Laminate metal plate, method for manufacturing laminate metal plate, and laminate metal container

Abstract

Provided is a laminate metal plate which is exceptional in both primary adhesion and adhesion after retort sterilization treatment, and does not undergo deterioration of appearance due to whitening even after retort sterilization treatment. A laminate metal plate 10 according to the present invention is configured such that a first film 31 is laminated on at least one surface of a metal plate 20. The first film 31 is a polyester film in which a polyester component is composed of a prescribed first polyester and second polyester. The mass ratio of the first polyester and the second polyester is 20:80 to 50:50, where 100 represents the entire amount of polyester in the first film 31. Two characteristic widths w1 and w2 calculated from an image obtained by binarizing a phase image, which is obtained by observing a cross-sectional part of the first film 31 using a dynamic force mode of a scanning probe microscope, satisfy a prescribed relationship.

Description

Laminated metal sheet, method for manufacturing laminated metal sheet, and laminated metal container

[0001] The present invention relates to a laminated metal sheet, a method for manufacturing a laminated metal sheet, and a laminated metal container.

[0002] Metal containers such as food cans, beverage cans, and 18L cans are made from metal sheets such as tin-free steel (TFS) and aluminum. These metal sheets are painted and baked to impart corrosion resistance, durability, weather resistance, and other properties. Baking metal sheets is complicated and requires a significant amount of processing time. In addition, a large amount of solvent is emitted when painting metal sheets. Therefore, as an alternative to painted metal sheets, laminated metal sheets, in which a thermoplastic resin film is laminated to a metal sheet, are used.

[0003] Examples of thermoplastic resin films used for laminated metal sheets include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. These thermoplastic resin films are required to have adhesion between the thermoplastic resin film and the metal sheet when formed into a laminated metal sheet, corrosion resistance, container formability when the laminated metal sheet is formed into a container, etc.

[0004] Metal containers are broadly classified into two-piece cans and three-piece cans. Two-piece cans are composed of two components: a cylindrical can body with a bottom and a lid member that closes an opening formed at one axial end of the can body. Three-piece cans are composed of three components: a cylindrical can body, a top lid that closes an opening formed at one end of the can body, and a bottom lid that closes an opening formed at the other end of the can body.

[0005] The can body of a three-piece can is often formed by cylindrical molding and welding. Furthermore, the thermoplastic resin film covering the laminated metal sheet is generally an insulator, making welding technically difficult. For this reason, the laminated metal sheet is often used for the bottom or top lid of a three-piece can.

[0006] Laminated metal sheets are also often used for the can bodies of two-piece cans. There are various methods for forming the can bodies of two-piece cans, such as Draw and Redraw (DRD), Draw and Ironing (DI), and Draw and Thin Redraw (DTR). All of these methods involve drawing and, if necessary, ironing. Therefore, laminated metal sheets are highly required to have good processability. In particular, polyester films, primarily PET, are often used as the thermoplastic resin film for laminated metal sheets used for the can bodies of two-piece cans.

[0007]

[0003] Incidentally, food cans are often subjected to a retort sterilization process in which the film is heated with high-temperature steam for sterilization. The retort sterilization process can sometimes cause minute bubbles to form inside the thermoplastic resin film. Since the bubbles have the property of scattering light, the thermoplastic resin film that has come to contain bubbles after the retort sterilization process appears cloudy, which can impair the appearance of the food can.

[0008] Attempts have been made to suppress such whitening of thermoplastic resin films. For example, Patent Documents 1 and 2 disclose polyester films and laminated metal sheets containing a specific ratio of polyester mainly composed of PET and polyester mainly composed of PBT and having a specific orientation state. Patent Document 3 discloses a laminated metal sheet including a resin layer containing crystals of PBT resin but not having stretch orientation. Furthermore, Patent Document 4 discloses a laminated metal sheet in which a polyester film containing a specific ratio of polyester mainly composed of PET and polyester mainly composed of PBT is laminated on the outer surface of a can and a PET-based film is laminated on the inner surface of the can, and the degree of residual orientation of each film is set to a specific value or less.

[0009] Japanese Patent Laid-Open No. 10-110046 Japanese Patent Laid-Open No. 6-155660 Japanese Patent Laid-Open No. 2019-150985 Japanese Patent Laid-Open No. 2014-166856

[0010] As described above, laminated metal sheets are required to have good adhesion between a thermoplastic resin film and a metal sheet (primary adhesion), good adhesion between a thermoplastic resin film and a metal sheet after retort sterilization, and to suppress whitening of the thermoplastic resin film after retort sterilization. However, the inventors have conducted studies and found that the laminated metal sheets of the above documents have room for improvement in terms of suppressing whitening after retort sterilization.

[0011] In view of the above problems, the present invention aims to provide a laminated metal sheet that has excellent primary adhesion and adhesion after retort sterilization and that does not suffer from deterioration in appearance due to whitening even after retort sterilization. The present invention also aims to provide a method for manufacturing such a laminated metal sheet and a laminated metal container using such a laminated metal sheet.

[0012] The present inventors conducted extensive research to solve the above-mentioned problems and have discovered the following: When a film to be laminated to a metal plate contains PET and PBT in a specific mass ratio, it is possible to ensure primary adhesion and adhesion after retort sterilization. Furthermore, when the microscopic dispersion state of PET and PBT in the film is specific, it is possible to suppress deterioration of appearance due to whitening even after retort sterilization.

[0013] The present invention was completed based on these findings and further investigations, and the gist of the present invention is as follows.

[0014] [1] A laminated metal sheet having a first film laminated on at least one surface of a metal sheet, wherein the first film is a polyester film whose polyester component is composed of a first polyester and a second polyester, the first polyester is composed of one or both of homopolyethylene terephthalate and copolymerized polyethylene terephthalate, and the second polyester is composed of one or both of homopolybutylene terephthalate and copolymerized polybutylene terephthalate, the mass ratio of the first polyester to the second polyester being 20:80 to 50:50, where the total amount of polyester in the first film is taken as 100, and two characteristic widths w1 and w2 calculated from a binarized image of a phase image obtained by observing a cross-sectional portion of the first film using a scanning probe microscope in dynamic force mode satisfy the following formulas (1) and (2): 10.0 nm≦w1≦25.0 nm ... (1) 10.0 nm≦w2≦25.0 nm ... (2) However, the threshold value for the binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delay are shown dark, the area % of the dark areas is equal to the mass % of the first polyester relative to the total amount of polyester in the first film, and the characteristic width w1 is a value obtained by dividing the area A1 of the dark areas after the binarization by the length l1 of the thin line obtained by applying a thin line processing to the dark areas, and the characteristic width w2 is a value obtained by dividing the area A2 of the bright areas after the binarization by the length l2 of the thin line obtained by applying a thin line processing to the bright areas.

[0015] [2] The laminated metal sheet according to [1] above, wherein the wide-angle X-ray diffraction spectrum of at least one surface of the metal sheet on which the first film is laminated satisfies the following formula (3): I(1) １００ / I(1) ａｍｏｒｐｈｏｕｓ ≦1.5 (3) Here, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by incident X-rays and reflected X-rays is perpendicular to the surface of the first film, and I(1) １００is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ=26.5±1.0°, and I(1) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

[0016] [3] The laminated metal sheet according to the above [1] or [2], wherein a second film is laminated on the other surface of the metal sheet, the polyester component of the second film is one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, the highest endothermic peak temperature in a temperature range of 280°C or less is 220°C or higher in a differential scanning calorimetry of the second film, and the wide-angle X-ray diffraction spectrum of the other surface of the metal sheet on which the second film is laminated satisfies the following formula (4). I(2) １００ / I(2) ａｍｏｒｐｈｏｕｓ ≦1.5 (4) Here, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by incident X-rays and reflected X-rays is perpendicular to the surface of the second film, and I(2) １００ is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ=26.5±1.0°, and I(2) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

[0017] [4] A method for producing a laminated metal plate, comprising: a step of preheating a metal plate to a preheating temperature of 300°C or less; a subsequent thermocompression bonding step of thermocompression bonding a film A to at least one surface of the metal plate using a laminating roll to form a thermocompression-bonded body; and a cooling step of liquid-cooling the thermocompression-bonded body to form a laminated metal plate, wherein the film A is a polyester film whose polyester components are made of a first polyester and a second polyester, the first polyester is made of one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, and the second polyester is made of one or both of homopolybutylene terephthalate and copolymer polybutylene terephthalate, and the mass ratio of the first polyester to the second polyester is 20:80 to 50:50, where the total amount of polyester in the film A is taken as 100, and the surface temperature of the film A in the thermocompression-bonded body immediately before being cooled in the cooling step is 205°C or less.

[0018] [5] The method for producing a laminated metal sheet according to [4], wherein the preheating temperature is −10°C or more and +50°C or less relative to the highest endothermic peak temperature in a temperature range of 280°C or less in a differential scanning calorimetry of the film A.

[0019] [6] The method for producing a laminated metal plate according to [4] or [5] above, wherein in the thermocompression bonding step, a film B is thermocompression bonded to the other surface of the metal plate, the polyester component of the film B is one or both of homopolyethylene terephthalate and copolymerized polyethylene terephthalate, the highest endothermic peak temperature in a temperature range of 280°C or less is 220°C or higher in a differential scanning calorimetry of the film B, and the preheating temperature of the metal plate is −5°C or higher and +60°C or lower relative to the endothermic peak temperature of the film B.

[0020] The method for producing a laminated metal sheet according to any one of [4] to [6] above, wherein two characteristic widths w'1 and w'2 calculated from a binarized phase image obtained by observing the cross-section of the film A using a dynamic force mode of a scanning probe microscope before the thermocompression bonding step satisfy the following formulas (5) and (6): 8.0 nm≦w'1≦17.0 nm ... (5) 8.0 nm≦w'2≦17.0 nm ... (6) However, the threshold value for the binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delay are shown dark, the area % of the dark areas is equal to the mass % of the first polyester relative to the total amount of polyester in the film A, the characteristic width w'1 is a value obtained by dividing the area A'1 of the dark areas after the binarization by the length l'1 of the thin line obtained by applying a thinning process to the dark areas, and the characteristic width w'2 is a value obtained by dividing the area A'2 of the bright areas after the binarization by the length l'2 of the thin line obtained by applying a thinning process to the bright areas.

[0021] [8] A laminated metal container comprising the laminated metal sheet according to any one of [1] to [3] above.

[0022] According to the present invention, it is possible to provide a laminated metal sheet and a method for manufacturing the same, which have excellent primary adhesion and adhesion after retort sterilization treatment and do not suffer from deterioration in appearance due to whitening even after retort sterilization treatment, as well as a laminated metal container using the laminated metal sheet.

[0023] 1 is a schematic diagram and an enlarged cross-sectional view of a laminated metal container according to one embodiment of the present invention; FIG. 2 is a phase image obtained for a cross-sectional view of a first film in Example 1; FIG. 3 is a binarized image of the phase image of FIG. 2; FIG. 4 is a phase image obtained for a cross-sectional view of a first film in Comparative Example 1;

[0024] Hereinafter, a laminated metal sheet according to one embodiment of the present invention will be described. Note that the embodiment described below is an example of a specific embodiment of the present invention, and the configuration of the present invention is not limited to this specific example.

[0025] (Laminated Metal Plate) The left side of Fig. 1 shows the configuration of a laminated metal container 100, and the right side of Fig. 1 shows an enlarged cross section of a wall portion of the laminated metal container 100. As shown in the enlarged cross section of Fig. 1, the laminated metal container 100 includes a laminated metal plate 10 as a material. The laminated metal plate 10 has a front surface 21, which is the outer surface of the laminated metal container 100, and a back surface 22, which is the inner surface of the laminated metal container 100. The laminated metal plate 10 has a first film 31 bonded to at least one of the front surface 21 and the back surface 22 of the metal plate 20. The laminated metal plate 10 may also have the first film 31 on one of the front surface 21 and the back surface 22 of the metal plate 20 and a second film 32 on the other surface. In FIG. 1 , the metal plate 20 has a first film 31 on the front surface 21 and a second film 32 on the back surface 22 .

[0026] [Metal Plate] The metal plate is not particularly limited, and may be an aluminum plate, a steel plate, or any of these plates that have been subjected to various surface treatments, which are widely used as materials for metal containers. In particular, it is preferable to use a surface-treated steel plate (TFS: Tin Free Steel) on which a film made of metallic chromium and hydrated chromium oxide is formed.

[0027] The steel sheet that serves as the base steel of the TFS is not particularly limited as long as it can be formed into a shape corresponding to the laminated metal container, but is preferably obtained by recrystallization annealing low carbon steel or IF (Interstitial Free) steel and rolling such as temper rolling. The steel sheet that serves as the base steel of the TFS may be subjected to overaging treatment as necessary. Furthermore, the steel sheet that serves as the base steel of the TFS may be subjected to secondary cold rolling.

[0028] The low-carbon steel may be, for example, one having a carbon content of 0.010% by mass or more and 0.10% by mass or less. Furthermore, the IF steel may be, for example, an ultra-low carbon steel having a carbon content of 0.003% by mass or less to which Nb, Ti, etc. have been added. Examples of recrystallization annealing include continuous annealing, tight annealing, and open annealing.

[0029] The mechanical properties of the steel sheet that constitutes the base steel of the TFS are not particularly limited as long as they can be formed into a shape corresponding to the laminated metal container. The yield point of the steel sheet is preferably 220 MPa or more and 580 MPa or less. The Lankford value of the steel sheet is preferably 0.8 or more. The absolute value of the in-plane anisotropy of the Lankford value of the steel sheet is preferably 0.7 or less, more preferably 0.0. The deposition amounts of the metal chromium layer and hydrated chromium oxide layer of the TFS are not particularly limited, but the deposition amount, in terms of Cr, of the metal chromium layer is 50 to 200 mg / m ２ , the chromium hydrate oxide layer is 3 to 30 mg / m ２ When the deposition weights of the metallic chromium layer and the hydrated chromium oxide layer are within the above-mentioned ranges, the film and the TFS are easily and sufficiently adhered to each other, and corrosion resistance is improved.

[0030] Although the thickness of the metal plate is not particularly limited, if the thickness of the metal plate is 0.10 mm or more, the rigidity when formed into a laminated metal container is improved. Therefore, the thickness of the metal plate is preferably 0.10 mm or more. On the other hand, if the thickness of the metal plate is 0.35 mm or less, the energy consumption when forming into a laminated metal container can be reduced. Therefore, the thickness of the metal plate is preferably 0.35 mm or less.

[0031] [First Film] The first film is a polyester film whose polyester component is composed of a first polyester and a second polyester.

[0032] The first polyester is made of one or both of homopolyethylene terephthalate and copolymerized polyethylene terephthalate. When the first polyester contains copolymerized polyethylene terephthalate, the content of the copolymerized component is preferably 1 mol% or more, more preferably 3 mol% or more. On the other hand, the content of the copolymerized component is preferably 15 mol% or less, more preferably 14 mol% or less, and even more preferably 8 mol% or less.

[0033] Examples of the copolymerization component of the first polyester include, as an acid component, aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodiumsulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, dimer acid, maleic acid, fumaric acid, dodecanedioic acid, and cyclohexanedicarboxylic acid; and ester derivatives thereof.

[0034] Examples of copolymerization components of the first polyester include alcohol components such as 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.

[0035] The copolymerization component of the first polyester may be one or more of the above-mentioned copolymers. It is preferable to use isophthalic acid as the copolymerization component of the first polyester. When isophthalic acid is contained as a copolymerization component at 1 mol% or more, adhesion between the first film and the metal sheet is favorable. Therefore, the content of isophthalic acid as a copolymerization component of the first polyester is preferably 1 mol% or more, more preferably 2 mol% or more, and even more preferably 3 mol% or more. On the other hand, when isophthalic acid is contained as a copolymerization component at 15 mol% or less, the first film is easily formed. Therefore, the content of isophthalic acid as a copolymerization component of the first polyester is preferably 15 mol% or less, more preferably 14 mol% or less, and even more preferably 8 mol% or less.

[0036] If the intrinsic viscosity of the first polyester is 0.65 dL / g or more, the formability of the laminated metal sheet can be favorably obtained. Therefore, the intrinsic viscosity of the first polyester is 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 first polyester is 1.00 dL / g or less, energy consumption in the polymerization step and extrusion step can be favorably suppressed. Therefore, the intrinsic viscosity of the first polyester is preferably 1.00 dL / g or less, and more preferably 0.90 dL / g or less.

[0037] The second polyester is composed of one or both of homopolybutylene terephthalate and copolymer polybutylene terephthalate. When the second polyester contains copolymer polybutylene terephthalate, the content of the copolymer component is preferably 1 mol% or more. On the other hand, if the content of the copolymer component is 15 mol% or less, the crystallization rate of the first film is improved, and deterioration of appearance due to whitening during retort sterilization can be more effectively suppressed. Therefore, when the second polyester contains copolymer polybutylene terephthalate, the content of the copolymer component is preferably 15 mol% or less, and more preferably 10 mol% or less.

[0038] The copolymerization components of the second polyester can be the acid component and alcohol component described for the first polyester. Ethylene glycol, which is the main component of the first polyester, can also be used as the copolymerization component. The copolymerization components of the second polyester can be one or more of the above-mentioned components.

[0039] If the intrinsic viscosity of the second polyester is 0.75 dL / g or more, the formability of the laminated metal sheet can be favorably obtained. Therefore, the intrinsic viscosity of the second polyester is preferably 0.75 dL / g or more, and more preferably 0.95 dL / g or more. On the other hand, if the intrinsic viscosity of the second polyester is 1.30 dL / g or less, energy consumption in the polymerization step and the extrusion step can be favorably suppressed. Therefore, the intrinsic viscosity of the second polyester is preferably 1.30 dL / g or less, and more preferably 1.20 dL / g or less.

[0040] The mass ratio of the first polyester to the second polyester is set to 20:80 to 50:50, with the total amount of polyester in the first film being 100.

[0041] If the content of the first polyester relative to the total polyester content in the first film is less than 20% by mass, the adhesion between the first film and the metal plate decreases. In this case, there is a risk that the first film will peel off from the metal plate when being formed into a laminated metal container or during retort sterilization. Therefore, the content of the first polyester relative to the total polyester content in the first film is set to 20% by mass or more, preferably 30% by mass or more. On the other hand, if the content of the first polyester relative to the total polyester content exceeds 50% by mass, the crystallization rate of the first film decreases, and the film appearance deteriorates during retort sterilization. Therefore, the content of the first polyester relative to the total polyester content in the first film is set to 50% by mass or less, preferably 45% by mass or less.

[0042] If the content of the second polyester relative to the total polyester content in the first film is less than 50% by mass, the crystallization rate of the first film decreases, resulting in deterioration of the film's appearance during retort sterilization. Therefore, the content of the second polyester relative to the total polyester content in the first film is set to 50% by mass or more, preferably 55% by mass or more. On the other hand, if the content of the second polyester relative to the total polyester content exceeds 80% by mass, the adhesion between the first film and the metal plate decreases. In this case, there is a risk of the first film peeling off from the metal plate during molding into a laminated metal container or during retort sterilization. Therefore, the content of the second polyester relative to the total polyester content in the first film is set to 80% by mass or less, preferably 70% by mass or less.

[0043] Two characteristic widths w1 and w2 calculated from a binarized phase image obtained by observing a cross-section of the first film using a scanning probe microscope in dynamic force mode satisfy the following formulas (1) and (2): 10.0 nm≦w1≦25.0 nm (1) 10.0 nm≦w2≦25.0 nm (2) The threshold value for binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delays are shown dark, the area percentage of dark areas is equal to the mass percentage of the first polyester relative to the total amount of polyester in the first film. The characteristic width w1 is the value obtained by dividing the area of ​​the dark areas after binarization by the length l1 of the thin line obtained by thinning the dark areas, and the characteristic width w2 is the value obtained by dividing the area of ​​the bright areas after binarization by the length l2 of the thin line obtained by thinning the bright areas. The thinning process can be performed using the Zhang-Suen method.

[0044] Figure 2 shows an example of a phase image obtained for a cross-section of the first film. Figure 3 shows an image of Figure 2 binarized using the above method. In Figures 2 and 3, areas with small phase delay are shown as dark areas. Because polyethylene terephthalate has a higher elastic modulus than polybutylene terephthalate, the first polyester has a smaller phase delay than the second polyester. Therefore, the dark areas in Figures 2 and 3 correspond to the first polyester.

[0045] The characteristic width w1 is a value representing the width of the dark area in Fig. 3 and represents the dispersion state of the first polyester. The characteristic width w2 is a value representing the width of the light area in Fig. 3 and represents the dispersion state of the second polyester.

[0046] When the characteristic width w1 is less than 10.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are finely dispersed and close to being compatible with each other, which reduces the crystallization rate of the first film and causes deterioration of the film appearance due to whitening during retort sterilization. Therefore, the characteristic width w1 is set to 10.0 nm or more, and preferably 12.0 nm or more. On the other hand, when the characteristic width w1 exceeds 25.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are unevenly dispersed, which reduces the crystallization rate locally in the first film and causes deterioration of the film appearance due to whitening during retort sterilization. Therefore, the characteristic width w1 is set to 25.0 nm or less, and preferably 20.0 nm or less.

[0047] When the characteristic width w2 is less than 10.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are finely dispersed and close to being compatible with each other, resulting in a decrease in the crystallization rate of the first film, and the film appearance deteriorates due to whitening during retort sterilization. Therefore, the characteristic width w2 is set to 10.0 nm or more, and preferably 12.0 nm or more. When the characteristic width w2 exceeds 25.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are unevenly dispersed, resulting in a local decrease in the crystallization rate of the first film, and the film appearance deteriorates due to whitening during retort sterilization. Therefore, the characteristic width w2 is set to 25.0 nm or less, and preferably 20.0 nm or less.

[0048] When one of the characteristic widths w1 and w2 is 10.0 nm or more and 25.0 nm or less and the other is less than 10.0 nm or more than 25.0 nm, the polybutylene terephthalate molecules and the polyethylene terephthalate molecules tend to have a dispersed structure other than a co-continuous structure, which reduces the crystallization rate and may cause deterioration of the film appearance due to whitening during retort sterilization.

[0049] The first polyester and the second polyester are preferably dispersed in a co-continuous structure as shown in FIG. 2 or 3 . The typical width of the co-continuous structure can be expressed as the ratio of the area of ​​each element constituting the co-continuous structure to the length of the thin line formed when each element is thinned, i.e., corresponds to the characteristic width of the present invention. The typical width of the co-continuous structure is preferably 10.0 nm or more and 25.0 nm or less. When the first polyester and the second polyester are dispersed in a co-continuous structure having a typical width of 10.0 nm or more and 25.0 nm or less, the first polyester having a slow crystallization rate and the second polyester having a fast crystallization rate are not compatible with each other. Therefore, the crystallization rate of the entire first film is improved. Furthermore, in the above case, uneven dispersion of the first polyester and the second polyester can be suppressed, thereby suppressing a local decrease in the crystallization rate and suitably suppressing deterioration of the appearance due to whitening during retort sterilization.

[0050] The characteristic width can be determined as follows. A cross-section of the first film is observed using a scanning probe microscope AFM5300E manufactured by Hitachi High-Tech Science Corporation. A laminated metal plate is immersed in hydrochloric acid to dissolve the metal plate, and an MD cross-section of the isolated first film is prepared using a microtome to serve as a sample. A Hitachi High-Tech Fielding Corporation back-alloy coated Si cantilever is used as the cantilever for the scanning probe microscope, and a 1 μm MD × 0.5 μm t field of view at the center of the film thickness direction is observed in DFM mode to obtain a phase image. Note that the phase image is observed so that areas with small phase delay are shown dark.

[0051] For the obtained phase image, the percentile method is applied to the phase delay to determine a binarization threshold so that the area percentage of the dark areas is equal to the mass percentage of the first polyester relative to the total amount of polyester in the first film, and a binarized image is obtained. For the binarized image, the area A1 of the dark areas is calculated using a program. Furthermore, for the binarized image, thinning is performed using the Zhang-Suen method to calculate the length l1 of the thin line. The characteristic width w1 of the dark areas is determined by dividing A1 by l1. Similarly, for the binarized image, the area A2 of the bright areas and the length l2 of the thin line are calculated, and the characteristic width w2 of the bright areas is determined.

[0052] Further investigation by the inventors led to the following findings: A laminated metal sheet that detects only a diffraction intensity below a certain magnification relative to the intensity of the amorphous halo in a wide-angle X-ray diffraction spectrum of a film on the laminated metal sheet retains film coverage even after extensive processing. Furthermore, in order to produce a laminated metal sheet that detects only a weak diffraction intensity, it is preferable that the preheating temperature of the metal sheet during lamination be higher than the melting peak of the film by a certain degree.

[0053] It is preferable that the wide-angle X-ray diffraction spectrum of one surface of the laminated metal sheet on which the first film is laminated satisfies the following formula (3): I(1) １００ / I(1) ａｍｏｒｐｈｏｕｓ ≦1.5 (3) Here, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by the incident X-ray and the reflected X-ray is perpendicular to the surface of the first film. １００ is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ = 26.5 ± 1.0°, and I(1) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

[0054] I (1) １００ / I(1) ａｍｏｒｐｈｏｕｓWhen formula (3) is satisfied, the crystalline content of polyethylene terephthalate is small, and therefore the formability of the first film is improved. As a result, breakage of the first film or the metal plate when forming the laminated metal plate into a laminated metal container can be suitably suppressed, and the corrosion resistance of the laminated metal container can be suitably improved. Therefore, I(1) １００ / I(1) ａｍｏｒｐｈｏｕｓ is preferably 1.5 or less, more preferably 1.0 or less. １００ / I(1) ａｍｏｒｐｈｏｕｓ The lower limit of is not particularly limited, but is generally 0.2 or more.

[0055] It is more preferable that the wide-angle X-ray diffraction spectrum of the one surface of the laminated metal sheet on which the first film is laminated satisfies the following formula (7): I(1′) １００ / I(1) ａｍｏｒｐｈｏｕｓ ≦1.5 (7) where I(1′) １００ is the net intensity of the 100 diffraction peak of polybutylene terephthalate appearing at 2θ=23.5±1.0°.

[0056] I(1') １００ / I(1) ａｍｏｒｐｈｏｕｓ When formula (7) is satisfied, the crystalline content of polybutylene terephthalate is small, and therefore the formability of the first film is improved. As a result, breakage of the first film or the metal plate when forming the laminated metal plate into a laminated metal container can be suitably suppressed, and the corrosion resistance of the laminated metal container can be suitably improved. Therefore, I(1') １００ / I(1) ａｍｏｒｐｈｏｕｓ is preferably 1.5 or less, more preferably 1.0 or less. １００ / I(1) ａｍｏｒｐｈｏｕｓ The lower limit of I(1') is not particularly limited. １００ / I(1) ａｍｏｒｐｈｏｕｓ is generally 0.7 or more.

[0057] It is more preferable that the first film does not exhibit any diffraction peaks other than the amorphous halo in the wide-angle X-ray diffraction spectrum at 2θ = 10.0 to 30.0°. When no diffraction peaks other than the amorphous halo are observed at 2θ = 10.0 to 30.0°, the amount of crystals of polyethylene terephthalate and polybutylene terephthalate is extremely small, thereby particularly improving the formability of the first film. As a result, breakage of the first film and the metal plate when forming the laminated metal plate into a laminated metal container can be effectively prevented, and the corrosion resistance of the laminated metal container can be effectively improved.

[0058] Wide-angle X-ray diffraction spectra can be measured as follows. Measurements are made using a wide-angle goniometer SmartLab manufactured by Rigaku Corporation under the following conditions using the θ-2θ method. The measurement is performed while rotating the laminated metal sheet sample. X-ray source: CuKα ray Tube voltage: 40 kV Tube current: 40 mA Entrance slit: 0.5° Entrance parallel slit: 5.0° Receiving slit: 0.6 mm Receiving parallel slit: 5.0° Monochromator slit: BBM Longitudinal limiting slit: 10.0 mm 2θ = 10.0 to 30.0° (0.1° / step) Counting time: 8.0 seconds / step

[0059] For the obtained wide-angle X-ray diffraction spectrum, the background intensity represented by the straight line connecting the diffraction intensity at 2θ = 10.0° and the diffraction intensity at 2θ = 30.0° was subtracted from the diffraction intensity at each 2θ to obtain the net intensity. In the measurement results, the peak appearing at 2θ = 26.5 ± 1.0° was attributed to the 100 diffraction of polyethylene terephthalate, and its intensity was expressed as I(1) １００ If no clear peak appears at 2θ = 26.5 ± 1.0°, the maximum net strength in the range of 2θ between 25.5° and 27.5° is defined as I(1) １００ The intensity of the amorphous halo that appears at 2θ = 20.0 ± 5.0° is expressed as I(1) ａｍｏｒｐｈｏｕｓ Let's say.

[0060] In addition, in the measurement results, the peak that appeared at 2θ=23.5±1.0° was attributed to 100 diffraction of polybutylene terephthalate, and its intensity was expressed as I(1') １００ If no clear peak appears at 2θ=23.5±1.0°, the maximum net strength in the range of 2θ=22.5° to 24.5° is defined as I(1′). １００ Let's say.

[0061] The first film preferably has at least one melting peak temperature of 200°C or higher and 230°C or lower. The melting peak temperature is determined by differential scanning calorimetry (DSC). If at least one melting peak temperature is 200°C or higher, the heat resistance of the first film is improved. Furthermore, if at least one melting peak temperature is 230°C or lower, deterioration of appearance due to whitening during retort sterilization can be suppressed.

[0062] Differential scanning calorimetry can be performed as follows. The thermal properties of the first film are measured using a differential scanning calorimeter DSCQ100 manufactured by TA Instruments Japan Co., Ltd. The laminated metal plate is immersed in hydrochloric acid to dissolve the metal plate, and the isolated first film is subjected to analysis as a sample. 5 mg of film is collected as a sample, cut into pieces, and placed in an aluminum dish. The sample is cooled to -50°C under a nitrogen atmosphere and measured in the first run while heating to 290°C at 10°C / min. After measurement, the sample is held at 290°C for 5 minutes and then quenched with liquid nitrogen. Thereafter, the second run is measured while heating again from -50°C to 290°C at 10°C / min. From the chart obtained in the second run, the endothermic peak temperature of 120°C or higher and 280°C or lower is taken as the melting peak temperature.

[0063] The first film may contain, in addition to the first polyester and the second polyester, additives such as an antioxidant, an inorganic lubricant, an organic lubricant, a crystal nucleating agent, a heat stabilizer, an antistatic agent, and a coloring pigment.

[0064] The first film preferably contains an antioxidant in an amount of 0.0001% by mass or more and 1.0000% by mass or less, thereby achieving favorable heat resistance. Therefore, the first film preferably contains an antioxidant in an amount of 0.0001% by mass or more and 1.0000% by mass or less. The antioxidant is not particularly limited, but known antioxidants such as hindered phenols, hydrazines, and phosphites can be used.

[0065] The first film contains an inorganic lubricant in a range of 0.01% by mass to 0.50% by mass, which allows the first film to be easily handled. Therefore, the inorganic lubricant is preferably contained in a range of 0.01% by mass to 0.50% by mass. The inorganic lubricant is not particularly limited, but known inorganic lubricants such as silicon oxide, diatomaceous earth, and talc can be used.

[0066] The first film may be formed of multiple layers in the thickness direction. A known method for laminating multiple layers may be used, such as a coextrusion method using a feed block or a multi-manifold, a method for laminating multiple films, or a method for directly laminating a molten resin onto a film. The coextrusion method is preferably used as the lamination method for the first film in order to increase productivity and reduce energy consumption.

[0067] When the first film is composed of multiple layers, it is preferable that the outermost layer contains an inorganic lubricant in a range of 0.01 mass % to 0.50 mass %, and that layers other than the outermost layer contain no inorganic lubricant or contain an inorganic lubricant in a range of 0.01 mass % or less. For example, when the first film is composed of three layers, namely, an air-side surface layer, a core layer, and a metal-sheet-side surface layer, an example of a configuration is that the air-side surface layer and the metal-sheet-side surface layer contain an inorganic lubricant, and the core layer does not contain an inorganic lubricant. By containing an inorganic lubricant only in the outermost layer, the amount of inorganic lubricant used can be reduced, which is economical.

[0068] When the first film contains an organic lubricant in the range of 0.01% by mass to 1.00% by mass, the formability of the laminated metal sheet is improved. Therefore, the first film preferably contains an organic lubricant in the range of 0.01% by mass to 1.00% by mass. When the first film is composed of multiple layers, it is preferable that the outermost layer contains an organic lubricant in the range of 0.01% by mass to 1.00% by mass. The organic lubricant is not particularly limited, but known organic lubricants such as carnauba wax, polyolefin wax, and modified polyolefin wax can be used.

[0069] If the average thickness of the first film is 8 μm or more, better corrosion resistance can be ensured when the laminated metal plate is formed into a laminated metal container. Therefore, the average thickness of the first film is preferably 8 μm or more, more preferably 10 μm or more, and even more preferably 13 μm or more. On the other hand, if the average thickness of the first film is 50 μm or less, the energy consumption required for heating during the production of the first film or laminated metal plate can be suitably reduced. Therefore, the average thickness of the first film is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0070] If the sample standard deviation of the thickness of the first film is 10% or less of the average thickness of the first film, breakage of the first film or metal plate can be suppressed when the laminated metal plate is formed into a laminated metal container. Therefore, the sample standard deviation of the thickness of the first film is preferably 10% or less of the average thickness of the first film, and more preferably 5% or less. On the other hand, although there is no particular limitation on the lower limit of the sample standard deviation of the thickness of the first film, the sample standard deviation is generally 0.05% or more.

[0071] The average thickness and sample standard deviation of the first film can be determined as follows: Measure the thickness of the first film in the longitudinal direction over 1,000 mm at 1 mm intervals using a constant pressure thickness meter. From the measurement results, the sample standard deviation and average can be calculated.

[0072] [Second Film] The second film has a polyester component consisting of one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate. The total content of homopolyethylene terephthalate and copolymer polyethylene terephthalate in the second film is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may even be 100% by mass. When the total content of homopolyethylene terephthalate and copolymer polyethylene terephthalate in the second film is 70% by mass or more, breakage of the second film and the metal plate can be suitably suppressed when the laminated metal plate is formed into a laminated metal container.

[0073] When the second film contains copolymerized polyethylene terephthalate, the content of the copolymerization component is preferably 20 mol% or less, more preferably 2 mol% to 16 mol%. The copolymerization component of the polyethylene terephthalate in the second film can be the acid component and the alcohol component described for the first polyester. The copolymerization component of the polyethylene terephthalate in the second film can be one of the above-mentioned components, or two or more of them can be used.

[0074] If the second film has a highest endothermic peak temperature of 220°C or higher in a temperature range of 280°C or lower in differential scanning calorimetry (DSC), the heat resistance of the second film is improved. Therefore, the second film preferably has an endothermic peak temperature of 220°C or higher. On the other hand, the second film has an endothermic peak temperature of approximately 260°C or lower. DSC can be measured in the same manner as for the first film.

[0075] It is preferable that the wide-angle X-ray diffraction spectrum of the metal plate on the other side on which the second film is laminated satisfies the following formula (4): I(2) １００ / I(2) ａｍｏｒｐｈｏｕｓ ≦1.5 (4) However, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by the incident X-ray and the reflected X-ray is perpendicular to the surface of the second film. １００is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ = 26.5 ± 1.0°, and I(2) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

[0076] I (2) １００ / I(2) ａｍｏｒｐｈｏｕｓ is preferably 1.5 or less, more preferably 1.0 or less. When the wide-angle X-ray diffraction spectrum of the laminated metal plate satisfies formula (4), the amount of crystals in the polyethylene terephthalate is small, and therefore the formability of the second film is improved. As a result, breakage of the second film or the metal plate can be suppressed when the laminated metal plate is formed into a laminated metal container, and the corrosion resistance of the laminated metal container can be improved. On the other hand, I(2) １００ / I(2) ａｍｏｒｐｈｏｕｓ The lower limit of I(2) is not particularly limited. １００ / I(2) ａｍｏｒｐｈｏｕｓ is generally 0.2 or more.

[0077] It is more preferable that the second film does not exhibit any diffraction peaks other than the amorphous halo in the wide-angle X-ray diffraction spectrum at 2θ = 10.0 to 30.0°. When no diffraction peaks other than the amorphous halo are observed at 2θ = 10.0 to 30.0°, the amount of crystals in the polyethylene terephthalate is extremely small, thereby particularly improving the formability of the second film. As a result, breakage of the second film or the metal plate when forming the laminated metal plate into a laminated metal container can be effectively suppressed, and the corrosion resistance of the laminated metal container can be effectively improved.

[0078] The wide-angle X-ray diffraction spectrum of the second film can be measured in the same manner as that of the first film. If no clear peak appears at 2θ=26.5±1.0°, the maximum net strength in the 2θ range of 25.5° to 27.5° is calculated as I(2) １００ Let's say.

[0079] If the intrinsic viscosity of the second film is 0.60 dL / g or more, the formation of microcracks in the second film can be suitably suppressed when the laminated metal sheet is formed into a laminated metal container. Therefore, the intrinsic viscosity of the second film is preferably 0.60 dL / g or more, and more preferably 0.62 dL / g or more. On the other hand, if the intrinsic viscosity of the second film is 1.10 dL / g or less, the amount of energy consumed in the polymerization step and the extrusion step can be suitably suppressed. Therefore, the intrinsic viscosity of the second film is preferably 1.10 dL / g or less, and more preferably 0.80 dL / g or less.

[0080] In addition to the homopolyethylene terephthalate and copolymer polyethylene terephthalate, the second film may contain additives such as antioxidants, inorganic lubricants, organic lubricants, crystal nucleating agents, heat stabilizers, antistatic agents, and coloring pigments.

[0081] If the second film contains an antioxidant in the range of 0.0001% by mass to 1.0000% by mass, the heat resistance of the second film can be favorably obtained. Therefore, the second film preferably contains an antioxidant in the range of 0.0001% by mass to 1.0000% by mass. The antioxidant is not particularly limited, but known antioxidants such as hindered phenols, hydrazines, and phosphites can be used.

[0082] If the second film contains an inorganic lubricant in the range of 0.01% by mass to 0.50% by mass, the second film can be easily handled. Therefore, the second film preferably contains an inorganic lubricant in the range of 0.01% by mass to 0.50% by mass. The inorganic lubricant is not particularly limited, but known inorganic lubricants such as silicon oxide, diatomaceous earth, and talc can be used.

[0083] The second film may be formed of multiple layers in the thickness direction. The multiple layers may be formed by any known method, such as coextrusion using a feed block or a multi-manifold, laminating multiple films together, or directly laminating a molten resin onto a film. The coextrusion method is preferably used as the method for laminating the second film in order to increase productivity and reduce energy consumption.

[0084] When the second film is composed of multiple layers, it is preferable that the outermost layer contains an inorganic lubricant in a range of 0.01 mass % to 0.50 mass %, and that layers other than the outermost layer contain no inorganic lubricant or contain an inorganic lubricant in a range of 0.01 mass % or less. For example, when the second film is composed of three layers, namely, an air-side surface layer, a core layer, and a metal-sheet-side surface layer, an example of a configuration is that the air-side surface layer and the metal-sheet-side surface layer contain an inorganic lubricant, and the core layer does not contain an inorganic lubricant. By containing an inorganic lubricant only in the outermost layer, the amount of inorganic lubricant used can be reduced, which is economical.

[0085] If the second film contains an organic lubricant in the range of 0.01% by mass to 3.00% by mass, the ease of removing contents from the laminated metal container is improved. Therefore, the second film preferably contains an organic lubricant in the range of 0.01% by mass to 3.00% by mass. If the second film is composed of multiple layers, it is preferable that the outermost layer contains an organic lubricant in the range of 0.01% by mass to 3.00% by mass. The organic lubricant is not particularly limited, but known organic lubricants such as carnauba wax, polyolefin wax, and modified polyolefin wax can be used.

[0086] The second film may also contain a coloring pigment. By containing the coloring pigment in the second film, the underlying metal plate can be concealed, and the design can be improved. The coloring pigment is not particularly limited, but for example, a white pigment, a yellow pigment, etc. can be used.

[0087] Examples of white pigments that can be used include oxide ceramics such as aluminum oxide, titanium oxide, and zinc oxide, as well as talc, calcium carbonate, barium sulfate, etc. Titanium oxide is particularly preferred as the white pigment from the viewpoints of dispersibility and whiteness, and rutile titanium oxide is more preferred.

[0088] As the yellow pigment, for example, isoindolinone yellow, disazo yellow, etc. can be used. As the yellow pigment, disazo yellow is particularly preferred from the viewpoint of heat resistance.

[0089] When the second film is composed of multiple layers, it is preferable that the color pigment be contained in a layer other than the outermost layer. By containing the color pigment in a layer other than the outermost layer, the production cost can be reduced while maintaining the coloring effect, and hygiene problems caused by the pigment coming into contact with the contents can be prevented.

[0090] The average thickness of the second film is preferably 8 μm or more, more preferably 10 μm or more, and even more preferably 13 μm or more, similar to that of the first film, while the average thickness of the second film is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, similar to that of the first film.

[0091] The sample standard deviation of the thickness of the second film is preferably 10% or less, more preferably 5% or less, of the average thickness of the second film, similar to that of the first film. On the other hand, although there is no particular lower limit for the sample standard deviation of the thickness of the second film, the sample standard deviation is generally 0.05% or more.

[0092] The average thickness and sample standard deviation of the second film can be determined in the same manner as the average thickness and sample standard deviation of the first film described above.

[0093] (Method for manufacturing laminated metal sheet) Next, a method for manufacturing a laminated metal sheet will be described. The method for manufacturing a laminated metal sheet includes a step of preheating a metal sheet to 300°C or less, a step of thermocompression bonding a film A to at least one surface of the metal sheet using a laminating roll to form a thermocompression-bonded body, and a step of liquid-cooling the thermocompression-bonded body to form a laminated metal sheet. Note that a first film is obtained by subjecting film A to the thermocompression bonding step and the cooling step, and a second film is obtained similarly from film B.

[0094] First, a metal plate and film A, which will become the laminate raw material, are prepared. Film A is a polyester film whose polyester components are a first polyester and a second polyester. As with the first film described above, the mass ratio of the first polyester to the second polyester in film A is 20:80 to 50:50, where the total amount of polyester in film A is 100.

[0095] Two characteristic widths w'1 and w'2 calculated from a binarized phase image obtained by observing the cross section of film A using a dynamic force mode of a scanning probe microscope before the thermocompression bonding step described below preferably satisfy the following formulas (5) and (6): 8.0 nm≦w'1≦17.0 nm (5) 8.0 nm≦w'2≦17.0 nm (6)

[0096] The characteristic widths w'1 and w'2 can be determined in the same manner as the characteristic widths w1 and w2 for the first film described above. Specifically, the threshold value for binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delays are displayed dark, the area percentage of the dark areas is equal to the mass percentage of the first polyester relative to the total amount of polyester in film A. The characteristic width w'1 is the value obtained by dividing the area A'1 of the dark areas after binarization by the length l'1 of the thin line obtained by thinning the dark areas. The characteristic width w'2 is the value obtained by dividing the area A'2 of the bright areas after binarization by the length l'2 of the thin line obtained by thinning the bright areas.

[0097] If the characteristic width w'1 or w'2 in the laminated raw film A is less than 8.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are finely dispersed and close to being compatible with each other. Therefore, the characteristic widths w1 and w2 in the first film obtained from film A through the thermocompression bonding and cooling processes described below may not satisfy formulas (1) and (2). Therefore, it is preferable that the characteristic widths w'1 and w'2 are each 8.0 nm or more. On the other hand, if the characteristic width w'1 or w'2 in the laminated raw film A is more than 17.0 nm, the polyethylene terephthalate molecules and polybutylene terephthalate molecules are unevenly dispersed. Therefore, the characteristic widths w1 and w2 in the first film obtained from film A through the thermocompression bonding and cooling processes described below may not satisfy formulas (1) and (2). Therefore, it is preferable that the characteristic widths w'1 and w'2 are each 17.0 nm or less.

[0098] Film A can be produced using various known methods. When laminating film A onto a metal plate to produce a laminated metal plate, an extrusion coating method may be used in which a molten film A extruded from a T-die of an extruder is directly thermocompressed onto the metal plate. Alternatively, film A may be produced on a film production line installed separately from the laminated metal plate production line, and then film A and the metal plate may be laminated on the laminated metal plate production line. A method for producing film A on a film production line will be described below. However, the present invention is not limited to the following description.

[0099] The production line for film A is composed of, for example, a non-stretched film production process in which an non-stretched film is obtained from a resin composition using an extruder, a stretched film production process in which a stretched film is obtained by stretching the non-stretched film, and a winding process in which the film is wound into a roll.

[0100] In the non-stretched film production process, raw material resins for the first polyester and the second polyester are used, along with additives such as antioxidants, inorganic lubricants, organic lubricants, crystal nucleating agents, heat stabilizers, antistatic agents, and coloring pigments as needed. The raw material resins for the first polyester and the second polyester are preferably in the form of pellets. From the viewpoint of handleability, the additives are preferably in the form of masterbatch pellets in which the additives are dispersed in the resin. The resin in the masterbatch pellets in which the additives are dispersed may be the first polyester or the second polyester, but from the viewpoint of economy, the commonly used homopolyethylene terephthalate is preferred. The raw material resins and additive pellets can be mixed by dry blending to form a resin mixture. The resin mixture is dried under hot air or vacuum as needed and then fed to an extruder.

[0101] The raw resin supplied to the extruder is heated above its melting point and melted. The additives and the molten raw resin are kneaded in the extruder to form a resin composition in which the first polyester, the second polyester, and the additives are dispersed. After foreign matter, modified resins, etc. are removed using a filter, the resin composition is extruded through a T-die and formed into a molten resin sheet. To improve the metering ability of the extrusion, it is preferable to install a feeder or gear pump in the extruder. To omit the drying process of the resin mixture and to suppress hydrolysis during extrusion, it is preferable to install a vacuum pipe to reduce the pressure inside the extruder.

[0102] When the film A is formed of multiple layers, for example, a co-extrusion method can be used to laminate the multiple layers to form the film A. In this case, a feed block or a multi-manifold die can be used to melt-extrude the resin composition or the like that will be the material for forming each layer using several extruders.

[0103] The molten resin sheet discharged from the T-die is cooled and solidified by a cooling device such as a cast roll to form an unstretched film. When cooling and solidifying the molten resin sheet, it is preferable to use electrostatic pinning, a vacuum chamber, or the like. By using these facilities, the adhesion between the cast roll or the like and the molten resin sheet can be improved, and a homogeneous unstretched film can be obtained.

[0104] In order for the characteristic widths w'1 and w'2 of film A to satisfy the formulas (5) and (6), it is preferable that the time from when the molten resin sheet is discharged from the T-die until when it comes into contact with the cooling device is 0.20 to 0.80 seconds.

[0105] In the stretched film production process, an unstretched film is stretched in the film travel direction and / or the film width direction. Stretching in the film travel direction is called longitudinal stretching, and stretching in the film width direction is called transverse stretching. In the stretched film production process, only longitudinal stretching or transverse stretching may be performed, but sequential biaxial stretching in which longitudinal stretching and transverse stretching are performed successively, or simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed simultaneously may also be performed. The stretched film production process may also be omitted.

[0106] Longitudinal stretching is performed, for example, using a longitudinal stretching machine equipped with a preheating roll and a stretching roll. The film before stretching is heated to a predetermined temperature when it passes through the preheating roll while being transported in the longitudinal direction. The film before stretching, heated to a predetermined temperature by the preheating roll, is then stretched in the longitudinal direction by the stretching roll, which rotates at a faster transport speed than the immediately preceding roll. In addition to the preheating roll, an infrared heater may be used to heat the film. The infrared heater is preferably installed between the stretching roll and the roll immediately preceding the stretching roll. By installing the infrared heater in such a position, it is possible to both suppress adhesion of the film to the preheating roll and reduce the torque during stretching.

[0107] The transverse stretching is carried out, for example, by gripping the widthwise edges of the film with clips and widening the clip interval in the widthwise direction of the film in a heating furnace. The heating furnace is preferably divided into several temperature zones from the inlet side to the outlet side.

[0108] The sequential biaxial stretching can be carried out by successively carrying out the longitudinal stretching and the transverse stretching. The order in which the longitudinal stretching and the transverse stretching are carried out can be determined appropriately. For example, the longitudinal stretching and the transverse stretching can be carried out once each, and then the longitudinal stretching can be carried out again.

[0109] Simultaneous biaxial stretching can be carried out, for example, by widening the clip spacing in the film width direction and simultaneously widening the clip spacing in the film longitudinal direction during the transverse stretching.

[0110] In any of longitudinal stretching, transverse stretching, sequential biaxial stretching, and simultaneous biaxial stretching, the maximum temperature of the film is preferably equal to or higher than the glass transition temperature of the unstretched film. The ratio of the film length before and after stretching in the stretching direction is called the stretch ratio, and the stretch ratio is preferably 2.0 times or more and 9.0 times or less.

[0111] In the stretched film production process, a heat setting treatment may be performed. The heat setting treatment can be performed, for example, after sequential biaxial stretching, by raising the temperature of the film to a temperature higher than the maximum temperature of the film during stretching, and, if necessary, by relaxing the tension on the film. The heat setting treatment can increase the heat resistance of the film and suppress dimensional changes of the film over time.

[0112] In the winding process, the unstretched film or the stretched film is wound into a roll to obtain a film roll. Before winding into a roll, it is preferable to use quality inspection equipment such as a thickness gauge or a defect detector to inspect the quality of the film. Although the quality inspection equipment may be installed in the unstretched film production process or the stretched film production process, it is more effective to install it in the winding process, which is the final process in the film production line.

[0113] It is also preferable to use a trimmer to remove the widthwise edges of the film before winding it into a roll, which has the effect of aligning the width of the film, contributing to stable production of laminated metal sheets, and suppressing folding defects at the widthwise edges of the film.

[0114] It is preferable to use oscillation rolling in the trimmer, in which the film is passed through while oscillating in the width direction. Oscillation rolling can prevent gauge band defects, which occur when unevenness in the film's thickness accumulates across the width and causes unevenness across the width of the film roll.

[0115] Film B can also be produced by various known methods, similar to the above-mentioned film A. Furthermore, it is preferable that the polyester component of film B comprises one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate.

[0116] [Thermocompression bonding step] In the thermocompression bonding step, a preheated metal plate and film A are thermocompression bonded using a laminating roll to produce a thermocompression bonded body. The thermocompression bonding step is performed by thermocompression bonding film A to at least one of the front and back surfaces of the metal plate. The metal plate used is cast and rolled to a predetermined thickness and width, and then optionally subjected to surface treatment such as annealing, temper rolling, or plating.

[0117] The thermocompression bonding step is performed by placing film A between a metal plate preheated to a predetermined temperature and a laminating roll, and pressing film A against the metal plate with the laminating roll. During this process, film A melts due to the heat of the metal plate and is pressure-bonded to the metal plate.

[0118] The surface temperature of the metal plate 0.5 seconds before the metal plate and film A come into contact is called the preheat temperature of the metal plate. If the preheat temperature of the metal plate exceeds 300°C, there is a risk that film A will completely melt while in contact with the laminating roll and adhere to the laminating roll. If the film adheres to the laminating roll, irregularities will occur on the roll surface, and these irregularities may be transferred to the subsequent laminated metal plate, forming a pattern. Therefore, the preheat temperature of the metal plate is preferably 300°C or lower. In addition, the preheat temperature of the metal plate is generally 230°C or higher.

[0119] The preheating temperature of the metal plate is preferably −10°C or higher than the highest endothermic peak temperature in the temperature range of 280°C or lower in differential scanning calorimetry of film A. When the preheating temperature of the metal plate is −10°C or higher than the endothermic peak temperature, it is possible to effectively prevent crystals of the first polyester or second polyester in film A from remaining on the laminated metal plate, thereby reducing processability. On the other hand, when the preheating temperature of the metal plate is +50°C or lower than the endothermic peak temperature, it is possible to effectively prevent film A from completely melting while in contact with the laminating roll and adhering to the laminating roll. If film A adheres to the laminating roll, irregularities may occur on the roll surface, and these irregularities may be transferred to the subsequent laminated metal plate, forming a pattern. Therefore, it is preferable that the preheating temperature of the metal plate be +50°C or lower than the endothermic peak temperature. The preheating temperature of the metal plate is more preferably −10° C. to +50° C. relative to the highest endothermic peak temperature in the temperature range of 280° C. or less in differential scanning calorimetry of film A.

[0120] In the differential scanning calorimetry of film A, the endothermic peak temperature located at the highest temperature below 280° C. corresponds to the melting peak temperature of the first polyester in film A. The differential scanning calorimetry is as described above.

[0121] In the thermocompression bonding step, the film A, the preheated metal plate, and the film B may be thermocompression bonded in this order to form a thermocompression-bonded body. In this case, the thermocompression bonding step is performed by thermocompression bonding the film A to one of the front and back surfaces of the metal plate and thermocompression bonding the film B to the other surface.

[0122] When film A and film B are thermocompression-bonded to a metal plate, film A and film B may be thermocompression-bonded to the metal plate sequentially, but it is preferable to thermocompression-bond them to the metal plate simultaneously. When film A and film B are thermocompression-bonded to the metal plate simultaneously, the energy consumption required to heat the metal plate can be reduced and the equipment configuration can be simplified.

[0123] When film A and film B are thermocompressed to a metal plate, it is preferable to preheat the metal plate to a temperature of 300°C or less, as this can prevent film A and film B from completely melting and adhering to the laminating roll while in contact with the laminating roll.

[0124] The preheating temperature of the metal plate is preferably −5°C or more and +60°C or less relative to the highest endothermic peak temperature in the temperature range of 280°C or less in differential scanning calorimetry of film B. If the preheating temperature of the metal plate is −5°C or more and +60°C or less relative to the endothermic peak temperature, it is possible to suitably prevent film B from completely melting and adhering to the laminating roll while in contact with the laminating roll. Furthermore, the polyethylene terephthalate in film B can be sufficiently amorphized, thereby improving the processability of the laminated metal plate. Note that the differential scanning calorimetry is as described above.

[0125] Film A and film B used in the thermocompression bonding step may be preheated. Film A is preferably heated to a temperature of 40°C or higher and 150°C or lower. Film B is preferably heated to a temperature of 70°C or higher and 180°C or lower. Heating film A or film B within these temperature ranges allows film A or film B to be transported smoothly and also reduces the preheating temperature of the metal plate.

[0126] If the pressure applied by the laminating roll is 0.35 MPa or more, it is possible to prevent air bubbles from being trapped at the interface between the metal plate and film A or film B, thereby improving the adhesion between the metal plate and film A or film B. Therefore, the pressure applied by the laminating roll is preferably 0.35 MPa or more, and more preferably 0.40 MPa or more. On the other hand, if the pressure applied by the laminating roll is 1.50 MPa or less, it is possible to suppress the amount of heat transferred from the metal plate through film A or film B to the laminating roll, thereby suitably suppressing energy consumption and wear of the laminating roll. Therefore, the pressure applied by the laminating roll is preferably 1.50 MPa or less, and more preferably 1.40 MPa or less.

[0127] The laminating roll is preferably heated to a temperature in the range of −20° C. to +50° C. relative to the glass transition temperature of film A. Heating the laminating roll can mitigate spontaneous temperature increases due to heat input from the metal plate, thereby suppressing variations in the properties of film A in the longitudinal direction. The glass transition temperature of film A is determined as follows: film A is heated from −50° C. to 290° C. at a rate of 10° C. / min, and differential scanning calorimetry is performed. When the baseline shifts, the average temperature is determined from the two intersections (glass transition onset temperature, glass transition end temperature) of the baselines before and after the shift and the tangent to the inflection point during the shift, and this is taken as the glass transition temperature.

[0128] Furthermore, the laminating roll in contact with film B is preferably heated to a temperature in the range of −20° C. to +50° C. below the glass transition temperature of film B. By heating the laminating roll in contact with film B in this manner, spontaneous temperature increases due to heat input from the metal plate can be mitigated, and variations in the properties of film B in the longitudinal direction can be suppressed. The glass transition temperature of film B can be determined in the same manner as the glass transition temperature of film A.

[0129] [Cooling Step] In the cooling step, the thermocompression-bonded body is liquid-cooled within 2 seconds after the thermocompression bonding step. In the cooling step, the thermocompression-bonded body may be cooled by spraying a refrigerant onto the thermocompression-bonded body or by immersing the thermocompression-bonded body in the refrigerant. Examples of refrigerants used for cooling include water, oils such as silicone oil, and organic solvents. Water is particularly preferred, and ion-exchanged water and distilled water are more preferred. Using ion-exchanged water or distilled water as the refrigerant reduces impurities such as minerals, thereby preventing the precipitation of impurities even when drying is performed after the cooling step. When industrial water or tap water is used as the refrigerant, it is preferable to rinse the body with ion-exchanged water or distilled water after rapid cooling to prevent appearance defects due to the precipitation of impurities.

[0130] If the surface temperature of film A in the thermocompression-bonded body immediately before cooling in the cooling step exceeds 205°C, the first polyester and the second polyester in film A are cooled while remaining compatible during the thermocompression bonding step, and the dispersion state is fixed. As a result, the crystallization rate of film A as a whole decreases, and the appearance of the film may deteriorate due to whitening during retort sterilization. Therefore, the surface temperature is set to 205°C or lower, preferably 200°C or lower, and more preferably 195°C or lower. On the other hand, if the surface temperature of film A in the thermocompression-bonded body immediately before cooling in the cooling step is 170°C or higher, crystallization of polyethylene terephthalate molecules in film A progresses, which can effectively prevent deterioration of the processability of the laminated metal sheet. Therefore, the surface temperature is preferably 170°C or higher, more preferably 180°C or higher, and even more preferably 185°C or higher.

[0131] The surface temperature of the film A in the thermocompression-bonded body immediately before being cooled in the cooling step is preferably 170° C. or higher and 210° C. or lower, more preferably 180° C. or higher and 200° C. or lower, and even more preferably 185° C. or higher and 195° C. The surface temperature of the film A in the thermocompression-bonded body immediately before being cooled is the surface temperature measured 0.2 seconds before being cooled.

[0132] If the time from when film A separates from the laminating roll in the thermocompression bonding step to when film A is cooled in the cooling step is 2.0 seconds or less, crystallization of polyethylene terephthalate molecules in film A can be suitably suppressed. In addition, the processability of the laminated metal sheet can be improved. Therefore, this time is preferably 2.0 seconds or less, and more preferably 1.5 seconds or less. On the other hand, if this time is 0.2 seconds or more, the temperature difference that occurred in the thickness direction within film A while in contact with the laminating roll is eliminated upon separation from the laminating roll, resulting in a uniform temperature distribution in the thickness direction within film A. Therefore, variation in the physical properties within film A can be effectively suppressed, and the processability of the laminated metal sheet can be suitably obtained. Therefore, this time is preferably 0.2 seconds or more, more preferably 0.5 seconds or more, and even more preferably 0.8 seconds or more. Furthermore, this time is preferably 0.2 seconds or more and 2.0 seconds or less, and more preferably 0.5 seconds or more and 1.5 seconds or less.

[0133] In the cooling step, the refrigerant may be heated to ensure operational stability. If the refrigerant temperature is 10°C or higher, freezing in the refrigerant tank and contamination due to condensation on the piping can be effectively prevented. Therefore, the refrigerant temperature is preferably 10°C or higher. On the other hand, if the refrigerant temperature is 40°C or lower than the glass transition temperature of film A, film A can be smoothly transported without sticking to the pass line rolls installed after the cooling step. Therefore, the refrigerant temperature is preferably 40°C or lower than the glass transition temperature of film A.

[0134] After cooling, the thermocompression-bonded body has the refrigerant removed by a squeeze roll. The thermocompression-bonded body is subjected to post-heating and oiling treatments as needed. The thermocompression-bonded body is inspected for surface defects, internal defects, plate thickness, etc. as needed, and then wound into a coil by, for example, a tension reel to form a laminated metal plate. The thermocompression-bonded body may be slit or sheared to form a sheet-shaped laminated metal plate.

[0135] (Laminated Metal Container) The left side of Fig. 1 shows the configuration of a laminated metal container 100. The laminated metal container 100 is formed in a cylindrical shape with a bottom and is provided with a lid for closing the container as needed. The laminated metal container 100 can be used, for example, for food cans, beverage cans, 18L cans, etc.

[0136] The laminated metal container may be either a three-piece can made by joining three members, i.e., a lid, a body, and a base, or a two-piece can made by joining two members, i.e., a lid and a body. Note that the laminated metal container may have an opening at one end of the body, for example, by omitting the lid.

[0137] The laminated metal container includes the above-mentioned laminated metal plate, and is formed by using a laminated metal plate for at least one of the members constituting the laminated metal container.

[0138] The body of a two-piece can is formed by a variety of forming methods, such as DRD forming, DI forming, and DTR forming. DI forming and DTR forming, in particular, involve ironing, and therefore require high formability from the laminated metal sheet before forming. The laminated metal sheet of the present invention has high formability and can be suitably used by any of the above forming methods. Forming into a laminated metal container is carried out by a known method. The laminated metal container can be efficiently formed, for example, by using a can-making machine.

[0139] The laminated metal container may be painted, printed, or wrapped in paper, and is particularly suitable for use as a container that will be subjected to retort sterilization.

[0140] In the above-described embodiment, the laminated metal plate has a front surface, which is the outer surface of the laminated metal container, and a back surface, which is the inner surface. The laminated metal plate can be freely provided depending on the embodiment. For example, the front surface of the metal plate may be the inner surface of the laminated metal container, and the back surface may be the outer surface of the laminated metal container. In this case, the first film may be provided only on the front surface, which is the inner surface of the laminated metal container.

[0141] As described above, the laminated metal sheet according to the present invention can maintain the covering properties of the first film and / or the second film on the metal sheet even after undergoing advanced processing. Furthermore, the laminated metal container according to the present invention can prevent deterioration of appearance due to whitening even after retort sterilization.

[0142] For steps and conditions not described in this specification, conventional methods can be used.

[0143] The present invention will be described in more detail below by way of examples, but the present invention is not necessarily limited thereto.

[0144] (Invention Example 1) A TFS was used as the metal plate. Low-carbon steel with a temper of T3CA and a thickness of 0.22 mm, which had been subjected to cold rolling, annealing, and temper rolling, was used as the base steel for the TFS. The low-carbon steel was degreased, pickled, and then chrome-plated to produce the TFS. The chrome-plated coating weight of the TFS was 120 mg / m2 of metallic chromium in terms of Cr. ２ , chromium hydrate oxide 10 mg / m ２ It was.

[0145] A polyester film containing a first polyester and a second polyester was prepared as film A to be laminated on the front surface of a metal plate. First pellets of copolymerized polyethylene terephthalate, obtained by copolymerizing isophthalic acid and diethylene glycol, were prepared as the raw material for the first polyester. Second pellets of homopolybutylene terephthalate were prepared as the raw material for the second polyester. As an additive, inorganic lubricant masterbatch pellets were prepared, in which 0.8% by mass of silicon oxide was dispersed in homopolyethylene terephthalate. The pellets were dry-blended in the mass ratios shown in Table 1 to form a resin mixture, which was then heated to 150°C under vacuum and dried for 3 hours.

[0146] The dried resin mixture was fed into an extruder and melt-kneaded at 275°C. Next, after passing through a sintered filter to remove foreign matter, the mixture was cooled and solidified on a cast roll with a surface temperature controlled at 30°C 0.45 seconds after being discharged from the T-die to obtain an unstretched film. Next, longitudinal stretching was performed to obtain a stretched film. The stretching temperature was 70°C, and the stretch ratio was 4.0 times. Finally, uneven thickness portions at the widthwise edges of the stretched film were removed with a trimmer, and the stretched film was wound into a roll to obtain Film A with a thickness of 20 μm. The sample standard deviation of the thickness of Film A was 4%.

[0147] A copolymerized polyethylene terephthalate film was prepared as film B to be laminated on the back surface of the metal plate. First pellets consisting of copolymerized polyethylene terephthalate obtained by copolymerizing isophthalic acid and diethylene glycol were prepared as the raw material. As an additive, inorganic lubricant masterbatch pellets were prepared, in which 0.8% by mass of silicon oxide was dispersed in homopolyethylene terephthalate. 95% by mass of copolymerized polyethylene terephthalate resin pellets and 5% by mass of inorganic lubricant masterbatch pellets were dry-blended to form a resin mixture, which was then heated to 150°C under vacuum and dried for 3 hours.

[0148] The dried resin mixture was fed into an extruder and melt-kneaded at 275°C. Next, after passing through a sintered filter to remove foreign matter, the mixture was cooled and solidified on a cast roll with a surface temperature controlled at 30°C 0.45 seconds after being discharged from the T-die to obtain an unstretched film. Next, longitudinal stretching was performed to obtain a stretched film. The stretching temperature was 90°C, and the stretch ratio was 4.5 times. Finally, uneven thickness portions at the widthwise edges of the stretched film were removed with a trimmer, and the film was wound into a roll to obtain Film B with a thickness of 20 μm. The sample standard deviation of the thickness of Film B was 3%.

[0149] Next, the metal plate, film A, and film B were laminated by thermocompression lamination. A pair of laminating rolls was arranged to sandwich the front and back surfaces of the metal plate, with film A arranged between the front surface of the metal plate and the laminating roll on the front surface side, and film B arranged between the back surface of the metal plate and the laminating roll on the back surface side. Lamination was performed by passing the preheated metal plate between the laminating rolls. The preheating temperature of the metal plate was 241°C, film A was 50°C, film B was 80°C, and the temperature of the laminating roll was 80°C.

[0150] The metal plate passed through the laminating roll, and 1.0 second after film A separated from the laminating roll on the front side, tap water heated to 60°C was sprayed onto the metal plate to cool it, yielding a laminated metal plate with the first film and the second film laminated on the front and back sides of the metal plate, respectively. The pressure applied by the laminating roll was adjusted so that the surface temperature of film A side just before cooling (temperature just before cooling) was 198°C. At this time, the pressure applied by the laminating roll was 0.60 MPa.

[0151] (Invention Examples 2 to 6, Comparative Examples 1 to 3) Laminated metal sheets were obtained under the conditions shown in Tables 1 and 2, respectively, for the types, mass ratios, and intrinsic viscosities of the raw materials of the first and second polyesters in Film A, the types and intrinsic viscosities of the raw materials of Film B, the preheating temperature of the metal sheet in the thermocompression bonding step, and the temperature just before cooling. The other conditions were the same as those in Invention Example 1. In Table 1, the "polyester ratio" indicates the mass ratio relative to the total amount of polyester.

[0152] For each example, observation by a scanning probe microscope, measurement of wide-angle X-ray diffraction spectrum, and differential scanning calorimetry were carried out according to the methods described above. The results are shown in Tables 1 and 2.

[0153]

[0154]

[0155] (Primary Adhesion) A sample measuring 120 mm in the conveyance direction and 15 mm in the width direction was cut out from the laminated metal sheet. A portion of the film was peeled off from the edge of the long side of the cut out sample. The peeled film was opened in the opposite direction to the peeling direction (angle: 180°), and a peel test was performed using a tensile tester at a tensile speed of 30 mm / min. The adhesion strength per 15 mm width was evaluated according to the following criteria: ⊚: 10.0 N / 15 mm or more; ◯: 5.0 N / 15 mm or more, less than 10.0 N / 15 mm; ×: less than 5.0 N / 15 mm

[0156] (Adhesion after retort sterilization) A sample measuring 100 mm in the conveyance direction and 30 mm in the plate width direction was cut out from a laminated metal plate. A portion of the film was peeled off from the long side edge of the cut-out sample. The peeled film was opened in the opposite direction to the peeled direction (angle: 180°), and a 100 g weight was fixed thereto, followed by retort sterilization for 25 minutes under pressurized steam at 125°C. The peeled length of the film after retort sterilization was measured and evaluated according to the following criteria: ◎: Less than 2 mm ○: 2 mm or more, less than 10 mm ×: 10 mm or more

[0157] (Appearance after retort sterilization) A sample with a diameter of 48 mm was punched out from the laminated metal sheet. The sample was attached to the bottom of a commercially available 350 mL negative pressure steel can (φ66 mm, height 122.2 mm) using a donut-shaped magnet with an outer diameter of φ50 mm and an inner diameter of φ30 mm. The steel can with the attached sample was subjected to retort sterilization for 10 minutes under pressurized steam at 130°C. After retort sterilization, the sample was removed from the steel can and visually observed for changes in appearance, and evaluated according to the following criteria: ◎: No change in appearance ○: Slight whitening in appearance (area ratio less than 5%) ×: Cloudy appearance (area ratio 5% or more)

[0158] (Processability of Laminated Metal Sheet) After applying paraffin wax to a laminated metal sheet, a sample with a diameter of 123 mm was punched out. The sample was drawn to obtain a shallow-drawn metal container with an inner diameter of 71 mm and a height of 36 mm. The obtained shallow-drawn can was loaded into a DI molding device and subjected to re-drawing and three-stage ironing at a punch speed of 200 mm / s and a stroke of 560 mm, resulting in a total reduction rate of 50%. Finally, a laminated metal container with an inner diameter of 52 mm and a height of 90 mm was obtained. During the DI molding, tap water was circulated at a temperature of 50°C. After can formation, the tear (scratch) area rate of the first film was evaluated according to the following criteria: ⊚: Scratch area rate less than 5%; ◯: Scratch area rate 5% to less than 15%; ×: Scratch area rate 15% or more.

[0159] (Evaluation Results) The evaluation results of the obtained laminated metal sheets of Invention Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 3. In addition, a phase image of a cross section of the first film of Invention Example 1, obtained by observation in dynamic force mode with a scanning probe microscope, is shown in Fig. 2, and a phase image of a cross section of the first film of Comparative Example 1 is shown in Fig. 4.

[0160]

[0161] Inventive Examples 1 to 6 obtained favorable results in the evaluation of primary adhesion, adhesion after retort sterilization, and appearance after retort sterilization. On the other hand, Comparative Examples 1 to 3 experienced deterioration in appearance after retort sterilization. Therefore, it was confirmed that the present invention can provide laminated metal sheets and laminated metal containers that have excellent primary adhesion and adhesion after retort sterilization and do not suffer from deterioration in appearance due to whitening even after retort sterilization. Furthermore, in Inventive Examples 1 to 2, 5, and 6, in which the preheating temperature and wide-angle X-ray diffraction spectrum of the metal sheets were within the preferred ranges, favorable results were obtained in the evaluation of the processability of the laminated metal sheets.

[0162] According to the present invention, it is possible to provide a laminated metal sheet and a method for manufacturing the same, which have excellent primary adhesion and adhesion after retort sterilization treatment and do not suffer from deterioration in appearance due to whitening even after retort sterilization treatment, as well as a laminated metal container using the laminated metal sheet.

[0163] 100 Laminated metal container 10 Laminated metal plate 20 Metal plate 21 Front surface of metal plate 22 Back surface of metal plate 31 First film 32 Second film

Claims

1. A laminated metal sheet comprising a first film laminated on at least one surface of a metal sheet, wherein the first film is a polyester film whose polyester components are composed of a first polyester and a second polyester, wherein the first polyester is composed of one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, and the second polyester is composed of one or both of homopolybutylene terephthalate and copolymer polybutylene terephthalate, and the mass ratio of the first polyester to the second polyester is 20:80 to 50:50, assuming that the total amount of polyester in the first film is 100, and wherein two characteristic widths w1 and w2 calculated from a binarized image of a phase image obtained by observing a cross-section of the first film using a scanning probe microscope in dynamic force mode satisfy the following formulas (1) and (2): 10.0 nm≦w1≦25.0 nm ... (1) 10.0 nm≦w2≦25.0 nm ... (2) However, the threshold value for the binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delay are shown dark, the area % of the dark areas is equal to the mass % of the first polyester relative to the total amount of polyester in the first film, and the characteristic width w1 is a value obtained by dividing the area A1 of the dark areas after the binarization by the length l1 of the thin line obtained by applying a thin line processing to the dark areas, and the characteristic width w2 is a value obtained by dividing the area A2 of the bright areas after the binarization by the length l2 of the thin line obtained by applying a thin line processing to the bright areas.

2. The laminated metal sheet according to claim 1, wherein the wide-angle X-ray diffraction spectrum of at least one of the surfaces of the metal sheet on which the first film is laminated satisfies the following formula (3): I(1) １００ / I(1) ａｍｏｒｐｈｏｕｓ ≦1.5 (3) Here, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by incident X-rays and reflected X-rays is perpendicular to the surface of the first film, and I(1) １００ is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ=26.5±1.0°, and I(1) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

3. The laminated metal sheet according to claim 1 or 2, wherein a second film is laminated on the other surface of the metal sheet, the polyester component of the second film is one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, the highest endothermic peak temperature in a temperature range of 280°C or less is 220°C or higher in a differential scanning calorimetry of the second film, and the wide-angle X-ray diffraction spectrum of the other surface of the metal sheet on which the second film is laminated satisfies the following formula (4). I(2) １００ / I(2) ａｍｏｒｐｈｏｕｓ ≦1.5 (4) Here, the wide-angle X-ray diffraction spectrum is measured by the θ-2θ method using CuKα radiation at a sample angle such that the plane formed by incident X-rays and reflected X-rays is perpendicular to the surface of the second film, and I(2) １００ is the net intensity of the 100 diffraction peak of polyethylene terephthalate appearing at 2θ=26.5±1.0°, and I(2) ａｍｏｒｐｈｏｕｓ is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

4. A method for manufacturing a laminated metal plate, comprising: a step of preheating a metal plate to a preheat temperature of 300°C or less; a subsequent thermocompression bonding step of thermocompression bonding film A to at least one surface of the metal plate using a laminating roll to form a thermocompression-bonded body; and a cooling step of liquid-cooling the thermocompression-bonded body to form a laminated metal plate, wherein the film A is a polyester film whose polyester components are composed of a first polyester and a second polyester, the first polyester is composed of one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, and the second polyester is composed of one or both of homopolybutylene terephthalate and copolymer polybutylene terephthalate, and the mass ratio of the first polyester to the second polyester is 20:80 to 50:50, assuming that the total amount of polyester in the film A is 100, and the surface temperature of the film A in the thermocompression-bonded body immediately before cooling in the cooling step is 205°C or less.

5. A method for manufacturing a laminated metal sheet as described in claim 4, wherein the preheating temperature is -10°C or more and +50°C or less relative to the highest endothermic peak temperature in the temperature range of 280°C or less in a differential scanning calorimetry of said film A.

6. A method for manufacturing a laminated metal plate according to claim 4 or 5, wherein in the thermocompression bonding step, a film B is thermocompression bonded to the other surface of the metal plate, the polyester component of said film B is one or both of homopolyethylene terephthalate and copolymer polyethylene terephthalate, the highest endothermic peak temperature in a temperature range of 280°C or less is 220°C or higher in a differential scanning calorimetry of said film B, and the preheating temperature of said metal plate is -5°C or higher and +60°C or lower relative to the endothermic peak temperature of said film B.

7. A method for manufacturing a laminated metal sheet according to any one of claims 4 to 6, wherein two characteristic widths w'1 and w'2 calculated from a binarized phase image obtained by observing the cross-section of the film A using a dynamic force mode of a scanning probe microscope before the thermocompression bonding step satisfy the following equations (5) and (6): 8.0 nm≦w'1≦17.0 nm ... (5) 8.0 nm≦w'2≦17.0 nm ... (6) However, the threshold value for the binarization is determined by applying the percentile method to the phase delay so that, when areas with small phase delay are shown dark, the area % of the dark areas is equal to the mass % of the first polyester relative to the total amount of polyester in the film A, the characteristic width w'1 is a value obtained by dividing the area A'1 of the dark areas after the binarization by the length l'1 of the thin line obtained by applying a thinning process to the dark areas, and the characteristic width w'2 is a value obtained by dividing the area A'2 of the bright areas after the binarization by the length l'2 of the thin line obtained by applying a thinning process to the bright areas.

8. A laminated metal container comprising the laminated metal sheet according to any one of claims 1 to 3.

Images