Polyester film, polyester film manufacturing method, laminated metal sheet, laminated metal sheet manufacturing method, and laminated metal container

Abstract

Provided are a polyester film and the like that make it possible to achieve stable production that saves energy at every production stage of the film, a laminate metal plate, and a laminate metal container and do not cause degradation of the appearance of the film, even, in particular, after a high-temperature sterilization treatment has been performed. A polyester film according to the present invention contains a first polyester and a second polyester. The first polyester is polyethylene terephthalate or a polyethylene terephthalate copolymer of polyethylene terephthalate and a copolymer component. The second polyester is polybutylene terephthalate or a polyethylene terephthalate copolymer of polybutylene terephthalate and a copolymer component. The ratio, by mass%, of the first polyester and the second polyester is 20:80–50:50, and the net intensity on a direct pole figure satisfies a prescribed condition.

Description

[Technical Field]

[0001] The present invention relates to a polyester film used in a laminated metal sheet, a method for producing a polyester film, a laminated metal sheet, a method for producing a laminated metal sheet, and a laminated metal container. [Background technology]

[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 give them corrosion resistance, durability, weather resistance, etc.

[0003] Baking metal sheets is complicated and requires a long processing time. Furthermore, a large amount of solvent is emitted when painting metal sheets. Therefore, laminated metal sheets, in which a thermoplastic resin film is laminated to a metal sheet, are used as an alternative to painted metal sheets.

[0004] Thermoplastic resin films used in laminated metal sheets include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and the like.

[0005] These thermoplastic resin films are required to have adhesion between the thermoplastic resin film and the metal plate when formed into a laminated metal plate, corrosion resistance, and container formability when the laminated metal plate is formed into a container.

[0006] Laminated metal containers, which are containers formed from laminated metal sheets, are also used for food cans. Such laminated metal containers are subjected to high-temperature sterilization treatments such as retort sterilization. When a thermoplastic resin film is placed in a high-temperature sterilization environment, minute bubbles may form inside the film. Because bubbles have the property of scattering light, thermoplastic resin films containing bubbles tend to become cloudy and lose their appearance.

[0007] Attempts have been made to suppress discoloration of such thermoplastic resin films. For example, Patent Documents 1 and 2 disclose biaxially oriented polyester films containing a polyester mainly composed of polyethylene terephthalate and a polyester mainly composed of polybutylene terephthalate in a specific ratio.

[0008] From the viewpoint of the stretching method, methods for producing polyester films can be classified into non-stretching and multi-stage stretching including longitudinal uniaxial stretching, transverse uniaxial stretching, sequential biaxial stretching, simultaneous biaxial stretching, and longitudinal re-stretching.

[0009] The advantage of the non-stretching method is that the equipment is cheaper than other stretching methods, while the disadvantage of the non-stretching method is that the productivity and the precision of the thickness of the produced polyester film are inferior to other stretching methods.

[0010] The advantage of longitudinal uniaxial stretching is that the equipment is relatively inexpensive compared to other stretching methods, while the disadvantage of longitudinal uniaxial stretching is that anisotropy occurs when forming into a laminated metal container due to the uniaxial orientation.

[0011] There are no notable advantages to uniaxial transverse stretching for laminated metal container films. Disadvantages of uniaxial transverse stretching include the relatively high cost of equipment compared to other stretching methods, and the fact that uniaxial orientation can lead to anisotropy during molding into laminated metal containers.

[0012] The advantages of sequential biaxial stretching include productivity, precision in the thickness of the produced polyester film, and superior in-plane isotropy of the produced polyester film compared to other stretching methods. The disadvantage of sequential biaxial stretching is that the equipment required is more expensive than other stretching methods.

[0013] The advantage of simultaneous biaxial stretching is that the in-plane isotropy of the produced polyester film is superior to that of other stretching methods, while the disadvantage of simultaneous biaxial stretching is that the equipment required is much more expensive than that of other stretching methods.

[0014] For films for laminated metal containers, multistage stretching such as longitudinal re-stretching has no notable advantages. Disadvantages of multistage stretching such as longitudinal re-stretching include the fact that the equipment is more expensive than other stretching methods and that it is not suitable for polyester films for laminated metal containers, considering that it strengthens the orientation of the polyester film.

[0015] In view of the above advantages and disadvantages, most of the thermoplastic resin films used in laminated metal containers are produced by sequential biaxial stretching.

[0016] In addition, the non-stretching method is often used to produce polyester films because it can reduce equipment costs, does not require a large-scale heating furnace, and is more energy-efficient than other stretching methods. Such polyester films are disclosed, for example, in Patent Document 3.

[0017] From the same viewpoint, polyester films are produced by longitudinal uniaxial stretching, as disclosed in Patent Document 4, for example. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Application Publication No. 10-110046 [Patent Document 2] Japanese Patent Application Publication No. 6-155660 [Patent Document 3] International Publication No. 2015 / 012222 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-279902 Summary of the Invention [Problem to be solved by the invention]

[0019] As described above, thermoplastic resin films are required to have adhesion between the thermoplastic resin film and a metal plate before and after high-temperature sterilization, to suppress discoloration of the thermoplastic resin film when subjected to high-temperature sterilization, and to be moldable into containers using laminated metal plates. Furthermore, non-stretched films and longitudinally uniaxially stretched films have been proposed as energy-saving polyester films that satisfy these requirements and do not require a large-scale heating furnace.

[0020] However, for the non-oriented polyester film disclosed in Patent Document 3, only an extrusion coating method in which a film extruded from a T-die of an extruder is directly thermocompressed onto a metal plate is described as an example. Furthermore, it is stated that a method in which the extruded film is once wound up and then separately laminated is inferior in terms of thinning, productivity, and handleability, and as can be seen from this, in practice, industrial production by methods other than extrusion coating is difficult.

[0021] On the other hand, in the extrusion coating method, the laminating equipment and the extruder are synchronized for production, so the production volume is limited by the extrusion volume from the T-die, and productivity is inferior to methods in which a film extruded from a wide die or stretched laterally is separately laminated after slitting. Another issue is that the laminating equipment must also be stopped when changing the resin type in the extruder.

[0022] Patent Document 4 discloses a method for producing a polyester film in which the film is longitudinally stretched at a temperature 80 to 100°C higher than the glass transition temperature of a polyester mainly composed of polybutylene terephthalate, and then the tension is released without heat setting to relieve internal stress. However, when the film is longitudinally stretched at a temperature 30°C or higher than the glass transition temperature, the softened polyester film tends to stick to the roll, making stable production difficult.

[0023] The present invention has been made in consideration of the above-mentioned problems. Specifically, it is an object of the present invention to provide a polyester film, a laminated metal sheet, and a laminated metal container that do not deteriorate in appearance even when subjected to high-temperature sterilization treatment such as retort sterilization, which is necessary for food cans and beverage cans. Another object of the present invention is to provide a method for producing a laminated metal sheet that can stably produce the film, laminated metal sheet, and laminated metal container with low energy consumption at all production stages. [Means for solving the problem]

[0024] In order to solve the above problems, the present invention has the following features.

[0025] [1] A polyester film containing a first polyester containing polyethylene terephthalate as a component and a second polyester containing polybutylene terephthalate as a component, the first polyester is polyethylene terephthalate or a polyethylene terephthalate copolymer containing polyethylene terephthalate and a copolymer component, polyethylene terephthalate; the second polyester is polybutylene terephthalate or a copolymer of polybutylene terephthalate and a copolymer of polybutylene terephthalate, a ratio of the first polyester to the second polyester is 20:80 to 50:50 on a mass % basis, A polyester film having a pole figure net strength that satisfies the following formulas (1) and (2):

number

number

[10] [8] or [9], a manufacturing method of a laminated metal sheet, a thermocompression bonding step of thermocompressing a preheated metal plate and the polyester film using a laminating roll to form a thermocompression bonded body; and a water cooling step of water-cooling the thermocompression-bonded body within 7 seconds after the thermocompression bonding, The method for manufacturing the laminated metal plate, wherein in the thermocompression bonding step, the polyester film and the metal plate are preheated to a temperature range of -20°C to +50°C of the melting point of the polyester film before thermocompression bonding is performed.

[11] A laminated metal container containing the laminated metal sheet described in [8] or [9] as a material. [Effects of the Invention]

[0026] The present invention provides a polyester film, a laminated metal sheet, and a laminated metal container that do not deteriorate in appearance even when subjected to high-temperature sterilization such as retort sterilization, which is particularly necessary for food cans and beverage cans. It also provides a method for producing a laminated metal sheet that can stably produce the film, the laminated metal sheet, and the laminated metal container with low energy consumption at any stage of production. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is an explanatory diagram of a laminated metal container. [Figure 2] This is a pole figure of a polyester film with a diffraction intensity of 100. [Figure 3] 010 diffraction intensity of the polyester film pole figure. [Figure 4] FIG. 1 is a flow diagram showing a method for producing a polyester film. [Figure 5] FIG. 2 is a flow chart showing a method for manufacturing a laminated metal sheet. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a laminated metal container. As shown in FIG. 1, the laminated metal container 100 is formed in the shape of a container with a bottom and has a lid that closes the container. The laminated metal container 100 is used, for example, for food cans, beverage cans, 18L cans, etc. An enlarged cross section of the wall of the laminated metal container 100 is shown on the right side of FIG. 1.

[0029] The laminated metal container 100 is not particularly limited and may be either a three-piece can formed by joining three members, a lid member, a body member, and a bottom member, or a two-piece can formed by joining two members, a lid member and a body member. Note that the laminated metal container 100 is not limited to a can, and may have an opening at one end of the body member, for example.

[0030] As shown in the enlarged cross-sectional view of Figure 1, the laminated metal container 100 includes a laminated metal plate 10 as a material. The laminated metal plate 10 has a metal plate 20 having a surface 21 that is the outer wall of the laminated metal container 100 and a back surface 22 that is the inner wall of the laminated metal container 100. The laminated metal plate 10 has a polyester film 30 bonded to at least one of the surface 21 and the back surface 22 of the metal plate 20. In Figure 1, the polyester film 30 is provided so as to cover the surface 21 of the metal plate 20.

[0031] The metal plate 20 is not particularly limited, but may be an aluminum plate or a steel plate, which are widely used as materials for metal containers, or these that have been subjected to various surface treatments. 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.

[0032] 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 100, 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 overaged as necessary. Furthermore, the steel sheet that serves as the base steel of the TFS may be subjected to secondary cold rolling.

[0033] 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.

[0034] 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 100. For example, the yield point of the steel sheet is preferably in the range of 220 to 580 MPa, the Lankford value is preferably 0.8 or more, and the absolute value of the in-plane anisotropy of the Lankford value is preferably 0.7 or less. There are no particular limitations on the deposition amounts of the metal chromium layer and chromium hydrate oxide layer of the TFS, but from the viewpoint of film adhesion and corrosion resistance, the metal chromium layer should be 50 to 200 mg / m2 in terms of Cr. 2 , chromium hydrate oxide layer is 3 to 30 mg / m 2 The range is preferred. The thickness of the metal plate is not particularly limited, but is preferably in the range of 0.10 to 0.35 mm from the viewpoint of formability into a laminated metal container and strength as a metal container.

[0035] The polyester film 30 contains a first polyester containing polyethylene terephthalate as a component, and a second polyester containing polybutylene terephthalate as a component.

[0036] The first polyester may be polyethylene terephthalate or a copolymer of polyethylene terephthalate and a copolymer component. When the first polyester is a polyethylene terephthalate copolymer, the content of the copolymer component is preferably 15 mol% or less, more preferably 1 to 14 mol%, and even more preferably 3 to 8 mol%.

[0037] 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.

[0038] 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.

[0039] The copolymerization component of the first polyester may be one of the above or two or more thereof.

[0040] It is preferable to use isophthalic acid as a copolymerization component from the viewpoints of ease of forming the polyester film 30 and adhesion to a metal sheet. When isophthalic acid is used as a copolymerization component, the content of isophthalic acid in the copolymer is preferably 1 to 15 mol%, more preferably 3 to 14 mol%, and particularly preferably 3 to 8 mol%.

[0041] The intrinsic viscosity of the first polyester is preferably in the range of 0.65 to 1.00 dL / g. If the intrinsic viscosity is 0.65 dL / g or more, the formability of the laminated metal sheet is better. If the intrinsic viscosity is 1.00 dL / g or less, energy consumption in the polymerization step and extrusion step can be more effectively reduced.

[0042] The second polyester can be polybutylene terephthalate or a copolymer of polybutylene terephthalate and a copolymer component. The second polyester is most preferably homopolybutylene terephthalate. When the second polyester is a polybutylene terephthalate copolymer, the content of the copolymer component in the copolymer is preferably 15 mol% or less, more preferably 10 mol% or less.

[0043] If the ratio of the copolymerization component in the copolymer is 15 mol % or less, a better crystallization rate can be obtained, and deterioration of the appearance of the polyester film 30 during retort sterilization treatment can be more effectively suppressed.

[0044] The copolymerization components of the second polyester can be the acid component and alcohol component described for the first polyester. Ethylene glycol, 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 of these, or two or more of them.

[0045] The second polyester preferably has an intrinsic viscosity of 0.75 to 1.30 dL / g. If the intrinsic viscosity is 0.75 dL / g or more, the formability of the laminated metal sheet is better. If the intrinsic viscosity is 1.30 dL / g or less, energy consumption in the polymerization step and extrusion step can be further reduced.

[0046] In the polyester film 30, the content ratio of the first polyester to the second polyester is 20:80 to 50:50 by mass. The content ratio of the first polyester is preferably 30% or more. The content ratio of the first polyester is preferably 45% or less. The content ratio of the first polyester to the second polyester is more preferably 30:70 to 45:55.

[0047] If the content of the first polyester in the polyester film 30 exceeds 50% by mass, the crystallization rate decreases, and the appearance of the film tends to deteriorate during retort sterilization. If the content of the first polyester is less than 20% by mass, the adhesion between the metal plate 20 and the polyester film 30 tends to decrease. Therefore, there is a risk that the polyester film 30 will peel off from the metal plate 20 when it is formed into the laminated metal container 100 or during retort sterilization.

[0048] The polyester film 30 preferably has at least one melting peak temperature of 200 to 230° C. The melting peak temperature is the peak temperature of an endothermic peak when the film is heated from −50° C. to 290° C. at a rate of 10° C. / min in differential scanning calorimetry (DSC).

[0049] If at least one melting peak temperature is 200°C or higher, the polyester film exhibits better heat resistance. If at least one melting peak temperature is 230°C or lower, energy consumption during polyester film production and deterioration of the polyester film's appearance during retort sterilization can be more effectively suppressed.

[0050] In addition to the first polyester and the second polyester, additives such as antioxidants, inorganic lubricants, organic lubricants, crystal nucleating agents, heat stabilizers, antistatic agents, coloring pigments, etc. may be added to the polyester film 30. In particular, to improve heat resistance, it is preferable to add antioxidants in an amount of 0.0001% by mass to 1.0000% by mass.

[0051] The antioxidant is not particularly limited, but known antioxidants classified into hindered phenols, hydrazines, phosphites, etc. can be used.

[0052] In order to improve the handleability of the polyester film 30, it is preferable that the polyester film contains an inorganic lubricant in an amount of 0.01 to 0.50% by mass based on the total mass of the polyester film.

[0053] The polyester film 30 may be formed of multiple layers. The polyester film 30 may be formed by any of the known methods, such as co-extrusion using a feed block or multi-manifold, laminating multiple films together, or laminating a molten resin directly onto a film. From the viewpoints of productivity and energy conservation, it is desirable to use the co-extrusion method for forming the polyester film 30.

[0054] When the polyester film 30 is formed as a multi-layer structure, the outermost layer preferably contains 0.01 to 0.50% by mass of an inorganic lubricant. For example, when the polyester film 30 is formed of three layers, it is recommended that an additive such as an inorganic lubricant be blended in the outermost layer. By blending the additive only in the outermost layer, the amount of additive added can be reduced.

[0055] The inorganic lubricant is not particularly limited, but known inorganic lubricants such as silicon oxide, diatomaceous earth, and talc can be used.

[0056] To improve the formability of the laminated metal container 100, the organic lubricant is preferably contained in an amount of 0.01 to 1.00 mass % of the entire polyester film 30. When the polyester film 30 is formed into a layered structure consisting of multiple layers, the organic lubricant is preferably contained in the outermost layer in an amount of 0.01 to 1.00 mass %.

[0057] The organic lubricant is not particularly limited, but known organic lubricants such as carnauba wax, polyolefin wax, and modified polyolefin wax can be used.

[0058] Fig. 2 is a pole figure of polyester film 30 with a diffraction intensity of 100. Fig. 3 is a pole figure of polyester film 30 with a diffraction intensity of 010. For polyester film 30, the net strength of the pole figures shown in Figs. 2 and 3 satisfies the following formulas (1) and (2).

[0059]

number

[0060] I 100 (60,0) is the net intensity at α=60° and β=0° in a pole figure with 100 diffraction intensities. 100 (60,0) is shown in FIG. 2 as a hatched dot.

[0061] I 100 (60,90) is the net intensity at α=60° and β=90° in a pole figure with 100 diffraction intensities. I 100 (60,90) are indicated by black dots in FIG.

[0062] I 010 (50,0) is the net intensity at α=50° and β=0° in the pole figure of the 010 diffraction intensity. 010 (50,0) is shown as a hatched dot in FIG.

[0063] I 010 (50,90) is the net intensity at α=50° and β=90° in the pole figure of the 010 diffraction intensity. 010 (50,90) are indicated by black dots in FIG.

[0064] The net intensity of the pole figure is the diffraction intensity obtained by subtracting the diffraction intensity of the point with the lowest diffraction intensity at α=15° from the diffraction intensity of each point in each pole figure (FIGS. 2 and 3).

[0065] I100 (60,0) , I 100 (60,90) represents the ratio of the (100) plane of the first polyester, i.e., the aromatic ring plane, facing β=0° and 90°, respectively.

[0066] I 100 (60,0) / I 100 (60,90) is 0.20 or more and 0.60 or less, and preferably 0.40 or more and 0.50 or less. 100 (60,0) / I 100 (60,90) By setting the ratio to be 0.20 or more and 0.60 or less, it is possible to improve the thickness uniformity of the polyester film 30. Furthermore, it is possible to suppress the thermal shrinkage of the polyester film 30 in the width direction when the film 30 is laminated to the metal plate 20, and it is possible to improve the tensile stability of the film 30 in the longitudinal direction.

[0067] On the other hand, I 100 (60,0) / I 100 (60,90) If the ratio is less than 0.20, the polyester film 30 tends to shrink in the width direction of the metal plate 20 when laminated to the metal plate 20. As a result, the tension of the polyester film 30 in the longitudinal direction of the metal plate 20 tends to become unstable.

[0068] Also, I 100 (60,0) / I 100 (60,90) If the stretch ratio is larger than 0.60, the stretching ratio of the polyester film 30 is small, and the thickness uniformity of the polyester film 30 tends to be impaired.

[0069] I 010 (50,0) , I 010 (50,90) represents the ratio of the first polyester's

[0010] direction to β=0° and 90°, respectively. 010 (50,0) / I 010 (50,90) is 0.30 or more and 0.85 or less, and preferably 0.50 or more and 0.80 or less. 010 (50,0) / I 010 (50,90) By setting the ratio to be 0.30 or more and 0.85 or less, it is possible to improve the thickness uniformity of the polyester film 30. Furthermore, when the polyester film 30 is laminated on the metal plate 20, it is possible to suppress thermal shrinkage of the polyester film 30 in the width direction of the metal plate 20. Therefore, it is possible to prevent the tension of the polyester film 30 in the longitudinal direction of the metal plate 20 from becoming unstable.

[0070] I 010 (50,0) / I 010 (50,90) If the elongation ratio is less than 0.30, the polyester film 30 tends to shrink in the width direction of the metal plate 20 when laminated onto the metal plate 20. Furthermore, the tension of the polyester film 30 in the longitudinal direction of the metal plate 20 tends to become unstable when laminated onto the metal plate 20.

[0071] Also, I 010 (50,0) / I 010 (50,90) If is greater than 0.85, the stretching ratio is small, and the thickness uniformity of the polyester film 30 decreases.

[0072] The polyester film of the present invention preferably has a sample standard deviation of thickness measured in the direction of incident X-rays when β=0° in a pole figure of 10% or less, more preferably 1% or less, of the average film thickness.

[0073] The thickness of the polyester film 30 is a value obtained by calculating the sample standard deviation and average of thicknesses measured at 1,000 points over 1,000 m in the direction of β=0° at 1 mm intervals using a constant pressure thickness gauge.

[0074] The direction of β=0° corresponds to the stretching direction of the polyester film 30. When the sample standard deviation of the thickness of the polyester film 30 is 10% or less of the average thickness of the polyester film 30, the polyester film 30 has been stretched to an elongation exceeding the range of neck stretching.

[0075] By making the polyester film 30 have such a thickness, stiffness is imparted to the polyester film 30, improving the handleability of the polyester film 30. Furthermore, when the polyester film 30 is laminated onto the metal plate 20, the tensile stability of the polyester film 30 in the longitudinal direction of the metal plate 20 can be improved. In addition, when the laminated metal plate 10 is formed into the laminated metal container 100, breakage of the polyester film 30 or the metal plate 20 can be suppressed.

[0076] The average thickness of the polyester film 30 is preferably 8 to 50 μm, more preferably 10 to 30 μm, and even more preferably 11 to 20 μm.

[0077] If the average thickness of the polyester film 30 is 8 μm or more, even when the laminated metal plate 10 is formed into a laminated metal container 100, better corrosion resistance can be ensured.

[0078] If the average thickness of the polyester film 30 is 50 μm or less, a more excellent energy saving effect can be obtained in the film production.

[0079] (Method for Producing Polyester Film) Next, a method for producing the polyester film 30 will be described below. FIG. 4 shows a production flow for the polyester film 30. As shown in FIG. 4, the method for producing the polyester film 30 involves a non-stretched film production step (step S101) in which an extruder is used to obtain a non-stretched film from a resin composition. Next, a longitudinal uniaxially stretched film production step (step S102) is carried out in which the non-stretched film is longitudinally stretched to obtain a longitudinal uniaxially stretched film. This is followed by a heat setting step (step S103) in which the longitudinal uniaxially stretched film is heated and heat set, thereby producing the polyester film 30.

[0080] In the non-stretched film production process in step S101, the first polyester and the second polyester are essential raw materials, to which additives such as antioxidants, inorganic lubricants, organic lubricants, crystal nucleating agents, heat stabilizers, antistatic agents, and coloring pigments may be added.

[0081] The raw material contains the first polyester and the second polyester in a ratio of 20:80 to 50:50 by mass. The content of the first polyester in the raw material is preferably 30% or more. The content of the first polyester is preferably 45% or less. The content ratio of the first polyester to the second polyester is more preferably 30:70 to 45:55.

[0082] These raw materials and a masterbatch in which additives such as the inorganic lubricant are dispersed in a resin are mixed in the form of pellets or the like, for example, by dry blending, to produce a resin mixture. The resin mixture is dried with hot air or under vacuum as necessary, and then fed to an extruder.

[0083] The first polyester and the second polyester are heated to or above their melting points in an extruder to melt. After foreign matter and modified resins are removed from the molten resin composition using a filter, the resin composition is fed to a T-die via a gear pump and extruded from the T-die. The resin composition is formed into a sheet when extruded from the T-die.

[0084] Here, when the polyester film 30 is formed of multiple layers, for example, a co-extrusion method can be used to laminate the multiple layers into a single polyester film 30. 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.

[0085] The molten resin composition extruded from the T-die is cooled and solidified by a cooling device such as a casting roll to form an unstretched polyester film (hereinafter also referred to as an unstretched film). When the molten resin composition is cooled and solidified, electrostatic pinning, a vacuum chamber, or the like is preferably used. The use of such equipment can improve the adhesion between the casting roll or the like and the resin composition, thereby producing a homogeneous unstretched film.

[0086] The longitudinal uniaxially stretched film preparation process in step S102 is performed by longitudinal stretching using a longitudinal uniaxial stretching machine equipped with a preheating roll and a stretching roll. Specifically, the unstretched film is heated to a predetermined temperature when passing through the preheating roll. The difference in peripheral speed between the preheating roll and the immediately preceding roll is preferably less than 2%.

[0087] The unstretched film is heated to a predetermined temperature by the preheating rolls and then stretched in the longitudinal direction between the stretching rolls and the final preheating roll immediately before the stretching rolls. The difference in peripheral speed between the stretching roll and the final preheating roll is preferably 50% or more.

[0088] In addition to the preheating rolls, an infrared heater may be used to raise the temperature of the unstretched film. For example, an infrared heater may be installed between the final preheating roll, which is the preheating roll closest to the stretching roll, and the stretching roll. By raising the temperature of the unstretched film with the infrared heater, the temperature of the final preheating roll can be lowered.

[0089] By setting the final preheating roll temperature to a low value in this manner, it is possible to suppress adhesion of the unstretched film to the preheating roll. Note that the longitudinal uniaxial stretching may be performed in multiple stages by providing multiple stretching rolls.

[0090] The stretching temperature in the longitudinal uniaxially stretched film production process is the maximum temperature of the film in the section between the final preheating roll and the stretching roll. The longitudinal uniaxially stretched film production process is carried out at a stretching temperature of 50°C or higher and 80°C or lower. The stretching temperature is preferably 60°C or higher. Also, the stretching temperature is preferably 75°C or lower. The stretching temperature is more preferably 60°C or higher and 75°C or lower.

[0091] If the stretching temperature is 50°C or higher, the film's breaking elongation increases, preventing excessive crystallization and reducing transparency. If the stretching temperature is 80°C or lower, the yield plateau in the stress-strain curve narrows, which tends to improve the thickness uniformity of the longitudinally uniaxially stretched film.

[0092] The stretching ratio of the longitudinal stretching is 3.0 times or more and 7.0 times or less. The stretching ratio of the longitudinal stretching is preferably 4.0 times or more. The stretching ratio of the longitudinal stretching is preferably 5.0 times or less. The stretching ratio of the longitudinal stretching is more preferably 4.0 times or more and 5.0 times or less. The stretching ratio of the longitudinal stretching can be expressed as the ratio of the conveying speed at the outlet side to the conveying speed at the inlet side of the longitudinal stretching machine.

[0093] When the stretching ratio is less than 3.0 times, I 010 (50,0) / I 010 (50,90) If the stretching ratio is greater than 7.0, I 010 (50,0) / I 010 (50,90) If the stretching ratio is greater than 7.0, the film tends to break easily during stretching.

[0094] The longitudinal uniaxially stretched film production process is carried out at a final preheating roll temperature of 40°C or higher and 80°C or lower. The final preheating roll temperature is preferably 60°C or higher. Also, the final preheating roll temperature is preferably 75°C or lower. The final preheating roll temperature is more preferably 60°C or higher and 75°C or lower.

[0095] If the final preheat roll temperature is less than 40°C, the polyester film may be stretched at a temperature lower than the glass transition point, and the resin composition film may tend to break easily during stretching.

[0096] If the temperature of the final preheating roll is higher than 80°C, the longitudinally uniaxially stretched film will stick to the roll, reducing productivity and tending to degrade the thickness accuracy of the longitudinally uniaxially stretched film.

[0097] The heat setting step in step S103 is an optional step. The heat setting is preferably performed by heating the polyester film 30 at a temperature that is at least 5°C higher than the final preheat roll temperature during stretching and at least 50°C lower than the melting point of the polyester film 30. The heat setting is preferably performed by heating the polyester film 30 at a temperature that is at least 5°C higher than the stretching temperature and at least 50°C lower than the melting point of the polyester film 30.

[0098] The longitudinally uniaxially stretched film can also be heated using a heated roll, similar to the preheating in the longitudinal stretching. In this case, it is preferable to preheat the roll to a temperature that is 5°C or more higher than the final preheating roll temperature during stretching, but lower than 110°C. It is possible to suppress adhesion of the longitudinally uniaxially stretched film to the roll.

[0099] During heat setting, the longitudinally uniaxially stretched film may be relaxed in the machine direction. The relaxation rate of the longitudinally uniaxially stretched film is preferably 0.5% or more and 5% or less. The longitudinally uniaxially stretched film may be relaxed using a pair of rolls with different peripheral speeds, but more preferably in multiple stages using multiple pairs of rolls.

[0100] By carrying out the heat setting step in step S103, residual stress due to stretching can be alleviated and stiffness can be imparted to the longitudinally uniaxially stretched film by thermal crystallization.

[0101] (Method for manufacturing laminated metal sheets) A method for manufacturing the laminated metal sheet 10 will now be described. Fig. 5 shows a manufacturing flow of the laminated metal sheet 10. As shown in Fig. 5, a metal sheet 20 and a polyester film 30 are thermocompression-bonded using a laminating roll to produce a thermocompression-bonded body (step S201).

[0102] In the thermocompression bonding step of step S201, a polyester film 30 is laminated onto at least one of the front surface 21 and the back surface 22 of the metal plate 20.

[0103] The thermocompression bonding step in step S201 is performed by placing the polyester film 30 between the metal plate 20, which has been preheated to a predetermined temperature, and a laminating roll, and pressing the polyester film 30 against the metal plate 20 with the laminating roll. At this time, the polyester film 30 is melted by the heat of the metal plate 20 and is pressure-bonded to the metal plate 20.

[0104] The metal plate 20 is preheated at a temperature between -20°C and +50°C below the melting point of the polyester film 30. Preferably, the preheating is performed at a temperature equal to or higher than the melting point of the polyester film 30. Also, the preheating is preferably performed at a temperature equal to or lower than +30°C below the melting point of the polyester film 30. More preferably, the preheating is performed at a temperature between the melting point of the polyester film 30 and +30°C above the melting point.

[0105] If the metal plate 20 is preheated to a temperature lower than -20°C, which is the melting point of the polyester film 30, the polyester film 30 may not melt and may not be able to adhere to the metal plate 20. If the metal plate 20 is preheated to a temperature higher than +50°C, which is the melting point of the polyester film 30, the polyester film 30 in contact with the laminating roll may melt, deteriorating the appearance. Also, the polyester film 30 may adhere to the laminating roll, reducing productivity.

[0106] The polyester film 30 used in the thermocompression bonding step of step S201 may be preheated. In this case, the heating temperature of the polyester film 30 should be 150° C. or less. Heating the polyester film 30 within this temperature range allows the polyester film 30 to be transported smoothly and also allows the preheating temperature of the metal plate 20 to be lowered.

[0107] The pressure applied by the laminating roll is preferably 0.35 to 1.50 MPa. If the pressure applied by the laminating roll is 0.35 MPa or more, better adhesion between the metal sheet 20 and the polyester film 30 can be obtained, and the appearance of the laminated metal sheet 10 can also be improved.

[0108] If the pressure of the laminating roll is 1.50 MPa or less, heat transfer from the metal plate 20 to the laminating roll is further suppressed, and the energy consumed during production can be further reduced. Furthermore, under these conditions, wear on the laminating roll is also further suppressed.

[0109] The laminating roll is preferably heated to a temperature between −30° C. and +40° C., which is the glass transition point of the polyester film 30. By heating the laminating roll, spontaneous temperature rise due to heat input from the metal plate can be alleviated, and the amount of crystals on the surface of the polyester film 30 can be easily controlled.

[0110] The thermocompression-bonded body, which is the laminated metal plate after thermocompression bonding, is water-cooled (step S202) within 7 seconds after the thermocompression bonding in step 201. The water-cooling step in step S202 is performed by spraying water onto the thermocompression-bonded body or by immersing the thermocompression-bonded body in water.

[0111] The cooling water used in the water-cooling step of step S202 may be heated for operational stability. The temperature of the cooling water is preferably the glass transition point of the polyester film 30 + 40°C or less.

[0112] After water cooling, the thermocompression-bonded body has the cooling water removed by a squeeze roll. The thermocompression-bonded body is subjected to post-heating treatment and oiling treatment as necessary. The thermocompression-bonded body is inspected for surface defects, internal defects, plate thickness, etc., and then wound into a coil by, for example, a tension reel. The thermocompression-bonded body may be slit or sheared to form a sheet-like product.

[0113] 1, the surface of the metal plate 20 laminated with the polyester film 30 should be positioned on the surface 21 of the laminated metal container 100. The metal plate 20 is cast and rolled to a predetermined thickness and width, and then subjected to surface treatment such as annealing, temper rolling, or plating as necessary.

[0114] The laminated metal sheet 10 thus produced preferably has a wide-angle X-ray diffraction spectrum that satisfies the following formula (3).

number

[0115] However, the wide-angle X-ray diffraction spectrum was measured by the θ-2θ method using CuKα radiation at sample angles of α = 90° and β = 0° in the pole figure. 100 (90,0) is the net intensity of the 100 diffraction peak appearing at 2θ = 24.0 ± 1.0°. amorphous (90,0) is the net intensity of the amorphous halo appearing at 2θ=20±5°.

[0116] If no clear peak appears at 2θ = 24.0 ± 1.0°, the maximum net strength in the range of 2θ = 23.0 to 25.0° is used as I 100 (90,0) The net intensity of a wide-angle X-ray diffraction spectrum is the diffraction intensity at each 2θ minus the background intensity, which is represented by the straight line connecting the diffraction intensity at 2θ=10° and the diffraction intensity at 2θ=30°.

[0117] When the wide-angle X-ray diffraction spectrum of the laminated metal plate 10 satisfies formula (3), the oriented crystals generated by stretching are amorphized by the heat applied during lamination, improving the formability of the polyester film 30. As a result, breakage of the polyester film during molding into the laminated metal container 100 and deterioration of the corrosion resistance of the polyester film can be suppressed. By producing the laminated metal plate 10 in this manner, the laminated metal container 100 can be produced more stably and with less energy consumption.

[0118] If the thermocompression-bonded body is air-cooled without performing the water-cooling step in step S202, or if the time from thermocompression bonding in step S202 to water-cooling exceeds 7 seconds, thermal crystallization of the polyester film 30 will proceed, making it difficult to control the wide-angle X-ray diffraction spectrum of the laminated metal sheet 10 within the range specified in the present invention.

[0119] As described above, by performing the thermocompression bonding step of step S201 using the above-mentioned thermocompression lamination method, it is possible to improve the adhesion between the polyester film 30 and the metal plate 20 in a high-temperature environment. This also makes it possible to produce the laminated metal plate 10 in an energy-saving manner. Specifically, it is possible to satisfy the requirements for adhesion between the polyester film 30 and the metal plate 20 before and after high-temperature sterilization treatment, suppression of discoloration of the polyester film 30 when high-temperature sterilization treatment is performed, and container formability.

[0120] Furthermore, the laminated metal sheet 10 laminated with the polyester film 30 so that its wide-angle X-ray diffraction spectrum has the above-mentioned diffraction intensity distribution can improve the processability of the resin layer. Therefore, when the laminated metal sheet 10 is molded into the laminated metal container 100, it can be molded stably and energy-savingly. Therefore, it can be more suitably used as the laminated metal sheet 10 for the laminated metal container 100.

[0121] The laminating equipment in which the thermocompression bonding step of step S201 is performed may be provided behind a continuous annealing line, a plating line, etc. By providing the laminating equipment in such a position, productivity can be improved.

[0122] Furthermore, a thermoplastic resin film different from the polyester film 30 may be provided on the back surface 22 of the metal plate 20, or a coating or the like may be applied. When a thermoplastic resin film different from the polyester film 30 is provided on the back surface 22 of the metal plate 20, the film may be provided at any timing. For example, the film may be provided by lamination at the same time as the polyester film 30.

[0123] Furthermore, the polyester film 30 may be provided on the metal plate 20 via an adhesive (not shown). By providing the polyester film 30 via an adhesive in this manner, the temperature for thermocompression bonding can be lowered, and the adhesion between the polyester film 30 and the metal plate 20 can be improved.

[0124] Examples of adhesives include polyester resins, alkyd resins, epoxy resins, acrylic resins, phenolic resins, polyurethane resins, polyamine resins, polyamidoamine resins, polyamide resins, etc., and these can be used alone or in combination of two or more. Additives can be added to the adhesive as needed.

[0125] (Method for manufacturing laminated metal containers) A laminated metal container 100 is formed by using a laminated metal sheet 10 for at least one of the multiple components that make up the laminated metal container 100. As described above, examples of the laminated metal container 100 include a three-piece can made up of three components and a two-piece can made up of two components.

[0126] For example, the body of a two-piece can is formed by a variety of forming methods, such as Draw and Redraw (DRD), Draw and Ironing (DI), and Draw and Thin Redraw (DTR).

[0127] DI forming and DTR forming are forming methods that involve ironing, and therefore require particular workability. The laminated metal sheet 10 has high formability and can be suitably used in any of the above forming methods.

[0128] The laminated metal container 100 may be painted or printed. Various laminated metal containers 100 can be formed by various known methods. The laminated metal container 100 can be formed, for example, by using a can manufacturing machine.

[0129] The laminated metal container 100 can be suitably used as a container that is particularly subjected to retort sterilization. [Example]

[0130] EXAMPLES The present invention will be described in more detail below with reference to examples, but is not necessarily limited thereto. Polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were prepared.

[0131] Example 1 As raw resins for the polyester film, pellets of a PET copolymer, pellets of homo-PBT, and an inorganic lubricant masterbatch were prepared.

[0132] The PET copolymer contains 5 mol% isophthalic acid and 3 mol% diethylene glycol as copolymerization components and has a melting point of 245°C. Homo PBT has a melting point of 224°C. The inorganic lubricant used was silicon dioxide dispersed in PET with a melting point of 254°C.

[0133] The pellets were blended so that the mass ratio of the total PET to the PBT was 40:60 and the silicon dioxide concentration was 0.04% relative to the total amount of PET and PBT. The pellets were then heated to 150°C under vacuum to remove moisture and dried for 3 hours. The dried pellets were then placed in a single-screw extruder and melt-kneaded at 275°C.

[0134] Next, after passing the mixture through a sintered filter with a 25 μm cutoff to remove foreign matter, the mixture was discharged from a T-die and cooled and solidified on a cast roll whose surface temperature was controlled at 20° C. to obtain an unstretched film.

[0135] Next, the film was preheated using a ceramic roll heated to 70°C, and longitudinal stretching was performed in one stage in the longitudinal direction of the film at a stretching ratio of 3.5 and a stretching temperature of 70°C. Thereafter, the film was gradually cooled to room temperature without heat setting or relaxation in the stretching direction, and the edges of the film were removed and taken up by a winder to obtain a polyester film with a thickness of 20 μm.

[0136] Examples 2 to 7 Examples 2 to 7 were prepared by varying the type of raw material resin for the polyester film, the mass ratio of PET to PBT, the stretch ratio for longitudinal stretching, the preheat roll temperature, and the stretch temperature for longitudinal stretching. Table 1 shows the type of raw material resin, the mass ratio of PET to PBT, the stretch ratio for longitudinal stretching, the preheat roll temperature, and the stretch temperature for longitudinal stretching for Examples 2 to 7. Other aspects are the same as in Example 1, so a description thereof will be omitted. The proportions of copolymerization components shown in Table 1 are in units of mol%.

[0137] (Comparative Examples 1 to 6) Comparative Examples 1 to 6 were prepared by varying the type of raw material resin for the polyester film, the mass ratio of PET to PBT, the stretch ratio for longitudinal stretching, the preheat roll temperature, and the stretching temperature for longitudinal stretching. Table 1 shows the type of raw material resin, the mass ratio of PET to PBT, the stretch ratio for longitudinal stretching, the preheat roll temperature, and the stretching temperature for longitudinal stretching for Comparative Examples 1 to 6. Other aspects are the same as in Example 1, so a description thereof will be omitted. The proportions of copolymerization components shown in Table 1 are in units of mol%.

[0138] (evaluation) For the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6, pole figures were created, and the thicknesses and melting peak temperatures of the polyester films were measured.

[0139] (Positive pole figure) Measurements were made using a wide-angle goniometer RINT-2000 manufactured by Rigaku Corporation and a multipurpose sample stage for pole points using the Schultz reflection method under the following conditions.

[0140] X-ray source: CuKα ray, tube voltage: 40 kV, tube current: 50 mA, divergence slit: 0.5°, scattering slit: 4 mm, receiving slit: 3 mm, divergence vertical limiting slit: 1.2 mm, filter: CuKβ ray filter, α: 15 to 90° (5° / step), β: 0 to 360° (5° / step continuous scan), β scan speed: 360° / min

[0141] The sample was set up in such a way that the elevation angle α = 0°, where the bisector of the incident and reflected X-rays is parallel to the film surface, and the in-plane rotation angle β = 90°, where the maximum diffraction intensity is achieved when α = 60° in the 100-diffraction pole figure.

[0142] From the wide-angle X-ray diffraction spectrum measured by the θ-2θ method while rotating the β axis with the sample installation direction of α=90°, the diffraction peak that appeared at 2θ=24.0° was assigned to 100 diffraction.

[0143] Regarding 010 diffraction, no diffraction peak was observed at 2θ=17.5±0.5° in the θ-2θ method. Therefore, the laminated metal sheet of Example 1 was heat-treated at 120°C for 15 minutes, and the wide-angle X-ray diffraction spectrum was measured again, and the diffraction peak that appeared at 2θ=17.0° was attributed to 010 diffraction. In addition, the diffraction angle of other polyester films was measured based on the diffraction angle 2θ=17.0° obtained for Example 1.

[0144] Therefore, the pole figures were measured at 2θ = 24.0° for 100 diffraction and 2θ = 17.0° for 010 diffraction. The net intensity in each pole figure was calculated by subtracting the diffraction intensity of the point with the lowest diffraction intensity at α = 15° from the diffraction intensity of each point.

[0145] From the obtained pole figure, the net strength at α=60° and β=0° in the pole figure of 100 diffractions is I 100 (60,0) In the pole figure of 100 diffractions, the net strength at α = 60° and β = 90° is I 100 (60,90) In the pole figure of the O10 diffraction, the net intensity at α = 50° and β = 0° is I 010 (50,0) In the pole figure of the O10 diffraction, the net strength at α = 50° and β = 90° is I 010 (50,90) The following equations (1) and (2) were verified.

[0146]

number

[0147] (Polyester film thickness measurement) The thickness of the polyester film was measured using a continuous thickness measuring instrument FT-A100 manufactured by Fuji Work Co., Ltd. equipped with an electric micrometer probe Millimar 1301 manufactured by Mahl Japan Co., Ltd.

[0148] A 1,000 mm length of polyester film was taken in the direction of β=0°, and measurements were made at 1 mm / step for 1,000 steps. The thickness at each point was measured. i For (i=1 to 1000), the values ​​shown in the following formula were used as the average thickness μ and the sample standard deviation σ.

number

[0149] (Measurement of the melting peak temperature of polyester film) The thermal properties of polyester film were measured using a TA Instruments Japan DSCQ100 differential scanning calorimeter. A 5 mg sample of polyester film was taken, cut, and placed in an aluminum dish. The sample was cooled to -50°C in a nitrogen atmosphere and heated to 290°C at 10°C / min for the first run. After holding at 290°C for 5 minutes, the sample was rapidly cooled in liquid nitrogen. The second run was then measured by heating from -50°C to 290°C at 10°C / min. The endothermic peak in the first run, excluding the enthalpy relaxation peak that appears near the glass transition point, was identified as the melting peak.

[0150] The evaluation results of the obtained polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 are shown in Table 1. The pole figures of the 100 diffraction intensity and the 010 diffraction intensity of the polyester film of Example 1 are shown in Figures 2 and 3, respectively.

[0151] [Table 1]

[0152] (Polyester film evaluation results) In Comparative Examples 4 and 5, the polyester film broke during longitudinal stretching in the manufacturing process, making it impossible to stably collect samples. In Comparative Example 6, the polyester film stuck to the preheating roll during longitudinal stretching in the manufacturing process, making it impossible to stably collect samples.

[0153] In contrast to this, in Examples 1 to 7 and Comparative Examples 1 to 3, the above-mentioned problems did not occur, and films could be produced stably.

[0154] (Creating laminated metal sheets) The polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were used to prepare laminated metal sheets.

[0155] TFS was used as the metal plate. The base metal of the TFS was 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. The TFS was prepared by degreasing, pickling, and then chromium plating the base metal. The TFS had a metal chromium layer with a coating weight of 120 mg / m2 in terms of Cr. 2 , chromium hydrate oxide layer: 10 mg / m 2 It was.

[0156] (Lamination onto metal plates using thermocompression lamination method) The polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were provided on the surface of a metal plate by thermocompression lamination. A biaxially oriented PET film with a melting point of 240°C and a thickness of 28 μm was provided on the back side. The pressure applied by the laminating roll was 0.60 MPa. The temperature of the laminating roll was 80°C.

[0157] A pair of laminating rolls was arranged to sandwich the front and back surfaces of the metal sheet. The polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were placed between the metal sheet and the laminating rolls, and the metal sheet was passed through the laminating rolls. The metal sheet was cooled with water one second after being pressed by the laminating rolls, to obtain a laminated metal sheet in which polyester films were bonded to both surfaces of the metal sheet.

[0158] During the thermocompression bonding, the lamination inlet sheet temperature was 240° C. Examples 2 to 7 and Comparative Examples 1 to 6 were produced in the same manner as Example 1, except that the polyester film was prepared using the polyester film and the lamination inlet sheet temperature was changed as shown in Table 2.

[0159] The laminated metal sheets obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were subjected to measurement of wide-angle X-ray diffraction spectrum.

[0160] (Wide-angle X-ray diffraction spectrum of laminated metal plate) Measurement was carried out using a wide-angle goniometer SmartLab manufactured by Rigaku Corporation by the θ-2θ method under the following conditions. 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, length limiting slit: 10.0 mm, 2θ = 10 to 30° (0.1° / step), counting time: 8 seconds / step

[0161] The sample was placed in the same direction as the pole figure, α = 90°, β = 0°. 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°, was subtracted from the diffraction intensity at each 2θ to obtain the net intensity. The peak that appeared at 2θ = 24.0° in the net intensity spectrum was assigned to 100 diffraction, and its intensity was calculated as I 100 (90,0) It was decided. If no clear peak appears at 2θ = 24.0 ± 1.0°, the maximum intensity in the range of 2θ = 23.0 to 25.0° is used as I 100 (90,0) The intensity of the amorphous halo that appeared at 2θ = 20.4° in the net intensity spectrum was calculated as I amorphous (90,0) Then, the following equation (3) was verified.

[0162]

number

[0163] The laminated metal sheets obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6 were evaluated for primary adhesion, adhesion after retort sterilization, and appearance after retort sterilization. These laminated metal sheets were also used to form laminated metal containers, and the formability of the laminated metal sheets was evaluated.

[0164] (Primary adhesion) Samples measuring 120 mm in the conveying direction and 15 mm in the plate width direction were cut out from the laminated metal sheets obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6. A portion of the polyester film was peeled off from the edge of the long side of each cut-out sample. The peeled polyester 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 pulling rate of 30 mm / min, and the adhesion strength per 15 mm width was evaluated according to the following criteria.

[0165] ◎: 10.0N / 15mm or more ○: 5.0N / 15mm or more, less than 10.0N / 15mm, ×: Less than 5.0N / 15mm

[0166] (Adhesion after retort sterilization) Samples measuring 100 mm in the conveying direction and 30 mm in the plate width direction were cut out from the laminated metal sheets obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6, and a portion of the film was peeled off from the edge of the long side of each cut-out sample. The peeled film was opened in the opposite direction to the peeling direction (angle: 180°), and a 100 g weight was fixed to it, and retort sterilization was performed 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.

[0167] ◎: Less than 2 mm ○: 2mm or more, less than 10mm ×: 10mm or more

[0168] (Appearance after retort sterilization) Samples with a diameter of 48 mm were punched out from the laminated metal sheets obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6. The samples were attached to the bottom of commercially available 350 mL negative pressure steel cans (diameter 66 mm, height 122.2 mm) using a doughnut-shaped magnet with an outer diameter of 50 mm and an inner diameter of 30 mm.

[0169] The steel cans to which the samples were attached were subjected to retort sterilization for 10 minutes in pressurized steam at 130° C. After the retort sterilization, the samples were removed from the steel cans, and changes in appearance were visually observed and evaluated according to the following scale.

[0170] ◎: No change in appearance ○: Slight cloudiness in appearance (less than 5% area) ×: Appearance is cloudy (area ratio 5% or more)

[0171] (Formability of laminated metal sheets) Paraffin wax was applied to the laminated metal plates obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6, and then the plates were punched out into φ123 disks and drawn to obtain shallow-drawn metal containers with an inner diameter of φ71 and a height of 36 mm.

[0172] This shallow-drawn can was placed in a DI molding machine and redrawn and ironed in three stages at a punch speed of 200 mm / s and a stroke of 560 mm, resulting in a total reduction of 50%. Finally, a laminated metal container with an inner diameter of 52 mm and a height of 90 mm was obtained. During DI molding, tap water was circulated at 50°C. After can formation, the area ratio of tears (scratches) in the polyester film on the target surface was evaluated according to the following criteria.

[0173] ◎: Scratch area ratio less than 5% ○: Scratch area ratio is 5% or more but less than 15% ×: Scratch area ratio 15% or more

[0174] Table 2 shows the evaluation results for the laminated metal plates and laminated metal containers obtained using the polyester films of Examples 1 to 7 and Comparative Examples 1 to 6.

[0175] [Table 2]

[0176] (Laminated metal sheet evaluation results) In Comparative Example 1, deterioration of appearance occurred after retort sterilization treatment. In Comparative Example 3, favorable results were not obtained in the evaluation of primary adhesion and adhesion after retort sterilization treatment. In Comparative Examples 2 to 6, favorable results were not obtained in the evaluation of formability of the laminated metal sheets. Specifically, in Comparative Examples 2 to 6, the tear (scratch) area ratio of the polyester film on the target surface exceeded the specified value, and stable production was not possible.

[0177] As shown in Table 2, Examples 1 to 7 obtained good results in the evaluation of all of the primary adhesion, adhesion after retort sterilization, appearance after retort sterilization, and formability of the laminated metal sheet. Furthermore, Examples 1 to 7 were able to be stably produced at all manufacturing stages of the laminated metal sheet and the laminated metal container.

[0178] In particular, in Examples 1 to 7, the deterioration of appearance after retort sterilization was rated as ○ or higher. Therefore, according to the present invention, it is possible to stably produce polyester films, laminated metal sheets, and laminated metal containers with energy savings at all production stages. In particular, it was confirmed that the appearance of the polyester film does not deteriorate even when subjected to high-temperature sterilization such as retort sterilization, which is necessary for canned food and beverage cans.

[0179] From the above, it was confirmed that Examples 1 to 7 are polyester films that satisfy the performance required for laminated metal containers and are excellent in productivity. [Explanation of symbols]

[0180] 100 Laminated Metal Containers 10. Laminated metal sheet 20 metal plate 21 Surface 22 Back side 30 Polyester film

Claims

1. A method for producing a polyester film containing a first polyester containing polyethylene terephthalate as a component and a second polyester containing polybutylene terephthalate as a component, the method comprising: the first polyester is polyethylene terephthalate or a polyethylene terephthalate copolymer containing polyethylene terephthalate and a copolymer component, polyethylene terephthalate; the second polyester is polybutylene terephthalate or a copolymer of polybutylene terephthalate and a copolymer of polybutylene terephthalate, a non-stretched film preparation step of extruding a resin composition containing the first polyester and the second polyester in a ratio of 20:80 to 50:50 on a mass % basis from a T-die using an extruder to obtain a non-stretched film; a longitudinal uniaxially stretched film preparation step of longitudinally stretching the unstretched film using a longitudinal uniaxially stretching machine equipped with a preheating roll and a stretching roll to obtain a longitudinal uniaxially stretched film, The longitudinal uniaxially stretched film production process is carried out at a stretching ratio of 3.0 times or more and 7.0 times or less, and at a final preheat roll temperature of 40°C or more and 80°C or less.

2. a heat setting step of heating the longitudinal uniaxially stretched film that has been subjected to the longitudinal uniaxially stretched film preparation step to perform heat setting, 2. The method for producing a polyester film according to claim 1, wherein the heat setting step heats the longitudinally uniaxially stretched film to a temperature that is at least 5°C higher than the final preheat roll temperature during stretching and at least 50°C lower than the melting point of the polyester film.

3. A method for producing a polyester film containing a first polyester containing polyethylene terephthalate as a component and a second polyester containing polybutylene terephthalate as a component, the method comprising: the first polyester is polyethylene terephthalate or a polyethylene terephthalate copolymer containing polyethylene terephthalate and a copolymer component, polyethylene terephthalate; the second polyester is polybutylene terephthalate or a copolymer of polybutylene terephthalate and a copolymer of polybutylene terephthalate, a non-stretched film preparation step of extruding a resin composition containing the first polyester and the second polyester in a ratio of 20:80 to 50:50 on a mass % basis from a T-die using an extruder to obtain a non-stretched film; a longitudinal uniaxially stretched film preparation step of longitudinally stretching the unstretched film using a longitudinal uniaxially stretching machine equipped with a preheating roll and a stretching roll to obtain a longitudinal uniaxially stretched film, The longitudinal uniaxially stretched film production process is carried out at a stretching ratio of 3.0 times or more and 7.0 times or less and at a stretching temperature of 50°C or more and 80°C or less.

4. a heat setting step of heating the longitudinal uniaxially stretched film that has been subjected to the longitudinal uniaxially stretched film preparation step to perform heat setting, The method for producing a polyester film according to claim 3, wherein the heat setting step heats the longitudinally uniaxially stretched film to a temperature that is 5°C or more higher than the stretching temperature and 50°C or more lower than the melting point of the polyester film.

5. A method for manufacturing a laminated metal plate using a polyester film manufactured by the method for manufacturing a polyester film according to any one of claims 1 to 4, comprising: a thermocompression bonding step of thermocompressing a preheated metal plate and the polyester film using a laminating roll to form a thermocompression bonded body; and a water cooling step of water-cooling the thermocompression-bonded body within 7 seconds after the thermocompression bonding, In the thermocompression bonding step, the metal plate is preheated to a temperature range of −20° C. to +50° C. of the melting point of the polyester film before thermocompression bonding.

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