JP6023227B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film in which, for example, oligomers (low molecular weight components of polyester, particularly ester cyclic trimers) are less precipitated even after being exposed to a high temperature.

  Polyester films are excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, etc., and are used in various fields.

  In particular, in recent years, the use for touch panels and the like has increased, and it has come to be used in place of glass as a base material for transparent conductive laminates. As such a transparent conductive laminate, there is one in which a polyester film is used as a base material and an ITO (indium tin oxide) film is formed by sputtering directly or via an anchor layer. As for the polyester film used for this use, what is heat-processed is common.

  As a specific example of the heat processing, for example, it is allowed to stand at 150 ° C. for 1 hour for low thermal shrinkage (Patent Document 1), and heat treatment is performed at 150 ° C. for crystallization of ITO (Patent Document 2). There is processing.

  However, as a problem peculiar to polyester films, when exposed to such high-temperature and long-time treatment, the ester cyclic trimer contained in the film precipitates and crystallizes on the film surface, thereby whitening the film appearance. Visibility degradation due to, defects in post-processing, contamination of the process and members, etc. occur. Therefore, the characteristics of the transparent conductive laminate based on the polyester film cannot be said to be sufficiently satisfactory.

  Further, as a measure for preventing the precipitation of the ester cyclic trimer, for example, it is proposed to provide a curable resin layer made of a crosslinked product of a silicone resin and an isocyanate resin on a polyester film (Patent Document 3). However, the curable resin layer is formed by thermosetting, requires high-temperature treatment for dissociation of the blocking agent of the isocyanate resin, and is in a situation where curling and sagging are likely to occur during processing. Care must be taken in handling.

  Therefore, when taking measures to reduce the amount of ester cyclic trimer deposited by the coating layer, the coating layer itself has better heat resistance and the sealing performance of the ester cyclic trimer of the coating layer itself is better. It is in a situation where it is necessary.

JP 2007-42473 A JP 2007-200823 A JP 2007-320144 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is to suppress, for example, ester cyclic trimers that are precipitated from the film when exposed to high temperatures. An object of the present invention is to provide a laminated polyester film that does not cause problems associated with ester cyclic trimers during processing.

  As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by providing a specific coating layer, and have completed the present invention.

That is, the gist of the present invention is that a resin having a styrene structure and a (meth) acrylic acid structure on at least one surface of a polyester film, and the proportion of the styrene structure is 40 mol% or more, a melamine compound, an oxazoline compound, an epoxy Having a coating layer having a thickness in the range of 0.005 to 0.5 μm formed from a coating solution containing at least one crosslinking agent selected from a compound, an isocyanate-based compound, and a carbodiimide-based compound The feature resides in a laminated polyester film.

  According to the laminated polyester film of the present invention, since the precipitation of the ester cyclic trimer from the surface is suppressed even after high-temperature and long-time treatment, an excellent appearance with no haze increase or generation of foreign matters Can be obtained, and its industrial utility value is high.

  The polyester film constituting the laminated polyester film in the present invention may have a single layer structure or a multilayer structure, and may have four layers or more unless the gist of the present invention is exceeded other than the two-layer or three-layer structure. The above multilayer may be used, and is not particularly limited.

  The base film of the laminated polyester film of the present invention is made of polyester. Such polyester may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred.

  Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyester includes polyethylene terephthalate and the like.

  On the other hand, the dicarboxylic acid component of the copolyester includes isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxybenzoic acid, etc.), etc. 1 type or 2 types or more are mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexane dimethanol, neopentyl glycol, is mentioned.

  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, an antimony compound is preferable because it is inexpensive. 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 transparency of the film becomes high.

  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.

  Precipitation of ester cyclic trimer after heat treatment by designing a layer using a polyester raw material with a low content of ester cyclic trimer in the outermost polyester layer of the polyester film, with a polyester film comprising three or more layers A method of reducing the amount is also possible.

  In the polyester layer of the film of the present invention, particles can be blended mainly for the purpose of imparting slipperiness and preventing scratches in each step. When the particles are blended, the kind of the particles to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness, and specific examples thereof include, for example, silica, calcium carbonate, magnesium carbonate, barium carbonate, sulfuric acid. Examples thereof include inorganic particles such as calcium, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, zirconium oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin. Furthermore, 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.

  Moreover, the average particle diameter of the particles is preferably 5.0 μm or less, and more preferably in the range of 0.01 to 3.0 μm. When the average particle diameter exceeds 5.0 μm, the surface roughness of the film becomes too rough, and problems may occur in various processes in the subsequent steps. Moreover, by using in the said range, haze is restrained low and it is easy to ensure transparency as the whole film.

  Furthermore, the particle content in the polyester layer is preferably less than 5% by weight, more preferably in the range of 0.0003 to 1% by weight, and still more preferably in the range of 0.0005 to 0.5% by weight. When there is no particle, or when the content is low, the transparency of the film becomes high and it becomes a good film, but the slipperiness may be insufficient, so by putting particles in the coating layer, Some ideas, such as improving slipperiness, may be required. In addition, when the particle content is high, haze increases and lacks transparency. For example, during various inspections, defects such as difficulty of defect inspection for foreign matters may occur.

  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 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 to the above-mentioned particles, conventionally known UV absorbers, antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film in the present invention as necessary. Can do.

  The thickness of the polyester film in the present invention is not particularly limited as long as it can be formed as a film, but it is preferably 10 to 300 μm, more preferably 20 to 250 μm.

  As a film forming method of the film of the present invention, a generally known film forming method can be adopted, and there is no particular limitation. For example, when producing a biaxially stretched polyester film, the polyester raw material described above is first melt-extruded from a die using an extruder, and the molten sheet is cooled and solidified with a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in the direction perpendicular to the first-stage stretching direction at usually 70 to 170 ° C. and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, a method of obtaining a biaxially oriented film by performing heat treatment at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% can be mentioned. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In the present invention, the simultaneous biaxial stretching method can be adopted for the production of the polyester film constituting the laminated polyester film. The simultaneous biaxial stretching method is a method in which the above-mentioned unstretched sheet is usually stretched and oriented in the machine direction and the width direction at a temperature controlled normally at 70 to 120 ° C., preferably 80 to 110 ° C. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Next, formation of the coating layer which comprises the laminated polyester film in this invention is demonstrated. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. More preferably, it is formed by in-line 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, coating is performed on either an unstretched sheet obtained by melting and rapid cooling, or a stretched uniaxially stretched film.

  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 coating layer formation can be performed at the same time, so there is an advantage in manufacturing cost. In addition, in order to perform stretching after coating, the thickness of the coating layer can be changed by the stretching ratio. Compared to offline coating, thin film coating can be performed more easily.

  The coating layer of the present invention is a coating solution containing a resin having a styrene structure and a (meth) acrylic acid structure (in the present invention, (meth) acrylic acid represents methacrylic acid or acrylic acid) and a crosslinking agent. It is an essential requirement to have the coating layer on at least one side of the polyester film. The coating solution 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 by 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.

  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 proportion of (meth) acrylic acid 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 10 to 80 mol%, still more preferably 15 to 40 mol%. It is. By using in the said range, precipitation of the ester cyclic trimer by heat processing can be suppressed effectively.

  As the crosslinking agent used for forming the coating layer of the film of the present invention, various known crosslinking agents can be used. For example, melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds Etc. Of these, epoxy compounds, isocyanate compounds, and carbodiimide compounds are preferably used from the viewpoint of suppressing the precipitation of ester cyclic trimers, and the appearance of the coating is improved by further suppressing the precipitation of ester cyclic trimers. From the viewpoint, melamine compounds and oxazoline compounds are preferably used, and melamine compounds are particularly preferable. In the case of using two or more kinds of cross-linking agents, a combination of a melamine compound and an oxazoline compound, a melamine compound and an epoxy compound, or an oxazoline compound and an epoxy compound is preferably used from the viewpoint of suppressing the precipitation of an ester cyclic trimer. Among these, those using a melamine compound in combination are more preferred.

  The melamine compound is a compound having a melamine skeleton in the compound. For example, an alkylolized 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 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 coating 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 5 It is in the range of ˜8 mmol / g. By using in the said range, durability of a coating film improves and it is effective also in prevention of precipitation of the ester cyclic trimer to the film surface by heating.

  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 the 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 dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, mercaptan compounds such as butyl mercaptan and dodecyl mercaptan, lactam compounds such as ε-caprolactam and δ-valerolactam , Amine compounds such as diphenylaniline, aniline, ethyleneimine, acetanilide, acid amide compounds of acetic acid amide, formaldehyde, acetoald Examples include oxime compounds such as 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 used to improve adhesion with various surface functional layers that can be formed on a coating layer and to improve the heat and humidity resistance of the coating layer. is there. 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-based compound is a carbodiimide equivalent (weight of the carbodiimide compound to give 1 mol of carbodiimide group [g]) and is usually 100 to 1000, preferably 250 to 800, more preferably 300. It is in the range of ˜650. By using it in the above range, the durability of the coating film is improved.

  In addition, in the formation of the coating layer of the film of the present invention, it is also possible to use a polymer in combination for the purpose of improving the coating appearance and improving the adhesion when various surface functional layers are formed in the coating layer. is there. However, when used in combination, if the amount is too large, precipitation of the ester cyclic trimer by heat treatment may not be effectively suppressed.

  Specific examples of the polymer include polyester resin, urethane resin, polyvinyl (polyvinyl alcohol, etc.), conductive polymer, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches and the like.

  In addition, particles can be used in combination for the purpose of blocking and improving slipperiness in forming the coating layer. 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 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably a range larger than the film thickness of the coating layer 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 antifoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant are necessary for forming a coating layer. Agents, foaming agents, dyes, pigments and the like can be used in combination.

  As a ratio in the coating layer constituting the laminated polyester 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 10 to 99% by weight, more preferably 20 to 80%. % By weight, more preferably in the range of 30-60% by weight. By using in the said range, precipitation of the ester cyclic | annular trimer on the film surface by heat processing can be suppressed.

  As a ratio in the coating layer which comprises the laminated polyester film in this invention, a crosslinking agent is 1 weight% or more normally, Preferably it is 10 to 99 weight%, More preferably, it is 20 to 80 weight%, More preferably, it is 40 to 70 weight%. % Range. When the amount is less than 1% by weight, precipitation of the ester cyclic trimer by heat treatment cannot be effectively suppressed. By using in the said range, precipitation of the ester cyclic | annular trimer on the film surface by heat processing can be suppressed. When using a melamine compound as a crosslinking agent, it is preferably in the range of 45 to 70% by weight.

  The thickness of the coating layer is preferably in the range of 0.003 to 1 μm, more preferably 0.005 to 0.5 μm, and still more preferably as the thickness of the coating layer on the finally obtained film. The range is 0.01 to 0.20 μm, particularly preferably 0.04 to 0.15 μm. By using in the said range, precipitation of the ester cyclic trimer by heat processing can be suppressed effectively, and an application | coating external appearance and blocking resistance will become favorable.

  Examples of methods for applying a coating solution to a polyester film include air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, and kiss roll coating. Conventional coating methods such as cast coating, spray coating, curtain coating, calendar coating, and extrusion coating can be used.

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

  For the laminated polyester 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 point of view, in order to cope with high transparency, the film haze change amount in heat treatment (150 ° C., 90 minutes) is preferably 1.0% or less, more preferably 0.7% or less, and still more preferably 0.5% or less. When the amount of change in film haze exceeds 1.0%, the visibility decreases as the film haze rises due to the precipitation of the ester cyclic trimer. For example, for a touch panel, a high degree of visibility is required. It may be inappropriate for the application.

Further, from the viewpoint of the precipitation amount of the ester cyclic trimer, the amount of the ester cyclic trimer extracted from the film surface by dimethylformamide by heat treatment (150 ° C., 90 minutes) of the laminated polyester film in the present invention is preferably It is 0.9 mg / m ² or less, more preferably 0.5 mg / m ² or less, and still more preferably 0.2 mg / m ² or less. If it exceeds 0.9 mg / m ² , the amount of ester cyclic trimer deposited increases in the subsequent process, for example, with a long-time heat treatment at 150 ° C. for 90 minutes, etc., and the film becomes transparent. There is a concern that the performance may deteriorate or contamination of the process.

  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 the intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. And dissolved 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 film thickness of coating 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).

(4) Heat treatment method of the film The sample is measured with the measurement surface exposed, and is overlapped with the Kent paper and fixed, and left in a nitrogen atmosphere at 150 ° C. for 90 minutes for heat treatment.

(5) Measuring method of film haze Film haze was measured for the sample film according to JIS-K-7136 with a haze meter “HM-150” manufactured by Murakami Color Research Laboratory.

(6) Method for measuring change in film haze by heat treatment On the surface of the polyester film opposite to the surface provided with the coating layer to be measured, 80 parts by weight of dipentaerythritol hexaacrylate, 2-hydroxy-3-phenoxy A mixed coating solution of 20 parts by weight of propyl acrylate, 5 parts by weight of a photopolymerization initiator (trade name: Irgacure 184, manufactured by Ciba Specialty Chemicals Co., Ltd.) and 200 parts by weight of methyl ethyl ketone was applied so that the dry film thickness was 3 μm. And cured to form a hard coat layer. The haze of the film on which the hard coat layer was formed was measured by the method (5). Subsequently, after heating by the method of (4) term, haze was measured by the method of (5). The difference between the haze after the heat treatment and the haze before the heat treatment was calculated and used as the amount of change in film haze.
The lower the film haze change amount, the less the ester cyclic trimer is precipitated by the high temperature treatment, which is better.

(7) Measurement of amount of ester cyclic trimer deposited on the surface of the laminated polyester film The polyester film is heated in air at 150 ° C. for 90 minutes. Thereafter, the heat-treated film is formed into a box shape with the measurement surface (coating 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 (dimethylsulfoamide) was placed in the box prepared by the above method and allowed to stand for 3 minutes, and then DMF was recovered and subjected to liquid chromatography (manufactured by Shimadzu Corporation: LC-7A, mobile phase A: Acetonitrile, mobile phase B: 2% aqueous acetic acid solution, column: “MCI GEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation, column temperature: 40 ° C., flow rate: 1 ml / min, detection wavelength: 254 nm) The amount of the ester cyclic trimer was determined, and this value was divided by the film area in contact with DMF to obtain the amount of the film surface ester cyclic trimer (mg / m ² ). The 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 pre-sorted ester cyclic trimer and dissolving it in accurately measured DMF.

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 by weight of ethyl acid phosphate to this reaction mixture, 0.04 part by weight 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 intrinsic viscosity of the obtained polyester (A) was 0.63.

<Method for producing polyester (B)>
In the polyester (A) production method, after adding 0.04 part by weight of ethyl acid phosphate, 0.2 part by weight of silica particles having an average particle diameter of 2 μm and 0.04 part by weight of antimony trioxide are added to obtain the intrinsic viscosity. A polyester (B) was obtained using the same method as the production method of the polyester (A) except that the polycondensation reaction was stopped at a time corresponding to 0.65. The obtained polyester (B) had an intrinsic viscosity of 0.65.

Examples of compounds constituting the coating layer are as follows.
Styrene acrylic copolymer (IA): Styrene acrylic copolymer copolymerized with styrene / acrylic acid = 80/20 (mol%) Styrene acrylic copolymer (IB): Styrene / acrylic acid / hydroxyethylacrylamide = Styrene acrylic copolymer / melamine compound (IIA) copolymerized at 70/20/10 (mol%): hexamethoxymethylolmelamine / oxazoline compound (IIB): acrylic polymer having oxazoline group and polyalkylene oxide chain Epocross (oxazoline) Base amount = 4.5 mmol / g, manufactured by Nippon Shokubai Co., Ltd.)
Oxazoline compound (IIC): acrylic polymer having oxazoline group Epocross (Oxazoline group amount = 7.7 mmol / g, manufactured by Nippon Shokubai Co., Ltd.)
・ Epoxy compound (IID): Polyglycerol polyglycidyl ether

Isocyanate compound (IIE): 1000 parts of block polyisocyanate hexamethylene diisocyanate obtained by the following production method 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. 58.9 parts of n-butanol was added and held at a reaction solution temperature of 80 ° C. for 2 hours, and then 0.86 part of 2-ethylhexyl acid phosphate was added to obtain a blocked polyisocyanate.

-Carbodiimide compound (IIF): Polycarbodiimide compound Carbodilite (carbodiimide equivalent = 600, manufactured by Nisshinbo Co., Ltd.)
Particle (III): Silica particles having an average particle size of 0.07 μm Melamine crosslinking catalyst (IV): 2-amino-2-methylpropanol hydrochloride Acrylic resin (VA): ethyl acrylate / n-butyl acrylate / methyl methacrylate Acrylic resin / styrene-vinyl acetate copolymer (VB) copolymerized with / N-methylolacrylamide / acrylic acid = 65/21/10/2/2 (% by weight): Styrene / vinyl acetate / 2,2'- Styrene vinyl acetate copolymer copolymerized with azobisisobutyronitrile = 65/35/1 (mol%)

Example 1:
The mixed raw materials obtained by mixing the polyesters (A) and (B) at a ratio of 90% and 10%, respectively, are used as the outermost layer (surface layer) raw material, and only the polyester (A) is used as the intermediate layer raw material in two extruders. Each is supplied, melted at 285 ° C., and then coextruded in a layer configuration of two types and three layers (surface layer / intermediate layer / surface layer = 1: 8: 1 discharge amount) on a cooling roll set at 40 ° C. Cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the difference in peripheral speed of the roll, and then the coating solution 1 shown in Table 1 below was applied to one side of the longitudinally stretched film, which was led to a tenter. Polyester having a thickness of 50 μm having a coating layer having a thickness of 0.05 μm after being stretched 4.3 times at 110 ° C. in the transverse direction and heat-treated at 235 ° C. and then 2% relaxed in the transverse direction. A film was obtained.

  The amount of change in film haze due to heat treatment of the obtained polyester film was as small as 0.1%, and the amount of precipitation of the ester cyclic trimer was small and good. The properties of this film are shown in Table 2 below.

Examples 2 to 23:
In Example 1, it manufactured similarly to Example 1 except having changed the coating agent composition into the coating agent composition shown in Table 1, and obtained the polyester film. As shown in Table 2, the finished laminated polyester film had a small amount of change in film haze due to the heat treatment, and the amount of precipitation of the ester cyclic trimer was small.

Comparative Example 1:
In Example 1, it manufactured like Example 1 except not providing an application layer, and obtained the polyester film. When the completed laminated polyester film was evaluated, as shown in Table 2, the film haze by heat treatment was greatly increased, and precipitation of the ester cyclic trimer was also large.

Comparative Examples 2-8:
In Example 1, it manufactured similarly to Example 1 except having changed the coating agent composition into the coating agent composition shown in Table 1, and obtained the polyester film. When the finished laminated polyester film was evaluated, the film haze was high, the film haze increased significantly due to heat treatment, and many ester cyclic trimers were precipitated, and contamination due to process and visual recognition due to whitening after heating There was concern about the deterioration of sex.

  The film of the present invention is used for applications that require the performance that the film is exposed to a high temperature atmosphere for a long time, and the increase in film haze is as small as possible and the precipitation of ester cyclic trimer is small even after a severe heat treatment step. The laminated polyester film can be suitably used, for example, as a base material of a transparent conductive laminate.

Claims (2)

A resin having a styrene structure and a (meth) acrylic acid structure on at least one side of the polyester film, and a ratio of the styrene structure of 40 mol% or more, a melamine compound, an oxazoline compound, an epoxy compound, an isocyanate compound, and a carbodiimide A laminated polyester film having a coating layer having a thickness in the range of 0.005 to 0.5 μm, formed from a coating solution containing at least one crosslinking agent selected from a system compound . The laminated polyester film according to claim 1, wherein the amount of change in film haze after heat treatment is 1.0% or less.