Resin-coated metal plate

Abstract

The present invention provides a resin-coated metal plate having both sliding properties, abrasion resistance and ink adhesion of a resin-coated layer. This resin-coated metal plate (1) is provided with, on at least one surface of a metal plate (2), a resin coating layer (3) containing a polyester resin in an amount of 75 mass% or more relative to the total resin, the resin coating layer (3) having an at least three-layer structure including an outermost layer (3a), an intermediate layer (3b), and a lowermost layer (3c), and having a melting point of 230-254 DEG C (inclusive), the outermost layer (3a) contains a polyolefin having a melting point of 80 DEG C or more and 140 DEG C or less, and the dispersion particle diameter of the polyolefin measured by Raman spectroscopy on the outermost surface and the thickness-direction interior of the resin coating layer (3) is 0.018 [mu] m or more and 5.0 [mu] m or less.

Description

Technical Field

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

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

[0003] In recent years, from the perspective of saving resources and reducing material costs, the thinning of the materials used for metal containers, especially the thinning of metal plates and resin coatings, has been promoted by making the processing conditions more stringent. As a result, the degree of processing during can manufacturing becomes higher, and in particular, the resin coating located on the outer surface side of the container after the molding process is likely to break or grind. Based on this, material design is sought to suppress the breakage or grinding of the resin coating during can manufacturing. As a technology for suppressing the breakage or grinding of the resin coating, Patent Documents 1 and 2 propose a method of adding a lubricating component to the resin coating to improve the sliding properties and wear resistance of the resin coating.

[0004] The resin coating layer located on the outer surface of the container after molding is printed to improve the design. If the affinity between the various inks used for printing and the resin coating layer is low, sufficient ink adhesion cannot be ensured, and the printing ink may peel off during the can body processing, which may damage the design and aesthetics of the can body appearance.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2019 / 116706

[0008] Patent Document 2: International Publication No. 2019 / 116707

[0009] The lubricating component added to the resin coating layer inhibits the breaking or grinding of the resin coating layer. On the other hand, it may hinder the affinity between the printing ink applied by the printing process and the surface of the resin coating layer, thereby causing ink peeling during processing. Therefore, a resin-coated metal plate that more highly balances the sliding and grinding resistance of the resin coating layer and the adhesion of the printing ink is required. Summary of the invention

[0010] Therefore, an object of the present invention is to provide a resin-coated metal sheet which satisfies both the sliding property and the wear resistance of the resin coating layer and the ink adhesion.

[0011] The present inventors have repeatedly conducted intensive studies to achieve the above-mentioned problems, and have obtained the following findings. Conventionally, only the dispersed particle size of the lubricating component locally present on the outermost surface of the resin coating layer has been captured. The present inventors have discovered the dispersed particle size range of the lubricating component that can achieve both the sliding property and the wear resistance and the ink adhesion of the resin coating layer by capturing the dispersed particle size of the lubricating component in a wider range three-dimensionally, including the dispersed particle size of the lubricating component present inside the thickness direction of the resin coating layer, and have completed the present invention.

[0012] The present invention has been accomplished based on the above findings. That is, the main configuration of the present invention is as follows.

[0013] [1] A resin-coated metal plate, comprising a resin coating layer containing 75% by mass or more of a polyester resin relative to all resins on at least one surface of the metal plate, wherein the resin coating layer has at least a three-layer structure including an outermost layer, an intermediate layer, and a lowermost layer, the melting point of the resin coating layer is 230° C. to 254° C., the outermost layer contains a polyolefin, the melting point of the polyolefin is 80° C. to 140° C., and the dispersed particle size of the polyolefin measured by Raman spectroscopy on the outermost surface and in the thickness direction of the resin coating layer is 0.018 μm to 5.0 μm.

[0014] [2] The resin-coated metal sheet according to [1] above, wherein the outermost layer contains 0.10 mass % to 1.0 mass % of the polyolefin.

[0015] [3] The resin-coated metal sheet according to [1] or [2] above, wherein the weight average molecular weight of the polyolefin is 2,500 to 80,000.

[0016] [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.

[0017] [5] The resin-coated metal sheet according to any one of [1] to [4] above, wherein the polyolefin has an acid value of 1.0 mgKOH / g or more and 80 mgKOH / g or less.

[0018] [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.

[0019] [7] The resin-coated metal sheet as described in any one of [1] to [6] above, wherein the thickness of the outermost layer and the lowermost layer are respectively 1.0 μm to 5.0 μm, and the thickness of the intermediate layer is 6.0 μm to 30 μm.

[0020] [8] A metal container formed using the resin-coated metal sheet according to any one of [1] to [7] above, wherein the resin coating layer is located on the outer side of the metal container.

[0021] Effects of the Invention

[0022] According to the present invention, it is possible to provide a resin-coated metal sheet that achieves both sliding properties and wear resistance and ink adhesion of the resin coating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a diagram schematically showing a cross section of a resin-coated metal plate. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

[0025] Figure 1 1 is a cross-sectional view showing the structure of a resin-coated metal sheet according to one embodiment of the present invention. Figure 1 As shown in FIG. 1 , the resin-coated metal plate 1 includes a metal plate 2, a resin coating layer 3 formed on the front side of the metal plate 2, and a resin coating layer 4 formed on the back side of the metal plate 2. It should be noted that the resin coating layer 3 and the resin coating layer 4 may be provided only on one side of the metal plate 2. The resin coating layer 3 and the resin coating layer 4 are located on the outer surface side and the inner surface side of the container, respectively, after the molding process. In addition, as shown in FIG. Figure 1 As shown, the resin coating layer 3 has at least a three-layer structure consisting of an outermost layer 3a, an intermediate layer 3b, and a lowermost layer 3c, and the resin coating layer 4 may also have a three-layer structure.

[0026] [Metal Plate]

[0027] The metal plate is preferably a steel plate. The metal plate is preferably a tin-plated steel plate or a tin-free steel plate (Tin Free Steel: TFS). As the tin-plated steel plate, a tin-plated steel plate having a coating weight of 0.5 g / m2 per single side is preferably used. 2 Above and 15g / m 2 The tin-plated steel sheet is preferably in the range of 50 mg / m2 on the surface. 2 Above and 200 mg / m 2 The following metal chromium layer and the metal chromium layer have a metal chromium conversion of 3 mg / m per single side. 2 Above 30mg / m 2 The following chromium oxide layer. The type of metal plate is not particularly limited as long as it can be formed into a target shape, but metal plates having the following components and production methods are preferred.

[0028] (1) A metal plate obtained by subjecting a low carbon steel having a C (carbon) content in the range of 0.010 mass % to 0.10 mass % to recrystallization annealing by continuous annealing.

[0029] (2) A metal sheet obtained by subjecting a low carbon steel having a C content in the range of 0.010 mass % to 0.10 mass % to recrystallization annealing and overaging treatment by continuous annealing.

[0030] (3) A metal plate obtained by subjecting a low carbon steel having a C content in the range of 0.010 mass % to 0.10 mass % to recrystallization annealing by box annealing.

[0031] (4) A metal sheet obtained by performing recrystallization annealing on a low carbon steel having a C content in the range of 0.010 mass % to 0.10 mass % by continuous annealing or box annealing, and then performing secondary cold rolling (double reduced rolling).

[0032] (5) A metal plate obtained by performing recrystallization annealing on an IF (Interstitial Free) steel in which an element such as Nb or Ti that forms a fixed solid solution of C is added to an ultra-low carbon steel having a C content of 0.003 mass % or less by continuous annealing.

[0033] The mechanical properties of the steel sheet are not particularly limited as long as it can be formed into a target shape. In order to obtain more suitable processability and more appropriately maintain the strength of the can body, the yield point (YP) of the steel sheet is preferably 220 MPa or more, preferably 580 MPa or less. In addition, a steel sheet having a Lankford value (r value) of 0.8 or more, which is an indicator of plastic anisotropy, is preferred. Furthermore, regarding the in-plane anisotropy Δr of the r value, a steel sheet having an absolute value of 0.7 or less is preferred.

[0034] The composition of the steel used to satisfy the above-mentioned mechanical properties is not particularly limited, for example, it may contain components such as Si, Mn, P, S, Al, and N. The Si content is preferably 0.001% by mass or more, and preferably 0.1% by mass or less. The Mn content is preferably 0.01% by mass or more, and preferably 0.6% by mass or less. The P content is preferably 0.002% by mass or more, and preferably 0.05% by mass or less. The S content is preferably 0.002% by mass or more, and preferably 0.05% by mass or less. The Al content is preferably 0.005% by mass or more, and preferably 0.100% by mass or less. The N content is preferably 0.0005% by mass or more, and preferably 0.020% by mass or less. In addition, the steel plate may contain other components such as Ti, Nb, B, Cu, Ni, Cr, Mo, and V. From the viewpoint of ensuring corrosion resistance, the content of these component elements is preferably 0.02% by mass or less in total.

[0035] The thickness of the metal plate is not particularly limited, and may be, for example, 0.20 mm or more, or 0.25 mm or less.

[0036] [Resin coating layer]

[0037] The resin coating layer 3 contains 75% or more of polyester resin in terms of solid content relative to the total resin. It should be noted that the content of polyester resin referred to here refers to the proportion of polyester resin in the resin obtained by subtracting the weight of additives such as polyolefin and inorganic particles contained in the resin coating layer. The resin coating layer 3 preferably contains 80% or more of polyester resin relative to the total resin, and preferably contains 100% or less of polyester resin.

[0038] Polyester resin is a polymer composed of dicarboxylic acid units and diol units.

[0039] As the dicarboxylic acid unit, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, sodium 5-sulfonate of isophthalic 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 cyclohexane dicarboxylic acid; and units derived from hydroxycarboxylic acids such as p-hydroxybenzoic acid can be used.

[0040] As the diol unit, there can be used aliphatic diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic diols such as cyclohexanedimethanol; aromatic diols such as bisphenol A and bisphenol S; units derived from diethylene glycol, and the like.

[0041] In addition, the above-mentioned dicarboxylic acid and diol may be used in combination of two or more in the range which does not impair the heat resistance and processability.

[0042] The melting point of the resin coating layer 3 is above 230°C and below 254°C. If the melting point of the resin coating layer 3 is above 230°C, the softening of the resin during the molding process can be well prevented, and the occurrence of breakage or grinding can be better prevented. In addition, if the melting point of the resin coating layer 3 is below 254°C, the crystallinity of the polyester resin contained therein is within a more preferred range, which can better prevent the occurrence of breakage or grinding in the resin coating layer 3 during the molding process. The melting point of the resin coating layer 3 is preferably above 234°C, and more preferably above 238°C. The melting point of the resin coating layer 3 is preferably below 252°C, and more preferably below 250°C. The melting point of the resin coating layer 3 is measured according to the following method. The resin coating layer 3 is measured using a differential scanning calorimeter, and the peak top temperature of the endothermic peak in the range of 200°C-280°C in the obtained heat flow is taken as the melting point.

[0043] The outermost layer 3a in the resin coating layer 3 contains polyolefin as a lubricating component. By containing polyolefin as a lubricating component, the outermost layer 3a can ensure excellent sliding properties and wear resistance, and can suppress the fracture or grinding of the resin coating layer 3 even in the tank molding under severe processing conditions. As a lubricating component, a polyolefin with excellent film-forming properties and dispersibility and a melting point in an appropriate range is used. In order to ensure sufficient affinity with the polyester resin as the main component of the resin coating layer 3, it is preferred to use a polyolefin with a polar group. As a polyolefin with a polar group, acid-modified polyolefins such as ethylene-maleic anhydride copolymers, oxidized polyolefins such as oxidized polyethylene, ethylene-acrylic acid copolymers, etc. can be exemplified. As a polyolefin, a variety of polyolefins can be used in combination.

[0044] The polyolefin is preferably at least one of an acid-modified polyolefin and an oxidized polyolefin. This is because by making the polyolefin at least one of an acid-modified polyolefin and an oxidized polyolefin, the acid value becomes sufficiently high, and the affinity between the outermost layer 3a and the printing ink is improved. The polyolefin may be a mixture of an acid-modified polyolefin and an oxidized polyolefin.

[0045] The melting point of the polyolefin is set to be above 80°C and below 140°C. When the melting point of the polyolefin is lower than 80°C, the polyolefin is easily enriched on the surface of the resin coating layer 3 due to the process of coating the resin coating layer 3 on the metal plate and the heat treatment performed during the molding of the resin-coated metal plate. The polyolefin enriched on the surface will hinder the adhesion of the printing ink, and the printing ink may be peeled off during the molding process. In addition, when the melting point of the polyolefin exceeds 140°C, sufficient sliding and wear resistance cannot be ensured, and the resin coating layer 3 may be broken or ground during the molding process. The melting point of the polyolefin is preferably above 90°C, and more preferably above 100°C. The melting point of the polyolefin is preferably below 130°C, and more preferably below 120°C. The melting point of the polyolefin is measured according to the method described in the examples described later.

[0046] The dispersed particle size of the polyolefin on the outermost surface and the inner part in the thickness direction of the resin coating layer 3 is greater than 0.018 μm and less than 5.0 μm. The dispersed particle size of the polyolefin is measured by using a confocal Raman spectrometer to analyze the peak intensity ratio of the Raman spectroscopic spectrum obtained by Raman spectroscopy. If it is this measurement method, the dispersed state of the polyolefin in the resin coating layer 3 can be calculated three-dimensionally without destruction and with high resolution, and the dispersed particle size of the polyolefin that cannot be captured in other analysis methods can be captured. In the case where the dispersed particle size of the polyolefin present on the outermost surface and the inner part in the thickness direction of the resin coating layer 3 is less than 0.018 μm, it is extremely small, so it is impossible to ensure sufficient sliding and wear resistance, and it is possible to break or grind during molding. In addition, in the case where the dispersed particle size of the lubricating component present on the outermost surface and the inner part in the thickness direction of the resin coating layer 3 exceeds 5.0 μm, during molding, the excessively large dispersed particles of the polyolefin may become the starting point, causing breakage or grinding. In addition, due to the influence of multiple heat treatments implemented during the molding process, the proportion of polyolefins enriched and exposed on the surface of the resin coating layer 3 becomes higher, which hinders the adhesion of the printing ink and may cause the printing ink to peel off during the molding process. The dispersed particle size of the polyolefin on the outermost surface and the inner part of the thickness direction of the resin coating layer 3 is preferably 0.030μm or more, and more preferably 0.050μm or more. The dispersed particle size of the polyolefin on the outermost surface and the inner part of the thickness direction of the resin coating layer 3 is preferably 3.0μm or less, more preferably 2.0μm or less, and further preferably 1.0μm or less. The dispersed particle size of the polyolefin on the outermost surface and the inner part of the thickness direction of the resin coating layer 3 is measured according to the method described in the examples described later.

[0047] In the past, there was a method for measuring the dispersed particle size of the lubricating component using a chemical microscope (CFM). In this method, only the surface of the resin coating layer is observed with a field of view of 1 μm×1 μm, and the dispersed particle size of the observed lubricating component particles is calculated based on the major and minor diameters. On the other hand, when Raman spectroscopy is used as in the present invention, the field of view of 50 μm (lamination direction of the resin-coated metal plate)×50 μm (direction orthogonal to the lamination direction within the plate surface of the resin-coated metal plate)×3 μm (thickness direction of the resin-coated metal plate) is measured in a larger range than the existing method and also includes the thickness direction, and the dispersed particle size is calculated. Therefore, compared with the existing method, Raman spectroscopy can capture more dispersed particles of polyolefins in the resin coating layer and can obtain a high-precision dispersed particle size.

[0048] Moreover, as another existing method, there is a method of etching the polyester resin of the surface layer of the resin coating layer with an alkaline aqueous solution, measuring the major and minor diameters of the remaining modified polyolefin particles one by one, and calculating the particle size. This method is a destructive measurement, and it is actually impossible to capture the dispersion state of the modified polyolefin particles dispersed in the resin coating layer. In addition, when etching the resin coating layer with an alkaline aqueous solution, the shape and particle size of the extracted modified polyolefin particles may also be different from the state dispersed in the resin coating layer. Therefore, it is difficult to judge how the modified polyolefin particles contribute to the required performance of the resin coating layer and the resin laminated metal plate by this method. On the other hand, when using Raman spectroscopy as in the present invention, the actual particle size and dispersion state of the polyolefin dispersed in the resin coating layer can be captured non-destructively and with high resolution, so it is possible to judge with high precision how the dispersed particles of the polyolefin contribute to the required performance.

[0049] The content of polyolefin in the outermost layer 3a is preferably 0.10% by mass or more, preferably 1.0% by mass or less, in terms of solid content. If the content of polyolefin in the outermost layer 3a is 0.10% by mass or more, more suitable sliding properties and wear resistance can be ensured during molding, and the fracture or grinding of the resin coating layer 3 can be prevented. If the content of polyolefin in the outermost layer 3a is 1.0% by mass or less, wear resistance and ink adhesion are more suitable. The content of polyolefin in the outermost layer 3a is more preferably 0.20% by mass or more, and more preferably 0.40% by mass or more. The content of polyolefin in the outermost layer 3a is more preferably 0.90% by mass or less, and more preferably 0.80% by mass or less.

[0050] The weight average molecular weight of the polyolefin is preferably 2500 or more, preferably 80000 or less. When the weight average molecular weight of the polyolefin is 2500 or more, it is possible to better prevent the polyolefin from being enriched on the surface of the resin coating layer 3, and further improve the ink adhesion. If the weight average molecular weight of the polyolefin is 80000 or less, more suitable sliding properties and abrasion resistance can be ensured during molding, and fracture or grinding in the resin coating layer 3 can be better prevented. The weight average molecular weight of the polyolefin is more preferably 3000 or more, and more preferably 3500 or more. The weight average molecular weight of the polyolefin is more preferably 70000 or less, and more preferably 65000 or less. The weight average molecular weight of the polyolefin is measured according to the method described in the embodiments described later.

[0051] The acid value of the polyolefin is preferably above 1.0 mgKOH / g, preferably below 80 mgKOH / g. When the acid value of the polyolefin is above 1.0 mgKOH / g, the affinity between the resin coating layer 3 and the printing ink can be fully ensured, and the adhesion of the printing ink can be improved. When the acid value of the polyolefin is below 80 mgKOH / g, it is not compatible with the resin coating layer 3, so it is possible to ensure more suitable sliding and wear resistance, and can better prevent fracture or grinding during molding. The acid value of the polyolefin is more preferably above 1.5 mgKOH / g, and more preferably above 2.0 mgKOH / g. The acid value of the polyolefin is more preferably below 50 mgKOH / g, and more preferably below 45 mgKOH / g. The acid value of the polyolefin is measured according to the method described in the embodiments described later.

[0052] In order to improve the design and aesthetics of the can body after printing, the resin coating layer 3 is sometimes required to be white. In this case, the intermediate layer 3b of the resin coating layer 3 preferably contains inorganic particles. This is because the intermediate layer 3b can make the resin coating layer 3 white by containing inorganic particles.

[0053] The intermediate layer 3b preferably contains more than 10% by mass of inorganic particles in terms of solid content conversion, preferably less than 30% by mass. If the inorganic particles contained in the intermediate layer 3b are more than 10% by mass, sufficient whiteness can be ensured. If the inorganic particles contained in the intermediate layer 3b are less than 30% by mass, even in processing under more severe processing conditions, it is possible to better prevent the resin coating layer 3 from breaking or grinding. The content of inorganic particles in the intermediate layer 3b is more preferably more than 12% by mass, and more preferably more than 15% by mass. The content of inorganic particles in the intermediate layer 3b is more preferably less than 25% by mass, and more preferably less than 20% by mass.

[0054] 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 titanium oxide with a purity of 90% or more. In the case where the inorganic particles contained in the intermediate layer 3b are the above-mentioned titanium oxide, when the polyester resin and the titanium oxide are mixed, the titanium oxide shows good dispersibility and uniform whiteness, thereby improving the design and aesthetics of the appearance.

[0055] In the case where the resin coating layer 3 has at least a three-layer structure consisting of a top layer 3a, an intermediate layer 3b and a bottom layer 3c, the thickness of the top layer 3a and the bottom layer 3c are preferably 1.0 μm or more, preferably 5.0 μm or less. In addition, the thickness of the top layer 3a and the bottom layer 3c may also be different from each other. By making the thickness of the top layer 3a and the bottom layer 3c within the above range, more suitable sliding properties and wear resistance can be ensured during molding, and fracture or grinding in the resin coating layer 3 can be better prevented. The thickness of the top layer 3a and the bottom layer 3c is more preferably 1.5 μm or more, and more preferably 2.0 μm or more. The thickness of the top layer 3a and the bottom layer 3c is more preferably 4.0 μm or less, and more preferably 3.0 μm or less. The thickness of the top layer 3a and the bottom layer 3c is measured according to the method described in the embodiments described later.

[0056] 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, the increase or decrease in the absolute amount of polyolefin can be suppressed without changing the thickness of the outermost layer 3a and the lowermost layer 3c. Therefore, the dispersed particle size is controlled within a more appropriate range, which can better prevent the resin coating layer 3 from being broken or ground during the molding process. In addition, the adhesion of the 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, and more preferably 10 μm or more. The thickness of the intermediate layer 3b is more preferably 25 μm or less, and more preferably 20 μm or less. The thickness of the intermediate layer 3b is measured according to the method described in the embodiments described later.

[0057] The outermost layer 3a and the lowermost layer 3c preferably contain 95% by mass or more and 100% by mass of polyester resin in terms of solid content. In addition, the intermediate layer 3b preferably contains 70% by mass or more and 100% by mass of polyester resin in terms of solid content. It should be noted that the content of polyester resin mentioned here refers to the proportion of polyester resin in the resin obtained by subtracting the weight of additives such as polyolefin contained in the resin coating layer 3.

[0058] By using the above-mentioned resin-coated metal sheet, it is possible to manufacture a metal container that satisfies both the sliding property and the wear resistance and the ink adhesion of the resin coating layer 3. The metal container can be manufactured by a conventional method.

[0059] Next, an example of a method for manufacturing a resin-coated metal plate is described. In one example, a method for manufacturing a resin-coated metal plate is to press-bond a resin film having at least a three-layer structure including an outermost film, an intermediate film, and a lowermost film to at least one side of the metal plate to form a resin coating layer 3. After being pressed to the metal plate, the outermost film, the intermediate film, and the lowermost film become an outermost layer 3a, an intermediate layer 3b, and a lowermost layer 3c, respectively.

[0060] When manufacturing a resin-coated metal plate, first, a resin film crimped to the metal plate is manufactured. The method for manufacturing the resin film is not particularly limited. In one example, first, in order to make the outermost film contain polyolefin, polyolefin is added to a resin containing 75% by mass or more of polyester resin relative to the total resin. There is no particular limitation on the method for adding polyolefin to the resin, and it is preferred to use a method in which a masterbatch of polyolefin is dispersed in the resin at a high concentration using a mixing extruder. During the film-making of the film, the resin particles are mixed with the above-mentioned masterbatch at a prescribed ratio and introduced into the mixing extruder. When mixing the resin particles and the masterbatch, it is preferred to set the extrusion temperature to a temperature higher than the melting point of the resin particles. In one example, it is preferred to mix at an extrusion temperature of 30°C higher than the melting point of the polyester resin and above 260°C. In addition, the extrusion temperature is preferably below 284°C. In order to control the dispersed particle size of the polyolefin, the extrusion temperature is more preferably above 265°C. In addition, in order to control the dispersed particle size of the polyolefin, the screw speed of the extruder is preferably set to 12rpm or more and 18rpm or less. In addition, inorganic particles can be appropriately mixed in the resin that becomes the intermediate film.

[0061] In one example, a mixture of a resin and a polyolefin to be the outermost film, a resin to be the middle film, and a resin to be the bottom film are coextruded, formed into a sheet using a T-die and discharged, and extruded onto a cooling body such as a casting drum. By cooling and solidifying the extruded sheet, an unstretched laminated film can be obtained.

[0062] After the unstretched laminated film is prepared, it is preferably stretched once in the film-forming direction and once in a direction orthogonal 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 the unstretched laminated film is prepared is preferably 2.0 times or more, more preferably 3.0 times or more. The stretching ratio after the unstretched laminated film is prepared is preferably 5.0 times or less, more preferably 4.5 times or less.

[0063] The produced resin film is heated to a temperature higher than the melting start temperature and is pressed onto a metal plate by laminating rolls (thermocompression film lamination method). This thermocompression film lamination method is excellent in terms of suppressing production costs and enabling energy-saving production.

[0064] In addition, the manufacturing conditions other than the above conditions can be carried out by conventional methods.

[0065] Example

[0066] The thickness of the plate is 0.22mm, and the chromium layer is 120mg / m 2 , Chromium oxide layer is calculated as 10mg / m per single surface in terms of metallic chromium 2, TFS with a tempering degree of T3CA is used as a metal plate. As the mechanical properties of the above-mentioned metal plate, YP is 400MPa, r value is 1.0, and Δr is 0.5. In addition, a three-layer resin film is manufactured by a biaxial stretching method using the resins, polyolefins and titanium oxide shown in Tables 1 and 2. It should be noted that the resin coating layer used in the present embodiment and the comparative example is a resin coating layer containing 100% by mass of polyester resin relative to the total resin, and the composition of the resin is shown in Tables 1 and 2. The metal plate is heated and a resin film is hot-pressed on both sides of the metal plate by a hot-pressing film lamination method. After 1.5 seconds after hot-pressing, water cooling is performed in a water cooling box, thereby coating the resin coating layers of Invention Examples 1 to Invention Examples 22 and Comparative Examples 1 to Comparative Examples 8 on both sides of the metal plate. The outermost layer contains polyolefins in the amounts described in Tables 1 and 2. The intermediate layer contains titanium oxide in the amounts described in Tables 1 and 2. The coating conditions are shown in the following Tables 1 and 2. In addition, paraffin wax was added instead of polyolefin in Comparative Example 7. The item of Comparative Example 7 in Table 2 shows the amount of paraffin wax added, the melting point, the weight average molecular weight, and the dispersed particle size.

[0067] The resin-coated metal plate produced by the above method is analyzed by the method shown below with respect to the melting point of the resin coating layer and 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.

[0068] (1) Melting point of the resin coating

[0069] First, the resin-coated metal plate for the container is 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. Using a differential scanning calorimeter: DSCQ100 manufactured by TA Instruments, the peeled resin coating layer is measured under the conditions of an atmosphere gas of N2, a flow rate of 50 ml / min, a temperature range of from 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-280°C in the obtained heat flow is taken as the melting point.

[0070] (2) Melting point of polyolefin

[0071] After peeling off the resin coating layer from the resin-coated metal plate in the same manner as in (1), the resin coating layer is dissolved using hexafluoro-2-propanol (HFIP) as a solvent. After centrifugation of the dissolved resin coating layer, pressure filtration is performed using filters with pore sizes of 1 μm and 0.1 μm in sequence, thereby extracting the polyolefin contained in the outermost layer of the resin coating layer. Furthermore, Soxhlet extraction using xylene as a solvent is performed on the above-mentioned filter, and polyolefin is additionally extracted after concentration, reprecipitation, and centrifugation. The lubricating component extracted as described above is measured using a differential scanning calorimeter: DSCQ100 manufactured by TA Instruments under the conditions of an atmosphere gas of N2, a flow rate of 50 ml / min, a temperature range of from 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-150°C in the obtained heat flow is taken as the melting point.

[0072] (3) Dispersed particle size of polyolefin present on the outermost surface and inside of the resin coating layer

[0073] The LabRAM HR VIS-NIR microscopic laser Raman spectrometer manufactured by Horiba, Ltd. was used to measure the outermost surface of the resin-coated metal plate. The laser power was 10%, the aperture was 25 μm, the exposure time was 0.08 sec, the number of exposures was 1, the grating was 300 lines / mm, the objective lens was 100 times, and the wave number range was 310 to 3400 cm. -1 The Raman spectroscopic spectrum measurement based on Raman spectroscopy is carried out under the conditions. It should be noted that the measurement range is 50μm (lamination direction of the resin-coated metal plate) × 50μm (direction orthogonal to the lamination direction within the plate surface of the resin-coated metal plate) × 3μm (thickness direction of the resin-coated metal plate). In addition, the measurement interval is set to 0.5μm in the lamination direction, in the direction orthogonal to the lamination direction within the plate surface, and in the thickness direction. Based on the obtained Raman spectrum data, the CH stretching vibration peak (2850cm -1 ) and the CH stretching vibration peak (2960 cm) derived from the polyester as the main component of the resin coating layer -1 ) intensity ratio and mapping, thereby calculating the major diameter of the dispersed particles of each polyolefin. Measurement Three fields of view were randomly selected from each sample, and the dispersed particles of all polyolefins in the measurement field of view were measured.

[0074] (4) Weight average molecular weight of polyolefin

[0075] The polyolefin extracted in the same manner as in (2) was measured using an Agilent gel permeation chromatography analyzer: PL-GPC220, with an Agilent PLgelOlexis×2+Guard column and o-dichlorobenzene as the eluent. In addition, a calibration curve was prepared from the molecular weight and elution time of standard polystyrene. Using this calibration curve, the weight average molecular weight of the polyolefin was calculated based on the elution time of the polyolefin.

[0076] (5) Acid value of polyolefin

[0077] The acid value of the polyolefin extracted in the same manner as in (2) was measured based on JIS K5902. According to JIS K5902, a predetermined amount of polyolefin corresponding to the estimated acid value was measured and dissolved in 100 ml of a neutral solvent, and then titrated with a 0.1 mol / L potassium hydroxide standard solution using phenolphthalein as an indicator. When the color change of the indicator continued for 30 seconds, it was regarded as the end point of neutralization, and the acid value was calculated by the following formula.

[0078] (acid value) = 5.611 × A × F / B

[0079] A: Amount of 0.1 mol / L potassium hydroxide standard solution used (ml)

[0080] B: Sample collection amount (g)

[0081] F: Factor of 0.1 mol / L potassium hydroxide standard solution

[0082] (6) Thickness of each layer of the resin coating

[0083] After the resin coating layer was peeled off from the resin-coated metal plate in the same manner as in (1), the outermost surface of the resin coating layer was coated with Pt, and a cross section was prepared using an ion milling device: EM TIC 3X manufactured by Leica Microsystems Co., Ltd. The prepared cross section was observed using a scanning electron microscope (SEM): Regulus 8220 manufactured by Hitachi High-Technologies Corporation, Ltd., and reflected electron images were observed under two conditions of observation magnifications of 2500 times and 8000 times, and the thickness of each layer of the outermost layer, the middle layer, and the lowermost layer of the resin coating layer was calculated based on the observed images.

[0084] The resin-coated metal plates of Inventive Examples 1 to 22 and Comparative Examples 1 to 8 were evaluated for sliding properties, wear resistance, and ink adhesion of the resin coating layer by the following methods.

[0085] (7) Evaluation of sliding properties and wear resistance

[0086] The resin-coated metal plates of Invention Examples 1 to Invention Examples 22 and Comparative Examples 1 to Comparative Examples 8 were punched into a circular shape with a diameter of 68 mm, and a sliding test was performed using a rotary wear tester manufactured by Takachiho Seiki Co., Ltd., with 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 super steel ball indenter (Φ10 mm). Four test quantities were performed on each sample, and the sliding properties were evaluated by the obtained friction coefficient, and the wear resistance was visually evaluated by the degree of wear of the resin coating layer after the test.

[0087] Evaluation criteria for sliding properties

[0088] Evaluation "0": The friction coefficient is 0.135 or less.

[0089] Evaluation "△": The friction coefficient is greater than 0.135 and less than 0.160.

[0090] Evaluation "×": The friction coefficient is 0.160 or more.

[0091] Evaluation criteria for wear resistance

[0092] Evaluation "0": No wear was visually observed in all four tests of the sample.

[0093] Evaluation "△": Grinding was visually observed in one of four samples tested.

[0094] Evaluation "x": Grinding was visually observed in two or more tests among four tests of the sample.

[0095] (8) Evaluation of ink adhesion

[0096] The resin-coated metal plates of Invention Examples 1 to Invention Examples 22 and Comparative Examples 1 to Comparative Examples 8 were subjected to heat treatment at 240°C for 2 minutes in a hot air drying furnace and cooled to room temperature. Then, for each sample after the above heat treatment, a polyester-based printing ink (red) was printed on the resin coating layer using a universal printing tester manufactured by Kumagai Riki Industry Co., Ltd., and heat treatment was performed at 180°C for 1 minute in a hot air drying furnace, and cooled to room temperature. The ink-printed surface of the obtained sample was used as the object, and a load-variable friction and wear tester: HHS2000 manufactured by Shinto Scientific Co., Ltd. was used to face the lamination direction of the sample. A scratch test was performed from the printed end using a sapphire indenter (Φ0.6 mm) under the conditions of a continuous load of 10 to 500 gf, a moving speed of 0.5 mm / sec, and a moving distance of 30 mm. Each sample was subjected to 10 tests (2 pieces × 5 tests), and the ink peeling load was calculated based on the obtained ink peeling length to evaluate the ink adhesion.

[0097] [Evaluation criteria for ink adhesion]

[0098] Evaluation "0": The average value of the peel load is 100 g or more.

[0099] Evaluation “△”: The average value of the peel load is 80 g or more and less than 100 g.

[0100] Evaluation "x": The average value of the peel load was less than 80 g.

[0101]

[0102]

[0103] Table 3

[0104]

[0105] Description of Reference Numerals

[0106] 1 Resin coated metal sheet

[0107] 2 Metal Plate

[0108] 3 Resin coating

[0109] 3a Top layer

[0110] 3b Middle layer

[0111] 3c bottom layer

[0112] 4 Resin coating

Claims

1. A resin-coated metal sheet comprising a resin coating layer on at least one surface of the metal sheet, wherein the resin coating layer contains 75% by mass or more of a polyester resin relative to the total resin, in, The resin coating layer has at least a three-layer structure including an outermost layer, an intermediate layer, and a lowermost layer. The melting point of the resin coating layer is 230° C. or higher and 254° C. or lower. The outermost layer contains polyolefin, The melting point of the polyolefin is 80° C. or higher and 140° C. or lower. The dispersed particle size of the polyolefin measured by Raman spectroscopy at 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.

2. The resin-coated metal sheet according to claim 1, wherein The outermost layer contains 0.10 mass % or more and 1.0 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. The 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. The 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 mass % or more and 30 mass % or less of inorganic particles.

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

8. A metal container, comprising the resin-coated metal sheet according to any one of claims 1 to 7, wherein: The resin coating layer is located on the outer side of the metal container.

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