Laminated Polyester Film

Abstract

To provide a laminated polyester film that can prevent decrease in visibility due to whitening of film appearance; occurrence of a defect in post-processing; and occurrence of a defect such as contamination in a process or material by reducing precipitation of oligomer from a polyester film during treatment thereof at a high temperature, and that prevents detachment of a release layer due to improvement of adhesion and aging adhesion between a base polyester film and the release layer.SOLUTION: There is provided a laminated polyester film that is configured to include a cured resin layer on at least one side of the polyester film. The cured resin layer is a cured product of a cured resin layer composition containing a resin having a styrene structure and a cross-linking agent. The cross-linking agent is two or more kinds selected from a melamine compound, an epoxy compound, an organosilicon compound, an oxazoline compound, an isocyanate compound, and a carbodiimide compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated polyester film, specifically a film having a polyester film substrate and a cured resin layer and a release layer formed in that order. The laminated polyester film suppresses the deposition of oligomers (low-molecular-weight polyester components, particularly cyclic ester trimers) on the surface of the polyester film even after exposure to high temperatures, and exhibits excellent adhesion between the substrate film and the release layer over time, preventing problems associated with oligomer deposition and problems due to the release layer peeling off over time. [Background technology]

[0002] BACKGROUND ART Polyester films have been used in various applications because they have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and also have excellent cost performance.

[0003] In recent years, release films are often exposed to high temperatures in their applications. For example, transparent conductive laminates in which an ITO (indium tin oxide) film is formed by sputtering, which are increasingly used in touch panels, are generally exposed to heat of about 150°C for one hour or more during the ITO crystallization process (Patent Document 1).

[0004] When bonding such transparent conductive laminates, it is common to use an adhesive layer sandwiched between release films (Patent Document 2). The adhesive layer and release film are laminated onto the transparent conductive laminate before crystallization, and both may undergo the crystallization process.

[0005] Furthermore, as an example of a release film in which a polyester film is used as the base material, Patent Document 3 discloses a release film having a coating layer on at least one side of a polyester film and a release layer on the coating layer, characterized in that the coating layer contains a copolymerized polyester resin having at least an acid component having a condensed polycyclic aromatic structure and an aliphatic acid component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-200823 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-76432 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-164959 Summary of the Invention [Problem to be solved by the invention]

[0007] However, a problem with polyester films is that oligomers contained in the film precipitate from inside the film when exposed to high-temperature treatment for a long period of time. Therefore, in Patent Documents 1 to 3, the precipitated oligomers pass through the release layer or the like and crystallize inside the adhesive layer to become foreign matter, which can cause problems in visual inspection.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and the problem to be solved is to provide a laminated polyester film that can prevent problems such as reduced visibility due to whitening of the film appearance, the occurrence of defects in post-processing, and contamination of processes and components by reducing the precipitation of oligomers from the polyester film when processed at high temperatures, and that has good adhesion and adhesion over time between the base polyester film and the release layer, preventing the release layer from falling off. [Means for solving the problem]

[0009] In view of the above circumstances, the present inventors have conducted extensive research and found that the above problems can be easily solved by using a laminated polyester film having a specific structure, and have thus completed the present invention. That is, the present invention provides the following items [1] to

[11] . [1] A laminated polyester film having a cured resin layer on at least one side of a polyester film, the cured resin layer being a cured product of a cured resin layer composition containing a resin having a styrene structure and a crosslinking agent, and the crosslinking agent being two or more compounds selected from a melamine compound, an epoxy compound, an organosilicon compound, an oxazoline compound, an isocyanate compound, and a carbodiimide compound. [2] The laminated polyester film according to [1], wherein the film haze change (ΔH) before and after heat treatment under conditions of 150°C for 90 minutes is 1.0% or less. [3] The laminated polyester film according to [1] or [2], wherein the content of the resin having a styrene structure in the non-volatile components of the cured resin layer composition is 10 to 80 mass %. [4] The laminated polyester film according to any one of [1] to [3], wherein the styrene structure is a structural unit derived from styrene or a styrene derivative. [5] The laminated polyester film according to [4], wherein the resin having a styrene structure has a structure derived from a polymerizable monomer copolymerizable with styrene or a styrene derivative. [6] The laminated polyester film according to any one of [1] to [5], wherein the total content of the crosslinking agent in the non-volatile components of the cured resin layer composition is 5 to 95 mass %. [7] The laminated polyester film according to any one of [1] to [6], further comprising a release layer containing a curable silicone resin on the cured resin layer. [8] The laminated polyester film according to [7], which has an adhesive layer on the release layer. [9] A film laminate obtained by laminating the adhesive layer side of the laminated polyester film according to [8] to an adherend.

[10] The film laminate according to [9], wherein the adherend is any one of a transparent conductive layer, a polarizing element, and a resin film.

[11] The method for producing a laminated polyester film according to any one of [1] to [8], wherein the cured resin layer is provided by in-line coating (coating and stretching method). [Effects of the Invention]

[0010] According to the laminated polyester film of the present invention, even when subjected to high-temperature, long-term treatment, oligomer precipitation from the polyester film surface is suppressed, making it possible to obtain products with excellent appearance without the formation of foreign matter on the release layer surface.This prevents problems such as reduced visibility due to whitening of the film appearance, defects in post-processing, and contamination within the process or on components.In addition, it is possible to provide a laminated polyester film that has good adhesion and adhesion over time between the base polyester film and the release layer, preventing the release layer from falling off, making it highly valuable for industrial use. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0012] [Laminated polyester film] The polyester film has a cured resin layer on at least one side thereof, the cured resin layer being a cured product of a cured resin layer composition containing a resin having a styrene structure and a crosslinking agent, and the crosslinking agent being two or more compounds selected from the group consisting of melamine compounds, epoxy compounds, organosilicon compounds, oxazoline compounds, isocyanate compounds, and carbodiimide compounds. The laminated polyester film of the present invention has the above-mentioned characteristics, which can prevent precipitation of oligomers from the polyester film and improve the adhesion between the laminated polyester film and a release layer described below.

[0013] The mechanism by which the precipitation of oligomer components contained in the polyester film is suppressed is presumed to be as follows: When a polyester film is heated to a temperature above its glass transition point, oligomer components precipitate on its surface, but by forming a cured resin layer containing a resin composition having a styrene structure on the polyester film, the aromatic rings in the styrene structure are stacked parallel to the polyester film, which is presumed to suppress the precipitation of oligomer components from the polyester film. Regarding the mechanism by which the adhesion between the base polyester film and the release layer is improved, it is thought that when the cured resin layer is heated to dry and harden, hydroxyl groups are generated from the epoxy compounds or organosilicon compounds contained in the cured resin layer, which then bond or interact with functional groups contained in the release layer formed on top of it, thereby improving the adhesion between the base material and the release layer.

[0014] <Polyester film> The polyester film constituting the laminated polyester film of the present invention may be a single-layer or multi-layer structure, and may be a two-layer or three-layer structure or a four-layer or more multi-layer structure as long as it does not deviate from the gist of the present invention, and is not particularly limited. In the present invention, a polyester film having at least a three-layer structure is preferred. Furthermore, as the polyester film, a biaxially oriented polyester film is preferred from the viewpoints of thinning and dimensional stability.

[0015] In the present invention, the polyester used as the raw material for the polyester film may be either a homopolyester or a copolymer polyester. In the case of a homopolyester, one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol is preferred. Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. A representative polyester is polyethylene terephthalate. On the other hand, examples of dicarboxylic acid components of copolymer polyesters include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and hydroxycarboxylic acids (e.g., p-hydroxybenzoic acid). Examples of glycol components include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, and neopentyl glycol.

[0016] The polymerization catalyst for polyester is not particularly limited, and conventionally known compounds can be used, such as antimony compounds, titanium compounds, germanium compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds. Among these, titanium compounds and germanium compounds are preferred because they have high catalytic activity, can be polymerized in small amounts, and leave little metal residue in the polyester film, resulting in high brightness of the polyester film. Furthermore, since germanium compounds are expensive, it is more preferred to use titanium compounds.

[0017] In the case of polyesters using a titanium compound, the titanium element content is preferably 50 ppm by mass or less, more preferably 1 to 20 ppm by mass, and even more preferably 2 to 10 ppm by mass. If the titanium compound content is too high, deterioration of the polyester may be accelerated during the melt-extrusion process, resulting in a polyester film with a strong yellow tint. On the other hand, if the content is too low, polymerization efficiency may be poor, resulting in increased costs and in the failure to obtain a polyester film with sufficient strength. Furthermore, when using a polyester containing a titanium compound, it is preferable to use a phosphorus compound to reduce the activity of the titanium compound in order to prevent deterioration during the melt extrusion process. As the phosphorus compound, orthophosphoric acid is preferred in consideration of the productivity and thermal stability of the polyester. The content of the phosphorus compound is preferably 1 to 300 ppm by mass, more preferably 3 to 200 ppm by mass, and even more preferably 5 to 100 ppm by mass, in terms of the phosphorus element content, relative to the amount of polyester to be melt extruded. When the content of the phosphorus compound is equal to or less than the upper limit, gelation or foreign matter does not occur. When the content of the phosphorus compound is equal to or more than the lower limit, the activity of the titanium compound can be sufficiently reduced, coloration can be suppressed, and a yellowish polyester film does not result.

[0018] In order to suppress the amount of precipitation of oligomer components, the polyester film may be produced using a polyester having a low content of oligomer components as the raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used, such as a method in which solid-state polymerization is carried out after the polyester is produced.

[0019] The polyester film may be made of three or more layers, and the outermost layer of the polyester film may be made of a polyester raw material having a low content of oligomer components, thereby suppressing the amount of oligomer components that precipitate. The polyester may also be obtained by esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature.

[0020] The polyester film may contain an ultraviolet absorber to improve the weather resistance of the laminated polyester film and prevent deterioration of the adherend (e.g., polarizing element), etc. The ultraviolet absorber is a compound that absorbs ultraviolet light and is not particularly limited as long as it can withstand the heat applied in the polyester film production process.

[0021] The ultraviolet absorber includes organic ultraviolet absorbers and inorganic ultraviolet absorbers, and organic ultraviolet absorbers are preferred from the viewpoint of transparency.The organic ultraviolet absorbers are not particularly limited, but examples thereof include cyclic imino esters, benzotriazoles, benzophenones, etc.From the viewpoint of durability, cyclic imino esters and benzotriazoles are more preferred.In addition, two or more types of ultraviolet absorbers can be used in combination.

[0022] Particles can also be incorporated into polyester films for the primary purposes of imparting lubricity and preventing scratches during each process. When particles are incorporated, the type of particles to be incorporated is not particularly limited as long as they are capable of imparting lubricity. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, zirconium oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a portion of a metal compound such as a catalyst during the polyester production process can also be used. Among these, silica particles and calcium carbonate particles are preferred because they are particularly effective even in small amounts.

[0023] The average particle size of the particles is preferably 5.0 μm or less, more preferably 0.01 to 3.0 μm. When the average particle size is 5.0 μm or less, the surface roughness of the laminated polyester film does not become too rough, and problems do not occur in various post-processing steps. Furthermore, by using the particles in the above range, haze is kept low, making it easier to ensure transparency for the entire laminated polyester film.

[0024] Furthermore, the particle content in the polyester film is preferably less than 5% by mass, more preferably 0.0003 to 1% by mass, and even more preferably 0.0005 to 0.5% by mass. By setting the particle content at or above the lower limit, the slipperiness of the laminated polyester film is improved, and production efficiency in subsequent processes is likely to be improved. Furthermore, by setting the particle content at or below the upper limit, the haze of the laminated polyester film is not increased and sufficient transparency is obtained, so that, for example, the difficulty of defect inspection such as foreign matter during various inspections is not increased. In the case of a three or more layer structure, the particle content in the polyester layers on both surfaces is required to be within the above range.

[0025] The shape of the particles to be used is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0026] The method for adding particles to the polyester layer is not particularly limited, and any conventionally known method can be used. For example, the particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add the particles after the completion of the esterification or transesterification reaction.

[0027] In addition to the above-mentioned particles, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film of the present invention as required.

[0028] The thickness of the polyester film in the present invention is not particularly limited as long as it is within a range that allows film formation, but is preferably 10 to 300 μm, more preferably 15 to 250 μm, even more preferably 20 to 200 μm, and still more preferably 23 to 125 μm.

[0029] In the present invention, the polyester film can be produced by any commonly known film production method without any particular limitation. For example, when producing a biaxially stretched polyester film, the aforementioned polyester raw material is first melt-extruded through a die using an extruder, and the molten sheet is cooled and solidified using a cooling roll to obtain an unstretched sheet. In this case, it is preferable to increase the adhesion between the sheet and a rotating cooling drum to improve the sheet's flatness, and electrostatic adhesion or liquid application adhesion is preferably used. The resulting unstretched sheet is then stretched in one direction using a roll or tenter-type stretching machine. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the sheet is stretched in a direction perpendicular to the first-stage stretching direction, usually at 70 to 170°C, at a stretching ratio of usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the sheet is heat-treated at a temperature of 180 to 270°C under tension or relaxation of 30% or less to obtain a biaxially oriented film. In the above stretching, a method in which unidirectional stretching is performed in two or more stages may also be used. In this case, it is preferable to carry out the stretching so that the final stretching ratios in both directions are within the above ranges.

[0030] A simultaneous biaxial stretching method can also be used to produce polyester films. In this method, the unstretched sheet is simultaneously stretched and oriented in both the machine direction and the width direction under temperature control, typically at 70 to 120°C, and preferably at 80 to 110°C. The area stretch ratio is typically 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, the sheet is heat-treated at a temperature of 170 to 270°C under tension or relaxation of 30% or less to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching apparatus used in the above-described stretching method, any conventionally known stretching method, such as a screw method, a pantograph method, or a linear drive method, can be used.

[0031] <Cured resin layer> Next, the formation of the cured resin layer constituting the laminated polyester film of the present invention will be described. In the present invention, the cured resin layer may be formed by in-line coating (coating and stretching method), which treats the film surface during the polyester film production process, or by off-line coating, which applies the resin to a film already produced outside the system. In-line coating is more preferred.

[0032] Inline coating is a method of coating within the film production process. Specifically, it is a method of coating at any stage from melt extrusion of the film raw material to stretching, heat treatment, and winding up. Typically, coating is performed on an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat treatment, or a film after heat treatment and before winding up. While not limited to the following, for example, in sequential biaxial stretching, a method in which coating is performed on a uniaxially stretched film stretched in the longitudinal direction (machine direction) and then stretched in the transverse direction is particularly advantageous. This method offers advantages in terms of production costs, as film production and formation of a cured resin layer can be performed simultaneously. Furthermore, because stretching is performed after coating, the thickness of the cured resin layer can be changed by changing the stretch ratio, making thin-film coating easier than offline coating.

[0033] The inline coating process has a major advantage over offline coating, which involves a separate coating process, because the thickness of the laminated polyester film does not change significantly depending on whether or not a cured resin layer is formed, and the risk of scratches or foreign matter adhesion also does not change significantly depending on whether or not a cured resin layer is formed.

[0034] Furthermore, by providing a cured resin layer on the polyester film before stretching, the cured resin layer can be stretched together with the film, thereby allowing the cured resin layer to adhere firmly to the film. Furthermore, in the production of biaxially stretched films, the polyester film can be restrained in both the longitudinal and transverse directions by stretching the film while holding the film edges with clips or the like, and high temperatures can be applied during the heat treatment process while maintaining smoothness and without wrinkles. Therefore, the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, which improves the film-forming properties of the cured resin layer, allows for stronger adhesion between the cured resin layer and the polyester film, and further results in a stronger cured resin layer. Furthermore, as described above, by stretching the polyester film while holding its edges and then subjecting it to a heat treatment step to form a cured resin layer, there is an advantage in that the heat resistance of the laminated polyester film can be improved.

[0035] The heat treatment temperature for the cured resin layer formed by in-line coating is preferably 70 to 290° C., more preferably 90 to 280° C., even more preferably 170 to 270° C., and still more preferably 200 to 250° C. The heat treatment time is preferably 3 to 200 seconds.

[0036] If necessary, the heat treatment may be combined with irradiation with active energy rays such as ultraviolet rays. The surface of the polyester film of the present invention may be subjected to a surface treatment such as a corona treatment or a plasma treatment before providing the cured resin layer.

[0037] Regarding the formation of the cured resin layer, it is preferable to produce a laminated polyester film by coating a film with a cured resin layer composition prepared by preparing a solution or dispersion in a solvent of a series of compounds described below and adjusting the solid content concentration to approximately 0.1 to 80% by mass. When forming the cured resin layer by in-line coating, the cured resin layer composition is preferably an aqueous solution or dispersion, but the cured resin layer composition may contain a small amount of organic solvent for the purposes of improving dispersibility in water, film-forming properties, etc. Furthermore, only one type of organic solvent may be used, or two or more types may be used in combination.

[0038] Examples of a method for applying the cured resin layer composition to the polyester film that is the substrate of the laminated polyester film include conventionally known application methods such as air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calendar coating, and extrusion coating.

[0039] In the present invention, the cured resin layer is a cured product of a cured resin layer composition containing a resin having a styrene structure and a crosslinking agent, and the crosslinking agent is two or more compounds selected from a melamine compound, an epoxy compound, an organosilicon compound, an oxazoline compound, an isocyanate compound, and a carbodiimide compound.

[0040] (Resin with styrene structure) In the present invention, the styrene structure of the resin having a styrene structure is exemplified by the following general formula (1).

[0041] [ka]

[0042] In the above general formula (1), R 1 is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. 1 may be the same or different. Z is a substituent introduced into the aromatic ring and is a monovalent hydrocarbon group having 1 to 10 carbon atoms. n is an integer of 0 to 3, and when n is 0, the aromatic ring has a hydrogen atom instead of a substituent. When n is 2 or more, each Z may be the same or different.

[0043] In the present invention, the styrene structure of the resin having a styrene structure is preferably a structural unit derived from styrene or a styrene derivative. When the styrene structure is a structural unit derived from styrene or a styrene derivative, it is easier to suppress the precipitation of oligomers from the polyester film due to heat treatment. From the viewpoint of improving the ability to prevent oligomer precipitation due to heat treatment, the structural unit derived from styrene or a styrene derivative is preferably a structural unit derived from styrene or a styrene in which an alkyl group having 4 or less carbon atoms is substituted on the aromatic ring, more preferably a structural unit derived from styrene or a styrene derivative such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, o-ethylstyrene, and p-ethylstyrene, and even more preferably a structural unit derived from styrene.

[0044] In the present invention, the resin having a styrene structure preferably has a structural unit derived from a polymerizable monomer copolymerizable with styrene or a styrene derivative, which makes it easier to suppress precipitation of oligomer components from the polyester film. Examples of copolymerizable monomers include (meth)acrylate, various (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutylhydroxyfumarate, and monobutylhydroxyitaconate. Examples of suitable copolymerizable copolymers include various hydroxyl group-containing compounds such as (meth)acrylamide, diacetone acrylamide, N-methylolacrylamide, and (meth)acrylonitrile, various nitrogen-containing compounds such as vinyl propionate and vinyl acetate, various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane, phosphorus-containing vinyl monomers, various vinyl halides such as vinyl chloride and vinylidene chloride, and various conjugated dienes such as butadiene. Among these, copolymerization of a hydroxyl group-containing compound is preferred for its high oligomer precipitation prevention properties. When a hydroxyl group-containing compound is copolymerized, the content of the hydroxyl group-containing compound in the resin having a styrene structure is preferably 1 to 30 mol%, more preferably 5 to 25 mol%, and even more preferably 10 to 20 mol%. When the content of the hydroxyl group-containing compound is within the above range, precipitation of oligomers due to heat treatment can be more effectively suppressed, and deterioration of the appearance of the cured resin layer can be easily suppressed.

[0045] The proportion of styrene structures in the resin having a styrene structure is preferably 5 to 95 mol%, more preferably 20 to 90 mol%, and even more preferably 40 to 85 mol%. When the proportion of styrene structures is within the above range, precipitation of oligomers due to heat treatment can be effectively suppressed.

[0046] In the resin having a styrene structure, the proportion of constitutional units derived from polymerizable monomers copolymerizable with styrene or styrene derivatives is preferably 5 to 95 mol%, more preferably 10 to 80 mol%, and even more preferably 15 to 40 mol%. When the proportion of constitutional units derived from polymerizable monomers copolymerizable with styrene or styrene derivatives is within the above range, precipitation of oligomers due to heat treatment can be effectively suppressed.

[0047] (Crosslinking agent) In the present invention, the crosslinking agent is two or more selected from a melamine compound, an epoxy compound, an organosilicon compound, an oxazoline compound, an isocyanate compound, and a carbodiimide compound, and is preferably two or more selected from a melamine compound, an epoxy compound, and an organosilicon compound. The inclusion of a crosslinking agent in the cured resin layer composition can suppress the precipitation of oligomers on the surface of the laminated polyester film or in the adhesive layer due to heat treatment, facilitate the improvement of the durability of the cured resin layer, and improve the coatability of the cured resin layer composition during processing. As the crosslinking agent, a melamine compound is preferably used from the viewpoint of preventing oligomer precipitation on the film surface due to heating and improving the durability of the cured resin layer, and an epoxy compound or an organosilicon compound is preferably used from the viewpoint of improving adhesion to the release layer.

[0048] In the present invention, by using two or more crosslinking agents, it is possible to improve the adhesion between the film and the release layer as well as the prevention of oligomer precipitation after heating. As the combination of crosslinking agents, a combination of a melamine compound and an epoxy compound, a combination of a melamine compound and an organosilicon compound, and a combination of a melamine compound, an epoxy compound and an organosilicon compound are preferred, and a combination of a melamine compound, an epoxy compound and an organosilicon compound is more preferred.

[0049] The melamine compound refers to a compound having a melamine structure within the compound. Examples of such compounds include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohols to partially or completely etherify them, and mixtures thereof. Suitable alcohols for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. The melamine compound may be either a monomer or an oligomer of dimer or higher, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be used to increase the reactivity of the melamine compound.

[0050] The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin with a hydroxyl group or an amino group of ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc., polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

[0051] The organosilicon compound is exemplified by compounds represented by the following general formula (2). Si(X) d (Y) e (R 2 ) f …(2)

[0052] In the general formula (2), X is an organic group having at least one selected from an epoxy group, a mercapto group, a (meth)acryloyl group, an alkenyl group, a haloalkyl group, and an amino group; R 2 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, Y is a hydrolyzable group, d is an integer of 1 or 2, e is an integer of 2 or 3, f is an integer of 0 or 1, and d+e+f=4.

[0053] The organosilicon compound represented by the general formula (2) can be one having two hydrolyzable groups Y (D unit source) or three hydrolyzable groups Y (T unit source) that can form a siloxane bond by hydrolysis and condensation reaction.

[0054] In the above general formula (2), a monovalent hydrocarbon group R having 1 to 10 carbon atoms 2 As the alkyl group, a methyl group, an ethyl group, and a propyl group are particularly preferred.

[0055] In the above general formula (2), examples of the hydrolyzable group Y include the following: methoxy group, ethoxy group, butoxy group, isopropenoxy group, acetoxy group, butanoxime group, and amino group. These hydrolyzable groups may be used alone or in combination. The use of a methoxy group or an ethoxy group is particularly preferred because it can impart good storage stability to the coating material and has appropriate hydrolysis properties.

[0056] Examples of organosilicon compounds include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, vinyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 5-hexenyltrimethoxysilane, p-styryltrimethoxysilane, trifluoropropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropylmethyldiisopropenoxysilane.

[0057] The oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferred. The oxazoline compound can be obtained by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of the addition-polymerizable oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. These monomers can be used alone or in combination. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. The other monomer is not limited as long as it is copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl(meth)acrylate (the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, or cyclohexyl); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, or the like); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl(meth)acrylate, etc. Examples of the alkyl group include unsaturated amides such as acrylamides and N,N-dialkyl(meth)acrylamides (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexyl group, and the like); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride, vinylidene chloride, and vinyl fluoride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and one or more of these monomers can be used.

[0058] These crosslinking agents are used in a design that allows them to react during the drying process or film-forming process to improve the performance of the cured resin layer, and it is assumed that the completed cured resin layer contains unreacted crosslinking agents, reacted compounds, or a mixture of these.

[0059] Furthermore, when forming the cured resin layer of the present invention, it is preferable to use in combination a polymer other than the resin having a styrene structure and the crosslinking agent in order to improve the appearance of the cured resin layer and to improve adhesion when an adhesive layer is formed on the cured resin layer.

[0060] Specific examples of other polymers include polyester resin, acrylic resin, urethane resin, polyvinyl (such as polyvinyl alcohol), polyalkylene glycol, polyalkyleneimine, methyl cellulose, hydroxycellulose, starches, etc. Among these, from the viewpoint of improving the durability of the cured resin layer, it is preferable to use polyester resin, acrylic resin, or urethane resin, and from the viewpoint of improving adhesion to the release layer, it is preferable to use polyester resin, acrylic resin, or polyvinyl (such as polyvinyl alcohol).

[0061] It is also preferred that the cured resin layer contains particles in order to improve the blocking and slip properties of the laminated polyester film. The average particle size of the particles used in the cured resin layer is preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less, from the viewpoint of film transparency. The lower limit of the particle size of the light metal particles is preferably 0.005 μm or more, more preferably 0.01 μm or more, in order to more effectively improve slipperiness. Specific examples of particles used in the cured resin layer include silica, alumina, kaolin, calcium carbonate, organic particles, etc. Among these, silica is preferred from the viewpoint of transparency.

[0062] Furthermore, within the scope of the present invention, it is possible to use antifoaming agents, coating property improvers, thickeners, organic lubricants, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, etc. in combination as needed to form the cured resin layer.

[0063] In the present invention, the content of the resin having a styrene structure in the non-volatile components of the cured resin layer composition is preferably 10 to 80 mass %, more preferably 15 to 70 mass %, even more preferably 20 to 60 mass %, and particularly preferably 25 to 50 mass %. When the content of the resin having a styrene structure is within the above range, the cured resin layer has excellent appearance and can effectively suppress precipitation of oligomers due to heat treatment.

[0064] In the present invention, the total content of the crosslinking agent in the non-volatile components of the cured resin layer composition is preferably 5 to 95 mass %, more preferably 15 to 85 mass %, even more preferably 30 to 75 mass %, and particularly preferably 45 to 70 mass %. When the total content of the crosslinking agent is within the above range, precipitation of oligomers after heating can be effectively suppressed.

[0065] When a melamine compound is selected as one of the crosslinking agents from the viewpoint of preventing oligomer precipitation after heating, the content of the melamine compound in the non-volatile components of the cured resin layer composition is preferably 5 to 80 mass %, more preferably 10 to 75 mass %, and even more preferably 30 to 65 mass %. By keeping the content of the melamine compound within the above range, precipitation of oligomer after heating can be effectively suppressed.

[0066] When an epoxy compound is selected as one of the crosslinking agents from the viewpoint of improving adhesion to the release layer, the content of the epoxy compound in the non-volatile components of the cured resin layer composition is preferably 1 to 70 mass %, more preferably 3 to 60 mass %, and even more preferably 5 to 40 mass %. By keeping the content of the epoxy compound within the above range, precipitation of oligomers after heating can be effectively suppressed and good adhesion to the release layer can be obtained.

[0067] When an organosilicon compound is selected as one of the crosslinking agents from the viewpoint of improving adhesion to the release layer, the content of the organosilicon compound in the non-volatile components of the cured resin layer composition is preferably 1 to 70 mass %, more preferably 3 to 50 mass %, and even more preferably 5 to 40 mass %. When the content of the organosilicon compound is within the above range, precipitation of oligomers after heating can be effectively suppressed and good adhesion to the release layer can be obtained.

[0068] The thickness of the cured resin layer on the final film is preferably 0.003 μm to 1 μm, more preferably 0.005 μm to 0.6 μm, even more preferably 0.01 μm to 0.3 μm, and even more preferably 0.02 μm to 0.2 μm. By making the thickness of the cured resin layer 0.003 μm or more, it is easy to suppress precipitation of oligomers from the polyester film. Furthermore, by making the thickness 1 μm or less, it is easy to suppress deterioration of the appearance of the cured resin layer and blocking.

[0069] <Laminated polyester film structure> The laminated polyester film of the present invention may have a cured resin layer on at least one side of the polyester film, and may have a laminated structure in which a cured resin layer is formed on one or both sides of the polyester film, or in which a cured resin layer is formed on one side of the polyester film and another layer is formed on the other side, or in which another layer is further formed on the cured resin layer formed on the polyester film. Examples of the "other layers" include a release layer, an adhesive layer, an antistatic layer, an antiblocking layer, and the like.

[0070] (Release layer) The laminated polyester film of the present invention preferably has a release layer on the cured resin layer of the laminated polyester film, since it exhibits excellent adhesion stability over time to a release layer described below. The release layer is not particularly limited in terms of the constituent components thereof as long as it has good release properties, but from the viewpoint of obtaining good release properties, it is preferable that the release layer contains a curable silicone resin. Furthermore, the release layer preferably contains a type containing a curable silicone resin as the main component, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin, or a fluorosilicone resin.

[0071] The curable silicone resin may be any of the existing curing reaction types, such as heat-curable types such as addition types or condensation types, or electron beam-curable types such as ultraviolet curable types, or a combination of multiple types of curable silicone resins. Furthermore, there are no particular limitations on the form of application of the curable silicone resin when forming the release layer, and it may be in the form of a solution in an organic solvent, in the form of an aqueous emulsion, or in a solventless form.

[0072] Although there is no limitation on the type of silicone resin used in the present invention, it is preferable to use a curable silicone resin containing an alkenyl group from the viewpoint of excellent release properties such as easy peelability. Examples of the curable silicone resin containing an alkenyl group include diorganopolysiloxanes represented by the following general formula (3): R 2 (3-a) W a SiO-(R 2 WSiO) p -(R 2 2SiO) q -SiW a R 2 (3-a) …(3)

[0073] In the above general formula (3), R 2 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and W is an organic group containing an alkenyl group. a is an integer of 0 to 3, preferably 1, and p is 0 or greater, but when a=0, p is 2 or greater, and p and q are each numbers that satisfy 100≦p+q≦20000. Furthermore, the above general formula (3) does not mean a block copolymer.

[0074] R 2 Specific examples of the alkyl group include alkyl groups such as methyl, ethyl, propyl, and butyl; cycloalkyl groups such as cyclohexyl; and aryl groups such as phenyl and tolyl, with methyl and phenyl being particularly preferred. W is preferably an alkenyl-containing organic group having 2 to 10 carbon atoms, and specific examples thereof include a vinyl group, an allyl group, a hexenyl group, an octenyl group, an acryloylpropyl group, an acryloylmethyl group, a methacryloylpropyl group, a cyclohexenylethyl group, and a vinyloxypropyl group. Of these, a vinyl group, a hexenyl group, and the like are particularly preferred. Specific examples include a dimethylsiloxane-methylhexenylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups (96 mol% dimethylsiloxane units, 4 mol% methylhexenylsiloxane units), a dimethylsiloxane-methylhexenylsiloxane copolymer terminated at both molecular chain ends with dimethylvinylsiloxy groups (97 mol% dimethylsiloxane units, 3 mol% methylhexenylsiloxane units), and a dimethylsiloxane-methylhexenylsiloxane copolymer terminated at both molecular chain ends with dimethylhexenylsiloxy groups (95 mol% dimethylsiloxane units, 5 mol% methylhexenylsiloxane units).

[0075] The release layer is preferably a layer formed by curing a silicone resin composition containing the curable silicone resin and a crosslinking agent that cures the curable silicone resin. Examples of crosslinking agents used in the release layer include polyorganosiloxanes containing SiH groups. The polyorganosiloxanes containing SiH groups react with the curable silicone resins containing alkenyl groups to form stronger silicone release layers. The polyorganosiloxanes containing SiH groups are organohydrogenpolysiloxanes having at least two, preferably three or more, hydrogen atoms bonded to silicon atoms in one molecule, and may be linear, branched, or cyclic. Examples of suitable polyorganosiloxanes include, but are not limited to, compounds represented by the following general formula (4): H b R 3 (3-b)SiO-(HR 3 SiO) x -(R 3 2SiO) y -SiR 3 (3-b) H b …(4)

[0076] In the above general formula (4), R 3 is a monovalent hydrocarbon group containing no aliphatic unsaturated bonds and having 1 to 6 carbon atoms, b is an integer of 0 to 3, and x and y are each an integer.

[0077] Specific examples of compounds represented by the above general formula (4) include methylhydrogenpolysiloxanes terminally capped with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers terminally capped with trimethylsiloxy groups, methylhydrogenpolysiloxanes terminally capped with dimethylhydrogensiloxy groups, and dimethylsiloxane-methylhydrogensiloxane copolymers terminally capped with dimethylhydrogensiloxy groups. The molar ratio of Si-H groups to alkenyl groups ([Si-H groups] / [alkenyl groups]) in the silicone resin composition is preferably 0.1 to 2.0, more preferably 0.2 to 1.9, and even more preferably 0.3 to 1.8.

[0078] Specific examples of commercially available silicone resins that can be used in the present invention include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-62-2461, X-62-1387, X-62-5039, X-62-5040, KNS-3051, X-62-1496, KNS320A, KNS316, X-62-1574A / B, X-62-7052, X-62-7028A / B, X-62-7619, X-62-7213, and X-41-3035 manufactured by Shin-Etsu Chemical Co., Ltd.; and YSR-3022, TPR-6700, and TPR-6700 manufactured by Momentive Performance Materials. -6720, TPR-6721, TPR6500, TPR6501, UV9300, UV9425, XS56-A2775, XS56-A2982, UV9430, TPR6600, TPR6604, TPR6605, Dow Corning Toray Co., Ltd. products: SRX357, SRX211, SD7220, SD7292, LTC750A , LTC760A, LTC303E, LTC856, LTC761, SP7259, BY24-468C, SP7248S, BY24-452, DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, and DEHESIVE 636, 919, 920, 921, 924, 929, etc., from the DEHESIVE series manufactured by Wacker Asahi Kasei Silicones Co., Ltd.

[0079] The release layer preferably uses a platinum-based catalyst that promotes addition reactions. Therefore, the silicone resin composition preferably further contains a platinum-based catalyst. Examples of this component include platinum-based compounds such as chloroplatinic acid, an alcohol solution of chloroplatinic acid, a complex of chloroplatinic acid with an olefin, and a complex of chloroplatinic acid with an alkenylsiloxane, as well as platinum black, platinum-supported silica, and platinum-supported activated carbon. The content of the platinum-based catalyst in the release layer is preferably 0.01 to 10.0% by mass, more preferably 0.01 to 5.0% by mass. When the content of the platinum-based catalyst in the release layer is 0.01% by mass or more, sufficient release force is obtained, the curing reaction proceeds sufficiently, and problems such as deterioration of surface condition do not occur. On the other hand, if the content of the platinum-based catalyst in the release layer is 3.0 mass % or less, it is advantageous in terms of cost, and in addition, the reactivity is increased, and process defects such as the generation of gel foreign matter do not occur.

[0080] In addition, because addition reactions are very reactive, acetylene alcohol may be added as a reaction inhibitor in some cases. The component is an organic compound having a carbon-carbon triple bond and a hydroxyl group, and is preferably a compound selected from the group consisting of 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, and phenylbutynol.

[0081] A catalyst can be used in the release layer of the laminated polyester film to promote hydrolysis and condensation reactions. Specific examples of catalysts include organic acids such as acetic acid, butyric acid, maleic acid, and citric acid; inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid; basic compounds such as triethylamine; organometallic salts such as tetrabutyl titanate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, dibutyltin diolate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis(triethoxysiloxy)tin, and dibutyltin benzyl maleate; and fluorine-containing compounds such as KF and NHF. The above catalysts can be used alone or in combination of two or more. Among these, organometallic salts are preferred because they provide excellent coating durability.

[0082] Various release control agents may be used in combination to adjust the release properties of the release layer. To increase the release strength, the content of organopolysiloxane resins, silica particles, or silicone species with high release strength is generally adjusted appropriately in the release layer to achieve the desired release strength. Specific examples of commercially available high release agents include KS-3800 and X-92-183 manufactured by Shin-Etsu Chemical Co., Ltd., and SDY7292, BY24-843, and BY24-4980 manufactured by Dow Corning Toray Co., Ltd. To decrease the release strength, various low-molecular-weight siloxanes are selected and their content is adjusted appropriately in the release layer so that the siloxane migrating components exhibit release properties. Examples of low-molecular-weight siloxane compounds include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane. Other compounds of the former low molecular weight cyclic siloxane include dimethylsiloxane oligomers terminated at both molecular chain ends with trimethylsiloxy groups and dimethylsiloxane oligomers terminated at both molecular chain ends with dimethylhydroxysiloxy groups, and the above compounds may be used in combination as needed. These low molecular weight siloxane compounds are incorporated into the silicone resin as migratory components in amounts of typically 0.1 to 15.0% by mass, preferably 0.1 to 10.0% by mass, and more preferably 0.1 to 5% by mass, to achieve the desired light release properties. A content of 0.1% by mass or more provides sufficient migratory components and exhibits sufficient releasability. On the other hand, a low molecular weight siloxane content of 15.0% by mass or less prevents excessive precipitation of migratory components, eliminating the problem of process contamination.

[0083] In addition, it is preferable to use an organosilicon compound represented by the above general formula (2) in the release layer in order to improve adhesion to the polyester film.

[0084] When an organosilicon compound is used in combination with the release layer, the content of the organosilicon compound is preferably 0.5 to 5.0 mass %, more preferably 0.5 to 2.0 mass %, relative to 100 mass % of the curable silicone resin. If the content of the organosilicon compound is 0.5 mass % or more, the desired adhesion can be easily ensured, while if it is 5.0 mass % or less, the adhesion to the opposing resin layer to be laminated is not too strong, and peeling can be easily performed when peeling is actually required.

[0085] The release layer composition that forms the release layer may contain, as necessary, an antifoaming agent, a coating property improver, a thickener, inorganic or organic particles, an organic lubricant, an antistatic agent, a conductive agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, a pigment, etc.

[0086] The release layer is formed by coating the release layer composition onto the film, and may be formed by inline coating performed during the film production process, or by so-called offline coating, in which the release layer composition is applied outside the system onto a film that has already been produced.

[0087] The release layer can be provided on the cured resin layer by any conventional coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, or curtain coating.

[0088] The curing conditions for forming a release layer on the cured resin layer of the laminated polyester film are not particularly limited. When the release layer is formed by offline coating, heat treatment is typically performed at 80°C or higher for 10 seconds or more, preferably at 100 to 200°C for 3 to 40 seconds, and more preferably at 120 to 180°C for 3 to 40 seconds. If necessary, heat treatment may be combined with irradiation with active energy rays such as ultraviolet light. Known devices and energy sources can be used as the energy source for curing by irradiation with active energy rays.

[0089] The thickness of the release layer is usually 0.005 μm or more and 3.0 μm or less, preferably 0.01 μm or more and 1.0 μm or less, more preferably 0.03 μm or more and 0.5 μm or less, and even more preferably 0.05 μm or more and 0.3 μm or less. When the thickness is 0.005 μm or more, excellent coating properties are obtained, and a uniform coating film can be stably obtained. On the other hand, when the thickness is 3.0 μm or less, the coating film adhesion and curing properties of the release layer itself are not reduced.

[0090] The peel strength of the release layer is not particularly limited, but is preferably 1 to 500 mN / cm, more preferably 2 to 300 mN / cm, even more preferably 3 to 200 mN / cm, and still more preferably 5 to 150 mN / cm. If it is 500 mN / cm or less, the layer can be smoothly peeled from the adherend.

[0091] The components of the cured resin layer and the release layer can be analyzed by surface analysis such as TOF-SIMS, ESCA, or fluorescent X-ray.

[0092] (Adhesive layer) The laminated polyester film of the present invention preferably further has an adhesive layer on the release layer for protecting the surface of the adherend. The adhesive layer can be formed by applying an adhesive composition onto a release film and curing it.

[0093] [Adhesive composition] The pressure-sensitive adhesive composition may be an acrylic pressure-sensitive adhesive composition containing an acrylic resin as the main component resin, a rubber-based pressure-sensitive adhesive composition containing rubber as the main component resin, a urethane-based pressure-sensitive adhesive composition containing a urethane resin as the main component resin, or a silicone-based pressure-sensitive adhesive composition containing a silicone resin as the main component resin. Among these, acrylic pressure-sensitive adhesive compositions containing an acrylic resin as the main component are preferred, as they allow the adhesive strength and peel strength to be adjusted in a well-balanced manner and are inexpensive.

[0094] The "main component resin" refers to the resin that accounts for the largest proportion of the resins that make up the pressure-sensitive adhesive composition. For example, it refers to a component that accounts for 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more of the total amount of resins that make up the pressure-sensitive adhesive composition. The upper limit is usually 99.99% by mass.

[0095] In addition to the above-mentioned main component resin, the pressure-sensitive adhesive composition may contain, as necessary, a crosslinking agent described below, as well as conventionally known additives such as a silane coupling agent, an antistatic agent, other acrylic pressure-sensitive adhesives, other pressure-sensitive adhesives, tackifiers such as urethane resins, rosin, rosin esters, hydrogenated rosin esters, phenolic resins, aromatic-modified terpene resins, aliphatic petroleum resins, alicyclic petroleum resins, styrene-based resins, and xylene-based resins, colorants, fillers, antioxidants, ultraviolet absorbers, and functional dyes, as well as additives such as compounds that change color or undergo color change when exposed to ultraviolet light or radiation. The amount of these additives blended is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less of the total pressure-sensitive adhesive composition. Furthermore, it is preferable to minimize the inclusion of low-molecular-weight components having a molecular weight of less than 10,000 as additives, in terms of excellent durability.

[0096] <Acrylic resin> Examples of the acrylic resin that is the main component resin of the pressure-sensitive adhesive composition include (meth)acrylic polymers. The (meth)acrylic polymer is a polymer whose main structural unit is a (meth)acrylic acid alkyl ester. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl and n-hexyl (meth)acrylate, isobornyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, methyl (meth)acrylate is preferred in terms of the compatibility of the (meth)acrylic polymer with the (meth)acrylate and the heat resistance of the cured resin layer. The (meth)acrylic polymer may have a radically polymerizable double bond.

[0097] The (meth)acrylic polymer can be copolymerized with (meth)acrylic acid esters other than (meth)acrylic acid alkyl esters, (meth)acrylic acid, or other compounds having a vinyl group, for the purpose of improving the glass transition temperature, mechanical properties, compatibility, etc. Examples of the (meth)acrylic acid esters other than (meth)acrylic acid alkyl esters include hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, alkoxyalkyl (meth)acrylates such as methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, and ethoxyethyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, and γ-butyrolactone (meth)acrylate. Examples of the compound having a vinyl group include acrylamide compounds such as dimethylacrylamide, hydroxyethylacrylamide, and dimethylaminopropylacrylamide; styrene compounds such as styrene, α-methylstyrene, and p-methoxystyrene; and maleic anhydride.

[0098] The glass transition temperature (Tg) can be calculated from the type and mass fraction of the monomers forming the (meth)acrylic polymer using the following Fox formula. 1 / Tg=Σ(W i / Tg i ) In the above Fox equation, Tg is the glass transition temperature of the (meth)acrylic polymer (unit: K), W i is the mass fraction of the structural unit derived from monomer i constituting the (meth)acrylic polymer, Tg i denotes the glass transition temperature (unit: K) of the homopolymer of monomer i. i The value of can be the value described in POLYMERHANDBOOK Volume 1 (WILEY-INTERSCIENCE).

[0099] In the present invention, the (meth)acrylic polymer preferably contains a structural unit derived from an acrylic monomer (a1), since this serves as a reaction site with the crosslinking agent described below.

[0100] The acrylic monomer (a1) becomes a reactive site for a crosslinked structure when copolymerized with other copolymerization components to form a (meth)acrylic polymer. It may be any monomer containing a functional group capable of reacting with a functional group contained in a crosslinking agent, which will be described later. Examples of such acrylic monomer (a1) include hydroxyl-containing monomers, amino-containing monomers, acetoacetyl-containing monomers, isocyanate-containing monomers, and glycidyl-containing monomers. Among these, hydroxyl-containing monomers are preferred because they can efficiently undergo crosslinking reactions with crosslinking agents. The acrylic monomer (a1) may be a single type or two or more types.

[0101] Examples of hydroxyl group-containing monomers include hydroxyalkyl acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl 2-hydroxyethyl phthalate and N-methylol (meth)acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro 2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate.

[0102] Among the above hydroxyl group-containing monomers, primary hydroxyl group-containing monomers are preferred because of their excellent reactivity with crosslinking agents, and 2-hydroxyethyl acrylate is more preferred because it contains fewer impurities such as di(meth)acrylates and is easy to form an adhesive layer.

[0103] In the present invention, the hydroxyl group-containing monomer forming the adhesive layer preferably contains 0.5% or less of di(meth)acrylate as an impurity, more preferably 0.2% or less, and even more preferably 0.1% or less. Specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, which are preferred because they have low molecular weights and are therefore easy to purify.

[0104] Examples of amino group-containing monomers include t-butylaminoethyl (meth)acrylate, ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.

[0105] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0106] Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

[0107] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0108] The content of the structural unit derived from the acrylic monomer (a1) in the (meth)acrylic polymer is preferably 0.01 to 20% by mass, more preferably 0.1 to 10% by mass, and even more preferably 0.2 to 3% by mass. When the content of the structural unit derived from the acrylic monomer (a1) is 0.01% by mass or more, sufficient crosslinking points can be formed in the adhesive layer, and the cohesive strength after crosslinking can be easily improved. Furthermore, when the content is 20% by mass or less, a decrease in adhesive strength can be easily suppressed.

[0109] In the present invention, the (meth)acrylic polymer preferably contains, as necessary, a structural unit derived from a copolymerizable monomer (a2) as a structural unit other than the structural unit derived from the acrylic monomer (a1). Examples of the copolymerizable monomer (a2) include (meth)acrylic acid alkyl ester monomers such as methyl methacrylate, ethyl (meth)acrylate, n-butyl methacrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, ethoxylated o-phenylphenyl (meth)acrylate, and phenoxyethyl (meth)acrylate. Examples of suitable monomers include aromatic ring-containing monomers such as diethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and styrene; amide monomers such as (meth)acryloylmorpholine, dimethyl (meth)acrylamide, diethyl (meth)acrylamide, and (meth)acrylamide; acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconate esters, dialkyl fumarate esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyl trimethylammonium chloride, and dimethyl allyl vinyl ketone.

[0110] The content of the structural unit derived from the copolymerizable monomer (a2) in the (meth)acrylic polymer is preferably 0.01 to 20 mass%, more preferably 1 to 15 mass%, and even more preferably 2 to 10 mass%. When the content of the structural unit derived from the copolymerizable monomer (a2) is within the above range, it is easy to prevent the adhesive properties of the adhesive layer from decreasing.

[0111] <Crosslinking agent> In the present invention, the pressure-sensitive adhesive composition may contain a crosslinking agent depending on the method for forming the pressure-sensitive adhesive layer. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, an amine-based crosslinking agent, etc. Among these, it is preferable to use an isocyanate-based crosslinking agent from the viewpoint of improving adhesion to the substrate and reactivity with the acrylic resin. The crosslinking agents may be used alone or in combination of two or more.

[0112] The content of the crosslinking agent in the pressure-sensitive adhesive composition is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the main component resin. By ensuring that the content of the crosslinking agent is within the above range, the cohesive strength is not insufficient, the desired durability can be obtained, and further, a decrease in flexibility and adhesive strength can be prevented.

[0113] Regarding the curing reaction, when photocuring by irradiation with active energy rays is used, it is preferable to blend a polyfunctional (meth)acrylate as a crosslinking agent into the pressure-sensitive adhesive composition. Examples of such polyfunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and glycerin polyglycidyl ether poly(meth)acrylate.

[0114] <Adhesive layer thickness> The thickness of the adhesive layer is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more, from the viewpoints of imparting sufficient adhesive strength and filling in unevenness or steps in the substrate to which the adhesive is attached. On the other hand, from the viewpoints of material use efficiency, permeability, and outgassing, the thickness is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 100 μm or less.

[0115] <Physical properties of laminated polyester film> (Amount of oligomer precipitate I) The amount of oligomer precipitated from the surface of the cured resin layer of the laminated polyester film of the present invention is determined by the amount of oligomer extracted from the surface of the cured resin layer with dimethylformamide after heat treatment of the laminated polyester film (150°C, 90 minutes), and is preferably 1.0 mg / m 2 or less, more preferably 0.7 mg / m 2 or less, more preferably 0.5 mg / m 2 The amount of oligomer precipitation in the laminated polyester film is 1.0 mg / m or less. 2 If the temperature is below this level, even if a long-term heat treatment is performed in a high-temperature atmosphere in a subsequent process, for example, at 150°C for 90 minutes, the amount of oligomer precipitation is small, the transparency of the film can be maintained, and there is no concern about contamination of the process. (Oligomer precipitation amount II) In the present invention, the amount of oligomer precipitated from the surface of the release layer in the laminated polyester film having a release layer on the cured resin layer is determined by the amount of oligomer extracted from the surface of the release layer with dimethylformamide after heat treatment (150°C, 90 minutes) of the laminated polyester film having a release layer on the cured resin layer, and is preferably 1.0 mg / m 2 or less, more preferably mg / m 2 or less, more preferably 0.5 mg / m 2 The amount of oligomer precipitation in the laminated polyester film having a release layer is 1.0 mg / m or less. 2If the temperature is below this level, even if a long-term heat treatment is performed in a high-temperature atmosphere in a subsequent process, for example, at 150°C for 90 minutes, the amount of oligomer precipitation is small, the transparency of the film can be maintained, and there is no concern about contamination of the process.

[0116] (Film haze change I) Regarding the film haze change of the laminated polyester film of the present invention, the film haze change (ΔH) before and after heat treatment of the laminated polyester film under conditions of 150°C for 90 minutes is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.0 to 0.3% or less. It is known that the film haze of polyester films usually increases due to the precipitation of oligomers on the film surface during heat treatment, and ΔH is an index showing the precipitation of oligomers on the surface of the laminated polyester film before and after heat treatment. When the film haze change (ΔH) of the laminated polyester film is 1.0% or less, it can be said that contamination due to oligomer precipitation is suppressed. On the other hand, when the film haze change ΔH exceeds 1.0%, the film haze increases due to oligomer precipitation, which may result in reduced visibility and increased contamination. (Film haze change II) In the present invention, with regard to the film haze of a laminated polyester film having a release layer on a cured resin layer, the change in film haze (ΔH) before and after heat treatment of a laminated polyester film having a release layer on a cured resin layer at 150°C for 90 minutes is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.0 to 0.3% or less. When the film haze change (ΔH) of a laminated polyester film having a release layer on a cured resin layer is 1.0% or less, it can be said that contamination due to oligomer precipitation is suppressed. On the other hand, when the film haze change (ΔH)ΔH exceeds 1.0%, the visibility may decrease and contamination may increase due to the increase in film haze caused by oligomer precipitation.

[0117] [Film laminate] The film laminate of the present invention has a configuration in which the adhesive layer side of the above-mentioned laminated polyester film having a cured resin layer on at least one side of a polyester film and a release layer and adhesive layer on the cured resin layer is bonded to an adherend.

[0118] (adherent) In the film laminate of the present invention, the adherend is any one of a transparent conductive layer, a polarizing element, and a resin film. In the present invention, since the adherend is any one of the above, the film laminate of the present invention can be suitably used for the production of various display components such as optical components used in liquid crystal displays and organic electroluminescence components, as well as for protecting various pressure-sensitive adhesive layers.

[0119] [Transparent conductive layer] The material of the transparent conductive layer is not particularly limited. Any material capable of forming a transparent conductive film can be used. Examples of such materials include thin films of indium oxide containing tin oxide (ITO), antimony-containing tin oxide (ATO), zinc oxide, zinc-aluminum composite oxide, indium-zinc composite oxide, and composite oxide containing indium oxide, zinc oxide, and gallium oxide (IGZO). These compounds can be made to be both transparent and conductive by selecting appropriate production conditions.

[0120] The thickness of the transparent conductive layer is preferably less than 100 nm, more preferably 15 nm or more or 50 nm or less, and most preferably 20 nm or more or less than 40 μm.

[0121] Known methods for forming a transparent conductive layer include vacuum deposition, sputtering, CVD, ion plating, and spraying. An appropriate method can be selected and used depending on the type of material and the required film thickness. For example, in the case of sputtering, normal sputtering using a compound target or reactive sputtering using a metal target can be used. In this case, reactive gases such as oxygen, nitrogen, and water vapor can be introduced, and ozone addition, ion assist, and other methods can also be used in combination.

[0122] As a condition for forming the transparent conductive layer, the temperature during formation is preferably room temperature to 100° C. This allows sufficient promotion of crystallization of the transparent conductive layer, and a transparent conductive film with low surface resistance can be obtained, which is suitable for use in displays such as organic EL displays.

[0123] [Polarizing element] The polarizing element is preferably made of, for example, a liquid crystal polarizing film. When the polarizing element is composed of a liquid crystal polarizing film, it is formed by applying an optically anisotropic composition containing a polymerizable liquid crystal compound. This liquid crystal polarizing film usually has an optically anisotropic layer obtained by applying an optically anisotropic composition containing a polymerizable liquid crystal compound and the like onto an alignment film formed on a substrate, and polymerizing the polymerizable liquid crystal compound in an aligned state. That is, the liquid crystal polarizing film may have an optically anisotropic layer made of an optically anisotropic composition and an alignment film. Alternatively, it may have only an optically anisotropic layer without an alignment film.

[0124] The polymerizable liquid crystal compound can be aligned by a method using an alignment regulating force by an alignment film provided on a substrate, an alignment regulating force by an external field such as an electric field or a magnetic field, and / or a shear force during coating. In particular, the method using an alignment film is preferred from the viewpoint of achieving a liquid crystal polarizing film that can align the liquid crystal compound in a highly ordered state and exhibit good optical performance. The alignment film provided on the substrate is a layer having an alignment regulating force for aligning the liquid crystal compound described later in a desired direction. The alignment film preferably has solvent resistance so that the optically anisotropic composition solution is not dissolved when applied, moderate solution affinity so that the optically anisotropic composition solution is not repelled, and heat resistance in the heating treatment during solvent drying and liquid crystal alignment. In order to control the orientation direction, the alignment film may be subjected to an alignment treatment by a known method (such as a rubbing method, a method of forming grooves (fine groove structures) on the surface of the alignment film (photoalignment method) using polarized ultraviolet light or a polarized laser, an alignment method by forming an LB film, or an alignment method by oblique deposition of an inorganic material) as described, for example, on pages 226 to 239 of "Liquid Crystal Handbook" (Maruzen Co., Ltd., published October 30, 2000). In particular, the rubbing method and the photoalignment method are preferred from the viewpoint of easily achieving a high degree of orientation. The thickness of the alignment film is usually 10 nm to 1000 nm, preferably 50 nm to 800 nm. When the thickness is within this range, it is possible to achieve both an alignment control force sufficient to align the liquid crystal compound and a thin film.

[0125] The optically anisotropic composition may be a composition containing, in addition to a polymerizable liquid crystal compound and a photopolymerization initiator, a polymerization initiator, and, if necessary, various additives such as a polymerization inhibitor, a polymerization aid, a polymerizable non-liquid crystal compound, a non-liquid crystal compound, a surfactant, a leveling agent, a coupling agent, a pH adjuster, a dispersant, an antioxidant, an organic or inorganic filler, or a metal oxide, or a solvent, and exhibits the optical function as a polarizing element. When the polarizing element is a liquid crystal polarizing film, the composition preferably contains a dye. The dye is preferably a dichroic dye, and examples of the dichroic dye include iodine and dichroic organic dyes. The dichroic dye used may be one type, or a combination of multiple different dyes. The dichroic organic dye is not particularly limited, but examples thereof include azo dyes, quinone dyes (including naphthoquinone dyes, anthraquinone dyes, etc.), stilbene dyes, cyanine dyes, phthalocyanine dyes, indigo dyes, condensed polycyclic dyes (including perylene dyes, oxazine dyes, acridine dyes, etc.), etc. Among these dyes, azo dyes are preferred because they have a large molecular long-to-short axis ratio and can exhibit good dichroism.

[0126] ≪Polymerizable liquid crystal compound≫ A polymerizable liquid crystal compound is a liquid crystal compound having a polymerizable functional group, and has both the properties of a polymerizable monomer and the properties of a liquid crystal. Therefore, when this compound is polymerized and cured in an oriented state, a cured product consisting of a polymer with fixed orientation, i.e., an optically anisotropic material, can be obtained. Therefore, a polarizing film having optical anisotropy can be formed by applying an optically anisotropic composition containing a polymerizable liquid crystal compound to a substrate and curing the composition in an aligned state. The polymerizable liquid crystal compound used may be one type, or a combination of multiple compounds with different structures. The polymerizable liquid crystal compound may be either a low molecular weight liquid crystal compound having a polymerizable functional group or a high molecular weight liquid crystal compound having a polymerizable functional group. Among them, a low molecular weight liquid crystal compound is preferred because a polymerizable liquid crystal compound tends to easily give a cured product exhibiting high alignment. The liquid crystal phase exhibited by the polymerizable liquid crystal compound can be appropriately selected from nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, discotic liquid crystal, etc., but from the viewpoint of ease of production and obtaining a highly ordered orientation state, it is preferable that the polymerizable liquid crystal compound exhibits nematic liquid crystal or smectic liquid crystal. The polymerizable functional group is preferably a photopolymerizable group because it is easy to fix the orientation structure.Specific examples include an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, an acryloylamino group, a methacryloylamino group, a vinyl group, a vinyloxy group, an ethynyl group, an ethynyloxy group, a 1,3-butadienyl group, a 1,3-butadienyloxy group, an oxiranyl group, an oxetanyl group, a glycidyl group, a glycidyloxy group, a styryl group, and a styryloxy group.Among these, a (meth)acryloyl group or a (meth)acryloyloxy group is preferred.

[0127] Polarizing elements are used by being incorporated into image display devices such as liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical system (MEMS) displays.

[0128] [Resin film] The resin film is preferably a resin film selected from, for example, a polyester film, a polyimide film, or a cyclic polyolefin film. When the resin film is any of the above, it can be suitably used as an optical member for a liquid crystal display.

[0129] From the viewpoint of handling, the thickness of the film laminate of the present invention is preferably 80 to 250 μm, more preferably 80 to 200 μm, still more preferably 80 to 175 μm, and of these, particularly 80 to 150 μm.

[0130] <Application> Since the laminated polyester film of the present invention has the above-mentioned configuration, it is suitable for applications in which it is exposed to a high-temperature atmosphere for a long period of time, and is suitably used for, for example, various applications in which materials are bonded via an adhesive layer, such as for producing capacitive touch panels, for producing optical components used in liquid crystal displays (polarizing elements, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) and organic electroluminescence components, and for producing various display components, as well as for protecting various adhesive layers. Furthermore, since the film laminate of the present invention has the above-described configuration, it is suitably used for applications in the manufacture of various display components, such as optical components (polarizing elements, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) used in liquid crystal displays and components for organic electroluminescence. [Example]

[0131] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. The evaluation methods used in the examples and comparative examples are as follows.

[0132] (1) Measurement method for intrinsic viscosity of polyester 1 g of polyester from which other polymer components incompatible with the polyester and pigments had been removed was precisely weighed, dissolved in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent, and measured at 30°C.

[0133] (2) Measurement method for average particle size (d50 (μm)) The cumulative 50% (mass basis) value in the equivalent sphericity distribution measured using a centrifugal sedimentation particle size distribution analyzer (SA-CP3 model, manufactured by Shimadzu Corporation) was taken as the average particle size.

[0134] (3) Method for measuring the thickness of the cured resin layer and the release layer The surfaces of the cured resin layer and the release layer were stained with RuO4 and embedded in epoxy resin. Then, sections prepared by ultrathin sectioning were stained with RuO4, and the cross sections of the cured resin layer and the release layer were measured using a TEM (Hitachi High-Tech H-7650, accelerating voltage 100 kV).

[0135] (4) Heat treatment method for laminated polyester film The laminated polyester film was placed on top of Kent paper with the exposed surface, and then heat-treated by leaving it at 150°C for 90 minutes in a nitrogen atmosphere.

[0136] (5) Measurement of film haze increase (ΔH) due to heat treatment In the laminated polyester films of the Examples and Comparative Examples and the laminated polyester film having a release layer, the following hard coat layer coating agent was applied to the surface opposite to the surface on which the cured resin layer or the release layer was provided, so that the thickness after curing would be 5 μm, and the coating agent was dried for 1 minute in a hot air drying oven set at 80° C. Next, the coating agent was irradiated with ultraviolet light to cure the hard coat layer, and a measurement sample was obtained. The film haze of the obtained measurement sample was measured in accordance with JIS-K-7136 using the cured resin layer or release layer side as the measurement surface, using a haze meter "HM-150" manufactured by Murakami Color Research Institute Co., Ltd. (Haze 1 (film haze before heat treatment)). Next, the measurement sample was heat treated by the method (4) above, and then the film haze was measured in the same manner as above (Haze 2 (film haze after heat treatment)). The change in film haze (ΔH) was calculated using the following formula from the obtained haze 1 and haze 2. The lower the change in film haze (ΔH), the less oligomer precipitation due to high-temperature treatment, which is favorable. [Film haze change (ΔH)] = [Haze 2] - [Haze 1]

[0137] <Coating agent for hard coat layer> Dipentaerythritol hexaacrylate: 80 parts by mass 2-Hydroxy-3-phenoxypropyl acrylate: 20 parts by mass Photopolymerization initiator (product name: Irgacure 184, manufactured by BASF Japan Ltd.): 5 parts by mass Methyl ethyl ketone: 200 parts by weight

[0138] (6) Measurement of oligomer deposition amount on the surface of laminated polyester film The laminated polyester films and laminated polyester films with release layers of the examples and comparative examples were heated in air at 150°C for 90 minutes. The heat-treated films were then cut into an open-topped box-like shape, 10 cm long and wide, and 3 cm high, with the measurement surface (cured resin layer or release layer) facing inward. Next, 4 mL of DMF (dimethyl sulfamide) was placed in the box-shaped film and allowed to stand for 3 minutes, after which the DMF was recovered. The recovered DMF was fed to a liquid chromatograph (Shimadzu Corporation: LC-7A, mobile phase A: acetonitrile, mobile phase B: 2% aqueous acetic acid solution, column: Mitsubishi Chemical Corporation "MCI GEL ODS 1HU", column temperature: 40°C, flow rate: 1 mL / min, detection wavelength: 254 nm) to determine the amount of oligomer in the DMF. The determined amount of oligomer was divided by the area of ​​the film surface contacted with DMF to determine the amount of oligomer precipitated on the film surface (mg / m). 2 ) was decided. The oligomer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing a previously collected oligomer and dissolving it in an accurately weighed amount of DMF.

[0139] (7) Peeling force One side of a double-sided adhesive tape (Nitto Denko Corporation's "No. 502") was attached to the release layer surface of the laminated polyester film having a release layer in each of the Examples and Comparative Examples, and the film was cut to a size of 50 mm x 300 mm. After leaving the film at room temperature for 1 hour, the peel strength was measured. The peel strength was measured using a tensile tester (Intesco Corporation's "Intesco Model 2001"), with 180° peeling at a tensile speed of 300 mm / min.

[0140] (8) Adhesion of the release layer over time (evaluation of practical properties) The release surface of the laminated polyester film having a release layer was rubbed three times in one direction with the pad of an index finger, and the degree of peeling of the release layer was visually judged according to the following criteria. <Evaluation conditions> Condition I: Immediately after creating the release film Condition II: After leaving the mold film in a constant temperature and humidity chamber under an atmosphere of 23°C x 50% RH for 30 days Condition III: After leaving the mold film in a constant temperature and humidity chamber under an atmosphere of 23°C x 50% RH for 60 days <Judgment criteria> A: No peeling of the release layer was observed. B: The rubbed area turned slightly white and the release layer was slightly removed, but it was still usable. no problem. C: The rubbed area turned white and the release layer easily fell off, which is problematic for practical use.

[0141] (9) Molecular weight measurement of curable silicone resin The chromatogram was measured using a GPC measurement system, and the number-average molecular weight (Mn) and weight-average molecular weight (Mw) were determined based on a calibration curve using standard polystyrene. These are shown in Table 2. Specifically, 4 mg of the sample to be measured was dissolved in 4 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution was injected into the GPC measurement system for measurement. Tetrahydrofuran (THF) was used as the eluent. The analysis was performed using an Ecosec 8320 (manufactured by Tosoh Corporation), a TSKgel guard column HXL-L (manufactured by Tosoh Corporation), and four TSKgel GMHXL columns (manufactured by Tosoh Corporation) connected together. The oven temperature was 40°C, and the THF flow rate was 1.0 mL / min. RI was used for detection.

[0142] (10) Composition analysis of curable silicone resin The composition of the curable silicone resin was analyzed using a 400 MHz NMR (Bruker Avance400M). 1The H-NMR measurement was carried out at a temperature of 30°C using CDCl3 as a solvent and the peak derived from the methyl group of dimethylsiloxane as the chemical shift reference.

[0143] Examples of compounds that may form the cured resin layer are as follows: (Resin with styrene structure) (A) Aqueous dispersion of a styrene-acrylic copolymer polymerized in the following composition: Styrene / acrylic acid = 85 / 15 (mass%), non-volatile components: 30 mass% (Crosslinking agent) (B) Hexamethoxymethylolmelamine (C) Polyglycerol polyglycidyl ether (D) γ-Glycidoxypropyltrimethoxysilane (E) Epocross, an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd.) (Oxazoline group amount 4.5mmol / g) (particle) (F) Silica particles with an average particle size of 0.07 μm

[0144] <Preparation of Release Layer Composition> The release layer composition was prepared as follows. Curable silicone resin: KS-847H (Shin-Etsu Chemical Co., Ltd.): 100 parts by weight Platinum-containing catalyst: cat PL-50T (Shin-Etsu Chemical Co., Ltd.): 1 part by mass The above compound was diluted with a mixed solvent of MEK / toluene / n-heptane=1 / 4 / 5 (mass ratio) to prepare a coating solution with a solid content concentration of 2 mass %.

[0145] The polyesters used in the examples and comparative examples were prepared as follows. <Method for producing polyester (a)> Esterification reaction was carried out under a nitrogen atmosphere at 260°C using 100 parts by mass of dimethyl terephthalate, 60 parts by mass of ethylene glycol, 30 ppm of ethyl acid phosphate based on the polyester, and 100 ppm of magnesium acetate tetrahydrate as a catalyst based on the polyester. Subsequently, 50 ppm of tetrabutyl titanate based on the polyester was added, and the mixture was heated to 280°C over 2 hours and 30 minutes, while the absolute pressure was reduced to 0.3 kPa. Melt polycondensation was carried out for a further 80 minutes to obtain polyester (a) with an intrinsic viscosity of 0.63 dl / g.

[0146] <Method for producing polyester (b)> Esterification reaction was carried out at 225°C under a nitrogen atmosphere using 100 parts by mass of dimethyl terephthalate, 60 parts by mass of ethylene glycol, and 900 ppm of magnesium acetate tetrahydrate as a catalyst relative to the polyester. Subsequently, 3500 ppm of orthophosphoric acid and 70 ppm of germanium dioxide relative to the polyester were added, and the mixture was heated to 280°C over 2 hours and 30 minutes while the absolute pressure was reduced to 0.4 kPa. Melt polycondensation was carried out for a further 85 minutes to obtain polyester (b) with an intrinsic viscosity of 0.64 dl / g.

[0147] <Method for producing polyester (c)> Polyester (c) was obtained in the same manner as in the production method of polyester (a), except that 0.3 parts by mass of silica particles having an average particle size of 2 μm was added before melt polymerization.

[0148] Example 1: The outermost layer (surface layer) was made of a mixed raw material obtained by mixing polyesters (a), (b), and (c) in proportions of 91%, 3%, and 6% by mass, respectively, and the middle layer was made of a mixed raw material obtained by mixing polyesters (a) and (b) in proportions of 97% and 3% by mass, respectively. These materials were fed into two extruders, melted at 285°C, and then co-extruded onto a cooling roll set at 40°C in a layer structure of two types and three layers (surface layer / middle layer / surface layer = discharge rate 1 / 18 / 1), cooled, and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85°C using the difference in roll peripheral speed, and then cured resin layer composition 1 shown in Table 1 was applied to one side of this longitudinally stretched film, which was then introduced into a tenter and stretched 4.3 times in the transverse direction at 110°C. After heat treatment at 235°C, the film was relaxed by 2% in the transverse direction to obtain a 38 μm thick laminated polyester film (biaxially stretched polyester film) having a cured resin layer with a film thickness (after drying) of 0.05 μm.

[0149] As shown in Table 2, the amount of oligomer precipitation on the surface of the cured resin layer of the obtained laminated polyester film of Example 1 due to the heat treatment was small, and the amount of change in film haze was also small and good.

[0150] Next, the above-mentioned release layer composition was applied onto the cured resin layer of the obtained laminated polyester film using a bar coating method with a No. 4 bar, dried at a temperature of 150°C for 30 seconds, heat-treated, and cured to obtain a laminated polyester film having a release layer in which a cured resin layer and a release layer were laminated in order.

[0151] As shown in Table 2, the amount of oligomer precipitation on the surface of the release layer of the laminated polyester film having the release layer of Example 1 obtained by heat treatment was small, the film haze change was small and good, and the results of the coating adhesion and peel force of the release layer over time were also good.

[0152] Examples 2 to 10: A laminated polyester film was obtained in the same manner as in Example 1, except that the composition of the cured resin layer composition was changed to the composition shown in Table 1. Furthermore, a laminated polyester film having a release layer was obtained in the same manner as in Example 1. The obtained laminated polyester film and the laminated polyester film having a release layer were evaluated for the amount of change in film haze, coating adhesion over time, and releasability. The evaluation results are shown in Table 2. In all of the laminated polyester films of Examples 2 to 10, the amount of oligomer precipitation was small, the amount of film haze change was small, and the results of the coating adhesion over time and peel strength of the release layer were also good.

[0153] Comparative Example 1: A laminated polyester film was obtained by the same production method as in Example 1, except that the cured resin layer was not provided. Subsequently, the release layer composition described above was applied to the laminated polyester film and cured to obtain a laminated polyester film having a release layer.

[0154] When the laminated polyester film having the release layer of Comparative Example 1 was evaluated, it was found that a large amount of oligomers precipitated due to the heat treatment, the film haze also increased significantly, and there was concern about contamination of the process, as shown in Table 2. In addition, the coating adhesion of the release layer over time was also poor.

[0155] Comparative Example 2: A laminated polyester film was obtained in the same manner as in Example 1, except that the composition of the cured resin layer composition was changed to the composition shown in Table 1. Furthermore, a laminated polyester film having a release layer was obtained in the same manner as in Example 1. As shown in Table 2, the laminated polyester film of Comparative Example 2 and the polyester film having a release layer had a small amount of oligomer precipitation and a small change in film haze, which was good, but the coating adhesion of the release layer over time was poor.

[0156] Comparative Example 3: A laminated polyester film was obtained in the same manner as in Example 1, except that the composition of the cured resin layer composition was changed to the composition shown in Table 1. Furthermore, a laminated polyester film having a release layer was obtained in the same manner as in Example 1. As shown in Table 2, the laminated polyester film of Comparative Example 3 and the polyester film having a release layer showed a large amount of oligomer precipitation due to heat treatment, and the film haze also increased significantly, raising concerns about process contamination.

[0157] Comparative Example 4: A laminated polyester film was obtained in the same manner as in Example 1, except that the composition of the cured resin layer composition was changed to the composition shown in Table 1. Furthermore, a laminated polyester film having a release layer was obtained in the same manner as in Example 1. As shown in Table 2, the laminated polyester film and the polyester film having a release layer in Comparative Example 4 showed a large amount of oligomer precipitation from the surface of the release layer due to heat treatment, and the film haze also increased significantly, raising concerns about process contamination. In addition, the coating adhesion of the release layer over time was poor.

[0158] [Table 1]

[0159] [Table 2] [Industrial Applicability]

[0160] The laminated polyester film of the present invention has the property of causing little precipitation of oligomers, and is therefore suitable for applications in which it is exposed to high-temperature atmospheres for long periods of time. For example, it is suitable for various applications in which films are bonded via an adhesive layer, such as for producing capacitive touch panels, for producing optical components used in liquid crystal displays (polarizing elements, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) and organic electroluminescence components, and for producing various display components, as well as for protecting various adhesive layers.

Claims

1. A cured resin layer is provided on at least one side of the polyester film, the cured resin layer is a cured product of a cured resin layer composition containing a resin having a styrene structure and a crosslinking agent, the crosslinking agent is two or more selected from a melamine compound, an epoxy compound, and an organosilicon compound, the crosslinking agent contains a melamine compound and one or more compounds selected from the group consisting of an epoxy compound and an organosilicon compound, the content of the resin having a styrene structure in the non-volatile components of the cured resin layer composition is 25 to 50 mass %, the total content of the crosslinking agent in the non-volatile components of the cured resin layer composition is 45 to 70 mass %, the content of the melamine compound in the non-volatile components of the cured resin layer composition is 30 to 65 mass %, When an epoxy compound is selected as one of the crosslinking agents, the content of the epoxy compound in the non-volatile components of the cured resin layer composition is 10 to 40 mass %, A laminated polyester film, wherein when an organosilicon compound is selected as one of the crosslinking agents, the content of the organosilicon compound in the non-volatile components of the cured resin layer composition is 10 to 40 mass %.

2. 2. The laminated polyester film according to claim 1, wherein a change in film haze (ΔH) before and after heat treatment at 150° C. for 90 minutes is 1.0% or less.

3. 3. The laminated polyester film according to claim 1, wherein the styrene structure is a structural unit derived from styrene or a styrene derivative.

4. The laminated polyester film according to claim 3 , wherein the resin having a styrene structure has a structure derived from a polymerizable monomer copolymerizable with styrene or a styrene derivative.

5. 5. The laminated polyester film according to claim 1, further comprising a release layer containing a curable silicone resin on the cured resin layer.

6. The laminated polyester film according to claim 5 , further comprising an adhesive layer on the release layer.

7. A film laminate obtained by laminating the adhesive layer side of the laminated polyester film according to claim 6 to an adherend.

8. The film laminate according to claim 7 , wherein the adherend is any one of a transparent conductive layer, a polarizing element, and a resin film.

9. The method for producing a laminated polyester film according to any one of claims 1 to 6, wherein the cured resin layer is provided by in-line coating.

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