JP6176270B2 - Release film - Google Patents

Description

  The present invention relates to a release film, and more specifically, a film having a polyester film as a base material and an undercoat layer and a release layer provided in sequence. For example, the present invention relates to a release film that suppresses oligomer precipitation on the surface of a polyester film even after being exposed to a high temperature and does not cause problems associated with the oligomer.

  A polyester film is excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, etc., and a release film with a release layer mainly composed of a polyester resin and a silicone resin as a main component Is used in many fields.

  In particular, in recent years, as a use application of a release film, it is often exposed to a high temperature. For example, transparent conductive laminates with ITO (Indium Tin Oxide) films, which are increasingly used for touch panels and the like, are sputtered with ITO at about 150 ° C. for 1 hour or more in the crystallization process. Is common (Patent Document 1).

  When bonding such a transparent conductive laminated body, it is common to use the adhesion layer pinched | interposed with the release film (patent document 2). The pressure-sensitive adhesive layer and the release film are laminated on the transparent conductive laminate before crystallization, and both may be subjected to a crystallization step.

  However, as a problem of the polyester film, when exposed to such high temperature and long time treatment, oligomers contained in the film (polyester low molecular weight component, especially ester cyclic trimer) are precipitated from the inside of the film. come. The oligomer thus precipitated passes through the release layer and crystallizes inside the adhesive layer to become a foreign substance, thereby causing a problem of hindering the appearance inspection.

  Moreover, it cannot be said that the characteristics of a transparent conductive laminate using a release film based on a polyester film are sufficiently satisfactory.

  Therefore, when taking measures to reduce the amount of oligomer precipitation by the undercoat layer, the undercoat layer itself is required to have an oligomer precipitation preventing property more than before.

JP 2007-200823 A JP 2009-76432 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is to provide a release film having excellent optical characteristics and visibility even after being processed as a product for an optical member, Specifically, for example, even after undergoing a process under harsh conditions such as a long-time heat treatment at 150 ° C., a sputtering process, and a durability test under a high temperature and high humidity atmosphere, It is providing the release film which can suppress the foreign material production | generation resulting from this.

  As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by a release film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a film in which an undercoat layer and a release layer are sequentially provided on at least one surface of a polyester film, and the undercoat layer has a styrene structure and a (meth) acrylic acid structure. And a release film characterized in that it is formed from a coating solution containing an oxazoline compound, a melamine compound, or both crosslinking agents by a coating stretching method.

  According to the release film of the present invention, since the oligomer precipitation from the surface is suppressed even after high-temperature and long-time treatment, a product having an excellent appearance with no generation of foreign matters on the release layer surface is obtained. It can be obtained and its industrial utility value is high.

  The base film of the release film of the present invention is made of polyester. Such polyesters include dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, 4,4′-diphenyldicarboxylic acid, 1,4-cyclohexyldicarboxylic acid or esters thereof. It is a polyester produced by melt polycondensation with glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol. Polyesters composed of these acid components and glycol components can be produced by arbitrarily using a commonly used method.

  For example, a transesterification reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or a direct esterification of an aromatic dicarboxylic acid and a glycol, to form a substantially bisglycol of an aromatic dicarboxylic acid A method is employed in which an ester or a low polymer thereof is formed and then polycondensed by heating under reduced pressure. Depending on the purpose, an aliphatic dicarboxylic acid may be copolymerized.

  Typical examples of the polyester of the present invention include polyethylene terephthalate, polyethylene-2,6-naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, and the like. It may be a polymerized polyester and may contain other components and additives as necessary.

  There is no restriction | limiting in particular as a polymerization catalyst of polyester, A conventionally well-known compound can be used, For example, an antimony compound, a titanium compound, a germanium compound, a manganese compound, an aluminum compound, a magnesium compound, a calcium compound etc. are mentioned. Among these, antimony compounds have the advantage of being inexpensive and having high catalytic activity. Titanium compounds and germanium compounds are preferable because they have high catalytic activity and can be polymerized in a small amount, and since the amount of metal remaining in the film is small, the brightness of the film is increased. Furthermore, since a germanium compound is expensive, it is more preferable to use a titanium compound.

  The polyester film which is the base material of the release film in the present invention may have a single layer structure or a multilayer structure. In the case of a multilayer structure, the surface layer and the inner layer, or both the surface layer and each layer can be made of different polyesters depending on the purpose.

  In this invention, in order to suppress the precipitation amount of the ester cyclic trimer after heat processing, manufacturing a film from polyester with little content of ester cyclic trimer is mentioned. Various known methods can be used as a method for producing a polyester having a low ester cyclic trimer content. Examples thereof include a method of solid-phase polymerization after polyester production.

  The content of the ester cyclic trimer contained in the polyester film is about 1% by weight in a general production method, but from the viewpoint of preventing precipitation of the ester cyclic trimer, the content of the ester cyclic trimer Is preferably 0.7% by weight or less, more preferably 0.6% by weight or less. When the polyester cyclic trimer content is 0.7% by weight or less, the effect of preventing the precipitation of the ester cyclic trimer on the film surface is particularly high.

  The polyester used for forming the polyester layer can use a polyester raw material with a low ester cyclic trimer content, and the ester cyclic trimer content is preferably 0.7% by weight or less, More preferably, it is 0.6 weight% or less, Most preferably, it is 0.5 weight% or less. When the content of the ester cyclic trimer in the polyester raw material is 0.7% by weight or less, it becomes possible to more effectively suppress the precipitation amount of the ester cyclic trimer after the heat treatment.

  The polyester layer is preferably composed of 70% by weight or more of polyester having an ester cyclic trimer content of 0.7% by weight or less, more preferably 80% by weight or more. When comprised from 70 weight% or more, it becomes possible to exhibit the ester cyclic trimer precipitation prevention effect to the film surface after heat processing highly.

  In the present invention, the polyester film has a structure of three or more layers, and the outermost polyester layer is designed with a layer using a polyester raw material having a small content of the ester cyclic trimer. A method of suppressing the amount of precipitation is also possible.

  When the polyester film has a multilayer structure, it is preferable that at least one layer of the polyester film has a polyester layer of 0.7% by weight or less, more preferably, the outermost two layers are 0.7% by weight or less of polyester. It is having a layer, More preferably, all the layers have a polyester layer of 0.7 weight% or less. By setting it as the structure mentioned above, it becomes possible to suppress highly precipitation of the ester cyclic trimer after heat processing.

  Moreover, precipitation of the ester cyclic trimer from the polyester film is effectively suppressed when the polyester layer having a polyester film having an ester cyclic trimer content of 0.7% by weight or less is thicker. The thickness of the 0.7% by weight or less polyester layer is preferably 1.5 μm or more, more preferably 2.0 μm or more, and particularly preferably 2.5 μm or more. When the film thickness of the polyester layer of 0.7% by weight or less is 1.5 μm or more, the heat treatment for a long time at 150 ° C., the sputtering process under high tension, Even when used in a processing step under severe conditions such as a durability test, the ester cyclic trimer is less likely to precipitate on the surface, and the increase in film haze can be further suppressed.

  The polyester film, which is the base material of the release film in the present invention, can contain particles for the purpose of ensuring the running property of the film and preventing scratches. Examples of such particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium phosphate, kaolin, talc, aluminum oxide, titanium oxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. Further, organic particles such as crosslinked polymer particles and calcium oxalate, and precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  The particle size and content of the particles to be used are selected according to the use and purpose of the film, but the average particle size (d50) is preferably 3 μm or less, more preferably 0.02 μm to 2.8 μm, and even more preferably. It is in the range of 0.03 μm to 2.5 μm. If the average particle size is too large, the surface roughness of the film becomes too rough, or the particles easily fall off from the film surface.

  The particle content is preferably 3% by weight or less, more preferably 0.0003 to 1% by weight, and still more preferably 0.0005 to 0.5% by weight with respect to the polyester layer containing the particles. When there are no or few particles, the transparency of the film will be high and a good film will be obtained, but the slipperiness may be insufficient, so it is easy to put particles in the undercoat layer. In some cases, it is necessary to improve the lubricity. Moreover, when there is too much particle content, the transparency of a film may be inadequate.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but it is preferably added after completion of esterification or transesterification.

  In addition, in the polyester film which is the base material of the release film in the present invention, conventionally known antioxidants, ultraviolet absorbers, thermal stabilizers, lubricants, dyes, pigments as necessary in addition to the above-mentioned particles Etc. can be added.

  The thickness of the polyester film that is the base material of the release film in the present invention is not particularly limited as long as it can be formed as a film, but is preferably 10 to 300 μm, more preferably 15 to 250 μm, Preferably it is the range of 20-200 micrometers.

  As a method for forming a polyester film film, which is a base material of a release film in the present invention, a generally known film forming method can be adopted, and there is no particular limitation. For example, a sheet obtained by melt extrusion is first stretched 2 to 6 times at 70 to 145 ° C. by a roll stretching method to obtain a uniaxially stretched polyester film, and then perpendicular to the previous stretching direction in the tenter. A film is obtained by extending | stretching 2 to 6 times at 80-160 degreeC to the direction, and also heat-processing at 150-250 degreeC for 1 to 600 seconds. Further, at this time, it is preferable to perform relaxation within 20% in the longitudinal direction and / or the transverse direction in the heat treatment zone and / or the cooling zone at the heat treatment outlet.

  The undercoat layer of the polyester film that is the substrate of the release film in the present invention is a so-called off-line coating in which an undercoat layer is provided later on the formed film, and an undercoat layer is provided during film formation of the film. Any of so-called in-line coatings can be provided. It is preferably provided by in-line coating, particularly by a coating stretching method in which stretching is performed after coating.

  In-line coating is a method of coating within the process of manufacturing a polyester film, and specifically, a method of coating at any stage from melt extrusion of a polyester to heat setting after stretching and winding up. Usually, it is either a substantially amorphous unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after winding and before winding. Coating. Although not limited to the following, for example, in sequential biaxial stretching, a method of stretching in the transverse direction after coating a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction) is particularly excellent. According to such a method, film formation and undercoat layer coating can be performed at the same time, so there is an advantage in production cost. In order to perform stretching after coating, a thin film and uniform coating can be obtained. The characteristics are stable.

  In addition, the polyester film before biaxial stretching is first coated with a resin layer constituting the undercoat layer, and then the film and the undercoat layer are stretched at the same time, thereby strengthening the base film and the undercoat layer. It will be in close contact. In addition, the biaxial stretching of the polyester film is that the film is constrained in the longitudinal / lateral direction by gripping the end of the film with a tenter clip etc. High temperature can be applied while maintaining flatness. Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the film forming property of the undercoat layer is improved, and the undercoat layer and the polyester film are firmly adhered. As the polyester film provided with the undercoat layer, the uniformity of the undercoat layer, the improvement of the film forming property, and the adhesion between the undercoat layer and the film often produce preferable characteristics.

  In the case of the coating stretching method, the coating solution to be used is preferably an aqueous solution or an aqueous dispersion for safety reasons in terms of handling, working environment, and preferably water is the main medium. In addition, as long as it does not exceed the gist of the present invention, an organic solvent may be contained.

  The release film of the present invention is a film in which an undercoat layer and a release layer are sequentially provided on at least one surface of a polyester film, and the undercoat layer comprises a resin having a styrene structure and a (meth) acrylic acid structure. Containing it is an essential requirement. The undercoat layer may contain other components.

  The styrene structure refers to styrene and styrene derivatives. For example, it may be introduced into styrene as a substituent such as an alkyl group such as a methyl group or an ethyl group or a phenyl group. From the viewpoint of the effect of preventing precipitation of the ester cyclic trimer by heat treatment, styrene substituted with an alkyl group having 4 or less carbon atoms or styrene having no substituent is preferred, and styrene is more preferred.

The (meth) acrylic acid structure is a derivative in which a substituent is introduced into (meth) acrylic acid and (meth) acrylic acid. From the viewpoint of the effect of preventing precipitation of the ester cyclic trimer after the heat treatment, (meth) acrylic acid is preferred, and acrylic acid is more preferred.

  The resin having a styrene structure and a (meth) acrylic acid structure can be combined with another polymerizable monomer copolymerizable with a compound having a styrene structure and a (meth) acrylic acid structure. Examples of the copolymerizable monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth) acrylate. Various (meth) acrylic acid esters, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutylhydroxy fumarate, monobutylhydroxyitaco Various hydroxyl-containing compounds such as nates, various nitrogen-containing compounds such as (meth) acrylamide, diacetone acrylamide, N-methylol acrylamide or (meth) acrylonitrile, vinyl propionate, vinyl acetate, etc. Various vinyl esters; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, etc .; phosphorus-containing vinyl monomers; various halogens such as vinyl chloride and vinylidene chloride Vinyl chlorides; various conjugated dienes such as butadiene. Among these, it is preferable to copolymerize a hydroxyl group-containing compound in order to prevent precipitation of a high degree of ester cyclic trimer. When the hydroxyl group-containing compound is copolymerized, it is preferably in the range of 1 to 30 mol%, more preferably 5 to 25 mol%, still more preferably 10 to 20 mol%. When outside the above range, precipitation of the ester cyclic trimer due to heat treatment may not be effectively suppressed, or the appearance of the undercoat layer may be deteriorated.

  The ratio of the styrene structure in the resin having a styrene structure and a (meth) acrylic acid structure is preferably in the range of 5 to 95 mol%, more preferably 20 to 90 mol%, and still more preferably 40 to 85 mol%. By using in the said range, precipitation of the ester cyclic trimer by heat processing can be suppressed effectively.

  The ratio of the (meth) acrylic acid structure in the resin having a styrene structure and a (meth) acrylic acid structure is preferably 5 to 95 mol%, more preferably 10 to 80 mol%, and still more preferably 15 to 40 mol%. It is a range. By using in the said range, precipitation of the ester cyclic trimer by heat processing can be suppressed effectively.

  In the formation of the undercoat layer of the release film of the present invention, from the viewpoint of preventing precipitation of the ester cyclic trimer on the film surface and the adhesive layer by heat treatment, and improving the durability and coatability of the undercoat layer, It is possible to use a polymer other than a resin having a crosslinking agent or a styrene structure and a (meth) acrylic acid structure. Among these, it is preferable to use a crosslinking agent in combination in order to prevent precipitation of a higher degree of ester cyclic trimer.

  Various known crosslinking agents can be used as the crosslinking agent, and examples thereof include oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and silane coupling compounds. Among these, an oxazoline compound is preferably used from the viewpoint of improving the appearance of the undercoat layer. A melamine compound is preferably used from the viewpoint of preventing precipitation of the ester cyclic trimer on the film surface by heating and improving the durability of the undercoat layer.

  The oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferable, and can be prepared by polymerization of an addition polymerizable oxazoline group-containing monomer alone or with another monomer. 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, 2-isopropenyl-5-ethyl-2-oxazoline, and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not limited as long as it is a monomer copolymerizable with an addition polymerizable oxazoline group-containing monomer. For example, alkyl (meth) acrylate (the alkyl group includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, (meth) acrylic acid esters such as n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene Unsaturated carboxylic acids such as sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile, methacrylonitrile; (meth) acrylamide, N-alkyl ( (Meth) acrylamide, N, N-dialkyl (meth) acrylamide, As the alkyl group, unsaturated amides such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group and cyclohexyl group); vinyl acetate Vinyl esters such as vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α, β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride And α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and the like, and one or more of these monomers can be used.

  The amount of the oxazoline group of the oxazoline compound contained in the coating solution forming the undercoat layer constituting the laminated polyester film in the present invention is usually 0.5 to 10 mmol / g, preferably 3 to 9 mmol / g, more preferably It is in the range of 5 to 8 mmol / g. By using it in the above range, the durability of the coating film is improved.

  The melamine compound is a compound having a melamine structure in the compound, for example, an alkylolated melamine derivative, a compound partially or completely etherified by reacting an alcohol with an alkylolated melamine derivative, and these Mixtures can be used. As alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used. Moreover, as a melamine compound, either a monomer or a multimer more than a dimer may be sufficient, or a mixture thereof may be used. Further, a product obtained by co-condensing urea or the like with a part of melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

  The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensates of epichlorohydrin with ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A and the like hydroxyl groups and amino groups, There are polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like. Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane. Examples of the polyglycidyl ether and diepoxy compound include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and propylene glycol diglycidyl ether. , Polypropylene glycol diglycidyl ether, poly Examples of tetramethylene glycol diglycidyl ether and monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl amine compounds such as N, N, N ′, N′-tetraglycidyl-m-xylyl. Examples include range amine and 1,3-bis (N, N-diglycidylamino) cyclohexane.

  The isocyanate compound is a compound having an isocyanate derivative structure typified by isocyanate or blocked isocyanate. Examples of isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate, and aromatic rings such as α, α, α ′, α′-tetramethylxylylene diisocyanate. Aliphatic isocyanates such as aliphatic isocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis (4-cyclohexyl isocyanate), isopropylidene dicyclohexyl diisocyanate Ne Alicyclic isocyanates such as bets are exemplified. Further, polymers and derivatives such as burettes, isocyanurates, uretdiones, and carbodiimide modified products of these isocyanates are also included. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to avoid yellowing due to ultraviolet rays.

  When used in the state of blocked isocyanate, the blocking agent includes, for example, bisulfites, phenolic compounds such as phenol, cresol, and ethylphenol, and alcohols such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol. Compounds, active methylene compounds such as methyl isobutanoyl acetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, mercaptan compounds such as butyl mercaptan, dodecyl mercaptan, ε-caprolactam, δ-valerolactam, etc. Lactam compounds, amine compounds such as diphenylaniline, aniline, ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, Examples include oxime compounds such as maldehyde, acetoald oxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

  In addition, the isocyanate compound in the present invention may be used alone, or may be used as a mixture or bond with various polymers. In the sense of improving the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or a bond with a polyester resin or a urethane resin.

  A carbodiimide-based compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule, but for better adhesion, etc., the polycarbodiimide having two or more in the molecule More preferred are system compounds.

  The carbodiimide compound can be synthesized by a conventionally known technique, and generally a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and any of aromatic and aliphatic compounds can be used. Specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexa Examples include methylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

  The content of the carbodiimide group contained in the carbodiimide compound is carbodiimide equivalent (weight of the carbodiimide compound to give 1 mol of carbodiimide group [g]), and is usually 100 to 1000, preferably 250 to 700, more preferably 300. It is in the range of ~ 500. By using it in the above range, the durability of the coating film is improved.

  Furthermore, in order not to lose the effect of the present invention, in order to improve the water solubility and water dispersibility of the polycarbodiimide compound, adding a surfactant, polyalkylene oxide, quaternary ammonium salt of dialkylamino alcohol, You may add and use hydrophilic monomers, such as a hydroxyalkyl sulfonate.

  These cross-linking agents may be used alone or in combination of two or more kinds, but it has been found that the combination of two or more kinds further improves the precipitation prevention property of the ester cyclic trimer after heating. Among them, a combination of a melamine compound and an oxazoline compound is optimal and preferable.

  However, from the viewpoint of not inhibiting the curing reaction of the release layer provided on the undercoat layer, the melamine compound and the oxazoline compound are each preferably used alone, and prevent precipitation of the ester cyclic trimer after heating. Balance is important.

  These cross-linking agents are used in a design that improves the performance of the undercoat layer by reacting in the drying process or the film forming process. It can be inferred that the resulting undercoat layer contains unreacted products of these crosslinking agents, compounds after the reaction, or a mixture thereof.

  When such a crosslinking component is contained, a component for accelerating crosslinking, for example, a crosslinking catalyst can be used in combination.

  Further, the formation of the undercoat layer of the present invention has a styrene structure and a (meth) acrylic acid structure for the purpose of improving the coating appearance and improving the adhesion when an adhesive layer is formed on the undercoat layer. It is also possible to use a polymer other than the resin and the crosslinking agent in combination. However, when the content is increased, the precipitation prevention property of the ester cyclic trimer after heating may be deteriorated.

  Specific examples of the polymer include polyester resin, acrylic resin, urethane resin, polyvinyl (polyvinyl alcohol, etc.), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches and the like. Among these, it is preferable to use a polyester resin, an acrylic resin, and a urethane resin from the viewpoint of improving the durability of the undercoat layer.

  The polyester resin includes, for example, those composed of the following polyvalent carboxylic acid and polyvalent hydroxy compound as main constituent components. That is, as the polyvalent carboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4′-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 2,6 -Naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutar Acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt and ester-forming derivatives thereof can be used. As the polyvalent hydroxy compound, ethylene Recall, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol , Neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol Polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, and the like can be used. One or more compounds may be appropriately selected from these compounds, and a polyester resin may be synthesized by a conventional polycondensation reaction.

  The acrylic resin is a polymer composed of a polymerizable monomer including acrylic and methacrylic monomers. These may be either homopolymers or copolymers, and copolymers with polymerizable monomers other than acrylic and methacrylic monomers. Moreover, the copolymer of these polymers and other polymers (for example, polyester, polyurethane, etc.) is also included. For example, a block copolymer or a graft copolymer. Alternatively, a polymer (possibly a mixture of polymers) obtained by polymerizing a polymerizable monomer in a polyester solution or a polyester dispersion is also included. Similarly, a polymer obtained by polymerizing a polymerizable monomer in a polyurethane solution or a polyurethane dispersion (sometimes a mixture of polymers) is also included. Similarly, a polymer (in some cases, a polymer mixture) obtained by polymerizing a polymerizable monomer in another polymer solution or dispersion is also included. Moreover, in order to improve adhesiveness more, it is also possible to contain a hydroxyl group and an amino group.

  The polymerizable monomer is not particularly limited, but particularly representative compounds include, for example, various carboxyl groups such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid. Monomers, and salts thereof; such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutyl hydroxyl fumarate, monobutyl hydroxy itaconate Various hydroxyl group-containing monomers; various (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate; (Meth) acrylamide, Various nitrogen-containing compounds such as acetone acrylamide, N-methylol acrylamide or (meth) acrylonitrile; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, and various vinyls such as vinyl propionate Esters; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, etc .; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and biridene chloride Various conjugated dienes such as butadiene.

  The urethane resin is a polymer compound having a urethane bond in the molecule. Usually, urethane resin is prepared by reaction of polyol and isocyanate. Examples of the polyol include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

  Polycarbonate polyols are obtained from a polyhydric alcohol and a carbonate compound by a dealcoholization reaction. Examples of the polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane. Diol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decane Diol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like can be mentioned. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate. Examples of polycarbonate polyols obtained from these reactions include poly (1,6-hexylene) carbonate, poly (3- And methyl-1,5-pentylene) carbonate.

  Polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides. Product and polyhydric alcohol (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol 2-methyl-2-propyl-1 3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexane Diol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyl dialkanolamine, lactone diol, etc.).

  Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and the like.

  Among the above polyols, polycarbonate polyols and polyester polyols are more preferably used for improving the film forming property of the undercoat layer.

  Examples of the polyisocyanate compound used for obtaining the urethane resin include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate, α, α, α ′, α ′. -Aliphatic diisocyanates having aromatic rings such as tetramethylxylylene diisocyanate, aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl Methanzi Cyanate, alicyclic diisocyanates such as isopropylidene dicyclohexyl diisocyanates. These may be used alone or in combination.

  A chain extender may be used when synthesizing the urethane resin, and the chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group. Alternatively, a chain extender having two amino groups can be mainly used.

  Examples of the chain extender having two hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol and butanediol, aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene, and esters such as neopentyl glycol hydroxypivalate. And glycols such as glycols. Examples of the chain extender having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine, ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3- Propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10- Aliphatic diamines such as decane diamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isoprobilitincyclohexyl-4,4′-diamine, 1,4-diaminocyclohexane, 1 , 3-Bisaminomethylcyclohexa And alicyclic diamines such as

  The urethane resin in the present invention may use a solvent as a medium, but preferably uses water as a medium. In order to disperse or dissolve the urethane resin in water, there are a forced emulsification type using an emulsifier, a self-emulsification type in which a hydrophilic group is introduced into the urethane resin, and a water-soluble type. In particular, the self-emulsification type in which an ionic group is introduced into the structure of the urethane resin to form an ionomer is preferable because of excellent storage stability of the liquid and water resistance, transparency and adhesion of the resulting undercoat layer.

  Examples of the ionic group to be introduced include various groups such as a carboxyl group, sulfonic acid, phosphoric acid, phosphonic acid, quaternary ammonium salt, and the like, and a carboxyl group is preferable. As a method for introducing a carboxyl group into a urethane resin, various methods can be taken in each stage of the polymerization reaction. For example, there are a method of using a carboxyl group-containing resin as a copolymer component during prepolymer synthesis, and a method of using a component having a carboxyl group as one component such as polyol, polyisocyanate, and chain extender. In particular, a method in which a desired amount of carboxyl groups is introduced using a carboxyl group-containing diol depending on the amount of this component charged is preferred.

  For example, dimethylolpropionic acid, dimethylolbutanoic acid, bis- (2-hydroxyethyl) propionic acid, bis- (2-hydroxyethyl) butanoic acid and the like are copolymerized with a diol used for polymerization of a urethane resin. Can do. The carboxyl group is preferably in the form of a salt neutralized with ammonia, amine, alkali metal, inorganic alkali or the like. Particularly preferred are ammonia, trimethylamine and triethylamine. In such a polyurethane resin, a carboxyl group from which the neutralizing agent has been removed in the drying step after coating can be used as a crosslinking reaction point by another crosslinking agent. Thereby, it is possible to further improve the durability, solvent resistance, water resistance, blocking resistance and the like of the obtained undercoat layer as well as excellent stability in a liquid state before coating.

  Among the above-mentioned polymers, an acrylic resin is particularly preferable from the viewpoint of not inhibiting the precipitation suppression of the ester cyclic trimer.

  In addition, in the formation of the undercoat layer, particles can be used in combination for the purpose of blocking and improving slipperiness. The average particle diameter is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less from the viewpoint of transparency of the film. Further, the lower limit is preferably 0.005 μm or more, more preferably 0.01 μm or more, in order to improve the slipperiness more effectively. Specific examples of the particles include silica, alumina, kaolin, calcium carbonate, and organic particles. Among these, silica is preferable from the viewpoint of transparency.

  Furthermore, as long as it does not impair the gist of the present invention, an undercoating layer is formed as necessary, such as an antifoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant. Agents, foaming agents, dyes, pigments and the like can be used in combination.

  As a ratio with respect to all the non-volatile components in the coating liquid forming the undercoat layer constituting the release film in the present invention, the resin having a styrene structure and a (meth) acrylic acid structure is usually 1% by weight or more, preferably 5 to 5%. The range is 95% by weight, more preferably 10 to 80% by weight, still more preferably 20 to 70% by weight, and particularly preferably 30 to 60% by weight. By using in the said range, it is excellent in the external appearance of an undercoat layer, and precipitation of the ester cyclic | annular trimer after a heating can be suppressed effectively.

  From the viewpoint of preventing precipitation of the ester cyclic trimer after heating and the appearance of the undercoat layer, when using a cross-linking agent, the ratio of the cross-linking agent as a ratio to the total nonvolatile components in the coating solution forming the undercoat layer is: Preferably it is the range of 5-95 weight%, More preferably, it is the range of 15-85 weight%, More preferably, it is the range of 30-70 weight%. When the ratio is out of the above range, precipitation of the ester cyclic trimer after heating cannot be effectively suppressed or the appearance of the undercoat layer may be deteriorated.

  From the viewpoint of preventing precipitation of the ester cyclic trimer after heating, when selecting a melamine compound as one of the crosslinking agents, the ratio of the melamine compound as a ratio to the total nonvolatile components in the coating solution forming the undercoat layer is The range is preferably 3 to 95% by weight, more preferably 15 to 70% by weight, and still more preferably 30 to 65% by weight. When the ratio is within the above range, precipitation of the ester cyclic trimer after heating can be effectively suppressed.

  In the case of selecting an oxazoline compound as one of the crosslinking agents from the viewpoint of the appearance and adhesion of the undercoat layer, the ratio of the oxazoline compound is preferably 3 as a ratio to the total nonvolatile components in the coating liquid forming the undercoat layer. It is the range of -95 weight%, More preferably, it is the range of 10-70 weight%, More preferably, it is the range of 15-35 weight%. When the ratio is within the above range, a result excellent in the appearance of the undercoat layer can be obtained.

  From the viewpoint of improving the durability of the undercoat layer, when a polymer is used in combination, as a ratio to the total nonvolatile components in the coating liquid forming the undercoat layer, other than a resin having a styrene structure and a (meth) acrylic acid structure and a crosslinking agent The proportion of the polymer is usually less than 30% by weight, preferably less than 20% by weight, more preferably less than 10% by weight, and still more preferably not contained. When the ratio is within the above range, the prevention of precipitation of the ester cyclic trimer after heating and the durability of the undercoat layer can be highly compatible.

  Further, the thickness of the undercoat layer is usually in the range of 0.003 μm to 1 μm, preferably 0.005 μm to 0.6 μm, more preferably as the thickness of the undercoat layer on the finally obtained film. It is in the range of 0.01 μm to 0.4 μm. When the thickness is less than 0.003 μm, the amount of ester cyclic trimer precipitated from the film may not be sufficiently reduced. On the other hand, when the thickness is larger than 1 μm, problems such as deterioration of the appearance of the undercoat layer and easy blocking may occur.

  Examples of the method for applying the coating solution to the polyester film that is the substrate of the release film include air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, and transfer roll. Conventionally known coating methods such as coat, gravure coat, kiss roll coat, cast coat, spray coat, curtain coat, calendar coat, and extrusion coat can be used.

  In order to improve the coating property and adhesion of the coating solution to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment or the like before coating.

  With respect to the polyester film that is the base material of the release film in the present invention, for example, for a touch panel, a high degree of transparency may be required even after being exposed to a high temperature atmosphere for a long time. From this viewpoint, in order to cope with a high degree of transparency, the film haze change amount (ΔH) in the heat treatment (180 ° C., 30 minutes) is preferably 1.0% or less, more preferably 0.6% or less. More preferably, it is 0.3% or less. When ΔH exceeds 1.0%, the visibility may decrease as the film haze increases due to precipitation of the ester cyclic trimer.

Further, from the viewpoint of the precipitation amount of the ester cyclic trimer, the ester cyclic trimer extracted from the film surface with dimethylformamide is subjected to heat treatment (180 ° C., 30 minutes) on the polyester film which is the base material of the release film in the present invention. The amount of the monomer is preferably 1.0 mg / m ² or less, more preferably 0.7 mg / m ² or less, and still more preferably 0.4 mg / m ² or less. If it exceeds 1.0 mg / m ² , the amount of ester cyclic trimer deposited increases in the subsequent process, for example, at a high temperature atmosphere such as 180 ° C. for 30 minutes, resulting in increased transparency of the film. May deteriorate and the appearance inspection may be hindered.

  In the present invention, a release layer containing a curable silicone resin is further provided on the undercoat layer of the film obtained as described above. A type having a curable silicone resin as a main component may be used, or a graph with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin and a modified silicone type by polymerization or the like may be used.

  As the type of the curable silicone resin, any of the curing reaction types such as an addition type, a condensation type, an ultraviolet ray curable type, an electron beam curable type, and a solventless type can be used. Among these, in the curing process, an addition type silicone using an addition reaction between a vinyl group and a group having a silicon-hydrogen bond is preferable because it has excellent characteristics such as light release, migration, and low temperature curability.

  As the polyhydrogensiloxane compound which is a crosslinking agent for the cured silicone used in the present invention, a conventionally known compound can be adopted and there is no particular limitation. Examples thereof include polymethyl hydrogen siloxane and polymethyl hydrogen siloxane-polymethyl siloxane copolymer.

  In the addition type silicone used in the present invention, the content ratio (SiH / Vi ratio) of ≡SiH group and vinyl group of siloxane involved in the crosslinking reaction is usually 1.2 to 10, preferably 1.5 to 7. More preferably, it is 2-5.

  Specific examples of the curable silicone resin include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X manufactured by Shin-Etsu Chemical Co., Ltd. -62-2461, DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, manufactured by Dow Corning Asia Co., Ltd., YSR-3022, TPR-6700, TPR-6720, manufactured by Toshiba Silicone Co., Ltd. TPR-6721, Toray Dow Corning Co., Ltd. SD7220, SD7226, SD7229, etc. are mentioned. Further, a release control agent may be used in combination to adjust the release property of the release layer.

  The form of the silicone paint in the present invention is not particularly defined. Examples include a so-called solvent type in which high-viscosity silicone is diluted and applied, a solvent-free type in which low-viscosity silicone is applied as it is, and an aqueous dispersion type in which fine dispersion is performed in an aqueous liquid.

  Among these, a solvent type is preferably used in a release film of a polyester base material in which the coating appearance is particularly important.

  Diluting solvents in this case include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane and heptane, esters such as ethyl acetate and butyl acetate, ethyl methyl ketone (MEK), and isobutyl methyl ketone. Examples thereof include ketones, alcohols such as ethanol and 2-propanol, and ethers such as diisopropyl ether and dibutyl ether, and are used singly or in combination in consideration of solubility, coating property, boiling point and the like.

  The molecular weight of the silicone used in the present invention is not particularly limited, but is selected according to the use form and coating equipment. In the solvent type, a viscosity of 1000 to 100000 (mPa · s), preferably 1000 to 20000 (mPa · s) as a main component is 30% toluene solution. preferable.

  Moreover, in order to adjust the characteristics of the release layer, auxiliary agents such as a reaction modifier, an adhesion enhancer, and a release modifier may be used in combination.

  There are no particular restrictions on the release modifier, but a reactive modifier of the type that reacts with the siloxane polymer of the release coating and is taken in when the coating is dried is preferred because it can suppress migration.

  In the present invention, as a method for providing a release layer on the polyester film, a conventionally known coating method such as reverse roll coating, gravure coating, bar coating, doctor blade coating, or the like can be used.

The coating amount of the release layer in the present invention is usually in the range of 0.01 to 1 g / m ² as a dry film after the release layer is formed. The coating amount of the release layer can be calculated from the weight concentration and coating area of the coating material and the usage amount of the coating material. When the coating amount is less than this, it becomes difficult to obtain uniform release properties, and when it is more than this, problems such as blocking occur.

In addition, the thickness of a mold release layer can also be calculated | required by confirming from a cross section with a transmission electron microscope as mentioned above, and dividing by specific gravity. Generally, the specific gravity of the curable silicone is often about 0.9 to 1.2. When the specific gravity is 1, the coating amount of the release layer having a thickness of 0.1 μm is 0.1 g / m ² .

  In the present invention, the energy source in the curing treatment of the silicone release layer is not particularly limited, and examples thereof include heat treatment, ultraviolet irradiation, and electron beam irradiation. Although these are used alone or in combination, heat treatment alone or combined treatment of heat and ultraviolet light is preferably used.

  The release force of the release film is usually 3 to 50 mN / cm, preferably 5 to 25 mN / cm. When the peeling force is within the above range, problems such as the pressure sensitive adhesive shifting to the release film and the release film floating before use do not occur.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

  In addition, the evaluation method in an Example and a comparative example is as follows.

(1) Method for Measuring Intrinsic Viscosity of Polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C.

(2) Measuring method of average particle size (d50: μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Measuring method of contained ester cyclic trimer contained in polyester raw material:
About 200 mg of the polyester raw material is weighed and dissolved in 2 ml of a mixed solvent having a ratio of chloroform / HFIP (hexafluoro-2-isopropanol) of 3: 2. After dissolution, add 20 ml of chloroform, and then add 10 ml of methanol little by little. The precipitate is removed by filtration, and the precipitate is washed with a mixed solvent of chloroform / methanol ratio 2: 1. The filtrate / washing solution is collected, concentrated by an evaporator, and then dried. After the dried product was dissolved in 25 ml of DMF (dimethylformamide), this solution was supplied to liquid chromatography (“LC-7A” manufactured by Shimadzu Corporation) to determine the amount of ester cyclic trimer in DMF. The value is divided by the amount of the polyester raw material dissolved in the chloroform / HFIP mixed solvent to obtain the amount of ester cyclic trimer (weight%). The amount of ester cyclic trimer 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 the ester cyclic trimer previously collected and dissolving it in accurately measured DMF.

The conditions for the liquid chromatograph were as follows.
Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: “MCI GEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(4) Calculation method of ester cyclic trimer contained in polyester film:
Calculation was based on the amount of ester cyclic trimer contained in the polyester raw material obtained by the method (3).

(5) Method for measuring film thickness of undercoat layer The surface of the coating layer was dyed with RuO ₄ and embedded in an epoxy resin. Thereafter, the section prepared by ultramicrotomy stained with RuO _4, a coating layer cross-section was measured by using a TEM (Hitachi High Technologies Corporation H-7650, accelerating voltage 100 V). The film thickness was measured at a location not including the particle portion.

(6) Heat treatment method of polyester film The sample measurement surface is exposed and fixed by being overlapped with Kent paper, and is left to stand at 180 ° C. for 30 minutes in a nitrogen atmosphere for heat treatment.

(7) Measurement of polyester film haze increase (ΔH) by heat treatment First, the following coating composition is applied to the surface of the polyester film before processing the release layer on the side opposite to the surface provided with the undercoat layer of the present invention. The coating agent consisting of was applied so that the thickness after curing was 3 μm, and dried in a hot air drying oven set at 80 ° C. for 1 minute. Subsequently, it was irradiated with ultraviolet rays and cured to form a hard coat layer.

<< Coating composition >>
Mixing of 80 parts by weight of dipentaerythritol hexaacrylate, 20 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, 5 parts by weight of a photopolymerization initiator (trade name: Irgacure 184, manufactured by Ciba Specialty Chemicals), and 200 parts by weight of methyl ethyl ketone A coating solution was used.
The haze of the obtained sample was measured according to JIS-K-7136 with a haze meter “HM-150” manufactured by Murakami Finger Color Research Laboratory Co., Ltd. (haze 1).
Next, the surface opposite to the active energy ray-curable resin layer of the sample was used as a measurement surface, and after heating by the method of (6), haze was measured by the method described above (haze 2).
ΔH = (haze 2) − (haze 1)
A lower ΔH indicates that less precipitation of the ester cyclic trimer due to the high temperature treatment is better.

(8) Measurement of amount of ester cyclic trimer deposited on the surface of the polyester film The polyester film before processing the release layer is heated in air at 180 ° C. for 30 minutes. Thereafter, the heat-treated film is formed into a box shape with the measurement surface (undercoat layer) as the inner surface so that the upper part is 10 cm in length and width and the height is 3 cm. Next, 4 ml of DMF is placed in the box prepared by the above method and left for 3 minutes, and then DMF is recovered. The recovered DMF was supplied to liquid chromatography (manufactured by Shimadzu Corporation: LC-7A) to determine the amount of ester cyclic trimer in DMF, and this value was divided by the film area in contact with DMF. The amount of ester cyclic trimer precipitated on the film surface (mg / m ² ) was used. The amount of ester cyclic trimer in DMF was calculated according to the absolute calibration curve method described in (3) Method for measuring amount of oligomer contained in polyester raw material.

(9) Adhesive layer optical defect inspection Acrylic adhesive Coponil N-2233 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was applied to the release surface of the release film obtained in the present invention to 3 μm after drying. And an adhesive layer was provided. The release film was attached to the glass plate through this adhesive layer, and then left to stand at 150 ° C. for 1 hour in a nitrogen atmosphere to perform heat treatment. Subsequently, after heating at 80 ° C. for 300 hours, the foreign matter generated in the adhesive layer was examined under an optical microscope. In the inspection, an area of 50 mm × 50 mm was selected from 12 arbitrary positions of the sample, and the number of crystals of the ester cyclic trimer having a size of 5 μm or more was counted. Except for the two locations where the number of crystals was the largest among all the 12 inspection ranges, the following criteria were used to determine from the number of crystals within the 10 inspection ranges.
○: Ester cyclic trimer crystals are not found Δ: Ester cyclic trimer crystals are 1 or more and less than 3 (practically problematic)
X: Three or more crystals of ester cyclic trimer (practical problem)

(10) Evaluation of silicone adhesion-Lab-off test The release surface of the sample film stored for 10 days in a constant temperature and humidity chamber adjusted to an air temperature of 23 ° C and a relative humidity of 50% after coating is unidirectional with the index finger. By rubbing three times, the degree of removal of the release layer was judged by peeling off the adhesive tape at the rubbed portion. If the base material adhesion of silicone is poor, the coating film falls off due to friction, and the peeling of the part becomes heavy.
<Criteria>
○: There was no difference in the peeling force between the rubbed part and the non-rubbed part, and it was able to peel off smoothly.
Δ: Slightly heavier at the rubbed part, but could be peeled off smoothly.
X: It caught on the rubbed part and was not able to peel smoothly.

(11) Measurement of peel force After affixing an adhesive tape (“No. 31B” base material thickness 25 μm, manufactured by Nitto Denko Corporation) to the release surface of the release film obtained in the present invention, a size of 50 mm × 300 mm The peel strength after standing for 1 hour in a measurement atmosphere of 23 ° C. and 50% RH was measured. The peel force was “Intesco Model 2001” manufactured by Intesco Co., Ltd., and 180 ° peeling was performed under the condition of a tensile speed of 0.3 (m / min).

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 part of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.63 and an ester cyclic trimer content of 0.97% by weight.

<Method for producing polyester (B)>
The polyester (A) is pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C., and has an intrinsic viscosity of 0.75 and an ester cyclic trimer content of 0.46% by weight. Polyester (B) was obtained.

<Method for producing polyester (C)>
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 30 ppm of ethyl acid phosphate with respect to the resulting polyester, and 100 ppm of magnesium acetate tetrahydrate with respect to the resulting polyester as the catalyst at 260 ° C. in a nitrogen atmosphere at 260 ° C. The reaction was allowed to proceed. Subsequently, 50 ppm of tetrabutyl titanate was added to the resulting polyester, the temperature was raised to 280 ° C. over 2 hours and 30 minutes, the pressure was reduced to 0.3 kPa in absolute pressure, and melt polycondensation was further carried out for 80 minutes. A polyester (C) having a polyester (A) ester cyclic trimer content of 0.61 and a content of 1.02% by weight was obtained.

<Method for producing polyester (D)>
Polyester (C) was pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 210 ° C., with an intrinsic viscosity of 0.72 and an ester cyclic trimer content of 0.50% by weight. Polyester (D) was obtained.

<Method for producing polyester (E)>
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.5 part of silica particles having an average particle diameter (d50) of 1.6 μm dispersed in ethylene glycol were added. Polyester (E) was obtained using the same method as the production method of polyester 1 except that .04 parts was added and the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.65. The obtained polyester (E) had an intrinsic viscosity of 0.65 and an ester cyclic trimer content of 0.82% by weight.

Moreover, the following was used as a composition contained in the coating liquid which forms an undercoat layer.
(A1): Styrene acrylic copolymer polymerized with the following composition: Styrene acrylic copolymer copolymerized with styrene / acrylic acid = 80/20 (mol%).
(A2): Styrene acrylic copolymer polymerized with the following composition: Styrene acrylic copolymer copolymerized with styrene / acrylic acid / hydroxyethyl acrylamide = 70/20/10 (mol%).

(B1): Hexamethoxymethylol melamine.
(B2): Epocros (made by Nippon Shokubai Co., Ltd.) which is an oxazoline compound. Oxazoline group amount 7.7 mmol / g.
(B3): Epocros (made by Nippon Shokubai Co., Ltd.) which is an oxazoline compound. Oxazoline group amount 4.5 mmol / g.
(B4): Polyglycerol polyglycidyl ether.

(B5): Block polyisocyanate synthesized by the following method.
1000 parts of hexamethylene diisocyanate was stirred at 60 ° C., and 0.1 part of tetramethylammonium capryate was added as a catalyst. After 4 hours, 0.2 part of phosphoric acid was added to stop the reaction, and an isocyanurate type polyisocyanate composition was obtained. 100 parts of the obtained isocyanurate type polyisocyanate composition, 42.3 parts of methoxypolyethylene glycol having a number average molecular weight of 400, and 29.5 parts of propylene glycol monomethyl ether acetate were charged and maintained at 80 ° C. for 7 hours. Thereafter, the reaction solution temperature was kept at 60 ° C., 35.8 parts of methyl isobutanoyl acetate, 32.2 parts of diethyl malonate, and 0.88 part of 28% methanol solution of sodium methoxide were added and kept for 4 hours. Block polyisocyanate obtained by adding 58.9 parts of n-butanol, maintaining the reaction solution temperature at 80 ° C. for 2 hours, and then adding 0.86 part of 2-ethylhexyl acid phosphate.
(B6): Carbodilite (manufactured by Nisshinbo Chemical Co., Ltd.), which is a polycarbodiimide compound. Carbodiimide equivalent 340.

(C1): Aqueous dispersion of acrylic resin polymerized with the following composition: Emulsification weight of ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylol acrylamide / acrylic acid = 65/21/10/2/2 (% by weight) Combined (emulsifier: anionic surfactant)
(C2): Styrene vinyl acetate copolymer polymerized with the following composition: styrene / vinyl acetate copolymerized with styrene / vinyl acetate / 2,2′-azobisisobutyronitrile = 65/35/1 (mol%) Coalescence.
(D1): 2-amino-2-methylpropanol hydrochloride (E1) which is a melamine crosslinking catalyst: silica particles having an average particle size of 0.07 μm

The coating liquid for forming the release layer is prepared as follows.
<Preparation of release agent solution>
Curable silicone resin: KS-847H (manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts by weight Platinum-containing catalyst: catPL-50T (Shin-Etsu Chemical Co., Ltd.) 1 part by weight These are mixed solvents of MEK / toluene / isooctane (mixing weight ratio is 1: 4: 5) to prepare a coating solution having a solid content concentration of 2% by weight.

Example 1:
Polyesters (B) and (E) blended at a weight ratio of 80/20 as the surface layer and polyester (A) alone as the raw material for the intermediate layer were each fed to two extruders and heated to 285 ° C. After heating and melting, the layer A is the outermost layer (surface layer), the layer B is the intermediate layer, and the thickness composition ratio is A / B / A = 2.5 / 45/2 with two types and three layers (A / B / A). The film was coextruded so as to be .5, and cooled and solidified while being in close contact with a mirror-cooled drum having a surface temperature of 45 ° C. by using an electrostatic contact method, thereby preparing an unstretched polyethylene terephthalate film. The film was stretched 3.4 times in the longitudinal direction using the difference in peripheral speed of the roll while passing through a heated roll group at 85 ° C., and then the aqueous coating solution shown in Table 1 below was formed on one side of the longitudinally stretched film. 1 is applied to a tenter stretching machine, stretched 4.0 times in the transverse direction at 100 ° C., further heat treated at 230 ° C., and then subjected to a relaxation treatment of 2% in the transverse direction to form a film of the undercoat layer A biaxially oriented polyethylene terephthalate film having a thickness (after drying) having an undercoat layer of 0.05 μm and a thickness of 50 μm was obtained. Further, the release agent solution was applied to the obtained film by a reverse gravure coating method so that the coating amount after drying was 0.1 g / m ^2, and then dried and heat-treated at 150 ° C. for 30 seconds to obtain a polyester. A release film in which an undercoat layer and a release layer were laminated on the film in order was obtained.

  The film haze increase value by heat treatment of the obtained polyester film was small, and the precipitation amount of the ester cyclic trimer was small and good. Moreover, the rub-off test and peeling force were also favorable, and the performance of the release layer was also satisfactory.

Examples 2-9:
A release film was obtained in the same manner as in Example 1 except that the coating composition was changed to the coating composition shown in Tables 1 and 2 in Example 1. The obtained release film had the characteristics shown in Table 3, and was excellent in that precipitation of crystals of the ester cyclic trimer on the polyester surface and the adhesive layer by heat treatment was suppressed. The release layer performance was also good.

Example 10:
In Example 8, a release film was obtained in the same manner as in Example 8 except that the thickness of the polyester film was changed to 25 μm and the thickness component ratio was changed to A / B / A = 5/15/5. Table 3 shows the properties of the obtained release film.

Example 11:
In Example 8, a release film was obtained in the same manner as in Example 8 except that the thickness of the polyester film was changed to 125 μm and the thickness component ratio was changed to A / B / A = 5/115/5. Table 3 shows the properties of the obtained release film.

Example 12:
Polyester (D) and (E) blended at a weight ratio of 80/20 as the surface layer and polyester (D) alone as the raw material for the intermediate layer were fed to the two extruders, respectively, at 285 ° C. After heating and melting, the layer A is the outermost layer (surface layer), the layer B is the intermediate layer, and the thickness composition ratio is A / B / A = 2.5 / 45/2 with two types and three layers (A / B / A). The film was coextruded so as to be .5, and cooled and solidified while being in close contact with a mirror-cooled drum having a surface temperature of 45 ° C. by using an electrostatic contact method, thereby preparing an unstretched polyethylene terephthalate film. The film was stretched 3.4 times in the longitudinal direction using the difference in peripheral speed of the roll while passing through a heated roll group at 85 ° C., and then the aqueous coating solution shown in Table 1 below was formed on one side of the longitudinally stretched film. 7 is applied to a tenter stretching machine, stretched 4.0 times in the transverse direction at 100 ° C., further heat treated at 230 ° C., and then subjected to a relaxation treatment of 2% in the transverse direction to form a film of the undercoat layer A biaxially oriented polyethylene terephthalate film having a thickness (after drying) having an undercoat layer of 0.05 μm and a thickness of 50 μm was obtained. The release layer was produced in the same manner as in Example 1 to obtain a release film.

Examples 13-17, 21-25 and Reference Examples 1-3 :
(Adjustment of silane coupling agent)
As a silane coupling agent, 3-methacryloyloxypropyltrimethoxysilane (trade name: “KBM-503”, manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared. 70 parts by mass of the silane coupling agent, 14.5 parts by mass of pure water and 14.5 parts by mass of alcohol are put into a stainless steel container, and 1 part by mass of 0.01 mol / liter hydrochloric acid is added while stirring, Stirring was continued in a clean room for 1 hour to obtain a hydrolyzate (molecular weight: 248.4) of a silane coupling agent.

Comparative Example 1:
In Example 1, a release film was obtained in the same manner as in Example 1 except that no undercoat layer was provided. When the release film thus completed was evaluated, precipitation of oligomer crystals by heat treatment was confirmed, and the rub-off test was also deteriorated.

Comparative Example 2:
In Example 8, it manufactured like Example 1 except not providing a mold release layer. When the completed film was evaluated, precipitation of oligomer crystals by heat treatment was suppressed, but the peel strength was poor.

Comparative Examples 3-7:
In Example 1, it manufactured like Example 1 except changing an application agent composition into an application agent composition shown in Table 1, and a release film was obtained. When the completed release film was evaluated, as shown in Table 3, precipitation of oligomer crystals on the polyester surface and the adhesive layer by heat treatment was confirmed.

  The release film of the present invention can be suitably used in applications that undergo a severe heat treatment step that is exposed to a high temperature atmosphere for a long time.

Claims (1)

An undercoat layer and a release layer are sequentially provided on at least one surface of a polyester film, the undercoat layer contains a resin having a styrene structure and a (meth) acrylic acid structure , and an oxazoline compound A release film characterized by being formed by a coating stretching method from a coating solution containing a melamine compound, or both crosslinking agents .