Resin-coated metal sheet

Abstract

Provided is a resin-coated metal sheet that achieves both the slidability and scraping resistance of the resin coating layer and the ink adhesion. A resin-coated metal sheet (1) comprises: a metal sheet (2); and a resin coating layer (3) containing 75 mass or more of polyester resin relative to total resin, wherein the resin coating layer (3) has at least a three-layer structure including an outermost layer (3a), an intermediate layer (3b), and an undermost layer (3c), a melting point of the resin coating layer (3) is 230 °C or higher and 254 °C or lower, the outermost layer (3a) contains a polyolefin, a melting point of the polyolefin is 80 °C or higher and 140 °C or lower, and a dispersed particle size of the polyolefin measured by Raman spectroscopy is 0.018 μm or more and 5.0 μm or less.

Description

Resin-coated metal sheet

[0001] The present invention relates to a resin-coated metal sheet.

[0002] Laminated steel sheets have been developed, in which the surface of metal sheets, such as tin-free steel (TFS) and aluminum, used as materials for metal containers, is coated with a thermoplastic resin film. Laminated steel sheets are widely used in the fields of beverage cans and food cans, which require strict forming processes.

[0003] In recent years, from the viewpoint of resource conservation and material cost reduction, the materials used for metal containers, particularly the metal plates and resin coating layers, have been made thinner by tightening processing conditions. As a result, the degree of processing during can body production increases, and there is a possibility that the resin coating layer located on the outer surface of the container may be broken or scraped, particularly after molding. In light of this, there is a need for material designs that suppress breakage or scraping of the resin coating layer during can body production. As a technology for suppressing breakage or scraping of the resin coating layer, Patent Documents 1 and 2 propose methods of adding a lubricating component to the resin coating layer to improve the slip properties and scraping resistance of the resin coating layer.

[0004] After molding, the resin coating layer located on the outer surface of the container is printed to improve its design. If the affinity between the various inks used for printing and the resin coating layer is low, sufficient ink adhesion cannot be ensured, which can cause the printing ink to peel off during can processing, potentially damaging the design and aesthetic appeal of the can's appearance.

[0005] International Publication No. WO 2019 / 116706 International Publication No. WO 2019 / 116707

[0006] The lubricating component added to the resin coating layer prevents the resin coating layer from breaking or scraping. However, it may also impair the affinity between the printing ink applied during printing and the surface of the resin coating layer, which may result in ink peeling during processing. Therefore, there is a demand for a resin-coated metal sheet that achieves a high level of both the slipperiness and scraping resistance of the resin coating layer and the adhesion of the printing ink.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a resin-coated metal sheet that has a resin coating layer that is both smooth and scratch-resistant, and that has good ink adhesion.

[0008] The present inventors have conducted extensive research to achieve the above-mentioned object, and as a result have discovered the following: Conventionally, only the dispersed particle size of the lubricating component present locally on the outermost surface of the resin coating layer has been understood. However, by capturing the dispersed particle size of the lubricating component in a wider range and in a three-dimensional manner, including the dispersed particle size of the lubricating component present inside the resin coating layer in the thickness direction, the present inventors have found a dispersed particle size range of the lubricating component that satisfies both the lubricity, abrasion resistance, and ink adhesion of the resin coating layer, and have completed the present invention.

[0009] The present invention has been made based on the above findings. That is, the gist and configuration of the present invention are as follows.

[0010] [1] A resin-coated metal sheet comprising a resin coating layer on at least one surface of the metal sheet, the resin coating layer containing 75% by mass or more of polyester resin based on the total resin, wherein the resin coating layer has a three-layer structure including an outermost layer, an intermediate layer, and a bottom layer, the resin coating layer has a melting point of 230°C or more and 254°C or less, the outermost layer contains a polyolefin, the melting point of the polyolefin is 80°C or more and 140°C or less, and the dispersed particle size of the polyolefin measured by Raman spectroscopy on the outermost surface and inside in the thickness direction of the resin coating layer is 0.018 μm or more and 5.0 μm or less.

[0011] [2] The resin-coated metal sheet according to the above [1], wherein the outermost layer contains 0.10 mass % or more and 1.0 mass % or less of the polyolefin.

[0012] [3] The resin-coated metal sheet according to [1] or [2] above, wherein the weight average molecular weight of the polyolefin is 2,500 or more and 80,000 or less.

[0013] [4] The resin-coated metal sheet according to any one of [1] to [3] above, wherein the polyolefin is at least one of an acid-modified polyolefin and an oxidized polyolefin.

[0014] [5] The resin-coated metal sheet according to any one of [1] to [4] above, wherein the acid value of the polyolefin is 1.0 mg KOH / g or more and 80 mg KOH / g or less.

[0015] [6] The resin-coated metal sheet according to any one of [1] to [5] above, wherein the intermediate layer contains 10% by mass or more and 30% by mass or less of inorganic particles.

[0016] [7] The outermost layer and the lowermost layer have a thickness of 1.0 μm or more and 5.0 μm or less, respectively, and the intermediate layer has a thickness of 6.0 μm or more and 30 μm or less. [1] The resin-coated metal sheet according to any one of [6] to [7].

[0017] [8] A metal container made using the resin-coated metal sheet according to any one of [1] to [7] above, wherein the resin coating layer is located on the outside of the metal container.

[0018] According to the present invention, it is possible to provide a resin-coated metal sheet that has a resin coating layer that exhibits both good slip properties and abrasion resistance, as well as good ink adhesion.

[0019] FIG. 2 is a diagram showing an outline of a cross section of a resin-coated metal plate.

[0020] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0021] Fig. 1 is a cross-sectional view showing the configuration of a resin-coated metal sheet according to one embodiment of the present invention. As shown in Fig. 1, the resin-coated metal sheet 1 includes a metal sheet 2, a resin coating layer 3 formed on the front surface of the metal sheet 2, and a resin coating layer 4 formed on the back surface of the metal sheet 2. The resin coating layers 3 and 4 may be provided on only one surface of the metal sheet 2. The resin coating layers 3 and 4 are located on the outer and inner surfaces of the container, respectively, after molding. As shown in Fig. 1, the resin coating layer 3 has at least a three-layer structure consisting of an outermost layer 3a, an intermediate layer 3b, and a bottom layer 3c, and the resin coating layer 4 may also have a three-layer structure.

[0022] [Metal Sheet] The metal sheet is preferably a steel sheet. The metal sheet is preferably tinplate or tin-free steel (TFS). For tinplate, the plating amount per side is 0.5 g / m ２ 15g / m or more ２ It is preferable to use tinplate within the following range: TFS has a coating amount of 50 mg / m per side. ２ 200mg / m or more ２ The following metal chromium layer and the metal chromium layer have a metal chromium equivalent coating amount of 3 mg / m per side. ２ 30mg / m or more ２ It is preferable that the metal sheet has the following chromium oxide layer on its surface. The type of metal sheet is not particularly limited as long as it can be formed into the desired shape, but metal sheets with the following components and manufacturing methods are preferred. (1) A metal sheet obtained by recrystallization annealing low-carbon steel having a C (carbon) content in the range of 0.010% by mass to 0.10% by mass using continuous annealing. (2) A metal sheet obtained by recrystallization annealing low-carbon steel having a C content in the range of 0.010% by mass to 0.10% by mass using continuous annealing and overaging treatment. (3) A metal sheet obtained by recrystallization annealing low-carbon steel having a C content in the range of 0.010% by mass to 0.10% by mass using box annealing. (4) A metal sheet obtained by recrystallization annealing low-carbon steel having a C content in the range of 0.010% by mass to 0.10% by mass using continuous annealing or box annealing, followed by secondary cold rolling (double reduced rolling). (5) A metal plate obtained by recrystallization annealing an IF (Interstitial Free) steel, which is an ultra-low carbon steel having a C content of 0.003 mass% or less and to which an element that fixes the dissolved C, such as Nb or Ti, is added, through continuous annealing.

[0023] The mechanical properties of the steel sheet are not particularly limited as long as they can be formed into the desired shape. In order to obtain better formability and maintain better can body strength, the yield point (YP) of the steel sheet is preferably 220 MPa or more and 580 MPa or less. Furthermore, the Lankford value (r value), which is an index of plastic anisotropy, is preferably 0.8 or more. Furthermore, the absolute value of the in-plane anisotropy Δr of the r value is preferably 0.7 or less.

[0024] The steel components required to satisfy the above mechanical properties are not particularly limited, but may contain, for example, Si, Mn, P, S, Al, N, and other components. The Si content is preferably 0.001 mass% or more and 0.1 mass% or less. The Mn content is preferably 0.01 mass% or more and 0.6 mass% or less. The P content is preferably 0.002 mass% or more and 0.05 mass% or less. The S content is preferably 0.002 mass% or more and 0.05 mass% or less. The Al content is preferably 0.005 mass% or more and 0.100 mass% or less. The N content is preferably 0.0005 mass% or more and 0.020 mass% or less. Furthermore, the steel sheet may contain other components such as Ti, Nb, B, Cu, Ni, Cr, Mo, and V. However, from the viewpoint of ensuring corrosion resistance and the like, the total content of these component elements is preferably 0.02 mass% or less.

[0025] The thickness of the metal plate is not particularly limited, but may be, for example, 0.20 mm or more and 0.25 mm or less.

[0026] [Resin Coating Layer] The resin coating layer 3 contains polyester resin in an amount of 75% by mass or more, calculated as solid content, based on the total resin. The polyester resin content here refers to the proportion of polyester resin in the resin, minus the weight of additives such as polyolefin and inorganic particles contained in the resin coating layer. The resin coating layer 3 preferably contains polyester resin in an amount of 80% by mass or more, and preferably 100% by mass or less, based on the total resin.

[0027] Polyester resins are polymers consisting of dicarboxylic acid units and glycol units.

[0028] As the dicarboxylic acid unit, units derived from aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfoisophthalic acid, and phthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and oxycarboxylic acids such as p-oxybenzoic acid can be used.

[0029] As the glycol unit, units derived from aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S; and diethylene glycol can be used.

[0030] The above-mentioned dicarboxylic acids and glycols may be used in combination in such a manner that the heat resistance and processability are not impaired.

[0031] The resin coating layer 3 has a melting point of 230°C or higher and 254°C or lower. A melting point of 230°C or higher can effectively prevent the resin from softening during molding, thereby more effectively preventing breakage or abrasion. Furthermore, a melting point of 254°C or lower can ensure that the crystallinity of the polyester resin contained therein is within a more suitable range, more effectively preventing breakage or abrasion of the resin coating layer 3 during molding. The melting point of the resin coating layer 3 is preferably 234°C or higher, more preferably 238°C or higher. The melting point of the resin coating layer 3 is preferably 252°C or lower, more preferably 250°C or lower. The melting point of the resin coating layer 3 is measured using a differential scanning calorimeter. The melting point of the resin coating layer 3 is determined by the peak-top temperature of the endothermic peak in the heat flow chart, which is in the range of 200°C to 280°C.

[0032] The outermost layer 3a of the resin coating layer 3 contains a polyolefin as a lubricating component. By including a polyolefin as a lubricating component in the outermost layer 3a, excellent slip properties and abrasion resistance can be ensured, and fracture or abrasion of the resin coating layer 3 can be suppressed even during can body molding under severe processing conditions. A polyolefin having excellent film-forming and dispersibility properties and a melting point within an appropriate range is used as the lubricating component. Preferably, a polyolefin having a polar group is used to ensure sufficient affinity with the polyester resin, which is the main component of the resin coating layer 3. Examples of polyolefins having a polar group include acid-modified polyolefins such as ethylene-maleic anhydride copolymers, oxidized polyolefins such as polyethylene oxide, and ethylene-acrylic acid copolymers. A combination of multiple types of polyolefins may be used as the polyolefin.

[0033] The polyolefin is preferably at least one of an acid-modified polyolefin and an oxidized polyolefin. This is because the acid value of the polyolefin is sufficiently high, improving the affinity between the outermost layer 3 a and the printing ink. The polyolefin may also be a mixture of an acid-modified polyolefin and an oxidized polyolefin.

[0034] The melting point of the polyolefin is 80°C or higher and 140°C or lower. If the melting point of the polyolefin is lower than 80°C, the polyolefin is likely to thicken on the surface of the resin coating layer 3 due to the heat treatment performed during the process of coating the metal plate with the resin coating layer 3 and during the molding of the resin-coated metal plate. The polyolefin thickened on the surface may inhibit the adhesion of the printing ink, which may cause the printing ink to peel off during molding. Furthermore, if the melting point of the polyolefin exceeds 140°C, sufficient slip properties and abrasion resistance may not be ensured, and the resin coating layer 3 may break or be chipped during molding. The melting point of the polyolefin is preferably 90°C or higher, more preferably 100°C or higher. The melting point of the polyolefin is preferably 130°C or lower, more preferably 120°C or lower. The melting point of the polyolefin is measured according to the method described in the Examples below.

[0035] The dispersed particle size of the polyolefin on the outermost surface and in the depth direction of the resin coating layer 3 is 0.018 μm or more and 5.0 μm or less. The dispersed particle size of the polyolefin is measured by peak intensity ratio analysis of Raman spectroscopy spectra obtained by Raman spectroscopy using a confocal Raman spectrometer. This measurement method allows for non-destructive, high-resolution, three-dimensional calculation of the dispersion state of the polyolefin in the resin coating layer 3, making it possible to capture the dispersed particle size of the polyolefin that cannot be captured by other analytical methods. If the dispersed particle size of the polyolefin present on the outermost surface and in the depth direction of the resin coating layer 3 is less than 0.018 μm, it is too small to ensure sufficient slip properties and abrasion resistance, and there is a risk of breakage or abrasion during molding. Furthermore, if the dispersed particle size of the lubricating component present on the outermost surface and in the depth direction of the resin coating layer 3 exceeds 5.0 μm, excessively large dispersed particles of polyolefin may become the starting point for breakage or abrasion during molding. Furthermore, due to the influence of multiple heat treatments performed during molding, the proportion of polyolefin concentrated and exposed on the surface of the resin coating layer 3 increases, which may hinder the adhesion of printing ink and cause peeling of the printing ink during molding. The dispersed particle size of the polyolefin on the outermost surface and inside the thickness direction of the resin coating layer 3 is preferably 0.030 μm or more, more preferably 0.050 μm or more. The dispersed particle size of the polyolefin on the outermost surface and inside the thickness direction of the resin coating layer 3 is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less. The dispersed particle size of the polyolefin on the outermost surface and inside the thickness direction of the resin coating layer 3 is measured according to the method described in the Examples below.

[0036] A conventional method for measuring the dispersed particle size of lubricating components is to use a chemical force microscope (CFM). This method involves observing only the surface of the resin coating layer in a 1 μm × 1 μm field of view, and calculating the dispersed particle size of the observed lubricating component particles from their major and minor axes. On the other hand, when using Raman spectroscopy as in the present invention, a wider field of view than conventional methods is measured, including the thickness direction, of 50 μm (in the lamination direction of the resin-coated metal sheet) × 50 μm (in the direction perpendicular to the lamination direction within the surface of the resin-coated metal sheet) × 3 μm (in the thickness direction of the resin-coated metal sheet), and the dispersed particle size is calculated. Therefore, Raman spectroscopy can capture more dispersed particles of polyolefin in the resin coating layer than conventional methods, and highly accurate dispersed particle size can be obtained.

[0037] Another conventional method involves etching the surface polyester resin of a resin coating layer with an alkaline aqueous solution, measuring the major and minor axes of the remaining modified polyolefin particles one by one, and calculating the particle size. This method is destructive and cannot capture the actual dispersion state of the modified polyolefin particles dispersed in the resin coating layer. In addition, when the resin coating layer is etched with an alkaline aqueous solution, the shape and particle size of the extracted modified polyolefin particles may differ from the state of dispersion in the resin coating layer. Therefore, it is difficult to use this method to determine how the modified polyolefin particles contribute to the required performance of the resin coating layer or resin-laminated metal sheet. On the other hand, when using Raman spectroscopy as in the present invention, the particle size and dispersion state of the polyolefin actually dispersed in the resin coating layer can be captured non-destructively and with high resolution, allowing for highly accurate determination of how the dispersed polyolefin particles contribute to the required performance.

[0038] The polyolefin content in the outermost layer 3a is preferably 0.10% by mass or more, and preferably 1.0% by mass or less, calculated as solid content. If the polyolefin content in the outermost layer 3a is 0.10% by mass or more, more suitable slip properties and abrasion resistance can be ensured during molding, and breakage or abrasion of the resin coating layer 3 can be prevented. If the polyolefin content in the outermost layer 3a is 1.0% by mass or less, more suitable abrasion resistance and ink adhesion are achieved. The polyolefin content in the outermost layer 3a is more preferably 0.20% by mass or more, and even more preferably 0.40% by mass or more. The polyolefin content in the outermost layer 3a is more preferably 0.90% by mass or less, and even more preferably 0.80% by mass or less.

[0039] The weight-average molecular weight of the polyolefin is preferably 2500 or more and preferably 80,000 or less. If the weight-average molecular weight of the polyolefin is 2500 or more, thickening of the polyolefin on the surface of the resin coating layer 3 can be more effectively prevented, and ink adhesion can be further improved. If the weight-average molecular weight of the polyolefin is 80,000 or less, more preferable slip properties and abrasion resistance can be ensured during molding processing, and breakage or abrasion of the resin coating layer 3 can be more effectively prevented. The weight-average molecular weight of the polyolefin is more preferably 3,000 or more, and even more preferably 3,500 or more. The weight-average molecular weight of the polyolefin is more preferably 70,000 or less, and even more preferably 65,000 or less. The weight-average molecular weight of the polyolefin is measured according to the method described in the Examples below.

[0040] The acid value of the polyolefin is preferably 1.0 mgKOH / g or more, and preferably 80 mgKOH / g or less. If the acid value of the polyolefin is 1.0 mgKOH / g or more, the affinity between the resin coating layer 3 and the printing ink can be sufficiently ensured, and the adhesion of the printing ink can be improved. If the acid value of the polyolefin is 80 mgKOH / g or less, the polyolefin is not compatible with the resin coating layer 3, thereby ensuring more suitable slip properties and abrasion resistance, and more preferably preventing breakage or abrasion during molding. The acid value of the polyolefin is more preferably 1.5 mgKOH / g or more, and even more preferably 2.0 mgKOH / g or more. The acid value of the polyolefin is more preferably 50 mgKOH / g or less, and even more preferably 45 mgKOH / g or less. The acid value of the polyolefin is measured according to the method described in the Examples below.

[0041] The resin coating layer 3 may be required to be white in order to enhance the design and beauty of the appearance of the can body after printing. In this case, it is preferable that the intermediate layer 3b of the resin coating layer 3 contains inorganic particles. This is because the resin coating layer 3 can be made white by containing inorganic particles in the intermediate layer 3b.

[0042] The intermediate layer 3b preferably contains 10% by mass or more, and preferably 30% by mass or less, of inorganic particles in terms of solid content. If the intermediate layer 3b contains 10% by mass or more of inorganic particles, sufficient whiteness can be ensured. If the intermediate layer 3b contains 30% by mass or less of inorganic particles, fracture or abrasion of the resin coating layer 3 can be more suitably prevented even under more severe processing conditions. The content of inorganic particles in the intermediate layer 3b is more preferably 12% by mass or more, and even more preferably 15% by mass or more. The content of inorganic particles in the intermediate layer 3b is more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0043] The inorganic particles contained in the intermediate layer 3b are not particularly limited. The inorganic particles are preferably titanium oxide. The titanium oxide is preferably rutile-type titanium oxide having a purity of 90% or more. When the inorganic particles contained in the intermediate layer 3b are the above-mentioned titanium oxide, the titanium oxide exhibits good dispersibility when mixed with the polyester resin, and the uniform whiteness improves the design and beauty of the appearance.

[0044] When the resin coating layer 3 has at least a three-layer structure consisting of a surface layer 3a, an intermediate layer 3b, and a bottom layer 3c, the thicknesses of the surface layer 3a and the bottom layer 3c are preferably 1.0 μm or more and 5.0 μm or less, respectively. The thicknesses of the surface layer 3a and the bottom layer 3c may be different from each other. Having the thicknesses of the surface layer 3a and the bottom layer 3c within the above ranges ensures more favorable slip properties and abrasion resistance during molding, and more favorably prevents breakage or abrasion of the resin coating layer 3. The thicknesses of the surface layer 3a and the bottom layer 3c are each more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. The thicknesses of the surface layer 3a and the bottom layer 3c are each more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. The thicknesses of the surface layer 3a and the bottom layer 3c are measured according to the method described in the Examples below.

[0045] The thickness of the intermediate layer 3b is preferably 6.0 μm or more and preferably 30 μm or less. When the thickness of the intermediate layer 3b is within the above range, there is no need to vary the thicknesses of the outermost layer 3a and the bottom layer 3c, and the absolute amount of polyolefin is suppressed from increasing or decreasing. As a result, the dispersed particle size falls within a more appropriate range, which more effectively prevents the resin coating layer 3 from breaking or being scraped during molding. Furthermore, the adhesion of printing ink to the resin coating layer 3 can be further improved. The thickness of the intermediate layer 3b is more preferably 8.0 μm or more, even more preferably 10 μm or more. The thickness of the intermediate layer 3b is more preferably 25 μm or less, even more preferably 20 μm or less. The thickness of the intermediate layer 3b is measured according to the method described in the Examples below.

[0046] The outermost layer 3 a and the bottom layer 3 c preferably contain 95% by mass or more and 100% by mass or less of polyester resin in terms of solid content, and the intermediate layer 3 b preferably contains 70% by mass or more and 100% by mass or less of polyester resin in terms of solid content. The polyester resin content here refers to the proportion of polyester resin in the resin, minus the weight of additives such as polyolefin contained in the resin coating layer 3.

[0047] By using the resin-coated metal plate described above, it is possible to manufacture a metal container that satisfies both the lubricity and abrasion resistance of the resin coating layer 3 and the ink adhesion. The metal container can be manufactured by a conventional method.

[0048] Next, an example of a method for manufacturing a resin-coated metal sheet will be described. In this example, a resin film having at least a three-layer structure including a top layer, an intermediate layer, and a bottom layer is pressure-bonded to at least one surface of the metal sheet to form a resin coating layer 3. After pressure-bonding to the metal sheet, the top layer, the intermediate layer, and the bottom layer become the top layer 3a, the intermediate layer 3b, and the bottom layer 3c, respectively.

[0049] In producing a resin-coated metal sheet, a resin film to be pressure-bonded to the metal sheet is first produced. The method for producing the resin film is not particularly limited. In one example, to incorporate polyolefin into the outermost film, polyolefin is first added to a resin containing 75% by mass or more of polyester resin relative to the total resin. The method for adding polyolefin to the resin is not particularly limited, but a method using a masterbatch in which polyolefin is dispersed at a high concentration in the resin using a kneading extruder is preferred. During film production, resin pellets and the masterbatch are mixed at a predetermined ratio and introduced into the kneading extruder. When mixing the resin pellets and the masterbatch, it is preferable to set the extrusion temperature to a temperature higher than the melting point of the resin pellets. In one example, mixing is preferably performed at an extrusion temperature of 260°C or higher, which is 30°C higher than the melting point of the polyester resin. Furthermore, the extrusion temperature is preferably 284°C or lower. In order to control the dispersed particle size of the polyolefin, it is more preferable to set the extrusion temperature to 265°C or higher. In order to control the dispersed particle size of the polyolefin, the screw rotation speed of the extruder is preferably set to 12 rpm or more and 18 rpm or less. Inorganic particles may be mixed into the resin that will form the interlayer.

[0050] In one example, a mixture of a resin and a polyolefin that will form the top layer, a resin that will form the intermediate layer, and a resin that will form the bottom layer are co-extruded, formed into a sheet using a T-die, and then extruded onto a cooling body such as a casting drum. The extruded sheet is cooled and solidified to obtain an unstretched laminated film.

[0051] After producing the unstretched laminated film, it is preferably biaxially stretched once in the film-forming direction and once in the direction perpendicular to the film-forming direction to form a resin film. Furthermore, in order to control the dispersed particle size of the polyolefin, the stretching ratio after producing the unstretched laminated film is preferably 2.0 times or more, more preferably 3.0 times or more. The stretching ratio after producing the unstretched laminated film is preferably 5.0 times or less, more preferably 4.5 times or less.

[0052] The produced resin film is heated above its melting point and pressed onto a metal plate using a laminating roll (thermocompression film lamination method). This thermocompression film lamination method is advantageous in that it reduces production costs and enables energy-saving production.

[0053] The manufacturing conditions other than those mentioned above can be the same as those in the ordinary method.

[0054] Plate thickness: 0.22 mm, metal chromium layer: 120 mg / m per side ２ , the chromium oxide layer is 10 mg / m per side in terms of metallic chromium ２ TFS with a temper of T3CA was used as the metal plate. The mechanical properties of the metal plate were a YP of 400 MPa, an r-value of 1.0, and a Δr of 0.5. Furthermore, a three-layer resin film was produced by biaxial stretching using the resins, polyolefins, and titanium oxide shown in Tables 1 and 2. The resin coating layer used in the present examples and comparative examples contained 100% by mass of polyester resin relative to the total resin, and the resin composition is shown in Tables 1 and 2. The metal plate was heated, and resin films were thermocompression-bonded to both the front and back surfaces of the metal plate using a thermocompression film lamination method. After 1.5 seconds of thermocompression bonding, the metal plate was water-cooled in a water-cooled tank, thereby coating both surfaces of the metal plate with the resin coating layers of Invention Examples 1 to 22 and Comparative Examples 1 to 8. The outermost layer contained polyolefin in the amount shown in Tables 1 and 2. The middle layer contained titanium oxide in the amount shown in Tables 1 and 2. The coating conditions are as shown in Tables 1 and 2. In Comparative Example 7, paraffin wax was added instead of polyolefin. The item for Comparative Example 7 in Table 2 shows the amount of paraffin wax added, its melting point, weight average molecular weight, and dispersed particle size.

[0055] The resin-coated metal sheets prepared by the above method were analyzed using the methods described below to determine the melting point of the resin coating layer, the melting point of the polyolefin, the dispersed particle size of the polyolefin present on the outermost surface and inside of the resin coating layer, the weight-average molecular weight of the polyolefin, the acid value of the polyolefin, and the thickness of each layer of the resin coating layer.

[0056] (1) Melting Point of Resin Coating Layer First, the resin-coated metal plate for containers was immersed in a mixed solution of concentrated hydrochloric acid (30 wt%) and distilled water (1:1) at room temperature to dissolve the metal plate, thereby peeling off the resin coating layer. ２ The peeled resin coating layer was measured under the conditions of a flow rate of 50 ml / min, a temperature range of room temperature to 290°C, and a heating rate of 10°C / min. The peak top temperature of the endothermic peak in the range of 200°C to 280°C in the obtained heat flow was taken as the melting point.

[0057] (2) Melting Point of Polyolefin After peeling the resin coating layer from the resin-coated metal plate in the same manner as in (1), the resin coating layer was dissolved using hexafluoro-2-propanol (HFIP) as a solvent. The dissolved resin coating layer was centrifuged and then pressure-filtered through filters with pore sizes of 1 μm and 0.1 μm in sequence to extract the polyolefin contained in the outermost layer of the resin coating layer. Furthermore, Soxhlet extraction was performed on the filter using xylene as a solvent, and after concentration, reprecipitation, and centrifugation, additional polyolefin was extracted. The lubricating components extracted as described above were measured using a differential scanning calorimeter: DSCQ100 manufactured by TA Instruments, under conditions of atmospheric gas of N ２ The measurement was carried out under the conditions of a flow rate of 50 ml / min, a temperature range of room temperature to 290°C, and a heating rate of 10°C / min. The peak top temperature of the endothermic peak in the range of 70°C to 150°C of the obtained heat flow was taken as the melting point.

[0058] (3) Dispersed particle size of polyolefin present on the outermost surface and inside of the resin coating layer Using a microscopic laser Raman spectrometer manufactured by Horiba, Ltd.: LabRAM HR VIS-NIR, the outermost surface of the resin-coated metal plate was measured with a confocal laser under the following conditions: laser power: 10%, aperture: 25 μm, exposure time: 0.08 sec, number of exposures: 1, grating: 300 lines / mm, objective lens: 100x, wave number range: 310 to 3400 cm －１The Raman spectrum was measured by Raman spectroscopy under the following conditions. The measurement range was 50 μm (lamination direction of the resin-coated metal plate) × 50 μm (direction perpendicular to the lamination direction within the plate surface of the resin-coated metal plate) × 3 μm (thickness direction of the resin-coated metal plate). The measurement pitch was 0.5 μm in all of the lamination direction, the direction perpendicular to the lamination direction within the plate surface, and the thickness direction. Based on the obtained Raman spectrum data, a CH stretching vibration peak (2850 cm) derived from polyethylene was detected. －１ ) and a CH stretching vibration peak (2960 cm ) derived from polyester, which is the main component of the resin coating layer. －１ The intensity ratio to the measured value was calculated and mapped to calculate the major axis of the dispersed particles of each polyolefin. Three fields of view were randomly selected for each sample, and measurements were performed on all dispersed particles of polyolefin within the measurement fields.

[0059] (4) Weight-average molecular weight of polyolefins Using an Agilent gel permeation chromatograph analyzer: PL-GPC220, polyolefins extracted in the same manner as in (2) were measured under the conditions of two Agilent PLgel Olexis columns + Guard and an o-dichlorobenzene eluent. A calibration curve was also created from the molecular weight of standard polystyrene and the elution time. Using this calibration curve, the weight-average molecular weight of the polyolefin was calculated based on the elution time of the polyolefin.

[0060] (5) Acid Value of Polyolefin The acid value of polyolefin extracted in the same manner as in (2) was measured in accordance with JIS K5902. A predetermined amount of polyolefin corresponding to the estimated acid value in accordance with JIS K5902 was weighed into a flask and dissolved in 100 ml of a neutral solvent. The solution was titrated with 0.1 mol / L potassium hydroxide standard solution using phenolphthalein as an indicator. The acid value was calculated using the following formula, with the end point of neutralization being the point at which the indicator continued to change color for 30 seconds: (Acid value) = 5.611 x A x F / B, where A is the amount of 0.1 mol / L potassium hydroxide standard solution used (ml), B is the amount of sample taken (g), and F is the factor of 0.1 mol / L potassium hydroxide standard solution.

[0061] (6) Thickness of each resin coating layer After peeling the resin coating layer from the resin-coated metal plate in the same manner as in (1), a Pt coating was applied to the outermost surface of the resin coating layer, and a cross section was prepared using an ion milling device: EM TIC 3X manufactured by Leica Microsystems Co., Ltd. For the prepared cross section, backscattered electron images were observed at two magnifications of 2500x and 8000x using a scanning electron microscope (SEM): Regulus 8220 manufactured by Hitachi High-Technologies Corporation, and the thicknesses of the outermost layer, middle layer, and bottom layer of the resin coating layer were calculated from the observed images.

[0062] The resin-coated metal sheets of Examples 1 to 22 and Comparative Examples 1 to 8 were evaluated for lubricity, abrasion resistance, and ink adhesion of the resin coating layer by the methods described below. The evaluation results are shown in Table 3.

[0063] (7) Evaluation of Sliding Property and Abrasion Resistance The resin-coated metal plates of Examples 1 to 22 and Comparative Examples 1 to 8 were punched into a circle with a diameter of 68 mm, and a sliding test was carried out using a rotary abrasion tester manufactured by Takachiho Seiki Co., Ltd., under the conditions of a load of 44 N, a sample temperature of 145±3°C, a rotation speed of 370 rpm, and a rotation radius of 20 mm, using a carbide ball indenter (Φ10 mm). Four tests were carried out for each sample, and the sliding property was evaluated from the obtained friction coefficient, and the abrasion resistance was visually evaluated from the degree of abrasion of the resin coating layer after the test.

[0064] Evaluation criteria for slipperiness Evaluation "good": coefficient of friction is 0.135 or less Evaluation "fair": coefficient of friction is greater than 0.135 and less than 0.160 Evaluation "poor": coefficient of friction is 0.160 or more.

[0065] Evaluation criteria for abrasion resistance Evaluation "Good": No abrasion was observed visually in all four tested samples. Evaluation "Average": Abrasion was observed visually in one of the four tested samples. Evaluation "Poor": Abrasion was observed visually in two or more of the four tested samples.

[0066] (8) Evaluation of Ink Adhesion The resin-coated metal plates of Examples 1 to 22 and Comparative Examples 1 to 8 were subjected to a heat treatment in a hot air drying oven, reaching 240°C in 2 minutes, and then cooled to room temperature. After the heat treatment, a polyester-based printing ink (red) was printed on the resin coating layer of each sample using a universal printing tester manufactured by Kumagai Riki Kogyo Co., Ltd., and then subjected to a heat treatment in a hot air drying oven, reaching 180°C in 1 minute, and then cooled to room temperature. A scratch test was performed on the ink-printed surface of each sample, facing the lamination direction of the sample, using a load-varying friction and wear tester (HHS2000) manufactured by Shinto Scientific Co., Ltd., with a sapphire indenter (Φ0.6 mm) under conditions of a continuous load of 10 to 500 gf from the edge of the print, a movement speed of 0.5 mm / sec, and a movement distance of 30 mm. Ten tests (two sheets x 5 tests) were performed on each sample, and the ink peel load was calculated from the resulting ink peel length to evaluate ink adhesion. [Evaluation criteria for ink adhesion] Evaluation "good": The average peel load was 100 g or more. Evaluation "fair": The average peel load was 80 g or more and less than 100 g. Evaluation "poor": The average peel load was less than 80 g.

[0067]

[0068]

[0069]

[0070] 1 Resin coated metal plate 2 Metal plate 3 Resin coating layer 3a Outermost layer 3b Intermediate layer 3c Bottom layer 4 Resin coating layer

Claims

1. A resin-coated metal sheet having a resin coating layer on at least one side of the metal sheet, the resin coating layer containing 75% or more by mass of polyester resin based on the total resin, wherein the resin coating layer has a three-layer structure including a top layer, an intermediate layer, and a bottom layer, the melting point of the resin coating layer is 230°C or higher and 254°C or lower, the top layer contains a polyolefin, the melting point of the polyolefin is 80°C or higher and 140°C or lower, and the dispersed particle size of the polyolefin measured by Raman spectroscopy on the top surface and inside in the thickness direction of the resin coating layer is 0.018 μm or higher and 5.0 μm or lower.

2. The resin-coated metal sheet according to claim 1, wherein the outermost layer contains 0.10% by mass or more and 1.0% by mass or less of the polyolefin.

3. The resin-coated metal sheet according to claim 1 or 2, wherein the weight-average molecular weight of the polyolefin is 2,500 or more and 80,000 or less.

4. A resin-coated metal sheet according to any one of claims 1 to 3, wherein the polyolefin is at least one of an acid-modified polyolefin and an oxidized polyolefin.

5. A resin-coated metal sheet according to any one of claims 1 to 4, wherein the acid value of the polyolefin is 1.0 mgKOH / g or more and 80 mgKOH / g or less.

6. The resin-coated metal sheet according to any one of claims 1 to 5, wherein the intermediate layer contains 10% by mass or more and 30% by mass or less of inorganic particles.

7. A resin-coated metal sheet according to any one of claims 1 to 6, wherein the thickness of the outermost layer and the bottom layer is 1.0 μm or more and 5.0 μm or less, respectively, and the thickness of the intermediate layer is 6.0 μm or more and 30 μm or less.

8. A metal container made using the resin-coated metal sheet according to any one of claims 1 to 7, wherein the resin coating layer is located on the outside of the metal container.