Resin-coated metal sheet for containers

Abstract

The object of this invention is to provide a resin-coated metal sheet for containers that exhibits excellent basic properties of adhesion and coating of the resin film required for raw materials used in food canning, and further, excellent processability after heat treatment. One type of resin-coated metal sheet for containers comprises a metal sheet on both sides coated with an extended film containing polyester resin, wherein the polyester resin contains at least 92 mol% polyethylene terephthalate units, and the extended direction of the film surface after coating the metal sheet is measured at 1725 cm⁻¹ based on Raman spectroscopy. ‑1 ±5cm ‑1 The half-width at half maximum (FWHM) of the C=O peak is 20 cm. ‑1 ~25cm ‑1 Based on the above Raman spectral analysis, 1725 cm⁻¹ ‑1 ±5cm ‑1 The C=O peak intensity at 1615 cm⁻¹ is similar to that at 1615 cm⁻¹. ‑1 ±5cm ‑1 The ratio of C=C peak intensity (I) 1725 / I 1615 The value is above 0.50 and below 0.70.

Description

Technical Field

[0001] The present invention relates to resin-coated metal sheets for containers such as can bodies and lids for food canning, beverage canning, and aerosol canning. Background Technology

[0002] Previously, coatings were applied to metal sheets such as TFS (Tungsten Steel) and aluminum, which are used as raw materials for food canning, to improve their corrosion resistance, durability, and weather resistance. However, the coating process is complex, requires a lot of processing time, and results in the discharge of large amounts of solvent.

[0003] To address these issues, film-laminated metal sheets, which are made by laminating thermoplastic resin films onto heated metal sheets, have been developed to replace coated steel sheets. These sheets are used industrially as raw materials for food cans, beverage cans, and aerosol cans.

[0004] For these raw materials, in addition to basic properties such as processability and sealing, properties related to heat resistance and post-heat treatment processability are also required for processing after printing heat treatment, such as printing and distortion printing on the outer surface of the can. For metal sheets previously coated with polyester resin, the composition and melting point range of the polyester resin are controlled to improve heat resistance and post-heat treatment processability.

[0005] For example, in Patent Document 1, a polyester film with a resin composition and melting point within a specific range is applied to a metal container. However, although the dimensional change rate is less than 2.0% during heating for 2 minutes at 210°C, the processability after heat treatment is insufficient, resulting in film peeling and other issues after processing, such as in distorted printing.

[0006] Furthermore, Patent Document 2 discloses a film-laminated metal sheet using a polyester film. This polyester film is made by blending polyester primarily composed of polybutylene terephthalate (PET) and polyester primarily composed of polyethylene terephthalate (PET) in a specific ratio, and adjusting the heat shrinkage rate to a specific range at 130°C for 15 minutes. It can suppress the formation of shrinkage wrinkles during drying after the adhesive layer is applied. In addition, it exhibits excellent formability of the can, particularly in deep drawing and thinning, and also excellent heat lamination properties with metal, impact resistance, and flavor and aroma retention. However, because it contains 40% to 80% by mass of PET primarily composed of PET with a melting point between 200°C and 223°C, crystallization of the film occurs during post-printing heat treatment, resulting in insufficient processability after heat treatment.

[0007] Patent Document 3 discloses a two-piece laminated metal sheet for cans, comprising a first polyester resin layer formed on the surface that becomes the outer surface after the container is formed, and a second polyester resin layer formed on the surface that becomes the inner surface after the container is formed. The first polyester resin layer contains 30% to 60% by mass of polyethylene terephthalate or a copolymer of polyethylene terephthalate with a copolymer content of less than 6 mol%, 40% to 70% by mass of polybutylene terephthalate or a copolymer of polyethylene terephthalate with a copolymer content of less than 5 mol%, and 0.01% to 3.0% by external proportion of a polyolefin wax. The second polyester resin layer is a copolymer of polyethylene terephthalate with a copolymer content of less than 22 mol%, and the residual orientation degree of both the first and second polyester resin layers is less than 30%. However, the first polyester resin layer contains more than 40% and less than 70% by mass of polybutylene terephthalate. Therefore, although the boiling whitening property is improved, the processability after heat treatment is not sufficient because the film crystallizes due to heat treatment.

[0008] Patent document 4 discloses a biaxially extended polyester film made by copolymerizing a polyester film containing a specific amount of ternary or higher carboxylic acid components in the acid component of the polyester film. By setting the melting point and limiting viscosity of this polyester film within a specific range, a polyester film for metal lamination with excellent heat-lamination properties with a metal sheet can be obtained. In addition, the advanced processability during can forming after heat lamination is also excellent, and the generation of fuzz at the cut portion of the heat-laminated metal sheet is suppressed, and the impact resistance of the formed can is not reduced. However, although the generation of fuzz is suppressed, the heating temperature after printing is limited because the melting point is above 210°C and below 235°C, and the heat resistance is not sufficient.

[0009] Existing technical documents

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2006-289989

[0012] Patent Document 2: Japanese Patent Application Publication No. 2009-221315

[0013] Patent Document 3: Japanese Patent Application Publication No. 2014-166856

[0014] Patent Document 4: Japanese Patent Application Publication No. 2010-168432 Summary of the Invention

[0015] Problems to be solved by the invention

[0016] In view of the above, the object of the present invention is to provide a resin-coated metal sheet for containers that has excellent basic properties of adhesion and coating of the resin film required for raw materials for food canning, and further excellent processability after heat treatment.

[0017] Methods for solving problems

[0018] The inventors conducted in-depth research to solve this problem. The results showed that an extended film containing polyester resin, having contained more than 92 mol% polyethylene terephthalate units, and coated with a metal plate, exhibited a Raman spectral analysis at 1725 cm⁻¹ on the extension direction of the film surface. -1 ±5cm -1 The half-width of the nearby C=O peak is 20 cm. -1 Above and 25cm -1 Below, 1725cm -1 ±5cm -1 The C=O peak intensity at 1615 cm⁻¹ is similar to that at 1615 cm⁻¹. -1 ±5cm -1 The ratio of C=C peak intensity (I) 1725 / I 1615 The Raman spectroscopy value is between 0.50 and 0.70, indicating that in addition to excellent basic properties such as adhesion and coating, the film also exhibits excellent processability after heat treatment. It should be noted that the Raman spectroscopy analysis at this point was performed on the film surface before heat treatment.

[0019] Furthermore, the elongation direction after heat treatment of the polyester resin surface coated on the metal plate at 180°C for 10 minutes, as well as the direction at 45° and 135° relative to the aforementioned elongation direction, were measured using Raman spectroscopy at a depth of 1725 cm⁻¹. -1 ±5cm -1 The difference in half-peak width at half-peak height of Raman Peak is 0.8 cm. -1 Above and 1.2cm -1 The following ensures high workability after heat treatment.

[0020] This invention is based on the above insights, and its main points are as follows.

[0021] [1] A resin-coated metal plate for a container, comprising a stretched film containing a polyester resin coated on both sides, wherein the polyester resin contains 92 mol% or more of polyethylene terephthalate units, and the stretched direction of the film surface after coating the metal plate is Raman spectroscopy analysis at 1725 cm⁻¹. -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is 20 cm. -1 Above and 25cm -1The following is based on the above Raman spectroscopy analysis at 1725 cm⁻¹. -1 ±5cm -1 The C=O peak intensity at 1615 cm⁻¹ is similar to that at 1615 cm⁻¹. -1 ±5cm -1 The ratio of C=C peak intensity (I) 1725 / I 1615 The value is above 0.50 and below 0.70.

[0022] [2] According to the resin-coated metal plate for containers described in [1], wherein the extension direction of the film surface coated on the metal plate after heat treatment at 180°C for 10 minutes, and the directions at 45° and 135° relative to the extension direction, are measured at 1725 cm⁻¹ based on Raman spectroscopy. -1 ±5cm -1 The difference in the full width at half maximum (FWHM) of the C=O peaks is 0.8 cm. -1 Above and 1.2cm -1 the following.

[0023] [3] A container resin-coated metal sheet according to [1] or [2], wherein the film that forms the outer surface of the container after molding contains less than 30% by mass of titanium oxide.

[0024] [4] According to the resin-coated metal plate for container as described in [3], the film that becomes the outer surface side of the container after molding has at least two layers. In the case of two layers, there is an upper layer with a film thickness of 1.0 μm or more and 5.0 μm or less and a lower layer with a film thickness of 7 μm or more and 35 μm or less, wherein the lower layer faces the metal plate. In the case of three or more layers, there is an outermost layer and a bottommost layer with film thicknesses of 1.0 μm or more and 5.0 μm or less, and an intermediate layer with a film thickness of 6 μm or more and 30 μm or less, wherein the bottommost layer faces the metal plate. The upper layer, the outermost layer and the bottommost layer contain 0% by mass and 2% by mass of titanium oxide, and the intermediate layer and the bottom layer contain 10% by mass and 30% by mass of titanium oxide.

[0025] Invention Effects

[0026] According to the present invention, a resin-coated metal sheet for containers can be obtained, which has excellent adhesion and coating properties of the resin film required as a raw material for food canning, and further excellent processability after heat treatment. Attached Figure Description

[0027] Figure 1 This is a schematic cross-sectional view of the resin-coated metal plate for containers according to the present invention. Detailed Implementation

[0028] like Figure 1As shown, the resin-coated metal plate for containers of the present invention has a film (resin coating layer 3, 4) containing polyester resin coated on both sides of the metal plate 2.

[0029] The resin-coated metal plate for containers of the present invention will now be described in detail. First, the metal plate 2 used in the present invention will be described.

[0030] As the metal plate 2 of the present invention, aluminum plates, mild steel plates, etc., which are widely used as can materials can be used. In particular, surface-treated steel plates (hereinafter referred to as TFS) with a two-layer coating consisting of a lower layer containing metallic chromium and an upper layer containing chromium hydroxide are most suitable.

[0031] Regarding the coating amount of TFS, from the perspective of post-processing adhesion and corrosion resistance, calculations are all based on Cr, with the preferred chromium layer being 70 mg / m³. 2 Above and 200mg / m 2 The chromium hydroxide layer is preferably 10 mg / m³. 2 Above and 30mg / m 2 the following.

[0032] Next, the films (resin coating layers 3 and 4) containing polyester resin on both sides of the resin-coated metal plate for containers of the present invention will be described. It should be noted that the stretch film includes a uniaxial or biaxial stretch film, preferably a biaxial stretch film.

[0033] The aforementioned membrane comprises a polyester resin, wherein the polyester resin layer is primarily composed of polyethylene terephthalate (PET), and heat resistance is required; therefore, the PET unit content is 92 mol% or more, preferably 93 mol%.

[0034] To ensure properties such as mechanical strength, heat resistance, and corrosion resistance, terephthalic acid, as an acid component, is essential. However, further copolymerization with isophthalic acid improves processability and adhesion. Copolymerization of isophthalic acid at a concentration of 2 mol% to 10 mol% relative to terephthalic acid improves deep drawing formability and post-processing adhesion, making it a preferred option.

[0035] On the other hand, other dicarboxylic acid components and diol components can also be copolymerized within a range that does not impair the above-mentioned properties. Examples of dicarboxylic acid components include: aromatic dicarboxylic acids such as diphenylcarboxylic acid, sodium isophthalate-5-sulfonate, and phthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acids, maleic acid, and fumaric acid; aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid; and hydroxycarboxylic acids such as p-hydroxybenzoic acid. Examples of other diol components include: aliphatic diols such as propylene glycol, butanediol, pentanediol, hexanediol, and neopentanediol; alicyclic diols such as cyclohexanediol; aromatic diols such as bisphenol A and bisphenol S; diethylene glycol; and polyethylene glycol. It should be noted that two or more of these dicarboxylic acid components and diol components can also be used in combination. Furthermore, as long as it does not impair the effects of the present invention, multifunctional compounds such as trimellitic acid, pyromellitic acid, and trimethylolpropane can also be copolymerized.

[0036] Furthermore, the resin material is not limited by its manufacturing method. For example, there is a method that involves esterification of terephthalic acid, ethylene glycol, and a copolymer, followed by polycondensation of the resulting reaction product to produce a copolyester. Another method involves transesterification of dimethyl terephthalate, ethylene glycol, and a copolymer, followed by polycondensation of the resulting reaction product to produce a copolyester, thus forming a resin material. In the manufacture of copolyesters, additives such as fluorescent whitening agents, antioxidants, heat stabilizers, ultraviolet absorbers, and antistatic agents can be added as needed. The addition of fluorescent whitening agents is effective in improving whiteness.

[0037] Furthermore, for the polyester resin layer, which is mainly composed of polyethylene terephthalate, covering both sides of the container resin-coated metal plate of the present invention, the extension direction of the film surface behind the metal plate, based on Raman spectroscopy analysis, is 1725 cm⁻¹. -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is 20 cm. -1 Above and 25cm -1 The following range, 1725cm -1 ±5cm -1 The C=O peak intensity at 1615 cm⁻¹ is similar to that at 1615 cm⁻¹. -1 ±5cm -1 The ratio of C=C peak intensity (I) 1725 / I 1615 It is important that the film thickness is in the range of 0.50 or higher and 0.70 or lower. This is the most important element in this invention, thereby ensuring the adhesion, coverage, and workability after heat treatment that are the objectives of this invention. Here, "film surface covered behind the metal plate" refers to the film surface on the side not facing the metal plate. The reasons for this will be explained below.

[0038] 1725 cm⁻¹ was determined using Raman spectroscopy.-1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is an indicator of the crystallinity of polyethylene terephthalate resin.

[0039] Here, at 1725cm -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is less than 20 cm. -1 In this case, it exhibits high crystallinity and a relatively regular arrangement of polyethylene terephthalate molecular chains. As a result, it tends to have increased fracture strength but decreased flexibility and elongation at break. On the other hand, at 1725 cm⁻¹... -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is greater than 25 cm. -1 In this case, the crystallinity is low and the molecular chains of polyethylene terephthalate are arranged relatively randomly. As a result, there is a tendency for lower tensile strength but higher flexibility, thus increasing elongation at break. Therefore, low crystallinity is advantageous to ensure processability, while high crystallinity is advantageous to ensure corrosion resistance. Therefore, 1725cm -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak was set to 20 cm. -1 Above and 25cm -1 the following.

[0040] 1725cm -1 ±5cm -1 The C=O peak intensity and 1615 cm⁻¹ -1 ±5cm -1 The ratio of C=C peak intensity (I) 1725 / I 1615 When the concentration is less than 0.50, the proportion of the benzene ring and carbonyl group from terephthalic acid adopting a random conformation increases. As a result, the intermolecular chain interactions weaken, making the film more susceptible to cracking under impact stress. On the other hand, when (I... 1725 / I 1615 When the value is greater than 0.70, the proportion of benzene rings and carbonyl groups from terephthalic acid arranged in the same plane increases, the molecular chains become more compact and their ductility decreases, thus they cannot follow the deformation during processing. Therefore, (I 1725 / I 1615 Set it to be above 0.50 and below 0.70.

[0041] Furthermore, from the viewpoint of processability after heat treatment, it is preferable that the structural changes of the polyester film caused by heating have small and uniform anisotropy in all directions.

[0042] Furthermore, to improve processability after heat treatment, it is preferable to measure the elongation direction of the polyester resin surface coated on the metal plate after heat treatment at 180°C for 10 minutes, as well as the direction at 45° relative to the aforementioned elongation direction and the direction at 135° relative to the aforementioned elongation direction, based on Raman spectroscopy, at 1725 cm⁻¹. -1 ±5cm -1 The difference in the full width at half maximum (FWHM) of the C=O peaks is 0.8 cm. -1 Above and 1.2cm -1 Below. If the difference in half-width at half-maximum (FWHM) of Raman peak is 1.2 cm. -1 The following results in better film adhesion during processing. More preferably, the difference in the full width at half maximum (FWHM) of the Raman peak is 0.8 cm. -1 Above and 1.0cm -1 the following.

[0043] Furthermore, to ensure high processability, good demolding properties during molding, and to prevent stacking during transport in continuous molding production lines, it is preferable to add wax to the resin coating layer on the outer surface of the container after molding. The type of wax is not particularly limited; olefin waxes such as polyethylene, polypropylene, acid-modified polyethylene, and acid-modified polypropylene, fatty acid waxes such as palmitic acid, stearic acid, sodium stearate, and calcium stearate, and natural waxes such as carnauba wax can be used. Regarding the amount of wax added, it is preferable that the resin coating layer on the outer surface of the container after molding contains 0.10% by mass or more and 2.0% by mass or less.

[0044] The intrinsic viscosity (IV) of the polyester resin coating layer on the outer or inner surface of the container after molding is preferably 0.50 dl / g or higher and 0.90 dl / g or lower. More preferably, it is 0.52 dl / g or higher and 0.80 dl / g or lower, and more preferably 0.55 dl / g or higher and 0.75 dl / g or lower. If the intrinsic viscosity of the resin coating layer is 0.50 dl / g or higher, the molecular weight of the resin coating layer is high, which ensures sufficient mechanical strength. On the other hand, if the intrinsic viscosity of the resin coating layer is 0.90 dl / g or lower, excellent film-forming properties can be obtained. It should be noted that the intrinsic viscosity (IV) of the resin coating layer can be adjusted by controlling the polymerization conditions (polymerization catalyst amount, polymerization temperature, polymerization time, etc.) and by further solid-phase polymerization under an inactive atmosphere such as nitrogen or under vacuum after melt polymerization.

[0045] To improve the appearance design during molding and printing, the polyester resin coating that becomes the outer surface of the container after molding is sometimes required to be white. In this case, if the titanium oxide content is 30% by mass or less relative to the total weight of the resin coating, it will not affect the adhesion and processability of the metal sheet to the resin coating during molding processes with higher processing degrees. If the titanium oxide content is 8% or more, sufficient whiteness can be ensured after processing, which is preferred. Therefore, it is preferable to contain at least 8%, more preferably 10%, and even more preferably 12% or more of titanium oxide. The more preferred upper limit of the titanium oxide content is 25% or less, and even more preferably 20% or less.

[0046] As a method for adding titanium oxide, various methods shown in (1) to (3) below can be used. It should be noted that when adding titanium oxide using method (1), it is preferable to add titanium oxide to the reaction system in the form of a slurry dispersed in diol. In addition, in order to ensure the whiteness after processing, the thickness of the resin film layer 3 with added titanium oxide is preferably set to 10 μm or more. More preferably, the lower limit is 12 μm or more, and even more preferably, 15 μm or more. If the thickness of the resin layer containing titanium oxide is 10 μm or more, cracks will not occur, and more stringent processing can be carried out. On the other hand, if the thickness of the resin layer containing titanium oxide is 40 μm or less, it is economical. More preferably, it is 35 μm or less, and even more preferably, 25 μm or less.

[0047] (1) Adding titanium dioxide before the end of the transesterification or esterification reaction or before the start of the polycondensation reaction during the synthesis of copolyester;

[0048] (2) A method of adding to copolyester for melt blending;

[0049] (3) In methods (1) and (2), a method of manufacturing a masterbatch with a large amount of titanium oxide added, and blending it with a copolyester that does not contain particles to make it contain a specified amount of titanium oxide.

[0050] The polyester resin coating layer that becomes the inner or outer surface of the container after molding can also be in the form of a multilayer structure, with each layer having a function. For example, it can have a two-layer structure with an upper layer and a lower layer facing the metal plate, or a structure with at least three layers including an outermost layer (upper layer), an intermediate layer (main layer), and a bottommost layer facing the metal plate (lower layer). As an example of making each layer functional in the form of a multilayer structure, examples include: containing wax in the outermost layer and / or the bottommost layer to suppress the amount of wax in the resin coating layer as a whole, thereby effectively controlling processability. It is also considered that by adding slightly more pigment to the intermediate layer in a multilayer structure, the overall color tone of the layer can be controlled while ensuring processability, etc. In this case, the film thickness of the outermost layer and the bottommost layer is set to be 1.0 μm or more and 5.0 μm or less. The preferred lower limit of the film thickness of the outermost layer and the bottommost layer is 1.5 μm or more, more preferably 2.0 μm or more. The preferred upper limit of the film thickness of the outermost layer and the bottommost layer is 4.0 μm or less, and more preferably 3.0 μm or less. Furthermore, the thickness of the intermediate layer is set to be 6 μm or more and 30 μm or less. The preferred lower limit for the thickness of the intermediate layer is 8 μm or more, more preferably 10 μm or more. The preferred upper limit for the thickness of the intermediate layer is 25 μm or less, more preferably 20 μm or less. To balance whiteness and processability as layers, the outermost and bottommost layers may contain 0% to 2% by mass of titanium oxide, and the intermediate layer may contain 10% to 30% by mass of titanium oxide.

[0051] Furthermore, in the case of a two-layer structure, it can be cited that by including wax in the upper layer, the amount of wax per resin layer is reduced, effectively controlling processability. Similar to the three-layer case, the thickness of the upper layer is set to be 1.0 μm or more and 5.0 μm or less. The preferred lower limit for the upper layer thickness is 1.5 μm or more, more preferably 2.0 μm or more. The preferred upper limit for the upper layer thickness is 4.0 μm or less, more preferably 3.0 μm or less. Additionally, the thickness of the lower layer is 7 μm or more and 35 μm or less. The preferred lower limit for the lower layer thickness is 9 μm or more, more preferably 11 μm or more. The preferred upper limit for the lower layer thickness is 30 μm or less, more preferably 25 μm or less. To balance whiteness and processability as layers, the upper layer may contain 0% by mass or more and 2% by mass or less titanium oxide, and the lower layer may contain 10% by mass or more and 30% by mass or less titanium oxide.

[0052] Especially when titanium oxide is added to the outermost layer, the adhesion to printing ink is improved, and printability is enhanced. From the viewpoint of printability, the amount of titanium oxide in the outermost layer is preferably 0.5% by mass or more. On the other hand, if the amount of titanium oxide in the outermost layer is 2% by mass or less, the processability of the resin coating is better; therefore, the amount of titanium oxide in the outermost layer is preferably set to 2% by mass or less.

[0053] As described above, when each layer of the three-layer structure is functional, the outermost and bottommost layers function more effectively if their film thickness is 1.0 μm or more. That is, it more effectively suppresses the occurrence of cracking or wear of the resin coating layer and sufficiently ensures the gloss of the polyester resin coating layer that becomes the outer surface of the container after molding. On the other hand, when the outermost and bottommost layers are functional in this way, a thickness of 5.0 μm or less is economical.

[0054] [Manufacturing Method]

[0055] Next, the method for manufacturing the resin-coated metal sheet for containers of the present invention will be described. First, the method for manufacturing the multi-layered resin layer coated on the metal sheet will be described.

[0056] There are no particular limitations on the manufacturing method of the resin layer. One example is shown below. Each polyester resin is dried as needed and then fed into a known melt-lamination extruder, where it is extruded in sheet form from a slit-shaped die. Next, it is brought into contact with a casting drum by electrostatic application or other methods, and then cooled and cured to obtain an unstretched sheet. By stretching this unstretched sheet along the length and width directions of the film, a biaxially stretched film is obtained. The stretch ratio can be arbitrarily set according to the orientation, strength, elastic modulus, etc., of the target film. From the perspective of film quality, the stretching method preferably uses a tenter frame, and preferably a sequential biaxial stretching method where stretching is performed along the length direction followed by stretching along the width direction, or a simultaneous biaxial stretching method where stretching is performed approximately simultaneously in both the length and width directions.

[0057] Next, a method for manufacturing a resin-coated metal plate by laminating a resin layer (film) onto a metal plate will be described. In this invention, for example, a method is used whereby the metal plate is heated to a temperature above the melting point of the film, and a pressure roller (hereinafter referred to as a laminating roller) is used to bring the resin film into contact with both sides of the metal plate and perform thermal bonding (hereinafter referred to as lamination).

[0058] The lamination conditions are appropriately set to obtain the resin layer specified in this invention. First, the surface temperature of the metal plate at the start of lamination needs to be set above the Tm (melting point) of the resin layer in contact with the metal plate. Specifically, it needs to be controlled to be above Tm°C and below (Tm+40)°C. By setting the surface temperature of the metal plate above the Tm of the resin layer, the resin layer melts and wets the surface of the metal plate, ensuring good adhesion to the metal plate. On the other hand, when the temperature exceeds (Tm+40)°C, the resin layer may adhere to the lamination rollers, and it becomes difficult to control the crystal structure of the resin layer on the film surface after coating the metal plate within the range specified in this invention. Therefore, the desired 1725 cm⁻¹ based on Raman spectroscopy analysis cannot be obtained. -1 ±5cm -1The full width at half maximum (FWHM) of the C=O peak. Preferably, it is above Tm℃ and below (Tm+25)℃, more preferably above Tm℃ and below (Tm+15)℃.

[0059] In this invention, it is necessary to control the crystal structure of the resin layer on the surface of the film coated on the metal plate to an appropriate state. Therefore, it is necessary to adjust the surface temperature of the laminating roller to be above the Tg (glass transition temperature) of the resin layer. Specifically, it is necessary to adjust the surface temperature of the laminating roller in contact with the resin layer to be above Tg℃ and below (Tg+80)℃.

[0060] In addition, adjusting the contact time with the laminating roller is also an important factor. The contact time needs to be controlled to be between 10 and 20 milliseconds. By adjusting the surface temperature of the laminating roller and the contact time to the above range, the desired crystal structure can be achieved.

[0061] When the surface temperature of the laminating roller is below Tg℃ or the contact time with the laminating roller is less than 10 milliseconds, the proportion of benzene rings and carbonyl groups from terephthalic acid arranged in the same plane increases. (I) 1725 / I 1615 The value exceeds 0.70. Furthermore, when the surface temperature of the laminating roller exceeds (Tg+80)℃ or the contact time with the laminating roller exceeds 20 milliseconds, the proportion of the benzene ring and carbonyl group from terephthalic acid adopting a random conformation increases, (I... 1725 / I 1615 (less than 0.50)

[0062] Furthermore, it is preferable to heat the resin layer before lamination. By pre-softening the resin layer, a more uniform temperature distribution can be achieved within the cross-section of the resin layer during lamination. Consequently, the crystal structure within the resin layer cross-section becomes a crystal structure with a gradual structural change from the interface with the metal plate to the surface layer, resulting in more homogeneous performance. Specifically, it is preferable to control the temperature of the resin layer before lamination to be above Tg℃ and below (Tg+30)℃.

[0063] After lamination, rapid quenching (water cooling) is required to fix the crystal structure of the resin layer. The quenching time should be limited to less than 1 second, preferably less than 0.7 seconds. The quenching water temperature should be below the Tg of the resin layer.

[0064] Example

[0065] The embodiments of the present invention will be described below.

[0066] (Methods for manufacturing metal sheets)

[0067] Using steel sheets with a thickness of 0.22 mm and a width of 977 mm that have undergone cold rolling, annealing, and surface finishing, chrome plating is performed after degreasing and pickling to manufacture chrome-plated steel sheet (TFS). Chrome plating is carried out in a process containing CrO3 and F... - 、SO4 2- Electroplating is performed in a plating bath containing CrO3 and F, followed by an intermediate rinse. - Electrolytic treatment is carried out in the chemical conversion solution. During the chemical conversion treatment, the electrolysis conditions (current density, charge, etc.) are adjusted so that the amount of metallic chromium and chromium hydroxide deposited, calculated as Cr, are each 120 mg / m³. 2 15mg / m 2 .

[0068] (Method for manufacturing a resin-coated film on the inner and outer surfaces of a container)

[0069] Following conventional methods, the polyester resin with the resin composition shown in Table 1 is dried and melted, co-extruded from a T-die, and then cooled and solidified on a cooling drum to obtain an unstretched film. The obtained unstretched film is then biaxially stretched and heat-fixed to obtain a biaxially stretched polyester film.

[0070]

[0071] (Manufacturing method of resin-coated metal sheet for container)

[0072] The chrome-plated steel sheet obtained above is laminated with a polyester film. The polyester film (A) that forms the outer surface of the container after it is formed is laminated on one side, and the polyester film (B) that forms the inner surface of the container is laminated on the other side. Figure 1 The diagram shows a schematic of a resin-coated steel sheet.

[0073] When laminating a polyester film (A) onto a metal plate, the surface temperature of the metal plate is controlled to be above Tm℃ and below (Tm+40)℃ of the polyester resin layer (a1) constituting the polyester film (A). Furthermore, the surface temperature of the laminating roller (a) is set to be above Tg℃ and below (Tg+80)℃ of the polyester film (A). The surface temperature of the laminating roller (b) is set to be above (Tg+10)℃ and below (Tg+110)℃ of the polyester film (B), and the contact time with the metal plate is set to be above 10 milliseconds and below 20 milliseconds. Laminating rollers a and b are internally water-cooled, and temperature control during film bonding is achieved by circulating cooling water within the rollers. The temperature of the resin layer before lamination is set to be above (Tg+30)℃ and below (Tg+100)℃ of the polyester film (A) to achieve uniform temperature distribution within the cross-section of the resin layer. Then, water cooling is performed using a metal strip cooling device to manufacture a resin-coated metal plate for containers.

[0074] (Evaluation of resin-coated metal sheets for containers)

[0075] The following characteristics were measured and evaluated on the resin-coated metal plate and the resin layer on the metal plate obtained according to the above. The measurement and evaluation methods are shown below.

[0076] (1) Evaluation of crystallinity of film surface based on Raman spectroscopy

[0077] For a flat sample of a laminated metal sheet before heat treatment, the half-peak widths (FWHMs) of the Raman peaks in the length direction (0°) and width direction (90°) of the laminated steel sheet were determined. It should be noted that in this embodiment, each length and width direction corresponds to the film's extension direction. Furthermore, based on this measurement, 1725 cm⁻¹ was determined. -1 ±5cm -1 The C=O peak intensity and 1615 cm⁻¹ -1 ±5cm -1 The ratio of the C=C peak intensities.

[0078] Next, a heat treatment of 180℃ for 10 minutes was performed. The angles of the heat-treated plate sample along its length (0°), width (90°), and rotations of 45° and 135° clockwise relative to its length were measured to a depth of 1725 cm. -1 ±5cm -1 Find the half-width at half-maximum (WHM) of the Raman peak and calculate the difference in WHM between different orientations.

[0079] (Measurement conditions)

[0080] Measurement apparatus: Almega XR Raman spectroscopy analyzer manufactured by Thermo Fisher Scientific Co., Ltd.

[0081] Excitation source: Semiconductor laser (λ = 532 nm)

[0082] Microscope magnification: ×100

[0083] Aperture: 25μmφ

[0084] Measurement directions: The laser polarization plane, relative to the cross-section of the laminated metal plate, is parallel to the film's length direction (0°), width direction (90°), and directions rotated clockwise by 45° and 135° from the length direction, respectively.

[0085] (2) Fit

[0086] A sample was prepared by cutting a resin-coated metal plate into dimensions of 120 mm in length and 30 mm in width. A portion of the film was peeled off from the short side of the inner surface of the sample. The peeled portion of the film was then unfolded in the opposite direction (angle: 180°) to the chrome-plated steel plate from which the film was peeled off, and a peeling test was conducted at a tensile speed of 30 mm / min. The adhesion force was evaluated for every 15 mm of width.

[0087] (score)

[0088] ◎◎:11N / 15mm and above

[0089] ◎: 8N / 15mm or more and less than 11N / 15mm

[0090] 〇: 5N / 15mm or more and less than 8N / 15mm

[0091] ×: Less than 2N / 15mm

[0092] The above are judged as having the expected closeness.

[0093] (3) Coverability

[0094] After applying wax to the resin-coated metal plate, a circular plate with a diameter of 165 mm is punched out, and a shallow-drawn can is obtained with a drawing ratio of 1.52. Next, this shallow-drawn can is further drawn with a drawing ratio of 1.60 to produce a deep-drawn can. The processing condition of the film on the deep-drawn can is then visually observed.

[0095] (score)

[0096] ◎: No damage was observed in the film after forming.

[0097] ○: The membrane can be formed, but localized damage (less than 3 mm) is observed.

[0098] ×: The tank is ruptured and cannot be repaired.

[0099] Anything above 0 is considered to have the desired coverage.

[0100] (4) Film adhesion of the sample after heat treatment (processability after heat treatment)

[0101] The cans that can be formed (○ or above) in the above-mentioned coating evaluation (3) are taken as the objects. Using the formed cans, a peel test is performed at a tensile speed of 30 mm / min, and the adhesion force is evaluated for every 15 mm width. The evaluation object is the can body part of the inner surface of the can.

[0102] (score)

[0103] ◎◎:7N / 15mm or more

[0104] ◎: 5N / 15mm or more but less than 7N / 15mm

[0105] 〇: 3N / 15mm or more but less than 5N / 15mm

[0106] △: 1N / 15mm or more but less than 3N / 15mm

[0107] ×: Less than 1N / 15mm

[0108] A value of 0 or higher is considered to indicate that the material has the desired workability after heat treatment.

[0109] The evaluation results of sealing, coating, and post-heat treatment processability are summarized in Table 2.

[0110] [Table 2]

[0111] tightness Coverability Processability after heat treatment Example 1 ◎ ○ ◎ Example 2 ◎ ○ ○ Example 3 ◎◎ ◎ ◎ Example 4 ◎◎ ◎ ◎◎ Example 5 ◎ ○ ○ Example 6 ◎ ◎ ◎ Example 7 ◎ ◎ ◎◎ Example 8 ◎ ◎ ○ Example 9 ◎ ◎ ◎ Comparative Example 1 ◎ ◎ △ Comparative Example 2 × × - Comparative Example 3 ○ ○ × Comparative Example 4 ◎ ○ △

[0112] In the examples of this invention, excellent adhesion and coating properties result in excellent processability after heat treatment. In contrast, in comparative examples that deviate from the scope of this invention, at least one of the adhesion, coating properties, and processability after heat treatment is poor.

[0113] Industrial availability

[0114] The resin-coated metal sheet for containers of the present invention is suitable for container and packaging applications as a raw material for food canning and aerosol cans. Furthermore, it can be used as a raw material for containers subjected to deep drawing processes, etc.

[0115] Symbol Explanation

[0116] 1. Resin-coated metal sheet for container

[0117] 2 Metal Plates

[0118] 3, 4 Resin Coating (Film)

Claims

1. A resin-coated metal sheet for containers, wherein both sides of the metal sheet are coated with a biaxially stretched film comprising polyester resin, wherein... The polyester resin contains more than 92 mol% of polyethylene terephthalate units. The extension direction of the film surface behind the metal plate at 1725 cm⁻¹ based on Raman spectroscopy analysis -1 ±5cm -1 The full width at half maximum (FWHM) of the C=O peak is 20 cm. -1 Above and 25cm -1 the following, Based on the Raman spectroscopy analysis, 1725 cm⁻¹ -1 ±5cm -1 The C=O peak intensity at 1615 cm⁻¹ is similar to that at 1615 cm⁻¹. -1 ±5cm -1 The ratio of C=C peak intensity to I 1725 / I 1615 Values ​​between 0.50 and 0.70 The extension direction of the membrane surface is the length direction and the width direction of the membrane.

2. The resin-coated metal plate for containers according to claim 1, wherein, The extension direction of the film surface coated on the metal plate after heat treatment at 180°C for 10 minutes, and the directions rotated 45° clockwise and 135° clockwise relative to the length direction, based on Raman spectroscopy at 1725 cm⁻¹. -1 ±5cm -1 The difference in the full width at half maximum (FWHM) of the C=O peaks is 0.8 cm. -1 Above and 1.2cm -1 the following.

3. The resin-coated metal sheet for containers according to claim 1 or 2, wherein, The membrane, which becomes the outer surface of the container after forming and processing, contains less than 30% by mass of titanium dioxide.

4. The resin-coated metal plate for containers according to claim 3, wherein, The membrane, which becomes the outer surface of the container after forming and processing, has at least two layers. In the case of a two-layer structure, the upper layer has a film thickness of 1.0 μm or more and 5.0 μm or less, and the lower layer has a film thickness of 7 μm or more and 35 μm or less, wherein the lower layer faces the metal plate. In the case of three or more layers, there is an outermost layer and a bottommost layer, each with a film thickness of 1.0 μm or more and 5.0 μm or less, and an intermediate layer with a film thickness of 6 μm or more and 30 μm or less, wherein the bottommost layer faces the metal plate. The upper layer, the outermost surface layer, and the lowermost layer contain more than 0% by mass and less than 2% by mass of titanium dioxide. The intermediate layer and the lower layer contain more than 10% by mass and less than 30% by mass of titanium dioxide.

Images