Laminated polyester film for metal plate lamination, laminated metal plate, metal container, and production methods therefor

Abstract

One purpose of the present invention is to provide a laminated polyester film for metal plate lamination, the film having concealability, being capable of reducing or preventing shaving of the polyester film that could occur during molding (for example, during molding of a metal container), and further being capable of avoiding or mitigating excessively low ink adhesion. Another purpose is to provide a production method therefor. Another purpose of the present invention is to provide a laminated metal plate, a metal container, and production methods therefor. The laminated polyester film for metal plate lamination includes a polyester film and a coating layer. The polyester film contains a white pigment in the amount of 5 mass% to 30 mass%. The coating layer is formed of a coating liquid, and the coating liquid contains a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C. The laminated metal plate includes a metal plate and the laminated polyester film for metal plate lamination laminated on the metal plate. The metal container includes the laminated metal plate.

Description

Laminated polyester film for bonding metal sheets, laminated metal sheets, metal containers, and methods for manufacturing the same.

[0001] This invention relates to laminated polyester films for bonding metal sheets, laminated metal sheets, metal containers, and methods for manufacturing the same.

[0002] Metal containers (hereinafter sometimes referred to as "cans" or "metal cans") are generally painted to prevent corrosion on their interior and exterior surfaces. In recent years, for the purpose of simplifying processes, improving hygiene, and preventing pollution, coating with thermoplastic resin films such as polyester film has been adopted as a method to provide rust prevention without using organic solvents. Specifically, after laminating a thermoplastic resin film onto a metal sheet such as tinplate, tin-free steel, or aluminum, rigorous molding processes such as drawing and thinning-walled drawing are performed to form food cans, beverage cans, aerosol cans, etc. Cans used for these applications (i.e., food cans, beverage cans, aerosol cans, etc.) are increasingly being manufactured using thinning-walled drawing and ironing processes with even stricter processing conditions from the perspective of cost reduction.

[0003] When such severe forming processes are performed, the thermoplastic resin film also becomes thinner as the metal sheet becomes thinner. The outer surface of the cans used for these applications is generally printed to enhance the design. In the case of cans formed from a metal sheet laminated with a thermoplastic resin film, that is, a laminated metal sheet, a thermoplastic resin film containing white or various colored pigments is used to conceal the color of the metal sheet as the printing base. When such a laminated metal sheet is subjected to severe processing, the thickness of the thermoplastic resin film becomes significantly thinner, and the absolute amount of the pigment in the thickness direction decreases, resulting in the problem that the color of the metal sheet cannot be sufficiently concealed by the thermoplastic resin film (that is, sufficient concealability cannot be obtained). If a large amount of pigment is added to the thermoplastic resin film in advance in anticipation of this problem, the strength of the thermoplastic resin film decreases, and the thermoplastic resin film is likely to be scraped or damaged during the forming process. Furthermore, a phenomenon occurs where the thermoplastic resin film cracks and peels off. Therefore, it is difficult to improve the concealability, maintain the high strength of the thermoplastic resin film, and ensure sufficient formability.

[0004] For example, a method (Patent Document 1) has been proposed in which a biaxially stretched polyester film is laminated on a metal sheet and used as a can-making material. However, when performing more severe processing and forming, the biaxially stretched polyester film is scraped or damaged, and in extreme cases, breakage occurs. Also, a method (Patent Document 2) has been proposed in which an unstretched polyester film is laminated on a metal sheet and used as a can-making material. However, since the unstretched film is very brittle, it is easily cut during film formation or handling, and there is a problem of poor productivity.

[0005] In response to such problems, in Patent Document 3, even when severe processing or high-temperature heat treatment is performed, excellent formability is exhibited in which the film is not scraped or cracked when forming into cans or the like after lamination. Also, it has been proposed that a biaxially stretched polyester film having excellent concealability, appearance, and printability, and capable of obtaining molded products such as cans, has a water contact angle of 70° to 120°.

[0006] However, after the laminated metal sheet is formed into a can, a wide variety of prints are applied to the outer surface of the can. The ends of the can body are then shaped into the final can shape using forming tools. At this stage, if the adhesion between the printed ink and the film is insufficient, the ink will peel off, which can damage the appearance.

[0007] JP 11-342577, JP 11-348218, JP 2017-30231

[0008] The present invention has been made in view of the above, and its objective is to provide a laminated polyester film for bonding metal plates, which has opacity, can reduce or prevent abrasion of the polyester film that may occur during molding (for example, during the molding of a metal container), and can avoid or mitigate excessive lack of ink adhesion, as well as a method for manufacturing the same. The present invention also aims to provide laminated metal plates, metal containers, and methods for manufacturing them.

[0009] The present invention comprises the following configuration [1]: [1] A laminated polyester film for bonding metal plates, comprising a polyester film and a coating layer provided on the polyester film, wherein the polyester film contains 5% to 30% by mass of a white pigment, and the coating layer is formed of a coating liquid, the coating liquid containing a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C.

[0010] The present invention preferably comprises the following configurations [2] and later: [2] The laminated polyester film for metal plate lamination according to [1], wherein the content of the lubricating substance in the coating layer is 1% to 20% by mass, preferably 2% to 15% by mass. [3] The laminated polyester film for metal plate lamination according to [1] or [2], wherein the coating liquid contains a crosslinking agent, and the content of the crosslinking agent in the coating liquid is 0.1% to 30% by mass, preferably 0.5% to 25% by mass, of 100% by mass of the solid content of the coating liquid. [4] The laminated polyester film for metal plate lamination according to any one of [1] to [3], wherein the coating layer contains 0.01% to 30% by mass of particles with an average particle size of 0.01 μm to 3 μm. [5] The laminated polyester film for metal plate lamination according to any one of [1] to [4], wherein the polyester film is a biaxially oriented polyester film. [6] A laminated polyester film for metal plate lamination according to any one of [1] to [5], wherein the polyester film contains polyethylene terephthalate. [7] A laminated polyester film for metal plate lamination according to any one of [1] to [6], wherein the polyethylene terephthalate is copolymerized polyethylene terephthalate, preferably polyethylene terephthalate polymerized with at least one compound selected from the group consisting of isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedimethanol, and neopentyl glycol. [8] A laminated polyester film for metal plate lamination according to any one of [1] to [7], wherein the melting point of the copolymerized polyethylene terephthalate is 220°C to 255°C, preferably 225°C to 255°C. [9] A laminated polyester film for metal plate lamination according to any one of [1] to [8], wherein the white pigment contains at least one of titanium dioxide and zinc sulfide, preferably titanium dioxide.

[10] The laminated polyester film for bonding metal plates according to any one of [1] to [9], wherein the white pigment is titanium dioxide or zinc sulfide, preferably titanium dioxide.

[11] The laminated polyester film for metal plate lamination according to any one of [1] to

[10] , wherein the polyester film comprises a first polyester layer, a second polyester layer, and a third polyester layer, and in the polyester film, the first polyester layer, the second polyester layer, and the third polyester layer are arranged in this order, and preferably the second polyester layer contains the white pigment.

[12] The laminated polyester film for metal plate lamination according to any one of [1] to

[11] , wherein the thickness of the polyester film is 6 μm to 75 μm, preferably 10 μm to 75 μm.

[13] The laminated polyester film for metal plate lamination according to any one of [1] to

[12] , wherein the content of the acrylic resin in the coating layer is 45% by mass or more, preferably 55% by mass or more.

[14] The laminated polyester film for metal plate lamination according to any one of [1] to

[13] , wherein the content of the acrylic resin in the coating layer is 99% by mass or less, preferably 98% by mass or less.

[15] A laminated polyester film for bonding metal plates according to any one of [1] to

[14] , wherein the glass transition temperature of the acrylic resin is 30°C to 90°C, preferably 40°C to 80°C.

[16] A laminated polyester film for bonding metal plates according to any one of [1] to

[15] , wherein the lubricating substance contains wax, preferably wax.

[17] A laminated polyester film for bonding metal plates according to any one of [1] to

[16] , wherein the coating liquid contains a surfactant, preferably at least one of a nonionic surfactant and an anionic surfactant.

[18] A laminated polyester film for bonding metal plates according to any one of [1] to

[17] , wherein the thickness of the coating layer is 0.01 μm to 0.3 μm, preferably 0.02 μm to 0.25 μm.

[19] A laminated metal plate comprising a metal plate and a laminated polyester film for bonding metal plates according to any one of [1] to

[18] laminated to the metal plate.

[20] A metal container containing the laminated metal plate described in

[19] .

[21] A method for manufacturing a laminated polyester film for metal plate lamination, comprising the steps of: applying a coating liquid containing a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C to a polyester film containing 5% to 30% by mass of a white pigment; and drying the coating liquid.

[22] The method for manufacturing a laminated polyester film for metal plate lamination according to

[21] , wherein the content of the lubricating substance in the coating liquid is 1% to 20% by mass, preferably 2% to 15% by mass, of 100% by mass of the solid content of the coating liquid.

[23] The method for manufacturing a laminated polyester film for metal plate lamination according to

[21] or

[22] , further comprising the steps of: stretching the polyester film that has undergone the step of drying the coating liquid in at least one direction; and heat-fixing the polyester film that has been stretched in at least one direction.

[24] A method for manufacturing a laminated polyester film for metal plate lamination according to any one of [1] to

[18] , wherein the laminated polyester film for metal plate lamination is the laminated polyester film for metal plate lamination according to any one of

[21] to

[23] .

[25] A method for manufacturing a laminated metal plate, comprising the steps of: manufacturing a laminated polyester film for metal plate lamination using the method for manufacturing a laminated polyester film for metal plate lamination according to any one of

[21] to

[24] ; and heat-pressing the laminated polyester film for metal plate lamination onto a metal plate.

[26] A method for manufacturing a laminated metal plate according to

[25] , wherein in the step of heat-pressing the laminated polyester film for metal plate lamination onto the metal plate, the laminated polyester film for metal plate lamination is heat-pressed onto the metal plate with the polyester film of the laminated polyester film facing the metal plate.

[27] A method for manufacturing a metal container, comprising the steps of: manufacturing a laminated metal sheet using the method for manufacturing a laminated metal sheet described in

[25] or

[26] ; and shaping the laminated metal sheet.

[0011] According to the present invention, it is possible to provide a laminated polyester film for bonding metal plates that has opacity, can reduce or prevent abrasion of the polyester film that may occur during molding (for example, during the molding of a metal container), and can avoid or mitigate excessive lack of ink adhesion, as well as a method for manufacturing the same. According to the present invention, it is also possible to provide laminated metal plates, metal containers, and methods for manufacturing them.

[0012] <Introduction> The embodiments of the present invention will be described in detail below.

[0013] The laminated polyester film for bonding metal plates according to this embodiment (hereinafter sometimes referred to as "laminated polyester film") comprises a polyester film and a coating layer provided on the polyester film (hereinafter sometimes referred to as "coating film"), wherein the polyester film contains 5% to 30% by mass of a white pigment, and the coating layer is formed of a coating liquid, the coating liquid containing a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C.

[0014] Since the white pigment content in the polyester film is 5% by mass or more, the laminated polyester film can have opacity.

[0015] Furthermore, because the coating layer contains a lubricating substance, friction between the coating layer and the tool (for example, a die) during molding can be reduced, and therefore, abrasion of the polyester film that may occur during molding can be reduced or prevented.

[0016] Furthermore, since the glass transition temperature of the acrylic resin in the coating solution is 20°C or higher, it is possible to further reduce or prevent abrasion of the polyester film (specifically, the polyester film constituting the laminated polyester film) that may occur during molding. This is thought to be because it is possible to avoid the coating layer becoming excessively mobile due to the heat applied to the laminated polyester film during molding, and as a result, it is possible to avoid the coating layer being excessively damaged or excessively removed by a tool (for example, a die).

[0017] Furthermore, since the glass transition temperature of the acrylic resin in the coating solution is 100°C or lower, excessive lack of ink adhesion can be avoided or mitigated. This is thought to be because the coating layer can avoid becoming excessively hard, and therefore the coating layer can absorb or disperse the stress caused by the volume shrinkage of the ink when it dries.

[0018] <Laminated Polyester Film> The laminated polyester film of this embodiment will be described in more detail below.

[0019] The laminated polyester film of this embodiment includes a polyester film and a coating layer provided on the polyester film. The coating layer may be laminated on the polyester film. The coating layer may be laminated on one side of the polyester film.

[0020] The polyester film can form one of the two surfaces of the laminated polyester film of this embodiment. The coating layer can form the other surface of the laminated polyester film of this embodiment.

[0021] <Polyester Film> (Polyester) The polyester film contains polyester. The polyester content in the polyester film is preferably 70% by mass or more, more preferably 75% by mass or more.

[0022] The polyester constituting the polyester film may be either homopolyester or copolymer polyester. Here, the polyester constituting the polyester film refers to the polyester within the polyester film. The copolymer polyester constituting the polyester film may, for example, be obtained by a transesterification reaction between copolymer polyester as a resin raw material and homopolyester as a resin raw material.

[0023] Preferred homopolyesters include, for example, homopolyethylene terephthalate and homopolybutylene terephthalate. Preferred copolymer polyesters include, for example, polyethylene terephthalate copolymer (i.e., copolymerized polyethylene terephthalate) and polyethylene-2,6-naphthalate copolymer. Among these, polyethylene terephthalate copolymer is preferred. The polyethylene terephthalate copolymer may be obtained by a transesterification reaction between at least one of homopolyethylene terephthalate and polyethylene terephthalate copolymer as resin raw materials and homopolybutylene terephthalate as resin raw materials.

[0024] The melting point of the polyester constituting the polyester film is preferably 220°C to 260°C. A melting point of 220°C or higher further reduces the abrasion of the polyester film that may occur during molding. A melting point of 260°C or lower makes it easier to stretch the laminated polyester film during molding, and therefore reduces the occurrence of cracks during molding. The melting point of the polyester is more preferably 230°C to 260°C, even more preferably 240°C to 258°C, and particularly preferably 250°C to 257°C.

[0025] Examples of such polyesters include homopolyesters, preferably homopolyethylene terephthalate, and copolymerized polyesters, preferably copolymerized polyethylene terephthalate, that fall within the above melting point range and have a relatively high melting point (i.e., a relatively small amount of copolymerization). Homopolyethylene terephthalate is particularly preferred because it can further reduce the abrasion of the polyester film that may occur during molding. Note that homopolyethylene terephthalate here does not exclude the inclusion of diethylene glycol, which is inevitably present. Furthermore, copolymerized components of such copolymerized polyesters with relatively high melting points include the copolymerized components in copolymerized polyesters described later, and the type and amount of copolymerized components can be adjusted to fall within the above melting point range.

[0026] (Copolymerized Polyester) As the polyester constituting the polyester film, copolymerized polyester with a melting point of 220°C to 255°C is preferred. By using such polyester, it is possible to further reduce abrasion of the polyester film that may occur during molding and to reduce the occurrence of cracks during molding. Specifically, because the melting point is 220°C or higher, it is possible to further reduce abrasion of the polyester film that may occur during molding. Because the melting point is 255°C or lower, it is possible to reduce the occurrence of cracks during molding.

[0027] The copolymer components of such copolymerized polyester may be either acidic or alcoholic components. Examples of acidic components include aromatic dicarboxylic acids other than the main acidic components such as isophthalic acid, phthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid. Examples of alcoholic components include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, diethylene glycol, polyoxyalkylene glycol, etc. Also, examples include aliphatic diols such as 1,6-hexanediol and alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used individually or in combination of two or more. When ethylene terephthalate is the main component of the polyester, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedimethanol, and neopentyl glycol are preferred among these, with isophthalic acid being particularly preferred.

[0028] The copolymerization ratio of the copolymer components of the copolymerized polyester described above should be such that the melting point of the copolymerized polyester is in the range of 220°C to 260°C, preferably 230°C to 260°C, more preferably 235°C to 257°C, and even more preferably 240°C to 255°C.

[0029] For the resin raw material used to produce polyester film, for example, copolymerized polyester alone may be used, or a blend of copolymerized polyester and homopolyester may be used. When polyester film is produced using the latter method, the copolymerized polyester constituting the polyester film is formed by a transesterification reaction between copolymerized polyester as a resin raw material and homopolyester as a resin raw material. Of these, the former method (i.e., using copolymerized polyester alone as the resin raw material) is preferred from the viewpoint of moldability when forming into cans and the stability of film quality.

[0030] When using a blend of copolymerized polyester and homopolyester as a resin raw material, it is preferable that the homopolyester content is in the range of 30% to 60% by mass in 100% by mass of the resin raw material.

[0031] (White Pigment) The polyester film contains a white pigment. The white pigment content is 5% to 30% by mass, preferably 10% to 30% by mass, and more preferably 15% to 25% by mass, when the mass of the polyester film is 100% by mass. Since the white pigment content is 5% by mass or more, the laminated polyester film can have opacity. Since the white pigment content is 30% by mass or less, it is possible to prevent the polyester film from becoming excessively brittle. Therefore, film breakage is less likely to occur when the film is stretched, and the occurrence of cracks or breakage during molding can be reduced. The white pigment may be inorganic or organic, but inorganic is preferred. Examples of inorganic white pigments include alumina, titanium dioxide, calcium carbonate, barium sulfate, and zinc sulfide, with titanium dioxide and zinc sulfide being more preferred.

[0032] (Other Additives) Other additives, such as fluorescent whitening agents, antioxidants, heat stabilizers, ultraviolet absorbers, and antistatic agents, may be added to the polyester film as needed, within limits that do not hinder the objectives of the present invention. Fluorescent whitening agents may be particularly effective in improving whiteness. Adding a small amount of coloring agent to give the white a slight saturation, such as redness or blueness, may also be effective in improving the aesthetic appeal. Inert particles may be added to improve handling in the film-making and molding processes. The inert particles are not particularly limited as long as they can exist stably in the polymer, and known particles can be used. For example, polymers or copolymers of monomers selected from polystyrene, methyl polyacrylate, ethyl polyacrylate, methyl polymethacrylate, ethyl polymethacrylate, and divinylbenzene, organic materials such as polytetrafluoroethylene, polyacrylonitrile, benzoguanamine, and silicone, and inorganic materials such as silica, kaolin, talc, and graphite are preferred. The preferred particle size of these inert particles is 0.1 μm to 10 μm, and the preferred content is in the range of 0.002% by mass to 0.5% by mass.

[0033] (Intrinsic Viscosity) The intrinsic viscosity of the polyester constituting the polyester film is preferably 0.46 dL / g or higher, more preferably 0.48 dL / g or higher, even more preferably 0.50 dL / g or higher, and particularly preferably 0.52 dL / g or higher. When the intrinsic viscosity is 0.46 dL / g or higher, film breakage is less likely to occur during film stretching, and the occurrence of cracks or breakage during molding can be reduced. A high intrinsic viscosity is desirable from the viewpoint of moldability, but 0.80 dL / g or lower is preferable. When it is 0.80 dL / g or lower, problems such as a decrease in productivity can be eliminated. More preferably 0.75 dL / g or lower.

[0034] Here, the intrinsic viscosity of polyester is determined by dissolving the polyester film in o-chlorophenol, removing solid components other than the resin, such as white pigment, using a centrifuge, and then measuring the viscosity in the 35°C solution.

[0035] (Film composition) The polyester film may have a single-layer or multi-layer structure. Examples of multi-layer structures include a two-layer structure using two types of raw materials, a three-layer structure in which one of the two types is placed as a layer on both sides of the layer made of the other raw materials, and a multi-layer structure in which the two types of raw materials are arranged alternately. A multi-layer structure using three or more types of raw materials may also be formed. In such a multi-layer structure, the white pigment may be added to any layer, and as a result, the above-mentioned preferred amount of addition should be achieved on average across all layers. The amount of white pigment added to each layer (i.e., polyester layer) can be adjusted arbitrarily, but in order to prevent abrasion that is likely to occur during harsh molding processes, it is preferable that the amount of white pigment added to the outermost layer in the multi-layer structure after bonding to the metal plate be as small as possible, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass.

[0036] When a polyester film has a multilayer structure, the polyesters constituting each layer can be different from each other, but it is preferable that the difference in melting points of each polyester is 4°C or less. A difference in melting points of 4°C or less can reduce the deterioration of the appearance of the polyester film that may occur when heating is performed to remove molding stress after the metal container has been formed. This is because it is possible to suppress or reduce excessive melting or flow of the layer with the lowest melting point, and as a result, it is possible to suppress or reduce surface irregularities of the polyester film that may occur due to thermal shrinkage of other layers.

[0037] (Thickness) The thickness of the polyester film can be changed as needed, but a range of 6 μm to 75 μm is preferable, and among these, a range of 10 μm to 75 μm, and particularly a range of 15 μm to 50 μm, is preferable. If the thickness is 6 μm or more, it becomes less likely to be scraped or torn during molding, while if it is 75 μm or less, it is economical. If the polyester film has a multilayer structure, the thickness of each layer can be appropriately determined, provided that the above preferred range of polyester film thickness is satisfied. For example, in the case of a three-layer structure in which one of two types is placed as a layer on both sides of a layer made of the other type of raw material, the ratio XA / XB of the sum of the thicknesses of the outer layers on both sides (XA) to the thickness of the central layer (XB) is preferably 0.10 to 0.60, more preferably 0.15 to 0.55, and even more preferably 0.20 to 0.45.

[0038] <Coated Layer> The coated layer can be formed by applying a coating solution containing a lubricating substance and an acrylic resin with a glass transition temperature of 20°C to 100°C to one side of the aforementioned polyester film, and then allowing the coating solution to dry at least partially.

[0039] (Acrylic resin) The content of acrylic resin with a glass transition temperature of 20°C to 100°C in the coating liquid is preferably 45% by mass or more, and more preferably 55% by mass or more, out of 100% by mass of the solid content of the coating liquid. The upper limit may be, for example, 99% by mass or 98% by mass. The content of acrylic resin with a glass transition temperature of 20°C to 100°C in the coating liquid is the content of the solid content of acrylic resin with a glass transition temperature of 20°C to 100°C in the coating liquid. The solid content of the coating liquid is the component that forms the coating layer among the components contained in the coating liquid. The solid content of the acrylic resin is the component that forms the coating layer among the components that can be contained in the acrylic resin.

[0040] Examples of acrylic resins with a glass transition temperature of 20°C to 100°C include those obtained by polymerizing acrylic monomers as exemplified below. Examples of acrylic monomers include alkyl acrylates and alkyl methacrylates (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; monomers containing carboxyl groups or their salts, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); acrylamide, methacrylate monomers containing amide groups such as luamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups), N-alkoxyacrylamide, N-alkoxymethacrylamide, N,N-dialkoxyacrylamide, and N,N-dialkoxymethacrylamide (alkoxy groups include methoxy, ethoxy, butoxy, and isobutoxy groups), acryloylmorpholine, N-methylolacrylamide, N-methylolmethacrylamide, N-phenylacrylamide, and N-phenylmethacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride;Examples of monomers include vinyl isocyanates, allyl isocyanates, styrene, α-methylstyrene, vinyl methyl ethers, vinyl ethyl ethers, vinyl trialkoxysilanes, alkyl maleic acid monoesters, alkyl fumaric acid monoesters, alkyl itaconic acid monoesters, acrylonitriles, methacrylonitriles, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene, and oxazoline group-containing monomers (e.g., 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline). In particular, monomers containing hydroxyl groups, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-methylolacrylamide, N-methylolmethacrylamide, and monomers containing oxazoline groups, such as 2-isopropenyl-2-oxazoline, are preferred. The content of monomers containing hydroxyl groups is preferably 1 mol% to 20 mol%, more preferably 2 mol% to 10 mol%. The content of monomers containing oxazoline groups is preferably 10 mol% to 60 mol%, more preferably 20 mol% to 50 mol%. Acrylic resins with a glass transition temperature of 20°C to 100°C can be used as one type or a mixture of two or more types.

[0041] The glass transition temperature of the acrylic resin is 20°C to 100°C, more preferably 30°C to 90°C, and even more preferably 40°C to 80°C. Since the glass transition temperature of the acrylic resin is 20°C or higher, it is possible to reduce or prevent abrasion of the polyester film that may occur during molding. On the other hand, since it is 100°C or lower, good adhesion of the printing ink is achieved.

[0042] The explanation of the acrylic resin content with a glass transition temperature of 20°C to 100°C in the coating layer is omitted because it overlaps with the explanation of the acrylic resin content with a glass transition temperature of 20°C to 100°C in the coating liquid (based on 100% by mass of solids in the coating liquid).

[0043] (Crosslinking agent) It is preferable that the coating liquid contains a crosslinking agent. When the coating liquid contains a crosslinking agent, it is possible to enhance the cohesive force of the coating layer, and it is possible to further reduce or prevent the scraping of the polyester film that may occur during the molding process. Moreover, it is possible to further avoid or mitigate an excessive deficiency in ink adhesion. The type of the crosslinking agent is not limited, and examples thereof include a compound having an epoxy group, a compound having an isocyanate group, melamine and its reaction product, a compound having a silanol group, and hydrosilane. The content of the crosslinking agent in the coating liquid is preferably 0.1% by mass to 30% by mass, more preferably 0.5% by mass to 25% by mass, and still more preferably 1% by mass to 20% by mass in 100% by mass of the solid content of the coating liquid. Here, the content of the crosslinking agent in the coating liquid is the content of the solid content of the crosslinking agent in the coating liquid. The solid content of the crosslinking agent is a component that forms the coating layer among the components that can be contained in the crosslinking agent. When it is 0.1% by mass or more, the cohesive force of the coating layer can be enhanced. When it is 30% by mass or less, it is possible to further avoid or mitigate an excessive deficiency in ink adhesion. The description of the content of the crosslinking agent in the coating layer is omitted because it overlaps with the description of the content of the crosslinking agent in the coating liquid (based on 100% by mass of the solid content of the coating liquid).

[0044] (Lubricating substance) The content of the lubricating substance in the coating liquid is 1% by mass to 20% by mass, preferably 2% by mass to 15% by mass in 100% by mass of the solid content of the coating liquid. Here, the content of the lubricating substance in the coating liquid is the content of the solid content of the lubricating substance in the coating liquid. The solid content of the lubricating substance is a component that forms the coating layer among the components that can be contained in the lubricating substance. If this content is 1% by mass or more, it is possible to reduce or prevent the scraping of the polyester film that may occur during the molding process. If it is 20% by mass or less, it is possible to alleviate the decrease in ink adhesion caused by the lubricating substance. The description of the content of the lubricating substance in the coating layer is omitted because it overlaps with the description of the content of the lubricating substance in the coating liquid (based on 100% by mass of the solid content of the coating liquid).

[0045] Lubricating substances are substances that can reduce friction between the coated layer and the tool (for example, a die). Examples of the above-mentioned lubricating substances include various waxes. Specific examples of aliphatic waxes include plant-based waxes such as carnauba wax, candelilla wax, rice wax, wood wax, jojoba oil, palm wax, rosin-modified wax, uricuri wax, sugarcane wax, esparto wax, and bark wax; animal-based waxes such as beeswax, lanolin, whale wax, privet wax, and shellac wax; mineral-based waxes such as montan wax, ozokerite, and ceresin wax; petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolactam; synthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax, oxidized polyethylene wax, polypropylene wax, and oxidized polypropylene wax; and amide waxes such as stearate amide, oleate amide, erucate amide, and ethylenebisstearate amide. Among these, carnauba wax, paraffin wax, stearic acid and its ester waxes, bisamide waxes, polyethylene wax, and oxidized polyethylene wax are more preferred due to their good ink adhesion. Using an aqueous dispersion of wax is preferable for preparing a wax-containing coating solution, considering environmental concerns and ease of handling.

[0046] The melting point of the lubricating substance may be, for example, 40°C or higher, or 50°C or higher. The melting point of the lubricating substance may also be, for example, 200°C or lower, or 170°C or lower. The melting point of the lubricating substance can be measured using a differential scanning calorimeter.

[0047] (Particles) The coating liquid preferably contains particles with an average particle diameter of 0.01 μm to 3 μm. The content of particles with an average particle diameter of 0.01 μm to 3 μm in the coating liquid is preferably 0.01% to 30% by mass based on 100% by mass of the solid content of the coating liquid. If the content of these particles is 0.01% by mass or more, shaving of the polyester film that may occur during molding can be further reduced. If the content of these particles is 10% by mass or less, deterioration of ink adhesion caused by these particles can be alleviated. The average particle diameter is more preferably 0.02 μm to 2 μm, and even more preferably 0.03 μm to 1 μm. The content of particles with an average particle diameter of 0.01 μm to 3 μm is more preferably 0.02% to 25% by mass, and even more preferably 0.05% to 20% by mass. The content of particles with an average particle diameter of 0.01 μm to 3 μm is preferably adjusted according to the average particle diameter. For example, for particles with an average particle diameter of 0.04 μm, 5% to 20% by mass is preferable, and for particles with an average particle diameter of 1.5 μm, 0.05% to 0.2% by mass is preferable. Also, two or more types of particles with an average particle diameter of 0.01 μm to 3 μm can be added, and adding two or more types of particles with different particle diameters can be exemplified as a preferable form.

[0048] Examples of the above particles include inorganic fine particles such as silica, calcium carbonate, magnesium carbonate, calcium oxide, zinc oxide, magnesium oxide, silicon oxide, sodium silicate, aluminum hydroxide, iron oxide, zirconium oxide, barium sulfate, titanium oxide, tin oxide, antimony trioxide, carbon black, molybdenum disulfide, etc., and organic fine particles such as acrylic crosslinked polymers, styrene crosslinked polymers, silicone resins, fluorine resins, benzoguanamine resins, phenol resins, nylon resins, melamine resins, etc. Among these, for water-insoluble solid substances, in order to avoid sedimentation in the aqueous dispersion, it is preferable to select ultrafine particles with a density not exceeding 3 g / cm ３ 3.

[0049] The description of the content of particles with an average particle diameter of 0.01 μm to 3 μm in the coating layer is omitted because it overlaps with the description of the content of particles with an average particle diameter of 0.01 μm to 3 μm in the coating liquid (based on 100% by mass of the solid content of the coating liquid).

[0050] (Surfactants) The coating solution is preferably used in the form of an aqueous coating solution such as an aqueous solution, an aqueous dispersion, or an emulsion. In order to apply the coating solution to the polyester film with high quality, it is preferable to add a chemically inert surfactant to the coating solution.

[0051] Such surfactants promote the wetting of the polyester film with the aqueous coating solution. Examples include anionic and nonionic surfactants such as polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, fatty acid metal soaps, alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. Alkylbenzene sulfonate can be given as an example of an alkyl sulfonate. It is preferable to add an amount of surfactant that allows the surface tension of the aqueous coating solution to be less than or equal to the surface tension of the polyester film. The surfactant content in the coating solution is preferably 1% to 20% by mass of 100% by mass of the solid content of the coating solution. In addition to the function of promoting the wetting of the polyester film with the aqueous coating solution, the surfactant may also exhibit other functions. For example, it may exhibit an antistatic function.

[0052] The explanation of the surfactant content in the coating layer is omitted because it overlaps with the explanation of the surfactant content in the coating solution (based on 100% by mass of the solid content of the coating solution).

[0053] (Other additives) Other additives, such as antistatic agents, colorants, thickeners, devisers, defoamers, and UV absorbers, may be added to the coating layer as needed.

[0054] (Thickness of the coating layer) The amount of coating liquid applied is preferably such that the thickness of the coating layer, specifically the thickness of the coating layer after drying, is in the range of 0.01 μm to 0.3 μm, more preferably 0.02 μm to 0.25 μm. If the thickness of the coating layer is 0.01 μm or more, excessive lack of ink adhesion can be further avoided or mitigated. If the thickness of the coating layer is 0.3 μm or less, blocking can be suppressed or reduced when winding the laminated polyester film into a roll. The thickness of the coating layer is preferably adjusted according to the average particle size of the particles that can be added to the coating layer. The ratio of the thickness of the coating layer to the average particle size (or the average particle size of the largest particle if multiple types of particles are used) (i.e., thickness of the coating layer / average particle size) is preferably 1 / 10 to 2 / 1.

[0055] (Coating Method) Any known method can be used as the coating method for providing the coating layer. For example, roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, etc., can be used individually or in combination. It is preferable that the coating layer be formed on the side of the polyester film opposite to the side that faces the metal plate during lamination.

[0056] The solid content concentration of the coating liquid used for coating the coating layer is usually 20% by mass or less, but is particularly preferably 1% to 10% by mass. If this ratio is 1% by mass or more, it is not necessary to apply a large amount of coating liquid to the polyester film, while if it is 20% by mass or less, the stability of the coating liquid and the appearance of the coating layer can be improved.

[0057] The coating of the coating solution onto the polyester film can be carried out at any stage, but it is preferable to carry it out during the manufacturing process of the polyester film, and more preferably before orientation crystallization is completed. Here, the polyester film before crystallization is completed includes unstretched film, uniaxially oriented film obtained by oriented an unstretched film in either the longitudinal direction (i.e., the mechanical direction) or the transverse direction (i.e., the width direction), and even film obtained by low-magnification stretching orientation in both the longitudinal and transverse directions (biaxially oriented film before final re-stretching in the longitudinal or transverse direction to complete orientation crystallization). In particular, it is preferable to apply the coating solution to an unstretched film or a uniaxially oriented film oriented in one direction, and then immediately perform longitudinal stretching and / or transverse stretching and heat fixing. When applying the coating solution to the film, physical treatments such as corona surface treatment, flame treatment, and plasma treatment may be applied to the surface of the polyester film as a preliminary treatment to improve coatability.

[0058] <Method for Manufacturing Laminated Polyester Film> The method for manufacturing laminated polyester film described above is not particularly limited. For example, first, a polyester resin raw material for polyester film, which has a predetermined amount of white pigment already contained in it, is thoroughly dried. Then, using an extruder, it is melt-extruded at the crystal melting peak temperature (Tp) in DSC + 30°C to Tp + 70°C, and discharged from a slit die to produce an unstretched sheet. When forming a multilayer structure, an extruder is prepared for each type of resin, and after thoroughly drying the polyester resin that will be the raw material for each layer, it is melt-extruded in the same manner as above. In a molten state, multiple types of molten resins are stacked in a layered structure using a feed block or multi-manifold die and discharged from a slit die to produce an unstretched film (hereinafter sometimes referred to as an "unstretched sheet").

[0059] Next, it is preferable to sequentially or simultaneously biaxially stretch the unstretched sheet and then heat-set it. When forming a film by sequential biaxial stretching, it is preferable to heat the unstretched sheet by roll heating, infrared heating, etc., and first stretch it in the longitudinal direction, and then stretch it transversely with a stent. At this time, it is preferable to set the stretching temperature to a temperature 10°C to 50°C higher than the glass transition temperature of the polyester resin constituting the polyester film, and to set the longitudinal stretching ratio in the range of 3.0 to 4.2 times and the transverse stretching ratio in the range of 3.1 to 4.5 times. As described above, in order to form a coating layer, a coating liquid can be applied to the unstretched sheet or the uniaxially oriented film after longitudinal stretching. Next, it is preferable to perform heat-setting. The heat-setting temperature is preferably determined according to the Tp of the polyester resin, and it is preferable to adjust it in the range of Tp-70°C to Tp-15°C.

[0060] A laminated metal sheet can be obtained by laminating a laminated polyester film to a metal sheet, that is, by laminating the laminated polyester film to the metal sheet. To laminate the laminated polyester film to the metal sheet, it is preferable to heat-press the laminated polyester film to the metal sheet. Specifically, it is preferable to heat-press the laminated polyester film to the metal sheet with the polyester film facing the metal sheet.

[0061] A metal sheet for can manufacturing is preferred as the metal sheet to which the laminated polyester film is laminated. Suitable metal sheets for can manufacturing include tinplate, tin-free steel, and aluminum. The lamination temperature is preferably one that balances the adhesion of the laminated polyester film with the moldability of the metal container. A metal can can be formed using a known molding method with a metal sheet laminated with a laminated polyester film.

[0062] Laminated polyester film can be suitably used on the exterior surface of cans. This allows the laminated polyester film to protect the metal from the environment and achieve excellent design properties as a base for printing inks. Laminated polyester film may also be used on the interior surface of cans. It may be used on both the exterior and interior surfaces of cans. Furthermore, it may be used on can lids, bottoms, and mounting cups of aerosol cans to protect the metal.

[0063] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each characteristic value was measured by the following method.

[0064] (1) The polyester component sample is dissolved in deuterated chloroform and analyzed using a VARIAN 400-MR nuclear magnetic resonance (NMR) spectrometer. １ ¹H-NMR analysis was performed. The molar ratio was determined from the ratio of the integral values.

[0065] (2) Melting point The melting point was measured according to the method described in JIS-K-7121:2012. Specifically, about 10 mg of resin was sealed in an aluminum pan for measurement, and this was mounted on a differential scanning calorimeter (TA Instruments, DSCQ100), and the temperature was raised from 20°C to 300°C at a rate of 20°C / min. The melting point was determined from the crystal melting peak temperature (i.e., the temperature at the top of the crystal melting peak) in the curve obtained by this differential scanning calorimeter measurement, i.e., the DSC curve.

[0066] (3) Glass transition temperature (Tg) Approximately 10 mg of resin was sealed in an aluminum pan for measurement, and mounted on a differential scanning calorimeter (TA Instruments, DSCQ100). The temperature was raised from 20°C to 250°C at a rate of 20°C / min, held for 3 minutes, cooled to 25°C at a rate of 20°C / min, and then raised again from 20°C to 250°C at a rate of 20°C / min. The glass transition temperature was determined from the midpoint glass transition temperature in the DSC curve obtained by this differential scanning calorimeter measurement. The midpoint glass transition temperature is the temperature at the point where a line equidistant in the vertical direction from a pair of lines extending each baseline intersects with the curve of the stepwise change portion of the glass transition.

[0067] (4) After dissolving the intrinsic viscosity sample in 25 ml of o-chlorophenol, the sample was cooled and insoluble materials such as pigments were removed by centrifugation. The viscosity of the solution was measured at a temperature of 35°C using an Ostwald viscosity tube. A calibration curve was created from the solution viscosity and the intrinsic viscosity was calculated. For the evaluation films prepared in Examples 5 to 10 and Comparative Examples 1 to 3, the layer formed with resin A was scraped off from the evaluation film as a sample in order to determine the intrinsic viscosity of the layer formed with resin A.

[0068] (5) On one of the two sides of the film used to evaluate moldability, a tin-free steel sheet with a thickness of 0.230 mm, heated to the melting point of the resin (specifically, the melting point of resin S1 in Examples 1 to 4, the melting point of resin A in Examples 5 to 10 and Comparative Examples 1 to 3, and the melting point of resin S2 in Comparative Example 4) + 10°C, was bonded to the side opposite to the coating (or any side in the case of the evaluation film for Comparative Example 3, which does not have a coating), and then water-cooled. From the resulting laminated steel sheet, a 140 mm diameter disc-shaped sample (i.e., a disc-shaped laminated steel sheet) was cut out. This sample was subjected to a four-stage drawing process using a die and punch to produce 1000 seamless side containers (hereinafter sometimes referred to as "cans") with a diameter of 52 mm and a height of 141 mm. The abrasion and crack occurrence of the biaxially oriented polyester film on the can wall of the 1000 cans were evaluated according to the following criteria.

[0069] [Abrasion] ◎: The incidence rate of abrasion reaching the tin-free steel plate (hereinafter sometimes referred to as "deep abrasion") is 0% (i.e., 0 cans with deep abrasion), and the incidence rate of abrasion that does not reach the tin-free steel plate (hereinafter sometimes referred to as "shallow abrasion") is less than 0.1% (i.e., fewer than 10 cans with shallow abrasion). ○: The incidence rate of deep abrasion is 0%, and the incidence rate of shallow abrasion is between 0.1% and 0.5%. △: The incidence rate of deep abrasion is greater than 0% and 0.5% or less. ×: The incidence rate of deep abrasion is greater than 0.5%.

[0070] [Cracks] ○: No cracks are observed in the biaxially oriented polyester film. △: Small cracks are observed in the biaxially oriented polyester film, but no large cracks are observed. ×: Large cracks are observed in the biaxially oriented polyester film.

[0071] (6) Ink Adhesion Ink adhesion was evaluated using a pencil hardness test. Specifically, 700 of the 1000 cans were coated with a known thermosetting ink (DIC Corporation, MCQLR-3 Red-3) and a thermosetting finishing varnish (DIC Corporation, 6WB117), and then baked in an oven at 200°C for 30 seconds. The 700 cans obtained in this way (hereinafter sometimes referred to as "printed cans") were cut open, and the can bodies were flattened to obtain 700 test pieces. The ink-printed surface of each test piece was scanned at a speed of 1 mm / sec under a 750 g load using a pencil hardness tester (Marubishi Kagaku Kikai Seisakusho, PS-310). In other words, the pencil lead was pressed against the ink layer of each test piece with a load of 750 g while moving at a speed of 1 mm / sec. This procedure was performed on pencils in order from lowest hardness to highest hardness, and the hardness of the pencil that caused the ink layer to peel off (hereinafter sometimes referred to as "ink peeling") was determined. The hardness of the pencil immediately preceding the one that caused ink peeling (i.e., the hardness of the hardest pencil that did not cause ink peeling) (hereinafter sometimes referred to as "maximum pencil hardness") was determined. Of the maximum pencil hardness of 700 test pieces, the softest is shown in Table 2 according to the following classifications. ◎: Maximum pencil hardness of 3H or higher ○: Maximum pencil hardness of 2H △: Maximum pencil hardness of H ×: Maximum pencil hardness of F or lower

[0072] (7) Opacity The 700 cans obtained above were visually inspected, and their opacity was evaluated according to the following criteria. ○: In all 700 cans, the color of the tin-free steel sheet was not visible at all. ×: In at least one of the 700 cans, the color of the tin-free steel sheet was visible.

[0073] (8) Overall evaluation ◎: Scratching, cracking, ink adhesion, and opacity are not all ×, and scratching and ink adhesion are not △. ○: Scratching, cracking, ink adhesion, and opacity are not all ×, and at least one of scratching and ink adhesion is △. ×: At least one of scratching, cracking, ink adhesion, and opacity is ×.

[0074] [Examples 1-4] A 10 mol% isophthalic acid copolymer polyethylene terephthalate resin (melting point 230°C, intrinsic viscosity 0.62 dL / g) (hereinafter sometimes referred to as "resin S1") containing 10% by mass of rutile-type titanium dioxide with an average particle size of 0.23 μm and 0.1% by mass of spherical silica with an average particle size of 1.2 μm was dried. Resin S1 was melt-extruded from a slit die using an extruder at a resin temperature of 270°C, and rapidly cooled and solidified to obtain an unstretched film. Next, this unstretched film was longitudinally stretched 3.0 times at 100°C, and then the coating liquids listed in Table 2 were applied to one side of the film using a roll coater. All coating liquids were aqueous dispersions with a solid content concentration of 3% by mass, and the solid content of each coating liquid is as shown in Table 1. Next, the coating liquids were dried at 95°C, stretched 3.1 times in the transverse direction at 120°C, and heat-set at 160°C. This resulted in the acquisition of an evaluation film having a biaxially oriented polyester film with a thickness of 20 μm and a coating. The intrinsic viscosity of the evaluation film was 0.59 dL / g, and the thickness of the coating was as shown in Table 2. The evaluation results of the obtained evaluation film are shown in Table 2.

[0075] [Examples 5-10, Comparative Examples 1-2] A 2 mol% isophthalic acid copolymer polyethylene terephthalate resin (melting point 248°C, intrinsic viscosity 0.73 dL / g) (hereinafter sometimes referred to as "Resin A") containing 0.1% by mass of spherical silica with an average particle size of 1.2 μm, and a 2 mol% isophthalic acid copolymer polyethylene terephthalate resin (melting point 248°C, intrinsic viscosity 0.60 dL / g) (hereinafter sometimes referred to as "Resin B") containing 20% ​​by mass of rutile-type titanium dioxide with an average particle size of 0.23 μm, were dried. Resin A was melted at 290°C in a first extruder, and Resin B was melted at 290°C in a second extruder. Using a three-layer feed block, Resin A was laid on both sides of Resin B, and this was melt-extruded through a slit die and rapidly cooled and solidified to obtain an unstretched film. Next, the unstretched film was longitudinally stretched to 3.0 times its original size at 100°C, and then the coatings listed in Table 2 were applied to one side of the film using a roll coater. All coatings were aqueous dispersions with a solid content concentration of 3% by mass, and the solid content of each coating is as shown in Table 1. The coatings were then dried at 95°C, stretched transversely to 3.1 times its original size at 120°C, and heat-set at 165°C. This resulted in an evaluation film having a biaxially oriented polyester film with a thickness of 20 μm and a coating film. The thickness of each outer layer (i.e., each layer formed with resin A) of the biaxially oriented polyester film was 2.5 μm, and the thickness of the intermediate layer (i.e., the layer formed with resin B) was 15.0 μm. The intrinsic viscosity of the outer layer (specifically, the layer formed with resin A) of the evaluation film was 0.65 dL / g, and the thickness of the coating film was as shown in Table 2. The evaluation results of the obtained evaluation film are shown in Table 2. In Comparative Example 1, since the abrasion test was unsuccessful in the moldability test, neither the ink adhesion test nor the opacity test was performed.

[0076] [Comparative Example 3] An evaluation film, i.e., a biaxially oriented polyester film with a thickness of 20 μm, was prepared using the same method as in Example 5, except that no coating film was formed. The evaluation results of the evaluation film are shown in Table 2. Note that, because the abrasion test was unsuccessful in the moldability test, neither the ink adhesion test nor the opacity test was performed.

[0077] [Comparative Example 4] An evaluation film (specifically, an evaluation film having a 20 μm thick biaxially oriented polyester film and a coating) was prepared in the same manner as in Example 2, except that a 10 mol% isophthalic acid copolymer polyethylene terephthalate resin (melting point 229°C, intrinsic viscosity 0.65 dL / g) (hereinafter sometimes referred to as "resin S2") containing 3% by mass of rutile-type titanium oxide with an average particle size of 0.23 μm and 0.1% by mass of spherical silica with an average particle size of 1.2 μm was used instead of resin S1. The intrinsic viscosity of the evaluation film was 0.61 dL / g, and the thickness of the coating was as shown in Table 2. The evaluation results of the obtained evaluation film are shown in Table 2. As shown in Table 2, the opacity was poor. Note that ink adhesion was not evaluated in Comparative Example 4.

[0078] [Comparative Example 5] An evaluation film was prepared in the same manner as in Example 2, except that a 10 mol% isophthalic acid copolymer polyethylene terephthalate resin (melting point 230°C, intrinsic viscosity 0.51 dL / g) containing 32% by mass of rutile-type titanium oxide with an average particle size of 0.23 μm and 0.1% by mass of spherical silica with an average particle size of 1.2 μm was used instead of resin S1. However, sporadically, breakage occurred during the longitudinal stretching process, and as a result, an evaluation film could not be prepared.

[0079]

[0080]

[0081] Comparative Example 1, which used coating solution 8 (i.e., a coating solution containing an acrylic resin with a glass transition temperature of 17°C), showed poor abrasion. Comparative Example 2, which used coating solution 9 (i.e., a coating solution containing an acrylic resin with a glass transition temperature of 102°C), showed poor ink adhesion. Comparative Example 3, in which no coating film was formed, showed poor abrasion. Comparative Example 4, in which the biaxially oriented polyester film contained 3% by mass of rutile-type titanium dioxide, showed poor opacity. On the other hand, Examples 1 to 10 showed no poor abrasion, ink adhesion, or opacity.

[0082] Since the present invention relates to laminated polyester films for bonding metal sheets, laminated metal sheets, metal containers, and methods for manufacturing the same, the present invention has industrial applicability.

Claims

1. A laminated polyester film for bonding metal plates, comprising a polyester film and a coating layer provided on the polyester film, wherein the polyester film contains 5% to 30% by mass of a white pigment, and the coating layer is formed of a coating liquid, the coating liquid containing a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C.

2. The laminated polyester film for bonding metal plates according to claim 1, wherein the content of the lubricating substance in the coating layer is 1% by mass to 20% by mass.

3. The laminated polyester film for bonding metal plates according to claim 1, wherein the coating liquid contains a crosslinking agent, and the content of the crosslinking agent in the coating liquid is 0.1% to 30% by mass of 100% by mass of the solid content of the coating liquid.

4. The laminated polyester film for bonding metal plates according to claim 1, wherein the coating layer contains 0.01% to 30% by mass of particles with an average particle size of 0.01 μm to 3 μm.

5. The laminated polyester film for bonding metal plates according to claim 1, wherein the polyester film is a biaxially oriented polyester film.

6. A laminated metal plate comprising a metal plate and a laminated polyester film for bonding metal plates according to any one of claims 1 to 5, which is laminated to the metal plate.

7. A metal container comprising the laminated metal plate according to claim 6.

8. A method for manufacturing a laminated polyester film for bonding metal plates, comprising the steps of: applying a coating liquid containing a lubricating substance and an acrylic resin having a glass transition temperature of 20°C to 100°C to a polyester film containing 5% to 30% by mass of white pigment; and drying the coating liquid.

9. The method for manufacturing a laminated polyester film for bonding metal plates according to claim 8, wherein the content of the lubricating substance in the coating liquid is 1% by mass to 20% by mass of 100% by mass of the solid content of the coating liquid.

10. A method for manufacturing a laminated polyester film for bonding metal plates according to claim 8, further comprising the steps of: stretching the polyester film having undergone the step of drying the coating liquid in at least one direction; and heat-fixing the polyester film that has been stretched in at least one direction.

11. A method for manufacturing a laminated metal sheet, comprising the steps of: manufacturing a laminated polyester film for metal sheet lamination using the method for manufacturing a laminated polyester film for metal sheet lamination according to any one of claims 8 to 10; and heat-pressing the laminated polyester film for metal sheet lamination onto a metal sheet.

12. A method for manufacturing a metal container, comprising the steps of: manufacturing a laminated metal sheet using the method for manufacturing a laminated metal sheet described in claim 11; and shaping the laminated metal sheet.

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