Resin-coated metal plate, metal container, and method for manufacturing resin-coated metal plate

Abstract

The present invention provides a resin-coated metal plate in which the sliding property, the wear resistance, and the ink adhesion of a resin coating layer are excellent. The resin-coated metal plate of the present invention is a resin-coated metal plate in which a resin coating layer containing a polyester resin and satisfying prescribed requirements is provided on one surface, and the surface layer of the resin coating layer contains a polyolefin satisfying prescribed requirements, and the average area m of N Voronoi polygons obtained by performing Voronoi partition with the center of gravity of each particle of the polyolefin as the parent point satisfies 500 μm 2 ~ 20000 μm 2 , σ defined by the following formula (1) 2 is 1.0 or less. Here, N: total number of Voronoi polygons m: average area (μm 2 ) of N Voronoi polygons S i : area (μm 2 ) of the i-th Voronoi polygon among N Voronoi polygons, i is an integer in the range of 1 to N.

Description

Technical Field

[0001] This invention relates to resin-coated metal sheets, metal containers, and methods for manufacturing resin-coated metal sheets. Background Technology

[0002] Laminated metal sheets have been developed, in which a thermoplastic resin film is coated onto the surface of metal sheets such as tin-strength steel (TFS) and aluminum, which are used as blanks for metal containers. These laminated metal sheets are widely used in the beverage and food can industries, where demanding forming processes are required.

[0003] In recent years, from the perspective of conserving resources and reducing material costs, there has been a push to thin the walls of materials used in metal containers, particularly metal sheets and resin coatings, through stringent processing conditions. This results in higher processing requirements during can manufacturing, especially as the resin coating on the outer surface of the metal container may fracture or wear after molding. Therefore, there is a need for material designs that can suppress fracture or wear of the resin coating during can manufacturing. As a technique to suppress fracture or wear of the resin coating, Patent Document 1 proposes a method of adding lubricating components to the resin coating to improve its sliding properties and wear resistance.

[0004] In addition, to improve design, the resin coating layer on the outer surface of the container after molding is printed. However, if the affinity between the printing ink and the resin coating layer is low, sufficient ink adhesion cannot be ensured, potentially leading to ink peeling during can manufacturing and compromising the design and aesthetics of the can.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2019 / 116706 Summary of the Invention

[0008] The lubricating components added to the resin coating inhibit breakage or abrasion of the resin coating. On the other hand, there is a risk of hindering the affinity between the printing ink applied through the printing process and the surface of the resin coating, which may lead to ink peeling during processing. Therefore, resin-coated metal sheets are required to have excellent ink adhesion in addition to the lubricity and abrasion resistance of the resin coating.

[0009] Therefore, the object of the present invention is to provide a resin-coated metal sheet with excellent sliding properties, abrasion resistance and ink adhesion, and a method for manufacturing the same.

[0010] To address the aforementioned problems, the inventors conducted in-depth research and obtained the following insights. As in the past, even if only the amount and particle size of the lubricating component in the resin coating are specified, excellent properties cannot be guaranteed if the distribution of the lubricating component deviates. Therefore, by controlling the dispersion state of the lubricating component present on the outermost surface of the resin coating, a resin coating with excellent sliding properties, abrasion resistance, and ink adhesion can be obtained. Furthermore, by setting the stretching conditions of the sheet-shaped molded body during the manufacturing of the laminated film hot-pressed onto a metal sheet to specified conditions, and by setting the temperatures of the metal sheet and the laminating rollers during the hot-pressing of the laminated film onto the metal sheet to an appropriate range, the dispersion state of the lubricating component can be controlled.

[0011] That is, the essence of the present invention is as follows.

[0012] [1] A resin-coated metal sheet, wherein at least one side of the metal sheet has a resin coating layer comprising polyester resin.

[0013] The aforementioned resin coating has a structure of at least three layers, comprising an outermost layer, a middle layer, and a bottommost layer.

[0014] The melting point of the above-mentioned resin coating is 230℃~260℃.

[0015] The outermost layer contains more than 0.010% by mass and less than 1.0% by mass of polyolefin.

[0016] The aforementioned polyolefin is at least one of acid-modified polyolefin and oxidized polyolefin.

[0017] The melting points of the aforementioned polyolefins are 70℃~145℃.

[0018] The aforementioned polyolefin is dispersed in particulate form in the outermost layer.

[0019] The dispersion state of the aforementioned polyolefin particles satisfies the following condition: on the outermost surface, the average area m of the N Voronoi polygons obtained by dividing the surface using the centroid of each polyolefin particle as the parent point is 500 μm. 2 ~20000μm 2 σ is defined by the following formula (1) 2 It is below 1.0.

[0020]

[0021] in,

[0022] N: The total number of the above Voronoi polygons

[0023] m: the average area (μm) of the above N Voronoi polygons 2 )

[0024] S i The area (μm) of the i-th Voronoi polygon among the N Voronoi polygons mentioned above. 2 ), where i is an integer in the range of 1 to N.

[0025] [2] The resin-coated metal plate according to [1] above, wherein the weight-average molecular weight of the polyolefin is 2000 to 50000.

[0026] [3] The resin-coated metal plate according to [1] or [2] above, wherein the acid value of the polyolefin is 1.0 mg KOH / g to 90 mg KOH / g.

[0027] [4] The resin-coated metal plate according to any one of [1] to [3] above, wherein the outermost layer and the lowermost layer each contain 0.010% to 10.0% by mass of slippery inorganic particles.

[0028] [5] A resin-coated metal plate according to any one of [1] to [4] above, wherein the intermediate layer contains 10% to 35% by mass of inorganic particles.

[0029] [6] The resin-coated metal plate according to any one of [1] to [5] above, wherein the thickness of the outermost layer and the bottommost layer is 1.0 μm to 5.0 μm, and the thickness of the intermediate layer is 6.0 μm to 30 μm.

[0030] [7] A metal container, which is a metal container made by coating a metal sheet with the resin described in any one of [1] to [6] above.

[0031] The resin coating is located on the outside of the metal container.

[0032] [8] A method for manufacturing a resin-coated metal plate, comprising:

[0033] A process in which a first composition comprising polyester resin and 0.010% by mass and less than 1.0% by mass of polyolefin, a second composition comprising polyester resin, and a third composition comprising polyester resin are co-extruded in a compounding extruder and discharged from a T-die to obtain a sheet-shaped molded body with the first composition, the second composition, and the third composition as the first layer, the second layer, and the third layer, respectively, wherein the polyolefin is at least one of acid-modified polyolefin and oxidized polyolefin and has a melting point of 70°C to 145°C;

[0034] The process of cooling and solidifying the above-mentioned molded body to obtain a laminated film;

[0035] Next, the laminated film is stretched at least once at a stretching temperature of 80°C to 110°C and a stretching ratio of 3.0 to 6.0 times to obtain a resin film comprising the first layer, the second layer, and the third layer; and

[0036] Next, the resin film is hot-pressed onto at least one side of a metal plate controlled at 260°C to 290°C using a laminating roller controlled at 110°C to 120°C, to obtain a resin-coated metal plate having a resin coating layer on at least one side of the metal plate. The resin coating layer has at least a three-layer structure with the first layer, the second layer, and the third layer as the outermost layer, the middle layer, and the bottom layer, respectively, and has a melting point of 230°C to 260°C.

[0037] [9] In the method for manufacturing the resin-coated metal sheet according to [8] above, the weight-average molecular weight of the polyolefin is 2,000 to 50,000.

[0038]

[10] The method for manufacturing a resin-coated metal sheet according to [8] or [9] above, wherein the acid value of the polyolefin is 1.0 mg KOH / g to 90 mg KOH / g.

[0039]

[11] The method for manufacturing a resin-coated metal sheet according to any one of [8] to

[10] above, wherein the first composition and the third composition each contain 0.010% to 10.0% by mass of slippery inorganic particles.

[0040]

[12] The method for manufacturing a resin-coated metal sheet according to any one of [8] to

[11] above, wherein the second composition contains 10% to 35% by mass of inorganic particles.

[0041]

[13] The method for manufacturing a resin-coated metal sheet according to any one of [8] to

[12] above, wherein the thickness of the outermost layer and the bottommost layer is 1.0 μm to 5.0 μm, and the thickness of the intermediate layer is 6.0 μm to 30 μm.

[0042] According to the present invention, a resin-coated metal sheet with excellent sliding properties, abrasion resistance, and ink adhesion, and a method for manufacturing the same, are available. Additionally, metal containers made using the resin-coated metal sheet are also available. Attached Figure Description

[0043] Figure 1 It is a schematic diagram showing the cross-section of a resin-coated metal sheet. Detailed Implementation

[0044] Hereinafter, embodiments of the resin-coated metal sheet, metal container, and method for manufacturing the resin-coated metal sheet of the present invention will be described. It should be noted that the embodiments described below are examples embodying the present invention and are not intended to limit the scope of the invention to these specific examples.

[0045] (Resin-coated metal plate)

[0046] Figure 1 This 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, the resin-coated metal plate 1 has 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. The resin coating layer 3 has at least a three-layer structure. Figure 1 The metal plate 2 has a three-layer structure consisting of an outermost layer 3a, a middle layer 3b, and a bottommost layer 3c. Additionally, the resin coating layer 4 can also have a three-layer structure. It should be noted that the resin coating layer 4 is arbitrary; it can also be a single layer where only the resin coating layer 3 is disposed on one side of the metal plate 2.

[0047] [Metal plate]

[0048] The metal sheet is preferably a steel sheet, and more preferably a tin-plated steel sheet or a tin-free steel sheet (TFS). As a tin-plated steel sheet, a plating weight of 0.5 g / m² per single side is preferred. 2 ~15g / m 2 Tin-plated steel sheets within the specified range. In the case of TFS, it is preferable to have a surface coating of 50 mg / m² per single side of the TFS. 2 ~200g / m 2 A metallic chromium layer thereon, and having a chromium content of 3 mg / m² per single side (calculated in terms of metallic chromium). 2 ~30g / m 2 A chromium oxide layer. There are no particular limitations on the type of metal sheet, as long as it can be formed into the desired shape; metal sheets with the composition and manufacturing method shown below are preferred.

[0049] (1) A metal plate obtained by recrystallization annealing of low carbon steel with a carbon content of 0.010% to 0.10% by mass through continuous annealing.

[0050] (2) A metal plate obtained by continuous annealing of low carbon steel with a carbon content of 0.010% to 0.10% by mass and recrystallization annealing and over-aging treatment.

[0051] (3) A metal plate obtained by recrystallizing annealing of low carbon steel with a C content of 0.010% to 0.10% by mass using box annealing.

[0052] (4) A metal sheet obtained by recrystallizing low carbon steel with a carbon content of 0.010% to 0.10% by mass after continuous annealing or box annealing and then performing double-reduced rolling.

[0053] (5) The metal plate is obtained by continuously annealing and recrystallizing IF (Interstitial Free) steel, which is made by adding Nb, Ti and other elements to fix the dissolved C in ultra-low carbon steel with a C content of less than 0.003% by mass.

[0054] There are no particular limitations on the mechanical properties of the sheet metal, as long as it can be formed into the desired shape. To obtain suitable processability and maintain tank strength well, the yield point (YP) of the sheet metal is preferably 220 MPa or higher, and more preferably 580 MPa or lower. Furthermore, for the Lankford value (r-value), which is an indicator of plastic anisotropy, a sheet metal with a value of 0.8 or higher is preferred. Moreover, regarding the in-plane anisotropy Δr of the r-value, a sheet metal with an absolute value of 0.7 or lower is preferred.

[0055] The composition of the metal plate used to meet the above mechanical properties is not particularly limited, and may contain, for example, Si, Mn, P, S, Al, N, etc. The Si content is preferably 0.001% by mass or more, and more preferably 0.1% by mass or less. The Mn content is preferably 0.01% by mass or more, and more preferably 0.6% by mass or less. The P content is preferably 0.002% by mass or more, and more preferably 0.05% by mass or less. The S content is preferably 0.002% by mass or more, and more preferably 0.05% by mass or less. The Al content is preferably 0.005% by mass or more, and more preferably 0.100% by mass or less. The N content is preferably 0.0005% by mass or more, and more preferably 0.020% by mass or less. Furthermore, the metal plate may contain other components such as Ti, Nb, B, Cu, Ni, Cr, Mo, V, etc. From the viewpoint of ensuring corrosion resistance, the total content of these components is preferably 0.02% by mass or less.

[0056] There is no particular limitation on the thickness of the metal sheet, but it is preferred to be 0.20 mm or more, and even more preferably 0.25 mm or less.

[0057] [Resin Coating]

[0058] The resin coating comprises polyester resin. Here, the polyester resin is a polymer composed of dicarboxylic acid units and diol units.

[0059] As dicarboxylic acid units, units derived from aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, sodium isophthalate-5-sulfonate, and phthalic acid can be used; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid can be used; alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid can be used; and hydroxycarboxylic acids such as p-hydroxybenzoic acid can be used.

[0060] As a diol unit, units derived from aliphatic diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and neopentanediol can be used; alicyclic diols such as cyclohexanediol; aromatic diols such as bisphenol A and bisphenol S; and diethylene glycol, etc.

[0061] It should be noted that the aforementioned dicarboxylic acids and diols can be used in combination in various ways without impairing heat resistance and processability.

[0062] If the melting point of the resin coating layer is 230°C or higher, resin softening during molding can be prevented, preventing breakage or abrasion, and excellent ink adhesion can be obtained. Therefore, the melting point of the resin coating layer is 230°C or higher, preferably 235°C or higher, and more preferably 240°C or higher. On the other hand, if the melting point of the resin coating layer is 260°C or lower, the crystallinity of the polyester resin is within a suitable range, preventing breakage or abrasion of the resin coating layer during molding, and excellent ink adhesion can be obtained. Therefore, the melting point of the resin coating layer is 260°C or lower, preferably 258°C or lower, and more preferably 255°C or lower.

[0063] The melting point of the resin coating can be determined by the following method. First, the resin-coated metal plate is immersed in a 1:1 mixture of concentrated hydrochloric acid (30 wt%) and distilled water at room temperature to dissolve the metal plate, thereby peeling off the resin coating. It should be noted that the resin coating is peeled off using the same method in the following determination. For the obtained resin coating, heat flux is measured using a TA Instruments DSCQ100 differential scanning calorimeter under N2 atmosphere conditions, 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 temperature of the endothermic peak in the range of 200 °C to 280 °C is taken as the melting point of the resin coating.

[0064] The resin coating has a structure of at least three layers, consisting of an outermost layer, an intermediate layer, and a bottommost layer. Each layer will be described below.

[0065] [The outermost layer of the resin coating]

[0066] The outermost layer of the resin coating contains polyolefin as a lubricant. By containing polyolefin in the outermost layer, excellent lubrication and wear resistance are ensured, and the resin coating can be prevented from breaking or grinding even in can molding under harsh processing conditions.

[0067] The polyolefin is at least one of acid-modified polyolefin and oxidized polyolefin. Acid-modified or oxidized polyolefins have polar groups and high acid values, thus improving the ink adhesion of the resin coating. The polyolefin can be acid-modified polyethylene, ethylene-maleic anhydride copolymer, or other acid-modified polyolefins, oxidized polyolefins such as oxidized polyethylene, or a mixture of acid-modified polyolefins and oxidized polyolefins.

[0068] When the polyolefin content of the outermost layer is less than 0.010% by mass, excellent sliding properties and wear resistance cannot be ensured. Therefore, the polyolefin content of the outermost layer, calculated in terms of solids, is 0.010% by mass or more, preferably 0.050% by mass or more, and more preferably 0.100% by mass or more. On the other hand, when the polyolefin content of the outermost layer is 1.0% by mass or more, excellent wear resistance cannot be ensured. Therefore, the polyolefin content of the outermost layer, calculated in terms of solids, is less than 1.0% by mass, preferably 0.99% by mass or less, more preferably 0.80% by mass or less, and even more preferably 0.60% by mass or less. It should be noted that the polyolefin content of the outermost layer can be adjusted by the amount of resin added before extrusion during manufacturing. In addition, the bottom layer may also contain polyolefin.

[0069] When the melting point of the outermost polyolefin layer is less than 70°C, the polyolefin tends to accumulate on the surface of the resin coating layer due to the heat treatment performed during the process of applying the resin coating layer to the metal plate and the molding of the resin-coated metal plate. This surface-accumulated polyolefin hinders the adhesion of printing inks, and ink peeling may occur during molding. Therefore, the melting point of the polyolefin is 70°C or higher, preferably 85°C or higher, and more preferably 95°C or higher. On the other hand, when the melting point of the polyolefin exceeds 145°C, sufficient sliding and abrasion resistance cannot be ensured, and breakage or abrasion may occur in the resin coating layer during molding. Therefore, the melting point of the polyolefin is 145°C or lower, preferably 135°C or lower, and more preferably 125°C or lower.

[0070] The melting point of polyolefins can be determined by the following method. First, the resin coating is peeled off using the method described above. The peeled resin coating is dissolved in hexafluoro-2-propanol (HFIP) as a solvent. After centrifugation, the dissolved resin coating is filtered under pressure sequentially through filters with pore sizes of 1 μm and 0.1 μm to extract the polyolefin contained in the outermost and bottommost layers of the resin coating. Then, Soxhlet extraction is performed on the filters using xylene as a solvent. After concentration, reprecipitation, and centrifugation, additional polyolefin is extracted. It should be noted that in the various determinations described below, polyolefin extraction refers to the steps up to the above. For the extracted polyolefin, heat flux is measured using a TA Instruments DSCQ100 differential scanning calorimeter under the following conditions: N2 atmosphere, flow rate of 50 ml / min, temperature range of room temperature to 290 °C, and heating rate of 10 °C / min. The peak temperature of the endothermic peak in the heat flow ranging from 60°C to 150°C is set as the melting point of the polyolefin.

[0071] The polyolefin is dispersed in particulate form in the outermost layer. This particulate dispersion is a prerequisite for determining the center of gravity of the polyolefin during the Voronoi fractionation described below.

[0072] The inventors investigated the effect of the distribution of polyolefins in the outermost layer on the sliding properties, abrasion resistance, and ink adhesion of the resin coating using Voronoi segmentation. Voronoi segmentation refers to a method of dividing a region based on which of the parent points (or progenitor points) at any location on a plane is closer to other points on the same plane. In a two-dimensional plane, the perpendicular bisecting lines between adjacent parent points are designated as Voronoi boundaries, and each segmented region enclosed by a Voronoi boundary is designated as a Voronoi polygon.

[0073] The inventors performed Voronoi division by drawing perpendicular bisecting lines between the centroids of adjacent polyolefins on the outermost surface, using the observed centroid of the polyolefin as the generatrix. The results showed that the average area m of the resulting N Voronoi polygons was 500 μm. 2 ~20000μm 2 σ is defined by the following formula (1) 2 When the value is below 1.0, the properties of the resin coating are improved. At m and σ... 2 Within the aforementioned range, the concentration range of polyolefin in the outermost layer is suitable, and the polyolefin is uniformly present. Therefore, it is possible to achieve a higher degree of balance between the sliding properties, abrasion resistance, and ink adhesion of the resin coating.

[0074]

[0075] in,

[0076] N: The total number of the above Voronoi polygons

[0077] m: the average area (μm) of the above N Voronoi polygons 2 ),

[0078] S i The area (μm) of the i-th Voronoi polygon among the N Voronoi polygons mentioned above. 2 ), where i is an integer in the range of 1 to N.

[0079] The average area m of the N Voronoi polygons is less than 500 μm. 2 In cases where the area of ​​the Voronoi polygon obtained by using the centroid of each polyolefin particle as the mother point is small, the amount of polyolefin added is excessive. In this dispersed state, the polyolefin hinders the affinity between the printing ink and the resin coating surface, resulting in poor ink adhesion. Therefore, the average area m is 500 μm. 2 The above, preferably 600μm 2 The above, more preferably 900μm 2 That's all. On the other hand, when m exceeds 20000μm... 2 In this case, insufficient addition of polyolefins fails to achieve excellent sliding and wear resistance. Therefore, the average area m is 20000 μm. 2 The preferred value is 10000μm. 2 Below, 8000μm is more preferred. 2 the following.

[0080] σ as defined by the above equation (1) 2 When the σ exceeds 1.0, i.e., when the dispersion of the Voronoi polygon area is large, the distribution of polyolefins is uneven. In this case, aggregates and deficiencies of polyolefins form on the surface of the resin coating, making it impossible to obtain excellent abrasion resistance and ink adhesion. Therefore, σ 2 It is 1.0 or less, preferably 0.8 or less, and more preferably 0.6 or less. On the other hand, σ 2 The lower limit is not specifically defined, σ 2 It can also be 0.0.

[0081] The above m and σ 2The result can be obtained using the following method. On the outermost surface of the resin-coated metal plate, a LabRAM HR VIS-NIR micro-laser Raman spectroscopy apparatus manufactured by Horiba Corporation was used to measure Raman spectra based on Raman spectroscopy. The measurement conditions were as follows: confocal laser, laser power 50%, aperture 25 μm, exposure time 0.05 sec, 1 exposure, grating 300 lines / mm, objective lens 100x, and wavenumber range 310–3400 cm⁻¹. －1 It should be noted that the measurement range is 200 μm (lamination direction of the resin-coated metal plate) × 200 μm (direction orthogonal to the lamination direction within the surface of the resin-coated metal plate). Furthermore, the measurement spacing is 0.5 μm in all directions. Based on the obtained Raman spectral data, the CH stretching vibration peak (2850 cm⁻¹) from polyethylene was calculated. －1 The CH stretching vibration peak (2960 cm⁻¹) from polyester, the main component of the resin coating layer, is similar to that of the other two components. －1 The intensity ratio of the polyolefin is used to perform mapping. For the obtained mapping, the centroid of the polyolefin is determined, and the Voronoi segmentation is performed with this position as the parent point to draw the Voronoi polygon. It should be noted that the measurement is performed in three randomly selected fields of view in each sample, and the Voronoi segmentation is performed with all polyolefin dispersed particles in the field of view as the object. In addition, the determination of the centroid of the polyolefin and the drawing of the Voronoi polygon can be performed visually or with image processing software. The total number of Voronoi polygons N, the area of ​​each Voronoi polygon, and the average area m of N Voronoi polygons are calculated from the drawing results. σ is calculated from the above formula (1). 2 m and σ are calculated from the results of the three fields of view. 2 The average values ​​of m and σ, representing the surface of the outermost layer of the resin-coated metal plate. 2 .

[0082] If the weight-average molecular weight of the polyolefin is 2000 or more, it can effectively prevent the polyolefin from accumulating on the surface of the resin coating, thus significantly improving ink adhesion. Therefore, the weight-average molecular weight of the polyolefin is preferably 2000 or more, more preferably 3000 or more, and even more preferably 3500 or more. On the other hand, if the weight-average molecular weight of the polyolefin is 50000 or less, suitable abrasion resistance can be ensured during molding and processing. Therefore, the weight-average molecular weight of the polyolefin is preferably 50000 or less, more preferably 45000 or less, and even more preferably 40000 or less.

[0083] The weight-average molecular weight of polyolefins can be determined by the following method. First, the polyolefin in the resin coating is extracted using the method described above. The extracted polyolefin is analyzed using an Agilent PL-GPC220 gel permeation chromatography system with two Agilent PLgel Olexis columns plus a Guard, and o-dichlorobenzene as the eluent. A standard curve is then constructed using the molecular weight of standard polystyrene and the elution time. Using the constructed standard curve, the weight-average molecular weight of the polyolefin is calculated based on the elution time.

[0084] If the acid value of the polyolefin is 1.0 mg KOH / g or higher, the affinity between the resin coating and the printing ink can be well ensured, and the ink adhesion can be significantly improved. Therefore, the acid value of the polyolefin is preferably 1.0 mg KOH / g or higher, more preferably 2.0 mg KOH / g or higher, and even more preferably 3.0 mg KOH / g or higher. On the other hand, if the acid value of the polyolefin is 90 mg KOH / g or lower, the polyolefin is not compatible with the resin coating, thus ensuring suitable abrasion resistance during molding and processing. Therefore, the acid value of the polyolefin is preferably 90 mg KOH / g or lower, more preferably 80 mg KOH / g or lower, and even more preferably 70 mg KOH / g or lower.

[0085] The acid value of polyolefins can be determined by the following method. First, the polyolefin of the resin coating is extracted using the method described above. According to JIS K5902, a specified amount of polyolefin corresponding to the estimated acid value is measured into a flask and dissolved in 100 ml of neutral solvent. Then, using phenolphthalein as an indicator, the endpoint of neutralization is determined when the indicator changes color for 30 seconds, and titrated with a 0.1 mol / L potassium hydroxide standard solution. The acid value is calculated from the titration result using the following formula (2).

[0086] (Acid value) = 5.611 × A × F / B ··· (2)

[0087] in,

[0088] A: Volume (ml) of 0.1 mol / L potassium hydroxide standard solution used

[0089] B: Sample size (g)

[0090] F: Factor for 0.1 mol / L potassium hydroxide standard solution.

[0091] The outermost and bottommost layers preferably contain slippery inorganic particles. If the slippery inorganic particles contained in the outermost and bottommost layers are each 0.010% by mass or more, the roller conveying and winding properties during the film formation of the resin coating are improved, and the adhesion between the resin coating layers is suppressed, while the roller unwinding property is also improved. Therefore, the slippery inorganic particles contained in the outermost and bottommost layers, calculated in terms of solid content, are preferably 0.010% by mass or more, more preferably 0.020% by mass or more, and even more preferably 0.040% by mass or more. On the other hand, if the slippery inorganic particles contained in the outermost and bottommost layers are each 10.0% by mass or less, the dispersion number of slippery inorganic particles present on the surface of the outermost and bottommost layers becomes a suitable range, the adhesion between the resin coating and the metal plate is improved, and suitable abrasion resistance can be obtained. Therefore, the amount of slippery inorganic particles contained in the outermost and bottommost layers, calculated on a solids basis, is preferably 10.0% by mass or less, more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less. It should be noted that the content of slippery inorganic particles in the outermost and bottommost layers may be the same or different. Furthermore, the content of slippery inorganic particles in the outermost and bottommost layers can be adjusted by the amount of resin added during manufacturing before extrusion.

[0092] There are no particular restrictions on the slippery inorganic particles contained in the outermost and bottommost layers; silica, lithium fluoride, kaolin, clay, calcium carbonate, alumina, calcium phosphate, etc., can be used.

[0093] [Intermediate layer of resin coating]

[0094] To enhance the design and aesthetics of the printed can, a white resin coating is sometimes required. In such cases, the intermediate layer of the resin coating preferably contains inorganic particles.

[0095] The inorganic particles contained in the intermediate layer are not particularly limited, but titanium dioxide is preferred. The presence of titanium dioxide in the intermediate layer enables the resin coating to be white. More preferably, the titanium dioxide used as the inorganic particle is rutile titanium dioxide with a purity of 90% or higher. When the intermediate layer contains rutile titanium dioxide with a purity of 90% or higher, the titanium dioxide exhibits good dispersibility when the polyester resin and titanium dioxide are mixed, resulting in uniform whiteness and improved design and aesthetics.

[0096] If the inorganic particles contained in the intermediate layer are 10% by mass or more, sufficient whiteness can be ensured. Therefore, the inorganic particles contained in the intermediate layer, converted from solid content, are preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 15% by mass or more. On the other hand, if the inorganic particles contained in the intermediate layer are 35% by mass or less, cracking or abrasion of the resin coating can be well prevented even under more severe processing conditions. Therefore, the inorganic particles contained in the intermediate layer, converted from solid content, are preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. It should be noted that the content of inorganic particles in the intermediate layer can be adjusted by the amount added to the resin before extrusion during manufacturing.

[0097] When the thicknesses of the outermost and bottommost layers are 1.0 μm to 5.0 μm, suitable wear resistance can be ensured during molding, effectively preventing breakage or grinding of the resin coating during molding. Therefore, the thicknesses of the outermost and bottommost layers are preferably 1.0 μm or more, more preferably 1.2 μm or more, and even more preferably 1.5 μm or more. Similarly, the thicknesses of the outermost and bottommost layers are preferably 5.0 μm or less, more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. It should be noted that the thicknesses of the outermost and bottommost layers can be equal or different.

[0098] When the thickness of the intermediate layer is 6.0 μm to 30 μm, the absolute increase or decrease in the amount of polyolefin can be suppressed without changing the thickness of the outermost and bottommost layers. Therefore, the dispersion is maintained within an appropriate range, effectively preventing breakage or abrasion of the resin coating layer during molding. Furthermore, the ink adhesion of the resin coating layer can be significantly improved. Therefore, the thickness of the intermediate layer is preferably 6.0 μm or more, more preferably 8.0 μm or more, and even more preferably 10 μm or more. Similarly, the thickness of the intermediate layer is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less.

[0099] The thicknesses of the outermost, middle, and bottommost layers can be determined using the following method. First, the resin coating is peeled off using the method described above. Pt is then applied to the outermost surface of the resulting resin coating, followed by resin embedding. A cross-section is then fabricated using an ion milling apparatus (EM TIC 3X) manufactured by Leica Microsystems Co., Ltd. For the fabricated cross-section, reflected electron images are observed using a scanning electron microscope (SEM) (Regulus 8220) manufactured by Hitachi High-Technologies Corporation, under two magnification conditions: 3500x and 8000x. Based on the observation results, the thicknesses of the outermost, middle, and bottommost layers of the resin coating can be determined.

[0100] (Metal container)

[0101] Using the aforementioned resin-coated metal sheet, it is possible to manufacture metal containers with excellent sliding properties, abrasion resistance, and ink adhesion of the resin coating. Conventional methods can be used to manufacture the metal containers. In these metal containers, the resin coating is preferably located on the outer surface of the metal container.

[0102] (Manufacturing method of resin-coated metal sheet)

[0103] Next, a method for manufacturing a resin-coated metal sheet according to one embodiment of the present invention will be described. It should be noted that the following embodiments describe a manufacturing method where the resin coating has a three-layer structure, but the resin coating may have a structure of four or more layers.

[0104] In manufacturing the resin-coated metal sheet of the present invention, firstly, a resin film is manufactured to form the resin coating layer. Firstly, a first composition, a second composition, and a third composition comprising a specified resin are co-extruded in a compounding extruder and discharged from a T-die to obtain a sheet-shaped molded body with the first composition, the second composition, and the third composition as the first layer, the second layer, and the third layer, respectively. The molded body is preferably extruded onto a cooling body such as a casting drum.

[0105] Since the first composition, the second composition, and the third composition respectively form the outermost, middle, and bottommost layers of the resin coating, they are added in such a manner that each layer contains the aforementioned polyolefin, slippery inorganic particles, and inorganic particles. The method of addition is not particularly limited, but the following method is preferred: preparing a masterbatch in which various additives are dispersed in a high concentration in the resin, mixing resin particles without additives and the masterbatch at a predetermined ratio, and feeding them into a compounding extruder. It should be noted that the content of additives in each layer, etc., is as described in the description of the resin coating. Specifically, the first composition contains polyester resin and 0.010% by mass and less than 1.0% by mass of a polyolefin having a melting point of 70°C to 145°C, which is at least one of acid-modified polyolefin and oxidized polyolefin. The second composition contains polyester resin, and the third composition also contains polyester resin.

[0106] The extrusion temperature is preferably 250°C or higher, which is about 20°C higher than the melting point of the polyester resin. On the other hand, the extrusion temperature is preferably 290°C or lower.

[0107] Next, the molded body is cooled and solidified on a cooling body such as a casting drum to obtain an unstretched laminated film. The cooling conditions can be achieved using conventional methods.

[0108] After preparing an unstretched laminated film, the laminated film is stretched at least once to form a resin film. At a stretching temperature of 80℃~110℃, the welding or breakage of the resin film during film formation can be suppressed, thereby preventing the agglomeration and coarsening of polyolefins and the reduction in their number, maintaining the dispersion state within an appropriate range. Therefore, it is possible to control m and σ. 2 The temperature is maintained within an appropriate range. Therefore, the stretching temperature is 80°C or higher, preferably 85°C or higher, and more preferably 90°C or higher. Similarly, the stretching temperature is 110°C or lower, preferably 105°C or lower, and more preferably 100°C or lower.

[0109] Furthermore, when the stretching ratio is 3.0 to 6.0 times, film breakage during film formation can be suppressed, the thickness of the resin film can be maintained within an appropriate range, and the generation of uneven thickness can be suppressed. Additionally, it can prevent the agglomeration and coarsening of polyolefins and the reduction in their number, maintaining the dispersion state within an appropriate range, thus maintaining m and σ within an appropriate range. Therefore, a stretching ratio of 3.0 times or more is preferred, 3.5 times or more, and more preferably 4.0 times or more. Similarly, a stretching ratio of 6.0 times or less is preferred, 5.5 times or less, and more preferably 5.0 times or less.

[0110] Next, the resin film is heated to above its melting point and then hot-pressed onto a metal plate using laminating rollers (hot-press lamination). Hot-press lamination is preferred in terms of reducing manufacturing costs and enabling energy-efficient production.

[0111] When the temperature of the metal plate during hot pressing is 260℃~290℃, which is about 30~60℃ higher than the melting point of the resin coating, the adhesion between the laminated film and the metal plate is improved, and the welding of the film to the laminating rollers can be suppressed. Furthermore, it prevents the agglomeration and coarsening of polyolefins in the resin coating and reduces their number, improving the dispersion state. Therefore, it is possible to combine m and σ... 2 The temperature is maintained within an appropriate range. Therefore, the temperature of the metal plate is 260°C or higher, preferably 265°C or higher, and more preferably 270°C or higher. Similarly, the temperature of the metal plate is 290°C or lower, preferably 288°C or lower, and more preferably 285°C or lower.

[0112] When the laminating roller temperature during hot pressing is 110℃~120℃, which is 30~40℃ higher than the glass transition temperature of the laminated film (approximately 80℃), the welding of the film to the laminating roller is suppressed, thereby preventing the agglomeration and coarsening of polyolefins in the resin coating layer and the reduction in their number. This improves the dispersion state, thus enabling the mixing of m and σ. 2The temperature is maintained within an appropriate range. Therefore, the laminating roller temperature is 110°C or higher, preferably 111°C or higher, and more preferably 113°C or higher. Similarly, the laminating roller temperature is 120°C or lower, preferably 119°C or lower, and more preferably 118°C or lower.

[0113] It should be noted that processes and conditions not described in this invention can be performed using conventional methods.

[0114] Example

[0115] The plate thickness is 0.22mm, and the chromium layer has a concentration of 120mg / m² per single side. 2 The chromium oxide layer, calculated in terms of metallic chromium, is 10 mg / m² per single side. 2 TFS (Wuxi-based steel sheet) with a quenching and tempering degree of T3CA was used as the metal sheet. The mechanical properties of this metal sheet were YP = 400 MPa, r = 1.0, and Δr = 0.5.

[0116] In each example, masterbatches containing various additives at high concentrations were prepared in polyester resin as the first, second, and third compositions. It should be noted that in this embodiment, the first and third compositions are the same masterbatch. In each example, the polyester resin composition of each composition is the same; the resin composition is shown in Tables 1 and 2. Furthermore, lubricating components and slippery inorganic particles were added to the masterbatches of the first and third compositions, and inorganic particles were added to the masterbatch of the second composition. The types, weight-average molecular weights, and acid values ​​of the lubricating components added to the first and third compositions in each example are shown in Tables 1 and 2. Additionally, silica was used as the slippery inorganic particle, and rutile titanium dioxide was used as the inorganic particle.

[0117] In each example, the prepared masterbatch and resin granules composed of the aforementioned resin-based polyester resin were mixed and fed into a compounding extruder, with the contents of each layer after molding as shown in Tables 1 and 2, to produce a laminated film. The extrusion temperature was 278°C. The laminated film was further stretched using a uniaxial stretching method to form a resin film. Then, a metal plate was heated, and the resin film was hot-pressed onto both sides of the metal plate using a hot-pressing film lamination method. The stretching conditions (stretching temperature and stretch ratio) and hot-pressing conditions (metal plate temperature and laminating roller temperature) for each example are shown in Tables 1 and 2. It should be noted that the pressure of the laminating roller during hot pressing was 400 kgf, and after hot pressing, the film was water-cooled in a 50°C water-cooling chamber after 0.7 seconds.

[0118] For the obtained resin-coated metal plates, the melting point of the resin coating, the thickness of each layer, the melting point of the polyolefin, the weight-average molecular weight of the polyolefin, the acid value of the polyolefin, and the surface properties (m and σ) of the resin coating were analyzed using the methods described above. 2 Tables 1 and 2 present the measurement results.

[0119]

[0120]

[0121] In each case, the sliding properties and abrasion resistance of the resin coating, as well as the ink adhesion, were evaluated using the methods shown below. The evaluation results are presented in Table 3.

[0122] [Evaluation of sliding properties and wear resistance]

[0123] The resin-coated metal sheets in each example were punched into circular shapes with a diameter of 68 mm, and sliding tests were conducted using a rotary abrasion testing machine manufactured by Takachiho Seiki Co., Ltd. The test conditions were: a load of 44 N, a sample temperature of 145 ± 3 °C, a rotation speed of 370 rpm, a rotation radius of 20 mm, and an ultra-hard ball indenter (Φ10 mm). It should be noted that the test object was the resin coating layer located on the outer surface of the container after molding. Four samples were prepared for each example and tested separately. Based on the results, the coefficient of friction at which the maximum static friction force was displayed was taken as the coefficient of friction, and the sliding performance was evaluated according to the criteria shown below. Furthermore, based on the degree of abrasion of the resin coating layer after the test, the wear resistance was visually evaluated according to the criteria shown below.

[0124] Evaluation criteria for slippage

[0125] Rating "◎": The coefficient of friction is below 0.110.

[0126] Evaluation "0": The coefficient of friction is greater than 0.110 and less than 0.135.

[0127] Evaluation "△": The coefficient of friction is greater than 0.135 and less than 0.160.

[0128] Evaluation "×": The coefficient of friction is above 0.160.

[0129] Evaluation criteria for wear resistance

[0130] Evaluation "0": No grinding was observed visually in all 4 tests.

[0131] Evaluation "△": Grinding was observed visually in one of the four tests.

[0132] Evaluation "×": Grinding was observed visually in more than 2 out of 4 tests.

[0133] [Evaluation of ink adhesion]

[0134] Each resin-coated metal plate was placed in a hot air drying oven and subjected to heat treatment at 240°C for 2 minutes, followed by cooling to room temperature. For each cooled sample, melamine-based printing ink was printed onto the resin coating layer on the outer surface of the container after molding using a universal printing testing machine manufactured by Kumagai Riki Kogyo Co., Ltd. The freshly printed samples were then placed in a hot air drying oven and subjected to heat treatment at 230°C for 1 minute, followed by cooling to room temperature. Using the ink-printed surface of each sample as the object, facing the long side of the sample, a scratch test was performed using a load-varying friction and wear testing machine HHS2000 manufactured by Shinto Science Co., Ltd. The test conditions were: a sapphire indenter (Φ0.6mm), a continuous load of 10–1000 gf from the printing end, a moving speed of 0.5 mm / sec, and a moving distance of 30 mm. Three samples were prepared, and five tests were performed at different locations on each sample. The peel load of the ink is calculated from the peel length of the ink in each test. The average value of the 15 peel loads is obtained, and the ink adhesion is evaluated according to the following criteria.

[0135] Evaluation criteria for ink adhesion

[0136] Evaluation "◎": The average peel load is over 400g.

[0137] Evaluation "0": The average peel load is above 300g and less than 400g.

[0138] Evaluation "△": The average peel load is above 200g and less than 300g.

[0139] Evaluation "×": The average peel load is less than 200g.

[0140]

[0141] Industrial availability

[0142] According to the present invention, a resin-coated metal sheet with excellent sliding properties, abrasion resistance, and ink adhesion, and a method for manufacturing the same, are available. Additionally, metal containers made using the resin-coated metal sheet are also available.

[0143] Symbol Explanation

[0144] 1 Resin-coated metal sheet

[0145] 2 Metal Plates

[0146] 3 Resin Coating

[0147] 3a Outermost layer

[0148] 3b Intermediate Layer

[0149] 3C bottom layer

[0150] 4. Resin Coating

Claims

1. A resin-coated metal sheet, wherein at least one side of the metal sheet has a resin coating layer comprising polyester resin. The resin coating has at least three layers, comprising an outermost layer, a middle layer, and a bottom layer. The melting point of the resin coating is 230℃~260℃. The outermost layer contains more than 0.010% by mass and less than 1.0% by mass of polyolefin. The polyolefin is at least one of acid-modified polyolefin and oxidized polyolefin. The melting point of the polyolefin is 70℃~145℃. The polyolefin is dispersed in particles on the outermost layer. The dispersion state of the polyolefin particles satisfies the following condition: on the outermost surface, the average area m of the N Voronoi polygons obtained by dividing the surface using the centroid of each polyolefin particle as the datum point is 500 μm. 2 ~20000μm 2 σ is defined by the following formula (1) 2 Below 1.0 in, N: The total number of the Voronoi polygons m: The average area of ​​the N Voronoi polygons, in μm. 2 , S i The area of ​​the i-th Voronoi polygon among the N Voronoi polygons, in μm². 2 , where i is an integer in the range of 1 to N.

2. The resin-coated metal plate according to claim 1, wherein, The weight-average molecular weight of the polyolefin is 2000 to 50000.

3. The resin-coated metal plate according to claim 1 or 2, wherein, The acid value of the polyolefin is 1.0 mg KOH / g to 90 mg KOH / g.

4. The resin-coated metal sheet according to any one of claims 1 to 3, wherein, The outermost layer and the bottommost layer each contain 0.010% to 10.0% by mass of slippery inorganic particles.

5. The resin-coated metal sheet according to any one of claims 1 to 4, wherein, The intermediate layer contains 10% to 35% by mass of inorganic particles.

6. The resin-coated metal sheet according to any one of claims 1 to 5, wherein, The outermost and bottommost layers have thicknesses of 1.0 μm to 5.0 μm, respectively, and the middle layer has a thickness of 6.0 μm to 30 μm.

7. A metal container, which is a metal container made by coating a metal sheet with resin according to any one of claims 1 to 6. The resin coating is located on the outside of the metal container.

8. A method for manufacturing a resin-coated metal sheet, comprising: A process in which a first composition comprising polyester resin and 0.010% by mass and less than 1.0% by mass of polyolefin, a second composition comprising polyester resin, and a third composition comprising polyester resin are co-extruded in a compounding extruder and discharged from a T-die to obtain a sheet-shaped molded body with the first composition, the second composition, and the third composition as the first layer, the second layer, and the third layer, respectively, wherein the polyolefin is at least one of acid-modified polyolefin and oxidized polyolefin and has a melting point of 70°C to 145°C; The process of cooling and solidifying the molded body to obtain a laminated film; Next, the laminated film is stretched at least once at a stretching temperature of 80°C to 110°C and a stretching ratio of 3.0 to 6.0 times to obtain a resin film comprising the first layer, the second layer, and the third layer; and Next, using a laminating roller controlled at 110°C to 120°C, the resin film is hot-pressed onto at least one side of a metal plate controlled at 260°C to 290°C, to obtain a resin-coated metal plate having a resin coating layer on at least one side of the metal plate. The resin coating layer has at least a three-layer structure with the first layer, the second layer, and the third layer as the outermost layer, the middle layer, and the bottom layer, respectively, and has a melting point of 230°C to 260°C.

9. The method for manufacturing a resin-coated metal sheet according to claim 8, wherein, The weight-average molecular weight of the polyolefin is 2000 to 50000.

10. The method for manufacturing a resin-coated metal sheet according to claim 8 or 9, wherein, The acid value of the polyolefin is 1.0 mg KOH / g to 90 mg KOH / g.

11. The method for manufacturing a resin-coated metal sheet according to any one of claims 8 to 10, wherein, The first composition and the third composition each contain 0.010% to 10.0% by mass of slippery inorganic particles.

12. The method for manufacturing a resin-coated metal sheet according to any one of claims 8 to 11, wherein, The second composition contains 10% to 35% by mass of inorganic particles.

13. The method for manufacturing a resin-coated metal sheet according to any one of claims 8 to 12, wherein, The outermost and bottommost layers have thicknesses of 1.0 μm to 5.0 μm, respectively, and the middle layer has a thickness of 6.0 μm to 30 μm.

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