Film for coating metal plate, resin-coated metal plate, method for producing film for coating metal plate, and method for producing resin-coated metal plate

Abstract

Provided are a film for coating a metal plate and a resin-coated metal plate that have exceptional ink adhesion. Provided is a film for coating a metal plate, the film having a polyester resin as a main component. The film 3 for covering a metal plate has a multilayer structure of two or more layers including a first outermost layer 3a and a second outermost layer 3b. The melting point of the film 3 is 230-260°C. The first outermost layer 3a contains 0.1-15 mass% of readily-sliding inorganic particles composed of silica having an average particle diameter of 0.2-1.0 μm. The number of readily-sliding inorganic particles distributed on the surface of the first outermost layer 3a is 400 or more per 1 mm2. The surface roughness Ra of the first outermost layer 3a is 0.30 μm or greater. The first outermost layer 3a contains at least 0.010 mass% and less than 1.0 mass% of a polyolefin as a lubrication component.

Description

Metal plate coating film, resin-coated metal plate, method for producing metal plate coating film, and method for producing resin-coated metal plate

[0001] The present invention relates to a film for covering metal sheets, a resin-coated metal sheet, a method for producing a film for covering metal sheets, and a method for producing a resin-coated metal sheet.

[0002] Laminated steel sheets have been developed, in which the surface of a metal plate, such as tin-free steel (TFS) or aluminum, used as a material for metal containers, is coated with a thermoplastic resin film. The thermoplastic resin film is formed by a non-stretching method, a uniaxial stretching method, or a biaxial stretching method, and the film-coated 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, especially 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.

[0004] As a technique for suppressing breakage or abrasion of a resin coating layer, Patent Document 1 proposes a method of adding a lubricating component to a resin coating layer whose main component is polyester resin to enhance the slip properties and abrasion resistance of the resin coating layer.

[0005] In the field of beverage cans and food cans, ink printing is applied to the resin coating layer located on the outer surface of the container after molding to improve the design of the can body product. Here, if the adhesion between the various inks used for printing and the resin coating layer is low, the printing ink may peel off during can body processing, potentially damaging the design and aesthetic appeal of the can body's appearance. Patent Document 1 attempts to ensure ink adhesion by controlling the amount and average particle size of the lubricating component, since the lubricating component added to impart sliding properties during molding inhibits affinity with the ink.

[0006] International Publication No. 2019 / 116706

[0007] As described above, ink is applied to the surface of the resin coating layer on the outer surface of a metal container to impart design features to the container. However, resin coating layers primarily composed of polyester resin do not have excellent affinity with ink. Furthermore, the lubricating component added to the resin coating layer to impart sliding properties further deteriorates the affinity with ink. Therefore, the method described in Patent Document 1 results in poor adhesion between the resin coating layer and the ink, which may result in ink peeling during processing. Therefore, a resin-coated metal sheet that has excellent adhesion to printing ink while incorporating a lubricating component is desired.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a film for coating metal sheets and a resin-coated metal sheet that have excellent ink adhesion.

[0009] The present inventors conducted extensive research to achieve the above-mentioned objectives and have discovered the following. Conventionally, ink adhesion has been ensured by controlling the amount, particle size, and dispersion state of the lubricating component contained in the resin coating layer. However, resin coating layers primarily composed of polyester resins do not inherently have excellent ink affinity, and lubricating components composed of polyolefins also have low ink affinity. Therefore, simply adjusting the lubricating component may result in ink peeling even with slight changes in processing or printing conditions. Therefore, the present inventors focused on the lubricating inorganic particles contained in the resin coating layer to prevent blocking between the resin coating layers. By adjusting the amount, particle size, surface distribution, and surface roughness of the lubricating inorganic particles, the anchoring effect between the resin coating layer surface and the ink is improved, and compositional conditions for the resin coating layer that provide excellent ink adhesion have been discovered, leading to the completion of the present invention.

[0010] That is, the gist and configuration of the present invention are as follows.

[0011] [1] A film for covering metal sheets, the main component of which is a polyester resin, the film having a multi-layer structure of two or more layers including a first outermost layer and a second outermost layer, the melting point of the film being 230°C or higher and 260°C or lower, the first outermost layer containing 0.1% by mass or higher and 15% by mass or lower of lubricating inorganic particles made of silica having an average particle size of 0.2 μm or higher and 1.0 μm or lower, the number of the lubricating inorganic particles distributed on the surface of the first outermost layer being 1 mm ２ a surface roughness Ra of the first outermost layer is 0.30 μm or more; and the first outermost layer contains 0.010 mass % or more but less than 1.0 mass % of a polyolefin as a lubricating component.

[0012] [2] The film for covering metal sheets according to [1], wherein the polyolefin comprises at least one of an acid-modified polyolefin and an oxidized polyolefin.

[0013] [3] The film for covering metal sheets according to [1] or [2], wherein the acid value of the polyolefin is 20 mg KOH / g or more and 90 mg KOH / g or less.

[0014] [4] The film for covering metal sheets according to any one of [1] to [3], wherein the melting point of the polyolefin is 70°C or higher and 140°C or lower.

[0015] [5] The film for covering metal sheets according to any one of [1] to [4], wherein the mass average molecular weight of the polyolefin is 2000 or more and 50,000 or less.

[0016] [6] The film for covering metal sheets according to any one of [1] to [5], wherein the second outermost layer contains 10% by mass or more and 40% by mass or less of inorganic particles for coloring when the film for covering metal sheets has a two-layer structure, and the intermediate layer disposed between the first outermost layer and the second outermost layer contains 10% by mass or more and 40% by mass or less of inorganic particles for coloring when the film for covering metal sheets has a three-layer or more structure.

[0017] [7] The film for covering metal sheets according to any one of [1] to [6], wherein the thickness of the first outermost layer is 1.0 μm or more and 10 μm or less.

[0018] [8] The film for covering metal sheets according to [6] or [7], wherein the thickness of the second outermost layer or the intermediate layer containing the inorganic coloring particles is 10 μm or more and 20 μm or less.

[0019] [9] A resin-coated metal plate having a resin coating layer made of the film according to any one of [1] to [8] on at least one surface of the metal plate.

[0020]

[10] A method for producing a film for covering metal plates according to any one of [1] to [8] above, comprising co-extruding a polyester resin containing the lubricating inorganic particles and the polyolefin, which will form the first outermost layer, and polyester resins which will form layers other than the first outermost layer constituting the film for covering metal plates, using a kneading extruder, forming the resulting sheet into a sheet using a multi-layer die, and discharging the sheet; cooling and solidifying the resulting sheet on a cooling body; and stretching the sheet at least once under conditions of a stretching temperature of 80°C to 100°C and a stretching ratio of 3.5 times to 5.0 times, thereby producing a laminated film for covering metal plates.

[0021]

[11] The method for producing a resin-coated metal sheet according to [9], wherein the second outermost layer of the film is thermocompressed to the heated metal sheet using a laminating roll so as to be in close contact with the heated metal sheet.

[0022] According to the present invention, it is possible to provide a film for coating metal sheets and a resin-coated metal sheet that have excellent ink adhesion.

[0023] 1 is a cross-sectional view showing the configuration of an example of a resin-coated metal sheet according to the present invention.

[0024] (Film for covering metal sheets and resin-coated metal sheets) Hereinafter, embodiments of the present invention will be described with reference to the drawings. The film for covering metal sheets according to the present invention is a film for covering metal sheets containing polyester resin as a main component, and has a multi-layer structure of two or more layers including a first outermost layer and a second outermost layer. The melting point of the film is 230°C or higher and 260°C or lower, and the first outermost layer contains 0.1% by mass to 15% by mass of lubricating inorganic particles made of silica having an average particle size of 0.2 μm to 1.0 μm. The number of lubricating inorganic particles distributed on the surface of the first outermost layer is 1 mm. ２ The first outermost layer has a surface roughness Ra of 0.30 μm or more, and contains 0.010 mass % or more and less than 1.0 mass % of polyolefin as a lubricating component.

[0025] The resin-coated metal sheet according to the present invention comprises a resin coating layer made of the above-described film for coating metal sheets according to the present invention on at least one surface of the metal sheet.

[0026] 1(a) and 1(b) are cross-sectional views showing an example of the configuration of a resin-coated metal sheet according to the present invention. As shown in Fig. 1(a), the resin-coated metal sheet 1 includes a metal sheet 2, a resin coating layer (metal sheet coating film) 3 formed on the front surface side of the metal sheet 2, and a resin coating layer 4 formed on the back surface side of the metal sheet 2. Note that Fig. 1 shows an example in which the resin-coated metal sheet 1 has the resin coating layer 3 provided on the front surface side of the metal sheet 2 and the resin coating layer 4 provided on the back surface side of the metal sheet 2, but the resin coating layers 3 and 4 may be provided on only one surface of the metal sheet 2.

[0027] 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 molding. As shown in FIG. 1(b), the resin coating layer 3 has a multi-layer structure of two or more layers including a first layer 3a and a second layer 3b. The first layer 3a corresponds to the "first outermost layer" of the metal plate coating film according to the present invention, and the second layer 3b corresponds to the "second outermost layer." In the illustrated example, the resin coating layer 3 has a two-layer structure. The resin coating layer 4 may also have a multi-layer structure, similar to the resin coating layer 3. Note that when the resin coating layer 4 has a single-layer structure, it needs to have formability that can withstand the molding of the metal plate 2.

[0028] The metal plate 2 is preferably a steel plate. The metal plate 2 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 which has the following properties:

[0029] For tin-free steel, the adhesion amount is 50 mg / m per side. ２ 200mg / m or more ２ a metal chromium layer having a coating amount of 3 mg / m2 per side in terms of metal chromium on the metal chromium layer; ２ 30mg / m or more ２ It is preferable that the surface of the substrate has a chromium oxide layer having the following properties:

[0030] The type of metal plate 2 is not particularly limited as long as it can be formed into the desired shape, but steel plates having the following components and manufacturing methods are preferred: (1) A steel plate obtained by recrystallization annealing low-carbon steel having a C (carbon) content of 0.010% by mass or more and 0.10% by mass or less through continuous annealing; (2) A steel plate obtained by recrystallization annealing and overaging low-carbon steel having a C content of 0.010% by mass or more and 0.10% by mass or less through continuous annealing; (3) A steel plate obtained by recrystallization annealing low-carbon steel having a C content of 0.010% by mass or more and 0.10% by mass or less through box annealing; (4) A steel plate obtained by recrystallization annealing low-carbon steel having a C content of 0.010% by mass or more and 0.10% by mass or less through continuous annealing or box annealing, followed by secondary cold rolling (double reduced rolling). (5) A steel sheet obtained by recrystallization annealing an IF (Interstitial Free) steel, which is made by adding an element that fixes dissolved C, such as Nb or Ti, to an ultra-low carbon steel having a C content of 0.003 mass% or less, through continuous annealing.

[0031] 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.

[0032] The components of the steel sheet that satisfy the above mechanical properties are not particularly limited, but may contain, for example, components such as Si, Mn, P, S, Al, and N. 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, it is preferable that the total content of these component elements be 0.02 mass% or less.

[0033] The thickness of the metal plate 2 is not particularly limited, but may be, for example, 0.20 mm or more and 0.25 mm or less.

[0034] The polyester resin, which is the main component of the metal sheet-covering film according to the present invention, is a polymer composed of dicarboxylic acid units and glycol units. In the present invention, "containing a polyester resin as the main component" means that the polyester resin content is 90% by mass or more. Examples of dicarboxylic acid units that can be used include 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.

[0035] 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.

[0036] 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.

[0037] The resin coating layer 3 has a melting point of 230°C or higher and 260°C or lower. If the melting point of the resin coating layer 3 is 230°C or higher, softening of the resin during molding can be suitably prevented, and breakage or scraping can be more suitably prevented. Furthermore, if the melting point of the resin coating layer 3 is 260°C or lower, the crystallinity of the polyester resin contained therein is more suitable, and breakage or scraping of the resin coating layer 3 can be more suitably prevented during molding. The melting point of the resin coating layer 3 is preferably 235°C or higher, and more preferably 240°C or higher. The melting point of the resin coating layer 3 is preferably 258°C or lower, and more preferably 255°C or lower.

[0038] The melting point of the resin coating layer 3 is measured by 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 to 280°C in the obtained heat flow is taken as the melting point.

[0039] The first layer 3a of the resin coating layer 3 contains silica as lubricating inorganic particles. By containing silica as lubricating inorganic particles in the first layer 3a, blocking can be prevented when the metal sheet coating film of the present invention is wound onto a roll, improving the film unwinding performance during lamination. Furthermore, the film transportability during film formation and lamination is improved. Silica, which has excellent film-forming properties, lubricity, and blocking resistance, is used as the lubricating inorganic particles.

[0040] The content of the lubricating inorganic particles in the first layer 3a is 0.1% by mass or more and 15% by mass or less in terms of solid content. If the content of the lubricating inorganic particles in the first layer 3a is less than 0.1% by mass, the film's blocking resistance is poor, and there is a possibility of film blocking when the film is wound into a roll. Furthermore, the film's slipperiness is poor during film formation and transport and lamination transport, and wrinkles may be introduced during transport. Furthermore, fine irregularities cannot be formed on the film surface, and an anchoring effect with the ink cannot be obtained, which may result in poor ink adhesion. The content of the lubricating inorganic particles is preferably 5.1% by mass or more, more preferably 10.1% by mass or more. On the other hand, if the content of the lubricating inorganic particles in the first layer 3a exceeds 15% by mass, the film may slip sideways during film formation and transport and lamination transport, resulting in scratches. Furthermore, there is a possibility that the film may be scraped from the lubricating inorganic particles aggregated during molding processing. The content of the lubricating inorganic particles in the first layer 3a is preferably 13% by mass or less.

[0041] The average particle size of the lubricating inorganic particles in the first layer 3a is 0.2 μm or more and 1.0 μm or less. If the average particle size of the lubricating inorganic particles in the first layer 3a is less than 0.2 μm, the lubricating properties of the film surface are poor, and there is a possibility of film blocking when the film is wound into a roll. Poor film release during lamination may result in scratches and wrinkles being introduced into the film. Furthermore, the lubricating properties may be poor during film formation and lamination transport, and wrinkles may be introduced during transport. Furthermore, adequate unevenness may not be formed on the film surface, and the anchoring effect with ink may not be obtained, resulting in poor ink adhesion. Furthermore, if the average particle size of the lubricating inorganic particles in the first layer 3a exceeds 1.0 μm, fine unevenness may not be formed on the film surface, and the anchoring effect with ink may not be obtained, resulting in poor ink adhesion. Furthermore, there is a possibility that the film may be scraped from the coarse lubricating inorganic particles during molding processing. The average particle size of the lubricating inorganic particles in the first layer 3a is preferably 0.3 μm or more, more preferably 0.4 μm or more. The average particle size of the lubricating inorganic particles in the first layer 3a is preferably 0.9 μm or less, and even more preferably 0.8 μm or less. The average particle size of the lubricating inorganic particles can be measured, for example, by the following method. Using a chemical force microscope (CFM), the surface of the resin coating layer of the resin-coated metal sheet is observed at room temperature in five fields of view (field area: 1 μm × 1 μm). For any 20 observed lubricating inorganic particles in each field of view, the particle size is calculated from the measurement results of the major axis and minor axis using the following formula (1), and the average value (5 fields of view × 20 points = 100 points average value) is defined as the average particle size of the lubricating inorganic particles. If 20 lubricating inorganic particles are not observed in the observed field of view, the calculation is performed for all lubricating inorganic particles in the field of view, and the average value is defined as the average particle size. (Particle size) = {(major axis) × (minor axis)}^(1 / 2) (1)

[0042] The number of the lubricating inorganic particles distributed on the surface of the first layer 3a is 1 mm ２ The number of the lubricating inorganic particles distributed on the surface of the first layer 3a is 400 or more per mm ２If the number of particles is less than 400 per mm, the film surface may not have sufficient fine irregularities, and the ink may not have a sufficient anchoring effect, resulting in poor ink adhesion. ２ More preferably, 450 or more per mm ２ There are more than 500 per

[0043] The surface roughness Ra of the first layer 3a is 0.30 μm or more. If the surface roughness Ra of the first layer 3a is less than 0.30 μm, sufficient fine irregularities cannot be formed on the film surface, which may result in an insufficient anchoring effect with the ink and poor ink adhesion. The surface roughness Ra of the first layer 3a is preferably 0.40 μm or more, more preferably 0.50 μm or more.

[0044] The first 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 first layer 3a, excellent slip properties and abrasion resistance can be ensured, and breakage or abrasion of the resin coating layer can be suppressed during can molding. As the lubricating component, a polyolefin having excellent film-forming and dispersibility properties and a melting point within an appropriate range is used. Furthermore, 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 polar groups include acid-modified polyolefins such as ethylene-maleic anhydride copolymers and oxidized polyolefins such as polyethylene oxide. A combination of multiple types of polyolefins may be used as the polyolefin.

[0045] The polyolefin includes at least one of an acid-modified polyolefin and an oxidized polyolefin. When the polyolefin is at least one of an acid-modified polyolefin and an oxidized polyolefin, the polyolefin has a polar group, which increases the acid value and improves the affinity with the resin coating layer 3 and the affinity between the first layer 3a and the printing ink. The polyolefin may be a mixture of an acid-modified polyolefin and an oxidized polyolefin.

[0046] The polyolefin content in the first layer 3a is 0.010% by mass or more and less than 1.0% by mass, calculated as solid content. If the polyolefin content in the first layer 3a is less than 0.010% by mass, sufficient slip properties and abrasion resistance cannot be ensured during molding, and the resin coating layer 3 may break or be abraded. If the polyolefin content in the first layer 3a is 1.0% by mass or more, abrasion of the resin coating layer 3 may occur from dispersed coarse polyolefin particles during molding. The polyolefin content in the first layer 3a is preferably 0.050% by mass or more, more preferably 0.10% by mass or more. The polyolefin content in the first layer 3a is preferably 0.80% by mass or less, and even more preferably 0.60% by mass or less.

[0047] The acid value of the polyolefin is preferably 20 mgKOH / g or more, and preferably 90 mgKOH / g or less. If the acid value of the polyolefin is 20 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 90 mgKOH / g or less, the polyolefin is not compatible with the resin coating layer 3, so that more suitable slip properties and abrasion resistance can be ensured during molding processing, and breakage or abrasion of the resin coating layer 3 can be more suitably prevented. The acid value of the polyolefin is more preferably 25 mgKOH / g or more, even more preferably 30 mgKOH / g or more. The acid value of the polyolefin is more preferably 80 mgKOH / g or less, even more preferably 70 mgKOH / g or less. The acid value of the polyolefin is measured according to the method described in the Examples below.

[0048] The melting point of the polyolefin is preferably 70°C or higher and 140°C or lower. If the melting point of the polyolefin is 70°C or higher, the polyolefin will not thicken on the surface of the resin coating layer 3 even during the lamination process and the heat treatment performed during the molding of the resin-coated metal sheet, ensuring sufficient printing ink adhesion. Furthermore, if the melting point of the polyolefin is 140°C or lower, more suitable slip properties and abrasion resistance can be ensured during molding, and breakage or abrasion of the resin coating layer 3 can be more suitably prevented. The melting point of the polyolefin is preferably 85°C or higher, more preferably 95°C or higher. The melting point of the polyolefin is preferably 135°C or lower, more preferably 125°C or lower. The melting point of the polyolefin is measured according to the method described in the Examples below.

[0049] The mass average molecular weight of the polyolefin is preferably 2000 or more and preferably 50,000 or less. If the mass average molecular weight of the polyolefin is 2000 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 mass average molecular weight of the polyolefin is 50,000 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 mass average molecular weight of the polyolefin is more preferably 3,000 or more, and even more preferably 3,500 or more. The mass average molecular weight of the polyolefin is more preferably 45,000 or less, and even more preferably 40,000 or less. The mass average molecular weight of the polyolefin is measured according to the method described in the Examples below.

[0050] 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, if the resin coating layer 3 has a two-layer structure, the second layer 3b of the resin coating layer 3 preferably contains coloring inorganic particles. If the metal plate coating film has a three-layer or more structure, the intermediate layer (not shown) disposed between the first layer 3a and the second layer 3b preferably contains coloring inorganic particles. This is because the resin coating layer 3 can be made white by containing coloring inorganic particles in the second layer 3b or the intermediate layer.

[0051] The second layer 3b or the intermediate layer preferably contains 10% by mass or more, and preferably 40% by mass or less, of inorganic coloring particles in terms of solid content. When the content of inorganic coloring particles in the second layer 3b or the intermediate layer is 10% by mass or more, sufficient whiteness can be ensured. When the content of inorganic coloring particles in the second layer 3b or the intermediate layer is 40% by mass or less, fracture or abrasion of the resin coating layer 3 can be more suitably prevented even under severe processing conditions. The content of inorganic coloring particles in the second layer 3b or the intermediate layer is more preferably 12% by mass or more, and even more preferably 15% by mass or more. The content of inorganic coloring particles in the second layer 3b or the intermediate layer is more preferably 35% by mass or less, and even more preferably 30% by mass or less. When the intermediate layer has a structure of two or more layers, it is sufficient that the content of inorganic coloring particles contained in the entire intermediate layer is within the above range; it is not necessary for all layers constituting the intermediate layer to contain inorganic coloring particles.

[0052] The inorganic coloring particles contained in the second layer 3b or the intermediate layer are not particularly limited. The inorganic coloring particles are preferably titanium oxide. The titanium oxide is preferably rutile-type titanium oxide having a purity of 90% or more. When the inorganic coloring particles contained in the second layer 3b or the intermediate layer 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.

[0053] The thickness of the first layer 3a is preferably 1.0 μm or more and preferably 10 μm or less. Having the thickness of the first layer 3a within the above range ensures more favorable slip properties and abrasion resistance during molding, and more favorably prevents the resin coating layer 3 from breaking or being abraded. Furthermore, the surface distribution number and surface roughness Ra of the lubricious inorganic particles contained in the first layer 3a become favorable, and the ink adhesion is improved due to the anchoring effect with the ink. The thickness of the first layer 3a is more preferably 1.2 μm or more, even more preferably 1.5 μm or more. The thickness of the first layer 3a is more preferably 9.0 μm or less, even more preferably 8.0 μm or less. The thickness of the first layer 3a is measured according to the method described in the Examples below.

[0054] The thickness of the second layer 3b containing inorganic coloring particles or the intermediate layer containing inorganic coloring particles is preferably 10 μm or more and preferably 20 μm or less. When the thickness of the inorganic coloring particle-containing layer is within the above range, there is no need to vary the thickness of the first layer 3a, and the surface distribution number and surface roughness Ra of the lubricating inorganic particles are suitable, thereby improving ink adhesion due to the anchoring effect with the ink. In addition, since the can body has suitable whiteness after molding, the design and aesthetics after ink printing are improved. The thickness of the inorganic coloring particle-containing layer is more preferably 12 μm or more, even more preferably 14 μm or more. The thickness of the inorganic coloring particle-containing layer is more preferably 18 μm or less, even more preferably 16 μm or less. The thickness of the inorganic coloring particle-containing layer is measured according to the method described in the Examples below.

[0055] By using the resin-coated metal plate described above, it is possible to manufacture a metal container having excellent adhesion between the resin coating surface and ink. The metal container can be manufactured by a conventional method.

[0056] (Method for producing a film for covering metal plates) The method for producing a film for covering metal plates according to the present invention is as follows. A polyester resin containing lubricating inorganic particles and a polyolefin, which will form the first outermost layer, and polyester resins which will form the layers other than the first outermost layer constituting the film for covering metal plates, are co-extruded using a kneading extruder, and then formed into a sheet using a multilayer die and discharged. The resulting sheet is cooled and solidified on a cooling body, and then stretched one or more times under conditions of a stretching temperature of 80°C to 100°C and a stretching ratio of 3.5 to 5.0, thereby producing a laminated film for covering metal plates.

[0057] First, in order to incorporate the lubricating inorganic particles into the first outermost layer, the lubricating inorganic particles and polyolefin are added to a resin containing a polyester resin as a main component.

[0058] The method for adding the lubricating inorganic particles to the polyester resin is not particularly limited. A preferred method is to prepare a master batch in which the lubricating inorganic particles are dispersed in a resin at a high concentration using a kneading extruder, and then mix the resin pellets and the master batch in a predetermined ratio and introduce the mixture into the kneading extruder during film formation.

[0059] When polyolefin is contained in the first outermost layer, the same method as in the case of the lubricating inorganic particles is preferably used: a masterbatch in which polyolefin is dispersed in a resin at a high concentration is prepared using a kneading extruder, and during film production, resin pellets and the masterbatch are mixed in a predetermined ratio and introduced into the kneading extruder.

[0060] Furthermore, when the second outermost layer or intermediate layer contains inorganic coloring particles, the same method as that for the lubricating inorganic particles is preferably used: a masterbatch is prepared in advance by dispersing the inorganic coloring particles in a resin at a high concentration using a kneading extruder, and during film formation, resin pellets and the masterbatch are mixed in a predetermined ratio and introduced into the kneading extruder.

[0061] When mixing the resin pellets and the master batch, the extrusion temperature is preferably set to a temperature higher than the melting point of the resin pellets. For example, mixing is preferably performed at an extrusion temperature of 270° C. or higher.

[0062] A mixture of polyester resin, lubricating inorganic particles, and polyolefin, which will form the first outermost layer, and a mixture of resin and coloring inorganic particles, which will form the second outermost layer or intermediate layer, are co-extruded and formed into a sheet using a multilayer T-die. The resulting sheet is then extruded onto a cooling body such as a casting drum. The extruded sheet is cooled and solidified to obtain an unstretched laminated film.

[0063] After producing an unstretched laminated film, the film is stretched one or more times to form a resin film, and the stretching temperature at this time is preferably 80°C or higher and 100°C or lower. If the stretching temperature is within the above range, welding and breakage of the film during film formation can be suppressed, and the dispersion state of the lubricating inorganic particles and polyolefin can be kept within an appropriate range. The stretching temperature is more preferably 85°C or higher, and even more preferably 88°C or higher. The stretching temperature is more preferably 98°C or lower, and even more preferably 96°C or lower.

[0064] Furthermore, the stretching ratio during stretching is preferably 3.5 times or more, and preferably 5.0 times or less. If the stretching ratio is within the above range, breakage during film formation can be suppressed, and the occurrence of thickness unevenness can be suppressed while keeping the film thickness within an appropriate range. Furthermore, the dispersion state of the lubricating inorganic particles and polyolefin can be kept within an appropriate range. The stretching ratio is more preferably 3.8 times or more, and even more preferably 4.0 times or more. The stretching ratio is more preferably 4.8 times or less, and even more preferably 4.6 times or less.

[0065] (Method for manufacturing resin-coated metal sheet) The method for manufacturing a resin-coated metal sheet according to the present invention is the method for manufacturing a resin-coated metal sheet according to the present invention described above, in which the second outermost layer of the metal sheet coating film according to the present invention is heat-pressed onto the heated metal sheet using a laminating roll so that it is in close contact with the heated metal sheet.

[0066] The film for covering metal plates produced by the method for producing a film for covering metal plates according to the present invention as described above is heated to a temperature above the melting initiation temperature and thermocompressed to a metal plate 2 using a laminating roll (thermocompression film lamination method). At this time, the temperature of the metal plate 2 is preferably 260°C or higher and preferably 290°C or lower. If the temperature of the metal plate 2 is within the above range, the adhesion between the film and the metal plate 2 is improved and welding of the film to the laminating roll can be suppressed. The temperature of the metal plate 2 is more preferably 265°C or higher, and even more preferably 270°C or higher. The temperature of the metal plate 2 is more preferably 288°C or lower, and even more preferably 285°C or lower.

[0067] Furthermore, the laminating roll temperature is preferably 90°C or higher and 120°C or lower. If the laminating roll temperature is within the above range, welding of the film to the laminating roll can be suppressed. The laminating roll temperature is more preferably 92°C or higher, and even more preferably 95°C or higher. The laminating roll temperature is more preferably 118°C or lower, and even more preferably 116°C or lower. This thermocompression film laminating method is advantageous in that it reduces production costs and enables energy-saving production.

[0068] The manufacturing conditions other than those mentioned above can be the same as those in the ordinary method.

[0069] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0070] 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 ２TFS (tin-free steel) with a temper of T3CA was used as the metal plate 2. The mechanical properties of the metal plate 2 were a YP of 400 MPa, an r value of 1.0, and a Δr of 0.5. Furthermore, a multilayer resin film (a film for coating a metal plate) was formed by a uniaxial stretching method using the resin, silica, polyolefin, and titanium oxide shown in Table 1. Thereafter, the metal plate 2 was heated, and resin films were thermocompression-bonded to both the front and back surfaces of the metal plate 2 as resin coating layers 3 and 4 by a thermocompression film lamination method.

[0071] When the resin film was thermocompression bonded to the metal plate 2, the temperature of the metal plate 2 was controlled to 260°C or higher and 290°C or lower, and the temperature of the laminating roll was controlled to 90°C or higher and 120°C or lower. After 0.5 to 1.0 second had elapsed since thermocompression bonding, the metal plate was water-cooled in a water-cooled tank at 60°C, thereby coating both sides of the metal plate 2 with the resin coating layers 3 and 4 of Invention Examples 1 to 25 and Comparative Examples 1 to 13. The first outermost layer 3a contained silica and polyolefin in the amounts shown in Tables 1 and 2. The coloring inorganic particle-containing layer contained titanium oxide in the amount shown in Tables 1 and 2. The coating conditions were as shown in Tables 1 and 2 below.

[0072]

[0073]

[0074] For the resin-coated metal plate 1 produced by the above method, the melting point of the resin coating layers 3 and 4, the number of easy-to-smooth inorganic particles distributed on the surface of the first outermost layer 3a, the surface roughness Ra of the first outermost layer 3a, the acid value of the polyolefin, the melting point of the polyolefin, the mass average molecular weight of the polyolefin, and the thickness of each of the resin coating layers 3 and 4 were measured using the methods described below.

[0075] (1) Melting Point of Resin Coating Layer The resin-coated metal sheet 1 was immersed in a mixed solution of concentrated hydrochloric acid (30% by mass):distilled water = 1:1 at room temperature to dissolve the metal sheet 2, thereby peeling off the resin coating layers 3 and 4. Thereafter, a differential scanning calorimeter: DSCQ100 manufactured by TA Instruments was used to measure the melting point of the resin coating layer 1 in a mixed solution of concentrated hydrochloric acid (30% by mass):distilled water = 1:1. ２The peeled resin coating layers 3 and 4 were 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.

[0076] (2) Number of lubricating inorganic particles distributed in the first outermost layer After osmium (Os) deposition was performed on the surface of the resin-coated metal sheet 1 to prevent static buildup, secondary electron image observation was performed using a low-acceleration scanning electron microscope (GeminiSEM 300) manufactured by Carl Zeiss under the conditions of 1000x magnification, 1 kV acceleration voltage, and 20 μm aperture. From the obtained secondary electron image, the number of surface convexities resulting from the lubricating inorganic particles distributed on the surface was counted, and the number of convexities per unit area mm ２ The number of easily slippery inorganic particles distributed on the surface of the first outermost layer 3a was calculated by converting the number of easily slippery inorganic particles per particle.

[0077] (3) Surface roughness Ra of first outermost layer The surface roughness Ra of the resin-coated metal sheet 1 (i.e., the first outermost layer 3a) was measured using a contact surface roughness measuring instrument SJ-210 manufactured by Mitutoyo Corporation under the conditions of a measurement length of 5 mm, a measurement speed of 0.50 mm / s, and a cutoff λc of 0.80 mm. At this time, measurements were taken at three randomly selected points in the lamination direction of the resin-coated metal sheet 1 and in the direction perpendicular to the lamination direction within the plate surface, and the average value of the surface roughness Ra data obtained for a total of six points was calculated.

[0078] (4) Acid Value of Polyolefin After the resin coating layers 3 and 4 were peeled from the resin-coated metal plate 1 in the same manner as in (1), the resin coating layers 3 and 4 were dissolved using hexafluoro-2-propanol (HFIP) as a solvent. The dissolved resin coating layers 3 and 4 were centrifuged and then pressure-filtered through filters with pore sizes of 1 μm and 0.1 μm, respectively, to extract the polyolefin contained in the first outermost layer 3 a of the resin coating layers 3 and 4. Furthermore, Soxhlet extraction was performed on the filter using xylene as a solvent, and after concentration, reprecipitation, and centrifugation, additional polyolefin was extracted. The acid value of the polyolefin extracted in this manner was measured in accordance with JIS K5902. According to JIS K5902, a predetermined amount of polyolefin corresponding to the estimated acid value was weighed into a flask and dissolved in 100 ml of a neutral solvent. Then, using phenolphthalein as an indicator, the solution was titrated with 0.1 mol / L potassium hydroxide standard solution. The neutralization endpoint was determined when the indicator continued to change color for 30 seconds, and the acid value was calculated using the following formula: (Acid value) = 5.611 x A x F / B, where A is the amount (ml) of 0.1 mol / L potassium hydroxide standard solution used, B is the amount (g) of sample taken, and F is the factor of 0.1 mol / L potassium hydroxide standard solution.

[0079] (5) Melting Point of Polyolefin The polyolefin extracted in the same manner as in (4) was measured using a differential scanning calorimeter DSCQ100 manufactured by TA Instruments under the condition 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 60°C to 150°C of the obtained heat flow was taken as the melting point.

[0080] (6) Mass average molecular weight of polyolefin Polyolefin extracted in the same manner as in (4) was measured using an Agilent gel permeation chromatograph analyzer: PL-GPC220, 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 and elution time of the standard polystyrene. Using this calibration curve, the mass average molecular weight of the polyolefin was calculated based on the elution time of the polyolefin.

[0081] (7) Thickness of each resin coating layer After peeling off the resin coating layers 3 and 4 from the resin-coated metal plate 1 in the same manner as in (1), a Pt coating was applied to the outermost surfaces of the resin coating layers 3 and 4, and the resin was embedded in resin. A cross section was then prepared using an ion milling device: EM TIC 3X manufactured by Leica Microsystems Co., Ltd. A backscattered electron image of the prepared cross section was observed using a scanning electron microscope (SEM): Regulus 8220 manufactured by Hitachi High-Technologies Corporation at two observation magnifications of 3500x and 8000x, and the thickness of each resin coating layer 3 and 4 was calculated from the observed image.

[0082] The resin-coated metal sheets 1 of Examples 1 to 28 and Comparative Examples 1 to 13 were evaluated for ink adhesion and moldability of the resin coating layers 3 and 4 by the methods described below. The evaluation results are shown in Table 3.

[0083]

[0084] (8) Evaluation of Ink Adhesion The resin-coated metal plates 1 of Examples 1 to 28 and Comparative Examples 1 to 13 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 molding, an alkyd-melamine thermosetting ink was printed on the surface of the resin coating layers 3 and 4 located on the outer surface of the container using a universal printing tester manufactured by Kumagai Riki Kogyo Co., Ltd. Immediately thereafter, the ink-printed surfaces of the obtained samples were subjected to a heat treatment in a hot air drying oven, reaching 200°C in 1 minute, and then cooled to room temperature. A scratch test was performed on the ink-printed surfaces of the obtained samples along the longitudinal direction of the samples using a load-varying friction and wear tester: HHS2000 manufactured by Shinto Scientific Co., Ltd. The test conditions were a continuous load of 10 to 1000 gf from the printed edge, a movement speed of 0.5 mm / sec, and a movement distance of 30 mm, using a sapphire indenter (Φ0.6 mm). Twenty tests were carried out for each sample (five tests on four sheets each), and the ink peel load value was calculated from the obtained ink peel length. Data within a 1σ range was extracted from all peel load value data for each example to evaluate ink adhesion.

[0085] Evaluation criteria for ink adhesion Evaluation "A": The lower limit of the peel load within the 1σ range is 100 g or more. No practical problems. Evaluation "B": The lower limit of the peel load within the 1σ range is 70 g or more and less than 100 g. No practical problems. Evaluation "C": The lower limit of the peel load within the 1σ range is 50 g or more and less than 70 g. There are practical problems. Evaluation "D": The lower limit of the peel load within the 1σ range is less than 50 g. There are practical problems.

[0086] (9) Evaluation of formability After wax was applied to the resin-coated metal sheets 1 of Examples 1 to 28 and Comparative Examples 1 to 13, they were punched into disks with a diameter of 123 mm and drawn into cups at a drawing ratio of 1.7 using a cupping press. The resulting cups were inserted into a DI forming device and subjected to redrawing and DI processing at a drawing ratio of 1.3 to form cans with an inner diameter of 52 mm and a can height of 90 mm. The surfaces of the resin coating layers 3 and 4 of the formed cans were visually observed to evaluate formability.

[0087] Evaluation criteria for formability Rating "A": No chipping is observed visually. No practical problems. Rating "B": Minor chipping is observed visually at a height of 10 mm or less from the flange of the can. No practical problems. Rating "C": Chips are observed visually at a height of more than 10 mm but less than 30 mm from the flange of the can. Problems in practical use. Rating "D": Chips reaching a height of more than 30 mm from the flange of the can or broken bodies are observed visually. Problems in practical use.

[0088] According to the present invention, it is possible to provide a film for coating metal sheets and a resin-coated metal sheet that have excellent ink adhesion.

[0089] REFERENCE SIGNS LIST 1 Resin-coated metal sheet 2 Metal sheet 3 Resin coating layer (film for coating metal sheet) 4 Resin coating layer 3a First layer (first outermost layer) 3b Second layer (second outermost layer)

Claims

1. A metal sheet covering film containing a polyester resin as a main component, The metal plate covering film has a multi-layer structure of two or more layers including a first outermost layer and a second outermost layer, The melting point of the film is 230°C or higher and 260°C or lower, the first outermost layer contains 0.1% by mass or more and 15% by mass or less of lubricating inorganic particles made of silica having an average particle size of 0.2 μm or more and 1.0 μm or less, The number of the lubricating inorganic particles distributed on the surface of the first outermost layer is 1 mm ２ More than 400 per the surface roughness Ra of the first outermost layer is 0.30 μm or more; The first outermost layer contains 0.010 mass% or more and less than 1.0 mass% of a polyolefin as a lubricating component. Film for covering metal plates.

2. 2. The film for covering metal sheets according to claim 1, wherein the polyolefin comprises at least one of an acid-modified polyolefin and an oxidized polyolefin.

3. 3. The film for covering metal sheets according to claim 1, wherein the acid value of the polyolefin is 20 mg KOH / g or more and 90 mg KOH / g or less.

4. 3. The film for covering metal sheets according to claim 1, wherein the melting point of the polyolefin is 70°C or higher and 140°C or lower.

5. 3. The film for covering metal sheets according to claim 1, wherein the polyolefin has a mass average molecular weight of 2,000 or more and 50,000 or less.

6. 3. The metal plate covering film according to claim 1, wherein the second outermost layer contains 10% by mass or more and 40% by mass or less of inorganic particles for coloring when the metal plate covering film has a two-layer structure, and the intermediate layer disposed between the first outermost layer and the second outermost layer contains 10% by mass or more and 40% by mass or less of inorganic particles for coloring when the metal plate covering film has a three-layer or more structure.

7. 3. The film for covering metal sheets according to claim 1, wherein the first outermost layer has a thickness of 1.0 μm or more and 10 μm or less.

8. 7. The film for covering metal sheets according to claim 6, wherein the thickness of the second outermost layer or the intermediate layer containing the inorganic coloring particles is 10 μm or more and 20 μm or less.

9. A resin-coated metal sheet comprising a resin coating layer made of the film according to claim 1 or 2 on at least one surface of a metal sheet.

10. The resin-coated metal sheet according to claim 9 , wherein the second outermost layer is in contact with the metal sheet.

11. A method for producing a metal sheet coating film according to claim 1 or 2, The polyester resin containing the lubricating inorganic particles and the polyolefin, which will form the first outermost layer, and the polyester resins which will form the layers other than the first outermost layer constituting the metal plate-covering film, are co-extruded using a kneading extruder, and then formed into a sheet shape using a multi-layer die and discharged; The obtained sheet is cooled and solidified on a cooling body, and then The film is stretched at least once under the conditions of a stretching temperature of 80°C or higher and 100°C or lower and a stretching ratio of 3.5 times or higher and 5.0 times or lower, to produce a laminated film, which is a film for covering a metal plate. A method for manufacturing a film for covering metal sheets.

12. The method for producing a resin-coated metal sheet according to claim 9, thermocompression bonding with a laminating roll so that the second outermost layer of the film is in close contact with the heated metal plate; A method for manufacturing a resin-coated metal sheet.