Polyester film, polyester film production method, laminated metal plate, laminated metal plate production method, and laminated metal container

Abstract

Provided is a polyester film or the like, enabling stable production while saving energy in any manufacturing stages of a film, a laminated metal plate, and a laminated metal container. Also provided is a polyester film or the like, having sufficient corrosion resistance even when subjected to molding processing to form a two-piece can or the like, for example. This polyester film contains a polyester including polyethylene terephthalate as a component. The net strength of the polyester film in a pole figure which is obtained by X-ray diffractometry and which represents a crystal orientation distribution satisfies a predetermined condition.

Description

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

[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.

[0002] Metal containers such as food cans, beverage cans, and 18L cans are made from metal plates such as tin-free steel (TFS) and aluminum. These metal plates are painted and baked to impart 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] The thermoplastic resin film used in the laminated metal sheet is made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or 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] 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 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.

[0007] The 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, laminated metal sheets are often used for the bottom or lid of three-piece cans. Furthermore, laminated metal sheets are also used for the body of two-piece cans.

[0008] There are various methods for forming two-piece can bodies, 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. For this reason, laminated metal sheets are strongly required to have good formability.

[0009] In particular, laminated metal sheets used as the body material of two-piece cans often use polyester films, primarily PET (Polyethylene terephthalate), as the thermoplastic resin film.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] The advantages of transverse uniaxial stretching are not particularly noteworthy for use in laminated metal containers, and its disadvantages include the fact that the equipment required is relatively expensive compared to other stretching methods, and that anisotropy occurs when the material is formed into a laminated metal container due to the uniaxial orientation.

[0014] 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.

[0015] 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.

[0016] There are no notable advantages of multistage stretching, such as longitudinal re-stretching, for use in laminated metal containers. A disadvantage of multistage stretching is that the equipment is more expensive than other stretching methods. Considering that multistage stretched films strengthen the orientation of polyester film, they are not suitable for polyester films used in laminated metal containers.

[0017] 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, which, however, requires a large-scale heating furnace for transverse stretching and heat setting.

[0018] Therefore, polyester films have been produced using a non-stretching method or longitudinal uniaxial stretching, which not only can reduce equipment costs but also does not require a large-scale heating furnace. Polyester films produced using a non-stretching method are disclosed, for example, in Patent Document 1. Polyester films produced using a longitudinal uniaxial stretching method are disclosed, for example, in Patent Document 2.

[0019] International Publication No. 2015 / 012222 Special Publication No. 2014-518781

[0020] As described above, 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, container formability when the laminated metal plate is formed into a container, etc. In addition, 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.

[0021] However, the only example of the non-oriented polyester film disclosed in Patent Document 1 is an extrusion coating method in which a film extruded from a T-die of an extruder is directly thermocompressed onto a metal plate. Patent Document 1 also describes that if the extruded film is wound up and then laminated separately, it is inferior in terms of thinning, productivity, and handleability. From these descriptions, one of the problems is that industrial production of polyester film is difficult using methods other than extrusion coating.

[0022] In addition, in the extrusion coating method, since the laminating equipment and the extruder are produced in synchronization, the production rate of the polyester film is limited by the extrusion rate from the T-die. Therefore, the extrusion coating method has a problem of being inferior in productivity compared to methods in which a film extruded from a wide die or transversely stretched is separately laminated after slitting. For the same reason, the extrusion coating method also has a problem in that when the resin type is changed, not only the extruder but also the laminating equipment must be stopped.

[0023] The laminated metal sheet described in Patent Document 2 is laminated with a polyester film that is uniaxially stretched longitudinally. This laminated metal sheet is produced by laminating a polyester film on a preheated metal sheet and then post-heating the laminated metal sheet. Therefore, the production of the laminated metal sheet described in Patent Document 2 requires two heating steps, which poses a problem of requiring a great deal of energy during production.

[0024] Furthermore, in the longitudinal uniaxial stretching described in Patent Document 2, the edges of the film must be trimmed before stretching. Patent Document 2 also describes trimming the edges of the film that has been longitudinally uniaxially stretched, as necessary. Considering the variation in film width due to longitudinal uniaxial stretching and the yield, there is a high probability that the film will be trimmed after longitudinal uniaxial stretching. Therefore, the longitudinal uniaxial stretching method described in Patent Document 2 requires two trimmings, and there is a demand for energy savings in the production process.

[0025] The present invention has been made in view of the above-mentioned problems, and aims to provide a polyester film or the like that can be produced stably and with energy savings at any stage of the production of films, laminated metal sheets, and laminated metal containers, and that has sufficient corrosion resistance even when subjected to molding processes such as two-piece cans.

[0026] In order to solve the above problems, the present invention has the following features.

[0027] [1] A polyester film containing a polyester containing polyethylene terephthalate as a component, wherein the net strength of a pole figure representing a crystal orientation distribution obtained by an X-ray diffraction method satisfies the following formulas (1) and (2): In the X-ray diffraction measurement using CuKα rays, the diffraction peak appearing at 2θ = 26.5 ± 1.0° is defined as 100 diffraction, and the diffraction peak appearing at 2θ = 23.0 ± 0.5° is defined as 1-10 diffraction; the pole figure is measured with the elevation angle α = 0°, where the bisector of the incident X-ray and the reflected X-ray are parallel to the film surface; and the in-plane rotation angle at which the maximum diffraction intensity occurs when α = 60° in the 100 diffraction pole figure is defined as β = 90°. 100 (60,0) is the net intensity at α=60° and β=0° in the pole figure of the 100 diffraction intensity, and I 100 (60,90) is the net intensity at α=60° and β=90° in the pole figure of the 100 diffraction intensity, and I 1-10 (60,0)is the net intensity at α=60° and β=0° in the pole figure of the 1-10 diffraction intensity, and I 1-10 (60,90) is the net intensity at α=60° and β=90° in the pole figure of the 1-10 diffraction intensity. [2] The polyester film according to [1], wherein the sample standard deviation of the thickness measured in the direction of incident X-rays when β=0° in the pole figure is 10% or less of the average of the measured thicknesses. [3] The polyester film according to [1] or [2], comprising: a first layer containing a polyester containing polyethylene terephthalate as a component; and a second layer laminated to the first layer, the second layer containing a polyester containing polyethylene terephthalate as a component and a lubricant. [4] The polyester film according to [3], wherein the first layer contains a pigment. [5] A method for producing a polyester film containing a polyester containing polyethylene terephthalate as a component, comprising: a non-stretched film production step of extruding the polyester through a T-die using an extruder to obtain an unstretched film; and a longitudinal uniaxially stretched film production step of longitudinally stretching the unstretched film in a longitudinal uniaxially stretching machine equipped with a preheating roll and a stretching roll to obtain a longitudinal uniaxially stretched film, wherein the longitudinal uniaxially stretched film production step is performed at a stretch ratio of 3.3 to 7.5 times and a final preheating roll temperature of 75°C to 110°C. [6] A laminated metal sheet, comprising a metal sheet having a front surface and a back surface, and the polyester film according to any one of [1] to [4] bonded to at least one of the front surface and the back surface. [7] A laminated metal sheet according to [6], whose wide-angle X-ray diffraction spectrum satisfies the following formula (3): 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, and 100 (90,0) is the net intensity of the 100 diffraction peak appearing at 2θ=26.5±1.0°, and I amorphous (90,0)is the net strength of the amorphous halo that appears at 2θ = 20.0 ± 5.0°. [8] A method for producing a laminated metal plate according to [6] or [7], comprising: a thermocompression bonding step of thermocompression bonding 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, wherein in the thermocompression bonding step, the polyester film and the metal plate are preheated within a range of -5°C to +50°C, the melting point of the polyester film, before the thermocompression bonding is performed. [9] A laminated metal container comprising the laminated metal plate according to [6] or [7] as a material.

[0028] According to the present invention, films, laminated metal sheets, and laminated metal containers can be produced stably and with reduced energy consumption. Furthermore, the polyester films of the present invention have sufficient corrosion resistance even when subjected to molding processes such as two-piece cans.

[0029] FIG. 1 is an explanatory diagram of a laminated metal container. FIG. 2 is a cross-sectional view of a polyester film composed of two layers. FIG. 3 is a cross-sectional view of a polyester film composed of three layers. FIG. 4 is a pole figure of a polyester film with a diffraction intensity of 100. FIG. 5 is a pole figure of a polyester film with a diffraction intensity of 1-10. FIG. 6 is a flow chart showing a method for manufacturing a polyester film. FIG. 7 is a flow chart showing a method for manufacturing a laminated metal plate.

[0030] 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.

[0031] 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.

[0032] 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 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 polyester film 30 bonded to at least one of the front 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 front surface 21 of the metal plate 20.

[0033] 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 plates 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.

[0034] 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.

[0035] The low-carbon steel may be, for example, one having a carbon content of 0.010% by mass or more and 0.100% 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.

[0036] 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 hydrated chromium 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 , the chromium hydrate oxide layer is 3 to 30 mg / m ２ The thickness of the metal plate is not particularly limited, but is preferably in the range of 0.10 to 0.60 mm from the viewpoint of formability into a laminated metal container and strength as a metal container.

[0037] The polyester film 30 contains a polyester containing polyethylene terephthalate as a component. The content of polyethylene terephthalate in the polyester film 30 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0038] The polyester may be polyethylene terephthalate or a copolymer of polyethylene terephthalate and a copolymer component. When the polyester is a polyethylene terephthalate copolymer, the content of the copolymer component is preferably 20 mol % or less, and more preferably 2 to 16 mol %.

[0039] Examples of copolymerization components of the polyester include, as acid components, 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.

[0040] Copolymerization components of the polyester include, as alcohol components, 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, bisphenol S, and the like.

[0041] As the copolymerization component of the polyester, one of the above may be used, or two or more of them may be used.

[0042] 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 plate. When isophthalic acid is used as a copolymerization component, the content of isophthalic acid in the copolymer is preferably 1 to 20 mol %, and more preferably 2 to 16 mol %.

[0043] The intrinsic viscosity of the polyester is preferably in the range of 0.62 to 1.10 dL / g. If the intrinsic viscosity is less than 0.62 dL / g, the formability of the laminated metal sheet tends to decrease. If the intrinsic viscosity is higher than 1.10 dL / g, the energy consumption in the polymerization process and extrusion process tends to increase.

[0044] In addition to polyester, additives such as lubricants, pigments, dyes, antioxidants, crystal nucleating agents, heat stabilizers, and antistatic agents can be added to the polyester film 30. In particular, to improve handleability, the polyester film 30 preferably contains 0.01 to 1.00 mass % of a lubricant.

[0045] The lubricant is not particularly limited, but inorganic lubricants such as silicon oxide, diatomaceous earth, and talc, and organic lubricants such as PMMA, carnauba wax, polyolefin wax, and modified polyolefin wax can be used.

[0046] The lubricant may be a combination of two or more of an inorganic lubricant and an organic lubricant. By incorporating an inorganic lubricant and an organic lubricant into the polyester film 30, the inorganic lubricant can improve the transportability of the polyester film 30 and the laminated metal sheet 10, while the organic lubricant can improve the formability of the polyester film 30 into a two-piece can body.

[0047] The pigment is not particularly limited, but may be, for example, a white pigment, a yellow pigment, etc. By including a pigment in the polyester film 30, the polyester film 30 can coat the underlying metal plate 20, thereby improving the design and print clarity.

[0048] Examples of white pigments that can be used include oxide ceramics such as aluminum oxide, titanium dioxide, and zinc oxide, as well as talc, calcium carbonate, barium sulfate, etc. In particular, titanium dioxide is preferably used as the white pigment from the viewpoints of dispersibility and whiteness, and rutile titanium dioxide is more preferably used.

[0049] As the yellow pigment, for example, isoindolinone yellow, disazo yellow, etc. can be used. From the viewpoint of heat resistance, disazo yellow is preferably used as the yellow pigment.

[0050] The polyester film 30 preferably contains an antioxidant in an amount of 0.0001% by mass to 1.0000% by mass. The antioxidant is not particularly limited, but known antioxidants classified as hindered phenols, hydrazines, phosphites, etc. can be used. By including the antioxidant, the heat resistance of the polyester film 30 can be improved.

[0051] The polyester film 30 may be formed of multiple layers. Fig. 2 shows a cross section of a two-layer polyester film 30. As shown in Fig. 2, the polyester film 30 includes a first layer 31 disposed on the surface 21 of the metal plate 20 and a second layer 32 laminated on the first layer 31.

[0052] The first layer 31 contains a polyester containing polyethylene terephthalate as a component and a pigment, and the second layer 32 contains a polyester containing polyethylene terephthalate as a component and a lubricant.

[0053] When the polyester film 30 is constructed of multiple layers, it is preferable that the second layer 32, which is the outermost layer farthest from the laminated metal sheet 10, contain a lubricant. In the example of the polyester film 30 shown in Figure 2, for example, the first layer 31 may contain 0.02 mass % or less of a lubricant. The second layer 32 may contain 0.01 to 1.00 mass % of a lubricant.

[0054] In addition, it is preferable that the outermost layer of the polyester film 30 is formed without adding any pigment, which can prevent the pigment from adhering to the user's hands or from leaking into the contents.

[0055] The polyester film 30 is not limited to a two-layer structure, but may be composed of three or more layers. Fig. 3 shows a cross section of a three-layer polyester film 30. As shown in Fig. 3, a second layer 32 may be provided to sandwich a first layer 31 in the stacking direction of the polyester film 30.

[0056] When the polyester film 30 is constructed in this manner, the additive is preferably added to the layer that can benefit from the additive. For example, the lubricant is preferably added to the second layer 32 in an amount of 0.01 to 1.00 mass %. In this case, the lubricant is preferably not added to the first layer 31. By selectively adding the lubricant to the second layer 32 in this manner, the manufacturing cost can be reduced while maintaining the effect of the lubricant. Note that the lubricant only needs to be contained in the outermost layer, and is preferably not contained in other layers.

[0057] Furthermore, for example, the pigment may be added to the first layer 31. In this case, the pigment may not be added to the second layer 32. By selectively adding the pigment to the first layer 31 in this way, it is possible to reduce manufacturing costs while maintaining the effect of the pigment. Furthermore, because the first layer 31 is covered by the second layer 32, which is the outermost layer, hygiene problems such as the pigment leaking into the contents can be prevented.

[0058] The polyester film 30 can be laminated by any known method, such as co-extrusion using a feed block or a multi-manifold, laminating with another film, or laminating a molten resin directly onto a film. From the viewpoints of productivity and energy saving, the co-extrusion method is preferred as the lamination method for the polyester film 30.

[0059] FIG. 4 is a pole figure of polyester film 30 with a diffraction intensity of 100. FIG. 5 is a pole figure of polyester film 30 with a diffraction intensity of 1-10. In FIGS. 4 and 5, the pole figures were obtained by X-ray diffraction and represent the crystal orientation distribution. Also, in FIGS. 4 and 5, 10 contour lines are displayed, dividing the net strength from the minimum value to the maximum value into 11 parts. The numbers added to the contour lines shown in FIGS. 4 and 5 represent the net strength expressed as a percentage of the maximum value. For polyester film 30, the net strength of the pole figures shown in FIGS. 4 and 5 satisfies the following formulas (1) and (2):

[0060] In X-ray diffraction measurement using CuKα radiation, the diffraction peak appearing at 2θ = 26.5 ± 1.0° is defined as 100 diffraction, and the diffraction peak appearing at 2θ = 23.0 ± 0.5° is defined as 1-10 diffraction. The pole figure was measured with the elevation angle α = 0°, at which the bisector of the incident X-ray and the reflected X-ray were parallel to the film surface, and the in-plane rotation angle at which the diffraction intensity reached its maximum when α = 60° in the 100 diffraction pole figure was defined as β = 90°.

[0061] I 100 (60,0) is the net intensity at α=60° and β=0° in a pole figure of 100 diffraction intensities. 100(60,0) are indicated by black dots in FIG.

[0062] I 100 (60,90) is the net intensity at α=60° and β=90° in a pole figure of 100 diffraction intensities. 100 (60,90) is shown as a hatched dot in FIG.

[0063] I 1-10 (60,0) is the net intensity at α=60° and β=0° in the pole figure of the 1-10 diffraction intensity. 1-10 (60,0) are indicated by black dots in FIG.

[0064] I 1-10 (60,90) is the net intensity at α=60° and β=90° in the pole figure of the 1-10 diffraction intensity. 1-10 (60,90) is shown as a hatched dot in FIG.

[0065] 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. 4 and 5).

[0066] I 100 (60,0) , I 100 (60,90) These represent the ratio of the (100) plane of the polyester polyethylene terephthalate, i.e., the aromatic ring plane, facing in the directions β=0° and 90°, respectively.

[0067] I 100 (60,0) / I 100 (60,90) is 0.30 or more and 0.63 or less, and preferably 0.35 or more and 0.50 or less. 100 (60,0) / I 100 (60,90)By setting the value of the tensile strength to 0.30 or more and 0.63 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 polyester film 30 is laminated to the metal plate 20, and it is possible to improve the tensile stability of the polyester film 30 in the longitudinal direction.

[0068] On the other hand, I 100 (60,0) / I 100 (60,90) If the tensile strength is less than 0.30, the polyester film 30 tends to shrink in the width direction of the metal plate 20 when the polyester film 30 is 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.

[0069] Also, I 100 (60,0) / I 100 (60,90) If the stretch ratio is larger than 0.63, the stretching ratio of the polyester film 30 is small, and the thickness uniformity of the polyester film 30 tends to be impaired.

[0070] I 1-10 (60,0) , I 1-10 (60,90) represents the ratio of the (1-10) plane of the polyester polyethylene terephthalate facing β = 0° and 90°, respectively. 1-10 (60,0) / I 1-10 (60,90) is 0.42 or more and 0.60 or less, and preferably 0.45 or more and 0.55 or less. 1-10 (60,0) / I 1-10 (60,90)By setting the ρ to be 0.42 or more and 0.60 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 suppress instability of the tension of the polyester film 30 in the longitudinal direction of the metal plate 20.

[0071] I 1-10 (60,0) / I 1-10 (60,90) If the tensile strength is less than 0.42, when the polyester film 30 is laminated onto the metal plate 20, the polyester film 30 tends to shrink in the width direction of the metal plate 20. Furthermore, when the polyester film 30 is laminated onto the metal plate 20, the tension of the polyester film 30 tends to become unstable in the longitudinal direction of the metal plate 20.

[0072] Also, I 1-10 (60,0) / I 1-10 (60,90) If the stretching ratio is larger than 0.60, the stretching ratio is small, and the thickness uniformity of the polyester film 30 decreases.

[0073] The polyester film of the present invention preferably has a sample standard deviation of the thickness measured in the direction of incident X-rays when β=0° in a pole figure of 10% or less, more preferably 5% or less, of the average film thickness.

[0074] 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.

[0075] 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.

[0076] 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 to the metal plate 20, the tensile stability of the polyester film 30 in the longitudinal direction of the metal plate 20 can be improved.

[0077] Furthermore, when the laminated metal plate 10 is formed into the laminated metal container 100, the polyester film 30 or the polyester film 30 and the metal plate 20 can be prevented from breaking.

[0078] The average thickness of the polyester film 30 is preferably 8 to 50 μm, more preferably 10 to 30 μm.

[0079] If the average thickness of the polyester film 30 is less than 8 μm, the thickness of the polyester film 30 will be reduced when the laminated metal plate 10 is formed into the laminated metal container 100, and corrosion resistance may not be ensured.

[0080] Even if the average thickness of the polyester film 30 is made thicker than 50 μm, it is difficult to obtain the above-mentioned corrosion resistance and the additional effects of workability that are achieved by imparting stiffness to the polyester film 30. Furthermore, if the average thickness of the polyester film 30 is made thicker than 50 μm, it becomes difficult to produce the polyester film 30 in an energy-saving manner.

[0081] (Method for Producing Polyester Film) Next, a method for producing the polyester film 30 will be described below. FIG. 6 shows a production flow for the polyester film 30. As shown in FIG. 6, the method for producing the polyester film 30 includes a non-stretched film production step (step S101) in which polyester is extruded through a T-die using an extruder to obtain an non-stretched film. Next, a longitudinal uniaxially stretched film production step (step S102) is performed in which the non-stretched film is longitudinally stretched to obtain a longitudinal uniaxially stretched film. Further, a heat setting step (step S103) in which the longitudinal uniaxially stretched film is heated to perform heat setting is performed, thereby producing the polyester film 30.

[0082] In the non-stretched film production process in step S101, the above-mentioned polyester is an essential raw material. Additives such as lubricants, pigments, dyes, antioxidants, crystal nucleating agents, heat stabilizers, and antistatic agents may be added to the raw material.

[0083] These raw materials and a masterbatch in which additives such as lubricants 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, if necessary, and then fed to an extruder.

[0084] The polyester is heated to or above its melting point in the extruder to melt it. After foreign matter and modified resins are removed from the molten resin composition using a filter, the composition is fed to a T-die via a gear pump and extruded from the T-die. The resin composition is molded into a sheet when extruded from the T-die.

[0085] 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.

[0086] The molten resin composition discharged 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.

[0087] 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%.

[0088] 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, where the difference in peripheral speed between the stretching roll and the final preheating roll is 50% or more.

[0089] 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.

[0090] 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.

[0091] The stretching ratio in the longitudinal stretching is 3.3 to 7.5 times. The stretching ratio in the longitudinal stretching is preferably 3.9 to 6.5 times. The stretching ratio in the longitudinal stretching can be expressed as the ratio of the conveying speed at the outlet side of the longitudinal stretching machine to the conveying speed at the inlet side.

[0092] When the stretching ratio is less than 3.3 times, I 1-10 (60,0) / I 1-10 (60,90) If the stretching ratio is more than 7.5 times, I 1-10 (60,0) / I 1-10 (60,90) If the stretching ratio is more than 7.5 times, the film tends to break easily during stretching.

[0093] The longitudinal uniaxially stretched film production process is carried out at a final preheating roll temperature of 75° C. or higher and 110° C. or lower. The final preheating roll temperature is preferably 80° C. or higher and 105° C. or lower. If the final preheating roll temperature is lower than 75° C., the polyester film may be stretched at a temperature lower than the glass transition point, and the resin composition film may be more likely to break during stretching.

[0094] For example, the glass transition point of the polyester film 30 can be determined by the temperature at which a baseline shift in heat flux occurs when the temperature is increased from −50° C. to 280° C. at a rate of 10° C. / min in a DSC.

[0095] If the temperature of the final preheating roll is higher than 110°C, the longitudinally uniaxially stretched film tends to stick to the roll, reducing productivity and decreasing the thickness accuracy of the longitudinally uniaxially stretched film.

[0096] The heat setting step in step S103 is an optional step, and is preferably performed by heating the polyester film 30 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 30.

[0097] The melting point of the polyester film 30 can be determined by, for example, the peak temperature of the highest endothermic peak when the temperature is increased from −50° C. to 280° C. at a rate of 10° C. / min in differential scanning calorimetry (DSC).

[0098] The longitudinally uniaxially stretched film can also be heated using a heated roll, as in 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 and lower than 150°C. In this way, adhesion of the longitudinally uniaxially stretched film to the roll can be suppressed.

[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] The longitudinally uniaxially stretched film is preferably trimmed to a predetermined width at its edges. If the heat setting step of step S103 is performed, trimming may be performed after the heat setting step. Note that trimming is an optional step.

[0102] The trimmed longitudinally uniaxially stretched film is wound into a roll and stored before use as a polyester film. Trimming the edges of the longitudinally stretched film allows the thickness in the width direction to be adjusted to a desired dimension. As a result, the longitudinally stretched film can be prevented from wrinkling and from telescoping.

[0103] By carrying out the longitudinal uniaxially stretched film production step in step S102 at the above-mentioned stretch ratio and final preheat roll temperature, a polyester film can be stably produced, and as a result, the desired dimensions can be achieved without trimming the edges of the film between the unstretched film production step in step S101 and the longitudinal uniaxially stretched film production step in step S102.

[0104] (Method for manufacturing laminated metal sheet) A method for manufacturing the laminated metal sheet 10 will now be described. Fig. 7 shows a manufacturing flow of the laminated metal sheet 10. As shown in Fig. 7, a metal sheet 20 and a polyester film 30 are thermocompression-bonded using a laminating roll of laminating equipment to generate a thermocompression-bonded body (step S201).

[0105] The thermocompression bonding step in step S201 is performed by laminating the polyester film 30 on at least one of the front surface 21 and the back surface 22 of the metal plate 20. 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.

[0106] 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.

[0107] The metal plate 20 is preheated at a temperature between −5° C. and +50° C., which is the melting point of the polyester film 30. It is preferable that the metal plate 20 is preheated at a temperature between the melting point of the polyester film 30 and +30° C., which is the melting point of the polyester film 30.

[0108] If the metal plate 20 is preheated to a temperature less than the melting point of the polyester film 30 minus 5°C, 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 the melting point of the polyester film 30 plus 50°C, the polyester film 30 in contact with the laminating roll may melt, deteriorating the appearance. In addition, the polyester film 30 may adhere to the laminating roll, reducing productivity.

[0109] The polyester film 30 used in the thermocompression bonding step of step S201 may be preheated. The heating temperature of the polyester film 30 is preferably 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.

[0110] The pressure of the laminating roll is preferably 0.35 to 1.50 MPa. By setting the pressure of the laminating roll to 0.35 MPa or more, air bubbles trapped at the interface between the metal sheet 20 and the polyester film 30 can be more effectively removed, thereby improving the adhesion between the metal sheet 20 and the polyester film 30. Furthermore, removing the air bubbles can prevent the appearance of the laminated metal sheet 10 from being impaired.

[0111] By setting the pressure of the laminating roll to 1.50 MPa or less, excessive heat transfer from the metal plate 20 to the laminating roll can be suppressed, and the energy consumed during manufacturing can be efficiently reduced. Furthermore, under these conditions, wear on the laminating roll can be suppressed.

[0112] 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 controlled.

[0113] 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 on the thermocompression-bonded body or by immersing the thermocompression-bonded body in water.

[0114] 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 equal to or lower than the glass transition point of the polyester film 30 + 40°C. The water used for water-cooling is not limited to water, and for example, an oil bath oil such as silicone oil may also be used.

[0115] 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.

[0116] The laminated metal sheet 10 thus produced preferably has a wide-angle X-ray diffraction spectrum that satisfies the following formula (3).

[0117] 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=26.5±1.0°. amorphous (90,0) is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

[0118] If no clear peak appears at 2θ=26.5±1.0°, the maximum net strength in the range of 2θ=25.5 to 27.5° 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 represented by the straight line connecting the diffraction intensity at 2θ=10.0° and the diffraction intensity at 2θ=30.0°.

[0119] I 100 (90,0) / I amorphous (90,0) is preferably 1.5 or less, more preferably 1.3 or less. When the wide-angle X-ray diffraction spectrum of the laminated metal plate 10 satisfies formula (3), the oriented crystals generated by stretching are amorphous due to 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 manufacturing the laminated metal plate 10 in this manner, the laminated metal container 100 can be manufactured more stably and with less energy consumption.

[0120] If the thermocompression-bonded body is air-cooled without performing the water-cooling step of step S202, 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.

[0121] In the water-cooling step of step S202, the polyester film needs to be water-cooled within 7 seconds after thermocompression bonding, and more preferably within 3 seconds after thermocompression bonding. By water-cooling in this manner, the progress of thermal crystallization of the polyester film can be suppressed, and the wide-angle X-ray diffraction spectrum of the laminated metal sheet 10 can be controlled to satisfy the above formula (3).

[0122] As described above, by performing the thermocompression bonding step of step S201 by the above-mentioned thermocompression lamination method, it is possible to improve the adhesion between the polyester film 30 and the metal plate 20 and to produce the laminated metal plate 10 in an energy-saving manner. Specifically, it is possible to satisfy performance requirements such as adhesion between the polyester film 30 and the metal plate 20 when formed into the laminated metal plate 10, corrosion resistance, and container formability when forming the laminated metal plate 10 into a container.

[0123] 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.

[0124] 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. The laminating equipment may also be configured with a minimum number of devices including a payoff reel, a tension reel, and a laminating unit.

[0125] Furthermore, for example, 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, it may be provided at any timing, for example, by lamination at the same time as the polyester film 30.

[0126] 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.

[0127] 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.

[0128] (Method for manufacturing a laminated metal container) The laminated metal container 100 is formed by using a laminated metal sheet 10 for at least one of the multiple members 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 members and a two-piece can made up of two members.

[0129] 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).

[0130] DI forming and DTR forming are forming methods that involve ironing, and require particular workability. The laminated metal sheet 10 has high formability even in such forming methods that require workability, and therefore can be suitably used in any of the above forming methods.

[0131] The laminated metal container 100 may be painted or printed. The laminated metal container 100 is formed by a known method. The laminated metal container 100 can be formed, for example, by using a can manufacturing machine.

[0132] The laminated metal container 100 can be suitably used as a container that is particularly subjected to retort sterilization.

[0133] In the above embodiment, the laminated metal plate 10 has a metal plate 20 having 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. The laminated metal plate 10 can be freely provided depending on the embodiment. For example, the front surface 21 of the metal plate 20 may be the inner surface of the laminated metal container 100, and the back surface 22 may be the outer surface of the laminated metal container 100. In this case, the polyester film 30 may be provided only on the front surface 21 which is the inner surface of the laminated metal container 100.

[0134] EXAMPLES The present invention will be described in more detail below with reference to examples, but is not limited thereto. Polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 were prepared.

[0135] Example 1 As raw resins for a polyester film, pellets of a copolymer of polyethylene terephthalate (PET) and pellets of a lubricant masterbatch were prepared.

[0136] The polyethylene terephthalate (PET) copolymer contains 5 mol % of isophthalic acid and 2 mol % of diethylene glycol as copolymerization components, and has a melting point of 245°C.

[0137] The lubricant masterbatch pellets used silicon dioxide as an inorganic lubricant, and were prepared by dispersing the lubricant in PET with a melting point of 254°C.

[0138] Pellets of these two types of raw resins were blended so that the silicon dioxide content was 0.04% by mass of the total resin mixture. The pellets were then heated to 150°C under vacuum to remove moisture, and held there for 3 hours to dry. The dried pellets were then placed in a single-screw extruder and melt-kneaded at 275°C.

[0139] 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 30° C. to obtain an unstretched film.

[0140] Next, the unstretched film was preheated using a ceramic roll heated to 90° C., and longitudinally stretched in one step at 5.0 times the original length in the longitudinal direction. 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 18 μm.

[0141] (Examples 2 to 5) Polyester films of Examples 2 to 5 were produced by changing the copolymerization components of PET, the types and amounts of additives, the stretch ratio in longitudinal stretching, and the final preheat roll temperature as shown in Table 1. Table 1 shows the copolymerization components of PET, the types and amounts of additives, the stretch ratio in longitudinal stretching, and the final preheat roll temperature of the polyester films of Examples 2 to 5. Other aspects are the same as those of Example 1, so explanations are omitted. The copolymerization components shown in Table 1 are in mol %. Furthermore, since the polyester films of Examples 1 to 5 were constructed with a single layer, this is listed as the first layer in Table 1.

[0142] Example 6 The polyester film of Example 6 was composed of three layers: a first layer and a second layer disposed on both sides of the first layer. As raw material resins for the polyester film of Example 6, pellets of copolymerized PET and pellets of a pigment masterbatch were prepared for the first layer. The copolymerized PET of the first layer contained 2 mol% isophthalic acid and 2 mol% diethylene glycol. The pigment masterbatch was prepared by dispersing rutile-type titanium dioxide, an inorganic pigment, in PET with a melting point of 254°C.

[0143] For the second layer, pellets of copolymerized PET and pellets of lubricant masterbatch were prepared. The copolymerized PET for the second layer contained 2 mol% isophthalic acid and 3 mol% diethylene glycol. The lubricant masterbatch was prepared by dispersing silicon dioxide, an inorganic lubricant, in PET with a melting point of 254°C.

[0144] The raw materials for the first layer were blended so that the amount of titanium dioxide was 15% by mass of the first layer, and the raw materials for the second layer were blended so that the amount of silicon dioxide was 0.04% by mass of the second layer.

[0145] The vacuum-dried raw materials for the first layer and the second layer were then fed into separate single-screw extruders and melt-kneaded. The melt-kneaded resin compositions were co-extruded using a feed block method to obtain an unstretched film. The polyester film of Example 6 was obtained in the same manner as in Example 1, except that the longitudinal stretching ratio and final preheat roll temperature were changed as shown in Table 1.

[0146] (Comparative Examples 1 to 3) Polyester films of Comparative Examples 1 to 3 were produced by changing the copolymerization components of PET, the types and amounts of additives, the stretch ratio in longitudinal stretching, and the final preheat roll temperature as shown in Table 1. Table 1 shows the copolymerization components of PET, the types and amounts of additives, the stretch ratio in longitudinal stretching, and the final preheat roll temperature of the polyester films of Comparative Examples 1 to 3. Other aspects are the same as in Example 1, so explanations are omitted. The units of copolymerization components shown in Table 1 are mol %.

[0147] (Comparative Example 4) The polyester film of Comparative Example 4 was composed of three layers, including a first layer and second layers disposed on both sides of the first layer, similar to Example 6. The polyester film of Comparative Example 4 differed from Example 6 only in the stretching ratio.

[0148] (Evaluation) For the polyester films of Examples 1 to 6 and Comparative Examples 1 to 4, pole figures were prepared, and the thickness and melting point of the polyester films were measured.

[0149] (Pole Figure) Measurement was carried out under the following conditions by the Schultz reflection method using a wide-angle goniometer RINT-2000 manufactured by Rigaku Corporation and a multipurpose pole figure sample stage.

[0150] 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

[0151] The sample was set up in such a way that the elevation angle α = 0°, where the bisector of the incident X-ray and the reflected X-ray are parallel to the film surface, and the in-plane rotation angle β = 90°, where the maximum diffraction intensity is obtained when α = 60° in the 100 diffraction pole figure.

[0152] From the wide-angle X-ray diffraction spectrum measured by the θ-2θ method while rotating the β axis in the sample installation direction of α=90°, the diffraction peak appearing at 2θ=26.5° was assigned to 100 diffraction.

[0153] Regarding 1-10 diffraction, no diffraction peak was observed at 2θ = 23.0 ± 0.5° in the θ-2θ method. Therefore, the laminated metal sheet of Example 1 was heat-treated at 150°C for 15 minutes and the wide-angle X-ray diffraction spectrum was measured again, and the diffraction peak that appeared at 2θ = 23.0° was assigned to 1-10 diffraction. Furthermore, measurements were made on the other polyester films based on the diffraction angle 2θ = 23.0° obtained for Example 1.

[0154] Therefore, the pole figures were measured at 2θ = 26.5° for 100 diffraction and 2θ = 23.0° for 1-10 diffraction. The net intensity in each pole figure was calculated by subtracting the diffraction intensity at the point with the lowest diffraction intensity at α = 15° from the diffraction intensity at each point.

[0155] From the obtained pole figure, the net intensity 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 intensity at α = 60° and β = 90° is I 100 (60,90) In the pole figure of 1-10 diffraction, the net intensity at α = 60° and β = 0° is I 1-10 (60,0) In the pole figure of 1-10 diffraction, the net strength at α = 60° and β = 90° is I 1-10 (60,90) The following formulas (1) and (2) were verified.

[0156]

[0157] (Measurement of Thickness of Polyester Film) 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 Mahr Japan Co., Ltd.

[0158] 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. i For (i = 1 to 1000), the values ​​shown in the following formula were taken as the average thickness μ and the sample standard deviation σ.

[0159] (Measurement of Melting Peak Temperature of Polyester Film) The thermal properties of the polyester film were measured using a differential scanning calorimeter DSCQ100 manufactured by TA Instruments Japan Co., Ltd. 5 mg of polyester film was collected as a sample, cut into pieces, and placed in an aluminum dish. The sample was cooled to -50°C in a nitrogen atmosphere, and the first run was measured while the temperature was increased to 290°C at 10°C / min. After holding at 290°C for 5 minutes, the sample was quenched with liquid nitrogen. Thereafter, the second run was measured while the temperature was increased again from -50°C to 290°C at 10°C / min. The endothermic peak of the first run, excluding the enthalpy relaxation peak appearing near the glass transition point, was identified as the melting point.

[0160] The evaluation results of the obtained polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 are shown in Table 1. Furthermore, the pole figure of the 100 diffraction intensity of the polyester film of Example 1 is shown in Fig. 4, and the pole figure of the 1-10 diffraction intensity is shown in Fig. 5.

[0161] IA: Isophthalic acid DEG: Diethylene glycol WAX: Acid-modified polyethylene wax

[0162] (Evaluation Results of Polyester Films) In Comparative Example 3, the stretching ratio was too high in the longitudinal stretching step in the production of the polyester film, causing breakage and making it impossible to stably obtain samples. In contrast, in Examples 1 to 6 and Comparative Examples 1, 2, and 4, polyester films could be stably produced. However, in Comparative Examples 2 and 4, the stretching ratio was too low. Therefore, I 100(60,0) / I 100 (60,90) and I 1-10(60,0) / I 1-10 (60,90) was larger than the upper limit values ​​of the formulas (1) and (2). In Comparative Examples 2 and 4, the sample standard deviation of the film thickness was 10% or more of the average.

[0163] In contrast, films could be stably produced in Examples 1 to 6 and Comparative Example 1. In Examples 1 to 6 and Comparative Example 1, the above-mentioned adverse effects were not observed, and it was confirmed that films could be stably produced.

[0164] (Preparation of Laminated Metal Sheets) Laminated metal sheets were prepared using the polyester films of Examples 1 to 6 and Comparative Examples 1 to 4.

[0165] TFS was used as the metal plate. Low-carbon steel with a temper of T3CA and a thickness of 0.22 mm was used as the base metal for the TFS. The base metal was degreased, pickled, and then chromium-plated. 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.

[0166] (Lamination onto metal plate by thermocompression lamination) The polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 were provided on the back surface of a metal plate by thermocompression lamination. A biaxially oriented PET film with a melting point of 248°C and a thickness of 20 μm was provided on the front surface. The pressure applied by the laminating roll was 0.60 MPa. The temperature of the laminating roll was 80°C.

[0167] A pair of laminating rolls was arranged to sandwich the front and back surfaces of a metal sheet. The polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 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.

[0168] The lamination inlet sheet temperature was set to 240° C., and the thermocompression bonding to the metal sheet was performed. Examples 2 to 6 and Comparative Examples 1 to 4 were prepared in the same manner as Example 1, except that the lamination inlet sheet temperature was changed as shown in Table 2.

[0169] The laminated metal sheets using the polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 were subjected to wide-angle X-ray diffraction spectrum measurement.

[0170] (Wide-angle X-ray diffraction spectrum of laminated metal sheet) Measurement was performed using a wide-angle goniometer SmartLab manufactured by Rigaku Corporation under the following conditions by the θ-2θ method: 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.

[0171] 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 appearing at 2θ = 26.5° in the net intensity spectrum was assigned to 100 diffraction, and its intensity was calculated as I. 100 (90,0) It was decided.

[0172] If no clear peak appears at 2θ=26.5°±1.0°, the maximum intensity in the range of 2θ=25.5 to 27.5° 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 defined as I amorphous (90,0) Then, the following formula (3) was verified.

[0173]

[0174] The laminated metal sheets obtained using the polyester films of Examples 1 to 6 and Comparative Examples 1 to 4 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 by measuring the degree of defects in the film.

[0175] (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 6 and Comparative Examples 1 to 4. 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 scale.

[0176] ◎: 15.0N / 15mm or more ○: 10.0N / 15mm or more, less than 15.0N / 15mm △: 5.0N / 15mm or more, less than 10.0N / 15mm ×: Less than 5.0N / 15mm

[0177] (Adhesion after retort sterilization) Samples measuring 100 mm in the conveyance 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 6 and Comparative Examples 1 to 4, 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 direction opposite 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.

[0178] ◎: Less than 2 mm ○: 2 mm or more, less than 5 mm △: 5 mm or more, less than 10 mm ×: 10 mm or more

[0179] (Formability of Laminated Metal Sheet) After applying paraffin wax to the laminated metal sheet obtained using the polyester film of Examples 1 to 6 and Comparative Examples 1 to 4, the laminated metal sheet was punched into a disk of φ123 and drawn so that the film to be evaluated was positioned on the inner surface, to obtain a shallow drawn metal container with an inner diameter of φ71 and a height of 36 mm.

[0180] This shallow-drawn can was loaded into a DI molding machine and subjected to redrawing and three-stage ironing processes at a punch speed of 200 mm / s, a stroke of 560 mm, and 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 DI molding, tap water was circulated at 50°C. After can formation, a 1% NaCl aqueous solution was poured into the can to fill it to a height of 60 mm. The Enamel Rate Value (ERV), which is the current value when a voltage of 6 V was applied between the can body and the electrolyte, was then measured. The formability of the laminated metal sheet was evaluated according to the following criteria. Specifically, the soundness of the film after molding, as measured by the ERV test, was evaluated as the formability of the laminated metal sheet.

[0181] ◎: Less than 0.01 mA ○: 0.01 mA or more and less than 0.1 mA △: 0.1 mA or more and less than 1 mA ×: 1 mA or more

[0182] Table 2 shows the evaluation results of the laminated metal sheets and laminated metal containers obtained using the polyester films of Examples 1 to 6 and Comparative Examples 1 to 4.

[0183]

[0184] (Evaluation results of laminated metal sheet) In Comparative Example 1, the lamination entry side sheet temperature was low, so I 100 (90,0) / I amorphous (90,0) was larger than the upper limit of formula (3). In Comparative Example 1, good results were not obtained with respect to the primary adhesion and the adhesion during retort sterilization treatment.

[0185] Furthermore, the thickness of the polyester film varied greatly in Comparative Examples 2 and 4. Therefore, in Comparative Examples 2 and 4, good results were not obtained in terms of formability of the laminated metal sheet.

[0186] In Comparative Example 3, the stretching ratio was too high. Therefore, the polyester film of Comparative Example 3 was 100(60,0) / I 100 (60,90) and I 1-10(60,0) / I 1-10 (60,90) was lower than the lower limit of the formula (1) and (2). In Comparative Example 3, the orientation of the polyester film was too advanced, so that the I 100 (90,0) / I amorphous (90,0) was larger than the upper limit of the formula (3). Therefore, in Comparative Example 3, good results were not obtained with respect to the adhesion during retort sterilization and the formability of the laminated metal sheet.

[0187] Examples 1 to 6 obtained good results in the evaluation of primary adhesion, adhesion during retort sterilization, and formability of the laminated metal sheets. Furthermore, Examples 1 to 6 were able to stably produce the laminated metal sheets and laminated metal containers at all manufacturing stages.

[0188] From the above, it was confirmed that Examples 1 to 6 satisfy the performance requirements for laminated metal sheets and polyester films, and that polyester films and laminated metal sheets can be produced stably and with energy savings at both production stages.

[0189] 100 Laminated metal container 10 Laminated metal plate 20 Metal plate 21 Surface 22 Back surface 30 Polyester film

Claims

1. A polyester film containing a polyester containing polyethylene terephthalate as a component, A polyester film, the net strength of which is obtained by X-ray diffraction and shows a crystal orientation distribution in a pole figure, satisfies the following formulas (1) and (2): [Equation 1] 0.30 ≦ I 100 (60,0) / I 100 (60,90) ≦ 0.63 ・・・(1) 0.42 ≦ I 1-10 (60,0) / I 1-10 (60,90) ≦ 0.60 ・・・(2) In X-ray diffraction measurement using CuKα rays, the diffraction peak appearing at 2θ=26.5±1.0° is defined as 100 diffractions, and the diffraction peak appearing at 2θ=23.0±0.5° is defined as 1-10 diffractions. The pole figure is measured by setting the elevation angle α = 0°, where the bisector of the incident X-ray and the reflected X-ray are parallel to the film surface. In the pole figure of 100 diffractions, the in-plane rotation angle at which the maximum diffraction intensity is obtained when α=60° is set to β=90°, I 100 (60,0) is the net intensity at α=60° and β=0° in the pole figure of the 100 diffraction intensity, I 100 (60,90) is the net intensity at α=60° and β=90° in the pole figure of the 100 diffraction intensity, I 1-10 (60,0) is the net intensity at α=60° and β=0° in the pole figure of the 1-10 diffraction intensity, I 1-10 (60,90) is the net intensity at α=60° and β=90° in the pole figure of the 1-10 diffraction intensity.

2. 2. The polyester film according to claim 1, wherein the sample standard deviation of the thickness measured in the direction of incident X-rays when β=0° in the pole figure is 10% or less of the average of the measured thicknesses.

3. a first layer containing a polyester containing polyethylene terephthalate as a component; 2. The polyester film according to claim 1, further comprising: a second layer laminated to the first layer and containing a polyester containing polyethylene terephthalate as a component and a lubricant.

4. a first layer containing a polyester containing polyethylene terephthalate as a component; 3. The polyester film according to claim 2, further comprising: a second layer laminated to the first layer and containing a polyester containing polyethylene terephthalate as a component and a lubricant.

5. The polyester film of claim 3 , wherein the first layer contains a pigment.

6. The polyester film of claim 4 , wherein the first layer contains a pigment.

7. A method for producing a polyester film containing a polyester containing polyethylene terephthalate as a component, comprising: a non-stretched film production step of extruding the polyester through a T-die using an extruder to obtain a non-stretched film; a longitudinal uniaxially stretched film production 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 3.3 times or more and 7.5 times or less, and at a final preheat roll temperature of 75°C or more and 110°C or less.

8. A laminated metal plate, comprising a metal plate having a front surface and a back surface, and the polyester film according to any one of claims 1 to 6 bonded to at least one of the front surface and the back surface.

9. The laminated metal sheet according to claim 8, wherein the wide-angle X-ray diffraction spectrum satisfies the following formula (3): [Equation 2] I 100 (90,0) / I amorphous (90,0) ≦ 1.5 ・・・(3) 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. I 100 (90,0) is the net intensity of the 100 diffraction peak appearing at 2θ=26.5±1.0°, I amorphous (90,0) is the net intensity of the amorphous halo appearing at 2θ=20.0±5.0°.

10. A method for manufacturing the laminated metal sheet according to claim 8, 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 polyester film and the metal plate are preheated to a temperature in the range of −5°C to +50°C (the melting point of the polyester film) before the thermocompression bonding is performed.

11. A method for manufacturing the laminated metal sheet according to claim 9, 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 polyester film and the metal plate are preheated to a temperature in the range of −5°C to +50°C (the melting point of the polyester film) before the thermocompression bonding is performed.

12. A laminated metal container comprising the laminated metal sheet described in claim 8 as a material.

13. A laminated metal container comprising the laminated metal sheet described in claim 9 as a material.