Film-laminated steel sheet and method for manufacturing di can

Abstract

[Problem] To further improve drawing moldability while maintaining punch release properties during DI molding. [Solution] A film-laminated steel sheet according to the present invention comprises: a steel sheet serving as a base material; a film layer composed of a thermoplastic polyester film and disposed on the front and back surfaces of the steel sheet; and a wax layer disposed on the film layer, wherein the coating weight of the wax layer is 0.030-0.120 g / m2 per surface, the coating weight of the wax layer differs between the front surface and the back surface of the steel sheet, and the coating weight ratio obtained by dividing the coating weight of the wax layer on a higher coating weight-side surface by the coating weight of the wax layer on a lower coating weight-side surface is in the range of 1.04-1.67.

Description

Manufacturing method of film-laminated steel sheet and DI can

[0001] The present invention relates to a method for manufacturing a film-laminated steel sheet and a DI can.

[0002] In recent years, paper-wrapped cans and distortion-printed cans have become the main cans used for food products. Since it is important that the printed pattern does not become distorted during molding, distortion-printed cans in particular have a relatively low can height, and drawing (DR) and drawing and redrawing (DRD) molding are often used as molding methods. On the other hand, because paper-wrapped cans do not require printing on the outer surface of the can body, drawing and ironing (DI) molding, which is more productive, has become increasingly popular in recent years.

[0003] DI forming is a forming method in which the can wall portion of a cup obtained by draw forming a steel sheet is ironed to reduce the can wall thickness to approximately 40-60% of the thickness of the raw steel sheet, thereby increasing the can height. Compared to DRD forming, DI forming is characterized by significantly greater deformation in the steel sheet thickness direction and can height direction, and a faster forming speed. During forming, the temperature of the steel sheet rises to nearly 200°C. For example, in DI forming of tinplate, a type of tin-plated steel sheet, a lubricant-containing coolant is sprayed onto the ironing die during forming to cool the ironing die. Since the coolant sprayed onto the ironing die also adheres to the formed DI can, a process is required to wash and remove the coolant from the formed DI can and dry the cleaned DI can. Furthermore, a processing facility for such coolant is required as part of the manufacturing equipment.

[0004] On the other hand, in the case of film-laminated steel sheets, wax can be applied to the film surface during the manufacturing process of the laminated steel sheet. Therefore, when cans are manufactured using film-laminated steel sheets, it is not necessary to apply a lubricant during molding, and the process of washing and drying the lubricant and the lubricant treatment equipment can be omitted. Due to these advantages, film-laminated steel sheets have been widely used in DRD food cans in recent years.

[0005] However, when film-laminated steel sheets are applied to forming processes such as DI forming, in which the can wall is ironed at high speed, the temperature of the steel sheet rises during forming, causing the film to soften, which makes the film more likely to chip and increases the probability of the can breaking during forming. Furthermore, the softening of the film causes the film on the inner surface of the can to adhere to the punch used during processing, making it difficult to remove the punch, i.e., poor punch-removal properties. Poor punch-removal properties can cause the can end to buckle and become wedged between the punch and the stopper, making the can body more likely to buckle. In this case, the can-making machine must be stopped to remove the can with its end wedged between the punch and the stopper, significantly reducing productivity. From this perspective, various film-laminated steel sheets that can be used in DI forming have been proposed.

[0006] For example, Patent Document 1 below discloses a laminated metal sheet for a two-piece can body having polyester resin film layers on both sides of the metal sheet, the polyester resin film layer on the outer surface side of the can body having a crystallization temperature of 60 to 100°C and a centerline surface roughness (Ra) of 0.25 to 1.8 μm. Furthermore, Patent Document 1 below also discloses a laminated metal sheet for a two-piece can body in which the polyester resin film layer on the outer surface side of the can body is composed of 40 to 100 mass% of a resin having butylene terephthalate as a main constituent unit and 0 to 60 mass% of a resin having ethylene terephthalate as a main constituent unit, and the film layer surface on the inner surface side of the can body has a centerline surface roughness (Ra) of 0.2 to 1.8 μm.

[0007] In addition, in the following Patent Document 2, convex portions having a height of 2 to 10 μm and a circle equivalent diameter d of 0.010 to 0.10 mm are formed on the surface of a film at 15 / mm.２ This document discloses a laminated steel sheet for containers that is formed as described above, and in which a space containing air or an inert gas exists between the resin film and the steel sheet directly below the convex portion, and that has excellent workability in punching and drawing can-making.

[0008] JP 2009-184262 A JP 2009-23193 A

[0009] As described above, in order to improve the ironing formability of film-laminated steel sheets, conventionally, the contact area has been reduced by providing irregularities on the film surface, thereby reducing friction. However, as described above, continuous high-speed DI forming increases the temperature of the steel sheet, and as a result, even when the laminated steel sheets disclosed in Patent Documents 1 and 2 are used, there is still room for improvement in terms of achieving both ironing formability and punch-removal property.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a film-laminated steel sheet that can further improve ironing formability while maintaining punch-release property during DI forming, and a method for manufacturing DI cans using such a film-laminated steel sheet.

[0011] In order to solve the above problems, the present inventors have conducted extensive research and have come up with the idea of ​​optimizing the balance between the sliding properties of the side of the film-laminated steel sheet that will become the inner surface of a can and the sliding properties of the side that will become the outer surface of a can, thereby maintaining punch-ejectability during DI forming and further improving ironing formability. The gist of the present invention, which was completed based on the above idea, is as follows. In the following description, the expression "(Numerical value A) to (Numerical value B)" means "(Numerical value A) or more and (Numerical value B) or less."

[0012] (1) A steel sheet as a base material, a film layer made of a thermoplastic polyester film provided on the front and back surfaces of the steel sheet, and a wax layer provided on the film layer, wherein the amount of wax applied to each surface is 0.030 to 0.120 g / m ２(2) A film-laminated steel sheet according to (1), wherein the melting point of the thermoplastic polyester film constituting the film layer on the surface with a higher adhesion amount is 215°C or higher and lower than 255°C, the melting point of the thermoplastic polyester film constituting the film layer on the surface with a lower adhesion amount is 220 to 260°C, and the melting point of the thermoplastic polyester film on the surface with a lower adhesion amount is 5°C or higher than the melting point of the thermoplastic polyester film on the surface with a higher adhesion amount. (3) A film-laminated steel sheet according to (1) or (2), wherein the wax constituting the wax layer has a penetration defined in JIS K2235:2022 of 5 to 20 at a test temperature of 25°C, and the melting point of the wax is 50.0 to 70.0°C. (4) A film-laminated steel sheet according to any one of (1) to (3), wherein the thickness of the film layer on the side having a higher adhesion amount is 12 to 40 μm. (5) A film-laminated steel sheet according to any one of (1) to (4), wherein the surface roughness of the steel sheet on the side having a higher adhesion amount is 0.10 to 0.50 μm in terms of arithmetic mean roughness Ra defined in JIS B0601:2013. (6) A method for manufacturing a DI can using a film-laminated steel sheet according to any one of (1) to (5), wherein the film-laminated steel sheet is arranged so that the side of the film-laminated steel sheet having a larger amount of wax layer adhered thereto becomes the outer surface of the DI can, and the side of the film-laminated steel sheet having a smaller amount of wax layer adhered thereto becomes the inner surface of the DI can, and the film-laminated steel sheet is subjected to DI forming.

[0013] As described above, according to the present invention, it is possible to further improve ironing formability while maintaining punch-release properties during DI forming. This makes it possible to improve the high-speed formability of DI cans without reducing the productivity of DI cans.

[0014] 1 is an explanatory diagram schematically illustrating the configuration of a film-laminated steel sheet according to an embodiment of the present invention.

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0016] (Regarding film-laminated steel sheet) <Regarding configuration of film-laminated steel sheet> Hereinafter, the configuration of a film-laminated steel sheet according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram schematically showing the configuration of a film-laminated steel sheet according to this embodiment.

[0017] The film-laminated steel sheet according to this embodiment is used as a material for DI cans. As shown in Fig. 1, the film-laminated steel sheet 1 according to this embodiment includes a base steel sheet 10 that serves as the base material of the film-laminated steel sheet 1, film layers 21 and 22 provided on the front and back surfaces of the base steel sheet 10, and wax layers 31 and 32 provided on the film layers.

[0018] In the film-laminated steel sheet 1 according to this embodiment, as will be described in detail below, the amount of wax deposited in the wax layer 31 is different from the amount of wax deposited in the wax layer 32. In Fig. 1, an example is shown in which the amount of wax deposited in the wax layer 32 is greater than the amount of wax deposited in the wax layer 31.

[0019] The difference in the amount of wax deposited in the wax layers 31, 32 as described above is important when manufacturing DI cans using such film-laminated steel sheet 1 as a material. As will be described in detail later, when manufacturing DI cans using the film-laminated steel sheet 1 according to this embodiment, the film-laminated steel sheet 1 is positioned so that the wax layer with the lesser amount of wax deposited is located on the side that will become the inner surface of the DI can. That is, in the case of the film-laminated steel sheet 1 shown in Fig. 1, the film-laminated steel sheet 1 is positioned in a forming device so that the side on which the wax layer 31 is present becomes the side that will become the outer surface of the DI can, and the side on which the wax layer 32 is present becomes the side that will become the inner surface of the DI can.

[0020] In the following description, for convenience, the film layer located on the side that will become the outer surface of the DI can will be referred to as the “outer can film layer,” and the wax layer located on the side that will become the outer can surface will be referred to as the “outer can wax layer.” Similarly, in the following description, for convenience, the film layer located on the side that will become the inner can surface will be referred to as the “inner can film layer,” and the wax layer located on the side that will become the inner can surface will be referred to as the “inner can wax layer.”

[0021] Furthermore, when referring to a film layer without distinguishing between the inner surface side and the outer surface side of the can, it may be simply abbreviated as "film layer." Similarly, when referring to a wax layer without distinguishing between the inner surface side and the outer surface side of the can, it may be simply abbreviated as "wax layer."

[0022] <<Base Steel Sheet 10>> In the film-laminated steel sheet 1 according to this embodiment, the steel sheet used as the base steel sheet 10 may be any known steel sheet for cans to be used for drawing.

[0023] Furthermore, among such steel sheets for cans for drawing, it is preferable to use one having an r-value of 0.95 or more and an absolute value of the Δr-value of 0.50 or less as the base steel sheet 10. By using such a steel sheet for cans, it is possible to further improve the DI formability of the film-laminated steel sheet 1 according to this embodiment.

[0024] Drawing and ironing is a forming method for thinning the can wall thickness by drawing out the can wall of a substantially cylindrical cup by ironing. Therefore, if the can wall thickness of the cup varies, the ironing resistance of the thicker portion increases, which may make the can wall more likely to break during ironing. By making the r-value of the steel plate used as the base steel plate 10 0.95 or more, it is possible to suppress the variation in the can wall thickness in the height direction of the cup and prevent the can wall from breaking during ironing. The r-value of the steel plate used as the base steel plate 10 is more preferably 1.05 or more. On the other hand, the upper limit of the r-value of the steel plate used as the base steel plate 10 is not particularly specified, but is practically about 1.20.

[0025] Furthermore, by making the absolute value of the Δr value 0.50 or less (i.e., -0.50≦Δr≦+0.50), it is possible to suppress variations in the thickness of the can wall in the circumferential direction of the cup, and to prevent fracture of the can wall during ironing. The absolute value of the Δr value of the steel sheet used as the base steel sheet 10 is more preferably 0.33 or less. Note that the lower limit of the Δr value of the steel sheet used as the base steel sheet 10 is not particularly specified, and the lower the better, with zero being most preferred.

[0026] The r value and Δr value are defined in JIS Z2254:2021 and can be measured in accordance with JIS Z2254:2021. The r value is also called the plastic strain ratio or Lankford value. The initial gauge length, width, and thickness of the tensile test specimen defined in JIS Z2254:2021 are defined as L and L, respectively. ０ , W ０ , T ０ When the above dimensions after tensile deformation within the range where necking does not occur change to L, W, and T, respectively, L ０ ×W ０ ×T ０ = L × W × T, and the value is defined by the following formula: r = ln(W ０ / W) / ln(T ０ / T) = ln(W ０ / W) / ln(LW / L ０ W０ )

[0027] The Δr value is an index of in-plane anisotropy. The r value when the angle between the tensile direction of the tensile test piece and the rolling direction of the material is θ is defined as r θ The value is defined by the following formula when the deformation characteristics in each direction are measured by changing θ. In the following formula, r ０ , r ４５ , r ９０ are the r values ​​at angles of 0°, 45°, and 90°, respectively, when the tensile direction is at an angle relative to the material rolling direction. Δr = (r ０ -2 x r ４５ +r ９０ ) / 2

[0028] Furthermore, if the steel sheet used as the base steel sheet 10 is hard, the can body is likely to break during forming due to the small elongation of the steel sheet during forming, and in addition, the heat generated by the steel sheet during ironing increases, making it easier for the film layer (described later) to soften due to the heat. Therefore, when forming DI cans with a high ironing ratio, it is particularly preferable to use a single-rolled material with a temper of T3 or less as the base steel sheet 10.

[0029] Furthermore, in DI cans, if the adhesive strength between the base steel sheet and the film layer is low, the film layer may peel off during ironing. Therefore, in the film-laminated steel sheet 1 according to this embodiment, it is more preferable that the adhesion between the base steel sheet 10 and the film layer is high. Specifically, a test piece measuring 15 mm wide and 50 mm high is taken from any location of the film-laminated steel sheet 1 of interest, and one of the film layers of the test piece is peeled at 180° at 20 mm / min. The peel strength is preferably 10 N / 15 mm or more. Such a peel strength is more preferably 15 N / 15 mm or more. Meanwhile, the higher the peel strength, the better, and there is no particular upper limit.

[0030] As will be described in detail below, the film layer in the film-laminated steel sheet 1 according to this embodiment is made of a thermoplastic polyester. Examples of steel sheets that have excellent adhesion to polyester include chromium-based tin-free steel (ECCS) and chromium-free tin-free steel.

[0031] Chromium-based tin-free steel is a plated steel sheet in which a metallic chromium layer and a chromium oxide hydrate layer are formed in this order on the front and back surfaces of a steel sheet substrate. The surface of this tin-free steel is prone to form hydrogen bonds with the hydroxyl and carbonyl groups of the polyester resin, improving adhesion between the film layer and the steel sheet.

[0032] Furthermore, the surface of a chrome-free tin-free steel sheet, which has a chromium-free coating formed on the front and back surfaces of the steel sheet, and which is composed of one or more elements selected from Zr, Al, Si, P, Ti, Ce, and W, O, and unavoidable elements, preferably has hydroxyl groups. These hydroxyl groups form hydrogen bonds with hydroxyl groups and carbonyl groups in the polyester resin, thereby improving adhesion to the film layer.

[0033] In addition to the above-mentioned chromium-based tin-free steel and chromium-free tin-free steel, examples of the base steel sheet 10 include, for example, a tinplate obtained by subjecting an electrolytic Sn-plated steel sheet to a chromate treatment, and a chromate-free tinplate obtained by subjecting an electrolytic Sn-plated steel sheet to the above-mentioned chromate-free coating.

[0034] By using the above-described steel sheet as the base steel sheet 10, the adhesion between the film layer and the steel sheet is improved, and the peel strength as previously explained can be easily achieved.

[0035] [Thickness of Base Steel Sheet] In the film-laminated steel sheet 1 according to this embodiment, the thickness of the base steel sheet 10 (thickness d Ｍ) is not particularly specified as long as it is a thickness that can achieve the desired can wall thickness after DI forming. The thickness of the base steel sheet 10 may be, for example, about 0.15 to 0.26 mm.

[0036] The thickness of the above-mentioned base steel sheet can be measured from the state of an already manufactured film-laminated steel sheet 1 as follows: the film-laminated steel sheet is immersed in boiling hydrogen peroxide water to peel off the film (the film usually peels off within 30 minutes), and the thickness of the base steel sheet after the film has been peeled off is measured with a micrometer.

[0037] [Surface Roughness of Base Steel Sheet] In general deep drawing, it is preferable that the surface roughness of the film of the laminated steel sheet is relatively large and that the die surface and the film convex surface are in point contact, as this reduces sliding resistance. However, in the case of DI forming, which is the focus of this embodiment, even if the surface roughness of the film layer is increased, the film softens as the steel sheet temperature rises during drawing and ironing, and the unevenness on the film layer surface is crushed. Therefore, it can be said that the surface roughness of the base steel sheet 10 has a greater effect on sliding resistance during DI forming than the surface roughness of the film layer.

[0038] Typically, in DI forming, ironing dies are arranged in multiple stages, and the raw steel sheet is formed into the desired shape. When a film-laminated steel sheet with a base steel sheet having an excessively small surface roughness is DI formed, the surface of the film layer is smoothed when it passes through the first ironing die. At the same time, wax that has accumulated in the depressions caused by the recesses in the base steel sheet is easily removed. As a result, the sliding properties of the film-laminated steel sheet are reduced when it passes through the second and subsequent ironing dies, which may make the film layer more susceptible to wear.

[0039] On the other hand, when a film-laminated steel sheet having a base steel sheet with too large a surface roughness is subjected to DI forming, if the film layer softens due to heat generated by the steel sheet as it passes through the first-stage ironing die, pinholes may be more likely to occur in the film layer present on the convex portions of the base steel sheet.

[0040] The above-described film layer scraping and pinhole formation in the film layer are phenomena related to the ironing properties during high-speed DI can forming, and both can occur in the can exterior film layer 21 shown in FIG. 1 . Therefore, in the film-laminated steel sheet 1 according to this embodiment, the surface of the base steel sheet 10 that will become the can exterior (i.e., the surface on which the can exterior film layer 21 is provided) preferably has a surface roughness of 0.10 to 0.50 μm in terms of arithmetic mean roughness Ra as defined in JIS B0601:2013. Having a surface roughness Ra of 0.10 to 0.50 μm for the base steel sheet 10 that will become the can exterior makes it possible to prevent film scraping and pinhole formation even when DI forming is performed at high speeds. The surface roughness Ra of the base steel sheet 10 that will become the can exterior is more preferably 0.10 μm or more. Furthermore, the surface roughness of the base steel sheet 10 on the side that will become the outer surface of the can is more preferably 0.30 μm or less in terms of Ra.

[0041] Furthermore, in the film-laminated steel sheet 1 according to this embodiment, the surface roughness of the base steel sheet 10 on the side that will become the outer surface of the can is 0.10 to 0.50 μm in Ra, and the thickness of the film layer 21 on the outer surface of the can, which will be described in detail below, is 12 to 40 μm, which further prevents the above-mentioned film scraping and pinholes from occurring, and also prevents the occurrence of pressure scratches on the film layer 21 on the outer surface of the can, making this even more preferable.

[0042] The surface roughness of the base steel sheet 10 as described above can be measured using a commercially available surface roughness meter (e.g., a Surfcom 570A surface roughness profiler manufactured by Tokyo Seiki Co., Ltd.) conforming to JIS B0601:2013. More specifically, the wax layer and film layer are removed from the film-laminated steel sheet 1 of interest by immersion treatment in boiling hydrogen peroxide to expose the base steel sheet 10, and a measurement sample measuring 200 mm x 200 mm is taken from any location on the surface of the base steel sheet 10. Then, measurements are taken three times at any three locations on the measurement sample, along the rolling direction of the base steel sheet 10 and along a direction perpendicular to the rolling direction. The average of the measurements thus obtained may be used as the surface roughness of the base steel sheet 10.

[0043] <Film Layer> Next, the film layer of the film-laminated steel sheet 1 according to this embodiment will be described in detail.

[0044] The film layers in the film-laminated steel sheet 1 according to this embodiment are layers provided on the front and back surfaces of the base steel sheet 10, as shown in Fig. 1, and are made of thermoplastic polyester films. Note that the above-mentioned "thermoplastic polyester" means "a thermoplastic polymer compound having an ester bond (-COO-)."

[0045] [Melting Point of Thermoplastic Polyester Constituting the Film Layer] ◇Can Outer Film Layer 21 As mentioned above, when a laminated steel sheet is continuously DI-formed to produce a can, the temperature of the steel sheet rises to a maximum of approximately 200°C. Therefore, if the melting point of the film layer on the can outer surface side is low, the film will soften and become easily scraped during ironing. Therefore, it is preferable that the thermoplastic polyester film constituting the film layer on the can outer surface side of the film-laminated steel sheet 1 (can outer film layer 21 in Figure 1) is a thermoplastic film that does not soften even at around 200°C. If the melting point is 215°C or higher, the film will not soften to a great extent even when the steel sheet temperature reaches 200°C, making it possible to suppress the occurrence of film scraping. From this perspective, in the film-laminated steel sheet 1 according to this embodiment, the melting point of the thermoplastic polyester film constituting the can outer film layer 21 is preferably 215°C or higher. The melting point of the thermoplastic polyester film constituting the can outer film layer 21 is more preferably 216°C or higher, and even more preferably 218°C or higher.

[0046] On the other hand, in the film-laminated steel sheet 1, if the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21 exceeds 260°C, the film has high deformation resistance when the mold temperature is still low immediately after the start of DI molding, and the film may tear in areas where bending strain is large, such as the punch shoulder and the ring-shaped portion of the can bottom. Setting the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21 to 260°C or less is preferable because it makes it possible to prevent such film tearing. Furthermore, as described below, the melting point of the thermoplastic polyester film constituting the can inner surface film layer 22 is preferably 5°C or more higher than the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21. Taking into account this difference in melting point, the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21 is preferably less than 255°C. The melting point of the thermoplastic polyester film constituting the can outer surface film layer 21 is more preferably 240°C or less, and even more preferably 235°C or less.

[0047] ◇Can Inner Film Layer 22 Regarding the side of the film-laminated steel sheet 1 that will become the can inner surface, when the steel sheet temperature rises and the film layer softens, the film becomes more likely to adhere to the punch, which may result in a decrease in punch-ejection ability. As a result of the difficulty in punch-ejection, the edge of the can may get caught on the stopper provided in the mold, resulting in deformation of the edge of the can. However, if the film softens less than the film layer on the side that will become the can outer surface, the slipperiness of the side that will become the can inner surface is relatively better than that of the side that will become the can outer surface when the punch is pulled out. From this perspective, it is preferable that the melting point of the thermoplastic polyester film that constitutes the film layer on the can inner surface side of the film-laminated steel sheet 1 (i.e., the can inner film layer 22 in Figure 1) be higher than the melting point of the thermoplastic polyester film that constitutes the can outer film layer 21.

[0048] Based on the above idea, the inventors conducted detailed studies and found that the punch-ejectability is improved when the melting point of the thermoplastic polyester film constituting the can inner surface film layer 22 is at least 5°C higher than the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21.

[0049] Based on the above findings, in the film-laminated steel sheet 1 according to this embodiment, the melting point of the thermoplastic polyester film constituting the can outer surface side film layer 21 is preferably 215°C or higher. The melting point of the thermoplastic polyester film constituting the can outer surface side film layer 21 is more preferably 218°C or higher, and even more preferably 220°C or higher.

[0050] On the other hand, in the film-laminated steel sheet 1, if the melting point of the thermoplastic polyester film constituting the can inner surface film layer 22 exceeds 260°C, as in the case of the can outer surface film layer 21, the film has high deformation resistance when the mold temperature is still low immediately after the start of DI forming, and the film may tear in areas where bending strain is large, such as the punch shoulder and the ring-shaped portion of the can bottom. Setting the melting point of the thermoplastic polyester film constituting the can inner surface film layer 22 to 260°C or less makes it possible to prevent such film tearing, and is therefore preferable. The melting point of the thermoplastic polyester film constituting the can inner surface film layer 22 is more preferably 255°C or less, and even more preferably 250°C or less.

[0051] As described above, the can inner surface film layer 22 according to this embodiment preferably uses a thermoplastic polyester film having a melting point in the range of 220 to 260°C and at least 5°C higher than the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21. The difference in melting point between the thermoplastic polyester film on the can inner surface side and the thermoplastic polyester film on the can outer surface side is more preferably 10°C or more, and even more preferably 15°C or more. The upper limit of the difference in melting point between the thermoplastic polyester film on the can inner surface side and the thermoplastic polyester film on the can outer surface side is not particularly specified, but the upper limit is substantially about 30°C.

[0052] To determine whether a polyester film is used as a film layer in a film-laminated steel sheet 1 based on the state of the film-laminated steel sheet 1 that has already been manufactured, a sample is taken from any location of the film layer in the film-laminated steel sheet 1 of interest and analyzed by, for example, Fourier transform infrared spectroscopy (FT-IR). If the analysis results indicate the presence of ester bonds, it can be determined that the film layer of interest is composed of a polyester film. Furthermore, by checking whether the sample softens when heated, it can be determined whether the resin constituting the film layer of interest is thermoplastic.

[0053] The melting point of the thermoplastic polyester film can be determined by collecting a sample of about 5 to 10 mg from any location on the film layer of the film-laminated steel sheet 1 of interest, analyzing the obtained sample by differential scanning calorimetry (DSC), and confirming the temperature at which the main endothermic peak appears in the analysis results. For example, a commercially available differential scanning calorimeter (e.g., DSC7030 manufactured by Hitachi High-Tech Science Corporation) can be used to measure the melting point of the obtained sample sealed in an aluminum pan at a heating rate of 10°C / min in the range of 50 to 350°C.

[0054] [Details of the thermoplastic polyester film] In the film-laminated steel sheet 1 according to this embodiment, the thermoplastic polyester film used for the film layer is preferably a film that does not leach out resin components into the food contents contained therein or adsorb flavor components thereto, even when subjected to can-forming, baking, and retort treatment.

[0055] The thermoplastic polyester film used for the film layer preferably has an elongation of 100% or more by itself, which can further prevent the film layer from breaking when the film-laminated steel sheet 1 is subjected to DI forming.

[0056] ◇Can outer surface film layer 21 In the film-laminated steel sheet 1 of this embodiment, the thermoplastic polyester film constituting the can outer surface film layer 21 preferably has a melting point of 215°C or higher, as mentioned above, in addition to the properties for food contents and film elongation as described above.

[0057] Examples of such thermoplastic polyester films include polybutylene terephthalate resin, copolymer resin of butylene terephthalate and ethylene terephthalate and / or ethylene terephthalate isophthalate, blend resin of polybutylene terephthalate resin and polyethylene terephthalate resin and / or polyethylene isophthalate terephthalate resin, ethylene terephthalate isophthalate copolymer resin, and blend resin of polyethylene terephthalate resin and polyethylene terephthalate isophthalate copolymer resin.

[0058] In particular, in the case of a copolymer resin of butylene terephthalate and ethylene terephthalate and / or polyethylene isophthalate terephthalate, it is particularly preferred that the polybutylene terephthalate content be 50% by mass or more.Furthermore, in the case of a blend resin of polybutylene terephthalate resin and polyethylene terephthalate resin and / or polyethylene isophthalate terephthalate resin, it is particularly preferred that the polybutylene terephthalate content be 50% by mass or more, since this results in easy elongation and high breaking strength.

[0059] ◇Can inner surface film layer 22 In the film-laminated steel sheet 1 according to this embodiment, the thermoplastic polyester film constituting the can inner surface film layer 22 preferably has a melting point that is at least 5°C higher than the melting point of the thermoplastic polyester film constituting the can outer surface film layer 21, in addition to the properties for food contents and film elongation as described above.

[0060] Examples of such thermoplastic polyester films include polyethylene terephthalate resin, polyethylene terephthalate isophthalate copolymer resin, polyethylene terephthalate butylene terephthalate copolymer resin, blend resin of polyethylene terephthalate resin and polyethylene terephthalate isophthalate copolymer resin, blend resin of polyethylene terephthalate and polybutylene terephthalate resin, blend resin of polyethylene terephthalate isophthalate copolymer resin and polyethylene terephthalate butylene terephthalate copolymer resin, and stretched or unstretched films of the blend resins of the above resins.

[0061] In the film-laminated steel sheet 1 according to this embodiment, the thermoplastic polyester film used for the film layer may be a stretched film or a non-stretched film. However, since it is important to pay attention to the elongation of the film in DI forming, when a stretched film is used, it is preferable that the stretch ratio is 3 or less.

[0062] Furthermore, within the range in which the above-mentioned properties are satisfied, the film used in the film-laminated steel sheet 1 may be a multi-layer film having two or three layers.

[0063] In addition, in the film-laminated steel sheet 1 according to this embodiment, various additives such as pigments, lubricants, antioxidants, heat stabilizers, antistatic agents, and nucleating agents may be added to the thermoplastic polyester film used in the film layer, as needed.

[0064] The elongation of the thermoplastic polyester film can be determined by measuring it in accordance with JIS K7161-1:2014 and JIS K7127:1999. Specifically, the wax layer of the film-laminated steel sheet 1 of interest is removed with hexane, and then a tensile test piece is taken from any location on the film layer in accordance with the above standards. The obtained tensile test piece is set in a tensile tester, and a tensile test is performed at a measurement temperature of 23 to 25°C.

[0065] [Thickness of the film layer] ◇Can outer surface side film layer 21 In the DI forming focused on in this embodiment, the film layer on the side of the film-laminated steel sheet 1 that will become the can outer surface (i.e., the can outer surface side film layer 21) is subjected to a strong shear force, particularly during ironing. Therefore, if the thickness of the can outer surface side film layer 21 is too thin, the surface of the film layer may be scraped, which may make pinholes more likely to occur. On the other hand, if the thickness of the can outer surface side film layer 21 is too thick, the film may be sheared and displaced when passing through the ironing die, which may result in scraping of the surface of the film layer, and the scraping debris may easily form dent marks or streak-like defects.

[0066] According to detailed studies by the present inventors, the thickness of the film layer 21 on the outer surface side of the can of the film-laminated steel sheet 1 (thickness d Ｆｏ It has been revealed that when the thickness of the outer film layer 21 of the can is 12 μm or more, the occurrence of pinholes can be further suppressed even if a strong shear force is applied to the surface of the film layer during DI molding. The thickness of the outer film layer 21 of the can is more preferably 15 μm or more.

[0067] On the other hand, detailed studies by the present inventors have revealed that when the thickness of the can outer surface side film layer 21 of the film-laminated steel sheet 1 is 40 μm or less, scraping of the film layer when passing through the ironing die can be prevented, and the formation of dents and streak-like defects can be further suppressed. The thickness of the can outer surface side film layer 21 is more preferably 35 μm or less.

[0068] In the film-laminated steel sheet 1 according to this embodiment, the thickness of the film layer on the can inner surface side (i.e., the can inner surface side film layer 22) may be appropriately set to a thickness that provides sufficient retort corrosion resistance depending on the corrosiveness of the contents of the can. For example, in the case of contents such as general boiled or oil-soaked foods that do not have a low pH value, the thickness of the can inner surface side film layer 22 (thickness d in FIG. 1) may be set to a thickness that is 0.05 mm. ＦｉBy making the thickness of the film layer 22 10 μm or more, good retort corrosion resistance can be obtained. In addition, since can contents with a low pH value are highly corrosive, it is preferable to make the thickness of the film layer 22 on the can inner surface as thick as possible. For example, by making the thickness of the film layer 22 20 μm or more, good retort corrosion resistance can be ensured even when can contents that are highly corrosive are stored.

[0069] However, if the thickness of the can inner surface film layer 22 exceeds 100 μm, the film may adhere to the punch during DI forming, making it difficult to slide, and may result in a decrease in punch-ejectability. Therefore, by setting the thickness of the can inner surface film layer 22 to 100 μm or less, it is possible to suppress a decrease in punch-ejectability while ensuring good retort corrosion resistance. The thickness of the can inner surface film layer 22 is more preferably 50 μm or less.

[0070] The thickness of the above-described film layer can be measured from an already manufactured film-laminated steel sheet 1 as follows. First, multiple sample pieces each measuring 100 × 100 mm are taken from any position on the sheet- or coil-shaped film-laminated steel sheet 1. To measure the thickness of the can exterior film layer 21 from the obtained sample pieces, first, the side of the can interior film layer 22 is scraped with sandpaper or the like, and then the film-laminated steel sheet 1 is immersed in 17% to 35% hydrochloric acid to dissolve the base steel sheet, and only the can exterior film layer 21 is peeled and extracted. The thickness of the can exterior film layer 21 can then be measured at any three positions using a micrometer. The average of the three measurements is taken as the thickness of the can exterior film layer 21. Furthermore, when measuring the thickness of the can inner surface film layer 22, the obtained sample piece is scraped on the side of the can outer surface film layer 21 with sandpaper or the like, and then the film-laminated steel sheet 1 is immersed in 17% to 35% hydrochloric acid to dissolve the base steel sheet, and only the can inner surface film layer 22 is peeled off and extracted. Then, the thickness of the can inner surface film layer 22 can be measured at any three points while changing the position using a micrometer. The average value of the three measured values ​​is taken as the thickness of the can inner surface film layer 22.

[0071] <<Regarding Wax Layer>> Next, the wax layer of the film-laminated steel sheet 1 according to this embodiment will be described in detail.

[0072] The wax layer in the film-laminated steel sheet 1 according to this embodiment is a layer provided on the above-described film layer, as shown schematically in FIG.

[0073] [Regarding the amount of wax layer attached] In the film-laminated steel sheet 1 according to the present embodiment, the amount of wax layer attached not only affects the scraping and galling of the can outer surface film layer 21 during DI forming, but also has a large effect on ironing formability. Therefore, the amount of wax layer attached is an extremely important factor in maintaining the punch-ejectability during DI forming while further improving the ironing formability.

[0074] The wax layers provided on the inner and outer can surfaces of the film-laminated steel sheet 1 melt as the steel sheet temperature rises during DI forming, forming a lubricating film on the surface of the laminated steel sheet (which can also be considered as the surface of the film layer in this embodiment), thereby providing good lubricity to the laminated steel sheet. After DI forming is completed, the wax that was melted during DI forming may solidify again and remain on the surface of the film layer.

[0075] In the film-laminated steel sheet 1 according to this embodiment, the amount of wax layer attached is 0.030 to 0.120 g / m per side. ２ The wax layer had a different deposition amount on the front side and the back side of the steel sheet. ２ This value corresponds to the minimum amount of wax on the side with the least amount of wax attached, and the amount of wax attached per side is 0.120 g / m ２ This value corresponds to the maximum amount of wax deposited on the surface with the larger amount of wax.

[0076] The amount of wax layer 31 attached to the outer surface of the can and the amount of wax layer 32 attached to the inner surface of the can will be described in detail below.

[0077] Can outer surface side wax layer 31 In the film-laminated steel sheet 1 according to this embodiment, the amount of the wax layer 31 on the outer surface side of the can is 0.030 g / m ２ Even more than this value, 0.050 g / m ２ The amount of wax layer 31 deposited on the outer surface of the can was 0.050 g / m ２ If the adhesion amount of the wax layer 31 on the outer surface of the can is less than 0.050 g / m, the frictional force during ironing increases, which may cause scraping or galling of the film layer in the ironed portion on the outer surface of the can, which is undesirable. ２ By setting the amount to the above, it is possible to suppress an increase in frictional force during ironing, and to prevent scraping or galling of the film layer in the ironed portion on the outer surface of the can. ２ More preferably, it is 0.080 g / m or more. ２ That's all.

[0078] On the other hand, in the film-laminated steel sheet 1 according to this embodiment, the amount of the wax layer 31 on the outer surface of the can is 0.120 g / m ２ The amount of wax layer 31 deposited on the outer surface of the can is 0.120 g / m or less. ２ If the deposition amount of the wax layer 31 on the outer surface of the can exceeds 0.120 g / m, excess wax will accumulate in the gaps of the ironing die, and in the areas where the wax has accumulated thickly, streaks and dents will easily appear on the surface of the film layer, which is not preferable. ２ By setting the wax layer thickness to 0.110 g / m or less, it is possible to prevent the occurrence of streaks and dents on the surface of the film layer. ２ or less, more preferably 0.100 g / m ２ The following is the result.

[0079] Wax layer 32 on the inner surface of the can Regarding the amount of wax layer 32 on the inner surface of the can in the film-laminated steel sheet 1 according to this embodiment, the present inventors have obtained the following findings: That is, if the slipperiness of the inner surface of the can is too good compared to the slipperiness of the outer surface of the can during DI forming, the punch becomes slippery, and strain is concentrated at the part of the can bottom where the punch shoulder comes into contact, causing breakage, which is known as "punch shoulder breakage," and this is undesirable.

[0080] On the other hand, if the slipperiness of the inner can surface is too poor compared to the slipperiness of the outer can surface during DI molding, the can body will be difficult to remove from the punch when the punch returns from the bottom dead center to the top dead center. As a result, the can body will move back together with the punch as it moves back, and the can end will likely hit the stopper provided on the mold side hard and become deformed. In some cases, the can body will buckle, forcing the can making process to be interrupted, which is undesirable.

[0081] Based on the above findings, the inventors conducted further studies and found that the above-mentioned buckling of the can body is likely to occur when the amount of wax layer 32 on the inner surface of the can is too small compared to the amount of wax layer 31 on the outer surface of the can, and that the above-mentioned punch shoulder fracture is more likely to occur as the amount of wax layer 32 on the inner surface of the can approaches the amount of wax layer 31 on the outer surface of the can.

[0082] As a result of further detailed investigations into this point, the inventors have found that, in the film-laminated steel sheet 1 according to this embodiment, can body buckling can be suppressed without leading to punch shoulder fracture by setting the deposition amount of the wax layer 32 on the can inner surface (i.e., the wax layer on the surface with the lesser deposition amount) within a range of 0.60 to 0.96 times the deposition amount of the wax layer 31 on the can outer surface (i.e., the wax layer on the surface with the moreer deposition amount). Here, the ratio obtained by dividing the deposition amount of the wax layer on the surface with the moreer deposition amount by the deposition amount of the wax layer on the surface with the lesser deposition amount is referred to as the "deposition amount ratio." Therefore, the above-mentioned range of 0.60 to 0.96 corresponds to a deposition amount ratio range of 1.04 (≈1.00 / 0.96) to 1.67 (≈1.00 / 0.60).

[0083] In view of the above, in the film-laminated steel sheet 1 according to this embodiment, the amount of the wax layer 31 on the outer surface of the can is set to 0.050 to 0.120 g / m ２ and the deposition amount of the wax layer 32 on the inner surface of the can is set to a range of 0.60 to 0.96 times the deposition amount of the wax layer 31 on the outer surface of the can (in other words, the deposition amount ratio specified above is set to a range of 1.04 to 1.67). As a result, the film-laminated steel sheet 1 according to this embodiment can maintain punch-ejectability during DI forming, while further improving ironing formability. As a result, continuous can-making performance can be further improved in the production of DI cans.

[0084] The deposition amount of the wax layer 32 on the inner surface of the can is preferably 0.65 times or more (a deposition amount ratio of 1.54 or less) the deposition amount of the wax layer 31 on the outer surface of the can, and more preferably 0.70 times or more (a deposition amount ratio of 1.43 or less) the deposition amount of the wax layer 31 on the outer surface of the can. The deposition amount of the wax layer 32 on the inner surface of the can is preferably 0.95 times or less (a deposition amount ratio of 1.05 or more) the deposition amount of the wax layer 31 on the outer surface of the can, and more preferably 0.90 times or less (a deposition amount ratio of 1.11 or more) the deposition amount of the wax layer 31 on the outer surface of the can.

[0085] In order to measure the amount of wax layer adhered as described above from the state of an already manufactured film-laminated steel sheet 1, the wax layer on the side of interest may be dissolved in a predetermined solvent and then the following treatment may be carried out.

[0086] First, multiple sample pieces, each measuring 200 mm x 200 mm, are taken from any position on the sheet- or coil-shaped film-laminated steel sheet 1. Then, to prevent wax from leaching from the wax layer on the side of interest, tape is sealed on the surface of the wax layer on the side of interest. Next, a solvent capable of dissolving wax (e.g., n-heptane) is poured onto the surface on the side not sealed with tape to dissolve the wax layer. The poured solvent is collected in an aluminum foil case (e.g., foil case S736210, deep opening, 11 μm thickness, mass: approximately 0.38 g, manufactured by Toyo Aluminum Eco Products Co., Ltd.) whose mass has been measured in advance using a precision balance.

[0087] Next, the aluminum foil case containing the solvent in which the wax has been dissolved is placed in a thermostatic bath at 100°C for 30 minutes to completely volatilize the solvent. The mass of the aluminum foil case from which the solvent has been volatilized is then measured using a precision balance. The mass of the wax can be calculated by subtracting the mass of the aluminum foil case before the solvent was recovered from the mass thus obtained. The mass of the wax thus obtained is then multiplied by the area (unit: m ２ By dividing the wax layer thickness by the wax layer thickness (converted to a thickness of 1 / 2 mm), the amount of wax layer attached on the surface of interest can be determined.

[0088] [Regarding Wax Penetration] Next, as mentioned above, in order to further prevent scraping of the can exterior film layer 21 that may occur during DI molding, it is more preferable that the wax have a certain degree of hardness. Here, the hardness of the wax can be expressed by the penetration defined in JIS K2235:2022-Item 6.4.

[0089] If the wax constituting the wax layer according to this embodiment has too small a penetration index, the wax is in a hard state, particularly at the start of molding when the mold temperature has not yet fully risen, and the wax is likely to fall off in the ironing section, resulting in the occurrence of indentation marks caused by the resulting wax residue. However, by using a wax having a penetration index of 5 or more at a test temperature of 25°C, the above-mentioned wax fall-off at the start of molding can be prevented. Therefore, in the wax layer according to this embodiment, the wax constituting the wax layer preferably has a penetration index of 5 or more at a test temperature of 25°C. The penetration index of the wax at a test temperature of 25°C is more preferably 10 or more.

[0090] On the other hand, if the wax constituting the wax layer according to this embodiment has a too large penetration index, it means that the viscosity of the wax is low. In this case, as the temperature of the mold increases during continuous can forming, the lubricity of the wax decreases, making the film layer more susceptible to scraping and galling. However, by using a wax having a penetration index of 20 or less at a test temperature of 25°C, it is possible to prevent the above-mentioned scraping and galling of the film layer caused by the viscosity of the wax. Therefore, in the wax layer according to this embodiment, the wax constituting the wax layer preferably has a penetration index of 20 or less at a test temperature of 25°C. The penetration index of the wax at a test temperature of 25°C is more preferably 15 or less.

[0091] The penetration of the wax can be measured in accordance with JIS K2235:2022.

[0092] [Regarding the Melting Point of the Wax] In the can exterior wax layer 31 according to this embodiment, if the melting point of the wax constituting the wax layer is too low, the molten wax will drip onto the outer surface of the can wall during DI molding, which is likely to cause wax stains, which is undesirable. Similarly, in the can interior wax layer 32, if the melting point of the wax constituting the wax layer is too low, it will be difficult to obtain adequate lubrication during DI molding, which will likely cause scraping of the film layer. However, by ensuring that the melting point of the wax constituting the wax layer is 50.0°C or higher, it is possible to further prevent dents and wax stains on the can exterior, as well as scraping of the film layer on the can interior. In the wax layer according to this embodiment, the melting point of the wax constituting the wax layer is more preferably 52.0°C or higher.

[0093] On the other hand, in the can exterior wax layer 31 according to this embodiment, if the melting point of the wax constituting the wax layer is too high, the wax will adhere to and fall off around the ironing die, making it more likely that dents will occur on the exterior can surface, which is undesirable. Similarly, in the can interior wax layer 32, if the melting point of the wax constituting the wax layer is too high, it will be difficult to obtain adequate lubrication during DI molding, making it more likely that the film layer will be chipped. However, by making the melting point of the wax constituting the wax layer 70.0°C or lower, it is possible to further prevent dents on the exterior can surface and chipping of the film layer on the interior can surface. In the wax layer according to this embodiment, the melting point of the wax constituting the wax layer is more preferably 68.0°C or lower.

[0094] The melting point of the wax constituting the wax layer can be measured by differential scanning calorimetry in the same manner as the melting point of the thermoplastic polyester constituting the film layer described above.

[0095] [Specific Examples of Wax] The wax used in the wax layer according to this embodiment is preferably selected taking into consideration not only the above-mentioned viewpoints but also wax removability after can manufacturing. Examples of waxes that are easily removably used after can manufacturing include n-paraffin wax having a carbon number of 24 to 32 and its urea adducts (e.g., various paraffin waxes, candelilla wax, carnauba wax, etc.), microwax, and mixtures of paraffin wax and microwax.

[0096] In the wax layer according to the present embodiment, it is more preferable to select a wax having an appropriate penetration and melting point from among the waxes exemplified above, taking into consideration the wax removability after can manufacturing as described above.

[0097] The film-laminated steel sheet 1 according to this embodiment has been described in detail above with reference to FIG.

[0098] (Method for manufacturing film-laminated steel sheet) Next, an example of a method for manufacturing the film-laminated steel sheet 1 according to this embodiment will be described.

[0099] <Preparation of Base Steel Sheet> First, a steel sheet that will serve as the base material for the film-laminated steel sheet 1 is prepared. Here, the method for manufacturing the base steel sheet is not particularly limited, and various known methods can be used for manufacturing. Furthermore, by adjusting the surface roughness of the rolling rolls used in the surface temper rolling process when manufacturing the base steel sheet, it is possible to achieve a desired surface roughness on the surface of the steel sheet. Alternatively, a commercially available steel sheet having the desired properties may be purchased and used as the base steel sheet.

[0100] <Formation of Film Layer> Next, the base steel sheet obtained in this manner is subjected to various pretreatments such as alkaline degreasing treatment, water washing treatment, pickling treatment, etc. as necessary to obtain a clean steel sheet surface. Thereafter, film layers are formed on the front and back surfaces of the base steel sheet using thermoplastic polyester films.

[0101] Here, the thermoplastic polyester film used to form the film layer may be manufactured by the manufacturer using any of a variety of known manufacturing methods to have the desired properties, or may be purchased from a commercial source to have the desired properties, or may be purchased from a commercial source and then further subjected to any of a variety of known processing methods to achieve the desired properties.

[0102] Next, as a method for forming film layers on the front and back surfaces of the base steel sheet as described above, various known film forming methods can be applied.

[0103] However, it is more preferable to use a method (thermal fusion method) in which the steel strip is heated by passing it through a jacket roll with a built-in heater or an induction heating (IH) furnace, and then the film is continuously fed from both sides of the steel strip and pressed onto the steel strip with heat-resistant rubber rolls to fuse the film (heat fusion method). The thermal fusion method makes it possible to form a film layer with a more uniform thickness on both sides of the base steel sheet. In this case, the thickness and surface roughness of the film layer can be controlled within the desired range by controlling the heating temperature of the base steel sheet, the roughness of the roll surface of the film laminating roll, and the temperature and pressure of the roll surface.

[0104] Specifically, it is preferable to heat the base steel sheet to a temperature of (the melting point of the film + 15°C) or higher, and to set the surface temperature of the film laminating roll to a temperature within the range of (the melting point of the film + 30°C) or higher and (the glass transition point of the film (Tg) + 20°C).

[0105] In order to optimize the nip time of the film laminating roll, it is preferable that the surface hardness of the film laminating roll be controlled within a range of 30 to 80° as measured by a durometer type A specified in JIS K6253-3: 2012. In addition, from the viewpoint of preventing air bubbles from being trapped during film formation, the nip pressure of the film laminating roll is controlled within a range of 100 to 300 N / cm. ２ It is preferable that the range is within the range.

[0106] Furthermore, the steel sheet after the film layer formation is preferably rapidly cooled in a water cooling bath within 1 second after lamination in order to suppress spherulitization, which causes embrittlement of the film.

[0107] <Formation of Wax Layer> Next, a wax layer is formed on the steel sheet on which the film layer has been formed. Here, the method for forming the wax layer is not particularly limited, and the wax layer may be formed by applying wax that has been heated to a temperature equal to or higher than the melting point of the wax to the surface of the film layer, or by preparing a wax solution in which wax is dissolved in a volatile solvent and applying this wax solution to the surface of the film layer. Furthermore, the steel sheet after the wax application may be dried by heating or air-dried.

[0108] The method for applying the wax (or wax solution) to the surface of the film layer is not particularly limited, and can be performed by a commonly known application method such as roll coating, curtain flow coating, immersion, bar coating, etc. When the wax is dried by heating, the heating method is not particularly limited, and any method may be used, such as hot air, near infrared rays, far infrared rays, induction heating, or a heating method using a combination of these.

[0109] Among the various methods for forming a wax layer as described above, from the viewpoint of ensuring productivity, it is simpler to adopt a method in which, in a continuous production line for producing film-laminated steel sheets, wax is heated to a temperature above its melting point, melted, applied to the surface of the film layer using a roll coater, and then air-cooled before winding up the steel sheet.

[0110] (Method for Manufacturing DI Cans Using Film-Laminated Steel Sheet) The film-laminated steel sheet 1 according to this embodiment can be drawn and ironed using a commercially available cupping press and DI forming equipment. More specifically, the film-laminated steel sheet described above is used as a material for a DI can. The film-laminated steel sheet is positioned so that the side with the larger amount of wax layer becomes the outer surface of the DI can, and the side with the smaller amount of wax layer becomes the inner surface of the DI can. Then, the film-laminated steel sheet is subjected to DI forming. The conditions for DI forming are not particularly specified, and the film-laminated steel sheet can be DI formed under typical DI forming conditions.

[0111] In the film-laminated steel sheet 1 according to this embodiment, a wax layer is provided on the film layer in advance. Furthermore, ironing formability and punch-release property are both ensured during DI forming, and ironing formability is further improved. Therefore, DI forming can be performed sufficiently without a coolant. Furthermore, when DI forming the film-laminated steel sheet 1 according to this embodiment, a coolant used in ordinary DI forming may be used in combination. The conditions for DI forming are not particularly limited.

[0112] When producing paper-wrapped cans, the can end of a DI-formed can body is trimmed to a desired shape and then flanged up to obtain a DI can. When printing on the can body, the can end of a DI-formed can body is trimmed to a desired shape. Subsequently, the can body is printed using letterpress offset printing or flatbed offset printing with a curved surface printing machine, and the printing is baked. The can end is then flanged up to obtain a DI can. After filling the produced DI can with contents, the DI can can be sealed by wrapping a lid around it.

[0113] The following examples will be used to specifically explain the film-laminated steel sheet and the method for manufacturing a DI can according to the present embodiment. However, the conditions in the examples shown below are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to the examples. As long as the object of the present invention is achieved without departing from the gist of the present invention, appropriate modifications may be made within the scope of the present invention. Therefore, the present invention may adopt various conditions, and all of these are included in the technical features of the present invention.

[0114] <Base Steel Plate> Steel plates M1 to M8 shown in Table 1 below were used as base steel plates. Here, one side of the base steel plate will be referred to as the "first side," and the side opposite to the first side will be referred to as the "second side." In each operation performed below, the base steel plate was handled so that the first side was the side with a larger amount of wax layer attached, and the second side was the side with a smaller amount of wax layer attached.

[0115] M1 to M6 are steel sheets with a thickness of 0.225 mm, temper = T3, r value = 1.05 to 1.10, and Δr = 0.00 to 0.40, on the surface of which a metal chromium layer (adhesion amount: 80 mg / m per side) is applied. ２ ) and a chromium hydrate oxide layer (adhesion amount: 10 mg / m per side) ２ The steel sheets M1 to M8 are tin-free steel sheets (manufactured by Nippon Steel Corporation) with different surface roughnesses, as shown in Table 1. M7 is a tin-plated steel sheet using a steel sheet with a thickness of 0.24 mm, temper = T3, r value = 1.10, and Δr = 0.15. From the steel sheet side, the following layers are coated: a Sn-Fe alloy layer (Sn content: 1.3 g / m per side) ２ ), pure Sn layer (Sn content: 1.5 g / m per side ２ ), chromium hydrate oxide layer (adhesion amount: 10 mg / m per side ２ M8 is a so-called tinplate steel sheet (manufactured by Nippon Steel Corporation) containing Zr hydroxide (Zr amount: 60 mg / m per side) on a cold-rolled steel sheet with a thickness of 0.195 mm, a temper of T3, an r value of 1.00, and a Δr of 0.45. ２The steel sheet is a chromate-free steel sheet (manufactured by Nippon Steel Corporation) with a chromate-free chemical conversion coating mainly composed of chromium.

[0116] A sample measuring 200 mm x 200 mm was cut from each base steel plate, and the arithmetic mean roughness Ra was measured three times at three diagonal points on the sample in each of the coil longitudinal direction and the coil width direction using a surface roughness and shape measuring instrument Surfcom 570A manufactured by Tokyo Seiki Co., Ltd. The average value of the obtained measurements was taken as the surface roughness Ra of each base steel plate. The obtained results are also shown in Table 1.

[0117]

[0118] <Resin Film> The resin films used to form the film layers of the film-laminated steel sheets are shown in Table 2. All of the films used were commercially available thermoplastic polyester-based stretched films.

[0119] F1 is a biaxially stretched film of ethylene dimethyl terephthalate / ethylene dodecanedioic acid copolymer resin (DMT / DDA-EG) with a melting point of 210°C, a thickness of 25 μm, and an elongation of 200%. F2 is a biaxially stretched film of ethylene terephthalate / butylene terephthalate copolymer resin (PET-PBT) with a melting point of 213°C, a thickness of 25 μm, and an elongation of 190%. F3 is a biaxially stretched film of ethylene terephthalate / butylene terephthalate copolymer resin (PET-PBT) with a melting point of 215°C, a thickness of 25 μm, and an elongation of 190%. F4 is a biaxially stretched film of ethylene terephthalate / butylene terephthalate copolymer resin (PET-PBT) with a melting point of 218°C, a thickness of 12 μm, and an elongation of 190%. F5 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 227°C, a thickness of 19 μm, and an elongation of 160%. F6 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 227°C, a thickness of 40 μm, and an elongation of 180%. F7 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 240°C, a thickness of 30 μm, and an elongation of 130%.

[0120] F8 is a biaxially stretched film of polyethylene terephthalate resin (PET) with a melting point of 242°C, a thickness of 20 μm, a stretch ratio of 2.9, and an elongation of 100%. F9 is a biaxially stretched film of polyethylene terephthalate resin (PET) with a melting point of 253°C, a thickness of 20 μm, a stretch ratio of 3.0, and an elongation of 100%. F10 is a biaxially stretched film of polyethylene terephthalate resin (PET) with a melting point of 258°C, a thickness of 19 μm, a stretch ratio of 3.1, and an elongation of 100%. F11 is a biaxially stretched film of polyethylene terephthalate resin (PET) with a melting point of 262°C, a thickness of 19 μm, a stretch ratio of 3.3, and an elongation of 100%.

[0121] F12 is a biaxially stretched film of ethylene terephthalate-butylene terephthalate copolymer resin (PET-PBT) with a melting point of 212°C, a thickness of 10 μm, and an elongation of 190%. F13 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 227°C, a thickness of 42 μm, and an elongation of 200%. F14 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 227°C, a thickness of 50 μm, and an elongation of 200%. F15 is a biaxially stretched film of ethylene terephthalate-ethylene isophthalate copolymer resin (PET-IA) with a melting point of 227°C, a thickness of 100 μm, and an elongation of 200%.

[0122] A sample of 5 to 8 mg was taken from each resin film and sealed in an aluminum pan. Measurements were carried out using a differential scanning calorimeter (DSC7030, manufactured by Hitachi High-Tech Science Corporation) in the range of 50 to 350°C at a heating rate of 10°C / min, and the temperature of the main endothermic peak was taken as the melting point of each resin film.

[0123]

[0124] <Formation of Film Layer> Using the above-described base steel sheet and resin film, film layers were formed on the front and back surfaces of the base steel sheet. To form the film layers, a dedicated resin film laminating device was used, equipped with a metal sheet supplying device, a metallic heating hot press for heating the metal sheet, front and back film supplying devices, heat-resistant rubber laminating rolls (the rubber roll surface temperature was controlled by a metallic heating backup roll), and a cooling water tank. Using this device, multiple steel sheets (sheet width 200 mm × sheet length 200 mm) with film layers formed thereon were produced at the levels shown in Tables 4-1 and 4-2 below.

[0125] <Wax> The waxes used to form the wax layer of the film-laminated steel sheet are shown in Table 3. All of the waxes shown below are commercially available.

[0126] W1 is a paraffin wax having a needle penetration of 29 at 25°C and a melting point of 48.0°C. W2 is a paraffin wax having a needle penetration of 22 at 25°C and a melting point of 50.0°C. W3 is a paraffin wax having a needle penetration of 20 at 25°C and a melting point of 50.0°C. W4 is a paraffin wax having a needle penetration of 15 at 25°C and a melting point of 52.0°C. W5 is a paraffin wax having a needle penetration of 13 at 25°C and a melting point of 66.3°C. W6 is a paraffin wax having a needle penetration of 11 at 25°C and a melting point of 69.4°C. W7 is a paraffin wax having a needle penetration of 5 at 25°C and a melting point of 75.0°C. W8 is a candelilla wax having a penetration of 1 at 25° C. and a melting point of 65.0° C. W9 is a carnauba wax having a penetration of 1 at 25° C. and a melting point of 82.0° C.

[0127] The penetration of each wax at 25°C was measured using an automatic penetration measuring device EX-210ED manufactured by Daiichi Rikagaku Co., Ltd. The melting point of each wax was measured using a differential scanning calorimeter (DSC7030 manufactured by Hitachi High-Tech Science Corporation) in the same manner as for the resin film, using 5 to 8 mg of a sample taken from each wax. The measurement conditions were a temperature rise rate of 10°C / min and a measurement temperature range of 50 to 350°C. The temperature of the main endothermic peak was taken as the melting point of each wax.

[0128]

[0129] <Formation of wax layer> First, two laminated steel plates (two plates of the same standard) each measuring 200 mm x 200 mm on which a film layer was formed by the method described above were treated as a pair, and the identical film surfaces were placed together, and the end faces were sealed with tape.

[0130] A predetermined amount of each wax shown in Table 3 was dissolved in hexane (a commercially available general reagent) as a solvent to prepare a wax hexane solution. Multiple types of such wax hexane solutions were prepared for each wax, with the wax concentration varied.

[0131] The steel plate sealed with tape as described above was immersed in a wax-hexane solution and then air-dried.

[0132] Next, the tape seal was peeled off, and the opposite surfaces were brought together and re-sealed with tape. The steel sheets were then immersed in wax hexane solutions of different concentrations and allowed to air dry. The tape seal was then peeled off, producing film-laminated steel sheets with different wax deposition amounts on the front and back surfaces. By repeating this procedure, multiple film-laminated steel sheets were produced for each of the levels shown in Tables 4-1 and 4-2 below. In Tables 4-1 and 4-2 below, the wax used on the front and back surfaces was the same level.

[0133] <Measurement of Wax Layer Adhesion Amount> The wax layer adhesion amount was measured as follows. First, for each level of film-laminated steel sheet (size 200 mm × 200 mm), the side on which the adhesion amount was not to be measured was sealed with commercially available tape that is not soluble in heptane. The tape sealing was performed to cover the side on which the adhesion amount was not to be measured and the side surface, and also to cover an area of ​​5 mm from both ends in the width and length directions on the side on which the adhesion amount was to be measured. As a result of this tape sealing, the size of the area on the side on which the adhesion amount was to be measured that was not tape-sealed was 190 mm × 190 mm.

[0134] Next, for each of the film-laminated steel sheets with the above-described tape seal, heptane (a commercially available general reagent) was poured onto the surface on which the wax was to be measured to dissolve the wax. The poured heptane was collected in an aluminum foil case (Toyo Aluminum Eco Products Co., Ltd., foil case No. S736210, deep opening, 11 μm thick, mass: approximately 0.38 g) whose mass had been measured in advance using a precision balance.

[0135] Next, the aluminum foil case containing the wax-dissolved heptane was placed in a thermostatic bath at 100°C for 30 minutes to completely volatilize the heptane. The mass of the aluminum foil case was then measured using a precision balance, and the mass of the wax was calculated from the difference in mass of the aluminum foil case before and after heptane recovery. The wax deposition amount was determined by dividing the resulting wax mass by the wax application area (190 mm x 190 mm excluding the tape seal area).

[0136] The structures of the film-laminated steel sheets thus prepared are shown in Tables 4-1 and 4-2 below.

[0137]

[0138]

[0139] <Forming of DI cans> Each film-laminated steel sheet prepared by the above method was punched into a blank sheet with a diameter of 126 mm. Each blank sheet was shallow-drawn at a speed of 60 cans / min using a cupping press, and then continuously ironed at an average can-making speed of 100 cans / min using a two-draw, three-ironing can-making machine (Bodymaker) with a punch stroke of 400 mm. Each blank sheet was placed in the drawing and ironing machine so that the first surface of the blank sheet faced the outer can surface and the second surface faced the inner can surface. The ironing conditions were a one-stage drawing ratio of 1.75, a two-stage drawing ratio of 1.35, an ironing punch diameter of 52.80 mm, and a total ironing rate of 48%, resulting in cans with a height of 100 mm or more.

[0140] <Evaluation Method> Each of the DI cans obtained as described above was evaluated from the viewpoints of "DI formability" and "degree of film damage." The details of the evaluation are as follows. The obtained evaluation results are summarized in Tables 5-1 and 5-2 below.

[0141] [Evaluation of DI formability] The DI formability was evaluated from the viewpoints of "degree of can end deformation" and "degree of cracking and necking at the can bottom punch shoulder." The degree of can end deformation was evaluated as follows: no can end deformation was given a rating of "A," slight can end deformation was given a rating of "B," and jamming was given a rating of "C." Ratings of "A" and "B" were considered acceptable.

[0142] The degree of cracking and necking at the bottom punch shoulder of the can was evaluated as follows: no cracking or necking at the bottom punch shoulder was given a rating of "A", slight necking was observed at the bottom punch shoulder was given a rating of "B", and cracking of the steel plate at the bottom punch shoulder was given a rating of "C". Ratings of "A" and "B" were considered to be acceptable.

[0143] [Evaluation of the Degree of Damage to the Film Surface on the Outer Side of Can Products] The degree of damage to the film surface on the outer side of can products prepared as described above was evaluated by visual inspection of the appearance and by the presence or absence of film pinholes using a pinhole tester. A rating of "A" was given for a case in which there were no film defects or indentations on the film surface on the outer side of the can. A rating of "B" was given for a case in which there were isolated small indentations on the film surface on the outer side of the can, or a case in which there were no visible defects on the appearance but there were five or more pinhole reactions using a pinhole tester. A rating of "C" was given for a case in which there were film scratches on the film surface on the outer side of the can, or an indentation large enough to dent the steel sheet. Ratings of "A" and "B" were considered acceptable.

[0144] The pinhole defect detection was performed using a pinhole tester (TRC-250A) manufactured by Sanko Electronics Laboratory Co., Ltd. A carbon brush electrode was attached to the anode side of the pinhole tester, and the earth side was attached to a portion of the can end where the film had been scraped off with sandpaper, and the entire surface of the can wall was probed with the carbon brush electrode at 500 V.

[0145] [Evaluation of the Degree of Damage to the Film Surface on the Inner Surface of Can Products] The degree of damage to the film surface on the inner surface of can products was evaluated by conducting a colored ERV (Enamel Rate Value) test on the can products prepared as described above. The evaluation was conducted as follows: a case where there were no colored ERV reaction sites on the film surface on the inner surface of the can was given a rating of "A," a case where there were five or fewer separate dot-like colored ERV reaction sites on the film surface on the inner surface of the can was given a rating of "B," and a case where there were more than five separate dot-like colored ERV reaction sites on the film surface on the inner surface of the can or where there were linear to planar colored ERV reaction sites on the film surface on the inner surface of the can was given a rating of "C." Ratings of "A" and "B" were considered pass.

[0146] The colored ERV test was carried out as follows: First, the inner surface of the can was washed with hexane to remove wax, and then an ERV test solution (ERV test solution composition: CuSO ) was poured into the can. ４ ・5H ２The can was filled with a solution of 1000 ppm CO [50 g / L], NaCl [60 g / L]. Next, the positive electrode of a digital enamel rate meter (Digital Enamel Rater NDE-1200, manufactured by Nichia Instruments Co., Ltd.) was immersed, and the negative electrode was connected to the can side. A current of 6.3 V was applied for 15 seconds, causing copper sulfate crystals to precipitate on the exposed metal. After that, the state of damage to the film surface on the inside of the can was visually evaluated.

[0147]

[0148]

[0149] As is clear from Tables 5-1 and 5-2 above, the film-laminated steel sheets corresponding to the Examples of the present invention were good in both DI formability and the degree of film damage, while the film-laminated steel sheets corresponding to the Comparative Examples of the present invention were poor in at least either DI formability or the degree of film damage. As such, the film-laminated steel sheets corresponding to the Examples of the present invention have good ironing formability in DI forming, and therefore are less likely to suffer from film layer abrasion or steel sheet scoring during ironing, and are also less likely to suffer from buckling, making them highly useful due to their excellent manufacturability.

[0150] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0151] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0152] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0153] REFERENCE SIGNS LIST 1 Film-laminated steel sheet 10 Base steel sheet 21 Film layer on outer surface of can 22 Film layer on inner surface of can 31 Wax layer on outer surface of can 32 Wax layer on inner surface of can

Claims

1. A laminated ... ２ and the wax layer has a different adhesion amount between the front side and the back side of the steel sheet, and the adhesion amount ratio obtained by dividing the adhesion amount of the wax layer on the side with a larger adhesion amount by the adhesion amount of the wax layer on the side with a smaller adhesion amount is within the range of 1.04 to 1.

67.

2. A film-laminated steel sheet as described in claim 1, wherein the melting point of the thermoplastic polyester film constituting the film layer on the side with a larger amount of adhesion is 215°C or higher and lower than 255°C, the melting point of the thermoplastic polyester film constituting the film layer on the side with a smaller amount of adhesion is 220 to 260°C, and the melting point of the thermoplastic polyester film on the side with a smaller amount of adhesion is 5°C or higher than the melting point of the thermoplastic polyester film on the side with a larger amount of adhesion.

3. A film-laminated steel sheet according to claim 1 or 2, wherein the wax constituting the wax layer has a penetration, as specified in JIS K2235:2022, of 5 to 20 at a test temperature of 25°C, and the melting point of the wax is 50.0 to 70.0°C.

4. A film-laminated steel sheet according to any one of claims 1 to 3, wherein the thickness of the film layer on the surface having a greater amount of adhesion is 12 to 40 μm.

5. A film-laminated steel sheet according to any one of claims 1 to 4, wherein the surface roughness of the steel sheet on the side having a greater amount of adhesion is 0.10 to 0.50 μm in terms of arithmetic mean roughness Ra as defined in JIS B0601:2013.

6. A method for manufacturing DI cans using the film-laminated steel sheet according to any one of claims 1 to 5, comprising: positioning the film-laminated steel sheet so that the side of the film-laminated steel sheet on which the wax layer is more adhered becomes the outer surface of the DI can, and the side of the film-laminated steel sheet on which the wax layer is less adhered becomes the inner surface of the DI can; and subjecting the film-laminated steel sheet to DI forming.

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