JP7806449B2 - Laminated Polyester Film - Google Patents

Description

The present invention relates to a laminated polyester film, and more specifically, to a film having a polyester film substrate on which a cured resin layer and a release layer are sequentially formed. For example, the present invention relates to a laminated polyester film that suppresses the precipitation 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 that exhibits excellent adhesion over time between the substrate film and the release layer, eliminating problems associated with oligomer precipitation and problems caused by the release layer peeling off over time.

Polyester film has traditionally been used for a variety of applications due to its excellent properties, including mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, as well as its excellent cost performance.

In recent years, many applications for release films involve exposure to high temperatures. For example, transparent conductive laminates in which an ITO (indium tin oxide) film is formed by sputtering, which are increasingly used in touch panels, typically require exposure to heat of around 150°C for more than an hour during the ITO crystallization process (Patent Document 1).

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 to the transparent conductive laminate before crystallization, and both may undergo the crystallization process.

In addition, Patent Document 3 discloses a release film using a polyester film as the base material. The release film has a coating layer on at least one side of the polyester film and a release layer on the coating layer, and the coating layer contains a copolymer polyester resin having at least an acid component having a condensed polycyclic aromatic structure and an aliphatic acid component.

Japanese Patent Application Laid-Open No. 2007-200823 JP 2009-76432 A Japanese Patent Application Laid-Open No. 2017-164959

However, one problem with polyester film is that when it is exposed to high-temperature processing for long periods of time, the oligomers contained in the film precipitate from within the film. As a result, in Patent Documents 1 to 3, the precipitated oligomers pass through the release layer, etc., and crystallize within the adhesive layer, becoming foreign matter, which can cause problems with visual inspection.

The present invention has been made in consideration of the above-mentioned circumstances, and its problem to be solved is to provide a laminated polyester film that reduces the precipitation of oligomers from polyester films when processed at high temperatures, thereby preventing problems such as reduced visibility due to whitening of the film's appearance, defects during post-processing, and contamination of processes and components, and that has good adhesion and adhesion over time between the polyester film substrate and the release layer, preventing the release layer from falling off.

In view of the above-mentioned circumstances, the present inventors have conducted extensive research and found that the above-mentioned problems can be easily solved by using a laminated polyester film having a specific configuration, 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 and 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], which has 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).

The laminated polyester film of the present invention suppresses oligomer precipitation from the polyester film surface even when subjected to long-term treatment at high temperatures, resulting in products with excellent appearance and no foreign matter on the release layer surface. This prevents problems such as reduced visibility due to whitening of the film's appearance, defects during post-processing, and contamination within the process or on components. Furthermore, the laminated polyester film provides good adhesion and adhesion over time between the polyester film substrate and the release layer, preventing the release layer from falling off. Therefore, the film has great industrial utility value.

An example of an embodiment of the present invention is described in detail below. However, the present invention is not limited to the embodiment described below, and can be modified and implemented as desired without departing from the spirit of the present invention.

[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 a melamine compound, an epoxy compound, an organosilicon compound, an oxazoline compound, an isocyanate compound, and a carbodiimide compound.
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.

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 heat is applied to the cured resin layer to dry and harden it, hydroxyl groups are generated from the epoxy compound or organosilicon compound 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.

<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, three-layer, or 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.

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.

Polyester polymerization catalysts are 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 and germanium compounds are preferred because they have high catalytic activity, allow polymerization to occur in small amounts, and leave little metal residue in the polyester film, resulting in higher brightness of the polyester film. Furthermore, because germanium compounds are expensive, it is more preferable to use titanium compounds.

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 tinge. 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 suppress deterioration during the melt-extrusion process. As the phosphorus compound, orthophosphoric acid is preferred, taking into consideration 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 the presence of foreign matter does not occur. When the content of the phosphorus compound is equal to or greater 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.

In addition, to reduce the amount of oligomer component precipitation, polyester films may be produced using polyesters with a low oligomer component content as raw materials. Various known methods can be used to produce polyesters with a low oligomer component content, such as solid-state polymerization after polyester production.

The amount of oligomer component precipitation can also be reduced by configuring the polyester film to have three or more layers and using a polyester raw material with a low oligomer component content as the outermost layer of the polyester film. Furthermore, the polyester can be obtained by esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature.

An ultraviolet absorber can also be incorporated into the polyester film to improve the weather resistance of the laminated polyester film and prevent deterioration of the adherend (e.g., polarizing element). There are no particular restrictions on the ultraviolet absorber, as long as it is a compound that absorbs ultraviolet light and can withstand the heat applied during the polyester film manufacturing process.

Ultraviolet absorbers include organic and inorganic types, with organic types being preferred from the standpoint of transparency. Organic types of ultraviolet absorbers are not particularly limited, but examples include cyclic iminoesters, benzotriazoles, and benzophenones. From the standpoint of durability, cyclic iminoesters and benzotriazoles are more preferred. It is also possible to use two or more types of ultraviolet absorbers in combination.

Particles can also be blended into polyester film for the primary purposes of imparting lubricity and preventing scratches during each process. When particles are blended, the type of particles to be blended 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 formed by precipitating and finely dispersing a portion of a metal compound, such as a catalyst, during the polyester manufacturing process can also be used. Among these, silica particles and calcium carbonate particles are preferred because they are particularly effective even in small amounts.

The average particle size of the particles is preferably 5.0 μm or less, and 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 will not become too rough, preventing problems in various post-processing steps. Furthermore, using particles within this range keeps haze low, making it easier to ensure transparency for the entire laminated polyester film.

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 the 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 for foreign matter and the like 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.

There are no particular limitations on the shape of the particles used; they may be spherical, lumpy, rod-like, flat, or any other shape. There are also no particular limitations on their hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination, if necessary.

There are no particular limitations on the method for adding particles to the polyester layer, and any conventionally known method can be used. For example, particles can be added at any stage in the production of the polyester that makes up each layer, but it is preferable to add them after the esterification or transesterification reaction is complete.

In addition to the particles described above, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may also be added to the polyester film of the present invention as needed.

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

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 oriented 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 typically 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is typically 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, typically at 70 to 170°C, at a stretching ratio of typically 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 with a 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 can 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.

In addition, simultaneous biaxial stretching can also be used to produce polyester film. In simultaneous biaxial stretching, the unstretched sheet is simultaneously stretched and oriented in the machine direction and width direction under temperature control, typically at 70 to 120°C, and preferably 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. The sheet is then subsequently 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 device that employs the above-mentioned stretching method, any conventionally known stretching method, such as a screw method, pantograph method, or linear drive method, can be used.

<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) in which the film surface is treated during the polyester film production process, or by off-line coating in which the cured resin layer is applied outside the system onto a film that has already been produced. In-line coating is more preferred.

In-line coating is a method of coating within the film production process. Specifically, it is a method in which coating is performed at any stage between melt extrusion of the film raw material, 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 manufacturing cost advantages by allowing film production and formation of the cured resin layer to 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.

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

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.

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

If necessary, heat treatment and irradiation with active energy rays such as ultraviolet light may be used in combination. The surface of the polyester film of the present invention may be subjected to a surface treatment such as corona treatment or plasma treatment before the cured resin layer is formed.

To form the cured resin layer, it is preferable to manufacture the laminated polyester film by applying a cured resin layer composition onto the film, prepared by preparing a solution or dispersion in a solvent of the series of compounds described below and adjusting the solids 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 to improve 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.

The cured resin layer composition can be applied to the polyester film that serves as the substrate for the laminated polyester film by any conventional coating method known in the art, 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, or extrusion coating.

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 the group consisting of melamine compounds, epoxy compounds, organosilicon compounds, oxazoline compounds, isocyanate compounds, and carbodiimide compounds.

(Resin having a styrene structure)
In the present invention, the styrene structure of the resin having a styrene structure is exemplified by those represented by the following general formula (1).

In the above general formula (1), R ¹ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. Each R 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.

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.

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 various (meth)acrylic acid esters such as (meth)acrylate, 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. various hydroxyl group-containing compounds such as (meth)acrylamide, diacetone acrylamide, N-methylolacrylamide, (meth)acrylonitrile, and the like, various nitrogen-containing compounds such as vinyl propionate and vinyl acetate, various vinyl esters 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 high oligomer precipitation prevention.
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.

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%. By keeping the proportion of styrene structures within this range, precipitation of oligomers due to heat treatment can be effectively suppressed.

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

(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 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, and can also facilitate the improvement of the durability of the cured resin layer and 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 the precipitation of oligomers 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.

In the present invention, the use of two or more crosslinking agents not only improves the ability to prevent oligomer precipitation after heating, but also improves the adhesion between the film and the release layer. Preferred combinations of crosslinking agents include 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, with a combination of a melamine compound, an epoxy compound, and an organosilicon compound being more preferred.

Melamine compounds are compounds that contain a melamine structure. Examples include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohol to partially or completely etherify them, and mixtures of these. Suitable alcohols for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. Furthermore, melamine compounds may be either monomers or dimers or higher oligomers, or mixtures of these. Furthermore, melamines partially co-condensed with urea or the like can also be used, and a catalyst can be used to increase the reactivity of the melamine compounds.

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.

The organosilicon compound is exemplified by compounds represented by the following general formula (2).
Si(X) _d (Y) _e (R ² ) _f ...(2)

In the above 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; ^R2 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.

The organosilicon compound represented by the above 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 through a hydrolysis/condensation reaction.

In the above general formula (2), the monovalent hydrocarbon group ^R2 having 1 to 10 carbon atoms is preferably a methyl group, an ethyl group, or a propyl group.

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

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.

Oxazoline compounds are compounds containing an oxazoline group within the molecule. Polymers containing oxazoline groups are particularly preferred. They can be obtained by polymerizing addition-polymerizable oxazoline group-containing monomers alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers 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 due to its industrial availability. The other monomer is not limited as long as it is a monomer 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 suitable monomers include unsaturated amides such as N,N-dialkyl(meth)acrylamides (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl); 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. One or more of these monomers can be used.

These crosslinking agents are used in a design that allows them to react during the drying and film-forming processes to improve the performance of the cured resin layer. It is likely that the finished cured resin layer contains unreacted crosslinking agents, reacted compounds, or a mixture of these.

In addition, when forming the cured resin layer of the present invention, it is preferable to use a polymer other than the resin having a styrene structure and the crosslinking agent in combination 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.

Specific examples of other polymers include polyester resin, acrylic resin, urethane resin, polyvinyl (such as polyvinyl alcohol), polyalkylene glycol, polyalkyleneimine, methyl cellulose, hydroxycellulose, and starches. Of these, polyester resin, acrylic resin, and urethane resin are preferred from the viewpoint of improving the durability of the cured resin layer, and polyester resin, acrylic resin, and polyvinyl (such as polyvinyl alcohol) are preferred from the viewpoint of improving adhesion to the release layer.

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.

Furthermore, within the scope of the present invention, defoamers, coatability improvers, thickeners, organic lubricants, antistatic agents, UV absorbers, antioxidants, foaming agents, dyes, pigments, etc. may also be used in combination as needed to form the cured resin layer.

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% by mass, more preferably 15 to 70% by mass, even more preferably 20 to 60% by mass, and particularly preferably 25 to 50% by mass. By keeping the content of the resin having a styrene structure within the above range, the cured resin layer has excellent appearance and can effectively suppress oligomer precipitation due to heat treatment.

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

When a melamine compound is selected as one of the crosslinking agents from the perspective 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% by mass, more preferably 10 to 75% by mass, and even more preferably 30 to 65% by mass. By keeping the melamine compound content within the above range, precipitation of oligomers after heating can be effectively suppressed.

When an epoxy compound is selected as one of the crosslinking agents from the perspective 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% by mass, more preferably 3 to 60% by mass, and even more preferably 5 to 40% by mass. By keeping the epoxy compound content within this range, it is possible to effectively suppress oligomer precipitation after heating and obtain good adhesion to the release layer.

When an organosilicon compound is selected as one of the crosslinking agents from the perspective 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% by mass, more preferably 3 to 50% by mass, and even more preferably 5 to 40% by 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.

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 the 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.

<Layer structure of laminated polyester film>
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.

(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 the 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.

The curable silicone resin can be any of the existing curing reaction types, such as heat-curable types such as addition or condensation types, or electron beam-curable types such as ultraviolet-curable types. Multiple types of curable silicone resins can also be used in combination. Furthermore, there are no particular restrictions on the form in which the curable silicone resin is applied when forming the release layer; it can be dissolved in an organic solvent, in the form of a water-based emulsion, or in a solvent-free form.

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 releasability. 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 ₂ SiO) _q -SiW _a R ² _(3-a) ...(3)

In the above general formula (3), ^R2 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; however, when a = 0, p is 2 or greater, and p and q are each numbers that satisfy 100≦p+q≦20,000. Furthermore, the above general formula (3) does not mean a block copolymer.

Specific examples of ^R2 include alkyl groups such as methyl, ethyl, propyl, and butyl; cycloalkyl groups such as cyclohexyl; and aryl groups such as phenyl and tolyl. Of these, methyl and phenyl are particularly preferred.
W is preferably an alkenyl-containing organic group having 2 to 10 carbon atoms. 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 and a hexenyl group are particularly preferred. Specific examples include a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups (96 mol% dimethylsiloxane units, 4 mol% methylhexenylsiloxane units), a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with dimethylvinylsiloxy groups (97 mol% dimethylsiloxane units, 3 mol% methylhexenylsiloxane units), and a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with dimethylhexenylsiloxy groups (95 mol% dimethylsiloxane units, 5 mol% methylhexenylsiloxane units).

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 can be linear, branched, cyclic, etc. Examples include compounds represented by the following general formula (4), but are not limited to these.
H _b R ³ _(3-b) SiO-(HR ³ SiO) _x -(R ³ ₂ SiO) _y -SiR ³ _(3-b) H _b ...(4)

In the general formula (4), ^R3 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.

Specific examples of the compound represented by the general formula (4) above include methylhydrogenpolysiloxanes capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methylhydrogenpolysiloxanes capped at both molecular chain terminals with dimethylhydrogensiloxy groups, and dimethylsiloxane-methylhydrogensiloxane copolymers capped at both molecular chain terminals 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.

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, and X-62-5 manufactured by Shin-Etsu Chemical Co., Ltd. 040, KNS-3051, X-62-1496, KNS320A, KNS316, X-62-1574A/B, X-62-7052, X-62-7028A/B, X-62-7619, X-62-7213, X-41-3035, and Momentive Performance Materials products such as YSR-3022, TPR-6700, and TPR -6720, TPR-6721, TPR6500, TPR6501, UV9300, UV9425, XS56-A2775, XS56-A2982, UV9430, TPR6600, TPR6604, TPR6605, and Dow Corning Toray Co., Ltd. products such as SRX357, SRX211, SD7220, SD7292, and 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 Silicone Co., Ltd.

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 and an olefin, and a complex of chloroplatinic acid and an alkenylsiloxane, 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, so that process problems such as the generation of gel foreign matter do not occur.

Addition-type reactions are very reactive, so in some cases acetylene alcohol may be added as a reaction inhibitor. This component is an organic compound containing a carbon-carbon triple bond and a hydroxyl group, preferably a compound selected from the group consisting of 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, and phenylbutynol.

A catalyst can be used in combination with the release layer constituting 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; organic metal 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 NH ₄ F. The above catalysts may be used alone or in combination of two or more. Among them, organic metal salts are preferred because they provide particularly good coating durability.

Various release control agents may be used in combination to adjust the release properties of the release layer. To achieve a stronger release force, the release layer typically contains an appropriate amount of organopolysiloxane resin, silica particles, or a silicone species with a stronger release force, adjusted to achieve the desired release force. Specific examples of commercially available stronger 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 achieve a lighter release force, various low-molecular-weight siloxanes are selected and their content adjusted to the release layer so that the siloxane migrating component exhibits 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 these compounds may be used in combination as needed. These low molecular weight siloxane compounds are typically contained in the silicone resin as migratory components in an amount of 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 demonstrates sufficient mold 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.

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.

When an organosilicon compound is used in the release layer, the content of the organosilicon compound is preferably 0.5 to 5.0% by mass, and more preferably 0.5 to 2.0% by mass, relative to 100% by mass of the curable silicone resin. An organosilicon compound content of 0.5% by mass or more makes it easy to ensure the desired adhesion, while an organosilicon compound content of 5.0% by mass or less ensures that the adhesion to the opposing resin layer is not too strong, allowing for easy peeling when peeling is actually required.

The release layer composition that forms the release layer may contain, as necessary, antifoaming agents, coatability improvers, thickeners, inorganic or organic particles, organic lubricants, antistatic agents, conductive agents, UV absorbers, antioxidants, foaming agents, dyes, pigments, etc.

The release layer is formed by coating the film with a release layer composition. This can be done by in-line coating during the film production process, or by applying the release layer composition outside the system onto a film that has already been produced, which is known as off-line coating.

To form a release layer on the cured resin layer, conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating can be used.

The curing conditions for forming a release layer on the cured resin layer of the laminated polyester film are not particularly limited. When forming a release layer by offline coating, heat treatment is typically carried out at 80°C or higher for 10 seconds or more, preferably at 100-200°C for 3-40 seconds, and more preferably at 120-180°C for 3-40 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 active energy ray irradiation.

The thickness of the release layer is typically 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. A thickness of 0.005 μm or more provides excellent coatability and a stable, uniform coating film. On the other hand, a thickness of 3.0 μm or less does not reduce the coating adhesion and curing properties of the release layer itself.

There are no particular restrictions on the peel strength of the release layer, but it is preferably 1 to 500 mN/cm, more preferably 2 to 300 mN/cm, even more preferably 3 to 200 mN/cm, and even more preferably 5 to 150 mN/cm. A peel strength of 500 mN/cm or less allows for smooth peeling from the adherend.

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

(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.

[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 them, acrylic pressure-sensitive adhesive compositions containing an acrylic resin as a main component are preferred, as they allow adjustment of a good balance between adhesive strength and peel strength and are inexpensive.

The term "main component resin" refers to the resin that accounts for the largest proportion of all 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 resin that makes up the pressure-sensitive adhesive composition. The upper limit is typically 99.99% by mass.

In addition to the above-mentioned main component resin, the pressure-sensitive adhesive composition may contain, as necessary, a crosslinking agent as 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 development 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.

<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 having a (meth)acrylic acid alkyl ester as a main constituent unit.
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 (meth)acrylate, 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 from the viewpoints 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.

The (meth)acrylic polymer can be copolymerized with (meth)acrylic acid esters other than alkyl (meth)acrylate 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 alkyl (meth)acrylate 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.

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 Fox formula, Tg represents the glass transition temperature (unit: K) of the (meth)acrylic polymer, W _i represents the mass fraction of the constituent unit derived from monomer i constituting the (meth)acrylic polymer, and Tg _i represents the glass transition temperature (unit: K) of a homopolymer of monomer i. The value of Tg _i can be the value described in POLYMERHANDBOOK Volume 1 (WILEY-INTERSCIENCE).

In the present invention, the (meth)acrylic polymer preferably contains structural units derived from acrylic monomer (a1), as these serve as reaction sites with the crosslinking agent described below.

The acrylic monomer (a1) serves as a reactive site for the crosslinking structure when copolymerized with other copolymerization components to form a (meth)acrylic polymer. It is sufficient for the acrylic monomer (a1) to contain a functional group capable of reacting with a functional group contained in the crosslinking agent described below. Examples of such acrylic monomers (a1) include hydroxyl group-containing monomers, amino group-containing monomers, acetoacetyl group-containing monomers, isocyanate group-containing monomers, and glycidyl group-containing monomers. Among these, hydroxyl group-containing monomers are preferred because they can efficiently undergo crosslinking reactions with the crosslinking agent. The acrylic monomer (a1) may be used alone or in combination of two or more types.

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; 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.

Of 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 even more preferred because it contains fewer impurities such as di(meth)acrylates and is easier to form an adhesive layer.

In the present invention, the hydroxyl group-containing monomer that forms the adhesive layer preferably contains 0.5% or less of the impurity di(meth)acrylate, more preferably 0.2% or less, and even more preferably 0.1% or less. Specific examples of hydroxyl group-containing monomers that are particularly preferred 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.

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

Examples of acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

Examples of isocyanate group-containing monomers include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

Examples of glycidyl group-containing monomers include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

The content of structural units derived from 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. By ensuring that the content of structural units derived from acrylic monomer (a1) is 0.01% by mass or more, sufficient crosslinking points can be formed within the adhesive layer, making it easier to improve the cohesive strength after crosslinking. Furthermore, by ensuring that the content is 20% by mass or less, it is easier to prevent a decrease in adhesive strength.

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, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

The content of the structural units derived from copolymerizable monomer (a2) in the (meth)acrylic polymer is preferably 0.01 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass. By keeping the content of the structural units derived from copolymerizable monomer (a2) within the above range, it is easy to prevent a decrease in the adhesive properties of the adhesive layer.

<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.

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, per 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.

When the curing reaction is carried out by photocuring through irradiation with active energy rays, 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.

<Thickness of adhesive layer>
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.

<Physical properties of laminated polyester film>
(Amount of Oligomer Precipitation 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 with dimethylformamide from the surface of the cured resin layer after heat treatment of the laminated polyester film (150°C, 90 minutes), and is preferably 1.0 mg/ ^m2 or less, more preferably 0.7 mg/ ^m2 or less, and even more preferably 0.5 mg/ ^m2 or less. When the amount of oligomer precipitated from the laminated polyester film is 1.0 mg/ ^m2 or less, 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 precipitated is small, the transparency of the film can be maintained, and there is no concern about contamination of the process.
(Amount of Oligomer Precipitation II)
In the present invention, the amount of oligomer precipitation from the surface of the release layer in a laminated polyester film having a release layer on a 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 a cured resin layer, and is preferably 1.0 mg/ ^m2 or less, more preferably mg/ ^m2 or less, and even more preferably 0.5 mg/ ^m2 or less. When the amount of oligomer precipitation in a laminated polyester film having a release layer is 1.0 mg/ ^m2 or less, even if a long-term heat treatment is performed in a post-process in a high-temperature atmosphere, 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.

(Film haze change I)
Regarding the film haze change of the laminated polyester film of the present invention, the film haze change (ΔH) of the laminated polyester film before and after heat treatment under conditions of 150°C and 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 a polyester film usually increases due to the precipitation of oligomers on the film surface by 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 a decrease in visibility and an increase in 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 the 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.

[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.

(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.

[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, and 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 even composite oxide containing indium oxide, zinc oxide, and gallium oxide (IGZO). These compounds can achieve both transparency and conductivity by selecting appropriate production conditions.

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.

Known methods for forming transparent conductive layers 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, sputtering can be performed using conventional sputtering with a compound target or reactive sputtering with a metal target. In this case, reactive gases such as oxygen, nitrogen, or water vapor can be introduced, or ozone can be added, or ion-assisted methods can be used in combination.

The transparent conductive layer is preferably formed at a temperature between room temperature and 100°C. This sufficiently promotes crystallization of the transparent conductive layer, resulting in a transparent conductive film with low surface resistance, making it suitable for use in displays such as organic electroluminescence (EL).

[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.

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 alignment direction, the alignment film may be subjected to an alignment treatment by a known method (rubbing method, method of forming grooves (fine groove structures) on the surface of the alignment film (photo-alignment method) using polarized ultraviolet light or polarized laser, alignment method by forming an LB film, alignment method by oblique deposition of inorganic material, etc.) described on pages 226 to 239 of "Liquid Crystal Handbook" (Maruzen Co., Ltd., published October 30, 2000). In particular, the rubbing method and the photo-alignment method are preferred from the viewpoint of easily achieving a high degree of alignment.
The thickness of the alignment film is usually 10 nm to 1000 nm, preferably 50 nm to 800 nm, which allows for both a sufficient alignment control force for aligning the liquid crystal compound and a thin film.

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.

≪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 allows for easier fixation of the oriented 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. Of these, a (meth)acryloyl group or a (meth)acryloyloxy group is preferred.

Polarizing elements are 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.

[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.

From the viewpoint of ease of handling, the thickness of the film laminate of the present invention is preferably 80 to 250 μm, more preferably 80 to 200 μm, even more preferably 80 to 175 μm, and particularly 80 to 150 μm.

<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 capacitance-type touch panels, for producing optical members used in liquid crystal displays (polarizing elements, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) and organic electroluminescence component members, and for producing various display component members, 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 displays.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. The evaluation methods used in the examples and comparative examples are as follows.

(1) Method for measuring the 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, and dissolved in 100 mL of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and the intrinsic viscosity was measured at 30°C.

(2) Method for measuring the average particle size (d50 (μm)) of particles The average particle size was determined as 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).

(3) Method for Measuring Film Thickness of Cured Resin Layer and Release Layer The surfaces of the cured resin layer and the release layer were stained with _RuO4 and embedded in epoxy resin. Then, slices 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 (H-7650 manufactured by Hitachi High-Technologies Corporation, accelerating voltage 100 kV).

(4) Heat Treatment Method for Laminated Polyester Film The laminated polyester film was placed on Kent paper in an exposed state and fixed, and then heat-treated by leaving it at 150° C. for 90 minutes in a nitrogen atmosphere.

(5) Measurement of film haze increase (ΔH) due to heat treatment For the laminated polyester films of Examples and Comparative Examples and the laminated polyester films 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 form a hard coat layer, and a measurement sample was obtained.
The film haze was measured in accordance with JIS-K-7136 using the cured resin layer or release layer side of the obtained measurement sample 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 from the obtained haze 1 and haze 2 using the following formula: 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]

<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 mass

(6) Measurement of Oligomer Precipitation Amount on the Laminated Polyester Film Surface The laminated polyester films of the Examples and Comparative Examples and laminated polyester films having a release layer were heated in air at 150°C for 90 minutes. The heat-treated films were then cut into an open-topped box-shaped container measuring 10 cm in length and width and 3 cm in height, with the measurement surface (cured resin layer or release layer) facing the inner surface. Next, 4 mL of DMF (dimethylsulfamide) was placed in the box-shaped container 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 amount of oligomer thus determined was divided by the area of the surface of the film that had been brought into contact with DMF to obtain the amount of oligomer precipitated on the surface of the film (mg/m ² ).
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.

(7) Peeling Force One side of a double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) was attached to the surface of the release layer of each of the laminated polyester films having a release layer in the Examples and Comparative Examples, and the film was cut to a size of 50 mm x 300 mm. The film was left at room temperature for 1 hour, and the peeling force was measured. The peeling force was measured using a tensile tester ("Intesco Model 2001" manufactured by Intesco Corporation) at a 180° peeling angle at a pulling rate of 300 mm/min.

(8) Coating adhesion of release layer over time (evaluation as a substitute for 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 the release film is produced. Condition II: After the mold film is left in a constant temperature and humidity chamber under an atmosphere of 23°C x 50% RH for 30 days. Condition III: After the mold film is left in a constant temperature and humidity chamber under an atmosphere of 23°C x 50% RH for 60 days. <Evaluation 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 this was not a problem in practical use.
C: The rubbed area turned white and the release layer easily fell off, making it unsuitable for practical use.

(9) Molecular Weight Measurement of Curable Silicone Resin A chromatogram was measured using a GPC measuring device, and the number average molecular weight (Mn) and weight average molecular weight (Mw) were determined based on a calibration curve using standard polystyrene, and 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 measuring device and measured. Tetrahydrofuran (THF) was used as the eluent. For the analysis, an "Ecosec 8320" manufactured by Tosoh Corporation was used, and a "TSKgel guard column HXL-L" manufactured by Tosoh Corporation was used as the guard column, and four "TSKgel GMHXL" manufactured by Tosoh Corporation were used in conjunction. The analysis was performed under conditions of an oven temperature of 40 ° C. and a THF flow rate of 1.0 mL/min, and RI was used for detection.

(10) Composition Analysis of Curable Silicone Resin The composition of the curable silicone resin was analyzed using a 400 MHz-NMR (Bruker Avance 400M).
^{The 1} H-NMR measurement was carried out at 30° C. using CDCl ₃ as a solvent and using the peak derived from the methyl group of dimethylsiloxane as the chemical shift reference.

Examples of compounds that may form the cured resin layer are as follows:
(Resin having a styrene structure)
(A) Aqueous dispersion of a styrene-acrylic copolymer polymerized with 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) EPOCROS, an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd.).
(Amount of oxazoline group: 4.5 mmol/g)
(particle)
(F) Silica particles with an average particle size of 0.07 μm

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

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 produced polyester, and 100 ppm of magnesium acetate tetrahydrate as a catalyst based on the produced polyester. Subsequently, 50 ppm of tetrabutyl titanate based on the produced 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) having an intrinsic viscosity of 0.63 dl/g.

<Method for producing polyester (b)>
Esterification reaction was carried out under a nitrogen atmosphere at 225° C. 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 produced polyester. Subsequently, 3,500 ppm of orthophosphoric acid and 70 ppm of germanium dioxide relative to the produced 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.

<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 the melt polymerization.

Example 1:
A mixed raw material obtained by mixing polyesters (a), (b), and (c) in proportions of 91%, 3%, and 6% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and a mixed raw material obtained by mixing polyesters (a) and (b) in proportions of 97% and 3%, respectively, was used as the raw material for the intermediate layer. Each of these raw materials was supplied to 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/intermediate layer/surface layer = discharge amount 1/18/1), followed by cooling and solidification 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, heat-treated at 235°C, and then relaxed by 2% in the transverse direction to give 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.

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

Next, the release layer composition was applied to the cured resin layer of the resulting laminated polyester film by bar coating using a No. 4 bar, and then dried at 150°C for 30 seconds, heat-treated, and cured to obtain a laminated polyester film with a release layer in which a cured resin layer and a release layer were laminated in that order.

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 due to heat treatment was small, the amount of change in film haze was also small and good, and the results for the coating adhesion and peel strength of the release layer over time were also good.

Examples 2 to 10:
A laminated polyester film was obtained by production 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 and peel strength of the release layer over time were also good.

Comparative Example 1:
A laminated polyester film was obtained by production in the same manner as in Example 1, except that no cured resin layer was provided in Example 1. Subsequently, the above release layer composition was applied to the laminated polyester film and cured to obtain a laminated polyester film having a release layer.

When the laminated polyester film having the release layer of Comparative Example 1 was evaluated, as shown in Table 2, significant oligomer precipitation occurred during heat treatment, and the film haze also increased significantly, raising concerns about process contamination. Furthermore, the release layer's coating adhesion over time was poor.

Comparative Example 2:
A laminated polyester film was obtained by production 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 were good, but the coating adhesion of the release layer over time was poor.

Comparative Example 3:
A laminated polyester film was obtained by production 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.

Comparative Example 4:
A laminated polyester film was obtained by production 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 the 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 also poor.

The laminated polyester film of the present invention exhibits minimal oligomer precipitation, making it suitable for applications involving prolonged exposure to high-temperature atmospheres. For example, it is suitable for various applications involving bonding via an adhesive layer, such as the manufacture of capacitance-type touch panels, as well as for the manufacture of various display components, such as optical components used in liquid crystal displays (polarizing elements, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) and organic electroluminescence components, as well as for protecting various adhesive layers.

Claims (9)

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 %. The laminated polyester film according to claim 1, in which the change in film haze (ΔH) before and after heat treatment at 150°C for 90 minutes is 1.0% or less. 3. The laminated polyester film according to claim 1 , wherein the styrene structure is a structural unit derived from styrene or a styrene derivative. 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. The laminated polyester film according to claim 1 , further comprising a release layer containing a curable silicone resin on the cured resin layer. The laminated polyester film according to claim 5 , further comprising an adhesive layer on the release layer. A film laminate obtained by laminating the adhesive layer side of the laminated polyester film according to claim 6 to an adherend. 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. 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.