Laminated polyester film

Abstract

The present invention aims to provide a laminated polyester film which has excellent adhesion to a coating agent such as a hard coat agent or a UV ink, and excellent maintenance of high-level adhesion over a long period of time. The present invention is a laminated polyester film which has a resin layer on at least one side of a polyester film, the contact angle of an ethylene glycol droplet of the resin layer is 48 degrees or more and 56 degrees or less, and the contact angle of a diiodomethane droplet is 24 degrees or more and 32 degrees or less, and further preferably the contact angle of a water droplet of the resin layer is 65 degrees or more and 75 degrees or less.

Description

Technical Field

[0001] This invention relates to laminated polyester films. More specifically, it relates to laminated polyester films having a coating layer with easy adhesion, which is optimally suited for all applications such as optics, packaging, and labeling.

[0002] Thermoplastic resin films, especially polyester films, possess excellent mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. Therefore, they are widely used in magnetic recording materials, packaging materials, solar cells, flat panel displays, and as optical films such as anti-reflective films, diffusers, and prisms, as well as label printing films. However, due to the highly crystalline orientation of the polyester film surface, it lacks adhesion to various coatings, resins, and inks during processing in these applications. Therefore, research has been conducted to impart adhesive properties to the surface of polyester films through various methods.

[0003] Conventional methods for imparting adhesiveness include surface activation methods such as corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment of the polyester film as a substrate. However, the adhesive effect obtained through these treatments decreases over time, making it difficult to maintain a high level of adhesiveness over extended periods. Therefore, methods that involve coating the surface of a polyester film with various resins to create a coating layer with easy-to-adhere properties are commonly used. Furthermore, a simple indicator of the easy-to-adhere properties of the coating layer is the contact angle of droplets of solvents such as water on the surface of these coating layers (see, for example, Patent Document 1).

[0004] Previously, a known technique involved applying a coating layer containing a copolyester resin or polyurethane resin, or a coating layer in which these resins were combined with a crosslinking agent, to improve the affinity with resin components such as polyurethane acrylates or ester acrylates used in hard coatings and prism lens agents, thereby imparting adhesion to these components (Patent Documents 2, 3). However, UV inks (ultraviolet-curing inks) used in label printing contain dyes or pigments in addition to resins to achieve hues, with pigments exhibiting good lightfastness comprising approximately 15-25% by mass of the ink component. Furthermore, in inks for white or black colors where opacity is important, the content of various pigments can reach as high as approximately 50% by mass. Therefore, the adhesion in the prior art is insufficient, particularly regarding adhesion at low radiation levels.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2002-67255

[0008] Patent Document 2: Japanese Patent Application Publication No. 2000-229355

[0009] Patent Document 3: Japanese Patent Application Publication No. 2004-35761 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] This invention was made with the aforementioned problems of the prior art in mind. Specifically, the object of this invention is to provide a laminated polyester film that exhibits excellent adhesion to coatings such as hard coatings and UV (ultraviolet) inks, and maintains excellent high-level adhesion over a long period.

[0012] Solution for solving the problem

[0013] In order to solve the above-mentioned problems, the inventors studied the causes of the problems and discovered that at least one side of the polyester film substrate has a resin layer, and the ethylene glycol droplets and diiodomethane droplets in the resin layer satisfy a contact angle within a specific range, thereby solving the problem of the present invention and thus completing the present invention.

[0014] That is, the present invention includes the following technical solutions.

[0015] 1. A laminated polyester film having a resin layer on at least one side of the polyester film, wherein the contact angle of ethylene glycol droplets in the resin layer is 48 degrees or more and 56 degrees or less, and the contact angle of diiodomethane droplets is 24 degrees or more and 32 degrees or less.

[0016] 2. The laminated polyester film according to the first description above, wherein the water droplet contact angle of the aforementioned resin layer is 65 degrees or more and 75 degrees or less.

[0017] 3. The laminated polyester film according to the first or second description above, wherein the absolute values ​​of the changes in the resistance to humid heat treatment (temperature 85°C, humidity 85%RH, 240 hours) of the ethylene glycol, diiodomethane and water droplet contact angle of the aforementioned resin layer before and after treatment are all less than 5 degrees.

[0018] The effects of the invention

[0019] The laminated polyester film of the present invention exhibits excellent adhesion to coating agents such as hard coating agents and UV inks, and maintains excellent high-level adhesion over a long period of time. Detailed Implementation

[0020] (Polyester film substrate)

[0021] In addition to polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6-naphthalenedicarboxylate, and polypropylene terephthalate, the polyester resin constituting the polyester film substrate of the present invention can also be a copolyester resin, which is formed by replacing a portion of the diol component or dicarboxylic acid component of the aforementioned polyester resin with a copolymer component such as diethylene glycol, neopentyl glycol, 1,4-cyclohexanediethanol, and polyalkylene glycol; and dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 5-(sodium sulfonyl) isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

[0022] The polyester resins suitable for use as polyester film substrates in this invention are mainly selected from polyethylene terephthalate, polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene 2,6-naphthalate. Among these polyester resins, polyethylene terephthalate is the most preferred due to its balance between physical properties and cost. Furthermore, the polyester film substrate made of these polyester resins is preferably a biaxially stretched polyester film, which can improve chemical resistance, heat resistance, and mechanical strength.

[0023] There are no particular limitations on the catalyst used for polycondensation in the manufacture of polyester resins, but antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. Additionally, germanium compounds or titanium compounds are also preferred. Further 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.

[0024] In addition, the polyester film substrate in this invention is not particularly limited in its layer composition. It can be a single-layer polyester film, or it can be composed of two layers with different compositions, or it can be a polyester film substrate formed by at least three layers having an outer layer and an inner layer.

[0025] (Resin layer)

[0026] In this invention, it is preferable to form a resin layer on at least one side of the polyester film, wherein the contact angle of ethylene glycol droplets is 48 degrees or more and 56 degrees or less, and the contact angle of diiodomethane droplets is 24 degrees or more and 32 degrees or less. The resin layer may be provided on both sides of the polyester film substrate, or only on one side of the polyester film, or a different type of resin layer may be provided on the other side. This resin layer can be formed as a surface layer of the polyester film substrate through chemical treatment with a surface treatment agent or physical treatment such as corona treatment, or the resin itself can be laminated onto the substrate through co-extrusion or the like. In particular, the design freedom is high; therefore, it is preferable to provide the resin layer on the surface of the substrate through coating or the like. There are no particular restrictions on the type of resin used in the resin layer, as long as it is within the range of the preferred contact angles in this invention; one type of resin or two or more types of resin can be used. From the perspective of the design freedom of the resin skeleton that satisfies the contact angles, polyurethane resin is preferred as the primary resin.

[0027] When the aforementioned polyurethane resin is used in the resin layer, there are no particular problems even if other resins are used in combination.

[0028] Other resins that can be cited include polyester resins, alkyd resins, acrylic resins, cellulose resins, polyolefin resins, and polyacetal resins. Among these resins, polyester resin is preferred from the viewpoint of adhesion to the substrate.

[0029] When polyurethane resin and polyester resin are used in combination, the polyurethane resin to polyester resin ratio is preferably in the range of 90 / 10 to 10 / 90 by mass, more preferably in the range of 80 / 20 to 20 / 80, and even more preferably in the range of 70 / 30 to 30 / 70. If the polyurethane resin and polyester resin are in the range of 90 / 10 to 10 / 90, the contact angle of the resin layer can be easily adjusted to the range preferred by the present invention, and as a result, adhesion is maintained, which is preferable.

[0030] From the viewpoint of improving adhesion and durability, a crosslinking agent is preferably incorporated into the resin layer. The type of crosslinking agent is not particularly limited; isocyanate-based, oxazoline-based, carbodiimide-based, epoxy-based, melamine-based, and acrylate-based crosslinking agents can be used. From the perspective of reactivity with polyurethane or polyester resins, isocyanate-based crosslinking agents are preferred. As for the mass ratio of the crosslinking agent to the total amount of the polyurethane or polyester resin, it is preferably in the range of 5 / 95 to 70 / 30, more preferably in the range of 10 / 90 to 60 / 40, and further preferably in the range of 15 / 85 to 50 / 50. If the mass ratio of the crosslinking agent to the total amount of the polyurethane or polyester resin is 95% by mass or less, the contact angle of the resin layer can be easily adjusted to the range preferred by this invention, resulting in improved adhesion. Furthermore, if the mass ratio of the crosslinking agent to the total amount of the polyurethane or polyester resin is 5% by mass or more, improved durability is preferred.

[0031] In addition to resin and crosslinking agent, inorganic or organic particles can be added to the resin layer. In films, particles are added to create an uneven surface for improved lubrication, but particles can also be added to the resin layer outside the film substrate. Especially in cases requiring transparency, such as optical films, it is preferable to add particles only to the resin layer, as this reduces the amount of particles that decrease transparency. When particles are not substantially added to the film substrate, the amount of particles added to the coating layer relative to the total mass of resin and crosslinking agent in the resin layer is preferably in the range of 0.05% to 20% by mass. A particle addition of 0.05% by mass or more is preferred for improved lubrication, while a particle addition of 20% by mass or less is preferred for good transparency.

[0032] In the resin layer of the present invention, known additives such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic slip agents, pigments, dyes, antistatic agents, nucleating agents, etc., may be added without impairing the effects of the present invention.

[0033] When a resin layer is formed by coating or other methods, there are no particular restrictions on the solvent, but from the viewpoint of the working environment, water is preferred. When water is used as the solvent, it is preferable to introduce hydrophilic groups into the resin backbone to dissolve or disperse the resin in water. One or more known hydrophilic groups such as hydroxyl, ether, carboxyl, and sulfonic acid groups can be used. However, among these hydrophilic groups, from the perspective of minimizing the impact of introducing hydrophilic groups on the contact angle, it is preferable to primarily use sulfonic acid or carboxyl groups.

[0034] The components of the coating layer will be described in further detail below.

[0035] (Polyurethane resin)

[0036] The polyurethane resin exemplified in this invention refers to a polyurethane resin derived at least from a polyol component and a polyisocyanate component, and further, if necessary, from a chain extender. In particular, to impart water solubility or water dispersibility to the polyurethane resin, it is preferable to have hydrophilic groups in the molecule or on the side chain. Here, "in the molecule" means present in or at the end of the aforementioned polyurethane resin's main chain. Furthermore, "side chain" refers to a molecular chain in which three or more terminal functional groups of any of the aforementioned raw material components constituting the molecular chain are present, thereby being introduced onto the branched molecular chain after synthesis and polymerization. As hydrophilic groups, anionic groups such as sulfonic acids, phosphonic acids, and carboxylic acids, cationic groups such as quaternary ammonium compounds, and nonionic groups such as oxoalkylene compounds can be used; however, in this invention, it is particularly preferable to have carboxyl groups primarily present in the molecule or on the side chain.

[0037] The polyurethane resin containing carboxyl groups preferably used in this invention is mainly obtained by using a carboxyl-containing polyol as the component of the urethane ester. Examples of the aforementioned carboxyl-containing polyol can be: higher molecular weight polyols, such as carboxyl-containing polyalkylene glycols, carboxyl-containing acrylic polyols, carboxyl-containing polyolefin polyols, and carboxyl-containing polyester polyols. Alternatively, lower molecular weight polyols can be used, such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvalerate. When introducing carboxyl groups, dimethylolpropionic acid and dimethylolbutyric acid are particularly preferred.

[0038] For polyurethane resins containing carboxyl groups, an acid value of 10–60 mg KOH / g is preferred, and an acid value of 20–50 mg KOH / g is more preferred. An acid value of 10 mg KOH / g or higher results in good hydrophilicity of the polyurethane resin itself, leading to good water solubility or dispersibility. Conversely, an acid value of 60 mg KOH / g or lower maintains the water resistance of the coating layer, preventing adhesion between films due to moisture absorption. Furthermore, in the polyurethane resins preferably used in this invention, other hydrophilic groups besides carboxyl groups, such as hydroxyl, alkyl groups, sulfonic acids, phosphonic acids, and quaternary ammonium groups, can be introduced within a range that does not degrade performance to compensate for the water solubility or dispersibility of the polyurethane resin.

[0039] The carboxyl groups in polyurethane resins can also be neutralized by alkaline compounds. Examples of alkaline 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 readily dissociate from the carboxyl groups upon heating are preferred. Examples of organic amine compounds include, for instance, straight-chain or branched 1,2- or tertiary amines with 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; monoisopropanolamine; methylethanolamine; methylisopropanolamine; dimethylethanolamine; diisopropanolamine; diethanolamine; triethanolamine; diethylethanolamine; and hydroxyl-containing amines such as triethanolamine.

[0040] Furthermore, regarding the composition of the polyurethane resin, from the perspective of achieving the preferred contact angle range of the present invention, a further ideal approach is to include at least 50% by mass of a soft segment structure mainly composed of straight-chain alkylene chains with C5 or more atoms. The number-average molecular weight of this soft segment is preferably in the range of 400 to 5000, more preferably in the range of 500 to 3000. If the molecular weight of the soft segment is in the range of 400 to 5000, it becomes easier to adjust to the preferred contact angle range of the present invention, which is preferable. The content or molecular weight of these soft segment structures can be adjusted by... 1The value can be calculated using known methods such as ¹H-NMR determination or GPC analysis after hydrolysis. Alternatively, it can be calculated based on the amounts of each component added during resin polymerization. Furthermore, examples of suitable backbones for this soft segment include polyester polyols primarily containing alkylene dicarboxylic acids or alkylene glycols, polyether polyols containing alkylene glycols, and polycarbonate polyols containing alkylene glycols. From the viewpoint of adhesion durability under high temperature and high humidity conditions, the use of polycarbonate polyols is further preferred.

[0041] The polyester polyol used to constitute the polyurethane resin of this invention preferably has a linear alkylene chain with 5 or more carbon atoms. Examples of linear alkylene dicarboxylic acids include heptanoic acid, octanoic acid, azelaic acid, and sebacic acid. Examples of linear alkylene diols include 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, and 1,9-nonanediol. Alicyclic, aromatic, and branched aliphatic dicarboxylic acids or diols other than those mentioned above can also be used in combination as long as they are in appropriate amounts. Furthermore, as long as it is within the physically permissible range, polycarboxylic acids, polyols, or unsaturated components with 3 or more functionalities can also be used.

[0042] As the polycarbonate polyol constituting the polyurethane resin of the present invention, an aliphatic polycarbonate polyol having a linear alkylene chain with 5 or more C5 or more is preferably used. Examples of linear aliphatic polycarbonate diols include aliphatic polycarbonate diols obtained by reacting one or more of 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,8-nonanediol with carbonates such as dimethyl carbonate, ethylene carbonate, and carbamate chloride. Furthermore, even diols other than those mentioned above can be used in combination as long as they are used in appropriate amounts.

[0043] For the synthesis and polymerization of the polyurethane resin of the present invention, other polyol components besides those described above may also be used. Examples of other polyol components include, for instance, ethylene-free polyether polyols, polyolefin polyols, dimer polyols, and organosilicon polyols. Among these, ethylene-free polyether polyols with good compatibility with the aforementioned main polyols are preferred.

[0044] Examples of polyisocyanates used in the synthesis and polymerization of the polyurethane resin of the present invention include: aliphatic diisocyanates containing aromatic rings such as xylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate; alicyclic diisocyanates such as 1,3-bis(isocyanate-methyl)cyclohexane; aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; modified polyisocyanates containing isocyanurate bonds, biuret bonds, or ureocarbamate bonds made from diisocyanates; and polyisocyanates obtained by pre-addition of one or more diisocyanates with trimethylolpropane, etc. Compared with the aforementioned aliphatic diisocyanates containing aromatic rings, the use of alicyclic diisocyanates or aliphatic diisocyanates without aromatic rings results in fewer yellowing problems and is therefore preferred.

[0045] Examples of chain extenders include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; polyols such as glycerol, trimethylolpropane, and pentaerythritol; diamines such as ethylenediamine, hexamethylenediamine, and piperazine; amino alcohols such as monoethanolamine and diethanolamine; thioglycols such as thiodiethylene glycol; and water. Additionally, polyols and polyamines with three or more functional groups can be used, even in small quantities.

[0046] In order to improve durability, the polyurethane resin of the present invention may have reactive groups such as end-capped isocyanates at the end or on the side chains.

[0047] (Polyester resin)

[0048] In the coating layer of the present invention, the polyester resin preferably used in conjunction with polyurethane resin or the like can be a linear resin, and more preferably a polyester resin whose constituent components are dicarboxylic acids and diols having branched structures or diols containing one or more ether bonds. Examples of dicarboxylic acids here include terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid, 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.

[0049] In addition, diols with branched structures refer to diols with branched alkylene groups, such as 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.

[0050] Furthermore, examples of diols containing one or more ether bonds include condensates of alkylene glycols such as diethylene glycol, triethylene glycol, and dipropylene glycol, as well as bisphenol-based ethylene oxide or propylene oxide adducts. The number of ether bonds in the molecule is not particularly limited, but since the strength or glass transition point of polyester resins decreases, four or fewer ether bonds are preferred, and two or fewer are even more preferred.

[0051] In the polyester resin, the branched diol component or the diol component containing one or more ether bonds, which is a more preferred embodiment described above, is preferably contained at a rate of 10 mol% or more, and more preferably at a rate of 20 mol% or more, in the total polyol component. If it is 10 mol% or more, crystallinity is suppressed, and the adhesion of the coating layer is improved, which is preferable. The upper limit of the diol component in the total polyol component is preferably 80 mol% or less, more preferably 70 mol%. If it is 80 mol% or less, the concentration of oligomers as byproducts is suppressed, and the transparency of the coating layer is good, which is preferable. Ethylene glycol is most preferred as the diol component other than the above-mentioned compounds. Propylene glycol, butanediol, hexanediol, or diols such as 1,4-cyclohexanediol, triethanolamine, glycerol, diglycerol, and other polyols having three or more hydroxyl groups in their molecules may also be used, as long as in small amounts.

[0052] For the dicarboxylic acid that is a component of the above-mentioned polyester resin, terephthalic acid or isophthalic acid is most preferred. In addition to the above-mentioned dicarboxylic acid, in order to impart water dispersibility to the copolymer polyester resin, it is preferable to copolymerize 5-sulfonoisophthalic acid or the like in the range of 1 to 10 mol%, for example, sulfonoterephthalic acid, 5-sulfonoisophthalic acid, 5-(sodium sulfono)isophthalic acid, etc.

[0053] Alternatively, this application can also be achieved using polyester resin in addition to polyurethane resin. In this case, the polyester resin preferably has 30 mol% or more of a linear alkylene chain component with 5 or more carbon atoms. This linear alkylene chain component with 5 or more carbon atoms can be derived from a dicarboxylic acid component or a diol component. Examples of linear alkylene dicarboxylic acids with 5 or more carbon atoms include pimelic acid, octanoic acid, azelaic acid, sebacic acid, and other linear aliphatic dicarboxylic acids. Examples of linear alkylene diols with 5 or more carbon atoms include 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and other aliphatic diols. Alicyclic, aromatic, and branched aliphatic dicarboxylic acids or diols other than those mentioned above can also be used, provided the amount is appropriate. Furthermore, polycarboxylic acids, polyols, or unsaturated components with 3 or more functionalities can also be used, provided the physical properties are permissible.

[0054] (Cross-linking agent)

[0055] As the crosslinking agent of the present invention, known isocyanate-based, epoxy-based, melamine-based, oxazoline-based, carbodiimide-based, etc., can be used. Durability can be further improved by using a crosslinking agent. Furthermore, isocyanate-based crosslinking agents are preferred from the perspective of the reactivity of the hydroxyl or urethane groups of the polyurethane resin with the hydroxyl groups of the polyester resin. End-capped isocyanate-based crosslinking agents are particularly preferred.

[0056] By forming a capped isocyanate system, the stability in the liquid coating state is improved. The crosslinking reaction initiation temperature can be changed according to the composition of the capping agent, thereby adjusting the crosslinking state.

[0057] Examples of end-capping agents include sodium bisulfite and other bisulfite compounds, 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, thiols such as butyl mercaptan and dodecyl mercaptan, amides such as acetanilide and acetamide, lactams such as ε-caprolactam and δ-valerolactam, imides such as succinimide and maleimide, oximes such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketone oxime, and amines such as diphenylaniline, aniline, and ethyleneimide.

[0058] Furthermore, in the isocyanate-based crosslinking agent, it is preferable to introduce hydrophilic groups in a manner that allows for easy mixing with water-soluble or water-dispersible polyurethane or polyester resins. Moreover, as the hydrophilic groups, anionic groups such as carboxyl or sulfonic acid groups, and nonionic groups such as oxyalkyl groups, are preferred. These hydrophilic groups can be prepared by pre-reacting a polyisocyanate, which forms the basis of the isocyanate, with a compound having hydrophilic groups and reactive groups such as hydroxyl or amino groups.

[0059] The upper limit of the dissociation temperature of the capping agent is preferably 200°C, more preferably 180°C, further preferably 160°C, particularly preferably 150°C, and most preferably 120°C. In the case of an online coating method, the capping agent dissociates during the film-forming process by applying heat after coating the coating solution and in the drying step, generating regenerated isocyanate groups. This allows for a crosslinking reaction with polyurethane resins, etc., improving the crosslinking state of the coating film.

[0060] The boiling point of the capping agent is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. When the boiling point of the capping agent is higher than that of the solvent in the coating liquid, the volatilization of the capping agent can be suppressed even during the drying process after coating with the coating liquid. Minor surface irregularities caused by unevenness in the coating surface are improved, and transparency is enhanced, which is therefore preferred. There is no particular upper limit to the boiling point of the capping agent, but from a productivity perspective, it is preferable to set the upper limit at around 300°C.

[0061] As a preferred end-capping agent in the end-capped isocyanate used in this invention, the end-capping agent has a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher. Examples of end-capping agents include pyrazole compounds such as sodium bisulfite, 3,5-dimethylpyrazole, and 3-methylpyrazole; malonate compounds such as dimethyl malonate and diethyl malonate; and oxime compounds such as acetone oxime and methyl ethyl ketone oxime. Among these, methyl ethyl ketone oxime, malonate compounds, or pyrazole compounds are preferred from the perspectives of resistance to damp heat and yellowing.

[0062] The aforementioned capped isocyanate is preferably 2 or more functional, and from the perspective of the crosslinking properties of the coating film, capped isocyanate with 3 or more functions is further preferred.

[0063] Polyisocyanates with three or more functions, which are precursors to the capped isocyanates of the present invention, can preferably be obtained by introducing isocyanate monomers. Examples include biuret bodies, isocyanurate bodies, and adducts obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, or alicyclic diisocyanates having two isocyanate groups.

[0064] Biuret bodies are self-condensed compounds with biuret bonds formed by the self-condensation of isocyanate monomers, such as biuret bodies of hexamethylene diisocyanate.

[0065] Isocyanurates are trimers of isocyanate monomers, such as trimers of hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate.

[0066] An adduct is an isocyanate compound with three or more functions, formed by reacting an isocyanate monomer with a compound containing low-molecular-weight active hydrogen. Examples include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate, compounds obtained by reacting trimethylolpropane with toluene diisocyanate, compounds obtained by reacting trimethylolpropane with xylene diisocyanate, and compounds obtained by reacting trimethylolpropane with isophorone diisocyanate.

[0067] Examples of the aforementioned isocyanate monomers include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, benzene diisocyanate, tetramethylxylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Aromatic diisocyanates such as esters, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, and xylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate; and aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate. From the perspectives of transparency, resistance to yellowing modification, adhesion, and resistance to damp heat, aliphatic and alicyclic isocyanates and their modified forms are preferred.

[0068] In this invention, two or more crosslinking agents can be used together. In particular, by using two or more different end-capped isocyanate-based crosslinking agents together, the crosslinking initiation temperature can be differentiated, and the crosslinking density can be controlled to a certain extent, thereby further improving the effect of this invention.

[0069] In this invention, the resin layer on the polyester film preferably has a contact angle of 48 degrees or more and 56 degrees or less for ethylene glycol droplets and a contact angle of 24 degrees or more and 32 degrees or less for diiodomethane droplets. To achieve this condition, the method described below is exemplified. First, a resin (polyurethane resin or polyester resin) containing a certain amount or more of the aforementioned C5 or higher linear alkylene chain component, a resin other than those mentioned above (polyurethane resin or polyester resin), and a crosslinking agent are prepared. The ratio of the resin containing a certain amount or more of the C5 or higher linear alkylene chain component to the resin other than those mentioned above is adjusted so that the contact angle of the ethylene glycol droplets is within a certain range. Next, the crosslinking agent is added to the resin while keeping the ratio of these resins constant, and the adjustment is performed so that the contact angle of the diiodomethane droplets is within a certain range. After adjustment, the contact angle of the ethylene glycol droplets is checked again, and the ratio of each resin can be finely adjusted as needed. However, these methods are merely examples, and other methods are not excluded.

[0070] Furthermore, in this invention, the resin layer on the polyester film, together with the aforementioned contact angle range, preferably has a water droplet contact angle of 65 degrees or more and 75 degrees or less. By ensuring the water droplet contact angle is within this range, the UV ink adhesion in low-radiation areas can be further improved. As an example of adjusting to this range, it can be achieved according to the crosslinking agent ratio as described above, but it can also be adjusted according to the resin composition or resin mixing ratio, etc.

[0071] Furthermore, in this invention, the resin layer on the polyester film preferably exhibits an absolute value of less than 5 degrees in the change of contact angle of each droplet before and after each damp heat treatment (temperature 85°C, humidity 85% RH, 240 hours). This small absolute value of contact angle change maintains the adhesion of UV inks or hard coatings even under high temperature and high humidity conditions. To achieve this, compared to polyester resins containing straight-chain alkylene chain components with C5 or more, a polyurethane resin formed from polyester glycol is preferably used as the resin layer, and more preferably a polyurethane resin formed from polycarbonate glycol containing straight-chain alkylene chain components with C5 or more. Compared to retaining straight-chain alkylene chain components with C5 or more in the resin via ester bonds, retaining them in the resin via highly hydrolysis-resistant polycarbonate bonds reduces the absolute value of the change in contact angle of each droplet before and after the damp heat treatment.

[0072] (Particles)

[0073] In this invention, particles can be added to the resin layer. The particles can be inorganic or organic, and there is no problem with either. Examples of inorganic particles include silicon dioxide, titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silicon dioxide, alumina, talc, kaolin, clay, calcium phosphate, mica, lithium montmorillonite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride. Examples of organic particles include styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and organosilicon-based organic polymer particles. These can be used individually or in combination. Titanium dioxide, alumina, zirconium oxide, and silicon dioxide are commonly used as particles, but silicon dioxide is preferred from the perspectives of particle hardness, specific gravity, and cost.

[0074] The preferred particle size range is 5–1000 nm, more preferably 10–800 nm, and even more preferably 20–500 nm. Larger particle sizes reduce transparency, while smaller particle sizes reduce slipability. Only one type of particle size may be used, or two or more different particle sizes or types may be used.

[0075] When using silica as particles, silica produced by the gas phase method can be dispersed in a solvent, or colloidal silica pre-dispersed in a solvent can be used.

[0076] In addition, to impart functionality to the resin layer beyond lubrication, particles with high or low refractive index, conductivity, ultraviolet light, or other reflective or absorptive properties can also be used.

[0077] The shape of the particles is not particularly limited as long as the purpose of this invention is met; spherical particles and amorphous, non-spherical particles can be used. The particle size of amorphous particles can be calculated in the form of the equivalent diameter of a circle. The equivalent diameter of a circle is obtained by dividing the observed area of ​​the particle by π, calculating the square root, and multiplying by 2.

[0078] (Manufacturing of laminated polyester film)

[0079] Regarding the method for manufacturing the laminated polyester film of the present invention, examples of using polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film substrates are given for illustration, but it is of course not limited thereto.

[0080] After the PET resin is thoroughly vacuum dried, it is fed to an extruder. Molten PET resin at approximately 280°C is extruded in sheet form from the T-die and then cooled and cured by electrostatic application to obtain unstretched PET sheets.

[0081] Furthermore, the aforementioned unstretched PET sheet can be a single layer or a multilayer structure based on co-extrusion. Additionally, as long as it is within the scope of achieving the effects of this invention, the polyester resin in each of these layers can contain various additives as needed. Examples of additives include antioxidants, lightfastness agents, anti-gelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants.

[0082] In addition, in order to adjust the operability of the film, such as its sliding properties, rollability, and anti-adhesion, as well as its wear resistance and scratch resistance, non-active particles can be included in the substrate film or the surface layer of the film, as long as it does not cause a deficiency in transparency.

[0083] Crystal orientation is achieved by subjecting the obtained unstretched PET sheet to uniaxial or biaxial stretching. For example, in biaxial stretching, the sheet is stretched 3.0 to 5.0 times its original length using rollers heated to 80–120°C to obtain a uniaxially stretched PET film. The ends of the film are then fixed with clamps and introduced into a hot air zone heated to 80–180°C, where it is stretched 3.0 to 5.0 times its original width. Alternatively, in uniaxial stretching, the unstretched PET sheet is stretched 3.0 to 5.0 times its original width in a tenter frame. After stretching, it is further heat-treated in a heat treatment zone at 180–230°C to complete crystal orientation.

[0084] Any known method can be used to coat the coating solution onto the PET film. Examples include reverse roller coating, gravure coating, lip coating, die coating, roller brush coating, spray coating, air knife coating, wire bar coating, tube doctor blade coating, dip coating, and curtain coating. These methods can be used individually or in combination.

[0085] The thickness of the coating layer in this invention can be appropriately set within the range of 0.001 to 2.00 μm, but to balance processability and adhesion, a range of 0.01 to 1.00 μm is preferred, 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 preferred due to good adhesion. A coating layer thickness of 2.00 μm or less is preferred due to reduced adhesion.

[0086] The upper limit of haze of the laminated polyester film of the present invention is preferably 2.0%, more preferably 1.8%, further preferably 1.5%, and particularly preferably 1.2%. If the haze is 2.0% or less, it is preferred in terms of transparency and is also suitable for optical film applications requiring transparency. The haze is preferably low, but can preferably be 0.1% or more, or 0.3% or more.

[0087] Example

[0088] 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.

[0089] (1) NMR analysis

[0090] The resin was dissolved in deuterated chloroform, and the analysis was performed using a Varian Gemini-200 nuclear magnetic resonance (NMR) analyzer. 1 ¹H-NMR analysis was used to determine the molar percentage of each component based on its integral ratio. Additionally, deuterated dimethyl sulfoxide was used as a substitute when the resin exhibited low solubility for deuterated chloroform.

[0091] (2) Particle size

[0092] The particle size distribution of the dispersion was measured using the high-concentration measurement unit (SALD-HC75) of the nanoparticle size distribution measuring device (SALD-7500nano) (manufactured by Shimadzu Corporation). The particle size distribution was calculated based on the LDR method (Light Intensity Distribution Reproduction Method), and a particle refractive index of 1.50 was selected from the silica based on the calculation results.

[0093] (3) Contact angle

[0094] Under conditions of 25°C and 50% RH, contact angles of water (1.8 μL), diiodomethane (0.9 μL), and ethylene glycol (0.9 μL) droplets were prepared on the resin layer of a thin film using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.: Fully Automatic Contact Angle Meter (DM-701)). The contact angles were measured after each liquid was dropped onto the resin layer and passed through various solvents (water, diiodomethane, and ethylene glycol) for 60 seconds, 30 seconds, and 30 seconds, respectively. The contact angles for each liquid were averaged at 7 points (excluding the maximum and minimum values) at different locations.

[0095] (4) Haze

[0096] The haze of the obtained laminated polyester film was measured according to JIS K 7136:2000 using a turbidimeter (Nippon Denshoku Corporation, NDH5000).

[0097] (5) Anti-adhesion

[0098] Two thin film samples were overlapped with their coating layers facing each other, and a load of 98 kPa was applied to allow them to adhere tightly in an atmosphere at 50°C for 24 hours. The films were then peeled off, and their peeling condition was determined according to the following criteria.

[0099] ○: Transfer without coating layer, can be gently peeled off.

[0100] △: The coating layer can be maintained, but the surface layer of the coating layer is partially transferred to the object surface.

[0101] ×: Two films are stuck together and cannot be peeled off, or even if they can be peeled off, the film substrate is split apart.

[0102] (6) Adhesion to UV ink

[0103] On the coated layer of the laminated polyester film, UV ink [manufactured by T&K TOKA Co., Ltd., trade name "BEST CURE UV161 Red S" or "BEST CURE UV161 Ink S"] is used for printing on a printing press [manufactured by Meisei Corporation, trade name "RItester"] with an ink suction tube at 4 graduations and 2 dividing rollers. Then, the ink-coated film is irradiated with a high-pressure mercury lamp at a radiation dose of 100 mJ / cm². 2 or 40mJ / cm 2 The UV-curable ink is cured by applying ultraviolet light. Next, using a 2mm-spaced tool guide, 100 grid-like cuts are made through the ink layer to the film substrate. Then, cellophane adhesive tape (Nichiban, No. 405; 24mm wide) is adhered to the grid-like cut surfaces. Afterward, the cellophane adhesive tape is peeled vertically from the ink layer of the ink laminate film, and the number of grids peeled off is visually counted. The adhesion between the ink layer and the film substrate is calculated using the following formula. It should be noted that partially peeled grids are also counted as peeled grids, and the ink adhesion is calculated using the following formula.

[0104] Ink adhesion (%) = 100 - (number of peeled meshes)

[0105] To distinguish ink adhesion (%) as follows, ◎ and 〇 are marked as qualified.

[0106] ◎: 100%, ○: 99-96%, △: 95-80%, ×: 79-0%

[0107] (7) Adhesion to hard coating

[0108] On the coated layer of the laminated polyester film, Opstar Z7503 (manufactured by Arakawa Chemical Industry Co., Ltd.) as a UV-curable hard coating agent was applied using a #5 wire rod and dried at 80°C for 1 minute. Next, the coated film was irradiated with a high-pressure mercury lamp at a radiation dose of 100 mJ / cm². 2 Ultraviolet light is used to obtain a hard coating film.

[0109] Next, using a tool guide with a 2mm gap, 100 grid-like cuts are applied to the hard coating surface, penetrating the hard coating and reaching the film substrate. Then, cellophane adhesive tape (Nichiban, No. 405; 24mm wide) is adhered to the grid-like cut surfaces and rubbed with an eraser to ensure complete adhesion. Afterward, the cellophane adhesive tape is peeled vertically from the hard coating surface of the hard-coated film, and the number of grids peeled off is visually counted. The adhesion between the hard coating and the film substrate is calculated using the following formula. It should be noted that partially peeled grids are also counted as peeled grids, and the hard coating adhesion is calculated as follows.

[0110] Hard coating adhesion (%) = 100 - (number of peeled meshes)

[0111] To distinguish the adhesion of the hard coating (%) as described below, ◎ and 〇 are marked as qualified.

[0112] ◎: 100%, ○: 99-96%, △: 95-80%, ×: 79-0%

[0113] (8) Resistance to damp heat

[0114] The UV ink coating or hard coating film prepared in the same manner as in (5) and (6) above was placed at 80°C and 80% RH for 500 hours with the coating surface perpendicular and not in contact with other films. After treatment, it was placed at 23°C and 65% RH for 10 minutes with the coating surface not in contact with other films. Immediately after the time elapsed, the adhesion of the coating surface was evaluated in the same manner as described above. However, the UV ink coating film was only made with "BEST CURE UV161 ink S" and irradiated with a radiation dose of 100 mJ / cm. 2 Ultraviolet rays.

[0115] (9) Contact angle variation

[0116] The laminated polyester film was placed at 85°C and 85% RH for 240 hours in a vertical position with the coated surface not in contact with other films. After treatment, it was placed at 23°C and 65% RH for 24 hours with the coated surface not in contact with other films. Immediately after the time elapsed, the contact angle of each solvent on the coated surface was measured in the same manner as described in (2) above, and the average value of the contact angle of each solvent was obtained. Furthermore, the absolute value of the difference between the average value of the contact angle of each solvent and the average value of the contact angle of each solvent measured in (2) above was calculated as the contact angle change in each solvent.

[0117] (Polyurethane)

[0118] (Polymerization of polyurethane resin A-1)

[0119] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 52.0 parts by weight of hydrogenated diphenylmethane diisocyanate, 8.5 parts by weight of dimethylolpropionic acid, 1.0 part by weight of polyethylene glycol with a number average molecular weight of 1000, 155.0 parts by weight of polycarbonate diol (1,6-hexanediol, 1,5-pentanediol type) with a number average molecular weight of 1000, and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 6.7 parts by weight of triethylamine were added to obtain a polyurethane resin (A-1) solution. Then, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 500 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred at a speed of 2000 min... -1 The mixture was stirred and mixed while adding the polyurethane polymer solution for aqueous dispersion. Then, methyl ethyl ketone (MEK), used as a solvent, was removed under reduced pressure. An aqueous dispersion (A-1WD) of polyurethane resin (A-1) with a solid content of 35% by mass was prepared by adjusting the concentration with water. The resin contained 69% by mass of the C5 and above linear alkylene chain components (from polycarbonate diol).

[0120] (Polymerization of polyurethane resin A-2)

[0121] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 64.5 parts by weight of hydrogenated diphenylmethane diisocyanate, 21.5 parts by weight of dimethylolpropionic acid, 3.0 parts by weight of neopentyl glycol, 150.5 parts by weight of polycarbonate diol (1,6-hexanediol type) with a number average molecular weight of 2000, and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 17.0 parts by weight of triethylamine were added to obtain a polyurethane resin (A-2) solution. Then, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 500 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred at a homogenizer for 2000 minutes. -1 The mixture was stirred and mixed while adding the polyurethane polymer solution for aqueous dispersion. Then, methyl ethyl ketone (MEK), used as a solvent, was removed under reduced pressure. An aqueous dispersion (A-2WD) of polyurethane resin (A-2) with a solid content of 35% by mass was prepared by adjusting the concentration with water. The resin contained 59% by mass of the C5 and above linear alkylene chain components (from polycarbonate diol).

[0122] (Polymerization of polyurethane resin A-3)

[0123] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 68.0 parts by weight of hydrogenated diphenylmethane diisocyanate, 19.8 parts by weight of dimethylolpropionic acid, 148.0 parts by weight of polycarbonate diol (1,6-hexanediol type) with a number average molecular weight of 2000, and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 2 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, 6.6 parts by weight of 2-butanone oxime were added, and the reaction was further stirred for 1 hour. After cooling the reaction solution to 40°C, 15.7 parts by weight of triethylamine were added to obtain a polyurethane prepolymer solution. Then, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 500 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred at a speed of 2000 min / min. -1 The mixture was stirred and mixed while adding a polyurethane prepolymer solution for aqueous dispersion. 1.1 parts by mass of a 10% by mass ethylenediamine aqueous solution was added and stirred to obtain polyurethane resin (A-3). Then, methyl ethyl ketone (MEK) was removed as a solvent under reduced pressure. An aqueous dispersion (A-3WD) of polyurethane resin (A-3) with a solid content of 35% by mass was prepared by adjusting the concentration with water. The content of the C5 and above linear alkylene chain components (from polycarbonate diol) in this resin was 57% by mass.

[0124] (Polymerization of polyurethane resin A-4)

[0125] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 43.0 parts by weight of hydrogenated m-xylene diisocyanate, 21.0 parts by weight of dimethylolpropionic acid, 147.0 parts by weight of polycarbonate diol (1,6-hexanediol type) with a number average molecular weight of 2000, and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 16.6 parts by weight of triethylamine were added to obtain a polyurethane resin (A-4) solution. Then, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 500 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred at a homogenizer for 2000 minutes. -1 The mixture was stirred and mixed while adding the polyurethane polymer solution for aqueous dispersion. Then, methyl ethyl ketone (MEK), used as a solvent, was removed under reduced pressure. An aqueous dispersion (A-4WD) of polyurethane resin (A-4) with a solid content of 35% by mass was prepared by adjusting the concentration with water. The resin contained 65% by mass of the C5 and above linear alkylene chain components (from polycarbonate diol).

[0126] (Polymerization of polyurethane resin A-5)

[0127] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 37.0 parts by weight of isophorone diisocyanate, 15.0 parts by weight of dimethylolpropionic acid, 140.0 parts by weight of a polyester polyol with a number average molecular weight of 2000 (composition: terephthalic acid / sebacic acid / / 1,6-hexanediol / ethylene glycol = 70 / 30 / / 60 / 40 (molar ratio)), and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 11.9 parts by weight of triethylamine were added to obtain a polyurethane resin (A-5) solution. Then, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 450 g of water was added, the temperature was adjusted to 25°C, and the polyurethane polymer solution was added for water dispersion while stirring at 2000 min⁻¹. Subsequently, methyl ethyl ketone (MEK) was removed as a solvent under reduced pressure. An aqueous dispersion (A-5WD) of polyurethane resin (A-5) with a solid content of 35% by mass was prepared by adjusting the concentration with water. The resin contained 69% by mass of the C5 and above linear alkylene chain components (from polyester diol).

[0128] (Polymerization of polyurethane resin A-6)

[0129] In a four-necked flask equipped with a stirrer, a serpentine condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 25.0 parts by weight of toluene diisocyanate, 15.0 parts by weight of dimethylolpropionic acid, 235 parts by weight of a polyester glycol with a number average molecular weight of 4000 containing the following composition (terephthalic acid / isophthalic acid / ethylene glycol / neopentyl glycol = 60 / 40 / 65 / 35 (mol%)), and 110 parts by weight of methyl ethyl ketone as a solvent were added. The mixture was stirred at 75°C for 2 hours under a nitrogen atmosphere to confirm that the reaction solution reached the specified amine equivalent. After cooling the reaction solution to 40°C, 10.0 parts by weight of N,N-dimethylethanolamine and 15.0 parts by weight of butyl cellosolve were added to obtain a polyurethane resin (A-6) solution. Next, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 500 g of water was added, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 minutes. -1 The mixture was stirred and mixed while a polyurethane polymer solution was added for aqueous dispersion. Then, under reduced pressure, methyl ethyl ketone was removed from the solvent, and the concentration was adjusted with water to prepare an aqueous dispersion (A-6WD) of polyurethane resin (A-6) with a solid content of 35% by mass. The resin contained 0% by mass of the C5 and above linear alkylene chain components. Furthermore, the resin had a Tg of 61°C as determined by DSC.

[0130] (Polyester)

[0131] (Polymerization of polyester resin B-1)

[0132] 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 added to a reaction vessel, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 6.0 parts by weight of 5-(sodium sulfonyl) isophthalic acid was added, and an esterification reaction was carried out at 240°C for 1 hour. Then, a polycondensation reaction was carried out at 250°C under reduced pressure (1.33–0.027 kPa) for 2 hours to obtain a polyester resin (B-1) with a molecular weight of 19500. The neopentyl glycol content in the diol component of this polyester resin (B-1) is... 1 H-NMR analysis showed a concentration of 50 mol%. Subsequently, 300 parts by mass of the polyester resin (B-1) and 140 parts by mass of the butyl cellosolve were stirred at 160°C for 3 hours to obtain a viscous melt. Water was slowly added to the melt, and after 1 hour, a uniform, pale white solid component of 15% by mass of polyester resin aqueous dispersion (B-1WD) was prepared.

[0133] (Polymerization of polyester resin B-2)

[0134] In a reaction vessel, 74 parts by mass of dimethyl terephthalate, 47 parts by mass of ethylene glycol, 37 parts by mass of diethylene glycol, 0.1 parts by mass of zinc acetate, and 0.1 parts by mass of antimony trioxide were added, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 5.7 parts by mass of 5-(sodium sulfo)-isophthalic acid and 20 parts by mass of sebacic acid were added, and an esterification reaction was carried out at 240°C for 1 hour. Then, a polycondensation reaction was carried out at 250°C under reduced pressure (1.33–0.027 kPa) for 2 hours to obtain a polyester resin (B-2) with a molecular weight of 21,000. The content of the C5 and above linear alkylene chain components (from hexanediol) and the diethylene glycol content in the glycol components of this polyester resin (B-2) were determined by… 1 H-NMR analyses showed values ​​of 20 mol% and 40 mol%, respectively. Subsequently, 300 parts by mass of the polyester resin (B-2) and 140 parts by mass of the butyl cellosolve were stirred at 160°C for 3 hours to obtain a viscous melt. Water was slowly added to the melt, and after 1 hour, a uniform, pale white solid component of 15 mol% polyester resin aqueous dispersion (B-2WD) was prepared.

[0135] (Polymerization of polyester resin B-3)

[0136] In a reaction vessel, 105 parts by mass of dimethyl 2,6-naphthalenedicarboxylate, 34 parts by mass of ethylene glycol, 27 parts by mass of diethylene glycol, 36 parts by mass of 1,6-hexanediol, 0.1 parts by mass of zinc acetate, and 0.1 parts by mass of antimony trioxide were added, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 8.6 parts by mass of 5-(sodium sulfo)-isophthalic acid and 8 parts by mass of sebacic acid were added, and an esterification reaction was carried out at 240°C for 1 hour. Then, a polycondensation reaction was carried out at 250°C under reduced pressure (1.33–0.027 kPa) for 2 hours to obtain a polyester resin (B-3) with a molecular weight of 18,000. The content of the C5 and above linear alkylene chain components (derived from sebacic acid and hexanediol) and the content of diethylene glycol in the glycol component of this polyester resin (B-3) were determined by… 1 H-NMR analyses showed values ​​of 34 mol% and 20 mol%, respectively. Furthermore, the content of the C5 and above linear alkylene chain components in this polyester resin (B-3) was determined by... 1 H-NMR analysis showed a concentration of 34 mol%. Further, 300 parts by weight of the polyester resin (B-3) and 140 parts by weight of butyl cellosolve were stirred at 160°C for 3 hours to obtain a viscous melt. Water was slowly added to the melt, and after 1 hour, a uniform, pale white solid component of 15% by weight of polyester resin aqueous dispersion (B-3WD) was prepared.

[0137] (Polyvinyl alcohol resin)

[0138] (Preparation of polyvinyl alcohol resin C-1 aqueous solution)

[0139] In a container equipped with a mixer and thermometer, add 90 parts by weight of water, and while stirring, slowly add 10 parts by weight of polyvinyl alcohol resin (C-1) with a degree of polymerization of 500 and a saponification degree of 70 mol%. After addition, heat the liquid to 95°C while stirring to dissolve the resin. After dissolution, cool to room temperature while stirring to prepare a polyvinyl alcohol aqueous solution (C-1WD) with a solid content of 10% by weight.

[0140] (Acrylic resins)

[0141] (Polymerization of acrylic resin C-2)

[0142] In a mixture of 356 parts by mass of methyl methacrylate, 16 parts by mass of acrylic acid, 5 parts by mass of n-butyl acrylate, 10 parts by mass of 2-hydroxyethyl methacrylate, and 372 parts by mass of methyl ethyl ketone, 2 parts by mass of tert-butyl peroxide-2-ethylhexanoate as a polymerization initiator were added. The mixture was stirred and heated to 50°C and maintained for 120 minutes, then heated to 70°C and maintained for 180 minutes. After cooling to 40°C, 13 parts by mass of triethylamine were added to obtain a methyl ethyl ketone solution of acrylic resin (C-2). While stirring, 150 parts by mass of water were slowly added to 200 parts by mass of this methyl ethyl ketone solution. The methyl ethyl ketone was removed from the solution under reduced pressure and at temperatures below 50°C, and the concentration was adjusted with water to obtain an aqueous dispersion (C-2WD) of acrylic resin (C-2) with a solid content of 40% by mass.

[0143] (Cross-linking agent)

[0144] (Synthesis of crosslinking agent D-1)

[0145] In a flask equipped with a stirrer, thermometer, and reflux condenser, 66.6 parts by weight of a polyisocyanate compound (Asahi Kasei Chemicals, Durnate TPA) with an isocyanurate structure, made from hexamethylene diisocyanate, and 17.5 parts by weight of N-methylpyrrolidone were added dropwise. The mixture was kept at 70°C for 1 hour under a nitrogen atmosphere. Then, 9.0 parts by weight of dimethylolpropionic acid were added dropwise. After confirming the disappearance of the isocyanate group absorption by measuring the infrared spectrum of the reaction solution, 6.3 parts by weight of N,N-dimethylethanolamine were added. The mixture was stirred directly for 1 hour, and then an appropriate amount of water was added to prepare an aqueous dispersion (D-1WD) of a 40% by weight end-capped isocyanate-based crosslinking agent (D-1).

[0146] (Synthesis of crosslinking agent D-2)

[0147] In a flask equipped with a stirrer, thermometer, and reflux condenser, 150.0 parts by weight of water and 250.0 parts by weight of methoxypropanol were added, and the mixture was heated to 80°C under a nitrogen atmosphere. Then, under a nitrogen atmosphere, while maintaining the temperature at 80°C, the following monomer mixture and polymerization initiator solution were added dropwise over 2 hours through a dropping funnel: the monomer mixture contained 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 methoxy polyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK ESTER AM-90G); the polymerization initiator solution contained 18.0 parts by weight of 2,2'-azobis(2-amidinylpropane) dihydrochloride as the polymerization initiator, and 170.0 parts by weight of water. After the addition was complete, the mixture was stirred at 80°C for 5 hours and then cooled to room temperature. Add an appropriate amount of water to prepare an aqueous dispersion (D-2WD) of 40% by mass of oxazoline crosslinking agent (D-2) with solid components.

[0148] (Synthesis of crosslinking agent D-3)

[0149] 100 parts by mass of polyester glycol (composition: adipic acid / / 1,6-hexanediol / neopentyl glycol = 4 / / 2 / 3 (molar ratio)) containing 2000 eq / t of hydroxyl groups were mixed with 41.4 parts by mass of xylene diisocyanate. The mixture was reacted at 80°C for 1 hour under a nitrogen atmosphere, then cooled to 60°C. 70 parts by mass of tetrahydrofuran were added and dissolved to obtain a urethane prepolymer solution. Next, the urethane prepolymer solution was brought to 40°C, and 45.5 parts by mass of a 20% by mass sodium bisulfite aqueous solution were added and stirred rapidly. The mixture was reacted at 40–50°C for 30 minutes. The infrared spectrum of the reaction solution was measured. After confirming the disappearance of isocyanate group absorption, the solution was diluted with water to obtain an aqueous dispersion (D-3WD) of a crosslinking agent (D-3) containing 20% ​​by mass of isocyanate groups and capped with sodium bisulfite.

[0150] (Synthesis of crosslinking agent D-4)

[0151] In a flask equipped with a stirrer, thermometer, and reflux condenser, 100.0 parts by weight of a polyisocyanate compound with an isocyanurate structure (Asahi Kasei Chemicals, Durnate TPA) based on hexamethylene diisocyanate and 33.0 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 500 were added. The mixture was kept at 80°C for 1 hour under a nitrogen atmosphere. Then, 47.0 parts by weight of 2-butanone oxime were added dropwise. The infrared spectrum of the reaction solution was measured, and after confirming the disappearance of the isocyanate group absorption, 7.2 parts by weight of HLB 16.2 polyoxyethylene oil ether was added and mixed. In a separate flask equipped with a stirrer, 300 parts by weight of water were added, and the mixture was stirred for 2000 minutes. -1While stirring, 100 parts by weight of the mixture were added dropwise to disperse it. Through these operations, an aqueous dispersion (D-4WD) of a 25% by weight end-capped polyisocyanate crosslinking agent (D-4) was prepared.

[0152] (Crosslinker D-5)

[0153] The commercially available melamine resin used is Amidia M3 (manufactured by DIC Corporation, 80% by weight of solids).

[0154] (Synthesis of crosslinking agent D-6)

[0155] In a flask equipped with a stirrer, thermometer, and reflux condenser, 40.0 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 700 and 20.0 parts by weight of sodium dioctyl sulfosuccinate were added. The mixture was stirred under reduced pressure to remove moisture and other contaminants, thus forming a mixture. Then, 200.0 parts by weight of a polyisocyanate compound with a biuret structure (Asahi Kasei Chemicals, Duranat 24A-100) based on hexamethylene diisocyanate was added dropwise. The mixture was kept at 90°C for 2 hours under a nitrogen atmosphere. This yielded a pale yellow polyisocyanate-based crosslinking agent, D-6.

[0156] (Synthesis of crosslinking agent D-7)

[0157] In a flask equipped with a stirrer, thermometer, and reflux condenser, 65.0 parts by weight of a polyisocyanate compound with an isocyanurate structure (Asahi Kasei Chemicals, Durnate TPA) based on hexamethylene diisocyanate, 17.5 parts by weight of N-methylpyrrolidone, 29.2 parts by weight of 3,5-dimethylpyrazole, and 21.9 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 500 were added. The mixture was kept at 70°C for 2 hours under a nitrogen atmosphere. Then, 4.0 parts by weight of trimethylolpropane were added dropwise. The infrared spectrum of the reaction solution was measured, and after confirming the disappearance of the isocyanate group absorption, 280.0 parts by weight of water were added. With the addition of an appropriate amount of water, an aqueous dispersion (D-7WD) of a 40% by weight end-capped polyisocyanate crosslinking agent (D-7) was prepared.

[0158] (Particles)

[0159] (Particle E-1)

[0160] Colloidal silica (Snowtex XL; manufactured by Nissan Chemical Co., Ltd.) with an average particle size of 40-60 nm and a solid content of 40% by mass is used directly as silica particles.

[0161] (Particle E-2)

[0162] As particles, 40% by mass of colloidal silica (MP2040; manufactured by Nissan Chemical Co., Ltd.) with an average particle size of 200 nm is used directly.

[0163] (Particle E-3)

[0164] Fumed silica (Aerosil OX50; manufactured by Nippon Aerosil Co., Ltd.) with an average primary particle size of 40 nm was used as the silica particles. Water was used as the dispersion medium, and the dispersion was carried out at 10,000 rpm for 60 minutes using an Ace homogenizer AM-7 (manufactured by Nippon Seiki Co., Ltd.) to obtain an aqueous dispersion with a solid content of 5.0% by mass. The particle size was measured to be 500 nm.

[0165] (Particle E-4)

[0166] Directly use silica dispersion, particle concentration 25g / ml, particle size 70nm (micromod silica particles Sicastar, product number 43-00-701).

[0167] (Manufacturing of polyester resin F-1 for substrate)

[0168] (Preparation of antimony trioxide solution)

[0169] Antimony trioxide (manufactured by Sigma-Aldrich Japan) and ethylene glycol were added to a flask and stirred at 150°C for 4 hours until dissolved. The solution was then cooled to room temperature to prepare a 20 g / L antimony trioxide ethylene glycol solution.

[0170] (Polymerization of polyester resin F-1 for substrate)

[0171] In a 2-liter stainless steel autoclave equipped with a stirrer, high-purity terephthalic acid and twice the molar amount of ethylene glycol were added, along with triethylamine at 0.3 mol% relative to the acid content. The reaction was carried out under pressure of 0.25 MPa and at 250°C, while simultaneously removing water by distillation, to obtain a mixture of bis(2-hydroxyethyl) terephthalate and oligomers with an esterification rate of approximately 95% (hereinafter referred to as the BHET mixture). In this BHET mixture, the aforementioned antimony trioxide solution was used as a polycondensation catalyst, added at 0.04 mol% (based on antimony atoms) relative to the acid content in the polyester. The mixture was then stirred for 10 minutes under a nitrogen atmosphere, at atmospheric pressure, and at 250°C. Then, the temperature was raised to 280°C over 60 minutes, and the pressure of the reaction system was slowly reduced to 13.3 Pa (0.1 Torr). Further, a polycondensation reaction was carried out at 280°C and 13.3 Pa for 68 minutes to obtain polyester resin F-1 with an intrinsic viscosity (IV) (solvent: phenol / tetrachloroethane = 60 / 40) of 0.61 dl / g and which is substantially free of particles.

[0172] (Manufacturing of polyester resin F-2 for substrate)

[0173] (Example of aluminum compound solution preparation)

[0174] An equal volume (by volume) of ethylene glycol was added to a flask along with a 20 g / L aqueous solution of basic aluminum acetate (hydroxyaluminum diacetate; manufactured by Sigma-Aldrich Japan). After stirring at room temperature for 6 hours, water was removed from the system by distillation under reduced pressure (133 Pa) at 70–90 °C for several hours while stirring, to prepare an ethylene glycol solution of aluminum compound at a concentration of 20 g / L.

[0175] (Example of preparation of phosphorus compound solution)

[0176] Diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate (Irganox 1222 (manufactured by BASF Corporation)) as a phosphorus compound was added to a flask together with ethylene glycol. The mixture was heated at 160°C for 25 hours under nitrogen purging with stirring to prepare an ethylene glycol solution of the phosphorus compound with a concentration of 50 g / L.

[0177] (Preparation of a mixture of solutions of aluminum compounds and solutions of phosphorus compounds)

[0178] The ethylene glycol solutions obtained in the above-mentioned aluminum compound preparation example and the above-mentioned phosphorus compound preparation example were added to a flask, and the mixture was stirred at room temperature for 1 day with an aluminum atom to phosphorus atom molar ratio of 1:2 to prepare a catalyst solution.

[0179] (Polymerization of polyester resin F-2 for substrate)

[0180] As a polycondensation catalyst, a mixture of the aforementioned aluminum compound solution and phosphorus compound solution was used instead of the antimony trioxide solution, added in amounts of 0.014 mol% and 0.028 mol% (calculated as aluminum atoms and phosphorus atoms, respectively) relative to the acid content in the polyester. Otherwise, polymerization was carried out in the same manner as with polyester resin F-1. The polymerization time was set to 68 minutes, resulting in polyester resin F-2 with an intrinsic viscosity (IV) of 0.61 dl / g and substantially free of particles.

[0181] (Example 1)

[0182] (1) Preparation of coating solution

[0183] The coating agent was mixed in a mixed solvent of water and isopropanol (80 / 20 parts by mass) with the solid content adjusted to 8% by mass, such that the solid content of the polyurethane resin aqueous dispersion (A-1WD) / polyester resin aqueous dispersion (B-1WD) / crosslinking agent aqueous dispersion (D-1WD) was 40 / 40 / 20, and the solid content of the particle (E-1) solution and the particle (E-2) solution was 8 and 0.5 respectively relative to the solid content of the aforementioned resin and crosslinking agent components. Then, 1 part by mass of an aqueous solution of an organosilicon surfactant with a solid content of 10% relative to 100 parts by mass of the mixture was mixed to form the coating liquid of Example 1. The mixing ratios of resin, crosslinking agent, and particles used in the coating liquids of each example and comparative example are summarized in Table 1.

[0184] (2) Manufacturing of laminated polyester film

[0185] As a polymer for film production, polyester resin F-1 granules were dried at 135°C for 6 hours under reduced pressure of 133 Pa. Afterward, the dried granules were fed to an extruder and melt-extruded into sheets at approximately 280°C. These sheets were then rapidly cooled and cured on a rotating cooling metal roller with a surface temperature maintained at 20°C to obtain unstretched PET sheets.

[0186] The unstretched PET sheet was heated to 100°C using a heated roller assembly and an infrared heater, and then stretched 3.5 times along its length on a roller assembly with a circumferential speed difference to obtain a uniaxially stretched PET film.

[0187] Next, the aforementioned coating solution was applied to one side of the PET film to achieve a coating weight of 6.0 g / m². 2 After the coating solution was dried, it was stretched to 4.0 times its original length in the width direction at 110°C. With the width direction of the film fixed, it was then heated at 230°C for 5 seconds. A further 3% relaxation treatment in the width direction was performed to obtain a 100 μm laminated polyester film. The evaluation results are shown in Table 2.

[0188] (Example 2)

[0189] For the coating liquid of Example 1, according to the mixing ratio of Example 2 in Table 1, the types and mass parts of polyurethane resin, polyester resin, crosslinking agent, and particles were changed. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0190] (Example 3)

[0191] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 3 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0192] (Example 4)

[0193] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 4 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0194] (Example 5)

[0195] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 5 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0196] (Example 6)

[0197] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 6 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0198] (Example 7)

[0199] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 7 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0200] (Example 8)

[0201] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 8 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0202] (Example 9)

[0203] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Example 9 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0204] (Example 10)

[0205] Polyester resin F-2 granules were used as the film raw material polymer, and otherwise, in the same manner as in Example 1, a laminated polyester film was obtained.

[0206] (Comparative Example 1)

[0207] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 1 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0208] (Comparative Example 2)

[0209] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 2 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0210] (Comparative Example 3)

[0211] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 3 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0212] (Comparative Example 4)

[0213] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 4 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0214] (Comparative Example 5)

[0215] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 5 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0216] (Comparative Example 6)

[0217] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 6 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0218] (Comparative Example 7)

[0219] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 7 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0220] (Comparative Example 8)

[0221] For the coating liquid of Example 1, the composition was changed according to the mixing ratio of Comparative Example 8 in Table 1. Otherwise, the laminated polyester film was obtained in the same manner as in Example 1.

[0222] Table 2 summarizes the evaluation results of each embodiment and comparative example.

[0223] As shown in Table 2, satisfactory results were obtained in each embodiment in terms of haze, anti-blocking properties, adhesion to UV ink, and adhesion to the hard coating. On the other hand, in Comparative Examples 1 to 9, the coating layer formed on at least one side of the polyester film substrate did not meet the preferred characteristics of the present invention, and therefore, the anti-blocking properties or adhesion to UV ink or hard coating could not be satisfied.

[0224] [Table 1]

[0225]

[0226] [Table 2]

[0227]

[0228] Industrial availability

[0229] According to the present invention, laminated polyester films suitable for all fields such as optical applications, packaging applications, and labeling applications can be provided.

Claims

1. A laminated polyester film having a resin layer on at least one side of the polyester film, wherein the contact angle of ethylene glycol droplets in the resin layer is 48 degrees or more and 56 degrees or less, and the contact angle of diiodomethane droplets is 24 degrees or more and 32 degrees or less. Polyurethane resin and polyester resin are used together in the resin layer. The polyurethane resin is composed of polycarbonate polyols with linear alkylene chains having a C5 or higher number of atoms. The polyester resin is composed of alkylene chains with a linear structure of C5 or higher.

2. The laminated polyester film according to claim 1, wherein, The water droplet contact angle of the resin layer is greater than 65 degrees and less than 75 degrees.

3. The laminated polyester film according to claim 1 or 2, wherein, The absolute values ​​of the changes in the contact angles of ethylene glycol, diiodomethane, and water droplets in the resin layer before and after the damp heat resistance treatment are all less than 5 degrees. The damp heat resistance treatment is performed by placing the resin layer at a temperature of 85°C and a humidity of 85%RH for 240 hours.

4. The laminated polyester film according to claim 1 or 2, wherein, The resin layer contains both polyurethane resin and polyester resin, wherein the polyurethane resin and the polyester resin are in a mass ratio of 90 / 10 to 10 / 90.

5. The laminated polyester film according to claim 4, wherein, The polyurethane resin has carboxyl groups in the molecule or on the side chain.

6. The laminated polyester film according to claim 4, wherein, The polyester resin is a polyester resin composed of dicarboxylic acid and diols with branched structures or diols containing one or more ether bonds.

7. The laminated polyester film according to claim 6, wherein, The diol with a branched structure or a diol containing one or more ether bonds is present in the total polyol composition at a rate of 10 mol% or more.

8. The laminated polyester film according to claim 1 or 2, wherein, A crosslinking agent is used in the resin layer, and the mass ratio of the crosslinking agent to the total amount of the polyurethane resin and the polyester resin is in the range of 5 / 95 to 70 / 30.

9. The laminated polyester film according to claim 8, wherein, The crosslinking agent is a 3-functional or higher capped isocyanate.

10. The laminated polyester film according to claim 1 or 2, wherein, Inorganic or organic particles are added to the resin layer.

11. The laminated polyester film according to claim 10, wherein, The inorganic particles are colloidal silica with a particle size ranging from 5 to 1000 nm.

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