Laminated polyester film

Abstract

To provide a laminated polyester film which is highly transparent, has blocking resistance, and is excellent in adhesion to a hard coat layer and adhesion to UV ink.SOLUTION: The laminated polyester film has a coating layer on at least one surface of a polyester film substrate. The coating layer is formed by curing a composition which contains a urethane resin having a polycarbonate structure and having a branched structure, a crosslinking agent, a polyester resin, and particles. The crosslinking agent is a compound having a tri- or higher functional blocked isocyanate group. The NCO equivalent of the blocked isocyanate is 100 or more and 500 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a laminated polyester film. More specifically, it relates to a laminated polyester film having an easily adhering coating layer that is optimal for all fields, including optics, packaging, and labeling.

[0002] Thermoplastic resin films, particularly polyester films, possess excellent mechanical, electrical, dimensional stability, transparency, and chemical resistance properties, making them widely used in magnetic recording materials, packaging materials, solar cells, optical films such as anti-reflective films, diffusion sheets, and prism sheets used in flat displays, and films for label printing. However, when other materials are coated and laminated onto polyester films in these applications, a drawback is that adhesion can be poor depending on the materials used.

[0003] Therefore, one known method for imparting adhesive properties to the surface of a polyester film is to apply various resins to the surface of the polyester film to create a coating layer with easy-adhesion properties.

[0004] Conventionally, techniques have been known for providing easy adhesion to hard coat processing, prism lens processing, etc., by using coating solutions containing copolymerized polyester resin and urethane resin, or coating solutions containing copolymerized polyester resin, urethane resin, and isocyanate compounds, as the coating layer (Patent Documents 1 and 2). However, these conventional techniques had problems such as poor blocking resistance and insufficient adhesion to UV inks (ultraviolet-curing inks) used in label printing.

[0005] Furthermore, a technique was known that uses urethane resin and blocked isocyanate in the coating layer to provide easy adhesion to hard coat processing, particularly used in the manufacture of front sheets for solar cells (Patent Document 3). However, such conventional techniques had the problem of low transparency. On the other hand, a technique for providing easy adhesion to label processing by using an acrylic copolymer and a polymer having an oxazoline group in the coating layer was known (Patent Document 4). However, this conventional technique had the problem of insufficient adhesion to the hard coat layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-229355 [Patent Document 2] Japanese Patent Publication No. 2004-35761 [Patent Document 3] Japanese Patent Publication No. 2016-015491 [Patent Document 4] Japanese Patent Publication No. 2004-082369 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide a laminated polyester film that has high transparency, blocking resistance, and excellent adhesion to hard coat layers and UV inks. [Means for solving the problem]

[0008] In order to solve the above problems, the inventors of the present invention, in the process of investigating the causes of the above problems, found that the problems of the present invention can be solved when a coating layer is provided on at least one surface of a polyester film substrate, and the coating layer is formed by curing a composition containing a crosslinking agent, a polyester resin, and a urethane resin having a polycarbonate structure and a branched structure, and thus the present invention was completed.

[0009] In other words, the present invention consists of the following configuration. 1. A laminated polyester film having a coating layer on at least one surface of a polyester film substrate, wherein the coating layer is formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin. 2. The laminated polyester film according to the first claim, wherein the crosslinking agent is a compound having three or more functional blocked isocyanate groups. 3. The laminated polyester film according to the first or second claim, wherein the urethane resin having a polycarbonate structure and a branched structure is obtained by synthesizing and polymerizing a polycarbonate polyol component and a polyisocyanate component, and the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of polycarbonate polyol component / mass of polyisocyanate component) during the synthesis and polymerization is 0.5 to 3. [Effects of the Invention]

[0010] The laminated polyester film of the present invention has high transparency, blocking resistance, and excellent adhesion to hard coat layers and UV inks. In particular, it exhibits excellent UV ink adhesion during low-dose processing. [Modes for carrying out the invention]

[0011] (Polyester film substrate) In the present invention, the polyester resin constituting the polyester film substrate is polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polytrimethylene terephthalate, etc., as well as a copolymerized polyester resin in which a part of the diol component or dicarboxylic acid component of the above-mentioned polyester resin is replaced with the following copolymer components. For example, the copolymer components can include diol components such as diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, and polyalkylene glycol, and dicarboxylic acid components such as adipic acid, sebatic acid, phthalic acid, isophthalic acid, 5-sodium isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

[0012] In the present invention, the polyester resins suitably used for the polyester film substrate are mainly selected from polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. Among these polyester resins, polyethylene terephthalate is the most preferred in terms of balancing physical properties and cost. Furthermore, the polyester film substrate composed of these polyester resins is preferably a biaxially oriented polyester film, which can improve chemical resistance, heat resistance, mechanical strength, and other properties.

[0013] While there are no particular limitations on the catalyst used for polycondensation in the production of polyester resins, antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. Germanium compounds or titanium compounds are also preferred. More preferred polycondensation catalysts include catalysts containing aluminum and / or its compounds and phenolic compounds, catalysts containing aluminum and / or its compounds and phosphorus compounds, and catalysts containing aluminum salts of phosphorus compounds. Particularly preferred is the use of a catalyst containing aluminum and / or its compounds and phosphorus compounds, which can improve the transparency of the film.

[0014] Furthermore, the polyester film substrate in the present invention is not particularly limited in terms of its layer structure. It may be a single-layer polyester film, a two-layer structure with different components, or a polyester film substrate consisting of at least three layers, including an outer layer and an inner layer.

[0015] (Coated layer) The laminated polyester film of the present invention preferably has a coating layer formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin on at least one side thereof in order to improve adhesion to a hard coat layer, adhesion to UV ink, and blocking resistance. Although it is considered that the coating layer described above has a structure in which a urethane resin or a polyester resin having a polycarbonate structure and a branched structure is crosslinked by a crosslinking agent and is cured, it is difficult to represent the crosslinked chemical structure itself. Therefore, it is expressed that a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin is cured and formed. The coating layer may be provided on both sides of the polyester film, or may be provided on only one side of the polyester film, and a different resin coating layer may be provided on the other side.

[0016] Hereinafter, each composition of the coating layer will be described in detail. (Urethane resin having a polycarbonate structure and a branched structure) The urethane resin having a polycarbonate structure in the present invention preferably has at least a urethane bond portion derived from a polycarbonate polyol component and a polyisocyanate component and a branched structure, and further contains a chain extender as necessary. The branched structure referred to here is preferably introduced by having three or more terminal functional groups of any of the raw material components as described above constituting the molecular chain, and forming a branched molecular chain structure after synthesis and polymerization.

[0017] In the urethane resin having a polycarbonate structure in the present invention, when the number of terminal functional groups in the molecular chain is 3 to 6 due to the branched structure, the resin is stably dispersed in an aqueous solution, and the blocking resistance can be improved, which is preferable.

[0018] When synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention, the lower limit of the mass ratio (mass of polycarbonate polyol component / mass of polyisocyanate component) of the polycarbonate polyol component to the polyisocyanate component is preferably 0.5, more preferably 0.6, still more preferably 0.7, particularly preferably 0.8, and most preferably 1.0. When it is 0.5 or more, it is preferable because the adhesion to UV ink can be improved. The upper limit of the mass ratio of the polycarbonate polyol component to the polyisocyanate component when synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention is preferably 3.0, more preferably 2.2, still more preferably 2.0, particularly preferably 1.7, and most preferably 1.5. When it is 3.0 or less, it is preferable because the blocking resistance can be improved.

[0019] The polycarbonate polyol component used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention preferably contains an aliphatic polycarbonate polyol excellent in heat resistance and hydrolysis resistance. Examples of the aliphatic polycarbonate polyol include aliphatic polycarbonate diols and aliphatic polycarbonate triols, and preferably an aliphatic polycarbonate diol can be used. Examples of the aliphatic polycarbonate diol used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention include one or more diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,8-nonanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol, and carbonates such as dimethyl carbonate, ethylene carbonate, and phosgene. Examples include aliphatic polycarbonate diols obtained by reacting them.

[0020] The number-average molecular weight of the polycarbonate polyol in the present invention is preferably 1000 to 3000. More preferably 1200 to 2900, and most preferably 1500 to 2800. A number-average molecular weight of 1000 or more is preferable because it improves ink adhesion. A number-average molecular weight of 3000 or less is preferable because it improves blocking resistance.

[0021] Examples of polyisocyanates used in the synthesis and polymerization of urethane resins having a polycarbonate structure in the present invention include aromatic aliphatic diisocyanates such as xylylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate and 1,3-bis(isocyanate-methyl)cyclohexane, aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, or polyisocyanates obtained by pre-adding these compounds, either individually or in combination, with trimethylolpropane or the like. When using the aforementioned aromatic aliphatic diisocyanates, alicyclic diisocyanates, or aliphatic diisocyanates, there is no problem of yellowing, which is preferable. Furthermore, the coating film does not become too hard, which is preferable as it can relieve stress due to thermal shrinkage of the polyester film substrate and provides good adhesion.

[0022] Examples of chain extenders include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; diamines such as ethylenediamine, hexamethylenediamine, and piperazine; amino alcohols such as monoethanolamine and diethanolamine; thiodiglycols such as thiodiethylene glycol; or water.

[0023] To form a branched structure in the urethane resin, for example, a method can be preferably employed in which the polycarbonate polyol component, polyisocyanate, and chain extender are reacted at an appropriate temperature and time, and then a compound having three or more functional hydroxyl groups or isocyanate groups is added to further allow the reaction to proceed.

[0024] Specific examples of compounds having three or more functional hydroxyl groups include caprolactone triol, glycerol, trimethylolpropane, butanetriol, hexanetriol, 1,2,3-hexanetriol, 1,2,3-pentanetriol, 1,3,4-hexanetriol, 1,3,4-pentanetriol, 1,3,5-hexanetriol, 1,3,5-pentanetriol, and polyethertriol. Examples of the aforementioned polyethertriol include compounds obtained by addition polymerization of one or more monomers such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, glycidyl ether, methylglycidyl ether, t-butylglycidyl ether, and phenylglycidyl ether, using one or more compounds having three active hydrogen atoms, such as glycerin, alcohols like trimethylolpropane, and diethylenetriamine, as initiators.

[0025] Specific examples of compounds having three or more functional isocyanate groups include polyisocyanate compounds having at least three isocyanate (NCO) groups in one molecule. In the present invention, examples of three or more functional isocyanate compounds include burettes, nurates, and adducts obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, aromatic aliphatic diisocyanates, and alicyclic diisocyanates, which have two isocyanate groups. Examples of aromatic diisocyanates include 1,3-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,4-phenylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-toluidinediisocyanate, dianisidinediisocyanate, and 4,4'-diphenyletherdiisocyanate. Examples of aliphatic diisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate. Examples of aromatic aliphatic diisocyanates include xylylene diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate. Alicyclic diisocyanates include, for example, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI or isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane. A biuret compound is a self-condensate having a biuret bond formed by the self-condensation of isocyanate monomers. Examples include the biuret compound of hexamethylene diisocyanate. Nurates are trimers of isocyanate monomers, such as the trimer of hexamethylene diisocyanate, the trimer of isophorone diisocyanate, and the trimer of tolylene diisocyanate. Adduct compounds are isocyanate compounds with three or more functions obtained by reacting the above-mentioned isocyanate monomer with a low-molecular-weight active hydrogen-containing compound with three or more functions. Examples include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate, compounds obtained by reacting trimethylolpropane with tolylene diisocyanate, compounds obtained by reacting trimethylolpropane with xylylene diisocyanate, and compounds obtained by reacting trimethylolpropane with isophorone diisocyanate.

[0026] Chain extenders having three or more functional groups include trimethylolpropane, as described above, and alcohols having three or more hydroxyl groups, such as pentaerythritol.

[0027] In the present invention, the coated layer is preferably provided using an aqueous coating solution by the in-line coating method described later. Therefore, it is desirable that the urethane resin of the present invention be water-soluble or water-dispersible. The above-mentioned "water-soluble or water-dispersible" means that it is dispersed in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.

[0028] To impart water dispersibility to urethane resin, sulfonic acid (salt) groups or carboxylic acid (salt) groups can be introduced (copolymerized) into the urethane molecular backbone. To maintain moisture resistance, it is preferable to introduce weakly acidic carboxylic acid (salt) groups. Nonionic groups such as polyoxyalkylene groups can also be introduced.

[0029] To introduce carboxylic acid (salt) groups into urethane resin, for example, a polyol compound having carboxylic acid groups, such as dimethylolpropanoic acid or dimethylolbutanoic acid, is introduced as a copolymer component and neutralized with a salt-forming agent. Specific examples of salt-forming agents include ammonia, trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine, N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine, and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These can be used individually or in combination of two or more.

[0030] When a polyol compound having a carboxylic acid (salt) group is used as a copolymer component to impart water dispersibility, the molar ratio of the polyol compound having a carboxylic acid (salt) group in the urethane resin is preferably 3 to 60 mol%, and more preferably 5 to 40 mol%, when the total polyisocyanate component of the urethane resin is considered to be 100 mol%. A molar ratio of 3 mol% or more is preferable because it provides water dispersibility. Furthermore, a molar ratio of 60 mol% or less is preferable because it maintains water resistance and provides resistance to humid heat.

[0031] The urethane resin of the present invention may have a blocked isocyanate structure at its ends to improve its rigidity.

[0032] (Crosslinking agent) In the present invention, a blocked isocyanate is preferred as the crosslinking agent contained in the coating layer-forming composition, a trifunctional or higher blocked isocyanate is more preferred, and a tetrafunctional or higher blocked isocyanate is particularly preferred. These improve blocking resistance and adhesion to the hard coat layer.

[0033] The lower limit of the NCO equivalent of the blocked isocyanate is preferably 100, more preferably 120, even more preferably 130, particularly preferably 140, and most preferably 150. An NCO equivalent of 100 or more is preferable as it reduces the risk of coating cracking. The upper limit of the NCO equivalent is preferably 500, more preferably 400, even more preferably 380, particularly preferably 350, and most preferably 300. An NCO equivalent of 500 or less is preferable as it maintains blocking resistance.

[0034] The lower limit of the boiling point of the blocking agent, the blocked isocyanate, is preferably 150°C, more preferably 160°C, even more preferably 180°C, particularly preferably 200°C, and most preferably 210°C. The higher the boiling point of the blocking agent, the more effectively the volatilization of the blocking agent is suppressed by the heat applied during the drying process after coating the coating solution or, in the case of the in-line coating method, during the film formation process. This suppresses the occurrence of minute surface irregularities on the coated surface and improves the transparency of the film. There is no particular upper limit to the boiling point of the blocking agent, but from the viewpoint of productivity, it is thought that the upper limit is around 300°C. Since the boiling point is related to the molecular weight, it is preferable to use a blocking agent with a large molecular weight in order to raise the boiling point of the blocking agent. The molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and even more preferably 80 or more.

[0035] The upper limit of the dissociation temperature of the blocking agent is preferably 200°C, more preferably 180°C, even more preferably 160°C, particularly preferably 150°C, and most preferably 120°C. The blocking agent dissociates from the functional groups due to the heat added during the drying process after application of the coating solution or, in the case of the in-line coating method, during the film formation process, generating regenerated isocyanate groups. As a result, the crosslinking reaction with urethane resin and the like proceeds, improving adhesion. When the dissociation temperature of the blocked isocyanate is below the above temperature, the dissociation of the blocking agent proceeds sufficiently, resulting in good adhesion, especially resistance to heat and humidity.

[0036] Examples of blocking agents used in the blocked isocyanates of the present invention that have a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher include: bisulfite compounds: such as sodium bisulfite; pyrazole compounds: such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole; active methylene compounds: such as malonic acid diesters (dimethyl malonate, diethyl malonate, di-n-butyl malonate, di-2-ethylhexyl malonate), methyl ethyl ketone, etc.; and triazole compounds: such as 1,2,4-triazole. Among these, pyrazole compounds are preferred in terms of resistance to humid heat and yellowing.

[0037] The trifunctional or more polyisocyanates, which are precursors to the blocked isocyanates of the present invention, can be suitably obtained by introducing isocyanate monomers. Examples include bilets, nurates, and adducts obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, aromatic aliphatic diisocyanates, or alicyclic diisocyanates having two isocyanate groups. A biuret compound is a self-condensate having a biuret bond formed by the self-condensation of isocyanate monomers. Examples include the biuret compound of hexamethylene diisocyanate. Nurates are trimers of isocyanate monomers, such as the trimer of hexamethylene diisocyanate, the trimer of isophorone diisocyanate, and the trimer of tolylene diisocyanate. Adduct compounds are isocyanate compounds with three or more functions, obtained by reacting an isocyanate monomer with a low-molecular-weight active hydrogen-containing compound with three or more functions. Examples include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate, trimethylolpropane with tolylene diisocyanate, trimethylolpropane with xylylene diisocyanate, and trimethylolpropane with isophorone diisocyanate.

[0038] The aforementioned isocyanate monomers include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4′-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4′-diisocyanate, 2,2′-diphenylpropane-4,4′-diisocyanate, and 3,3′ Examples include aromatic diisocyanates such as -dimethyldiphenylmethane-4,4′-diisocyanate, 4,4′-diphenylpropanediisocyanate, and 3,3′-dimethoxydiphenyl-4,4′-diisocyanate; aromatic aliphatic diisocyanates such as xylylenediisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethanediisocyanate, and 1,3-bis(isocyanate-methyl)cyclohexane; hexamethylene diisocyanate; and aliphatic diisocyanates such as 2,2,4-trimethylhexamethylenediisocyanate. From the viewpoint of transparency, adhesion, and resistance to moisture and heat, aliphatic and alicyclic isocyanates and their modified forms are preferred, and are preferred for optical applications where high transparency without yellowing is required.

[0039] In the present invention, the blocked isocyanate can be made water-soluble or water-dispersible by introducing hydrophilic groups into the precursor polyisocyanate. Examples of hydrophilic groups include (1) quaternary ammonium salts of dialkylamino alcohols and quaternary ammonium salts of dialkylaminoalkylamines, (2) sulfonates, carboxylates, phosphates, etc., and (3) polyethylene glycol and polypropylene glycol with one end sealed by an alkyl group. When hydrophilic moieties are introduced, the properties become (1) cationic, (2) anionic, or (3) nonionic. Among these, anionic and nonionic properties are preferred because many other water-soluble resins are anionic, allowing for easy compatibility. Furthermore, anionic properties offer excellent compatibility with other resins, and nonionic properties are preferred for improving heat and humidity resistance because they do not have ionic hydrophilic groups.

[0040] As anionic hydrophilic groups, those having a hydroxyl group for introduction into the polyisocyanate and a carboxylic acid group for imparting hydrophilicity are preferred. Examples include glycolic acid, lactic acid, tartaric acid, citric acid, oxybutyric acid, oxyvaleric acid, hydroxypivalic acid, dimethylolacetic acid, dimethylolpropanoic acid, dimethylolbutanoic acid, and polycaprolactone having a carboxylic acid group. Organic amine compounds are preferred for neutralizing the carboxylic acid group. Examples include linear, branched, primary, secondary, or tertiary amines having 1 to 20 carbon atoms, such as ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, and ethylenediamine; cyclic amines such as morpholine, N-alkylmorpholine, and pyridine; and hydroxyl-containing amines such as monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, and triethanolamine.

[0041] The nonionic hydrophilic group preferably has 3 to 50 repeating units of ethylene oxide and / or propylene oxide of polyethylene glycol or polypropylene glycol, which are one-ended with an alkyl group, and more preferably 5 to 30. If the repeating units are small, the compatibility with the resin will be poor and the haze will increase, and if they are large, the adhesion under high temperature and high humidity conditions may decrease. Nonionic, anionic, cationic, and amphoteric surfactants can be added to the blocked isocyanate of the present invention to improve its water dispersibility. Examples include nonionic surfactants such as polyethylene glycol and polyhydric alcohol fatty acid esters, anionic surfactants such as fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, sulfosuccinates, and alkyl phosphates, cationic surfactants such as alkylamine salts and alkyl betaines, and surfactants such as carboxylic acid amine salts, sulfonic acid amine salts, and sulfate ester salts.

[0042] Furthermore, the mixture can contain water-soluble organic solvents other than water. For example, the organic solvent used in the reaction can be removed, and another organic solvent can be added.

[0043] (Polyester resin) The polyester resin used to form the coating layer in the present invention may be linear, but more preferably it is a polyester resin composed of a dicarboxylic acid and a branched diol. The dicarboxylic acid referred to here may be terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid as its main component, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. Furthermore, branched glycols are diols having branched alkyl groups, and examples include 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol.

[0044] In the polyester resin, the branched glycol component, which is the more preferred embodiment described above, is preferably contained in a proportion of 10 mol% or more, and more preferably 20 mol% or more, within the total glycol component. If it is 10 mol% or less, the crystallinity will increase, and the adhesion of the coated layer may decrease. The upper limit of the glycol component within the total glycol component is preferably 80 mol% or less, and more preferably 70% by mass. If it is 80 mol% or more, the concentration of oligomers, which are by-products, will increase, and this may affect the transparency of the coated layer. Among glycol components other than the above compounds, ethylene glycol is the most preferred. In small amounts, diethylene glycol, propylene glycol, butanediol, hexanediol, or 1,4-cyclohexanedimethanol may also be used.

[0045] The most preferred dicarboxylic acid as a component of the above-mentioned polyester resin is terephthalic acid or isophthalic acid. In addition to the above-mentioned dicarboxylic acid, it is preferable to copolymerize 5-sulfoisophthalic acid or the like in the range of 1 to 10 mol% in order to impart water dispersibility to the copolymerized polyester resin. Examples include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid. A polyester resin containing a dicarboxylic acid having a naphthalene skeleton may be used, but in order to suppress a decrease in adhesion to UV ink, the quantitative proportion of the dicarboxylic acid is preferably 5 mol% or less of the total carboxylic acid component, and it may not be necessary to use it.

[0046] When the total solid content of the polyester resin, the urethane resin having a polycarbonate structure, and the crosslinking agent in the coating solution is 100% by mass, the lower limit of the crosslinking agent content is preferably 5% by mass, more preferably 7% by mass, even more preferably 10% by mass, and most preferably 12% by mass. A content of 5% by mass or more is preferable as it improves blocking resistance. The upper limit of the crosslinking agent content is preferably 50% by mass, more preferably 40% by mass, even more preferably 35% by mass, and most preferably 30% by mass. A content of 50% by mass or less is preferable as it increases transparency.

[0047] When the total solid content of the polyester resin, urethane resin having a polycarbonate structure, and crosslinking agent in the coating solution is 100% by mass, the lower limit of the content of the urethane resin having a polycarbonate structure is preferably 5% by mass. A content of 5% by mass or more is preferable as it improves adhesion to UV ink. The upper limit of the content of the urethane resin having a polycarbonate structure is preferably 50% by mass, more preferably 40% by mass, even more preferably 30% by mass, and most preferably 20% by mass. A urethane resin content of 50% by mass or less is preferable as it improves blocking resistance.

[0048] When the total solid content of polyester resin, urethane resin, and crosslinking agent in the coating solution is 100% by mass, the lower limit of the polyester resin content is preferably 10% by mass, more preferably 20% by mass, even more preferably 30% by mass, particularly preferably 35% by mass, and most preferably 40% by mass. A polyester resin content of 10% by mass or more is preferable because it results in good adhesion between the coating layer and the polyester film substrate. The upper limit of the polyester resin content is preferably 70% by mass, more preferably 67% by mass, even more preferably 65% ​​by mass, particularly preferably 62% by mass, and most preferably 60% by mass. A polyester resin content of 70% by mass or less is preferable because it results in good moisture and heat resistance of the hard coat film after hard coat processing.

[0049] (Additives) In the coating layer of the present invention, known additives such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc., may be added, as long as they do not impair the effects of the present invention.

[0050] In the present invention, it is also preferable to add particles to the coating layer in order to further improve the blocking resistance of the coating layer. Examples of particles to be contained in the coating layer in the present invention include titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof, as well as other general inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., used in combination with other inorganic particles, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

[0051] The average particle size of the particles in the coating layer (average particle size based on the number of particles measured by a scanning electron microscope (SEM); the same applies hereinafter) is preferably 0.04 to 2.0 μm, and more preferably 0.1 to 1.0 μm. An average particle size of 0.04 μm or more for inert particles is preferable because it facilitates the formation of irregularities on the film surface, improving handling properties such as film slipperiness and windability, and resulting in good processability during lamination. On the other hand, an average particle size of 2.0 μm or less for inert particles is preferable because particle shedding is less likely to occur. The particle concentration in the coating layer is preferably 1 to 20% by mass of the solid components.

[0052] The average particle size was measured by observing the particles in the cross-section of a laminated polyester film using a scanning electron microscope, observing 30 particles, and using the average value of these observations as the average particle size.

[0053] The shape of the particles is not particularly limited as long as it satisfies the objectives of the present invention, and spherical particles or irregularly shaped non-spherical particles can be used. The particle size of irregularly shaped particles can be calculated as the equivalent diameter of a circle. The equivalent diameter of a circle is obtained by dividing the area of ​​the observed particle by π, calculating the square root, and multiplying by 2.

[0054] (Manufacturing of laminated polyester film) The method for producing the laminated polyester film of the present invention will be explained using an example with a polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film substrate, but it is not limited to this.

[0055] After thoroughly vacuum-drying the PET resin, it is supplied to an extruder, and the molten PET resin at approximately 280°C is melt-extruded from the T-die onto a rotating cooling roll in a sheet shape. The molten PET resin is then cooled and solidified by electrostatic application to obtain an unstretched PET sheet. The unstretched PET sheet may be a single-layer structure or a multi-layer structure obtained by co-extrusion.

[0056] The obtained unstretched PET sheet is subjected to uniaxial or biaxial stretching to achieve crystal orientation. For example, in the case of biaxial stretching, the sheet is stretched 2.5 to 5.0 times in the longitudinal direction on a roll heated to 80 to 120°C to obtain a uniaxially oriented PET film. Then, the ends of the film are held with clips and guided into a hot air zone heated to 80 to 180°C, where it is stretched 2.5 to 5.0 times in the width direction. In the case of uniaxial stretching, it is stretched 2.5 to 5.0 times in a tenter. After stretching, it is then guided into a heat treatment zone and heat treatment is performed to complete the crystal orientation.

[0057] The lower limit of the heat treatment zone temperature is preferably 170°C, and more preferably 180°C. A temperature of 170°C or higher in the heat treatment zone is preferable because it ensures sufficient curing and good blocking properties in the presence of liquid water, eliminating the need for a longer drying time. On the other hand, the upper limit of the heat treatment zone temperature is preferably 230°C, and more preferably 200°C. A temperature of 230°C or lower in the heat treatment zone is preferable because it does not risk degrading the physical properties of the film.

[0058] The coating layer can be formed after the film is manufactured or during the manufacturing process. In particular, from the viewpoint of productivity, it is preferable to apply the coating solution to at least one side of the PET film after it has been unstretched or uniaxially stretched, thereby forming the coating layer.

[0059] Any known method can be used to apply this coating solution to the PET film. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, and the like. These methods can be used individually or in combination.

[0060] In the present invention, the thickness of the coating layer can be appropriately set within the range of 0.001 to 2.00 μm, but to achieve both processability and adhesion, the range of 0.01 to 1.00 μm is preferable, more preferably 0.02 to 0.80 μm, and even more preferably 0.05 to 0.50 μm. A coating layer thickness of 0.001 μm or more is preferable because it provides good adhesion. A coating layer thickness of 2.00 μm or less is preferable because it is less likely to cause blocking.

[0061] The upper limit of the haze of the laminated polyester film of the present invention is preferably 1.5%, more preferably 1.3%, even more preferably 1.2%, and particularly preferably 1.0%. A haze of 1.5% or less is preferable in terms of transparency, and can be suitably used in optical films where transparency is required. The lower the haze, the better; ideally, 0% is the most preferable, but 0.1% or more is also acceptable, and 0.3% or more is also practically acceptable. [Examples]

[0062] Next, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the following examples. First, the evaluation method used in the present invention will be described below.

[0063] (1) Hayes The haze of the obtained laminated polyester film was measured in accordance with JIS K 7136:2000 using a turbidimeter (NDH5000, manufactured by Nippon Denshoku).

[0064] (2) Blocking resistance Two film samples were placed on top of each other with their coated surfaces facing each other, a load of 98 kPa was applied, and they were left in contact for 24 hours in a 50°C atmosphere. After that, the films were peeled off, and the peeling state was judged according to the following criteria. ○: The coating layer does not shift and can be easily peeled off. △: The coating layer is maintained, but the surface layer of the coating layer has partially transferred to the mating surface. ×: Two films are stuck together and cannot be separated, or even if they can be separated, the film substrate is cleaved.

[0065] (3) Adhesion with UV ink On the coated layer of a laminated polyester film, UV ink [manufactured by T&K TOKA Co., Ltd., product name "BEST CURE UV161 Indigo S"] was used to print on a printing press [manufactured by Akira Seisakusho Co., Ltd., product name "RI Tester"], and then a high-pressure mercury lamp was used to apply 40 mJ / cm² to the film coated with the ink layer. 2 The UV-curing ink was cured by irradiating it with ultraviolet light. Next, 100 grid-like cuts were made on the ink layer surface using a cutter guide with a 2mm gap between the cuts, penetrating the ink layer and reaching the film substrate. Then, cellophane adhesive tape (Nichiban, No. 405; 24mm wide) was applied to the grid-like cut surface and rubbed with an eraser to ensure complete adhesion. After that, the cellophane adhesive tape was peeled vertically from the ink layer surface of the ink-laminated film, and the number of grids that peeled off from the ink layer surface of the ink-laminated film was visually counted. The adhesion between the ink layer and the film substrate was then calculated using the following formula. Note that grids that are only partially peeled off are also counted as peeled off. An ink adhesion of 100% is considered acceptable. Ink adhesion (%) = 100 - (number of peeled squares)

[0066] (4) Adhesion to the hard coat layer A hard coat layer forming solution with the following composition was applied to the coated layer of a laminated polyester film using a #5 wire bar, dried at 80°C for 1 minute, and the solvent was removed. Then, the film with the hard coat layer was subjected to a high-pressure mercury lamp at 300 mJ / cm². 2 A hard coat film was obtained by irradiating it with ultraviolet light. (Coating solution for forming a hard coat layer) Methyl ethyl ketone 36.00% by mass Toluene 18.00% by mass Cyclohexanone 6.00% by mass Urethane acrylate 40.00% by mass (BS577, manufactured by Arakawa Chemical Co., Ltd.) Surfactant 0.10% by mass Photopolymerization initiator 2.00% by mass (Irgacure 184, manufactured by Ciba Specialty Chemicals) Next, using a cutter guide with a 2mm gap, 100 grid-like cuts are made on the hard coat layer surface, penetrating the hard coat layer and reaching the film substrate. Then, cellophane adhesive tape (Nichiban, No. 405; 24mm wide) is applied to the grid-like cut surface and rubbed with an eraser to ensure complete adhesion. After that, the cellophane adhesive tape is peeled vertically from the hard coat layer surface of the hard coat laminate film, and the number of grids that have peeled off is visually counted. The adhesion between the hard coat layer and the film substrate is then calculated using the following formula. Note that grids that are only partially peeled off are also counted as peeled grids. A hard coat adhesion of 95% is considered acceptable. Hard court adhesion (%) = 100 - (number of peeled squares)

[0067] (Manufacturing of polyester pellets P-1) High-purity terephthalic acid and twice its molar volume of ethylene glycol were charged into a 2-liter stainless steel autoclave equipped with a stirrer. 0.3 mol% triethylamine was added relative to the acid component, and the esterification reaction was carried out at 250°C under a pressure of 0.25 MPa while distilling off water from the system to obtain a mixture of bis(2-hydroxyethyl) terephthalate and oligomer (hereinafter referred to as the BHET mixture) with an esterification rate of approximately 95%. Next, while stirring the BHET mixture, an ethylene glycol solution of antimony trioxide was added as a polymerization catalyst, so that the amount of antimony atoms relative to the acid component in the polyester was 0.04 mol%. The mixture was then stirred at 250°C for 10 minutes under atmospheric pressure and a nitrogen atmosphere. Subsequently, the temperature was raised to 280°C over 60 minutes while gradually lowering the pressure of the reaction system to 13.3 Pa (0.1 Torr), and a polycondensation reaction was carried out at 280°C and 13.3 Pa. Following the release of pressure, the resin was extruded in strand form into cold water under slight pressure and rapidly cooled. After being held in the cold water for 20 seconds, it was cut to obtain cylindrical pellets approximately 3 mm in length and 2 mm in diameter.

[0068] Polyester pellets obtained by melt polymerization were dried under reduced pressure (13.3 Pa or less, 80°C, 12 hours), followed by crystallization treatment (13.3 Pa or less, 130°C, 3 hours, and then 13.3 Pa or less, 160°C, 3 hours). After cooling, these polyester pellets were subjected to solid-phase polymerization in a solid-phase polymerization reactor while maintaining the system temperature at 13.3 Pa or less and 215°C to obtain polyester pellets P-1 with an intrinsic viscosity (solvent: phenol / tetrachloroethane = 60 / 40) of 0.62 dl / g.

[0069] (Preparation of aluminum compounds) A 20 g / l aqueous solution of basic aluminum acetate (hydroxyaluminum diacetate; manufactured by Aldrich), prepared by heat treatment at 80°C for 2 hours under stirring, and in which the peak position of the 27Al-NMR spectrum was confirmed to have chemically shifted to the lower magnetic field side, was charged with an equal volume (volume ratio) of ethylene glycol in a flask. After stirring at room temperature for 6 hours, water was distilled off from the system under reduced pressure (133 Pa) at 90-110°C for several hours while stirring to prepare a 20 g / l ethylene glycol solution of the aluminum compound.

[0070] (Preparation of phosphorus compounds) Irganox 1222 (manufactured by Ciba Specialty Chemicals), represented by [Chemical Formula 39], was charged into a flask with ethylene glycol. The mixture was heated at 160°C for 25 hours under nitrogen purging with stirring to prepare a 50 g / l ethylene glycol solution of the phosphorus compound. 31P-NMR spectroscopy confirmed that approximately 60 mol% of the phosphorus compound had been converted to hydroxyl groups. (Preparation of a mixture of aluminum compound ethylene glycol solution and phosphorus compound ethylene glycol solution) The ethylene glycol solutions obtained from the preparation of the aluminum compound and the phosphorus compound were placed in flasks and mixed at room temperature so that the molar ratio of aluminum atoms to phosphorus atoms was 1:2. The mixture was then stirred for one day to prepare the catalyst solution. Chemical shifts were observed in the 27Al-NMR spectrum and 31P-NMR spectra of the mixed solution in both cases.

[0071] (Manufacturing of polyester pellets P-2) The same procedure as for the production of polyester pellet P-1 was followed, except that a mixture of the above-mentioned "ethylene glycol solution of aluminum compound / ethylene glycol solution of phosphorus compound" was used as the polycondensation catalyst, and added to the polyester in the same amounts as aluminum atoms and phosphorus atoms (0.014 mol% and 0.028 mol%, respectively) relative to the acid component. A polyester pellet P-2 with an intrinsic viscosity (solvent: phenol / tetrachloroethane = 60 / 40) of 0.65 dl / g was obtained.

[0072] (5) Method for measuring the number-average molecular weight of polycarbonate polyols When a urethane resin with a polycarbonate structure is measured by proton nuclear magnetic resonance spectroscopy (1H-NMR), a peak originating from a methylene group adjacent to the OCOO bond is observed around 4.1 ppm. Furthermore, at a magnetic field approximately 0.2 ppm higher than this peak, a peak originating from a methylene group adjacent to the urethane bond formed by the reaction between polyisocyanate and polycarbonate polyol is observed. The number-average molecular weight of the polycarbonate polyol was calculated from the integral values ​​of these two peaks and the molecular weights of the monomers constituting the polycarbonate polyol.

[0073] (Polymerization of urethane resin A-1 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 27.5 parts by mass of hydrogenated m-xylylene diisocyanate, 6.5 parts by mass of dimethylolpropanoic acid, 61 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 1800, 5 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 2.2 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution reached the predetermined amine equivalent. After the reaction solution was cooled to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, in a reaction vessel equipped with a homodisperser capable of high-speed stirring, 450 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 min. -1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-1) with a solid content of 34% by mass was prepared by removing some of the acetone and water.

[0074] (Polymerization of urethane resin A-2 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 25 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 5 parts by mass of dimethylolpropanoic acid, 52 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2600, 6 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 10 parts by mass of a polyisocyanate compound having an isocyanurate structure (manufactured by Asahi Kasei Chemicals, Duranate TPA, trifunctional) derived from hexamethylene diisocyanate was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Subsequently, the reaction solution temperature was lowered to 50°C, and 4 parts by mass of methyl ethyl ketoxime were added dropwise. After cooling the reaction solution to 40°C, 5.17 parts by mass of triethylamine were added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C. The polyurethane prepolymer solution was then added and dispersed in water while stirring for 2000 min⁻¹. Subsequently, a water-dispersible urethane resin solution (A-2) with a solid content of 35% by mass was prepared by removing some of the acetone and water under reduced pressure.

[0075] (Polymerization of urethane resin A-3 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 22 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 20 parts by mass of polyethylene glycol monomethyl ether with a number average molecular weight of 700, 53 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2100, 5 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 75°C under a nitrogen atmosphere for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 9 parts by mass of a polyisocyanate compound having an isocyanurate structure (manufactured by Asahi Kasei Chemicals, Duranate TPA, trifunctional) derived from hexamethylene diisocyanate was added, and the mixture was stirred at 75°C under a nitrogen atmosphere for 1 hour, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Subsequently, the reaction solution temperature was lowered to 50°C, and 4 parts by mass of methyl ethyl ketoxime were added dropwise. After cooling the reaction mixture to 40°C, a polyurethane prepolymer solution was obtained. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C for 2000 min. -1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-3) with a solid content of 35% by mass was prepared by removing some of the acetone and water.

[0076] (Polymerization of urethane resin A-4 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 22 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 3 parts by mass of dimethylolbutanoic acid, 74 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2000, 1 part by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 75°C under a nitrogen atmosphere for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 2 parts by mass of trimethylolpropane were added, and the mixture was stirred at 75°C under a nitrogen atmosphere for 1 hour, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, the reaction solution was cooled to 40°C, and then 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, in a reaction vessel equipped with a homodisperser capable of high-speed stirring, 450 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 min. -1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-4) with a solid content of 34% by mass was prepared by removing some of the acetone and water.

[0077] (Polymerization of urethane resin A-5 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 47 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 21 parts by mass of polyethylene glycol monomethyl ether with a number average molecular weight of 700, 20 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 1200, 12 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 2.5 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, the reaction solution was cooled to 40°C, and then 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C for 2000 min.-1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-5) with a solid content of 34% by mass was prepared by removing some of the acetone and water.

[0078] (Polymerization of urethane resin A-6 having a polycarbonate structure) In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 23.5 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 4.5 parts by mass of dimethylolbutanoic acid, 70 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2000, 2 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added. The mixture was stirred at 75°C under a nitrogen atmosphere for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C for 2000 min. -1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-6) with a solid content of 34% by mass was prepared by removing some of the acetone and water.

[0079] (Polymerization of urethane resin A-7 having a polycarbonate structure) Into a four-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 27.5 parts by mass of hydrogenated m-xylene diisocyanate, 6.5 parts by mass of dimethylolpropanoic acid, 60 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 1800, 6 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were charged. Under a nitrogen atmosphere, it was stirred at 75 °C for 3 hours, and it was confirmed that the reaction solution reached a predetermined amine equivalent. After cooling this reaction solution to 40 °C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 °C, and stirred and mixed at 2000 min -1 while adding the polyurethane prepolymer solution to disperse it in water. Then, under reduced pressure, a part of acetone and water was removed to prepare an aqueous dispersion urethane resin solution (A-7) with a solid content of 34% by mass.

[0080] (Polymerization of urethane resin A-8 having a polycarbonate structure) Into a four-necked flask equipped with a stirrer, Dimroth cooler, nitrogen inlet tube, silica gel drying tube, and thermometer, 400 parts by mass of a polycarbonate polyol having a number average molecular weight of 2000 composed of 1,6-hexanediol and diethyl carbonate, 10.4 parts by mass of neopentyl glycol, 58.4 parts by mass of isophorone diisocyanate, 74.3 parts by mass of dimethylolbutanoic acid, and 320 parts by mass of acetone as a solvent were charged. Under a nitrogen atmosphere, it was stirred at 75 °C for 3 hours, and it was confirmed that the reaction solution reached a predetermined amine equivalent. After cooling this reaction solution to 40 °C, isophoronediamine was added to obtain a polyurethane prepolymer solution. Next, 1200 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 °C, and stirred and mixed at 2000 min -1 while adding the polyurethane prepolymer solution to disperse it in water. Then, under reduced pressure, a part of acetone and water was removed to prepare an aqueous dispersion urethane resin solution (A-8) with a solid content of 34% by mass.

[0081] (Polymerization of urethane resin A-9 that does not contain polycarbonate polyol components) 75 parts by weight of a 5000 molecular weight polyester polyol composed of terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol, 30 parts by weight of hydrogenated m-xylylene diisocyanate, 7 parts by weight of ethylene glycol, 6 parts by weight of dimethylolpropionic acid, and 84.00 parts by weight of acetone as a solvent were added and stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution reached the predetermined amine equivalent. After cooling the reaction solution to 40°C, 5.17 parts by weight of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C for 2000 min. -1 While stirring and mixing, the polyurethane prepolymer solution was added and dispersed in water. Then, under reduced pressure, a water-dispersible urethane resin solution (A-9) with a solid content of 34% by mass was prepared by removing some of the acetone and water.

[0082] (Polymerization of blocked isocyanate crosslinking agent B-1) In a flask equipped with a stirrer, thermometer, and reflux condenser, 66.04 parts by mass of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals) and 17.50 parts by mass of N-methylpyrrolidone were added dropwise to 23.27 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120°C, boiling point: 218°C). The mixture was held at 70°C for 1 hour under a nitrogen atmosphere. Subsequently, 8.3 parts by mass of dimethylolpropanoic acid were added dropwise. After measuring the infrared spectrum of the reaction solution and confirming the disappearance of the absorption of the isocyanate group, 5.59 parts by mass of N,N-dimethylethanolamine and 132.5 parts by mass of water were added to obtain a block polyisocyanate aqueous dispersion (B-1) with a solid content of 40% by mass. The number of functional groups of this block isocyanate crosslinking agent is 4, and the NCO equivalent is 280.

[0083] (Polymerization of blocked isocyanate crosslinking agent B-2) In a flask equipped with a stirrer, thermometer, and reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals), 55 parts by mass of propylene glycol monomethyl ether acetate, and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 750) were charged and held at 70°C for 4 hours under a nitrogen atmosphere. The reaction mixture temperature was then lowered to 50°C, and 49 parts by mass of methyl ethyl ketoxime were added dropwise. The infrared spectrum of the reaction mixture was measured to confirm the disappearance of absorption of the isocyanate group, and 210 parts by mass of water were added to obtain an oxime-blocked isocyanate crosslinking agent (B-2) with a solid content of 40% by mass. This blocked isocyanate crosslinking agent has 3 functional groups and an NCO equivalent of 170.

[0084] (Polymerization of carbodiimide B-3) In a flask equipped with a stirrer, thermometer, and reflux condenser, 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (M400, average molecular weight 400) were charged and stirred at 120°C for 1 hour. Then, 26 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phosphorene-1-oxide (2% by mass relative to the total isocyanate) were added as a carbodiimide catalyst, and the mixture was stirred for a further 5 hours at 185°C under a nitrogen stream. The infrared spectrum of the reaction solution was measured and it was confirmed that the absorption in the wavelength range of 220 to 2300 cm⁻¹ had disappeared. After cooling to 60°C, 567 parts by mass of deionized water were added to obtain a carbodiimide aqueous resin solution (B-3) with a solid content of 40% by mass.

[0085] (Polymerization of blocked isocyanate crosslinking agent B-4) 200 parts by weight of a polyester (molecular weight 2000) of a bisphenol A ethylene oxide 2-mol adduct and maleic acid was mixed with 33.6 parts by weight of hexamethylene diisocyanate, and the reaction was carried out at 100°C for 2 hours. The temperature of the system was then lowered to 50°C, 73 parts by weight of a 30% sodium bisulfite aqueous solution was added, and the mixture was stirred at 45°C for 60 minutes. The mixture was then diluted with 718 parts by weight of water to obtain a block polyisocyanate aqueous dispersion (B-1) with a solid content of 20% by mass. The number of functional groups of this block isocyanate crosslinking agent is 2, and the NCO equivalent is 1300.

[0086] (Polyester resin polymerization C-1) In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out at a temperature of 160°C to 220°C for 4 hours. The temperature was then raised to 255°C, the reaction system was gradually depressurized, and the reaction was carried out under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymerized polyester resin (C-1). The obtained copolymerized polyester resin (C-1) was pale yellow and transparent. The reduced viscosity of copolymerized polyester resin (C-1) was measured to be 0.70 dl / g. The glass transition temperature determined by DSC was 40°C.

[0087] (Preparation of polyester aqueous dispersion Cw-1) In a reactor equipped with a stirrer, thermometer, and reflux device, 15 parts by mass of polyester resin (C-1) and 15 parts by mass of ethylene glycol n-butyl ether were added and heated at 110°C, stirring to dissolve the resin. After the resin was completely dissolved, 70 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion (Cw-1) with a solid content of 15% by mass.

[0088] (Polyester resin polymerization C-2) In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 342.0 parts by mass of dimethyl 2,6-naphthalenedicarboxylate, 35.0 parts by mass of dimethyl terephthalate, 35.5 parts by mass of dimethyl-5-sodium sulfisophthalate, 198.6 parts by mass of ethylene glycol, 118.2 parts by mass of 1,6-hexanediol, and 0.4 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out at 160°C to 220°C for 4 hours. Furthermore, 60.7 parts by mass of sebacic acid was added, and an esterification reaction was carried out. The temperature was then raised to 255°C, the reaction system was gradually reduced in pressure, and the reaction was carried out under reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymer polyester resin (C-2). The obtained copolymer polyester resin was pale yellow and transparent.

[0089] (Preparation of polyester aqueous dispersion Cw-2) In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of copolymerized polyester resin (C-2) and 15 parts by mass of ethylene glycol-n-butyl ether were added and heated at 110°C, stirring to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion (Cw-2) with a solid content of 25% by mass.

[0090] (Example 1) (1) Preparation of the coating solution A coating solution was prepared by mixing the following coating agents with a mixed solvent of water and isopropanol, resulting in a solid content mass ratio of urethane resin solution (A-1) / crosslinking agent (B-1) / polyester aqueous dispersion (Cw-1) of 25 / 26 / 49. Urethane resin solution (A-1) 3.55 parts by mass Crosslinking agent (B-1) 3.16 parts by mass Polyester aqueous dispersion (Cw-1) 16.05 parts by mass Particles 0.47 parts by mass (Dry-processed silica with an average particle size of 200 nm, solid content concentration of 3.5% by mass) Particles 1.85 parts by mass (Silica sol with average particle size of 40-50 nm, solid content concentration of 30% by mass) Surfactant 0.30 parts by mass (Silicone-based, solid content concentration 10% by mass)

[0091] (2) Manufacturing of laminated polyester film As a film raw material polymer, polyester pellets P-1 were dried at 135°C for 6 hours under reduced pressure of 133 Pa. Then, they were fed into an extruder and melt-extruded into a sheet at approximately 280°C. The sheet was then rapidly cooled and solidified on a rotating, cooled metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet.

[0092] This unstretched PET sheet was heated to 100°C using a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction using a roll group with different peripheral speeds to obtain a uniaxially oriented PET film.

[0093] Next, the coating solution, which had been left to stand at room temperature for more than 5 hours, was applied to one side of the PET film by roll coating, and then dried at 80°C for 20 seconds. The final coating amount after drying (after biaxial stretching) was 0.15 g / m². 2 The film was adjusted to have a coating layer thickness of 150 nm after drying. Subsequently, it was stretched 4.0 times in the width direction at 120°C using a tenter, and with the length in the width direction of the film fixed, it was heated at 230°C for 5 seconds, and then subjected to a 3% widthwise relaxation treatment at 100°C for 10 seconds to obtain a 100 μm laminated polyester film. The evaluation results are shown in Table 1.

[0094] (Example 2) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-2).

[0095] (Example 3) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-3).

[0096] (Example 4) A laminated polyester film was obtained in the same manner as in Example 1, except that the crosslinking agent was changed to (B-2).

[0097] (Example 5) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-2) and the crosslinking agent to (B-2).

[0098] (Example 6) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-3) and the crosslinking agent to (B-2).

[0099] (Example 7) A laminated polyester film was obtained in the same manner as in Example 1, except that the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid content mass ratio of the urethane resin solution (A-2) / total crosslinking agent (B-1, B-2) / polyester aqueous dispersion (Cw-1) was changed to 25 / 25 / 50. Urethane resin solution (A-1) 3.55 parts by mass Crosslinking agent (B-1) 2.10 parts by mass Crosslinking agent (B-2) 1.00 parts by mass Polyester aqueous dispersion (Cw-1) 16.20 parts by mass Particles 0.47 parts by mass (Dry-processed silica with an average particle size of 200 nm, solid content concentration of 3.5% by mass) Particles 1.85 parts by mass (Silica sol with average particle size of 40-50 nm, solid content concentration of 30% by mass) Surfactant 0.30 parts by mass (Silicone-based, solid content concentration 10% by mass)

[0100] (Example 8) A laminated polyester film was obtained in the same manner as in Example 7, except that the urethane resin was changed to (A-2).

[0101] (Example 9) A laminated polyester film was obtained in the same manner as in Example 1, except that the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid content mass ratio of the urethane resin solution (A-1) / crosslinking agent (B-1) / polyester aqueous dispersion (Cw-1) was changed to 22 / 10 / 68. Urethane resin solution (A-1) 2.71 parts by mass Crosslinking agent (B-1) 1.00 parts by mass Polyester aqueous dispersion (Cw-1) 19.05 parts by mass Particles 0.47 parts by mass (Dry-processed silica with an average particle size of 200 nm, solid content concentration of 3.5% by mass) Particles 1.85 parts by mass (Silica sol with average particle size of 40-50 nm, solid content concentration of 30% by mass) Surfactant 0.30 parts by mass (Silicone-based, solid content concentration 10% by mass)

[0102] (Example 10) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-2).

[0103] (Example 11) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-3).

[0104] (Example 12) A laminated polyester film was obtained in the same manner as in Example 9, except that the crosslinking agent was changed to (B-3).

[0105] (Example 13) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-4).

[0106] (Example 14) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-5).

[0107] (Example 15) A laminated polyester film was obtained in the same manner as in Example 1, except that the polyester pellets were changed to (P-2) as the film raw material polymer.

[0108] (Comparative Example 1) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-6).

[0109] (Comparative Example 2) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-7).

[0110] (Comparative Example 3) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-6).

[0111] (Comparative Example 4) A laminated polyester film was obtained in the same manner as in Example 9, except that the urethane resin was changed to (A-7).

[0112] (Comparative Example 5) A laminated polyester film was obtained in the same manner as in Example 1, except that the solid content mass ratio of the urethane resin solution (A-6), crosslinking agent (B-1), and polyester aqueous dispersion (Cw-2) was changed to 38 / 7 / 55.

[0113] (Comparative Example 6) A laminated polyester film was obtained in the same manner as in Example 1, except that the solid content mass ratio of the urethane resin solution (A-8), crosslinking agent (B-4), and polyester aqueous dispersion (Cw-2) was changed to 22 / 12 / 66.

[0114] As shown in Table 1, satisfactory results were obtained in each example regarding haze, blocking resistance, adhesion to UV ink, and adhesion to the hard coat layer. Furthermore, Example 15, which used polyester pellets P-2, showed a lower haze value and improved film transparency compared to Examples 1-14, which used polyester pellets P-1. On the other hand, in Comparative Examples 1-6, the blocking resistance was not satisfactory because the coating layer formed on at least one side of the polyester film substrate did not contain a urethane resin with a branched structure.

[0115] (Comparative Example 7) A laminated polyester film was obtained in the same manner as in Example 1, except that the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid content ratio of the urethane resin solution (A-1) / crosslinking agent (B-1) was changed to 70 / 30. Urethane resin solution (A-1) 9.03 parts by mass Crosslinking agent (B-1) 3.38 parts by mass Particles 0.52 parts by mass (Dry-processed silica with an average particle size of 200 nm, solid content concentration of 3.5%) Particles 1.80 parts by mass (Silica sol with average particle size of 40 nm, solid content concentration of 30% by mass) Surfactant 0.30 parts by mass (Silicone-based, solid content concentration 10% by mass)

[0116] (Comparative Example 8) A laminated polyester film was obtained in the same manner as in Example 1, except that the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid content ratio of the urethane resin solution (A-1) to the crosslinking agent (B-1) was changed to 20 / 80. Urethane resin solution (A-1) 2.58 parts by mass Crosslinking agent (B-1) 9.00 parts by mass Particles 0.52 parts by mass (Dry-processed silica with an average particle size of 200 nm, solid content concentration of 3.5% by mass) Particles 1.80 parts by mass (Silica sol with average particle size of 40 nm, solid content concentration of 30% by mass) Surfactant 0.30 parts by mass (Silicone-based, solid content concentration 10% by mass)

[0117] As shown in Table 1, in Comparative Examples 7 and 8, the coating layer formed on at least one surface of the polyester film substrate did not contain polyester resin, resulting in reduced adhesion between the coating layer and the substrate, and unsatisfactory adhesion to the UV ink.

[0118] (Comparative Example 9) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-9).

[0119] As shown in Table 1, in Comparative Example 9, the coating layer formed on at least one surface of the polyester film substrate did not contain a urethane resin having a polycarbonate structure, and therefore the adhesion to the UV ink was not satisfactory.

[0120] Table 1 summarizes the evaluation results for each example and comparative example.

[0121] [Table 1] [Industrial applicability]

[0122] According to the present invention, it is possible to provide a laminated polyester film that can be suitably used in a wide range of fields, including optical applications, packaging applications, and label applications.

Claims

1. A laminated polyester film having a coating layer on at least one surface of a polyester film substrate, The coating layer is formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, a polyester resin, and particles. The crosslinking agent is a compound having three or more functional blocked isocyanate groups. Furthermore, the NCO equivalent of the compound having three or more functional blocked isocyanate groups is 100 or more and 500 or less. The aforementioned particles are inert particles, The inert particles are at least one inorganic particle selected from titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof. The average particle size of the inert particles is 0.04 to 2.0 μm. The particle concentration in the coating layer is 1 to 20% by mass of the solid component. Laminated polyester film.

2. The laminated polyester film according to claim 1, wherein the boiling point of the blocking agent of the compound having three or more functional blocked isocyanate groups is 150°C or higher and 300°C or lower.

3. The laminated polyester film according to claim 1, wherein the urethane resin having a polycarbonate structure and a branched structure is obtained by synthesizing and polymerizing a polycarbonate polyol component and a polyisocyanate component, and the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of polycarbonate polyol component / mass of polyisocyanate component) during the synthesis and polymerization is 0.5 to 3.

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