JP2013063610A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film having excellent adhesion to polarizers.SOLUTION: The laminated polyester film has a cover layer at least on one side of the polyester film. The cover layer includes a polyvinyl alcohol-based resin and a polyester-based resin. A surface of the cover layer has a nanophase separated structure composed of a phase having a condensed polyvinyl alcohol-based resin and a phase having a condensed polyester-base resin, wherein the area ratio of the polyvinyl alcohol phase is 30% or more and less than 99%.

Description

  The present invention relates to a laminated polyester film excellent in adhesiveness with a polarizer.

  In the liquid crystal display device, polarizing plates are arranged on both sides of a glass substrate that forms the surface of the liquid crystal panel due to the image forming method. The polarizing plate generally has a configuration in which a polarizer protective film is bonded to both surfaces of a polarizer made of a dichroic material such as a polyvinyl alcohol film and iodine via a hydrophilic adhesive such as a polyvinyl alcohol resin. have. As a protective film used for protecting a polarizer, a triacetyl cellulose film has been conventionally used from the viewpoint of optical properties and transparency.

  However, triacetyl cellulose is not sufficiently durable, and when a polarizing plate using a triacetyl cellulose film as a polarizer protective film is used at high temperature or high humidity, the performance of the polarizing plate such as the degree of polarization and hue deteriorates. There is a case. In recent years, there has been a demand for thinning the polarizing plate to cope with the thinning of the display. However, there is a limit to the thinning of the triacetyl cellulose film from the viewpoint of maintaining moisture barrier properties. Therefore, it has been proposed to use a polyester film as a polarizer protective film having durability and moisture barrier properties (see Patent Documents 1 to 5).

  The triacetyl cellulose film used as a polarizer protective film is subjected to alkali treatment or the like on its surface, and has an extremely high affinity with a hydrophilic adhesive. Therefore, the protective film made of a triacetyl cellulose film has extremely high adhesiveness with a polarizer coated with a hydrophilic adhesive. However, the polyester film has insufficient adhesion to the hydrophilic adhesive, and this tendency becomes more prominent particularly in the case of a polyester film having orientation by a stretching treatment. Then, in order to improve adhesiveness with the polarizer or the hydrophilic adhesive apply | coated to the polarizer, providing an easily bonding layer in a polyester film is proposed (patent documents 1-3 and 5).

JP-A-8-271733 JP-A-8-271734 JP 2009-157361 A JP 2010-277028 A JP 2011-8170 A

A polyester film has a low affinity for water, and this tendency is particularly remarkable in a polyester film having an aromatic dicarboxylic acid as a dicarboxylic acid component. Moreover, the polyester film which has crystal orientation by extending | stretching has a low affinity with water further. On the other hand, the polarizer and the adhesive applied on the polarizer are generally composed mainly of a polyvinyl alcohol resin and have high hydrophilicity. Due to such a difference in properties, the polyester film and the polarizer or the polyvinyl alcohol-based adhesive have low affinity, and it has been difficult to firmly bond the two. Therefore, even if it is a polyester film which has an easily bonding layer disclosed by patent documents 1-3 and 5, compared with a triacetyl cellulose film, sufficient adhesiveness is not yet acquired. Therefore, when a polarizing plate using a conventional polyester film as a protective film is used as a display member for a long time, floating or peeling occurs between the protective film and the polarizer, and the polarization characteristics deteriorate due to a change in the amount of moisture in the polarizer. In addition, the visibility such as white spots may deteriorate.

  Under such circumstances, an object of the present invention is to provide a polyester film provided with means for firmly bonding the polyester film and a polarizer or a polyvinyl alcohol-based resin layer such as an adhesive applied on the polarizer. For the purpose.

  The inventors of the present invention have made extensive studies and studies to solve the above-mentioned problems, and a layer containing a polyester resin having a high affinity with a polyester film and a polyvinyl alcohol resin having a high affinity with a polyvinyl alcohol resin layer. The idea of providing the film on the polyester film was reached. However, the present inventors have found that the function of closely adhering the polyester film and the polyvinyl alcohol-based resin layer due to each component cannot be sufficiently exhibited by simply combining these components. Therefore, as a result of repeated day and night studies, the present inventors have controlled the presence of the binder resin in the coating layer provided on the surface of the polyester film in the above concept, and the phase in which the polyester resin is aggregated and the polyvinyl alcohol resin. It has been found that by forming a nanophase separation structure composed of an aggregated phase on the surface of the coating layer, the adhesive action with the polarizer can be more effectively exhibited. Based on these findings, the present inventors have made further studies and considerations, and have invented the present invention.

Below, the typical example of this invention is shown.
Item 1. A laminated polyester film having a coating layer on at least one side of the polyester film,
The coating layer includes a polyvinyl alcohol resin and a polyester resin,
The surface of the coating layer has a nanophase separation structure composed of a phase in which a polyvinyl alcohol resin is aggregated and a phase in which a polyester resin is aggregated, and the area ratio of the polyvinyl alcohol phase is 30% or more and less than 99%. A laminated polyester film characterized by
Item 2. Item 2. The laminated polyester film according to item 1, wherein the saponification degree of the polyvinyl alcohol resin is 95% or less.
Item 3. Item 3. The laminated polyester film according to item 1 or 2, wherein the polyester resin has a glass transition temperature of 25 ° C or higher.
Item 4. Item 4. The laminated polyester film according to any one of Items 1 to 3, wherein the coating layer contains a crosslinking agent.
Item 5. Item 5. The laminated polyester film according to Item 4, wherein the crosslinking agent is a melamine crosslinking agent and / or an isocyanate crosslinking agent.
Item 6. Item 6. The laminated polyester film according to any one of Items 1 to 5, wherein a mass ratio of the polyvinyl alcohol resin and the polyester resin contained in the coating layer satisfies the following formula.

0.2 ≦ PVA / PEs ≦ 1.25
Item 7. A polarizing plate having a polarizer protective film on both sides of a polarizer,
The polarizing plate whose at least one polarizer protective film is the lamination polyester film in any one of claim | item 1 -6.

  The laminated polyester film of the present invention is excellent in adhesiveness with a polarizer typified by a polyvinyl alcohol resin layer or an adhesive applied thereon. Therefore, the laminated polyester film of the present invention can be suitably used as a protective film for a polarizer. By using such a polyester film of the present invention as a protective film for a polarizer, it is possible to produce a polarizing plate having superior durability and water barrier properties at a lower cost than before. Moreover, since the polarizing plate of the present invention is excellent in durability, it can be made thinner than before. Therefore, it is possible to further reduce the thickness of the liquid crystal display by using the polarizing plate of the present invention.

  Although not limited by theory, the laminated polyester film of the present invention has a phase in which a polyester resin is aggregated on the surface of the coating layer (hereinafter, referred to as “PEs phase” as appropriate) and a polyvinyl alcohol-based resin is aggregated. (Hereinafter referred to as “PVA phase” as appropriate), the formation of the nanophase separation structure results in strong adhesion to the polarizer or the adhesive provided thereon due to the PVA phase. It is thought that it is demonstrated.

The nanophase separation structure of the coating layer surface of the laminated film of Example 5 is shown. The scale unit is μm, and the actual size is 1 μm × 1 μm.

(Polyester film)
The polyester film used as a substrate in the present invention is a film mainly composed of a polyester resin. Here, “a film mainly composed of a polyester resin” means a film formed from a resin composition containing 50% by mass or more of a polyester resin. When blended with another polymer, it means that the polyester resin is contained in an amount of 50% by mass or more, and when copolymerized with another monomer, it means that the polyester structural unit is contained in an amount of 50 mol% or more. Preferably, the polyester film contains a polyester resin in an amount of 90% by mass or more, more preferably 95% by mass or more, and still more preferably 100% by mass.

  The material of the polyester resin is not particularly limited, but a copolymer formed by polycondensation of a dicarboxylic acid component and a diol component, or a blend resin thereof can be used. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and diphenyl. Carboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydro Isophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid The die Over acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

  Examples of the diol component constituting the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3- Examples include propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, and bis (4-hydroxyphenyl) sulfone.

  Each of the dicarboxylic acid component and the diol component constituting the polyester resin may be used alone or in combination of two or more. Further, other acid components such as trimellitic acid and other hydroxyl components such as trimethylolpropane may be appropriately added.

  Specific examples of the polyester resin include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, polyethylene terephthalate is preferable from the balance of physical properties and cost. Moreover, in order to control optical characteristics, such as polarization, it is also a preferable aspect that other copolymer components or other polymers are included. Preferred copolymer components from the viewpoint of controlling the optical properties of the polyester film include diethylene glycol and copolymer components having norbornene in the side chain.

  The polyester film of the present invention preferably has high transparency when used as a protective film for a polarizer. The transparency of the film of the present invention is preferably such that the total light transmittance is 85% or more, more preferably 87% or more, still more preferably 88% or more, still more preferably 89% or more, and 90% or more. Particularly preferred. The haze is preferably 3% or less, more preferably 2.5% or less, further preferably 2% or less, and particularly preferably 1.5% or less. The total light transmittance of a polyester film can be measured according to the method described in the Example mentioned later, for example.

  In order to improve handling properties such as slipperiness and rollability of the polyester film, inert particles may be included in the film. However, in order to maintain high transparency, the inert particles in the film may be included. The content is preferably as low as possible. Therefore, a multilayer structure in which particles are included only in the surface layer of the film, or particles are substantially not included in the film, and particles are included only in the coating layer laminated on at least one side of the polyester film. Is preferred.

  “Substantially no particles” means, for example, in the case of inorganic particles, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis, 50 ppm or less, preferably 10 ppm or less, most preferably detected The content is below the limit. This means that even if particles are not actively added to the base film, contaminants derived from foreign substances and raw material resin or dirt attached to the line or equipment in the film manufacturing process will peel off and will be inevitable in the film. This is because there is a case where it is mixed.

  In addition, when the base film has a multi-layer structure, the two-layer / three-layer structure that does not substantially contain inert particles in the inner layer and contains inert particles only in the outermost layer achieves both transparency and workability. It is possible and preferable.

  In the present invention, the thickness of the base film is not particularly limited. However, when the thickness of the polarizing plate is reduced to make the display thinner, the thickness of the film is preferably 200 μm or less, and more preferably 100 μm or less. . On the other hand, from the viewpoint of maintaining the mechanical strength as the protective film, the thickness of the film is preferably 10 μm or more, more preferably 12 μm or more, and further preferably 20 μm or more.

  The polyester film used as the substrate may be a single layer or a laminate of two or more layers. Moreover, as long as it exists in the range with the effect of this invention, various additives can be contained in a film as needed. Examples of the additive include an antioxidant, a light resistance agent, an antigelling agent, an organic wetting agent, an antistatic agent, an ultraviolet absorber, and a surfactant. When a film has a laminated structure, it is also preferable to contain an additive according to the function of each layer as needed. For example, in order to prevent photodegradation of the polarizer, it is also a preferred embodiment to add an ultraviolet absorber or the like to the inner layer.

  The polyester film can be produced according to a conventional method. For example, it can be obtained by a method in which the above polyester resin is melt-extruded into a film and cooled and solidified with a casting drum to form a film. As the polyester film of the present invention, either a non-stretched film or a stretched film can be used, but a stretched film is preferable from the viewpoint of durability such as mechanical strength and chemical resistance. When the polyester film is a stretched film, the stretching method is not particularly limited, and a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, a longitudinal and transverse simultaneous biaxial stretching method, and the like can be employed. When extending | stretching a polyester film, extending | stretching may be implemented before laminating | stacking the coating layer mentioned later, and may be implemented after laminating | stacking a coating layer. It is also possible to uniaxially stretch in the longitudinal or lateral direction before laminating the coating layer, and to stretch in the other direction after laminating the coating layer.

(1) Coating 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 is composed of a phase in which the polyvinyl alcohol resin is aggregated and a phase in which the polyester resin is aggregated. It has a nanophase separation structure. In the present invention, the phrase “the coating layer contains a polyvinyl alcohol resin and a polyester resin” means that the coating layer is a resin layer formed using a polyvinyl alcohol resin and a polyester resin as raw material components. Similarly, when the coating layer contains a component other than these resins (for example, a crosslinking agent), it means that it is a coating layer formed using these resins and other components (for example, a crosslinking agent) as raw materials. To do.

The nanophase separation structure on the surface of the coating layer refers to two types of nanoscale phases (or regions) of PVA phase and PEs phase that are clearly distinguished by detection of the surface of the coating layer using a scanning probe microscope described later. It means existing on the surface of the coating layer. As described above, the PVA phase is a phase formed by aggregation of polyvinyl alcohol-based resins. Therefore, although the PVA phase is mainly composed of a polyvinyl alcohol-based resin, as long as it can be distinguished from the PEs phase by a scanning probe microscope, the component constituting the other coating layer mixed with aggregation (for example, Crosslinkers and trace amounts of PEs) may be included. Similarly, the PEs phase is a phase formed by aggregating polyester resins. Therefore, the PEs phase is mainly composed of a polyester resin, but as long as it can be distinguished from the PVA phase by a scanning probe microscope, other components (for example, a cross-linking agent and a small amount of PVA) are mixed. You may do it.
The size and shape of the PVA phase and the PEs phase are not particularly limited as long as the structure satisfies the surface fraction of the PVA phase described later and is recognized as a nanophase separation structure in the technical field. Specific examples of the nanophase separation structure include a sea-island structure, a core / shell structure, and a laminated structure (lamella structure) in which phases are regularly arranged.

  When forming the nano isolation | separation structure whose coating layer surface is a sea island structure, any of a PVA phase and a PEs phase may form the phase corresponded to an island. As shown in FIG. 1, the sea-island structure may be an independent “island” -like form or may be a form in which “islands” are continuous. The size of the sea-island structure is not particularly limited. For example, the sea-island structure is mainly an island-shaped structure having a width in the minor axis direction of 20 nm to 500 nm at the maximum and a length in the major axis direction exceeding 50 nm. By having such a nano-sized dispersion structure, the properties of both resins can be suitably achieved.

The core-shell structure, which is one of the nanophase separation structures, is a structure in which, for example, the PVA phase is surrounded by the PEs phase, and further, the PEs phase is surrounded by the PVA phase. In any case, on the surface of the coating layer, when measured using a scanning probe microscope, a phase recognized as an aggregate of a polyvinyl alcohol resin and a phase recognized as an aggregate of a polyester resin, It is preferable from the viewpoint of exhibiting excellent adhesiveness that it is dispersed without significant deviation.
The coating layer surface having the nanophase separation structure as described above has an area ratio of the PVA phase defined by the following formula of 30% or more and less than 99%.
PVA phase surface fraction (%) = (PVA phase area / measurement area) × 100
The area of the PVA phase is measured by using a phase measurement mode of a scanning probe microscope, which will be described later, in which case the polyvinyl alcohol phase shows a dark hue in the phase image. Although the measurement area is not particularly limited, for example, it can be performed at 1 μm × 1 μm.

  The PVA surface fraction is preferably 30 to 99%. If it is less than 30%, the surface fraction of the PEs phase on the surface of the coating layer becomes relatively large, and the adhesion to the polarizer / water-based adhesive may decrease. On the other hand, when the PVA surface fraction is 99% or more, the frequency with which the adhesion to the base film is lowered may increase. The lower limit of the PVA surface fraction on the surface of the coating layer is preferably 30%, more preferably 35%, and even more preferably 40%. On the other hand, the upper limit of the PVA surface fraction is more preferably 99%, further preferably 95%, and still more preferably 90%.

  The PVA surface fraction of the nanophase separation structure can be measured by a paper weight method or an image analysis method described in Examples described later.

  The reason why the adhesion is improved by the nano-separation structure is considered as follows. Polyvinyl alcohol resins are rich in hydrophilicity, and polyester resins are rich in hydrophobicity. For this reason, simply mixing and applying the two resins causes the two resins to be completely separated and cannot exhibit sufficient adhesion. On the other hand, although both resins can be forcibly mixed with a surfactant or the like, sufficient adhesiveness cannot be exhibited in this case because the properties of both resins are impaired. On the other hand, both resins form a nanophase separation structure, and a predetermined proportion of PVA phase is present on the surface of the coating layer, so that adhesion with the polarizer or the adhesive provided thereon is caused by the PVA resin. And the adhesiveness with the polyester film due to the PEs resin can be efficiently exhibited at the same time.

  The nanophase separation structure on the surface of the coating layer can be confirmed by measuring in a phase measurement mode (phase mode) using a scanning probe microscope (SPM). The phase mode is a phase lag measurement mode that is performed simultaneously with surface morphology observation in a normal dynamic force mode (DFM mode; when SII NanoTechnology SPM is used).

  The measurement of the phase separation structure of the coating layer by the phase measurement mode (phase mode) of the scanning probe microscope (SPM) will be described. In the phase mode, the phase delay of the cantilever vibration when the DFM operation is performed is detected. In the DFM operation, the shape is measured by controlling the distance between the probe and the sample so that the vibration amplitude of the resonated cantilever is constant. Here, when the signal that vibrates the bimorph (piezoelectric element) for vibrating the cantilever is called an “input signal”, in the phase measurement mode, the phase delay of the effective cantilever vibration signal with respect to this “input signal” Is detected simultaneously with the vibration amplitude. The phase delay responds sensitively to the influence of surface properties, and the softer the sample surface, the greater the delay. By imaging the magnitude of this phase lag, it becomes possible to observe the distribution of surface physical properties (referred to as phase image or phase image). Thus, by using the phase measurement mode of the scanning probe microscope (SPM), it is possible to measure and confirm a phase separation structure in which a plurality of resin phases having different physical properties exist on the surface.

  For the evaluation of the phase separation structure of the coating layer, other modes such as the friction force measurement mode and the viscoelasticity measurement mode may be used in addition to the phase measurement mode as long as the surface property distribution evaluation mode is a scanning probe microscope. It is preferable to select an observation mode in which the phase separation structure can be evaluated. In the phase measurement mode, not only the phase lag due to the difference in viscoelasticity of the coating layer but also the phase lag due to the difference in surface physical properties such as the magnitude of the adsorption force can be detected.

  Since the coating layer of the present invention has a nanophase separation structure, it exhibits high adhesiveness equal to or higher than that of triacetylcellulose to polarizers and aqueous adhesives, particularly polyvinyl alcohol-based polarizers and aqueous adhesives. Specifically, the coating layer preferably has a residual area after peeling once of 90% or more, more preferably 95% or more, and further preferably 100% in the adhesion test shown in the examples described later. The remaining area after continuous peeling is preferably 75% or more, more preferably 85% or more, further preferably 95% or more, and the remaining area after 10 times continuous peeling is preferably 50% or more, more preferably 80% or more. More preferably, it is 90% or more, still more preferably 93% or more, and particularly preferably 95% or more.

  The phase separation structure as described above can be obtained by controlling the resin concentration, selection of the resin type, drying / heating conditions and the like as described later.

Hereinafter, each composition of the coating layer will be described in detail.
(Polyvinyl alcohol resin)
The polyvinyl alcohol resin used as a component of the coating layer is not particularly limited as long as it is recognized as a polyvinyl alcohol resin. Specific examples thereof include polyvinyl alcohol obtained by saponifying polyvinyl acetate; a derivative thereof; a saponified product of a copolymer of vinyl acetate and a monomer having copolymerizability; Modified polyvinyl alcohol which has been converted to ether, ether, graft, phosphoric ester or the like. Examples of the monomer include unsaturated carboxylic acids such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid, and esters thereof; α-olefins such as ethylene and propylene, (meth) Examples include allyl sulfonic acid (soda), sulfonic acid soda (monoalkyl malate), disulfonic acid soda alkyl maleate, N-methylol acrylamide, acrylamide alkyl sulfonic acid alkali salt, N-vinyl pyrrolidone, N-vinyl pyrrolidone derivatives, and the like. . These polyvinyl alcohol resins may be used alone or in combination of two or more.

  Examples of suitable polyvinyl alcohol resins used in the present invention include vinyl alcohol-vinyl acetate copolymer, vinyl alcohol-vinyl butyral copolymer, and ethylene-vinyl alcohol copolymer. Among these, vinyl alcohol-vinyl acetate copolymer is exemplified. A polymer and an ethylene-vinyl alcohol copolymer are preferred. The degree of polymerization of the polyvinyl alcohol-based resin is not particularly limited, but the degree of polymerization is preferably 3000 or less from the viewpoint of the coating solution viscosity.

  The copolymerization ratio of vinyl alcohol is represented by the degree of saponification. The degree of saponification of the polyvinyl alcohol resin of the present invention is not particularly limited as long as excellent adhesiveness is exhibited, but it is preferably 60 mol% or more. More preferably, the upper limit of the saponification degree of the polyvinyl alcohol resin is 95 mol%, preferably 85 mol%. More preferably, the degree of saponification is 65 mol% or more and 83 mol% or less, more preferably 68 mol% or more and 80 mol% or less, still more preferably 70 mol% or more and less than 80 mol%, and 71 mol% or more and 78 mol% or less. % Or less is even more preferable, and 73 mol% or more and 75 mol% or less is particularly preferable. When the degree of saponification of the polyvinyl alcohol-based resin is equal to or higher than the above lower limit, the water-based adhesive or the polarizer is suitably adhered, and the phase separation from the polyester-based resin can be suitably performed. Further, when the degree of saponification of the polyvinyl alcohol-based resin is not more than the above upper limit (or less), a nanophase separation structure can be formed more suitably with the polyester-based resin. The degree of saponification of the vinyl alcohol-based resin can be determined by the amount of alkali consumption required for hydrolysis of copolymer units such as vinyl acetate or the composition analysis by NMR.

  The content of the polyvinyl alcohol 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 further preferably 20% by mass or more and 50% by mass or less in the coating layer. When the content of the polyvinyl alcohol-based resin is equal to or more than the above lower limit, the PVA surface fraction increases, which is suitable for adhesiveness with a polarizer / water-based resin. On the other hand, it is suitable for adhesiveness with a polyester film base material that it is below the upper limit.

(Polyester resin)
The polyester resin used in the coating layer of the present invention is a copolymer formed by polycondensation of a dicarboxylic acid component and a diol component, and the dicarboxylic acid component and the diol component are described as a polyester film used as the above-mentioned substrate. Can be used. From the viewpoint of improving the adhesion to the polyester film substrate, it is preferable to use a dicarboxylic acid component having the same or similar structure and properties as the dicarboxylic acid component in the polyester film as the dicarboxylic acid component of the polyester resin. Therefore, for example, when an aromatic dicarboxylic acid is employed as the dicarboxylic acid component of the polyester film, it is preferable to use the 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 most preferred. For example, another aromatic dicarboxylic acid may be added and copolymerized within a range of 10 mol% or less with respect to the total dicarboxylic acid component.

  From the viewpoint of blocking resistance, the glass transition temperature of the polyester-based resin is preferably 25 ° C or higher, more preferably 30 ° C or higher, and further preferably 35 ° C or higher. Furthermore, the upper limit of the glass transition temperature is preferably 110 ° C. or less, more preferably 100 ° C. or less, and further preferably 90 ° C. or less. When the upper limit of the glass transition temperature is not more than the above, it becomes easy to suitably form phase separation by heat treatment described later. The glass transition temperature of the polyester-based resin can be controlled by introducing a copolymer component, particularly a branched glycol component, as will be described later.

  As the glycol component of the polyester-based resin, ethylene glycol and branched glycol are preferably used as constituent components. By having a branched structure, it is considered that it contributes to stress relaxation in the coating layer, and can suitably exhibit adhesiveness. Examples of the branched glycol component 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-n-hexyl-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, Such as 2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol. And the like.

  The molar ratio of the branched glycol component is preferably 10 mol%, particularly preferably 20 mol%, based on the total glycol component. On the other hand, the upper limit is preferably 80 mol%, more preferably 70 mol%, and particularly preferably 60 mol%. If necessary, diethylene glycol, propylene glycol, butanediol, hexanediol, 1,4-cyclohexanedimethanol or the like may be used in combination.

  The polyester resin used as a component of the coating layer in the present invention is preferably a water-soluble or water-dispersible resin from the viewpoint of forming a suitable nanophase separation structure with the polyvinyl alcohol resin. In order to make the polyester resin water-soluble or water-dispersed, it is preferable to copolymerize a compound containing a hydrophilic group such as a sulfonate group or a carboxylate group. Among these, a dicarboxylic acid component having a sulfonate group is preferable from the viewpoint of imparting hydrophilicity while maintaining a low acid value of the polyester-based resin and controlling the reactivity with the crosslinking agent. Examples of the dicarboxylic acid component having a sulfonate group include sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfonaphthaleneisophthalic acid-2,7-dicarboxylic acid, and 5- (4-sulfophenoxy) isophthalic acid or an alkali thereof. Examples of the metal salt include 5-sulfoisophthalic acid.

  1-15 mol% is preferable in the dicarboxylic acid component of a polyester resin, as for the dicarboxylic acid component which has a sulfonate group, 1.5-12 mol% is more preferable, and 2-10 mol% is further more preferable. When the dicarboxylic acid component having a sulfonate group is at least the above lower limit, it is suitable for water-solubilization or water-dispersion of the polyester resin. Moreover, when the dicarboxylic acid component which has a sulfonate group is below the said upper limit, it is suitable for adhesiveness with a polyester film base material.

  When a crosslinking agent is used in combination as described later, it is preferable that the polyester resin has few carboxylic acid groups which are reactive groups with the crosslinking agent, from the viewpoint of forming a suitable phase separation structure. By reducing the number of carboxyl groups that are reactive with the cross-linking agent, the reactivity with the cross-linking agent is reduced. As a result, the cross-linking polyvinyl alcohol-based resin does not completely mix with the polyvinyl alcohol-based resin. It is believed that the phase separation structure can be suitably maintained. From such a viewpoint, the acid value of the polyester-based resin is preferably 20 KOHmg / g or less, more preferably 15 KOHmg / g or less, further preferably 10 KOHmg / g or less, still more preferably 8 KOHmg / g or less, and even more preferably. Is 5 KOHmg / g or less. The acid value of the polyester resin can be theoretically determined from the result of component analysis by titration method described later or NMR.

  In order to control the acid value of the polyester-based resin within the above range, the introduction amount of the carboxylic acid base for water solubilization or water dispersion is reduced, or a hydrophilic group other than the carboxylic acid base is employed, It is preferable to lower the carboxylic acid terminal concentration of the polyester resin. As a method for lowering the carboxylic acid terminal concentration of the polyester resin, it is preferable to employ a polyester resin in which the carboxylic acid terminal group is modified, or a polyester resin having a large number average molecular weight of the polyester resin. For this reason, the number average molecular weight of the polyester-based resin is preferably 5000 or more, more preferably 6000 or more, and further preferably 10,000 or more. Moreover, it is preferable to make low content of the acid component which has a polyester-type resin as a structural component and has three or more carboxyl groups.

  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 further preferably 50% by mass or more and 80% by mass or less. When the content of the polyester resin is not less than the above lower limit, it is suitable for adhesiveness with a polyester film substrate, and when it is not more than the above upper limit, it is suitable for adhesiveness with a polarizer or a water-based adhesive provided thereon. is there.

(Crosslinking agent)
A nanophase separation structure can be more suitably formed by using a crosslinking agent in the coating layer. This is considered to be because the polyvinyl alcohol-based resin easily aggregates due to crosslinking of the hydroxyl groups of the polyvinyl alcohol-based resin, and as a result, a suitable separation structure is formed. Although it will not specifically limit as a crosslinking agent if it has a hydroxyl group and crosslinking property, Compounds, such as a melamine type, an isocyanate type, a carbodiimide type, an oxazoline type, an epoxy type, are mentioned. Melamine-based, isocyanate-based, carbodiimide-based, and oxazoline-based compounds are preferable from the viewpoint of the temporal stability of the coating solution. Further, the crosslinking agent is preferably a melamine compound or an isocyanate compound that suitably cross-links with the hydroxyl group of the polyvinyl alcohol resin. This is because a carbodiimide-based crosslinking agent reacts with a carboxyl group, whereas a melamine-based compound or an isocyanate-based compound reacts with a hydroxyl group, and thus forms a crosslinked structure more suitably with a polyvinyl alcohol-based resin having a hydroxyl group as a functional group. This is probably because of this. Furthermore, when a melamine compound or an isocyanate compound is used, the polyvinyl alcohol in the coating layer suitably forms a cross-linked structure, and easily moves to the surface opposite to the polyester film, so that the surface fraction of PVA is increased. This makes it possible to form a suitable sea-island structure. Especially, it is especially preferable to use an isocyanate type compound from a viewpoint that it forms a crosslinking reaction suitably with the hydroxyl group of polyvinyl alcohol-type resin, and is excellent in transparency. Moreover, in order to promote a crosslinking reaction, you may use a catalyst etc. suitably as needed.

  As the isocyanate compound, a low-molecular or high-molecular diisocyanate or a trivalent or higher polyisocyanate can be used. For example, as the isocyanate compound, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5 -Naphthylene diisocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane 4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiph Aromatic diisocyanates such as nil-4,4'-diisocyanate, aromatic aliphatic diisocyanates such as xylylene diisocyanate, isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, etc. Examples thereof include aliphatic diisocyanates such as alicyclic diisocyanates, hexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate, and trimers of these isocyanate compounds. Furthermore, an excess amount of these isocyanate compounds and low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, or polyester polyols, poly Mention may be made of a polymer containing a terminal isocyanate group of a polymer obtained by reacting a polymer active hydrogen compound such as ether polyols and polyamides.

  As the crosslinking agent used in the present invention, a blocked isocyanate compound is also preferable. By adding the blocked isocyanate compound, it is possible to more suitably improve the temporal stability of the coating solution.

  The blocked isocyanate compound can be prepared by subjecting the isocyanate compound and the blocking agent to an addition reaction by a conventionally known method. Examples of the isocyanate blocking agent include phenols such as phenol, cresol, xylenol, resorcinol, nitrophenol, and chlorophenol; thiophenols such as thiophenol and methylthiophenol; oximes such as acetoxime, methyl etiketooxime, and cyclohexanone oxime. Alcohols such as methanol, ethanol, propanol and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol ; Lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propyllactam; aromatic amines; imides; acetylacetone, acetoacetate Active methylene compounds such as malonic acid ethyl ester; mercaptans; imines; ureas; diaryl compounds; and sodium bisulfite and the like.

As the melamine compound, a melamine compound substituted with a substituent — (CH ₂ ) n—O—R (wherein n is an integer of 1 to 3 and R is an alkyl group having 1 to 4 carbon atoms). In which R is preferably methyl. The number of the substituents that one melamine structure has is preferably 3 to 6. Specific examples of melamine compounds include M-3, MK, M-6, M-100, MC, etc. of Sumitomo Chemical Co., Ltd. Sumitex Resin series and methylated melamine resin MW-22, MX manufactured by Sanwa Chemical Co., Ltd. -706, MX-042 and the like.
A melamine compound and an epoxy compound or an oxazoline compound may be used in combination, but the content of the epoxy compound or oxazoline compound in that case is preferably less than 10% by weight, more preferably less than 5% by weight, More preferably, it is less than 2% by weight, particularly preferably less than 1% by weight. If the content of the epoxy compound or oxazoline compound is larger than the above upper limit, depending on the ratio of polyester and polyvinyl alcohol in the coating layer, the PVA surface fraction cannot be kept high, and the adhesiveness may be inferior. .

  Further, an isocyanate compound and an epoxy compound or an oxazoline compound may be used in combination, but the content of the epoxy compound or oxazoline compound in that case is preferably less than 10% by weight, more preferably less than 5% by weight. Even more preferably, it is desired to be less than 2% by weight, particularly preferably less than 1% by weight. If the content of the epoxy compound or oxazoline compound is larger than the above upper limit, depending on the ratio of polyester and polyvinyl alcohol in the coating layer, the PVA surface fraction cannot be kept high, and the adhesiveness may be inferior. .

  As content of a crosslinking agent, 2 mass% or more and 50 mass% or less are preferable in a coating layer, 5 mass% or more and 40% mass% or less are more preferable, and 8 mass% or more and 30 mass% or less are more preferable. When the content of the cross-linking agent is not less than the above lower limit, it is suitable for forming a cross-linked polyvinyl alcohol resin, and when it is not more than the above upper limit, it is suitable for the expression of the adhesive effect by the binder resin.

  The blending ratio (B) / (A) of the polyester-based resin (A) and the polyvinyl alcohol-based resin (B) is preferably 0.2 to 1.25 in terms of mass ratio, and preferably 0.25 to 1. More preferably, it is more preferably 0.25 to 0.5, and particularly preferably 0.25 to 0.45. When (B) / (A) is at least the above lower limit, it is suitable for adhesion to a polyester film substrate, and when it is at most the above upper limit, it is suitable for adhesion to a polarizer / water-based resin.

  The blending ratio ((A) + (B)) / (C) of the polyester resin (A) and the polyvinyl alcohol resin (B) and the crosslinking agent (C) is preferably 2 to 50 in terms of mass ratio. More preferably, it is -40, and it is further more preferable that it is 8-30. When ((A) + (B)) / (C) is not less than the above lower limit, it is suitable for expression of the adhesive effect by the binder resin component, and when it is not more than the above upper limit, it is suitable for the adhesive effect by phase separation. .

(Additive)
In the coating layer of the present invention, known additives, for example, surfactants, antioxidants, catalysts, heat stabilizers, weathering stabilizers, ultraviolet absorbers, organic lubricants, as long as the effects of the present invention are not impaired. Pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, and the like may be added.

  In the present invention, in order to further improve the blocking resistance of the coating layer, it is also a preferred embodiment to add particles to the coating layer. Examples of the particles to be contained in the coating layer in the present invention include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay and the like, or a mixture thereof. Inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., and inorganic particles such as styrene, acrylic, melamine, benzoguanamine, and silicone Examples thereof include polymer-based particles.

  The average particle size of the particles in the coating layer (number average particle size based on SEM; the same applies hereinafter) is preferably 0.04 to 2.0 μm, more preferably 0.1 to 1.0 μm. When the average particle size of the inert particles is less than 0.04 μm, the formation of irregularities on the film surface becomes insufficient, so that the handling properties such as the slipping property and the winding property of the film are deteriorated and the film is stuck. The workability at the time of alignment may deteriorate. On the other hand, if it exceeds 2.0 μm, the particles are likely to fall off, which is not preferable. The particle concentration in the coating layer is preferably 1 to 20% by mass, more preferably 5 to 15% by mass in the solid component.

  In the present invention, the thickness of the coating layer can be appropriately set in the range of 0.01 to 2.00 μm, but in the range of 0.03 to 0.25 μm is preferable in order to achieve both workability and adhesiveness. More preferably, it is 0.05-0.25 micrometer, More preferably, it is 0.05-0.20 micrometer. Adhesiveness will become inadequate that the thickness of a coating layer is less than 0.03 micrometer. When the thickness of the coating layer exceeds 0.25 μm, blocking may occur.

(Manufacture of laminated polyester film)
The method for producing a laminated polyester film of the present invention will be described by taking as an example a case where polyethylene terephthalate (hereinafter abbreviated as PET) is used as a base film, but is not limited thereto.

  After sufficiently drying the PET resin in a vacuum, it is supplied to an extruder, melted and extruded at about 280 ° C. from a T-die into a rotating cooling roll into a sheet, cooled and solidified by an electrostatic application method, and unstretched PET sheet Get. The unstretched PET sheet may have a single layer structure or a multilayer structure by a coextrusion method.

  The obtained unstretched PET sheet is crystallized by uniaxial stretching or biaxial stretching. For example, in the case of biaxial stretching, the film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially stretched PET film, and then the end of the film is held with a clip And it guide | induces to the hot air zone heated at 80-180 degreeC, and extends | stretches 2.5 to 5.0 time in the width direction. In the case of uniaxial stretching, the film is stretched 2.5 to 5.0 times in the tenter. After stretching, the film is led to a heat treatment zone at 140 to 240 ° C., and heat treatment is performed for 1 to 60 seconds to complete crystal orientation.

  A coating layer can be provided after manufacture of a film or in a manufacturing process. In particular, from the viewpoint of productivity, it is preferable to apply a coating solution to at least one side of a PET film after unstretched or uniaxially stretched in the film production process to form a coating layer.

  Any known method can be used as a method for applying the coating solution to the PET film. For example, reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, etc. It is done. These methods are applied alone or in combination.

In the present invention, the finally obtained coating layer preferably has a thickness of 0.03 to 0.25 g / m ² . If it is less than 0.03 g / m < ² >, adhesiveness will fall, and if it is thicker than 0.25 g / m < ² >, since blocking property and sliding property will fall, it is not preferable.

  After coating of the coating solution, it is preferable to dry in a drying furnace. The temperature of the drying air hitting the coated surface is preferably 80 ° C. or higher and lower than 150 ° C. The wind speed is preferably 30 m / second or more. A more preferable drying temperature is 100 ° C. or higher and lower than 150 ° C. After drying the coating film at a temperature of 80 ° C. or higher and lower than 150 ° C. in the drying furnace, it is preferable to immediately cool the laminated film having the coating layer to near room temperature. By passing through the drying step, the fluidity of the coating liquid can be reduced, and a phase separation structure can be suitably performed.

  In the method for producing a laminated polyester film of the present invention, it is preferable to perform 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 improving the flow state of the binder in the coating layer. The reason is that by improving the flow state of the binder, a polyester resin with a lot of hydrophobic groups and a polyvinyl alcohol resin with a lot of hydrophilic groups are aggregated in a self-organized manner to form a suitable phase separation state. I think so. It is also considered that the cross-linking reaction of the cross-linking agent proceeds and the phase separation state can be accelerated. The temperature in each heat setting zone in the heat setting treatment step is slightly different depending on the type of the constituent resin of the thermoplastic resin film of the base material, but is within the temperature range of 140 to 240 ° C, more preferably 180 to 240 ° C. What is necessary is just to set suitably.

  When the maximum temperature in 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 nanophase separation structure in the coating layer. Furthermore, the thermal contraction rate of the obtained laminated film becomes large, which is not preferable.

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

(Polarizer)
The polarizing plate of the present invention is a polarizing plate having a polarizer protective film on both sides of the polarizer, and the polarizer protective film on at least one side is the above-mentioned coated polyester film for protecting a polarizer. preferable. The other polarizer protective film may be the above-described coating layer of the present invention, or a film having no birefringence such as a triacetyl cellulose film, an acrylic film, or a norbornene-based film is preferably used.

  Examples of the polarizer include a polyvinyl alcohol film containing a dichroic material such as iodine. The polarizer protective film is bonded to the polarizer directly or via an adhesive layer, but it is preferable to bond the polarizer protective film via an adhesive from the viewpoint of improving adhesiveness. In that case, it is preferable to arrange | position the coating layer of this invention to a polarizer surface or an adhesive bond layer surface. As a preferable polarizer for bonding the polyester film of the present invention, for example, iodine or dichroic material is dyed and adsorbed on a polyvinyl alcohol film, uniaxially stretched in a boric acid aqueous solution, and the stretched state is maintained. The polarizer obtained by performing washing | cleaning and drying is mentioned. The draw ratio of uniaxial stretching is usually about 4 to 8 times. Polyvinyl alcohol is suitable as the polyvinyl alcohol film. “Kuraray Vinylon” [manufactured by Kuraray Co., Ltd.], “Tosero Vinylon” [manufactured by Toh Cello Co., Ltd.], “Nichigo Vinylon” [Nippon Synthetic Chemical Co., Ltd.] Commercial products such as “made” can be used. Examples of the dichroic material include iodine, a disazo compound, and a polymethine dye.

  From the viewpoint of thinning the adhesive layer, the adhesive applied to the polarizer is preferably an aqueous one, that is, an adhesive component dissolved in water or dispersed in water. For example, a polyvinyl alcohol resin, a urethane resin, or the like is used as a main component, and a composition containing an isocyanate compound, an epoxy compound, or the like can be used as necessary in order to improve adhesiveness. The thickness of the adhesive layer is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

  When using polyvinyl alcohol resin as the main component of the adhesive, in addition to partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, amino group-modified A modified polyvinyl alcohol resin such as polyvinyl alcohol may be used. 1-10 mass% is preferable and, as for the density | concentration of the polyvinyl alcohol-type resin in an adhesive agent, 2-7 mass% is more preferable.

  Next, the present invention will be described in detail using examples, comparative examples, and reference examples, but the present invention is not limited to the following examples. The evaluation method used in the present invention is as follows.

(1) PVA surface fraction (1-1) Evaluation of phase separation structure The phase separation structure of the coating layer was evaluated using a scanning probe microscope (NaIINavi system / SPA300, manufactured by SII Nanotechnology). The mode (phase mode) was performed. In the phase image, the larger the phase lag, the brighter the color image, and the smaller the phase lag, the darker the image. A small phase lag means that it is hard or has a relatively low adsorption force compared to other phases. In the coating layer of the easily adhesive polyester film of the present invention, the dark hue is the polyvinyl alcohol layer β, and the light hue is the polyester layer α.

  The measurement principle of the phase measurement mode in the scanning probe microscope is described on the website of SII Nanotechnology Inc. (http://www.siint.com/products/spm/tec_mode/1_pm.html).

  As the cantilever used for measurement, DF3 (spring constant: about 1.6 N / m) was mainly used, and a new one was always used in order to prevent a decrease in sensitivity and resolution due to probe contamination. The scanner used was FS-20A. Further, the observation was performed with a resolution of 512 × 512 pixels or more, and the observation visual field was 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 were subjected to line scanning, and conditions were set so that observation can be performed with the highest sensitivity and resolution.

  The phase mode image (bitmap format, 512 × 512 pixels) obtained as described above is read into image processing software (manufactured by Adobe, Photoshop ver. 7.0) and displayed on the display so that the image size is 205 mm × 205 mm. Displayed. Next, a black line was drawn at the boundary between the light hue and the dark hue with the pencil tool (master diameter: 3 px) of the same software to clarify the boundary between both phases. Furthermore, using the paint tool of the same software, the dark hue was painted black and the light hue was painted white to binarize.

(1-2) Measurement 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 as described above was stored as a digital image in bitmap format. Next, this image was printed out on A4 size fine paper with a printer (manufactured by Xerox, Doccentre Color a250). For the output image (200 mm × 200 mm), the boundary between the light hue and the dark hue in the image was clarified with a 4B pencil in a bright room under 500 lux illumination by visual confirmation. At this time, since the dark hue having a diameter of 0.1 μm or less existing in the bright hue is confirmed to be particles contained in the coating layer unevenly distributed in the bright hue, no boundary line is drawn. , Included in light hue. After that, the boundary line that clarifies the light hue and the dark hue is divided by cutting with a cutter knife, and the mass of the paper of the light hue (polyester phase α) and the dark hue (polyvinyl alcohol phase β) is measured. The ratio of the mass of the dark hue (polyvinyl alcohol phase β) to the total mass of the dark hue paper was determined in units of%. This measurement operation was carried out with measurement samples taken from five different locations, and the average value was taken as the PVA surface fraction. In addition, when the phase separation did not occur, it described as x.

In addition to the paper weight method, the PVA surface fraction can also be measured using the following image analysis method.
(1-2-2) Image analysis method The binarized image is displayed with the same software, and a histogram with luminance (black, white) as the horizontal axis and frequency as the vertical axis is displayed to determine the area ratio of the black part. . This measurement operation is carried out with measurement samples taken from five different locations, and the average value is taken as the PVA surface fraction. In addition, when nanophase separation has not occurred, it is described as x.

(2) Glass transition temperature In accordance with JIS K7121, using a differential scanning calorimeter (Seiko Instruments, DSC6200), 10 mg of a resin sample was heated at a rate of 20 ° C / min over a temperature range of 25 to 300 ° C, and DSC The extrapolated glass transition start temperature obtained from the curve was defined as the glass transition temperature.

(3) Number average molecular weight 0.03 g of resin was dissolved in 10 ml of tetrahydrofuran, and a GPC-LALLS apparatus low-angle light scattering photometer LS-8000 (manufactured by Tosoh Corporation, tetrahydrofuran solvent, reference: polystyrene) was used at a column temperature of 30 ° C. The number average molecular weight was measured using a flow rate of 1 ml / min and a column (showex KF-802, 804, 806 manufactured by Showa Denko KK).

(4) Resin composition The resin is dissolved in deuterated chloroform, and ¹ H-NMR analysis is performed using a nuclear magnetic resonance analyzer (NMR) Gemini-200 manufactured by Varian, and the mol% ratio of each composition is determined from the integral ratio. Were determined.

(5) Acid value 1 g (solid content) of a sample was dissolved in 30 ml of chloroform or dimethylformamide, and titrated with 0.1 N potassium hydroxide ethanol solution using phenolphthalein as an indicator to determine the carboxyl groups per gram of the sample. The amount (mg) of KOH required for neutralization was determined.

(6) Saponification degree Residual acetate groups (mol%) of the polyvinyl alcohol resin were quantified using sodium hydroxide according to JIS-K6726, and the value was defined as the saponification degree (mol%). The sample was measured three times, and the average value was defined as the saponification degree (mol%).

(7) Total light transmittance of laminated polyester film The total light transmittance of the laminated polyester film was measured according to JIS K 7105 using a turbidimeter (Nippon Denshoku, NDH2000).

(8) Haze of laminated polyester film The haze of the laminated polyester film was measured using a turbidimeter (Nippon Denshoku, NDH2000) according to JIS K7136.

(9) PVA adhesive property A polyvinyl alcohol aqueous solution (Kuraray PVA117) adjusted to a solid content concentration of 5% by mass is coated on the surface of the laminated polyester film so that the thickness of the polyvinyl alcohol resin layer after drying is 2 μm. It apply | coated with the wire bar and dried for 5 minutes at 70 degreeC. As the polyvinyl alcohol aqueous solution, a solution in which a red dye was added so as to facilitate the determination was used. The prepared evaluation target film was attached to a glass plate having a thickness of 5 mm to which a double-sided tape was attached, and the opposite surface of the evaluation target laminated film on which the polyvinyl alcohol resin layer was formed was attached to the double-sided tape. Next, 100 grid-like cuts that penetrated through the polyvinyl alcohol resin layer and reached the base film were made using a cutter guide with a gap interval of 2 mm. Next, an adhesive tape (Cello Tape (registered trademark) CT-24; 24 mm width, manufactured by Nichiban Co., Ltd.) was attached to the grid-shaped cut surface. The air remaining at the interface at the time of pasting was pressed with an eraser to bring it into close contact, and then the work of peeling off the adhesive tape vigorously vertically was performed once, five times and ten times. The number of squares on which the polyvinyl alcohol resin layer was not peeled was counted to determine PVA adhesion. That is, when the PVA layer was not peeled off at all, the PVA adhesion rate was 100, and when all the PVA layer was peeled off, the PVA adhesion rate was 0. In addition, what was partially peeled within one square was also included in the number of peeled.

(10) PVA coating property A polyvinyl alcohol aqueous solution (PVA117 manufactured by Kuraray Co., Ltd.) adjusted to a solid content concentration of 5 mass% is coated on the surface of the laminated polyester film so that the thickness of the polyvinyl alcohol resin layer after drying is 2 μm. The coating condition of the polyvinyl alcohol resin layer after coating with a wire bar and drying at 70 ° C. for 5 minutes was evaluated according to the following criteria.

◎: The coated whole surface is neatly applied without repelling. ○: The coated whole surface is completely repelled without repelling. △: The coated portion is repelled.
X: It almost repels the whole coated surface.

(Polyester resin polymerization)
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, and 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate Then, 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was performed at a temperature of 160 ° C. to 220 ° C. over 4 hours. Next, the temperature was raised to 255 ° C., and the pressure of the reaction system was gradually reduced, followed by reaction for 1 hour 30 minutes under a reduced pressure of 30 Pa to obtain a copolymerized polyester resin (A-1). The obtained copolyester resin (A-1) was light yellow and transparent. It was 0.70 dl / g when the reduced viscosity of copolyester resin (A-1) was measured. The glass transition temperature by DSC was 40 ° C.

In the same manner, copolymer polyester resins (A-2) to (A-5) having different compositions were obtained. Table 1 shows the composition (molar ratio) and other characteristics of these copolyester resins measured by ¹ H-NMR.

(Adjustment of polyester aqueous dispersion)
30 parts by mass of polyester resin (A-1) and 15 parts by mass of ethylene glycol n-butyl ether were placed in a reactor equipped with a stirrer, a thermometer and a reflux device, and 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 to the polyester solution while stirring. After the addition, the solution 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, using the polyester resins (A-2) to (A-5) instead of the polyester resin (A-1), water dispersions are prepared, and the polyester water dispersions (Aw-2) to (Aw) are respectively produced. -5).

(Preparation of aqueous polyvinyl alcohol 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 polyvinyl alcohol resin (manufactured by Kuraray) (B-1) having a polymerization degree of 500 was gradually added while stirring. After the addition, the solution was heated to 95 ° C. while stirring to dissolve the resin. After 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, polyvinyl alcohol resins (B-2) to (B-8) were used instead of the polyvinyl alcohol resin (B-1) to prepare aqueous solutions, which were designated as (Bw-2) to (Bw-8), respectively. . Table 2 shows the degree of saponification of the polyvinyl alcohol resins (B-1) to (B-8).

(Polymerization of block polyisocyanate crosslinking agent C-1)
In a flask equipped with a stirrer, thermometer and reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure using hexamethylene diisocyanate as a raw material (manufactured by Asahi Kasei Chemicals, Duranate TPA), 55 parts by mass of propylene glycol monomethyl ether acetate, polyethylene 30 parts by mass of glycol monomethyl ether (average molecular weight 750) was charged, and kept at 70 ° C. for 4 hours under a nitrogen atmosphere. Thereafter, the reaction solution temperature was lowered to 50 ° C., and 47 parts by mass of methyl ethyl ketoxime was added dropwise. The infrared spectrum of the reaction solution was measured to confirm that the absorption of the isocyanate group had disappeared, and a block polyisocyanate aqueous dispersion (C-1) having a solid content of 75% by mass was obtained.

Example 1
(1) Adjustment of coating liquid The following coating agent was mixed and the coating liquid from which the mass ratio of polyester-type resin (A) / polyvinyl alcohol-type resin (B) became 70/30 was created. The polyester aqueous dispersion uses an aqueous dispersion (Aw-1) in which a polyester resin having an acid value of 2 KOH mg / g is dispersed, and the polyvinyl alcohol aqueous solution is an aqueous solution in which polyvinyl alcohol having a saponification degree of 74 mol% is dissolved. (Bw-4) was used.
Water 40.61 mass%
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 11.67 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 15.00 mass%
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

(2) Production of laminated polyester film As a film raw material polymer, intrinsic viscosity (solvent: phenol / tetrachloroethane = 60/40) is 0.62 dl / g, and PET resin pellets substantially free of particles are used. It was dried at 135 ° C. for 6 hours under a reduced pressure of 133 Pa. Thereafter, the sheet was supplied to an extruder, melted and extruded into a sheet at about 280 ° C., and rapidly cooled and solidified on a rotating cooling metal roll maintained at a surface temperature of 20 ° C. to obtain an unstretched PET sheet.

  This unstretched PET sheet was heated to 100 ° C. with a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction with a roll group having a difference in peripheral speed to obtain a uniaxially stretched PET film.

Subsequently, after apply | coating the said coating liquid to the single side | surface of PET film by the roll coat method, it dried at 80 degreeC for 15 second. The final coating amount (after biaxial stretching) was adjusted so that the coating amount after drying was 0.15 g / m ² . Subsequently, the film was stretched 4.0 times in the width direction at 150 ° C. with a tenter, and the film was heat-treated at 230 ° C. for 0.5 seconds, and further at 230 ° C. for 10 seconds. A relaxation treatment in the width direction of 3% was performed to obtain a laminated polyester film having a thickness of 38 μm. The evaluation results are shown in Table 3.

Example 2
A laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and relaxation treatment after the tenter stretching was changed to 180 ° C.

Example 3
A laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and relaxation treatment after tenter stretching was changed to 140 ° C.

Example 4
A laminated polyester film was obtained in the same manner as in Example 1 except that the following coating agent was mixed and changed so that the mass ratio of polyester resin / polyvinyl alcohol resin was 60/40.
Water 37.28% by mass
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 10.00 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 20.00 mass%
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Example 5
A laminated polyester film is obtained in the same manner as in Example 1 except that the following coating agent is mixed and the mass ratio of the polyester resin (A) / polyvinyl alcohol resin (B) is changed to 80/20. It was.
43.95% by weight of water
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 13.33 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 10.00 mass%
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Example 6
A laminated polyester film is obtained in the same manner as in Example 1 except that the following coating agent is mixed and the mass ratio of the polyester resin (A) / polyvinyl alcohol resin (B) is changed to 50/50. It was.
Water 33.95% by mass
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 8.33 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 25.00% by mass
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Example 7
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-2) in which a polyester resin having an acid value of 4 KOHmg / g was dispersed.

Example 8
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-3) in which a polyester resin having an acid value of 6 KOHmg / g was dispersed.

Example 9
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-5) in which a polyester resin having an acid value of 10 KOHmg / g was dispersed.

Example 10
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 polyvinyl alcohol having a saponification degree of polyvinyl alcohol of 67 mol% was dissolved.

Example 11
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 polyvinyl alcohol having a saponification degree of polyvinyl alcohol of 70 mol% was dissolved.

Example 12
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) in which the saponification degree of polyvinyl alcohol was 79 mol%.

Example 13
A laminated polyester film was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution (Bw-2) had a saponification degree of polyvinyl alcohol of 83 mol%.

Example 14
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 polyvinyl alcohol having a saponification degree of 88 mol% was dissolved.

Example 15
A laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating solution was changed as follows.
40.87% by mass of water
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 11.67 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 15.00 mass%
Melamine type crosslinking agent (C-2) 0.71 mass%
(Nikarak MX-042, manufactured by Sanwa Chemical Co., Ltd., solid content concentration 70%)
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Example 16
A laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating solution was changed as follows.
40.33% by mass of water
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 11.67 mass%
Polyvinyl alcohol aqueous solution (Bw-2) 15.00 mass%
Oxazoline-based crosslinking agent (C-3) 1.25% by mass
(Epocross WS-500, manufactured by Nippon Shokubai, solid concentration 40% by mass)
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Example 17
A laminated polyester film was obtained in the same manner as in Example 1 except that the composition of the coating solution was changed as follows.
40.58% by mass of water
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 11.67 mass%
Polyvinyl alcohol aqueous solution (Bw-2) 15.00 mass%
Epoxy crosslinking agent (C-4) 1.00% by mass
(Adeka Resin EM-051R ADEKA solid content 50% by mass)
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Comparative Example 1
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 polyester resin (A) / polyvinyl alcohol resin (B) was changed to 100/0. It was.
Water 50.62% by mass
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 16.66 mass%
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Comparative Example 2
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 polyester resin (A) / polyvinyl alcohol resin (B) was changed to 0/100. It was.
17.28% by mass of water
Isopropanol 30.00% by mass
Polyvinyl alcohol aqueous solution (Bw-4) 50.00 mass%
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Comparative Example 3
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 polyester resin (A) / polyvinyl alcohol resin (B) was changed to 90/10. It was.
Water 47.28% by mass
Isopropanol 30.00% by mass
Polyester water dispersion (Aw-1) 15.00 mass%
Polyvinyl alcohol aqueous solution (Bw-4) 5.00% by mass
Block isocyanate-based crosslinking agent (C-1) 0.67% by mass
1.25% by mass of particles
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (Organic tin compound, solid content concentration 14% by mass) 0.3% by mass
Surfactant 0.5% by mass
(Silicone, solid content concentration 10% by mass)

Comparative Example 4
A laminated polyester film was obtained in the same manner as in Example 1 except that tenter stretching after applying the coating solution was not performed.

Comparative Example 5
A laminated polyester film was obtained in the same manner as in Example 1 except that the temperature of the heat treatment and relaxation treatment after the tenter stretching was changed to 100 ° C.

Comparative Example 6
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-8) in which polyvinyl alcohol having a saponification degree of 99 mol% was dissolved.

Comparative Example 7
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-7) in which polyvinyl alcohol having a saponification degree of 40 mol% was dissolved.

Comparative Example 8
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 a polyester resin having an acid value of 25 KOHmg / g was dispersed.

Reference example 1
The adhesion test was conducted using a TAC film (manufactured by Fuji Film Co., Ltd., thickness 80 μm, saponified) as a laminated polyester film.

  About the laminated polyester film of Examples 1-17 produced as mentioned above and Comparative Examples 1-8, evaluation and measurement of each above-mentioned item were performed. The results are shown in Table 3 below together with the results of Reference Example 1.

  In the laminated polyester films of Examples 1 to 17, a nanophase separation structure was observed in all. As a reference, a phase contrast micrograph of the coating layer surface of the laminated polyester film of Example 5 is shown in FIG. The laminated polyester films of Examples 1 to 17 having a surface fraction of the PVA phase of 30% or more have no problem in coatability and are excellent PVA films that can be evaluated as equivalent to a TAC film in a single peel test. Adhesion was shown.

  The laminated polyester film of the present invention has high adhesiveness with a polarizer / water-based adhesive. Therefore, it can be suitably used as a polarizer protective member.

Claims (7)

A laminated polyester film having a coating layer on at least one side of the polyester film,
The coating layer includes a polyvinyl alcohol resin and a polyester resin,
The surface of the coating layer has a nanophase separation structure composed of a phase in which a polyvinyl alcohol resin is aggregated and a phase in which a polyester resin is aggregated, and the area ratio of the polyvinyl alcohol phase is 30% or more and less than 99%. A laminated polyester film characterized by that.   The laminated polyester film according to claim 1, wherein the degree of saponification of the polyvinyl alcohol resin is 95% or less.   The laminated polyester film according to claim 1 or 2, wherein the polyester-based resin has a glass transition temperature of 25 ° C or higher.   The laminated polyester film according to claim 1, wherein the coating layer contains a crosslinking agent.   The laminated polyester film according to claim 4, wherein the crosslinking agent is a melamine crosslinking agent and / or an isocyanate crosslinking agent. The laminated polyester film according to claim 1, wherein a mass ratio of the polyvinyl alcohol resin and the polyester resin contained in the coating layer satisfies the following formula.
0.2 ≦ PVA / PEs ≦ 1.25 A polarizing plate having a polarizer protective film on both sides of a polarizer,
The polarizing plate whose at least one polarizer protective film is the laminated polyester film in any one of Claims 1-6.

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