.

○: When viewed from the oblique direction, a part of the extremely pale rainbow spot was observed.

×: When observed from the oblique direction, the rainbow spot can be clearly observed.

(13) Tear strength

The tear strength of each film was measured in accordance with JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The tearing direction is performed in parallel with the direction of the main axis of the film, as judged below. In addition, the measurement of the direction of the alignment axis was measured by a molecular alignment meter (MOA-6004 type molecular alignment meter manufactured by Oji Scientific Instruments Co., Ltd.).

○: tear strength is 50mN or more

×: tear strength is less than 50mN

(polymerization of polyester resin)

In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux cooler, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, and 14.8 parts by mass of dimethyl group were added. -5-Sodium sulfoisophthalate, 233.5 parts by mass of diethylene glycol, 136.6 The mass part of ethylene glycol and 0.2 part by mass of tetra-n-butyl titanate are subjected to a transesterification reaction at a temperature of from 160 ° C to 220 ° C for 4 hours. Next, the temperature was raised to 255 ° C, and the reaction was gradually reduced, and the reaction was allowed to proceed for 1 hour and 30 minutes under a reduced pressure of 30 Pa to obtain a copolymerized polyester resin (A-1). The obtained copolymerized polyester resin (A-1) was light yellow transparent. The reduction viscosity of the copolymerized polyester resin (A-1) was measured and found to be 0.70 dl/g. The glass transition temperature as determined by DSC was 40 °C.

By the same method, a copolymerized polyester resin (A-2) to (A-5) of another composition was obtained. For these copolymerized polyester resins, the composition (mol% ratio) measured by ¹ H-NMR and other characteristics are shown in Table 1.

(Adjustment of polyester water dispersion)

In a reactor equipped with a stirrer, a thermometer, and a refluxing device, 30 parts by mass of a polyester resin (A-1) and 15 parts by mass of ethylene glycol n-butyl ether were added, and the mixture was heated and stirred at 110 ° C to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added while stirring in the polyester solution. After the addition, the mixture was cooled to room temperature while stirring, to prepare a milky white polyester aqueous dispersion (Aw-1) having a solid content of 30% by mass. Similarly, in place of the polyester resin (A-1), polyester resins (A-2) to (A-5) were used to prepare an aqueous dispersion, and each of them was a polyester aqueous dispersion (Aw-2) to (Aw). -5).

(Adjustment of polyvinyl alcohol aqueous solution)

In a container equipped with a stirrer and a thermometer, 90 parts by mass of water was added, and 10 parts by mass of a polyvinyl alcohol resin (manufactured by KURARAY) (B-1) having a polymerization degree of 500 was gradually added thereto with stirring. After the addition, the mixture was heated to 95 ° C while stirring to dissolve the resin. After the dissolution, the mixture was cooled to room temperature with stirring to prepare a polyvinyl alcohol aqueous solution (Bw-1) having a solid content of 10% by mass.

Similarly, in place of the polyvinyl alcohol resin (B-1), polyvinyl alcohol resins (B-2) to (B-8) were used to form an aqueous solution, and each of them was (Bw-2) to (Bw-8). Table 2 shows the degree of saponification of the polyvinyl alcohol resins (B-1) to (B-8).

(polymerization of blocked polyisocyanate crosslinker C-1)

In a flask equipped with a stirrer, a thermometer, and a reflux cooling tube, 100 parts by mass of a polyisocyanate compound having a hetero-cyanurate structure using hexamethylene diisocyanate as a raw material (Asahi Kasei Chemicals Co., Ltd.) was added. Duranate TPA), 55 parts by mass of propylene glycol monomethyl ether acetate, and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight: 750) were kept at 70 ° C for 4 hours under a nitrogen atmosphere. Then, the temperature of the reaction liquid was lowered to 50 ° C, and 47 parts by mass of methyl ethyl ketoxime was dropped. The infrared spectrum of the reaction liquid was measured, and it was confirmed that the absorption of the isocyanate group disappeared, and a blocked polyisocyanate aqueous dispersion (C-1) having a solid content of 75 mass% was obtained.

(Manufacturing Example 1 - Polyester A)

The temperature of the esterification reaction tank was raised, and 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added at a time point of reaching 200 ° C, and 0.017 parts by mass of antimony trioxide, 0.064 as a catalyst was added with stirring. Parts by mass of magnesium acetate tetrahydrate, 0.16 parts by mass of triethylamine. Next, the pressure was raised, and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C, and then the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ° C for 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, after 15 minutes, the dispersion treatment was carried out by a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tank, and a polycondensation reaction was carried out at 280 ° C under reduced pressure.

After completion of the polycondensation reaction, the filter was filtered through a Naslon filter having a 95% cut-off diameter of 5 μm, and the strand was extruded from the nozzle, and cooled and solidified by using cooling water previously subjected to filtration treatment (pore diameter: 1 μm or less). Cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g and contained substantially no inert particles and internal precipitated particles. (hereinafter, referred to as PET (A)).

(Manufacturing Example 2 - Polyester B)

Mix 10 parts by mass of dried UV absorber (2,2'-(1,4-phenylene) bis(4H-3,1-benzo) -4-ketone), 90 parts by mass of particle-free PET (A) (inherent viscosity: 0.62 dl/g), using a kneading extruder to obtain a polyethylene terephthalate resin containing a UV absorber (B). (hereinafter, referred to as PET(B)),

Example 1

The following coating agent was mixed to prepare a coating liquid having a mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) of 70/30. The polyester water dispersion system uses a polyester resin dispersed aqueous dispersion (Aw-1) having an acid value of 2 KOHmg/g, and a polyvinyl alcohol aqueous solution using a polyvinyl alcohol dissolved aqueous solution having a degree of saponification of 74 mol% ( Bw-4).

(矽, solid concentration 10% by mass)

As a raw material for the base film intermediate layer, 90 parts by mass of the PET (A) resin pellets containing no particles and 10 parts by mass of the PET (B) resin pellets containing the ultraviolet absorber were dried under reduced pressure at 135 ° C ( 1 Torr) After 6 hours, it is supplied to the extruder 2 (for the intermediate layer II layer), and the PET (A) is dried by a usual method and supplied to the extruder 1 (for the outer layer I and the outer layer III), at 285 °C melting. Each of the two kinds of polymers was filtered with a filter material of a stainless steel sintered body (nominal filtration accuracy of 10 μm particles 95% cut off), laminated by two types of three-layered flow blocks, and pressed into a sheet by a nozzle, and then static electricity was used. The casting method was applied, and the film was wound on a casting drum having a surface temperature of 30 ° C to be cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Then, the coating liquid was applied to both sides of the PET film by the reverse roll method so that the coating amount after drying was 0.15 g/m ² , and then dried at 80 ° C for 15 seconds to form a coating layer.

The unstretched film on which the coating layer was formed was guided to a tenter stretching machine, and while grasping the end portion of the film with a jig, it was guided to a hot air region at a temperature of 125 ° C and extended 4.0 times in the width direction.

Subsequently, the width extending in the width direction is maintained, heat treatment is performed at a temperature of 230 ° C for 0.5 second, and relaxation treatment in a width direction of 3% is performed at 230 ° C for 10 seconds to obtain a shaft-aligned PET film having a film thickness of about 50 μm. Polarized mirror protective film.

Example 2

The thickness of the unstretched film was changed by the same method as in Example 1 except that the coating liquid was applied to one side of the unstretched PET film. To obtain a polarizer protective film having a thickness of about 100 μm and axially aligning the PET film.

Example 3

The unstretched film produced by the same method as in Example 1 was heated to 105 ° C using a heated roll group and an infrared heater, and then extended 1.5 times in the traveling direction by a roll group having a peripheral speed difference. A polarizer protective film of a biaxially oriented PET film having a film thickness of about 50 μm was obtained by stretching 4.0 times in the width direction in the same manner as in Example 1.

Example 4

In the same manner as in Example 3, a polarizer protective film of a biaxially oriented PET film having a film thickness of about 50 μm was obtained by stretching 2.0 times in the traveling direction and 4.0 times in the width direction.

Example 5

In the same manner as in Example 3, a polarizer protective film of a biaxially oriented PET film having a film thickness of about 75 μm was obtained by extending 3.3 times in the traveling direction and 4.0 times in the width direction.

Example 6

In the same manner as in Example 1, a polarizing film protective film of a film having a thickness of 50 μm and a shaft-aligned PET film was obtained without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer. Although the obtained film has a rainbow-like color spot, the light transmittance at 380 nm is high, and the optical functional pigment is deteriorated.

Example 7

In the same manner as in Example 3, a polarizing mirror protective film having a film thickness of about 100 μm and a shaft-aligned PET film was obtained by extending 4.0 times in the traveling direction and 1.0 times in the width direction. The obtained film system Re was 3000 nm or more, and the visibility was good, but the mechanical strength was slightly inferior.

Example 8

In the same manner as in Example 3, a polarizer protective film of a biaxially oriented PET film having a film thickness of about 250 μm was obtained by extending 3.5 times in the traveling direction and 3.7 times in the width direction. The obtained film system Re was 4,500 nm or more, but since the Re/Rth ratio was less than 0.2, a very pale rainbow spot was observed in the oblique direction.

Example 9 In the same manner as in Example 1, a polarizing mirror protective film having a film thickness of about 75 μm and an axial alignment PET film was obtained by extending 1.0 times in the traveling direction and 3.5 times in the width direction. Example 10

In the same manner as in Example 1, a polarizer protective film of a shaft-aligned PET film having a thickness of about 275 μm was obtained by changing the thickness of the unstretched film.

Example 11

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and the relaxation treatment after stretching the tenter was changed to 180 °C.

Example 12

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and the relaxation treatment after stretching the tenter was changed to 140 °C.

Example 13

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the mass ratio of the polyester resin/polyvinyl alcohol resin was changed to 60/40.

Example 14

A laminate polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and the mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) was changed to 80/20. Polarized mirror protective film.

Example 15

A laminate polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and the mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) was changed to 50/50. Polarized mirror protective film.

Example 16

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the aqueous polyester dispersion was changed to an aqueous dispersion (Aw-2) in which the polyester resin having an acid value of 4 KOHmg/g was dispersed.

Example 17

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the aqueous polyester dispersion was changed to an aqueous dispersion (Aw-3) in which the polyester resin having an acid value of 6 KOHmg/g was dispersed.

Example 18

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the aqueous polyester dispersion was changed to an aqueous dispersion (Aw-5) in which the polyester resin having an acid value of 10 KOHmg/g was dispersed.

Example 19

A polarizer protection of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution was changed to an aqueous solution (Bw-6) in which the degree of saponification of polyvinyl alcohol was 67 mol%. membrane.

Example 20

A polarizer protection of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution was changed to an aqueous solution (Bw-5) in which the degree of saponification of polyvinyl alcohol was 70 mol%. membrane.

Example 21

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution was changed to a polyvinyl alcohol aqueous solution (Bw-3) having a saponification degree of polyvinyl alcohol of 79 mol%.

Example 22

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution (Bw-2) having a saponification degree of polyvinyl alcohol of 83 mol% was changed.

Example 23

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution was changed to an aqueous solution (Bw-1) in which a polyvinyl alcohol having a degree of saponification of 88 mol% was dissolved.

Example 24

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating liquid was changed as described below.

Example 25

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating liquid was changed as described below.

Example 26

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating liquid was changed as described below.

(矽, solid concentration 10% by mass)

Example 27

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 2 except that an antiglare layer was provided on the surface opposite to the surface having the coating layer. The rainbow spot observation is performed by changing the light source of the liquid crystal display device to an organic light emitting diode (OLED).

Comparative example 1

In the same manner as in Example 3, a polarizer protective film of a biaxially oriented PET film having a film thickness of about 38 μm was obtained by extending 3.6 times in the traveling direction and 4.0 times in the width direction. The resulting film had a low hysteresis value, and a rainbow-like stain was observed when viewed from the oblique direction.

Comparative example 2

In the same manner as in Example 1, a polarizer protective film of a shaft-aligned PET film having a thickness of about 10 μm was obtained by changing the thickness of the unstretched film. The obtained film was very easily cracked, and since it was not stiff, it could not be used as a polarizing film protective film. Also, the hysteresis value was low, and a rainbow-like stain was observed.

Comparative example 3

A polarizing film of a laminated polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and the mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) was changed to 100/0. Mirror protective film.

Comparative example 4

A laminate polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and the mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) was changed to 0/100. Polarized mirror protective film.

Comparative Example 5

A polarizing film of a laminated polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and the mass ratio of the polyester resin (A)/polyvinyl alcohol resin (B) was changed to 90/10. Mirror protective film.

Comparative Example 6

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and the relaxation treatment after stretching the tenter was changed to 100 °C.

Comparative Example 7

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyvinyl alcohol aqueous solution was changed to a solution (Bw-8) in which a polyvinyl alcohol having a degree of saponification of 99 mol% was dissolved.

Comparative Example 8

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the aqueous solution of polyvinyl alcohol was changed to an aqueous solution (Bw-7) in which the degree of saponification was 40 mol%.

Comparative Example 9

A polarizer protective film of a laminated polyester film was obtained in the same manner as in Example 1 except that the polyester aqueous dispersion was changed to an aqueous dispersion (Aw-4) in which the polyester resin having an acid value of 25 KOHmg/g was dispersed.

Comparative Example 10

The same manner as in the first embodiment except that the light source of the liquid crystal display device was a cold cathode tube.

Reference example 1

As the laminated polyester film, the adhesion test was carried out by using a TAC film (manufactured by Fuji FILM Co., Ltd., thickness: 80 μm, saponification treatment).

In the polarizer protective films of Examples 1 to 27, the nano phase separation structure was observed. For reference, Fig. 1 shows a phase difference micrograph of the surface of the coating layer of the polarizer protective film of Example 14. The polarizer protective film of Examples 1 to 27 having a surface fraction of 30% or more of the PVA phase showed no problem in coatability, and showed excellent adhesion to the PVA film in the same peeling test as that of the TAC film. Sex.

Industrial use possibility

By using the liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention, the adhesiveness is excellent, and the visibility is not lowered by the rainbow-colored color spots, which contributes to thinning and cost reduction of the LCD. Industrial use is extremely high.

Fig. 1 is a view showing the structure of the phase separation of the surface of the coating layer of the polarizer protective film of Example 14. The scale unit is μm, and the actual size is 1 μm × 1 μm.

Claims (12)

A polarizer protective film comprising a polarizer protective film having a coating layer on at least one side of a polyester film, the polyester film having a hysteresis value of 3,000 to 30,000 nm, the coating layer comprising a polyvinyl alcohol resin and a polyester resin The surface of the coating layer has a nanophase separation structure formed by a phase in which a phase in which a polyvinyl alcohol-based resin is agglomerated and a phase in which a polyester resin is agglomerated, and an area ratio of the polyvinyl alcohol phase is 30% or more and less than 99%. The polarizer protective film of claim 1, wherein the polyvinyl alcohol-based resin has a degree of saponification of 95% or less. The polarizer protective film according to claim 1 or 2, wherein the polyester resin has a glass transition temperature of 25 ° C or higher. The polarizer protective film according to any one of claims 1 to 3, wherein the coating layer contains a crosslinking agent. The polarizer protective film of claim 4, wherein the crosslinking agent is a melamine crosslinking agent and/or an isocyanate crosslinking agent. The polarizer protective film according to any one of claims 1 to 5, wherein a mass ratio of the polyvinyl alcohol resin (PVA) to the polyester resin (PEs) contained in the coating layer satisfies the following formula : 0.2 ≦ PVA / PEs ≦ 1.25. The polarizer protective film according to any one of claims 1 to 6, wherein the ratio of the hysteresis value to the thickness direction retardation value (Re/Rth) of the polyester film is 0.200 or more and 1.200 or less. The polarizer protective film according to any one of claims 1 to 7, wherein the polyester film is composed of at least three layers, and a layer other than the outermost layer contains an ultraviolet absorber, and a light transmittance of 380 nm is obtained. 20% or less. The polarizer protective film according to any one of claims 1 to 8, wherein a surface of the polyester film opposite to a surface having a coating layer is selected from the group consisting of a hard coat layer, an antiglare layer, and an antireflection. One or more layers of the group consisting of a layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an antistatic layer. A polarizing plate in which a polarizer protective film according to any one of claims 1 to 9 is laminated on at least one side of a polarizing mirror. A liquid crystal display device having a liquid crystal display device having a backlight source and a liquid crystal cell disposed between two polarizing plates, wherein a white light source having a continuous light emission spectrum is used as the backlight source, and the two polarizing plates are used At least one of them is a polarizing plate as in claim 10 of the patent application. The liquid crystal display device of claim 11, wherein the polarizer protective film disposed on the light-emitting side of the polarizing plate on the light-emitting side is a polarizer protective film according to claims 1 to 9.