Laminated Polyester Film

Abstract

 The present invention addresses the problem of providing a multilayer polyester film which has a coating layer that has excellent transparency (low haze) and excellent durability, while being suppressed in coating film defects, and which has high adhesiveness that is most suitable in various fields such as optical materials, packages and labels. The present invention is a multilayer polyester film which has a coating film that is formed from a coating liquid containing an aqueous dispersion of a hydrophobic blocked isocyanate compound that is hydrophilized by means of an anionic emulsifying agent, a water-dispersible polyurethane resin having a carboxyl group, and a water-dispersible polyester resin, wherein the separation defects of the coating film is less than 5.0 defects / m2.

Description

[Technical Field]

[0001] The present invention relates to a laminated polyester film. More specifically, the present invention relates to a laminated polyester film having excellent transparency (low haze), durability, a coating layer with few coating defects, and excellent adhesiveness suitable for a wide range of applications, including optical applications, packaging, and labels.

[0002] Thermoplastic resin films, especially polyester films, have excellent mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance, and are therefore widely used in magnetic recording materials, packaging materials, solar cell applications, optical films such as anti-reflection films, diffusion sheets, and prism sheets used in flat displays, and films for label printing. However, because the surface of polyester film is highly crystalline oriented, it has the disadvantage of poor adhesion to various paints, resins, and inks when processed for these applications. For this reason, a method is known in which a polyurethane resin or a polyurethane resin and an isocyanate-based crosslinking agent are applied to the surface of polyester film to form a coating layer with high adhesive properties (see Patent Document 1).

[0003] Furthermore, in recent years, from the viewpoints of environmental conservation of the atmosphere and wastewater and work safety during manufacturing processes and construction, emphasis has been placed on the use of aqueous (water-based) compositions that do not use organic solvents. Therefore, water-dispersible blocked isocyanate crosslinking agents that use blocking agents to suppress reactivity with water have been proposed (see Patent Document 2).

[0004] These water-dispersible blocked isocyanate crosslinking agents incorporate nonionic or anionic hydrophilic groups into their skeletons to impart water dispersibility to the crosslinking agent itself. If the amount of hydrophilic groups introduced is low, the water dispersibility of the crosslinking agent itself decreases, resulting in poor storage stability of the coating material. Furthermore, if the amount of hydrophilic groups introduced is high, the amount of blocked isocyanate in the crosslinking agent decreases relatively, resulting in insufficient performance such as durability of the coating film.

[0005] Furthermore, instead of making the crosslinking agent itself water-dispersible, forced water-dispersible blocked isocyanates using emulsifiers or the like have also been used. However, depending on the combination with other water-based resins or additives, the dispersion stability may decrease, which may cause problems.

[0006] As a solution to ensure the dispersion stability of these water-dispersible blocked isocyanate crosslinking agents, a core-shell emulsion has been proposed (see Patent Document 3). This emulsion is prepared by emulsifying a mixture of a blocked polyisocyanate component and a neutralized carboxyl-containing, isocyanate-terminated urethane prepolymer in water and then carrying out a chain extension reaction with a chain extender, resulting in the blocked isocyanate compound serving as the core component and a polyurethane resin obtained by chain-extending the carboxyl-containing, isocyanate-terminated urethane prepolymer serving as the shell component. These core-shell emulsions improve the dispersion stability of the coating solution, and when applied to polyester film substrates and cured sufficiently, good adhesion is achieved. However, if the curing is insufficient, peeling defects occur due to contact with traveling rolls, etc. In particular, in in-line coated films, where a coating layer is applied during the film production process, tension control rolls are often installed to suppress tension fluctuations during the cross-direction stretching process after coating and drying. Therefore, peeling defects of the coating layer at the relevant rolls tend to occur frequently. Furthermore, in the coating and drying processes in general, production line speeds are often increased to save energy or improve productivity, making it difficult to obtain the heat and time required to sufficiently cure the coating layer, and raising concerns about the occurrence of peeling defects such as those described above. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 60-199648 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-154674 [Patent Document 3] International Publication No. 2009 / 113412 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to solve the problems of polyester films as described above, and to provide a laminated polyester film that has excellent transparency (low haze), durability, a coating layer with few coating defects, and excellent adhesion properties that are optimal for all fields, such as optical applications, packaging, and labels. [Means for solving the problem]

[0009] That is, the present invention comprises the following: 1. A coating film formed from a coating solution containing a water dispersion of a hydrophobic blocked isocyanate compound hydrophilized with an anionic emulsifier, a water-dispersible polyurethane resin having a carboxyl group, and a water-dispersible polyester resin, and the number of peeling defects in the coating film is 5.0 / m 2 Laminated polyester film that is less than. 2. The laminated polyester film according to item 1 above, wherein the anionic emulsifier that hydrophilizes the aqueous dispersion of the hydrophobic blocked isocyanate compound is a water-dispersible polyurethane resin having a carboxyl group. 3. The laminated polyester film according to the above item 1 or 2, which has a core-shell structure with a hydrophobic blocked isocyanate compound as the core and a water-dispersible polyurethane resin having a carboxyl group as the shell. [Effects of the Invention]

[0010] The present invention makes it possible to provide a laminated polyester film that has excellent transparency (low haze), durability, a coating layer with few coating defects, and excellent adhesion properties that are optimal for a wide range of applications, including optical applications, packaging, and labels. In particular, the laminated polyester film of the present invention has excellent adhesion to ultraviolet (UV) curable resins such as hard coat layers, lens layers, and inks, and is particularly excellent in adhesion to UV inks. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Polyester film base) 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 copolymerized polyester resins in which a portion of the diol component or dicarboxylic acid component of the above-mentioned polyester resins is replaced with a copolymerization component such as the following. For example, the copolymerization component may include diol components such as diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, and polyalkylene glycol, and dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 5-sodium isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

[0012] In the present invention, polyester resins suitable for use in the polyester film substrate are primarily selected from polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. Among these polyester resins, polyethylene terephthalate is most preferred in terms of the balance between physical properties and cost. Furthermore, polyester film substrates made from these polyester resins are preferably biaxially oriented polyester films, which can improve chemical resistance, heat resistance, mechanical strength, and the like.

[0013] The catalyst for polycondensation used in producing the polyester resin is not particularly limited, but antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. It is also preferred to use a germanium compound or a titanium compound. More preferred polycondensation catalysts include catalysts containing aluminum and / or its compound and a phenolic compound, catalysts containing aluminum and / or its compound and a phosphorus compound, and catalysts containing an aluminum salt of a phosphorus compound.

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

[0015] (coating layer) The laminated polyester film of the present invention preferably has a coating layer formed from a hydrophobic blocked isocyanate compound, a water-dispersible polyurethane resin having a carboxyl group, and a water-dispersible polyester resin laminated thereon in order to improve adhesion to a hard coat layer, a lens layer, ink, etc. The coating layer may be formed on both sides of the polyester film, or may be formed on only one side of the polyester film with a coating layer of a different resin formed on the other side.

[0016] The coating layer of the present invention is preferably formed primarily from a hydrophobic blocked isocyanate compound hydrophilized with an anionic emulsifier, a water-dispersible polyurethane resin having carboxyl groups, and a water-dispersible polyester resin. Preferably, the anionic emulsifier that hydrophilizes the hydrophobic blocked isocyanate compound is a water-dispersible polyurethane resin having carboxyl groups. A particularly desirable configuration is one in which the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having carboxyl groups have a core-shell structure, with the hydrophobic blocked isocyanate compound as the core and the water-dispersible polyurethane resin having carboxyl groups as the shell. The aforementioned hydrophilization does not necessarily mean complete hydrophilization; the objective can be achieved by imparting water dispersibility that allows the preparation of an aqueous coating solution.

[0017] The weight ratio of the hydrophobic blocked isocyanate compound to the water-dispersible polyurethane resin having a carboxyl group is preferably in the range of 5 / 95 to 80 / 20, more preferably 10 / 90 to 70 / 30, and even more preferably 20 / 80 to 60 / 40. When the total amount of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group is 100 parts by weight, a ratio of 5 parts by weight or more of the hydrophobic blocked isocyanate compound is preferred, as this improves durability such as resistance to moist heat. When the total amount of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group is 100 parts by weight, a ratio of 20 parts by weight or more of the water-dispersible polyurethane resin having a carboxyl group is preferred, as this improves the stability over time of the coating solution, transparency (low haze), and adhesion to hard coat layers, lens layers, inks, etc. The weight ratio of the total of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group to the polyester resin is preferably in the range of 10 / 90 to 90 / 10, more preferably 20 / 80 to 80 / 20, and even more preferably 30 / 70 to 70 / 30. When the total of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group and the polyester resin is 100 parts by weight, a total of 10 parts by weight or more of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group is preferably 10 parts by weight or more, since this improves adhesion to hard coat layers, lens layers, inks, etc. Furthermore, a polyester resin of 10 parts by weight or more is preferably used, since peeling defects in the coating film are more likely to be suppressed.

[0018] In the coating film of the present invention, the peeling defects were 5.0 / m 2 It is preferable that the density is less than 4.0 particles / m 2 and more preferably less than 3.0 particles / m 2 Peeling defects are less than 5.0 / m 2 If the number of peeling defects is less than 5.0 / m, the yield of acceptable products due to peeling defects will be at a satisfactory level, which is preferable, especially for optical applications. 2In order to achieve a peeling defect of less than 0, it is preferable that the coating film be formed from a coating liquid containing an aqueous dispersion of a hydrophobic blocked isocyanate compound hydrophilized with an anionic emulsifier, a water-dispersible polyurethane resin having a carboxyl group, and a water-dispersible polyester resin, and it is particularly preferable that the compound, resin, and compound ratios are as described above. 2 It is most preferable that the number of particles is 0.5 / m. 2 It may be more than that. The composition of each coating layer will be described in detail below.

[0019] (Hydrophobic blocked isocyanate compound) The present invention uses a hydrophobic blocked isocyanate compound. Hydrophobicity means that the blocked isocyanate compound does not contain an amount of hydrophilic groups that would allow the compound to self-emulsify or disperse in water by itself. Examples of such hydrophilic groups include hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphonic acid groups, and polyoxyethylene groups. However, this does not exclude the presence of small amounts of hydrophilic groups that are introduced to adjust the physical properties of the compound or that originate from synthesis reaction residues or raw material impurities of the compound. In the present invention, by using a hydrophobic blocked isocyanate compound, it is possible to further improve the resistance to moist heat, such as adhesiveness.

[0020] Examples of blocking agents include pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole, phenols such as phenol and cresol, aliphatic alcohols such as methanol and ethanol, active methylene compounds such as dimethyl malonate and acetylacetone, mercaptans such as butyl mercaptan and dodecyl mercaptan, acid amides such as acetanilide and acetic acid amide, lactams such as ε-caprolactam and δ-valerolactam, acid imides such as succinimide and maleimide, oximes such as acetaldoxime, acetoneoxime, and methyl ethyl ketoxime, and amines such as diphenylaniline, aniline, and ethyleneimine. However, blocking agents that produce hydrophilic groups as a reaction product with an isocyanate group are less preferred, and examples thereof include compounds such as sulfites, hydrogencarbonates, and diethanolamine.

[0021] 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 during the drying process after application of the coating solution or, in the case of in-line coating, during the film formation process, generating regenerated isocyanate groups. This promotes crosslinking reactions with other polyurethane resins in the coating film, improving the crosslinked state of the coating film.

[0022] Examples of blocking agents having a dissociation temperature of 120°C or less that can be preferably contained in the hydrophobic blocked isocyanate of the present invention include the above-mentioned pyrazole compounds such as 3,5-dimethylpyrazole and 3-methylpyrazole, malonic acid ester compounds such as dimethyl malonate and diethyl malonate, acetone oxime, methyl ethyl ketoxime, etc. Among these, methyl ethyl ketoxime, malonic acid ester compounds, and pyrazole compounds are preferred from the viewpoints of moist heat resistance and yellowing.

[0023] The hydrophobic blocked isocyanate is preferably a bifunctional or higher functional blocked isocyanate, and more preferably a trifunctional or higher functional blocked isocyanate from the viewpoint of the crosslinkability of the coating film.

[0024] The tri- or higher functional polyisocyanate, which is the precursor of the hydrophobic blocked isocyanate of the present invention, can be suitably obtained by introducing an isocyanate monomer, such as a biuret, isocyanurate, or adduct obtained by modifying an isocyanate monomer, such as an aromatic diisocyanate, aliphatic diisocyanate, araliphatic diisocyanate, or alicyclic diisocyanate, each having two isocyanate groups. The biuret form is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer, and examples thereof include the biuret form of hexamethylene diisocyanate. The isocyanurate is a trimer of an isocyanate monomer, and examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate. The adduct refers to a tri- or higher functional isocyanate compound obtained by reacting an isocyanate monomer with a tri- or higher functional low-molecular-weight active hydrogen-containing compound, and examples thereof include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, and a compound obtained by reacting trimethylolpropane with isophorone diisocyanate.

[0025] Examples of the isocyanate monomer 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'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Examples of suitable diisocyanates include aromatic diisocyanates such as 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, and xylylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane, and aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate. Aliphatic and alicyclic isocyanates and their modified products are preferred in terms of transparency, yellowing resistance, adhesion, and moist heat resistance.

[0026] As mentioned above, the blocked isocyanate compound in the present invention is hydrophobic and does not have water dispersibility. Therefore, it is necessary to use an emulsifier or the like in addition to the blocked isocyanate compound to achieve water dispersibility. Anionic, cationic, nonionic, amphoteric surfactants, etc. can be used as the emulsifier, but anionic surfactants are preferred in the present invention. The use of an anionic surfactant can improve the dispersion stability of the blocked isocyanate compound. Low-molecular-weight or polymeric anionic surfactants can be used as the anionic surfactant in the present invention.

[0027] Low molecular weight anionic surfactants include carboxylic acid type, sulfate type, sulfonic acid type, phosphate type, etc. For example, carboxylic acid type surfactants include aliphatic monocarboxylates, polyoxyethylene alkyl ether carboxylates, N-acyl sarcosinates, N-acyl glutamine salts, etc., sulfate type surfactants include alkyl sulfates, polyoxyethylene alkyl ether sulfates, fat sulfate salts, etc., sulfonic acid type surfactants include dialkyl sulfosuccinates, alkanesulfonates, alpha olefin sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, N-acyl N-acyltaurate salts, etc., and phosphate type surfactants include alkyl phosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, etc.

[0028] Examples of polymeric anionic surfactants include polymers or copolymers of unsaturated monomers having an anionic group, such as acrylic acid, maleic acid, and styrenesulfonic acid; polyesters copolymerized with monomers having a sulfonic acid group, carboxylic acid, or phosphinic acid; and polyurethane resins.

[0029] In the present invention, it is preferable to use a polyurethane resin having a carboxyl group. More preferably, it has a core-shell structure with a hydrophobic blocked isocyanate compound as the core and a polyurethane resin having a carboxyl group as the shell. This makes it possible to maintain the dispersion stability of the blocked isocyanate compound over a long period of time, and the dispersion stability is less likely to decrease even when mixed with other resins or additives. Details of the core-shell structure will be described later.

[0030] (Polyurethane resin) The polyurethane resin of the present invention is preferably a water-dispersible polyurethane resin containing carboxyl groups, composed of at least a polyol component, a polyisocyanate component, and, optionally, a chain extender. The carboxyl groups of the polyurethane resin of the present invention are present in the molecule or on the side chain to impart water solubility or water dispersibility to the polyurethane resin. "In the molecule" here refers to those present in the main chain or at the terminal of the polyurethane resin. Furthermore, "side chain" refers to those introduced onto a branched molecular chain after synthesis and polymerization, where one of the raw material components constituting the molecular chain has three or more terminal functional groups. In the present invention, hydrophilic groups other than carboxyl groups can be introduced into the polyurethane resin without any problems. Examples of hydrophilic groups other than carboxyl groups include anionic groups such as sulfonic acid and phosphonic acid, cationic groups such as quaternary amines, and nonionic groups such as oxyalkylene groups. However, nonionic groups such as oxyalkylene groups are preferred because they are easy to introduce and do not react with carboxyl groups.

[0031] The carboxyl group-containing polyurethane resin of the present invention is obtained mainly by using a carboxyl group-containing polyol component as a component of the urethane resin. Examples of such carboxyl group-containing polyol components include the following. Relatively high molecular weight polyols, such as carboxyl group-containing polyalkylene glycols, carboxyl group-containing acrylic polyols, carboxyl group-containing polyolefin polyols, and carboxyl group-containing polyester polyols, can be used. Relatively low molecular weight polyols, such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid, can also be used. Dimethylolpropionic acid and dimethylolbutanoic acid are particularly suitable for introducing carboxyl groups.

[0032] The carboxyl group-containing polyurethane resin preferably has an acid value of 10 to 60 mgKOH / g, more preferably 20 to 50 mgKOH / g. An acid value of 10 mgKOH / g or more is preferable because the hydrophilicity of the polyurethane resin itself is improved and water solubility or water dispersibility is maintained. An acid value of 60 mgKOH / g or less is preferable because the water resistance of the coating layer is improved and there is no blocking problem due to moisture absorption. However, in the carboxyl group-containing polyurethane resin of the present invention, hydrophilic groups other than carboxyl groups, such as hydroxyl groups, oxyalkyl groups, sulfonic acid, phosphonic acid, and quaternary amines, may be introduced to compensate for the water solubility or water dispersibility of the polyurethane resin, as long as the performance is not impaired.

[0033] The carboxyl groups in the polyurethane resin may be neutralized with a basic compound. Examples of basic compounds used for neutralization include alkali metals such as sodium and potassium, alkaline earth metals such as magnesium and calcium, and organic amine compounds. Among these, organic amine compounds that easily dissociate from the carboxyl groups upon heating are preferred. Examples of organic amine compounds include ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, and ethylenediamine, linear and branched primary, secondary, and tertiary amines having 1 to 20 carbon atoms, such as morpholine, N-alkylmorpholine, and pyridine, and hydroxyl group-containing amines such as monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, and triethanolamine.

[0034] In the present invention, it is preferable to use polyester polyols and polycarbonate polyols in addition to the above-mentioned polyoxyalkylene glycols as the main polyol components used for synthesizing and polymerizing the urethane resin having a carboxyl group.

[0035] The number average molecular weight of the polyester polyol or polycarbonate polyol in the present invention is preferably 300 to 5000, more preferably 400 to 4000, and most preferably 500 to 3000. A molecular weight of 300 or more is preferable because adhesiveness can be improved. A molecular weight of 5000 or less is preferable because fusion between coating layers can be prevented (blocking resistance can be improved).

[0036] The polyester polyol in the present invention is preferably aliphatic or alicyclic. Therefore, examples of the dicarboxylic acid component of the polyester polyol include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the diol component include aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, and neopentyl glycol, and alicyclic diols such as cyclohexanedimethanol. Among these, it is preferred to primarily use long-chain fatty acids longer than adipic acid and long-chain diols longer than pentanediol in the present invention. However, tri- or higher functional polycarboxylic acids, polyols, or unsaturated or aromatic components may be used to the extent that they do not deteriorate the physical properties.

[0037] The polycarbonate polyol used in the present invention is preferably an aliphatic polycarbonate polyol. Examples of the aliphatic polycarbonate polyol include an aliphatic polycarbonate diol and an aliphatic polycarbonate triol, but an aliphatic polycarbonate diol is preferably used. Examples of the aliphatic polycarbonate diol used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention include aliphatic polycarbonate diols obtained by reacting 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 with carbonates such as dimethyl carbonate, ethylene carbonate, and phosgene.

[0038] In order to synthesize and polymerize the urethane resin of the present invention, other polyol components can be used in addition to those mentioned above. Examples of other polyol components include polyether polyols, polyolefin polyols, dimer polyols, and silicone polyols.

[0039] Examples of polyisocyanates used in the synthesis and polymerization of the water-dispersible urethane resin having a carboxyl group in the present invention include aromatic diisocyanates containing an aromatic ring, such as xylylene diisocyanate; alicyclic diisocyanates, such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; aliphatic diisocyanates, such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; modified polyisocyanates containing an isocyanurate bond, a biuret bond, or an allophanate bond, which are produced from diisocyanates; and polyisocyanates obtained by adding one or more diisocyanates in advance to trimethylolpropane or the like. The use of alicyclic diisocyanates or aliphatic diisocyanates is preferable to the use of aromatic diisocyanates containing an aromatic ring, as this reduces the problem of yellowing.

[0040] 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, aminoalcohols such as monoethanolamine and diethanolamine, thioglycols such as thiodiethylene glycol, and water. Furthermore, small amounts of polyols and polyamines having three or more functional groups may also be used.

[0041] The polymerization method for the polyurethane resin having a carboxyl group is not particularly limited, and a solvent-free polymerization method or a solvent-based polymerization method may be used. In the present invention, a solvent-based polymerization method is preferred from the viewpoint of using the resin as an emulsifier for the hydrophobic blocked isocyanate compound. Even if the solvent remains in the aqueous dispersion, the solvent may be removed, but from an environmental point of view, it is preferable to remove the solvent.

[0042] Although there are no particular limitations on the method for preparing a dispersion of a blocked isocyanate compound using a water-dispersible polyurethane resin having carboxyl groups as an emulsifier, it is preferable to mix a hydrophobic blocked isocyanate compound with a polyurethane resin having carboxyl groups and then perform water dispersion from the viewpoint of dispersion stability of the blocked isocyanate compound. In particular, a core-shell structure aqueous dispersion with a blocked isocyanate compound as the core and a polyurethane resin as the shell is preferred, in which the blocked isocyanate compound is mixed with the polyurethane prepolymer at the stage of aqueous dispersion, and after aqueous dispersion, a polyamine or the like is added to act as a chain extender in the aqueous dispersion state to form a polyurethane resin.

[0043] The water-dispersible polyurethane resin having a carboxyl group in the present invention may have a reactive group such as a blocked isocyanate at the end or in the side chain in order to improve hardness.

[0044] (polyester resin) The polyester resin used in the coating layer of the present invention is not particularly limited, but from the viewpoint of hydrolysis resistance and physical properties, it is preferable for the resin to contain at least 50 mol% of an aromatic dicarboxylic acid in the acid component. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. Other acid components that can be used as needed include aliphatic dicarboxylic acids such as adipic acid and sebacic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, acid anhydrides such as maleic anhydride, and tricarboxylic acids such as trimellitic acid and trimesic acid. It is preferable for the diol component to contain at least 30 mol% of ethylene glycol in the diol component. Examples of other diol components include linear aliphatic diols such as 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol; branched aliphatic diols such as 1,2-propanediol, 1,3-butanediol, 2,2-dimethyl-1,3-propanediol, and 3-methyl-1,5-pentanediol; alicyclic diols such as cyclohexanedimethanol; diglycols such as diethylene glycol and dipropylene glycol; polyoxyalkylene glycols such as polyethylene glycol; and polyoxyalkylene glycol derivatives such as bisphenol A.

[0045] To impart water dispersibility to the polyester resin, it is preferable for a hydrophilic group to be present on the molecular skeleton. As the hydrophilic group, a dicarboxylic acid having a phosphonic acid group, sulfonic acid group, or the like introduced into the dicarboxylic acid component may be used, or a polyether such as polyethylene glycol may be used as the diol component. Alternatively, a hydroxyl group terminal of the polymerized polyester may be reacted with a polycarboxylic acid anhydride to introduce a carboxyl group into the polyester skeleton. In the present invention, from the viewpoint of dispersion stability, it is preferable to use a sulfonic acid group as the hydrophilic group. It is preferable to polymerize a sulfonic acid group-containing dicarboxylic acid in the dicarboxylic acid component in an amount of 1 to 10 mol %. Examples of sulfonic acid group-containing dicarboxylic acids include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid.

[0046] In the present invention, other resins may be used in combination as long as the performance is not affected. Examples of resins that can be used in combination include non-carboxyl group-containing polyurethane resins, alkyd resins, acrylic resins, cellulose resins, polyolefin resins, and polyacetal resins.

[0047] Other crosslinking agents may be used in combination with the hydrophobic blocked isocyanate compound of the present invention. Examples of other crosslinking agents that can be used include hydrophilic blocked isocyanate, epoxy, melamine, oxazoline, and carbodiimide crosslinkers. By appropriately using the other crosslinking agent in an amount of 20% by mass or less, the crosslinking state can be adjusted, minimizing the effect on adhesiveness and other properties, while further improving durability such as resistance to moist heat. Furthermore, when a hydrophilic blocked isocyanate is used as the crosslinking agent, it is preferable to select a blocking agent different from the hydrophobic blocked isocyanate compound, since the crosslinking state can be adjusted by changing the crosslinking reaction initiation temperature depending on the composition of the blocking agent.

[0048] (additives) The coating layer of the present invention may contain known additives, such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, and nucleating agents, within the range that does not impair the effects of the present invention.

[0049] In the present invention, in order to further improve the blocking resistance of the coating layer, it is also a preferred embodiment to add particles other than those described above to the coating layer. Examples of particles to be contained in the coating layer in the present invention include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, etc., or mixtures thereof, and further include inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., used in combination with other general inorganic particles, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

[0050] The average particle size of other particles in the coating layer (average particle size based on the number of particles as determined by a scanning electron microscope (SEM); the same applies hereinafter) is preferably 0.02 to 2.00 μm, more preferably 0.04 to 1.00 μm. When the average particle size of the inactive particles is 0.04 μm or more, it is easy to form irregularities on the film surface, which further improves the handling properties of the film, such as slipperiness and winding ability, and improves processability during lamination, which is preferable. On the other hand, when the average particle size of the inactive particles is 2.00 μm or less, particle detachment is less likely to occur, which is preferable. The particle concentration in the coating layer is preferably 1 to 20 mass % of the solid components.

[0051] The average particle size of other particles was measured by observing particles on the cross section of the laminated polyester film with a scanning electron microscope, observing 30 particles, and determining the average particle size as the average value.

[0052] The shape of the other particles is not particularly limited as long as it satisfies the objectives of the present invention, and spherical particles and irregular, non-spherical particles can be used. The particle size of irregular particles can be calculated as the equivalent circle diameter. The equivalent circle diameter is calculated by dividing the observed particle area by π, calculating the square root, and then multiplying it by two.

[0053] (Manufacturing of laminated polyester film) The method for producing the laminated polyester film of the present invention will be explained using an example in which a polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film substrate is used and a coating layer is provided during the film-forming process, but of course the method is not limited to this.

[0054] After thorough vacuum drying, the PET resin is fed to an extruder, and the molten PET resin at about 280°C is extruded from a T-die onto a rotating cooling roll in the form of a sheet, which is then cooled and solidified by electrostatic application to obtain an unstretched PET sheet. The unstretched PET sheet may have a single layer structure or a multilayer structure formed by coextrusion.

[0055] The resulting unstretched PET sheet is uniaxially or biaxially stretched to achieve crystal orientation. For example, in the case of biaxial stretching, the sheet is stretched 3.0 to 5.0 times in the machine direction using rolls heated to 80 to 120°C to obtain a uniaxially stretched PET film. The film is then gripped at its edges with clips and introduced into a hot air zone heated to 80 to 180°C, where it is stretched 3.0 to 5.0 times in the width direction. In the case of uniaxial stretching, the unstretched PET sheet is stretched 3.0 to 5.0 times in a tenter. After stretching, the sheet is subsequently introduced into a heat treatment zone at 180 to 230°C, where it is heat-treated to complete the crystal orientation.

[0056] Any known method can be used to apply the coating solution to the PET film. Examples include reverse roll coating, gravure coating, kiss coating, die coating, roll brushing, spray coating, air knife coating, wire bar coating, pipe doctor coating, impregnation coating, and curtain coating. These methods can be used alone or in combination.

[0057] 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 in order to achieve both processability and adhesiveness, it is preferably within the range of 0.01 to 1.00 μm, 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 adhesiveness. A coating layer thickness of 2.00 μm or less is preferable because it is less likely to cause blocking.

[0058] The upper limit of the haze of the laminated polyester film of the present invention is preferably 2.0%, more preferably 1.8%, even more preferably 1.5%, and particularly preferably 1.2%. A haze of 2.0% or less is preferable in terms of transparency, and the film can be suitably used for optical film applications requiring transparency. A low haze is preferable, but it may be 0.1% or more, or even 0.3% or more. [Example]

[0059] 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 methods used in the present invention will be described below.

[0060] (1) Peeling defect detection method A sample film roll with a width of 1 m and a length of 10 m taken from the product film rolls obtained in the Examples and Comparative Examples was hung vertically in a dark room. Next, a non-glossy black cloth was placed over the entire back surface of the film, and an LED light (1000 lumens) was used from the front (coating layer surface) to observe the film from the front while changing the angle of the light in the range of about 10° to 45° relative to the film surface as the laminated film was unwound. 2 Defects with a major axis of 100 μm or more were detected visually or using a magnifying glass with a scale at 10 times magnification (SCALE LUPE × 10 manufactured by PEAK Co., Ltd.) and marked.

[0061] (2) Peeling defect detection method The defect area marked by the above-mentioned method was cut out and measured under the following conditions using a non-contact surface shape measurement system (VertScan R550H-M100, manufactured by Ryoka Systems Co., Ltd.). (Measurement conditions) Measurement mode: WAVE mode Objective lens: 10x 0.5x Tube Lens ·Measurement area 936μm×702μm (Analysis conditions) Area Correction: 4th Order Correction The defects measured were judged to be peeling defects if they met all of the following criteria A to E. The numerical values ​​of the defects in the depth direction were obtained by performing a cross-sectional analysis of the above measurement data. A. It is observed to be surrounded by a closed curve that does not intersect with itself, and the maximum width of the enclosed area is 200 μm or more. A. The inside of a closed curve is a concave C. The maximum depth of the outer periphery and interior of the closed curve is 70% or more of the thickness of the coating layer. d. The depth variation of the inner area of ​​the closed curve is within a range of less than 50% of the coating layer thickness. E. 50% or more of the closed curve has a gradient of 60° or more from the horizontal plane inside the curve. The number of peeling defects judged above is counted over 1m. 2 The coating thickness mentioned above can be calculated from the total solid concentration of the coating solution, the specific gravity of the resin, the coating amount, the stretching ratio, etc., or can be an analytical value from an SEM photograph of the film cross section, etc.

[0062] (3) Hayes The haze of the obtained laminated polyester film was measured in accordance with JIS K 7136:2000 using a turbidity meter (NDH5000, manufactured by Nippon Denshoku Corporation).

[0063] (4) Blocking resistance Two film samples were placed together with the coating surfaces facing each other, and a load of 98 kPa was applied. The samples were then left in close contact for 24 hours in an atmosphere at 50° C. The films were then peeled off, and the peeling condition was evaluated according to the following criteria. ◯: The coating layer was not transferred and could be easily peeled off. △: The coating layer is maintained, but the surface layer of the coating layer is partially transferred to the opposing surface. ×: The two films were stuck together and could not be separated, or even if they could be separated, the film substrate was cleaved.

[0064] (5) Adhesion to UV ink On the coating layer of the laminated polyester film, UV ink [manufactured by T&K TOKA Corporation, product name "BEST CURE UV161 Indigo S" or "BEST CURE UV161 White S"] was printed using a printing machine [manufactured by Akira Manufacturing Co., Ltd., product name "RI Tester"] with an ink pipette of 4 graduations and a two-division roll, and then the film with the ink layer was exposed to 100 mJ / cm using a high-pressure mercury lamp. 2The ink was then irradiated with ultraviolet light at 100 slits, curing the ultraviolet-curable ink. Next, using a cutter guide with a gap of 2 mm, 100 grid-shaped cuts were made on the ink layer surface, penetrating the ink layer and reaching the film substrate. Next, cellophane adhesive tape (Nichiban, No. 405; 24 mm wide) was applied to the grid-shaped cuts. The cellophane adhesive tape was then peeled perpendicularly from the ink layer surface of the ink laminated film, and the number of squares peeled from the ink layer surface of the ink laminated film was counted visually, and the adhesion between the ink layer and the film substrate was calculated using the following formula. Note that partially peeled squares were also counted as peeled squares, and the ink adhesion was calculated using the following formula. Ink adhesion (%) = 100 - (number of peeled squares) The ink adhesion (%) was classified as follows, with ⊚ and ◯ being considered acceptable. ◎: 100%, ○: 99-96%, △: 95-80%, ×: 79-0%

[0065] (6) Adhesion to the hard coat layer Opstar Z7503 (Arakawa Chemical Industries, Ltd.), a UV-curable hard coating agent, was applied onto the coating layer of the laminated polyester film using a #5 wire bar and dried at 80°C for 1 minute. Next, the coated film was irradiated with 100 mJ / cm using a high-pressure mercury lamp. 2 The hard coat film was then irradiated with ultraviolet light at 100 slits, resulting in a hard coat film. Next, using a cutter guide with a gap of 2 mm, 100 grid-shaped cuts were made on the surface of the hard coat layer, penetrating the hard coat layer and reaching the film substrate. Cellophane adhesive tape (Nichiban, No. 405; 24 mm wide) was then applied to the grid-shaped cuts and rubbed with an eraser to ensure complete adhesion. The cellophane adhesive tape was then peeled vertically from the hard coat layer surface of the hard coat laminate film, and the number of squares peeled from the hard coat layer surface of the hard coat laminate film was counted visually, and the adhesion between the hard coat layer and the film substrate was calculated using the following formula. Partially peeled squares were also counted as peeled squares, and the hard coat adhesion was calculated using the following formula. A hard coat adhesion of 100% was considered acceptable. Hard coat adhesion (%) = 100 - (number of peeled squares) The hard coat adhesion (%) was classified as follows, with ⊚ and ◯ being acceptable. ◎: 100%, ○: 99-96%, △: 95-80%, ×: 79-0%

[0066] (7) Moisture and heat resistance UV ink-coated or hard coat-coated films prepared in the same manner as in (5) and (6) above were left in an environment of 80°C and 80% RH with the coated surface vertical and without any other films in contact with the coated surface for 500 hours. After treatment, the films were left in an environment of 23°C and 65% RH for 10 minutes without any other films in contact with the coated surface. Immediately after the time had passed, the adhesion of the coated surface was evaluated in the same manner as above.

[0067] The various resins used in the coating liquid of the present invention will be explained below.

[0068] (Blocked isocyanate compounds) [BI-1]~[BI-6] [Synthesis of blocked isocyanate compound BI-1] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 514.1 parts by mass of hexamethylene diisocyanate isocyanurate trimer (isocyanate content 21.8%), 235.9 parts by mass of 2-butanone oxime, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was stirred at 80°C for 5 hours under a nitrogen atmosphere to allow the reaction to proceed. The infrared spectrum of the reaction solution was then measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This yielded a methyl ethyl ketone solution of blocked isocyanate compound BI-1.

[0069] [Synthesis of blocked isocyanate compound BI-2] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 506.4 parts by mass of hexamethylene diisocyanate isocyanurate trimer (isocyanate content 21.8%), 230.9 parts by mass of 2-butanone oxime, 12.7 parts by mass of polytetramethylene glycol with a number average molecular weight of 2000, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was stirred under a nitrogen atmosphere at 80°C for 5 hours to react. The infrared spectrum of the reaction solution was then measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This yielded a methyl ethyl ketone solution of blocked isocyanate compound BI-2.

[0070] [Synthesis of blocked isocyanate compound BI-3] A flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 495.6 parts by mass of polyisocyanate having a biuret structure obtained from hexamethylene diisocyanate (isocyanate content 23.5%), 14.6 parts by mass of polypropylene glycol having a number average molecular weight of 400, and 250 parts by mass of methyl ethyl ketone as a solvent. The mixture was stirred at 80°C for 2 hours under a nitrogen atmosphere, and then 239.8 parts by mass of 2-butanone oxime was added. The mixture was then stirred at 80°C for an additional 5 hours to allow the reaction to proceed. The infrared spectrum of the reaction solution was then measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This yielded a methyl ethyl ketone solution of blocked isocyanate compound BI-3.

[0071] [Synthesis of blocked isocyanate compound BI-4] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 402.09 parts by mass of isophorone diisocyanate, 347.89 parts by mass of 3,5-dimethylpyrazole, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was stirred at 80°C for 5 hours under a nitrogen atmosphere to allow the reaction to proceed. The infrared spectrum of the reaction solution was then measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This yielded a methyl ethyl ketone solution of blocked isocyanate compound BI-4.

[0072] [Synthesis of blocked isocyanate compound BI-5] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 474.0 parts by weight of hexamethylene diisocyanate isocyanurate trimer (isocyanate content 21.8%), 78 parts by weight of methoxypolyethylene glycol with a hydroxyl value of 8.1 mg KOH / g, 0.003 parts by weight of dioctyltin laurate as a urethane catalyst, and 250 parts by weight of methyl ethyl ketone as a solvent. After stirring for 3 hours at 85 ° C. under a nitrogen atmosphere, 198.0 parts by weight of 2-butanone oxime was added, and the mixture was further stirred at 80 ° C. for 2 hours to allow the reaction to proceed. After that, the infrared spectrum of the reaction solution was measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This resulted in a methyl ethyl ketone solution of a blocked isocyanate compound BI-5 having a nonionic group.

[0073] [Synthesis of blocked isocyanate compound BI-6] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 495.5 parts by mass of hexamethylene diisocyanate isocyanurate trimer (isocyanate content 21.8%), 57.5 parts by mass of dimethylolpropionic acid, and 250 parts by mass of methyl ethyl ketone as a solvent. The mixture was stirred at 85°C under a nitrogen atmosphere for 3 hours, after which 152.4 mass of 2-butanone oxime was added and the mixture was further stirred at 80°C for 2 hours to allow the reaction to proceed. The infrared spectrum of the reaction solution was then measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This yielded a methyl ethyl ketone solution of blocked isocyanate compound BI-6 having an anionic group.

[0074] (Water dispersion of blocked isocyanate compound) [Preparation of BI-1WD, BI-5WD, and BI-6WD] [Production of Water Dispersion A (BI-1WD-A) of Blocked Isocyanate Compound BI-1] To 100 parts by mass of a methyl ethyl ketone solution of blocked isocyanate compound BI-1, 15 parts by mass of anionic surfactant Pelex SS-H (Kao Corporation) with a solids concentration of 50% by mass was added, and 225 parts by mass of water was gradually added with stirring. From this solution, the methyl ethyl ketone was removed under reduced pressure at 50°C or lower, and the concentration was adjusted with water to obtain a water dispersion A (BI-1WD-A) of blocked isocyanate compound BI-1 emulsified with an anionic surfactant with a solids content of 25% by mass.

[0075] [Production of Water Dispersion B (BI-1WD-B) of Blocked Isocyanate Compound BI-1] To 100 parts by mass of a methyl ethyl ketone solution of blocked isocyanate compound BI-1, 7.5 parts by mass of a nonionic surfactant, Emulgen 430 (Kao Corporation), having a solids concentration of 100% by mass was added, and 225 parts by mass of water was gradually added while stirring. The methyl ethyl ketone was removed from this solution under reduced pressure at 50°C or lower, and the concentration was adjusted with water to obtain an aqueous dispersion B (BI-1WD-B) of blocked isocyanate compound BI-1 emulsified with a nonionic surfactant having a solids content of 25% by mass.

[0076] [Production of Water Dispersion of Blocked Isocyanate Compound BI-5 (BI-5WD)] To 100 parts by mass of a methyl ethyl ketone solution of blocked isocyanate compound BI-5, 225 parts by mass of water was gradually added while stirring. The methyl ethyl ketone was removed from this solution under reduced pressure at 50°C or lower, and the concentration was adjusted with water to obtain a water dispersion (BI-5WD) of self-emulsifying nonionic blocked isocyanate compound BI-5 with a solids content of 25% by mass.

[0077] Production of water dispersion of blocked isocyanate compound BI-6 (BI-6WD) To 100 parts by mass of a methyl ethyl ketone solution of blocked isocyanate compound BI-6, 225 parts by mass of water was gradually added with stirring. The methyl ethyl ketone was removed from this solution under reduced pressure at 50°C or lower, and the concentration was adjusted with water to obtain a water dispersion of self-emulsifying anionic blocked isocyanate compound BI-6 (BI-6WD) with a solids content of 25% by mass.

[0078] (Prepolymer) [P-1]~[P-4] [Synthesis of prepolymer P-1] A flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 498.5 parts by mass of polycarbonate diol having a number average molecular weight of 2000, 154.3 parts by mass of (cyclohexane-1,2-diylbismethylene) diisocyanate, 48.7 parts by mass of dimethylolpropionic acid, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was stirred at 80°C for 5 hours to cause reaction, producing a prepolymer P-1 solution having an anionic carboxyl group with a solids content of 73.7% by mass.

[0079] [Synthesis of prepolymer P-2] A flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 369.9 parts by mass of polycarbonate diol having a number average molecular weight of 2000, 266.4 parts by mass of dicyclohexylmethane-4,4'-diisocyanate, 59.6 parts by mass of dimethylolpropionic acid, 9.2 parts by mass of methyl ethyl ketoxime, 250 parts by mass of methyl ethyl ketone as a solvent, and 9.2 parts by mass of methyl ethyl ketoxime, and the mixture was stirred at 80°C for 5 hours to cause a reaction, thereby producing a solution of prepolymer P-1 having an anionic carboxyl group with a solid content of 73.8% by mass.

[0080] [Synthesis of prepolymer P-3] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 293.4 parts by mass of a polyester diol having a number average molecular weight of 500 obtained from a mixed dicarboxylic acid of ethylene glycol / neopentyl glycol = 1 / 1 (molar ratio) and terephthalic acid / isophthalic acid = 1 / 1 (molar ratio), 322.2 parts by mass of dicyclohexylmethane-4,4'-diisocyanate, 85.0 parts by mass of dimethylol butanoic acid, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was stirred at 80°C for 5 hours to cause a reaction, producing a prepolymer P-3 solution having an anionic carboxyl group and a solids content of 73.7% by mass.

[0081] [Synthesis of prepolymer P-4] A flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 486.5 parts by mass of polyethylene glycol having a number average molecular weight of 2000, 157.3 parts by mass of (cyclohexane-1,2-diylbismethylene) diisocyanate, 50.2 parts by mass of 1,6-hexanediol, and 250 parts by mass of methyl ethyl ketone as a solvent, and the mixture was reacted with stirring at 80°C for 5 hours to produce a nonionic prepolymer P-4 solution with a solids content of 73.5% by mass.

[0082] (Core-shell type waterborne polyurethane resin) [CS-1]~[CS-6] [Production of core-shell waterborne polyurethane resin CS-1] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 66.20 parts by weight of anionic carboxyl-containing prepolymer P-1 solution, 2.11 parts by weight of triethylamine, and 30 parts by weight of a methyl ethyl ketone solution of blocked isocyanate compound BI-1. The mixture was stirred for 5 minutes to obtain a mixture. A flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent. While stirring at 40°C, the mixture was added over 2 minutes and further stirred at 40°C for 30 minutes. 0.250 parts by weight of a 25% by weight aqueous solution of ethylenediamine was then added. After stirring at 40°C for 1 hour, the reaction mixture was analyzed by infrared spectroscopy, confirming that the isocyanate group absorption had disappeared. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-1 (CS-1WD) with a solids concentration of 30% by weight. This polyurethane resin CS-1 has a core made of a blocked isocyanate compound BI-1 and a shell made of a polyurethane formed from an anionic prepolymer P-1.

[0083] [Production of core-shell waterborne polyurethane resin CS-2] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 57.31 parts by weight of anionic carboxyl group-containing prepolymer P-2 solution, 2.69 parts by weight of triethylamine, and 40 parts by weight of blocked isocyanate compound BI-2 in methyl ethyl ketone, and stirred for 5 minutes to obtain a mixture. A flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent, and the mixture was added over 2 minutes while stirring at 40°C. The mixture was then stirred for an additional 30 minutes at 40°C. 0.180 parts by weight of a 25% by weight aqueous solution of ethylenediamine was added, and the mixture was stirred at 40°C for 1 hour. The infrared spectrum of the reaction solution confirmed the disappearance of the isocyanate group absorption. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-2 (CS-2WD) with a solids concentration of 30% by weight. This polyurethane resin CS-2 has a core made of a blocked isocyanate compound BI-2 and a shell made of a polyurethane formed from an anionic prepolymer P-2.

[0084] [Production of core-shell waterborne polyurethane resin CS-3] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 75.00 parts by weight of anionic carboxyl group-containing prepolymer P-3 solution, 3.64 parts by weight of triethylamine, and 20 parts by weight of a methyl ethyl ketone solution of blocked isocyanate compound BI-3. The mixture was stirred for 5 minutes to obtain a mixture. Separately, a flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent. While stirring at 40°C, the mixture was added over 2 minutes and further stirred at 40°C for 30 minutes. Next, 0.140 parts by weight of a 25% by weight aqueous solution of ethylenediamine was added. After stirring at 40°C for 1 hour, infrared spectroscopy of the reaction solution confirmed the disappearance of the isocyanate group absorption. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-3 (CS-3WD) with a solids concentration of 30% by weight. This polyurethane resin CS-3 has a core made of a blocked isocyanate compound BI-3 and a shell made of a polyurethane formed from an anionic prepolymer P-3.

[0085] [Production of core-shell waterborne polyurethane resin CS-4] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 66.20 parts by weight of anionic carboxyl-containing prepolymer P-1 solution, 2.11 parts by weight of triethylamine, and 30 parts by weight of a methyl ethyl ketone solution of blocked isocyanate compound BI-4. The mixture was stirred for 5 minutes to obtain a mixture. Separately, a flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent. While stirring at 40°C, the mixture was added over 2 minutes and further stirred at 40°C for 30 minutes. Next, 0.250 parts by weight of a 25% by weight aqueous ethylenediamine solution was added. After stirring at 40°C for 1 hour, infrared spectroscopy of the reaction solution confirmed the disappearance of the isocyanate group absorption. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-4 (CS-4WD) with a solids concentration of 30% by weight. This polyurethane resin CS-4 has a core made of a blocked isocyanate compound BI-4 and a shell made of a polyurethane formed from an anionic prepolymer P-1.

[0086] [Production of core-shell waterborne polyurethane resin CS-5] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 66.20 parts by weight of nonionic prepolymer P-4 solution and 30 parts by weight of a methyl ethyl ketone solution of blocked isocyanate compound BI-1. The mixture was stirred for 5 minutes to obtain a mixture. Separately, a flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent. While stirring at 40°C, the mixture was added over 2 minutes and further stirred at 40°C for 30 minutes. 0.250 parts by weight of a 25% by weight aqueous ethylenediamine solution was then added. After stirring at 40°C for 1 hour, the reaction mixture was analyzed by infrared spectroscopy, confirming the disappearance of the isocyanate group absorption. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-5 (CS-5WD) with a solids concentration of 30% by weight. This polyurethane resin CS-5 has a core made of a blocked isocyanate compound BI-1 and a shell made of a polyurethane formed from a nonionic prepolymer P-4.

[0087] [Production of core-shell waterborne polyurethane resin CS-6] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 52.40 parts by weight of anionic carboxyl-containing prepolymer P-1 and 42 parts by weight of a methyl ethyl ketone solution of nonionic blocked isocyanate compound BI-5. The mixture was stirred for 5 minutes. A separate flask equipped with a stirrer and thermometer was charged with 150 g of water and 0.02 g of antifoaming agent. While stirring at 40°C, the mixture was added over 2 minutes and further stirred at 40°C for 30 minutes. 0.250 parts by weight of a 25% by weight aqueous ethylenediamine solution was then added. After stirring at 40°C for 1 hour, the reaction mixture was analyzed by infrared spectroscopy, confirming the disappearance of the isocyanate group absorption. The ethyl methyl ketone solvent was removed under reduced pressure, and the concentration was adjusted with water to obtain an aqueous dispersion of core-shell waterborne polyurethane resin CS-6 (CS-6WD) with a solids concentration of 30% by weight. This polyurethane resin CS-6 has a core made of a nonionic blocked isocyanate compound BI-5, and a shell made of a polyurethane formed from an anionic prepolymer P-1.

[0088] (Composite water dispersion) [BI-PU-WD] [Production of Composite Water Dispersion A (BI-PU-WD-A) of Blocked Isocyanate Compound BI-1 and Polyurethane Resin PU-1 (described in detail below)] To 66.7 parts by mass of a blocked isocyanate compound BI-1 in methyl ethyl ketone, 101.8 parts by mass of a carboxyl-containing anionic polyurethane resin PU-1 in methyl ethyl ketone was added, and 375 parts by mass of water was gradually added while stirring. The solution was then cooled to 50°C or lower under reduced pressure to remove the methyl ethyl ketone, and the concentration was adjusted with water to obtain a composite aqueous dispersion A (BI-PU-WD-A) with a solids content of 25% by mass and a BI-1 / PU-1 ratio of 4 / 6.

[0089] [Production of Composite Water Dispersion B (BI-PU-WD-B) of Blocked Isocyanate Compound BI-1 and Polyurethane Resin PU-1 (described in detail below)] To 50.0 parts by mass of a blocked isocyanate compound BI-1 in methyl ethyl ketone was added 118.7 parts by mass of a carboxyl-containing anionic polyurethane resin PU-1 in methyl ethyl ketone, and 380 parts by mass of water was gradually added while stirring. The solution was then cooled to 50°C or lower under reduced pressure to remove the methyl ethyl ketone, and the concentration was adjusted with water to obtain a composite aqueous dispersion B (BI-PU-WD-B) with a solids content of 25% by mass and a BI-1 / PU-1 ratio of 3 / 7.

[0090] (Polyurethane resin) [Production of polyurethane resin PU-1] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 437.2 parts by weight of polycarbonate diol with a number average molecular weight of 2000, 192.2 parts by weight of dicyclohexylmethane-4,4'-diisocyanate, 60.8 parts by weight of dimethylolpropionic acid, 13.0 parts by weight of 1,6-hexanediol, and 250 parts by weight of methyl ethyl ketone as a solvent. The mixture was stirred at 80°C for 5 hours to react. The infrared spectrum of the reaction solution was measured, and it was confirmed that the absorption of the isocyanate group had disappeared. This produced a methyl ethyl ketone solution of polyurethane resin PU-1 with a solids content of 73.7% by weight. Separately, 225 parts by weight of water was gradually added to 100 parts by weight of the methyl ethyl ketone solution of polyurethane resin PU-1 while stirring. Methyl ethyl ketone was removed from this solution under reduced pressure at 50°C or below, and the concentration was adjusted with water to obtain an aqueous dispersion (PU-1WD) of an anionic polyurethane resin aqueous dispersion PU-1 having carboxyl groups with a solid content of 25% by mass.

[0091] (polyester resin) [Production of Polyester Resin PE-1] 95 parts by weight of dimethyl terephthalate, 95 parts by weight of dimethyl isophthalate, 35 parts by weight of ethylene glycol, 145 parts by weight of neopentyl glycol, 0.1 parts by weight of zinc acetate, and 0.1 parts by weight of antimony trioxide were charged into a reaction vessel and subjected to a transesterification reaction at 180°C for 3 hours. Next, 6.0 parts by weight of 5-sodium sulfoisophthalic acid was added, and an esterification reaction was carried out at 240°C for 1 hour. After that, a polycondensation reaction was carried out at 250°C under reduced pressure (1.33 to 0.027 kPa) for 2 hours to obtain a polyester resin (PE-1) with a molecular weight of 19,500. 300 parts by weight of this polyester resin (PE-1) and 140 parts by weight of butyl cellosolve were stirred at 160°C for 3 hours to obtain a viscous molten liquid. Water was gradually added to this molten liquid, and after 1 hour, a uniform, pale white polyester resin aqueous dispersion (PE-1WD) with a solids content of 15% by weight was prepared.

[0092] [Production of Polyester Resin PE-2] A reactor was charged with 105 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 50 parts by weight of ethylene glycol, 36 parts by weight of hexanediol, 0.1 parts by weight of zinc acetate, and 0.1 parts by weight of antimony trioxide, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 8.6 parts by weight of 5-sodium sulfoisophthalic acid and 8 parts by weight of sebacic acid were added, and an esterification reaction was carried out at 240°C for 1 hour. This was followed by a polycondensation reaction at 250°C under reduced pressure (1.33 to 0.027 kPa) for 2 hours to obtain a polyester resin (PE-2) with a molecular weight of 18,000. 300 parts by weight of this polyester resin (PE-2) and 140 parts by weight of butyl cellosolve were stirred at 160°C for 3 hours to obtain a viscous molten liquid. Water was gradually added to this molten liquid, and after 1 hour, a uniform, pale white polyester resin aqueous dispersion (PE-2WD) with a solids content of 15% by weight was prepared.

[0093] (Crosslinking agent) [Production of Crosslinking Agent OX-1] A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 150.0 parts by weight of water and 250.0 parts by weight of methoxypropyl alcohol and heated to 80°C under a nitrogen atmosphere. Subsequently, a monomer mixture consisting of 150.0 parts by weight of methyl methacrylate, 180.0 parts by weight of 2-isopropenyl-2-oxazoline, and 90.0 parts by weight of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AM-90G) and a polymerization initiator solution consisting of 18.0 parts by weight of 2,2'-azobis(2-amidinopropane) dihydrochloride as a polymerization initiator and 170.0 parts by weight of water were added dropwise from the dropping funnel over 2 hours under a nitrogen atmosphere while maintaining the flask at 80°C. After the addition, the mixture was stirred at 80°C for 5 hours and then cooled to room temperature. An appropriate amount of water was added to prepare an oxazoline-based crosslinker aqueous dispersion (OX-1WD) with a solids content of 40% by weight.

[0094] (acrylic resin) [Production of acrylic resin AC-1] 356 parts by weight of methyl methacrylate, 16 parts by weight of acrylic acid, 5 parts by weight of normal butyl acrylate, 10 parts by weight of 2-hydroxyethyl methacrylate, and 372 parts by weight of methyl ethyl ketone were added with 2 parts by weight of t-butylperoxy-2-ethylhexanoate as a polymerization initiator, and the mixture was stirred while heating to 50°C and maintained for 120 minutes. The mixture was then heated to 70°C and maintained for 180 minutes. After cooling to 40°C, 13 parts by weight of triethylamine was added to obtain a methyl ethyl ketone solution of acrylic resin (AC-1). 150 parts by weight of water was gradually added to 200 parts by weight of this methyl ethyl ketone solution while stirring. The solution was then heated under reduced pressure at 50°C or below to remove methyl ethyl ketone and adjust the concentration with water to obtain an aqueous dispersion of acrylic resin (AC-1WD) with a solids content of 40% by weight.

[0095] (particle) [Particle PA-1] As the particles (PA-1), colloidal silica (Snowtex ZL; manufactured by Nissan Chemical Industries, Ltd.) having a solid content concentration of 40% by mass and an average particle size of 80 nm was used as it was as a particle (PA-1) solution.

[0096] [Particle PA-2] As the particles (PA-2), colloidal silica (Snowtex XL; manufactured by Nissan Chemical Industries, Ltd.) having a solid content concentration of 40 mass % and an average particle size of 40 to 60 nm was used as it was as a particle (PA-2) solution.

[0097] (Production of polyester resin E-1 for substrates) (Preparation of antimony trioxide solution) Antimony trioxide (Sigma-Aldrich Japan LLC) was placed in a flask together with ethylene glycol, stirred at 150°C for 4 hours to dissolve, and then cooled to room temperature to prepare a 20 g / L ethylene glycol solution of antimony trioxide.

[0098] (Polymerization of polyester resin E-1 for substrate) High-purity terephthalic acid and twice the molar amount of ethylene glycol were charged into a 2-liter stainless steel autoclave equipped with a stirrer, and 0.3 mol % triethylamine based on the acid component was added. An esterification reaction was carried out at 250°C under a pressure of 0.25 MPa while distilling water out of the system, yielding a mixture of bis(2-hydroxyethyl) terephthalate and oligomers (hereinafter referred to as the BHET mixture) with an esterification rate of approximately 95%. The above antimony trioxide solution was added to this BHET mixture as a polycondensation catalyst so that the amount was 0.04 mol % in terms of antimony atoms based on the acid component in the polyester, and the mixture was then stirred for 10 minutes at 250°C under a nitrogen atmosphere and atmospheric pressure. The temperature was then raised to 280°C over 60 minutes while the pressure in the reaction system was gradually reduced to 13.3 Pa (0.1 Torr), and the polycondensation reaction was carried out at 280°C and 13.3 Pa for a further 68 minutes, yielding polyester resin E-1, which had an intrinsic viscosity (IV) (solvent: phenol / tetrachloroethane = 60 / 40) of 0.61 dl / L and contained substantially no particles.

[0099] (Production of polyester resin E-2 for substrates) (Example of preparing an aluminum compound solution) A 20 g / L aqueous solution of basic aluminum acetate (hydroxyaluminum diacetate; manufactured by Sigma-Aldrich Japan LLC) was charged into a flask together with an equal volume (by volume) of ethylene glycol. The mixture was stirred at room temperature for 6 hours, and then the mixture was stirred under reduced pressure (133 Pa) at 70-90°C for several hours while distilling off water from the system, to prepare a 20 g / L ethylene glycol solution of the aluminum compound.

[0100] (Example of preparation of phosphorus compound solution) Diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate (Irganox 1222 (BASF)) as a phosphorus compound was charged into a flask together with ethylene glycol, and the mixture was heated at a liquid temperature of 160°C for 25 hours with stirring under nitrogen substitution to prepare a 50 g / L ethylene glycol solution of the phosphorus compound.

[0101] (Preparation of a mixture of an aluminum compound solution and a phosphorus compound solution) The ethylene glycol solutions obtained in the above aluminum compound preparation example and the above phosphorus compound preparation example were charged into a flask, mixed at room temperature so that the molar ratio of aluminum atoms to phosphorus atoms was 1:2, and stirred for one day to prepare a catalyst solution.

[0102] (Polymerization of polyester resin E-2 for substrate) Instead of antimony trioxide solution, a mixture of the above-mentioned aluminum compound solution and phosphorus compound solution was used as a polycondensation catalyst, so that the aluminum atoms and phosphorus atoms were 0.014 mol % and 0.028 mol %, respectively, relative to the acid component in the polyester. Polymerization was carried out in the same manner as for polyester resin E-1, except that the polymerization time was set to 68 minutes, thereby obtaining polyester resin E-2 having an intrinsic viscosity (IV) of 0.61 dL / g and containing substantially no particles.

[0103] Example 1 (1) Preparation of coating solution The following coating agent was mixed with a mixed solvent of water and isopropanol (80 / 20 parts by mass) to prepare a total of 100 parts by mass. The solids mass ratio of the water dispersion of blocked isocyanate compound BI-1 (BI-1WD-A), the water dispersion of polyurethane resin (PU-1WD), and the water dispersion of polyester resin (PE-1WD) was 25 / 45 / 30, with a total solid resin concentration of 4% by mass. Furthermore, the solids mass ratios of particles PA-1 and particles PA-2 were 0.5 and 8, respectively, per 100 parts of the solids of the aforementioned resins. 1% by mass of a 10% aqueous solution of a silicone surfactant was added to the coating solution. The blending ratios of resins and other components in the coating solutions of the examples and comparative examples are shown in Table 1. Mixed solvent (water / isopropanol) 78.95 parts by mass Water dispersion of blocked isocyanate compound BI-1 (BI-1WD-A) 4.00 parts by mass Polyurethane resin water dispersion (PU-1WD) 7.20 parts by mass Polyester resin water dispersion (PE-1WD) 8.00 parts by mass Particle PA-1 solution 0.05 parts by mass Particle PA-2 solution 0.80 parts by mass Surfactant aqueous solution 1.00 parts by mass Total 100.00 parts by mass

[0104] (2) Manufacturing of laminated polyester film Resin pellets of polyester resin E-1, used as the raw polymer for the film, were dried at 135°C for 6 hours under a reduced pressure of 133 Pa. Then, the resin pellets 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 cooling metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet.

[0105] This unstretched PET sheet was heated to 100° C. using a group of heated rolls and an infrared heater, and then stretched 3.5 times in the longitudinal direction using a group of rolls with different peripheral speeds to obtain a uniaxially stretched PET film.

[0106] Next, the coating solution was applied to one side of a PET film in an amount of 6.0 g / m2 The film was then heat-treated at 90°C for 3 seconds and 40°C for 3 seconds and then dried. The coating surface of the film was then brought into contact with a 200mm diameter, hard chrome-plated tension control roll (surface roughness: 0.4S). The running conditions were a running speed of 20m / min, a wrap angle of 60°, and a running tension of 400-500N / m. The film was then stretched 4.0 times in the width direction at 110°C and, with the film fixed in the width direction, heated at 230°C for 5 seconds. A 3% relaxation treatment in the width direction was then performed to obtain a 100µm laminated polyester film. The evaluation results of this film are shown in Table 2.

[0107] Examples 2 to 9 A laminated polyester film was obtained in the same manner as in Example 1, except that the coating solution in Example 1 was changed according to the types of resins and additives and their blending ratios in each Example in Table 1.

[0108] Example 10 A laminated polyester film was obtained in the same manner as in Example 1, except that polyester resin E-2 was used instead of polyester resin E-1 as the raw polymer for the film.

[0109] (Comparative Examples 1 to 10) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating solution in Example 1 was changed according to the types of resins and additives and their blending ratios in each of the comparative examples in Table 1.

[0110] Table 2 summarizes the evaluation results for each example and comparative example.

[0111] As shown in Table 2, satisfactory results were obtained in haze, blocking resistance, adhesion to UV ink, adhesion to the hard coat layer, and moist heat resistance in each of Examples 1 to 10. On the other hand, the results were not satisfactory in Comparative Examples 1 to 10.

[0112] [Table 1]

[0113] [Table 2] [Industrial Applicability]

[0114] The present invention makes it possible to provide a laminated polyester film having optimum adhesive properties for use in a wide range of fields, including optical applications, packaging applications, and label applications.

Claims

1. A laminated polyester film having a polyester film substrate and a coating layer on one or both sides thereof, the coating layer is a coating film formed from a coating liquid containing an aqueous dispersion of a hydrophobic blocked isocyanate compound hydrophilized with an anionic emulsifier, a water-dispersible polyurethane resin having a carboxyl group, and a water-dispersible polyester resin; the mass ratio of the hydrophobic blocked isocyanate compound to the water-dispersible polyurethane resin having a carboxyl group is in the range of 20 / 80 to 60 / 40; a mass ratio of the total of the hydrophobic blocked isocyanate compound and the water-dispersible polyurethane resin having a carboxyl group to the polyester resin is in the range of 30 / 70 to 70 / 30; Peeling defects of the coating film: 5.0 / m ２ less than laminated polyester film.

2. A laminated polyester film as described in Claim 1, wherein the anionic emulsifier that hydrophilizes the aqueous dispersion of the hydrophobic blocked isocyanate compound is a water-dispersible polyurethane resin having the carboxyl group.

3. A laminated polyester film as described in claim 1 or 2, having a core-shell structure in which the hydrophobic blocked isocyanate compound is the core and the water-dispersible polyurethane resin having a carboxyl group is the shell.

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