Polyester laminated film for metal sheet coating and resin-coated metal sheet

Abstract

The present invention provides a polyester laminate film for coating metal sheets, which has lamination properties, can-forming processability, and feathering resistance, and a resin-coated metal sheet using the film. The polyester laminate film includes an A layer containing 70% by mass or more of a first polyester resin and an inorganic pigment, and a B layer laminated on at least one surface of the A layer, which contains 70% by mass or more of a second polyester resin, an inorganic lubricant, and a wax, wherein the first polyester resin and the second polyester resin each have a specific melting point and intrinsic viscosity, and the wax is a modified polyolefin wax having an acid value of 50 to 100 mgKOH / g, and the higher of the Young's modulus in the longitudinal direction and the Young's modulus in the transverse direction is E H , the lower one is E L The ratio of Young's modulus (E H / E L ) is 1.2 to 10 or less.

Description

[Technical Field]

[0001] The present invention relates to a polyester laminate film for covering metal sheets and a resin-coated metal sheet. [Background technology]

[0002] Conventionally, the inner and outer surfaces of metal containers made of tin-free steel (hereinafter referred to as TFS) or aluminum have been widely coated with paint for the purpose of corrosion prevention. Various thermosetting resins, such as epoxy resins and phenolic resins, have been used for such coatings. However, coating methods using thermosetting resins have the problems of requiring a long time for the paint to dry, resulting in reduced productivity, as well as consuming a great deal of energy and discharging a large amount of solvent.

[0003] To solve these problems, a method has been proposed in which a thermoplastic resin is laminated onto a metal plate to cover it. One method for laminating a thermoplastic resin onto a metal plate involves heating a metal plate that has been subjected to various surface treatments such as plating, and then laminating a thermoplastic resin film onto the metal plate by thermocompression bonding.

[0004] However, conventional thermoplastic resin films have problems such as thermal shrinkage when exposed to high-temperature atmospheres during thermocompression bonding, or the inclusion of air bubbles between the film and the metal plate, resulting in insufficient lamination. Another problem is that applying high tension to the film to prevent thermal shrinkage and the inclusion of air bubbles causes wrinkles in the film. Thermal shrinkage of thermoplastic resin films reduces the width of the product, resulting in reduced productivity. Additionally, the inclusion of defects such as air bubbles and wrinkles reduces product quality.

[0005] One approach to preventing thermal shrinkage of thermoplastic films is to lower the temperature of the metal plate during thermocompression bonding. However, lowering the temperature of the metal plate during thermocompression bonding poses the problem of poor adhesion between the metal plate and the thermoplastic film. Another problem is poor can-forming processability, particularly when attempting to form the film into cans, which require high processing. Poor can-forming processability can lead to chipping, breakage, peeling, and the like of the film, and in some cases, the entire film may break along with the metal plate.

[0006] Therefore, various techniques have been proposed to solve the problems caused by the poor lamination properties of thermoplastic resin films and to improve the adhesion between metal sheets and thermoplastic resin films.

[0007] For example, Patent Document 1 proposes a polyester composite film having a laminated structure of three layers: Layer A, Layer B, and Layer C. Layer A is a layer made of a resin with a high crystallization temperature that provides heat resistance, Layer B is a layer made of a high-melting-point resin that provides impact resistance and deformation resistance, and Layer C is a layer made of a resin with a low glass transition temperature that provides adhesion to a metal plate.

[0008] Furthermore, Patent Documents 2 to 4 propose lamination methods that suppress the entrapment of air bubbles. Specifically, Patent Document 2 controls the diameter of the laminating roll and the thickness of the rubber lining. Patent Document 3 blows gas onto a traveling metal strip near the laminating roll. Patent Document 4 reduces the pressure in the space upstream of the pressure roll when performing continuous lamination.

[0009] Furthermore, Patent Document 5 proposes a method of optimizing the Young's modulus and heat shrinkage rate by controlling the film production conditions, thereby suppressing bubbles and wrinkles.

[0010] Generally, metal containers are roughly divided into two types: two-piece cans, which are made up of two parts: a can body and a lid that are integrated with the can bottom, and three-piece cans, which are made up of three parts: a can body, a top lid, and a bottom lid. Two-piece cans have an attractive appearance because there are no welds in the can body, but they generally require high workability.

[0011] On the other hand, in recent years, from the viewpoint of reducing material costs and saving resources, the thickness of resin-coated metal sheets used for metal containers has been reduced. When a can body of the same shape is manufactured using a thinner resin-coated metal sheet, the degree of processing increases, and therefore, there is a possibility that the resin coating layer located on the outer surface side of the resin-coated metal sheet of the metal container may be broken or scraped.

[0012] Furthermore, various printing techniques are applied to the resin coating layer on the outer surface of metal containers to enhance their design, but cracks may occur in the resin coating layer when the can body is heat-treated during the printing process.These cracks are thought to occur when the crystals in the resin coating layer become oriented due to the processing during can manufacturing, reducing adhesion to the metal plate, and the oriented crystals in the resin coating layer shrink during the heat treatment.

[0013] Therefore, in order to manufacture highly processed two-piece can bodies, it is necessary to design materials that prevent breakage and scraping of the resin coating layer and the occurrence of cracks during heat treatment of the can body.

[0014] As techniques for manufacturing two-piece can bodies using resin-coated metal sheets, techniques such as drawing and ironing are proposed in Patent Documents 6 to 8. In addition, Patent Document 9 proposes a technique of adding an organic lubricating component to the resin coating layer as a technique for preventing breakage or scraping of the resin coating layer when manufacturing highly processed two-piece can bodies.

[0015] Furthermore, a phenomenon known as feathering, in which the coating resin remains, may occur during processes such as shearing a resin-coated metal sheet, punching a blank when manufacturing a two-piece can body, and opening an EOE (easy open end) can, which is a type of can lid. When feathering occurs, the remaining coating resin may fall off and become mixed into the can product or the can-making mold. Therefore, Patent Document 10 proposes a method for improving feathering resistance by controlling the thickness, elongation, crystallinity, and heat of crystalline fusion of the film coating the metal sheet. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Japanese Patent Application Publication No. 07-290666 [Patent Document 2] Japanese Patent Application Publication No. 06-008335 [Patent Document 3] Japanese Patent Application Publication No. 07-214724 [Patent Document 4] Japanese Patent Application Publication No. 07-186353 [Patent Document 5] International Publication No. 2020 / 090552 [Patent Document 6] Japanese Patent Application Publication No. 02-303634 [Patent Document 7] Japanese Patent Application Publication No. 04-091825 [Patent Document 8] Japanese Patent Application Laid-Open No. 2004-148324 [Patent Document 9] Japanese Patent Application Laid-Open No. 2017-30210 [Patent Document 10] Japanese Patent Application Publication No. 06-190965 Summary of the Invention [Problem to be solved by the invention]

[0017] However, the reality is that a resin-coated metal sheet that combines lamination properties, can-forming properties, and feathering resistance has yet to be realized.

[0018] Lamination For example, in order to prevent defects such as air bubbles and wrinkles from being introduced when a thermoplastic resin film is thermocompression laminated onto a metal plate, it is necessary to prevent the thermal shrinkage of the film and improve the stiffness of the film itself, as described above.

[0019] In Patent Document 1, heat resistance is improved by using a polyester composite film with a three-layer structure, but the heat resistance assumed in Patent Document 1 is heat resistance during can manufacturing and heat treatment after can manufacturing, and therefore, thermal shrinkage at high temperatures during lamination cannot be sufficiently suppressed.

[0020] Similarly, the methods of Patent Documents 2 to 4 cannot essentially suppress the thermal shrinkage of the film, and are ineffective under high lamination temperature conditions.

[0021] Furthermore, while the method of Patent Document 5 is effective in suppressing thermal shrinkage and improving stiffness of the film, it cannot suppress cracks in the resin coating layer that occur during the heat treatment of the can body during the printing process when manufacturing two-piece can bodies. This is because the film crystallizes too much with this method, resulting in the absence of a completely random molecular chain structure (mobile amorphous), which is important for adhesion to the metal plate and processability during can manufacturing. Furthermore, attempting to laminate at a higher temperature to melt the crystals in an overly crystallized film ultimately results in thermal shrinkage of the film and the introduction of defects. Furthermore, the film may overmelt and adhere to the laminating roll, significantly increasing the frequency of laminating roll replacement. Furthermore, a large amount of energy is required to heat the metal plate to a higher temperature.

[0022] ·Can manufacturing processability Furthermore, in order to prevent breakage and abrasion of the resin coating layer when manufacturing highly processed two-piece can bodies, it is necessary to improve can-making processability by adding a lubricant to the resin coating layer to ensure surface sliding properties or by reducing the crystallinity of the resin coating layer to ensure elongation.

[0023] However, the addition of a lubricant can impair adhesion between the resin coating layer and printing ink, resulting in a loss of aesthetic appeal. Therefore, conventional techniques have not achieved both the required processability and ink adhesion, making it impossible to obtain a resin-coated metal sheet that combines can-making processability with an aesthetic appearance after printing.

[0024] For example, the method of Patent Document 9 aims to achieve both processability and ink adhesion by adding a lubricant to the resin coating layer and controlling the water contact angle of the resin coating layer. However, a hydrophobic surface with a water contact angle of 80° or more may not be able to achieve sufficient affinity between the resin coating layer and the printing ink, and it is thought that peeling of the printing ink occurs during various processes after printing, such as filling the contents, sealing the lid, and transportation. Furthermore, methods that reduce the crystallinity of the resin coating layer make it difficult to achieve both anti-feathering properties, which will be described later.

[0025] Feathering resistance To improve feathering resistance, there is a method for controlling the crystallinity of the film to make it easier to tear, as described in Patent Document 10. However, in the case of resin-coated metal sheets that require a high degree of processability, such as two-piece cans, the coating resin is designed to have a low crystallinity, as described above, so when the resin-coated metal sheet is sheared or punched, the film stretches and remains. Therefore, it can be said that there is a trade-off between can-making processability and feathering resistance.

[0026] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyester laminate film for coating metal sheets, which has excellent lamination properties, can-forming processability, and feathering resistance, and a resin-coated metal sheet using the film. [Means for solving the problem]

[0027] As a result of intensive research conducted by the present inventors to solve the above problems, the following findings were obtained.

[0028] When a thermoplastic resin film is coated on a metal plate at high temperatures by thermocompression lamination, it is important to form the film into a laminate structure including a layer of polyester resin containing an inorganic lubricant in order to prevent the incorporation of bubbles and wrinkles due to thermal shrinkage of the film. In addition, it is also important to optimize the film manufacturing conditions and control the balance of the Young's modulus in the longitudinal and transverse directions of the film.

[0029] To prevent breakage or abrasion of the resin coating layer during severe can-making processes, such as those for two-piece can bodies, it is necessary to add a lubricating component to the resin coating layer to reduce friction between the surface of the resin coating layer and the die used during can-making. However, lubricating components have low compatibility with the thermoplastic resin that makes up the resin coating, resulting in poor dispersibility. As a result, the lubricating component may fall off during the can-making process, causing abrasion. Even if can-making is successful, the lubricating component may bleed out during the heat treatment process after printing. This hinders adhesion between the resin coating layer and the printing ink, resulting in a poor appearance. Therefore, it is important to thoroughly disperse the lubricating component in the thermoplastic resin.

[0030] The inventors have found that by controlling the intrinsic viscosity of the polyester resin as the matrix and the acid value and amount of the wax as the lubricating component within specific ranges, the lubricating component can be appropriately dispersed in the polyester resin, resulting in high sliding properties even during high-process can forming, and suppressing breakage and scraping of the resin coating layer.

[0031] Furthermore, when forming cans with a higher degree of processing, it is necessary to reduce the crystallinity of the resin coating and impart elongation to the resin coating in order to prevent breakage and scraping of the resin coating layer. However, while a resin coating with low crystallinity is excellent in can-forming processability, its high elongation causes feathering during the shearing and punching processes.

[0032] The present inventors have discovered that by adjusting the Young's modulus in the longitudinal and transverse directions of the film before thermocompression lamination and controlling the balance of anisotropy, excellent feathering resistance can be obtained in the resin-coated metal sheet after thermocompression lamination. The mechanism by which excellent feathering resistance is obtained is not clear, but it is thought to be as follows. Even if the crystals melt during thermocompression bonding and become amorphous-rich, oriented amorphous (rigid amorphous) remains. In such a state, the film is prone to tearing in the direction of strong rigid amorphous orientation, but has low elongation in the direction perpendicular to that orientation, thereby suppressing feathering.

[0033] Furthermore, when a resin-coated metal sheet is used for the body of a two-piece can, which is printed on the exterior surface of the can, it is necessary to incorporate an inorganic pigment into the resin film to increase whiteness and conceal the color of the metal sheet. Therefore, the present inventors attempted to separate functions by using a laminate structure to achieve both opacity and the above-mentioned lamination and can-forming processability. Specifically, they found that by laminating a layer containing an inorganic lubricant for lamination and a wax for can-forming processability with a layer containing an inorganic pigment for opacity, it was possible to satisfy all of the requirements for opacity, lamination, and can-forming processability.

[0034] The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

[0035] (1) A polyester laminate film comprising: a layer A containing 70% by mass or more of a first polyester resin and an inorganic pigment; and a layer B laminated on at least one surface of the layer A, the layer B containing 70% by mass or more of a second polyester resin, an inorganic lubricant, and a wax; the first polyester resin has a melting point of 240 to 255°C and an intrinsic viscosity of 0.55 to 0.75 dL / g; the second polyester resin has a melting point of 240 to 255°C and an intrinsic viscosity of 0.55 to 0.90 dL / g, which is greater than the intrinsic viscosity of the first polyester resin; The content of the inorganic pigment is 10 to 20% by mass based on the total components of the film, the content of the inorganic lubricant is 100 to 5000 ppm based on the total components of the layer B; the wax is a modified polyolefin wax having an acid value of 50 to 100 mgKOH / g, the content of the wax is 0.050 to 1.0% by mass based on the total components of the layer B, The higher of the Young's modulus in the longitudinal direction and the Young's modulus in the transverse direction is defined as E H , the lower one is E L The ratio of Young's modulus (E H / E L ) is 1.2 to 10.

[0036] (2)E H and E L The polyester laminate film for covering metal sheets according to (1) above, wherein each of the modulus and the compressive strength is 1,000 to 19,000 MPa.

[0037] (3)E H and E L The sum of (E H +E L ) is 3000 to 20000 MPa.

[0038] (4) The polyester laminate film for covering metal sheets according to any one of the above (1) to (3), which has a heat shrinkage rate at 160°C of 0 to 20% in both the longitudinal and transverse directions.

[0039] (5) The polyester laminate film for covering metal sheets according to any one of (1) to (4) above, wherein the modified polyolefin wax contained in the layer B is any one of acid-modified polyethylene wax, acid-modified polypropylene wax, oxidized polyethylene wax, and oxidized polypropylene wax, or a mixture thereof.

[0040] (6) The polyester laminate film for covering metal sheets according to any one of (1) to (5) above, which has a film thickness of 10 to 50 μm.

[0041] (7) The total thickness t of the B layer B The total thickness t of the A layer A The ratio (t A / t B ) is 2.5 to 7.5. The polyester laminate film for covering metal sheets according to any one of (1) to (6) above.

[0042] (8) The polyester laminate film for covering metal plates according to any one of (1) to (7) above, which is used for covering the surface of metal plates for containers.

[0043] (9) A resin-coated metal plate having, on at least one surface thereof, the polyester laminate film for coating metal plates according to any one of (1) to (8) above. [Effects of the Invention]

[0044] The polyester laminate film for covering metal sheets of the present invention can provide a resin-coated metal sheet that combines lamination properties, can-forming processability, and feathering resistance. Specifically, the present invention can suppress wrinkling and thermal shrinkage of the film during thermocompression lamination, especially at high temperatures. Furthermore, the present invention can suppress breakage and abrasion of the resin coating layer during can-forming, as well as cracking of the resin coating layer during the can-body heat treatment process, in the production of two-piece cans, which require a high degree of processing. Furthermore, the present invention can achieve excellent feathering resistance in addition to these properties. Furthermore, the polyester laminate film for covering metal sheets of the present invention can conceal the color of the metal sheet, imparting a high level of design to the product. DETAILED DESCRIPTION OF THE INVENTION

[0045] The present invention will be described in detail below. In this specification, the units of content, "%" and "ppm", represent "% by mass" and "ppm by mass", respectively, unless otherwise specified.

[0046] [Polyester laminated film for metal sheet coating] A polyester laminate film for covering metal sheets according to one embodiment of the present invention is a laminate film comprising Layer A and Layer B laminated on at least one surface of Layer A. Layer A contains 70% by mass or more of a first polyester resin and an inorganic pigment, while Layer B contains 70% by mass or more of a second polyester resin, an inorganic lubricant, and a wax.

[0047] The content of the polyester resin in the layer A is preferably 75% by mass or more, and more preferably 80% by mass or more. On the other hand, the upper limit of the content of the polyester resin in the layer A is not particularly limited, but is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0048] Similarly, the content of the polyester resin in the layer B is preferably 75% by mass or more, and more preferably 80% by mass or more. On the other hand, the upper limit of the content of the polyester resin in the layer B is not particularly limited, but is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, and even more preferably 99.7% by mass or less.

[0049] The layer B may be laminated on at least one surface of the layer A. Therefore, the polyester film may have a two-layer structure (A / B) or a three-layer structure (B / A / B). Furthermore, the polyester film may have layers other than the layers A and B as long as the effects of the present invention are not impaired.

[0050] In addition, when layer B is laminated on only one surface of layer A, for example, in the case of a two-layer structure A / B, layer A is the surface that is bonded to the metal plate, and layer B becomes the surface of the resin-coated metal plate.

[0051] The method for producing the polyester film having the laminated structure is not particularly limited, and any method can be used. For example, a coextrusion method using a feed block system or a multi-manifold system, a method of bonding with another film, or a lamination method in which a molten resin is directly laminated on a film can be used. From the viewpoint of lamination accuracy and productivity, a coextrusion method using a feed block system or a multi-manifold system is preferred.

[0052] (polyester resin) The polyester resin is preferably a resin obtained by polymerization of monomers containing, as main components, an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol, or a mixture thereof.

[0053] Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodiumsulfoisophthalic acid.

[0054] Examples of the aliphatic dicarboxylic acid include oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, dimer acid, maleic acid, fumaric acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof.

[0055] These dicarboxylic acids may be used alone or in combination of two or more kinds, and may also be copolymerized with an oxycarboxylic acid such as p-oxybenzoic acid.

[0056] Examples of the diol component include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbide (1,4:3,6-dianhydroglucitol, 1,4:3,6-dianhydro-D-sorbitol), spiroglycol, bisphenol A, and bisphenol S. Among these, it is preferable to use at least one of ethylene glycol and butanediol. These diol components may be used alone or in combination of two or more.

[0057] The polyester resin constituting the polyester laminate film for covering metal sheets of the present invention is preferably at least one of polyethylene terephthalate and its copolymers, and polybutylene terephthalate and its copolymers. These resins are suitable from the viewpoints of cost, ease of forming into a film, and adhesion to metal sheets. Mixtures of these resins can also be preferably used.

[0058] The polyester resin constituting the polyester laminate film for covering metal sheets of the present invention may be copolymerized with polyfunctional compounds such as trimellitic acid, trimesic acid, and trimethylolpropane, as long as the effects of the present invention are not impaired. Furthermore, resin components other than polyester may be added to impart functionality. Examples of resin components other than polyester include linear polyolefins such as polyethylene, polypropylene, poly(4-methylpentene-1), and polyacetal; alicyclic polyolefins obtained by ring-opening metathesis polymerization or addition polymerization of norbornenes, or addition copolymers with other olefins; biodegradable polymers such as polylactic acid and polybutyl succinate; polyamides such as nylon 6, nylon 11, nylon 12, and nylon 66; aramid; polymethyl methacrylate; polyvinyl chloride; polyvinylidene chloride; polyvinyl alcohol; and poly. Vinyl butyral, ethylene vinyl acetate copolymer, polyacetal, polyglycolic acid, polystyrene, styrene copolymer polymethyl methacrylate, polycarbonate, polyethersulfone, polyetheretherketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyarylate, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, etc. These may be copolymers or mixtures.

[0059] As long as the conditions described below are met, the polyester resin of layer A (first polyester resin) and the polyester resin of layer B (second polyester resin) may be the same type of polyester resin or different types of polyester resins.

[0060] (Melting point of polyester resin) First polyester resin: 240~255℃ If the melting point of the first polyester resin contained in the layer A is 240°C or higher, the occurrence of cracks in the resin coating layer and melting of the resin coating layer during the heat treatment of the can body in the printing process can be suppressed. Furthermore, if the melting point is 240°C or higher, the resin-coated metal sheet also has excellent feathering resistance. Therefore, the melting point of the first polyester resin is set to 240°C or higher, preferably 245°C or higher, and more preferably 247°C or higher. On the other hand, if the melting point is 255°C or lower, the occurrence of cracks in the resin coating layer and melting of the resin coating layer during the heat treatment of the can body in the printing process can be suppressed. Therefore, the melting point of the first polyester resin is set to 255°C or lower, preferably 253°C or lower.

[0061] Secondary polyester resin: 240~255℃ If the melting point of the second polyester resin contained in the layer B is 240°C or higher, the occurrence of cracks in the resin coating layer and melting of the resin coating layer during the heat treatment of the can body in the printing process can be suppressed. Furthermore, if the melting point is 240°C or higher, the resin-coated metal sheet also has excellent feathering resistance. Therefore, the melting point of the second polyester resin is set to 240°C or higher, preferably 245°C or higher, and more preferably 247°C or higher. On the other hand, if the melting point is 255°C or lower, the occurrence of cracks in the resin coating layer and melting of the resin coating layer during the heat treatment of the can body in the printing process can be suppressed. Therefore, the melting point of the second polyester resin is set to 255°C or lower, preferably 253°C or lower.

[0062] The melting points of the first polyester resin and the second polyester resin may be the same or different. However, if the melting points of the first polyester resin and the second polyester resin are close to each other, the co-extrudability of the A layer and the B layer is excellent, and a laminate film with high lamination accuracy can be obtained. In addition, when a resin-coated metal plate including the film is subjected to can forming processing, interfacial peeling between the A layer and the B layer can be suppressed. Therefore, the difference between the melting points of the first polyester resin and the second polyester resin is preferably 5°C or less, more preferably 3°C or less. The lower limit of the difference in melting points may be 0°C.

[0063] The melting point of the polyester resin can be measured by a differential scanning calorimeter (DSC). More specifically, it can be measured by the method described in the Examples. When the polyester resin is, for example, a copolymer or a mixture, or a resin with multiple crystalline forms, multiple melting peaks may be present when measured by a differential scanning calorimeter (DSC). In such cases, the melting peak with the largest heat of fusion among the multiple melting peaks is taken as the melting point. The melting point of the polyester resin can be controlled by the types of aromatic dicarboxylic acid or aliphatic dicarboxylic acid and diol that are the main constituent components, or the types and copolymerization amounts of copolymerized components in the case of a copolymer, or the mixing amounts thereof in the case of a mixture.

[0064] (intrinsic viscosity) Primary polyester resin: 0.55~0.75dL / g When the intrinsic viscosity of the first polyester resin is 0.55 dL / g or more, film breakage during stretching can be suppressed. Furthermore, the can-forming processability of a resin-coated metal sheet using the film is improved, suppressing film breakage during processing. Furthermore, feathering resistance is also improved. Therefore, the intrinsic viscosity of the first polyester resin is set to 0.55 dL / g or more, preferably 0.60 dL / g or more, and more preferably 0.62 dL / g or more. On the other hand, when the intrinsic viscosity of the first polyester resin is 0.75 dL / g or less, the can-forming processability of the resin-coated metal sheet can be improved. That is, when the intrinsic viscosity is 0.75 dL / g or less, the resin can be filtered using a fine filter, thereby increasing the filtration accuracy of foreign matter during film production and enabling melt extrusion. As a result, foreign matter in the film that causes film abrasion during can-forming can processing can be reduced. Therefore, the intrinsic viscosity of the first polyester resin is set to 0.75 dL / g or less, preferably 0.70 dL / g or less, and more preferably 0.68 dL / g or less.

[0065] Secondary polyester resin: 0.55~0.90dL / g If the intrinsic viscosity of the second polyester resin is 0.55 dL / g or more, film breakage can be suppressed when the film is stretched. Furthermore, the can-forming processability of a resin-coated metal sheet using the film is improved, and film breakage during processing can be suppressed. Therefore, the intrinsic viscosity of the second polyester resin is set to 0.55 dL / g or more, preferably 0.65 dL / g or more, and more preferably 0.70 dL / g or more. On the other hand, if the intrinsic viscosity of the second polyester resin is 0.90 dL / g or less, the can-forming processability of a resin-coated metal sheet using the film is improved, and film breakage during processing can be suppressed. Therefore, the intrinsic viscosity of the second polyester resin is set to 0.90 dL / g or less, preferably 0.85 dL / g or less, and more preferably 0.82 dL / g or less.

[0066] Furthermore, in the present invention, the intrinsic viscosity of the second polyester resin must be greater than that of the first polyester resin. If the intrinsic viscosity of the second polyester resin is greater than that of the first polyester resin, can-making processability is improved, and film abrasion during can-making can be suppressed. That is, Layer B, which directly contacts the mold during can-making, is subjected to high stress from the mold, making the film more susceptible to abrasion. Therefore, the intrinsic viscosity of the first polyester resin contained in Layer A is made smaller than that of the second polyester resin contained in Layer B. This allows Layer A to act as a cushion and mitigate damage caused by the mold.

[0067] The intrinsic viscosity of the polyester resin can be measured in accordance with JIS K7367-1 and JIS K7367-5. Specifically, it may be measured by the method described in the examples.

[0068] (inorganic pigments) The layer A contains an inorganic pigment. If the content of the inorganic pigment is 10% by mass or more based on the total film components, sufficient whiteness can be obtained for a two-piece can for printing, and excellent hiding power for the metal plate can be achieved. Furthermore, the inorganic pigment can easily tear during punching, resulting in excellent feathering resistance. Therefore, the content of the inorganic pigment is 10% by mass or more based on the total film components, preferably 11% by mass or more, and more preferably 12% by mass or more. On the other hand, if the content of the inorganic pigment is 20% by mass or less based on the total film components, excellent can-forming processability can be achieved when the film is made into a resin-coated metal plate, and film abrasion can be suppressed. Therefore, the content of the inorganic pigment is 20% by mass or less based on the total film components, preferably 18% by mass or less, and more preferably 16% by mass or less.

[0069] On the other hand, the layer B may or may not contain an inorganic pigment. When the layer B contains an inorganic pigment, the content of the inorganic pigment is the total content of the inorganic pigment contained in the layers A and B.

[0070] The inorganic pigment is not particularly limited, and any inorganic pigment can be used. It is preferable to use an inorganic pigment that turns a polyester film white when added to it. For example, at least one inorganic pigment selected from the group consisting of oxide ceramics such as silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, magnesium oxide, zinc oxide, barium titanate, and lead zirconate titanate, talc, mica, calcium carbonate, and barium sulfate can be used. Among these, titanium dioxide is preferred from the viewpoints of dispersibility in polyester resins and whiteness, and rutile titanium dioxide is more preferred.

[0071] The method for adding the inorganic pigment is not particularly limited. For example, the inorganic pigment may be added together with the polyester resin into an extruder for the A layer raw material during film production, and then kneaded and dispersed in the film-forming extruder. Alternatively, the polyester resin and the inorganic pigment may be kneaded in advance using a single extruder to prepare a masterbatch, and the inorganic pigment masterbatch may be added together with the polyester resin into the A layer raw material extruder during film production. Note that adding the inorganic pigment as a masterbatch is preferred because it allows the inorganic pigment to be added uniformly and with good dispersibility to the polyester resin.

[0072] (inorganic lubricant) The B layer contains an inorganic lubricant. If the content of the inorganic lubricant is 100 ppm or more relative to the total components of the B layer, it is possible to impart slipperiness to the film and suppress the incorporation of wrinkles during thermocompression lamination. Therefore, the content of the inorganic lubricant is 100 ppm or more, preferably 150 ppm or more, and more preferably 200 ppm or more relative to the total components of the B layer. On the other hand, if the content of the inorganic lubricant is 5000 ppm or less relative to the total components of the B layer, it is possible to improve can-forming processability and suppress film abrasion. Therefore, the content of the inorganic lubricant is 5000 ppm or less, preferably 3000 ppm or less, and more preferably 1000 ppm or less relative to the total components of the B layer.

[0073] On the other hand, the layer A may or may not contain an inorganic lubricant. When the layer A contains an inorganic lubricant, the content of the inorganic lubricant is preferably 3.0% or less relative to all components of the layer A. However, as mentioned above, in the case of a two-layer structure of A / B, the layer A is the surface that is bonded to the metal plate, and therefore the layer A is not exposed. Furthermore, in the case of a three-layer structure of B / A / B, the layer A is not exposed either. Therefore, there is no need to add an inorganic lubricant to the layer A, and from the viewpoint of cost, it is preferable that the layer A does not contain an inorganic lubricant.

[0074] Any inorganic lubricant can be used as long as it can impart lubricity to a polyester film by adding it, and examples of the inorganic lubricant include oxide ceramics such as silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, magnesium oxide, zinc oxide, barium titanate, and lead zirconate titanate, as well as talc, mica, calcium carbonate, and barium sulfate, and mixtures thereof may also be used.

[0075] The method for adding the inorganic lubricant is not particularly limited, and it can be added by any method. For example, during film production, the inorganic lubricant may be added together with the polyester resin into an extruder for the B layer raw material, and then kneaded and dispersed in the film-forming extruder. Alternatively, the polyester resin and the inorganic lubricant may be kneaded in advance using a single extruder to prepare a masterbatch, and during film production, the masterbatch of the inorganic lubricant may be added together with the polyester resin into the extruder for the B layer raw material. Note that the method of adding the inorganic lubricant as a masterbatch is preferred, as it allows a small amount of inorganic lubricant to be added uniformly and with good dispersibility to the polyester resin.

[0076] (wax) In addition to the inorganic lubricant, the layer B contains a wax, which is a modified polyolefin wax having an acid value of 50 to 100 mgKOH / g.

[0077] If the acid value of the wax is 50 mgKOH / g or more, the wax disperses well in the polyester resin of Layer B, resulting in excellent can-forming processability. Furthermore, when printing is performed during can-forming, adhesion can be improved depending on the type of ink used. Therefore, the acid value of the wax is set to 50 mgKOH / g or more, preferably 55 mgKOH / g or more, and more preferably 60 mgKOH / g or more. On the other hand, if the acid value of the wax is 100 mgKOH / g or less, the wax can be maintained in a well-dispersed state without excessively reacting with the polyester resin of Layer B. As a result, excellent can-forming processability can be achieved. Therefore, the acid value of the wax is set to 100 mgKOH / g or less, preferably 90 mgKOH / g or less, and more preferably 80 mgKOH / g or less. The acid value of the polyolefin wax is measured in accordance with JIS K5902. More specifically, it can be measured by the method described in the Examples.

[0078] An example of the modified polyolefin wax is an oxidized polyolefin wax obtained by introducing air into a polymer of an olefin monomer having 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, isobutene, isobutylene, or butadiene, or a thermal decomposition product thereof, in a molten state at 140°C to 180°C, to introduce a functional group through an oxidation reaction. Other examples include acid-modified polyolefin waxes obtained by random copolymerization, block copolymerization, or graft copolymerization of unsaturated carboxylic acids having 3 to 8 carbon atoms, such as acrylic acid, methacrylic acid, vinyl acetate, vinyl propionate, maleic acid, maleic anhydride, itaconic acid, and maleic acid monomethyl ester, metal salts of these acids neutralized in whole or in part with monovalent or divalent metal cations, such as sodium, potassium, lithium, zinc, magnesium, and calcium, and functional group-containing monomers, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isobutyl acrylate, isobutyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, maleic acid monomethyl ester, glycidyl acrylate, glycidyl methacrylate, vinyl acetate, acrylamine, and acrylamide. Alternatively, mixtures thereof may be used. Among these, acid-modified polyethylene wax, acid-modified polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, or a mixture thereof is preferred. The acid modification method is preferably maleic acid modification and / or maleic anhydride modification, and the functional group introduced by oxidation is preferably a carboxyl group, a ketone group, and / or a hydroxyl group.

[0079] When the wax content is 0.050% by mass or more, based on the total components of Layer B, the wax disperses well in the polyester resin of Layer B, resulting in excellent can-forming processability even under severe processing conditions. Therefore, the wax content is set to 0.050% by mass or more, preferably 0.060% by mass or more, and more preferably 0.070% by mass or more, based on the total components of Layer B. Similarly, when the wax content is 1.0% by mass or less, the wax disperses well in the polyester resin of Layer B, resulting in excellent can-forming processability even under severe processing conditions. Therefore, the wax content is set to 1.0% by mass or less, preferably 0.40% by mass or less, and more preferably 0.18% by mass or less, based on the total components of Layer B.

[0080] The number-average molecular weight of the modified polyolefin wax contained in the B layer is not particularly limited, but is preferably 500 to 20,000. When the number-average molecular weight of the modified polyolefin wax is within the above range, the modified polyolefin wax disperses well in the polyester resin of the B layer, further improving the can-forming processability of the resin-coated metal sheet. The number-average molecular weight is more preferably 1,000 or more, and even more preferably 1,500 or more. Furthermore, the number-average molecular weight is preferably 20,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less. The number-average molecular weight is more preferably 1,000 or more and 10,000 or less, and even more preferably 1,500 or more and 5,000 or less. The number-average molecular weight of the polyolefin wax is measured by gel permeation chromatography (GPC). More specifically, it may be measured by the method described in the Examples.

[0081] The melting point of the modified polyolefin wax contained in Layer B is not particularly limited, but is preferably 70° C. or higher and 180° C. or lower, more preferably 90° C. or higher and 160° C. or lower, and particularly preferably 100° C. or higher and 140° C. or lower. If the melting point of the modified polyolefin wax contained in Layer B is 70° C. or higher and 180° C. or lower, high sliding properties are exhibited due to heat generated during can forming, thereby further improving can forming processability.

[0082] The method for adding the wax is not particularly limited. For example, the wax may be added together with the polyester resin into an extruder for the B layer raw material during film production, and then kneaded and dispersed in the film-forming extruder. Alternatively, the polyester resin and the wax may be kneaded in advance using a single extruder to prepare a masterbatch, and the wax masterbatch may be added together with the polyester resin into the extruder for the B layer raw material during film production. Note that adding the wax as a masterbatch is preferred because it allows a small amount of wax to be added uniformly and with good dispersibility to the polyester resin.

[0083] E H / E L :1.2~10 The polyester laminate film for covering metal sheets of the present invention has a Young's modulus in the longitudinal direction or the width direction, whichever is higher, set to E H , the lower one is E L The ratio of Young's modulus (E H / E L ) is 1.2 to 10. H / E L By making E equal to or greater than 1.2, the anti-feathering property is improved. H / E L is preferably 2.0 or more, more preferably 3.6 or more, and most preferably 5.1 or more. H / E L By keeping the value of E at 10 or less, it is possible to prevent the film from shrinking in one direction at high temperatures during thermocompression bonding. As a result, it is possible to prevent a decrease in product width, wrinkles and film breakage due to film shrinkage, and air bubbles from getting between the film and the metal plate. It is also possible to prevent wrinkles from occurring due to the film becoming too weak in one direction. H / E L is preferably 9.0 or less, more preferably 8.0 or less, and most preferably 7.0 or less.

[0084] The term "longitudinal direction" as used herein is defined as the direction in which the film runs during film production. For example, in the case of a film that is produced by winding into a roll, the winding direction of the roll corresponds to the longitudinal direction. The term "width direction" as used herein is defined as the direction perpendicular to the longitudinal direction.

[0085] The Young's modulus can be measured by a tensile test. The tensile test may be carried out under conditions of a temperature of 23°C, an original length of 50 mm, and a tensile speed of 300 mm / min. More specifically, the Young's modulus can be measured by the method described in the Examples.

[0086] E H / E L In order to make the thickness fall within the above range, the polyester film may be uniaxially stretched in the machine or width direction under the conditions described below, and then heat-set.

[0087] As described above, in the present invention, E L E for H The desired effect is achieved by controlling the ratio of E H and E L However, from the viewpoint of improving the stiffness of the film and making it easier to keep the film smooth during transportation and thermocompression bonding, the value of E H and E L are preferably 1000 MPa or more, more preferably 1400 MPa or more, even more preferably 1800 MPa or more, and most preferably 2000 MPa or more. On the other hand, from the viewpoint of further improving can-making processability, E H and E L are preferably 19,000 MPa or less, more preferably 18,000 MPa or less, even more preferably 17,000 MPa or less, and most preferably 15,000 MPa or less.

[0088] E H and E LIn order to make both of the above ranges, the polyester film may be uniaxially stretched in the machine or width direction under the conditions described below, and then heat-set.

[0089] The polyester laminate film for covering metal sheets of the present invention is E H and E L The sum of (E H +E L ) is preferably 3000 to 20000 MPa. H +E L If the compressive strength is 3000 MPa or more, the stiffness of the film is further improved, and the film can be more easily kept smooth during transportation and thermocompression bonding. H +E L is more preferably 8000 MPa or more, even more preferably 10000 MPa or more, and most preferably 12000 MPa or more. H +E L If the elongation coefficient is 20,000 MPa or less, the can-making processability of the resin-coated metal sheet is further improved. H +E L is more preferably 19,000 MPa or less, even more preferably 18,000 MPa or less, and most preferably 17,000 MPa or less.

[0090] E H and E L The sum of (E H +E L ) can be set within the above ranges by uniaxially stretching the polyester film in the machine or width direction under the conditions described below, followed by heat setting.

[0091] The polyester laminate film for covering metal sheets of the present invention preferably has a heat shrinkage rate at 160°C of 0 to 20% in both the longitudinal and width directions. If the heat shrinkage rate at 160°C is 0% or more in both the longitudinal and width directions, the film is prevented from elongating during thermocompression bonding with the metal sheet, and wrinkles and film breakage due to film elongation can be further suppressed. On the other hand, if the heat shrinkage rate at 160°C is 20% or less in both the longitudinal and width directions, heat shrinkage during thermocompression bonding with the metal sheet can be suppressed, and wrinkles and film breakage due to film shrinkage, as well as the incorporation of air bubbles between the film and the metal sheet, can be further suppressed. The heat shrinkage rate at 160°C in both the longitudinal and width directions is more preferably 18% or less, even more preferably 16% or less, and most preferably 15% or less.

[0092] The heat shrinkage at 160°C is defined as the amount of displacement at 160°C when the temperature is increased from 25°C at a rate of 5°C / min using a thermomechanical analyzer. More specifically, it can be measured by the method described in the examples.

[0093] In order to make the heat shrinkage rate after heat treatment at 160°C fall within the above range in both the longitudinal and transverse directions, the polyester film may be stretched under the conditions described below and then heat-set.

[0094] The polyester laminate film for covering metal sheets of the present invention is not particularly limited and may have any thickness (hereinafter referred to as "film thickness"). However, if the film thickness is 10 μm or more, the film has sufficient stiffness, thereby exhibiting better film transportability, ensuring reliable coating during thermocompression bonding with the metal sheet, and achieving better corrosion resistance when used as a container. Therefore, the film thickness is preferably 10 μm or more, more preferably 12 μm or more, and even more preferably 15 μm or more. On the other hand, if the film thickness is 50 μm or less, the corrosion resistance when using the resin-coated metal sheet as a container can be maintained without compromising the corrosion resistance, and cost increases can be suppressed. Therefore, the film thickness is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less. The film thickness can be measured using a dial gauge. More specifically, it can be measured by the method described in the Examples.

[0095] The thickness of each of the A layer and the B layer is not particularly limited. However, the total thickness t B The total thickness t of the A layer A The ratio (t A / t B If the total thickness t of the layer B is 2.5 or more, the effect of the layer A containing the inorganic pigment is further improved, and the color of the metal plate can be more effectively concealed. B The total thickness t of the A layer A The ratio (t A / t B ) is preferably 2.5 or more, more preferably 3.0 or more, and even more preferably 4.0 or more. B The total thickness t of the A layer A The ratio (t A / t B If the total thickness t of the B layer is 7.5 or less, the effect of the B layer is further improved, and as a result, the occurrence of wrinkles during thermocompression bonding with the metal plate can be suppressed, and even better can-forming processability can be obtained. B The total thickness t of the A layer A The ratio (t A / t B ) is preferably 7.5 or less, more preferably 6.0 or less, and even more preferably 5.0 or less. A and total thickness t B can be measured by observing the cross section of the film with a scanning electron microscope. More specifically, they can be measured by the method described in the Examples.

[0096] The polyester laminate film for covering metal sheets can further contain an optional antioxidant. Adding an antioxidant improves heat resistance. Therefore, it is preferable that at least one of the A layer and the B layer contains an antioxidant, and it is more preferable that both layers contain an antioxidant. The content of the antioxidant in each layer is not particularly limited, but from the viewpoint of improving heat resistance, it is preferably 0.0001% by mass or more, more preferably 0.001% by mass or more. On the other hand, the content is preferably 1.0% by mass or less. The antioxidant is not particularly limited, and any antioxidant can be used. For example, at least one selected from the group consisting of hindered phenols, hydrazines, phosphites, etc. can be used.

[0097] The polyester laminate film for covering metal sheets may contain various additives in addition to the antioxidant, as long as the effects of the present invention are not impaired. For example, at least one selected from the group consisting of a crystal nucleating agent, a heat stabilizer, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, and a coloring pigment may be used.

[0098] [Manufacturing method] Next, a preferred method for producing a polyester laminate film for covering metal sheets according to one embodiment of the present invention will be described, although the present invention is not limited to the disclosure below.

[0099] The stretching during production of the polyester laminate film for covering metal plates of the present invention can be carried out by any method. For example, it may be carried out by a uniaxial stretching method or a biaxial stretching method. Furthermore, when stretching by a biaxial stretching method, sequential biaxial stretching may be carried out in which stretching is carried out in the longitudinal direction and then in the width direction, or simultaneous biaxial stretching may be carried out in which stretching is carried out in two directions at the same time. From the viewpoint of further enhancing the effects of the present invention, it is preferable to carry out stretching by a uniaxial stretching method in which stretching is carried out only in one direction, either the longitudinal direction or the width direction. In other words, it is preferable that the polyester laminate film for covering metal plates of the present invention is a uniaxially stretched film. Here, as an example, a case where stretching is carried out by a uniaxial stretching method will be described.

[0100] First, the resin for Layer A and the resin for Layer B are melt-kneaded in separate extruders to form molten resins. For the resin for Layer A, a mixture containing dried polyester resin and inorganic pigment is melt-kneaded in the extruder. For the resin for Layer B, a mixture containing dried polyester resin, inorganic lubricant, and wax is melt-kneaded in the extruder. The form of the polyester resin is not particularly limited, but may be, for example, pellets. The polyester resin is dried under hot air or vacuum, if necessary, and then fed to the extruder.

[0101] The polyester resin is heated to a temperature above its melting point and kneaded in an extruder to form a molten resin. When extruding the molten resin, it is preferable to make the extrusion rate uniform using a gear pump or the like. It is also preferable to remove foreign matter, modified resin, etc. by extruding the molten resin through a filter or the like.

[0102] The resins for layers A and B, which have been melted in separate extruders, are then fed through different flow paths to a lamination device, which may be, for example, a feed block or a multi-manifold die.

[0103] These molten resins are extruded into a sheet form from a T-die and cooled and solidified on a casting drum to form an unstretched film. In this case, in order to enhance the adhesion between the molten sheet and a cooling body such as a casting drum, it is preferable to use a wire-, tape-, needle-, or knife-shaped electrode to achieve electrostatic contact and rapid solidification. Also preferred are methods of blowing air from a slit-, spot-, or planar-shaped device to achieve close contact and rapid solidification, methods of using nip rolls to achieve close contact and rapid solidification, and combinations of these.

[0104] The unstretched film is then stretched. The stretching direction may be either the machine direction or the cross direction, but stretching in the machine direction is preferred in terms of facilitating an increase in the production speed.

[0105] Here, "longitudinal stretching" refers to stretching to impart molecular orientation to the film in the longitudinal direction. Longitudinal stretching is usually performed using a pair of rolls with different peripheral speeds, and the stretching ratio is controlled by the difference in peripheral speeds. Longitudinal stretching may be performed in one stage, or in multiple stages using multiple roll pairs.

[0106] Stretching in the transverse direction refers to stretching that imparts molecular orientation to the film in the width direction. Stretching in the transverse direction is usually performed using a tenter-type stretching machine. In a tenter-type stretching machine, the film is introduced while its edges are held by clips, and the film is stretched in the transverse direction as the clips expand in the width direction.

[0107] If the stretching ratio in the stretching is less than 3.0 times, stretching unevenness may occur, resulting in large thickness unevenness in the stretching direction, and productivity may also be poor. Therefore, the stretching ratio in the stretching is preferably 3.0 times or more. It is more preferably 4.0 times or more, and even more preferably 4.5 times or more. On the other hand, if the stretching ratio exceeds 8.0 times, excessive orientation in the stretching direction may result in heat shrinkage, or stiffness in the direction perpendicular to the stretching direction may be weakened, resulting in wrinkles. Therefore, the stretching ratio in the stretching is preferably 8.0 times or less, more preferably 6.0 times or less, and even more preferably 5.5 times or less.

[0108] If the stretching temperature is too low, the film may break during stretching or may become too oriented in the stretching direction, making it prone to thermal shrinkage. Therefore, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the polyester resin constituting the film, more preferably equal to or higher than (Tg + 10°C), and even more preferably equal to or higher than (Tg + 15°C). On the other hand, if the stretching temperature is too high, the unstretched film may undergo thermal crystallization, causing the film to break during stretching, or may become too soft and stick to rolls or clips. Therefore, the stretching temperature is preferably equal to or lower than (Tg + 50°C), more preferably equal to or lower than (Tg + 40°C), and even more preferably equal to or lower than (Tg + 30°C). Note that when multiple polyester resins with different glass transition temperatures are used, a single glass transition temperature is observed when the multiple polyester resins are mixed. Therefore, the stretching temperature can be determined based on the glass transition temperature.

[0109] The glass transition temperature of the polyester resin can be measured by a differential scanning calorimeter. More specifically, it can be measured by the method described in the examples.

[0110] The uniaxially stretched film is then preferably heat-set. In the case of longitudinal stretching, the heat-setting is preferably carried out while the film is running through rolls in a longitudinal stretching machine heated to a high temperature, and in the case of transverse stretching, the heat-setting is preferably carried out while the film is running through an oven in a tenter-type stretching machine heated to a high temperature.

[0111] The heat setting temperature is preferably equal to or higher than the stretching temperature and equal to or lower than the melting point -50°C. It is more preferably within the range of equal to or higher than the stretching temperature, equal to or lower than the stretching temperature +60°C, and equal to or lower than the melting point -50°C, and even more preferably within the range of equal to or higher than the stretching temperature +10°C, equal to or lower than the stretching temperature +50°C, and equal to or lower than the melting point -50°C. It is particularly preferably within the range of equal to or higher than the stretching temperature +20°C, equal to or higher than the stretching temperature +40°C, and equal to or lower than the melting point -50°C. Here, the melting point refers to the melting points of the first polyester resin and the second polyester resin, and when the melting points of the first polyester resin and the second polyester resin are different, it refers to the lower melting point.

[0112] This heat setting is important for reducing the residual stress in the uniaxially oriented film, but if the heat setting temperature is too low, the residual stress reduction effect may not be obtained, whereas if the heat setting temperature is too high, the film shrinks so much that wrinkles may be introduced into the film during transport, and in some cases, the film may break.

[0113] Furthermore, the heat setting may be performed while relaxing the film in the stretching direction. In this case, the relaxation rate is preferably 0.5% to 5%, more preferably 0.8% to 4%, and even more preferably 1% to 3%. By performing relaxation simultaneously with heat setting, the residual stress in the uniaxially oriented film is further reduced, which is preferable. If the relaxation rate is too low, the effect of reducing residual stress may not be achieved. On the other hand, if the relaxation rate is too high, the film may not shrink enough and may slacken during transport. The heat-set film is then cooled to obtain a uniaxially stretched film.

[0114] The polyester laminate film for covering metal sheets of the present invention can provide a resin-coated metal sheet that combines lamination properties, can-forming processability, and feathering resistance. Specifically, the present invention can suppress wrinkling and thermal shrinkage of the film during thermocompression lamination, especially at high temperatures. Furthermore, the present invention can suppress breakage and abrasion of the resin coating layer during can-forming, as well as cracking of the resin coating layer during the can-body heat treatment process, in the production of two-piece cans, which require a high degree of processing. Furthermore, the present invention can achieve excellent feathering resistance in addition to these properties. Furthermore, the polyester laminate film for covering metal sheets of the present invention can conceal the color of the metal sheet, imparting a high level of design to the product. [Example]

[0115] The present invention will be further described below based on examples, but the present invention is not limited to the following examples.

[0116] In the present examples, the properties of the first and second polyester resins, the modified polyolefin wax, and the finally obtained polyester laminate film for covering metal sheets were measured and evaluated by the following methods.

[0117] (1) Melting point, glass transition temperature (polyester resin, polyester laminated film, modified polyolefin wax) The melting points of the first and second polyester resins, polyester laminate film, and modified polyolefin wax, and the glass transition temperatures of the polyester resin and polyester laminate film were measured using a TA Instruments differential scanning calorimeter (DSCQ100). The first and second polyester resins and polyester laminate film were first cooled to -50°C under a nitrogen atmosphere and then heated to 290°C at 20°C / min (1st run). After heating to 290°C in the 1st run, they were held for 5 minutes and rapidly cooled in liquid nitrogen. They were then heated again from -50°C to 290°C at 20°C / min (2nd run). The melting points and glass transition temperatures were determined from the chart obtained in the 2nd run. Similar measurements were performed three times, and the average values ​​were used as the melting points and glass transition temperatures of the polyester resins, respectively. The melting point of the modified polyolefin wax was determined in the same manner as the melting point of the polyester resin, except that the heating temperature was changed from 290°C to 250°C.

[0118] (2) Intrinsic viscosity of polyester resin The intrinsic viscosities of the first and second polyester resins were measured in accordance with JIS K 7367-1 and JIS K 7367-5. The same measurement was carried out three times for each polyester resin, and the average value was taken as the intrinsic viscosity of the polyester resin.

[0119] (3) Acid value of wax The acid value of the wax was measured in accordance with JIS K 5902. A predetermined amount of wax corresponding to the estimated acid value in accordance with JIS K 5902 was weighed into a flask and dissolved in 100 ml of a neutral solvent. After that, it was titrated with a 0.1 mol / L potassium hydroxide standard solution using phenolphthalein as an indicator. The acid value was calculated using the following formula, with the neutralization endpoint being the time when the indicator changed color for 30 seconds. Acid value=5.611×A×F / B A: Amount (ml) of 0.1 mol / L potassium hydroxide standard solution used B: Sample collection amount (g) F: Factor of 0.1 mol / L potassium hydroxide standard solution

[0120] (4) Young's modulus Young's modulus was measured at a temperature of 23°C using a universal material testing machine (AG-X-5) manufactured by Shimadzu Corporation. The sample used for the measurement was cut out from the film so that it was 130 mm long in the measurement direction (longitudinal or transverse direction) and 10 mm long in the direction perpendicular to the measurement direction. The sample was stretched to an original length of 50 mm at a tensile speed of 300 mm / min to measure Young's modulus. The above measurement was repeated five times in both the longitudinal and transverse directions. The average value of the five measurements in the longitudinal direction was taken as the Young's modulus in the longitudinal direction, and the average value of the five measurements in the transverse direction was taken as the Young's modulus in the transverse direction. The higher of the Young's modulus in the longitudinal direction and the transverse direction was taken as the E H , the lower one is E L It was decided.

[0121] (5) Heat shrinkage rate The thermal shrinkage in the longitudinal and transverse directions was measured using a thermomechanical analyzer (TMA7100C) manufactured by Hitachi High-Tech Science Corporation. Samples were cut out and fixed between the chucks so that the distance between the chucks in the measurement direction (longitudinal or transverse direction) was 10 mm and the distance perpendicular to the measurement direction was 4 mm. The measurement mode was tension mode (measurement load: 29.4 mN), and the temperature was raised from 25°C to 200°C at a rate of 5°C / min in a nitrogen atmosphere with a flow rate of 100 ml / min. The TMA value (displacement) at 160°C was calculated from the chart obtained by the measurement. Contraction was defined as a positive value for the displacement, and expansion or elongation as a negative value. The thermal shrinkage after heat treatment at 160°C was calculated using the following formula, where L0 is the distance between the chucks before measurement and L1 is the displacement at 160°C. Heat shrinkage rate (%) = (L1 / L0) x 100

[0122] (6) Inorganic pigment content According to JIS K7250, a film with an initial mass of W0 was placed in a platinum crucible and first thoroughly burned with a gas burner. It was then completely incinerated for 1 hour in an electric furnace at 750-800°C, and the mass of the resulting ash, W1, was measured. Using the initial mass W0 and the mass of the ash, W1, the inorganic pigment content was calculated using the following formula. Similar measurements were performed three times for each film, and the average value was used as the inorganic pigment content (i.e., the inorganic pigment content of the total film components). Although the film developed this time contains an inorganic lubricant, the content of the inorganic lubricant is extremely small compared to the inorganic pigment, so the influence of the inorganic lubricant was ignored in measuring the inorganic pigment content. Inorganic pigment content (%) = (W1 / W0) x 100

[0123] (7) Film thickness The film thickness was measured using a dial gauge 2110S-10 (with a carbide ball probe) manufactured by Mitutoyo Corporation, installed on a dial gauge stand 7001-10 manufactured by Mitutoyo Corporation. The measurement was performed 10 times at different locations, and the average value was taken as the film thickness.

[0124] (8) Total thickness The total thickness of each of the A and B layers was measured by observing the cross section of the film using a scanning electron microscope. Specifically, the film was embedded in epoxy resin, and the cross section of the film was cut out using a microtome. The cross section of the obtained sample was then observed using a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation) to determine the thickness of each layer. Measurements were taken 10 times at different locations, and the average value was used as the total thickness of each layer.

[0125] (9) Number average molecular weight of modified polyolefin wax The number average molecular weight of the polyolefin wax was measured under the following conditions using a gel permeation chromatograph (Alliance GPC2000 model) manufactured by Waters Corp. A calibration curve prepared using commercially available monodisperse standard polystyrene was used to calculate the number average molecular weight. (Measurement conditions) Solvent: o-dichlorobenzene Columns: TSKgel GMH6-HT x 2, TSKgel GMH6-HTL column x 2 (Tosoh Corporation) Flow rate: 1.0ml / min Sample: 0.15 mg / ml o-dichlorobenzene solution Temperature: 140℃

[0126] (10) Fabrication of resin-coated metal sheets by pressure lamination The metal plate used was a TFS with a thickness of 0.22 mm. The coating weight of the metal chromium layer on the TFS was 120 mg / m² per side. 2 The amount of chromium oxide layer deposited is 10 mg / m per side in terms of metallic chromium. 2 The temper of the TFS base sheet was T3CA.

[0127] The polyester laminate film for metal sheet coating manufactured in the Examples and Comparative Examples described below was coated on at least one side of the metal sheet by a thermocompression lamination method (film lamination method). Specific lamination conditions were that the temperature of the metal sheet immediately before lamination was the same as the melting point of the film, and the lamination roll temperature was 60°C. Then, one second after thermocompression bonding, the sheet was water-cooled to obtain a resin-coated metal sheet in which resin coating layers were coated on both sides of the metal sheet.

[0128] (11) Lamination To evaluate lamination, the area ratio of air bubbles and the number of wrinkles in the resin-coated metal sheets obtained in step 10 above were checked. Based on the results, lamination was evaluated according to the following criteria. A rating of B or higher indicates no practical problems. A (Excellent): Air bubble area rate is less than 1% and there are no wrinkles. B (Good): Air bubbles in the area of ​​1% to less than 5%, or one wrinkle. C (unacceptable): Air bubbles in the area of ​​5% or more, or two or more wrinkles.

[0129] (12) Can-making processability To evaluate can-making processability, cans were manufactured using the resin-coated metal sheet obtained in Section 8 above according to the following procedure. First, paraffin wax was applied to the surface of the resin-coated metal sheet, and then a blank with a diameter of 123 mm was punched out. This blank was then drawn using a cupping press to form a cup with an inner diameter of 71 mm and a height of 36 mm, with the paraffin wax facing the outer surface. The resulting cup was placed in a DI (Drawing and Ironing) forming apparatus and subjected to redrawing and three-stage ironing processes to form a can with an inner diameter of 52 mm and a height of 90 mm. The redrawing process was carried out under the conditions of a punch speed of 200 mm / s and a stroke of 560 mm. The total reduction rate in the ironing process was 51%, and the reduction rates in each process were 23%, 25%, and 25%, respectively.

[0130] The molded can was placed in a hot air drying oven and heat-treated for 1 minute so that the can body temperature was the melting point of the resin coating -5° C. The can was then removed from the hot air drying oven and cooled to room temperature.

[0131] The resin coating layer on the outer surface of each of the cans obtained by the above procedure was visually inspected, and the can-making processability was evaluated according to the following criteria: If the evaluation was B or higher, there was no problem in practical use. A (Excellent): No chipping or cracks observed. B (Good): Slight chipping or cracks within 2 mm of the can flange. C (Unacceptable): Scraping or cracking occurs more than 2 mm from the can flange, or film breakage occurs.

[0132] (13) Feathering resistance To evaluate the feathering resistance, an EOE lid was produced using the resin-coated metal sheet obtained in Section 8 above, as follows: First, a blank was punched out from the resin-coated metal sheet from the side opposite the film-coated surface to a diameter of 68 mm. If any film remained, its length was measured. Next, the blank was press-molded using an EOE lid mold to produce an EOE lid. A V-shaped score mold was used to form the score, adjusting the thickness of the metal sheet at the score processing point to 70 μm. The score was formed on the side opposite the film-coated surface. Finally, a tab was attached to the EOE lid.

[0133] The can was opened by lifting the tab of the EOE lid and separating the panel and the outer ring. If any film remained at this time, its length was measured. The longer of the remaining film length when the blank was punched out and the remaining film length when the EOE can was opened was used to evaluate feathering resistance according to the following criteria. A rating of B or higher means there is no practical problem. A (Excellent): Remaining film length is less than 0.1 mm. B (Good): Remaining film length is 0.1 mm or more but less than 0.2 mm. C (unacceptable): Remaining film length is 0.2 mm or more.

[0134] Example 1 Resin composition A, which was used as a raw material resin for layer A of the film, was prepared in the following manner: First, pellets a and b shown below were prepared. Pellets a: Pellets of the first polyester resin Pellet b: Pellets of a masterbatch containing an inorganic pigment in the first polyester resin

[0135] The first polyester resin used was polyethylene terephthalate having a melting point of 249° C. and an intrinsic viscosity of 0.67 dL / g, and the inorganic pigment used was rutile titanium dioxide.

[0136] Each of the pellets a and b was thoroughly dried under high temperature in a vacuum to remove moisture. Then, the pellets a and b were blended to obtain a resin composition A. The content of the inorganic pigment in the resin composition A was 12% by mass. The content of the polyester resin in the A layer was 100% by mass minus the content of the inorganic pigment (12% by mass), and in the case of Example 1, it was 88% by mass.

[0137] Furthermore, a resin composition B as a raw material resin for layer B was prepared in the following manner: First, pellets c, d, and e shown below were prepared. Pellets C: Pellets of the second polyester resin Pellet d: Pellets of the masterbatch containing the second polyester resin and an inorganic lubricant Pellets e: Pellets of the masterbatch containing the second polyester resin and wax

[0138] The second polyester resin used was polyethylene terephthalate with a melting point of 247°C and an intrinsic viscosity of 0.81 dL / g. The inorganic lubricant used was silicon dioxide. The wax used was acid-modified polyethylene wax with an acid value of 60 mgKOH / g.

[0139] Each of the pellets c, d, and e was thoroughly dried under high temperature in a vacuum to remove moisture. Then, the pellets c, d, and e were blended to obtain resin composition B. The content of the inorganic lubricant in resin composition B was 400 ppm, and the content of the wax was 0.18 mass%. The content of the polyester resin in layer B was calculated by subtracting the content of the inorganic lubricant (400 ppm) and the content of the wax (0.18 mass%) from 100 mass%.

[0140] The resin compositions A and B were fed into two separate single-screw extruders and melt-kneaded at 278°C. After removing foreign matter through a sintered filter with a 25µm cutoff, the resins were merged in a feed block designed with a lamination ratio of 1 (B layer):8 (A layer):1 (B layer) to form a three-layer laminate in the thickness direction. The laminated molten resin was extruded from a T-die and cooled and solidified on a casting drum with a surface temperature controlled at 30°C to obtain an unstretched film.

[0141] Next, the film was preheated to 95°C using a heated ceramic roll and stretched 4.5 times in the longitudinal direction. It was then heat-set at 120°C using a heated mirror-finish HCr-plated roll. During this process, 1% relaxation in the longitudinal direction was achieved by utilizing the speed difference between two consecutive mirror-finish HCr-plated rolls. Finally, the film was slowly cooled to room temperature, and the edges were removed. The film was then wound up on a winder to obtain a polyester laminate film for metal sheet coating with a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the resulting film are shown in Table 1.

[0142] Example 2 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except for the following points. A polyester laminate film for covering metal sheets having a thickness of 20 μm, a melting point of 242°C, and a glass transition temperature of 79°C was obtained. The first polyester resin was polyethylene terephthalate having a melting point of 240°C and an intrinsic viscosity of 0.68 dL / g. The content of inorganic pigment in resin composition A was 20 mass%. The wax was an acid-modified polyethylene wax having an acid value of 80 mgKOH / g. The wax content in composition B was 0.07 mass%. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 242°C, and a glass transition temperature of 79°C. The physical properties of the obtained film are shown in Table 1.

[0143] Example 3 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except for the following points. The first polyester resin used was polyethylene terephthalate having a melting point of 255°C and an intrinsic viscosity of 0.68 dL / g. The wax used was an acid-modified polyethylene wax having an acid value of 80 mgKOH / g. The content of the wax in the resin composition B was 0.07% by mass. The stretching temperature was 100°C, and the stretching ratio was 4.0 times. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 252°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 1.

[0144] Example 4 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except for the following points. Polyethylene terephthalate having a melting point of 248°C and an intrinsic viscosity of 0.55 dL / g was used as the first polyester resin. Acid-modified polypropylene wax having an acid value of 60 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 247°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 1.

[0145] Example 5 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 4, except that polyethylene terephthalate having a melting point of 247°C and an intrinsic viscosity of 0.75 dL / g was used as the first polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 247°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 1.

[0146] Example 6 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic pigment in the resin composition A was 12.5% ​​by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 1.

[0147] Example 7 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic pigment in the resin composition A was 25% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 1.

[0148] Example 8 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 240°C and an intrinsic viscosity of 0.76 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 247°C, and a glass transition temperature of 79°C. The physical properties of the obtained film are shown in Table 1.

[0149] Example 9 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 255°C and an intrinsic viscosity of 0.70 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 250°C, and a glass transition temperature of 70°C. The physical properties of the obtained film are shown in Table 1.

[0150] Example 10 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 248°C and an intrinsic viscosity of 0.55 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 1.

[0151] Example 11 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 247°C and an intrinsic viscosity of 0.90 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 2.

[0152] Example 12 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic lubricant in the resin composition B was 100 ppm. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0153] Example 13 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic lubricant in the resin composition B was 5000 ppm. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0154] Example 14 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the wax content in the resin composition B was 0.5% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0155] Example 15 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the wax content in the resin composition B was 1.0 mass %. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0156] Example 16 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the wax content in the resin composition B was 0.2% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0157] Example 17 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that an oxidized polyethylene wax having an acid value of 50 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0158] Example 18 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that an oxidized polypropylene wax having an acid value of 50 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0159] Example 19 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that an acid-modified polyethylene wax with an acid value of 100 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0160] Example 20 An unstretched film was produced under the same conditions as in Example 1, except that the content of inorganic lubricant in the resin composition B was 200 ppm. Next, the film was preheated to 95°C using a heated ceramic roll, and the film was stretched 3.5 times in the longitudinal direction. The film was then introduced into a tenter-type stretching machine with the edges held by clips, and stretched 5.0 times in the width direction at 100°C. While still in this state, the film was heat-set at 160°C and relaxed 1% in the width direction. Finally, the film was slowly cooled to room temperature, and the edges were removed. The film was then wound up on a winder to obtain a polyester laminate film for metal sheet coating with a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the resulting film are shown in Table 2.

[0161] Example 21 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic lubricant in the resin composition B was 1000 ppm and the stretching ratio was 5.5 times. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 2.

[0162] Example 22 A polyester laminate film for metal plate coating was produced under the same conditions as in Example 1, except for the following points. The unstretched film was introduced into a tenter-type stretching machine with its edges held by clips, and stretched 3.0 times in the width direction at 120°C. While still in this state, the film was heat-set at 1120°C and relaxed 1% in the width direction. Finally, the film was slowly cooled to room temperature, and the edges were removed before being wound up on a winder. The polyester laminate film for metal plate coating had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the resulting film are shown in Table 5.

[0163] Example 23 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the stretching ratio was 5.5 times and the heat setting temperature was 180°C. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 5.

[0164] Example 24 A polyester laminate film for covering metal sheets having a thickness of 10 μm, a melting point of 248° C., and a glass transition temperature of 80° C. was produced under the same conditions as in Example 1, except for adjusting the melt extrusion amounts of the resin compositions A and B. The physical properties of the obtained film are shown in Table 5.

[0165] Example 25 A polyester laminate film for covering metal sheets having a thickness of 50 μm, a melting point of 248° C., and a glass transition temperature of 80° C. was produced under the same conditions as in Example 1, except for adjusting the melt extrusion amounts of the resin compositions A and B. The physical properties of the obtained film are shown in Table 5.

[0166] Example 26 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that a feed block with a lamination ratio of 1 (B layer):5 (A layer):1 (B layer) was used and the melt extrusion amounts of resin compositions A and B were adjusted. The polyester laminate film for covering metal sheets had a thickness of 25 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 5.

[0167] Example 27 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that a feed block with a lamination ratio of 1 (B layer):15 (A layer):1 (B layer) was used and the melt extrusion amounts of resin compositions A and B were adjusted. The polyester laminate film for covering metal sheets had a thickness of 25 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 5.

[0168] Example 28 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that a feed block with a lamination ratio of 4 (A layer):1 (B layer) was used. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 5.

[0169] (Comparative Example 1) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 238°C and an intrinsic viscosity of 0.67 dL / g was used as the first polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 241°C, and a glass transition temperature of 79°C. The physical properties of the obtained film are shown in Table 3.

[0170] (Comparative Example 2) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 256°C and an intrinsic viscosity of 0.68 dL / g was used as the first polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 253°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 3.

[0171] (Comparative Example 3) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 248°C and an intrinsic viscosity of 0.53 dL / g was used as the first polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 3.

[0172] Comparative Example 4 A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 247°C and an intrinsic viscosity of 0.76 dL / g was used as the first polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 3.

[0173] (Comparative Example 5) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic pigment in the resin composition A was 11.25% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 3.

[0174] (Comparative Example 6) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic pigment in the resin composition A was 25.25% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 3.

[0175] (Comparative Example 7) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 238°C and an intrinsic viscosity of 0.76 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 246°C, and a glass transition temperature of 79°C. The physical properties of the obtained film are shown in Table 3.

[0176] (Comparative Example 8) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 256°C and an intrinsic viscosity of 0.70 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 251°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 3.

[0177] (Comparative Example 9) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 248°C and an intrinsic viscosity of 0.53 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 3.

[0178] (Comparative Example 10) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene terephthalate having a melting point of 247°C and an intrinsic viscosity of 0.92 dL / g was used as the second polyester resin. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 4.

[0179] (Comparative Example 11) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic lubricant in the resin composition B was 90 ppm. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0180] (Comparative Example 12) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the content of the inorganic lubricant in the resin composition B was 5100 ppm. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0181] (Comparative Example 13) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the wax content in the resin composition B was 0.040% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0182] (Comparative Example 14) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the wax content in the resin composition B was 1.1% by mass. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0183] (Comparative Example 15) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that an acid-modified polyethylene wax with an acid value of 48 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0184] (Comparative Example 16) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that an acid-modified polyethylene wax with an acid value of 110 mgKOH / g was used as the wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0185] (Comparative Example 17) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that polyethylene wax was used instead of the acid-modified polyethylene wax. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0186] (Comparative Example 18) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 20, except that the stretching ratio in the width direction was 4.5 times. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248° C., and a glass transition temperature of 80° C. The physical properties of the obtained film are shown in Table 4.

[0187] (Comparative Example 19) A polyester laminate film for covering metal sheets was produced under the same conditions as in Example 1, except that the stretching temperature was 110°C and the stretch ratio was 8.2 times. The polyester laminate film for covering metal sheets had a thickness of 20 μm, a melting point of 248°C, and a glass transition temperature of 80°C. The physical properties of the obtained film are shown in Table 4.

[0188] [Table 1]

[0189] [Table 2]

[0190] [Table 3]

[0191] [Table 4]

[0192] [Table 5]

[0193] As can be seen from the results shown in Tables 1 to 5, films satisfying the conditions of the present invention combine lamination properties, can-forming processability, and feathering resistance. In addition, because the film of the present invention has Layer A containing an inorganic pigment, it is possible to conceal the color of the metal plate, thereby imparting high design appeal to products. Therefore, the polyester laminate film for covering metal plates of the present invention can be suitably used as a film for covering metal plates, particularly metal plates for containers. Furthermore, resin-coated metal plates comprising the polyester laminate film for covering metal plates of the present invention can be suitably used as materials for producing containers, particularly can bodies for two-piece cans, which require a high degree of processability.

Claims

1. A polyester laminate film comprising: a layer A containing 70% by mass or more of a first polyester resin and an inorganic pigment; and a layer B laminated on at least one surface of the layer A, the layer B containing 70% by mass or more of a second polyester resin, an inorganic lubricant, and a wax; the first polyester resin has a melting point of 240 to 255°C and an intrinsic viscosity of 0.55 to 0.75 dL / g; the second polyester resin has a melting point of 240 to 255°C and an intrinsic viscosity of 0.55 to 0.90 dL / g, which is greater than the intrinsic viscosity of the first polyester resin; The content of the inorganic pigment is 10 to 20% by mass based on the total components of the film, the content of the inorganic lubricant is 100 to 5000 ppm based on all components of the layer B; the wax is a modified polyolefin wax having an acid value of 50 to 100 mgKOH / g, the content of the wax is 0.050 to 1.0% by mass based on the total components of the layer B, The higher of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is defined as E Ｈ , the lower one is E Ｌ The ratio of Young's modulus (E Ｈ / E Ｌ ) is 1.2 to 10.

2. E Ｈ and E Ｌ The polyester laminate film for covering metal sheets according to claim 1, wherein each of the modulus of elasticity is 1000 to 19000 MPa.

3. E Ｈ and E Ｌ The sum of (E Ｈ +E Ｌ 3. The polyester laminate film for covering metal sheets according to claim 1, wherein the modulus of elastic modulus is 3,000 to 20,000 MPa.

4. 3. The polyester laminate film for covering metal sheets according to claim 1, wherein the heat shrinkage rate at 160°C is 0 to 20% in both the longitudinal and transverse directions.

5. 3. The polyester laminate film for covering metal sheets according to claim 1, wherein the modified polyolefin wax contained in the layer B is any one of an acid-modified polyethylene wax, an acid-modified polypropylene wax, an oxidized polyethylene wax, and an oxidized polypropylene wax, or a mixture thereof.

6. 3. The polyester laminate film for covering metal sheets according to claim 1, wherein the film thickness is 10 to 50 μm.

7. The total thickness t of the B layer Ｂ The total thickness t of the A layer Ａ The ratio (t Ａ / t Ｂ 3. The polyester laminate film for covering metal sheets according to claim 1, wherein the tensile strength is 2.5 to 7.

5.

8. 3. The polyester laminate film for covering metal plates according to claim 1, which is used for covering the surface of metal plates for containers.

9. A resin-coated metal sheet having, on at least one surface thereof, the polyester laminate film for coating metal sheets according to claim 1 or 2.

Images