Manufacturing method for film-laminated steel sheets and DI cans

Abstract

To further improve ironing formability while maintaining punch-release properties during DI molding. The film-laminated steel sheet according to the present invention comprises a steel sheet as a base material, film layers made of thermoplastic polyester films provided on the front and back surfaces of the steel sheet, and a wax layer provided on the film layer, and the wax layer has a deposition amount of 0.030 to 0.120 g / m per side. 2 and the wax layer has a different deposition amount on the front and back surfaces of the steel plate, and the deposition amount ratio obtained by dividing the wax layer deposition amount on the surface with a larger deposition amount by the wax layer deposition amount on the surface with a smaller deposition amount is within the range of 1.04 to 1.67.

Description

Technical Field

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

Background Art

[0002] In recent years, as cans used for food, mainly paper-wound cans and distortion-printed cans are often used. Particularly in the case of distortion-printed cans, since it is important that the printed pattern is not distorted during forming, the can height is set relatively low, and as forming methods, drawn (DR) forming and drawing and redrawing (DRD) forming are often used. On the other hand, since there is no need to print on the outer surface of the can body of a paper-wound can, in recent years, drawing and ironing (DI) forming, which is more productive, is often adopted.

[0003] DI forming is a forming method in which the wall thickness of a can is reduced to about 40 to 60% of the thickness of the steel sheet used as a raw material by ironing the part corresponding to the can wall of a cup obtained by draw-forming a steel sheet, and the can height is increased. DI forming is characterized in that the amount of deformation in the thickness direction and the can height direction of the steel sheet is very large and the forming speed is fast compared with DRD forming, and the temperature of the steel sheet during forming rises to nearly 200°C. Therefore, for example, in the DI forming of tinplate, which is a kind of tin-plated steel sheet, a coolant containing a lubricant 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 step of washing and removing the coolant from the formed DI can and drying the washed DI can is required. Also, as one of the manufacturing facilities, a processing facility for such a coolant is required.

[0004] On the one hand, in the manufacturing process of laminated steel sheets, wax can be applied to the film surface of film-laminated steel sheets. Therefore, when manufacturing cans using film-laminated steel sheets, it is not necessary to apply a lubricant during forming, and the lubricant cleaning and drying process, as well as the lubricant treatment equipment, can be omitted. Due to such advantages, film-laminated steel sheets have been widely used in DRD food cans in recent years.

[0005] However, when applying film-laminated steel sheets to forming processes such as DI forming where the can body is squeezed at high speed, the temperature of the steel sheet rises during forming, resulting in softening of the film. As a result, the film is likely to be shaved off, and the probability of the can bursting during forming increases. In addition, due to the softening of the film, the film on the inner surface of the can adheres to the punch used during processing, making it difficult to remove the punch when pulling it out, that is, the punch removal property deteriorates. When the punch removal property deteriorates, the can end buckles and bites into the space between the punch and the stopper, and the can body is also likely to buckle. In this case, the can-making machine must be stopped to remove the can with the can end biting into the space between the punch and the stopper, resulting in a significant decrease in productivity. From this perspective, various film-laminated steel sheets that can be used for DI forming have been proposed.

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

[0007] In addition, in Patent Document 2 below, projections with a height of 2 to 10 μm and a circular equivalent diameter d of 0.010 to 0.10 mm are formed at 15 or more per mm on the film surface, and air or an inert gas is present between the resin film directly under the projections and the steel sheet. There is disclosed a laminated steel sheet for containers excellent in punching and drawing can manufacturing workability. 2

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, in order to improve the ironing formability of the film-laminated steel sheet, conventionally, unevenness has been provided on the film surface to reduce the contact area and reduce friction. However, as described above, as a result of the high temperature of the steel sheet during continuous high-speed DI forming, even when using the laminated steel sheets disclosed in Patent Document 1 and Patent Document 2, there is still room for improvement from the viewpoint of achieving both ironing formability and punch-through resistance.

[0010] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a film-laminated steel sheet capable of further improving the ironing formability while maintaining the punch-through resistance during DI forming, and a method for manufacturing a DI can using such a film-laminated steel sheet.

Means for Solving the Problems

[0011] ​In order to solve the above problems, as a result of intensive studies by the present inventors, by optimizing the balance between the slidability on the side that becomes the inner surface of the can of the film-laminated steel sheet and the slidability on the side that becomes the outer surface of the can, while maintaining the punch-through property during DI forming, Furthermore, the idea was to further improve the ironing formability. The gist of the present invention completed based on the above idea is as follows. In the following description, the notation "(numerical value A) to (numerical value B)" means "(numerical value A) or more and (numerical value B) or less".

[0012] (1) It has a steel sheet as a base material, a film layer composed 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, and the adhesion amount of the wax layer is On one side of the steel sheet, it is in the range of 0.050 to 0.120 g / m 2 and on the other side of the steel sheet, it is in the range of 0.030 to 0.120 g / m 2 and Moreover, the adhesion amount of the wax layer is different 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 the larger adhesion amount by the adhesion amount of the wax layer on the side with the smaller adhesion amount is within the range of 1.04 to 1.67. Film-laminated steel sheet. (2) The melting point of the thermoplastic polyester film constituting the film layer on the side with the larger adhesion amount is 215°C or higher and less than 255°C, and the melting point of the thermoplastic polyester film constituting the film layer on the side with the smaller adhesion amount is 220 to 260°C, and the melting point of the thermoplastic polyester film on the side with the smaller adhesion amount is 5°C or higher than the melting point of the thermoplastic polyester film on the side with the larger adhesion amount. The film-laminated steel sheet according to (1). (3) The penetration of the wax constituting the wax layer as defined in JIS K2235:2022 is 5 to 20 at a test temperature of 25°C, and the melting point of the wax is 50.0 to 70.0°C. The film-laminated steel sheet according to (1) or (2). (4) The thickness of the film layer on the side with the larger adhesion amount is 12 to 40 μm. (1) or (2) The film-laminated steel sheet according to the above. (5) The thickness of the film layer on the side with the larger adhesion amount is 12 to 40 μm. The film-laminated steel sheet according to (3). ( 6 ) The surface roughness of the steel sheet on the side with a large amount of adhesion is an arithmetic mean roughness Ra defined in JIS B0601:2013 and is 0.10 to 0.50 μm. (1) or (2) The film-laminated steel sheet according to (7) The surface roughness of the steel sheet on the side with the larger adhesion amount is the arithmetic mean roughness Ra defined in JIS B0601:2013 and is 0.10 to 0.50 μm. The film-laminated steel sheet according to (3). (8) The surface roughness of the steel sheet on the side with the larger adhesion amount is the arithmetic mean roughness Ra defined in JIS B0601:2013 and is 0.10 to 0.50 μm. The film-laminated steel sheet according to (4). ( 9 )(1) or (2) A method for manufacturing a DI can using the film-laminated steel sheet according to

Effect of the Invention

[0013] As described above, according to the present invention, while maintaining the punch-through property during DI forming, it is further possible to further improve the ironing formability. As a result, it is possible to improve the high-speed formability of the DI can without reducing the productivity of the DI can.

Brief Description of the Drawings

[0014]

Figure 1

Mode for Carrying Out the Invention

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

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

[0017] The film-laminated steel sheet according to the present embodiment is used as a material for DI cans. As shown in FIG. 1, the film-laminated steel sheet 1 according to the present embodiment includes a base steel sheet 10 serving as a 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 the present embodiment, as will be described in detail below, the amount of wax adhered in the wax layer 31 and the amount of wax adhered in the wax layer 32 are different. In FIG. 1, a case where the amount of wax adhered in the wax layer 32 is larger than the amount of wax adhered in the wax layer 31 is illustrated as an example.

[0019] The difference in the amount of wax adhered in the wax layers 31 and 32 as described above is important when manufacturing a DI can using such a film-laminated steel sheet 1 as a material. Although the details will be described again below, when manufacturing a DI can using the film-laminated steel sheet 1 according to the present embodiment, the film-laminated steel sheet 1 is arranged so that the wax layer on the side with less wax adhesion is located on the side that becomes 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 arranged in the forming device such that the surface on the side where the wax layer 31 exists becomes the outer surface side of the DI can, and the surface on the side where the wax layer 32 exists becomes the inner surface side of the DI can.

[0020] Here, in the following description, for the sake of convenience, the film layer located on the side that becomes the outer surface of the DI can is referred to as the "outer can surface side film layer", and the wax layer located on the side that becomes the outer surface of the can is referred to as the "outer can surface side wax layer". Similarly, in the following description, for the sake of convenience, the film layer located on the side that becomes the inner surface of the DI can is referred to as the "inner can surface side film layer", and the wax layer located on the side that becomes the inner surface of the can is referred to as the "inner can surface side wax layer".

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

[0022] <<Regarding the base steel plate 10>> In the film laminate steel plate 1 according to the present embodiment, as the base steel plate 10, various known steel plates for cans for drawing forming can be used.

[0023] Among such steel plates for cans for drawing forming, those having an r value of 0.95 or more and an absolute value of the Δr value of 0.50 or less are preferably used as the base steel plate 10. By using such a steel plate for cans, it is possible to further improve the DI formability of the film laminate steel plate 1 according to the present embodiment.

[0024] Ironing forming is a forming method that reduces the wall thickness of a can by ironing the can wall of a substantially cylindrical cup. Therefore, if there is variation in the wall thickness of the can wall of the cup, the ironing resistance of the thicker part of the wall thickness increases, and the can wall part may be easily broken during ironing forming. By setting the r-value of the steel sheet used as the base material steel plate 10 to 0.95 or more, it is possible to suppress the variation in the wall thickness of the can wall in the height direction of the cup and prevent the can wall part from breaking during ironing forming. The r-value of the steel sheet used as the base material steel plate 10 is more preferably 1.05 or more. On the other hand, the upper limit value of the r-value of the steel sheet used as the base material steel plate 10 is not particularly defined, but substantially about 1.20 is the upper limit value.

[0025] Also, by setting the absolute value of the △r-value to 0.50 or less (that is, -0.50 ≦ △r ≦ +0.50), it is possible to suppress the variation in the wall thickness of the can wall in the circumferential direction of the cup and prevent the can wall part from breaking during ironing forming. The absolute value of the △r-value of the steel sheet used as the base material steel plate 10 is more preferably 0.33 or less. Note that the lower limit value of the △r-value of the steel sheet used as the base material steel plate 10 is not particularly defined, and the lower it is, the better, and zero is most preferable.

[0026] The above r-value and △r-value are defined in JIS Z2254:2021 and can be measured according to JIS Z2254:2021. The r-value is also called the plastic strain ratio and the R-value. The initial gauge length, width of the parallel part, and thickness of the tensile test piece defined in JIS Z2254:2021 are denoted as L0, W0, and T0 respectively. When the above dimensions after tensile deformation in the range where no necking occurs change to L, W, and T respectively, and L0×W0×T0 = L×W×T, it is a value defined by the following formula. r = ln(W0 / W) / ln(T0 / T) = ln(W0 / W) / ln(LW / L0W0)

[0027] In addition, the Δr value is an index indicating in-plane anisotropy. When the angle formed by the tensile direction of the above tensile test piece and the rolling direction of the material is θ, the r value is denoted as r θ and is defined by the following formula when the deformation characteristics in each direction are measured by changing θ. Here, in the following formula, r0, r 45 , r 90 are the r values at angles corresponding to 0°, 45°, and 90° with respect to the material rolling direction, respectively. Δr = (r0 - 2 × r 45 + r 90 ) / 2

[0028] In addition, when the steel plate used as the base material steel plate 10 is hard, the elongation of the steel plate during forming is small, so the can body is likely to break during forming. In addition, the calorific value of the steel plate during ironing forming increases, and the film layer described later is likely to soften due to heat. Therefore, when forming a DI can with a high ironing rate, it is particularly preferable to use a one-rolled material with a tempering degree of T3 or less as the base material steel plate 。

[0029] In addition, in a DI can, when the adhesive strength between the base material steel plate and the film layer is low, the film layer may peel off during ironing forming. Therefore, in the film laminate steel plate 1 according to the present embodiment, it is more preferable that the adhesion between the base material steel plate 10 and the film layer is high. Specifically, a test piece with a width of 15 mm × a height of 50 mm is taken from an arbitrary position of the film laminate steel plate 1 to be focused on, and when one of the film layers of the test piece is peeled off at 180° at 20 mm / min, the peel strength is preferably 10 N / 15 mm or more. Such peel strength is more preferably 15 N / 15 mm or more. On the other hand, the higher such peel strength is, the better, and the upper limit value is not particularly defined.

[0030] As described in detail below, the film layer in the film laminate steel sheet 1 according to the present embodiment is made of a thermoplastic polyester. Examples of steel sheets having excellent adhesion to polyester include chromium-based tin-free steel ECCS (Electrolytic Chromium Coated Steel) and chromium-free type 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 sequentially formed on the front and back surfaces of the steel sheet as a base material. Since the surface of such tin-free steel easily forms hydrogen bonds with the hydroxyl groups and carbonyl groups of the polyester resin, the adhesion between the film layer can be improved.

[0032] In addition, the surface of a chromium-free type tin-free steel sheet, which is composed of one or more elements selected from Zr, Al, Si, P, Ti, Ce, and W, O, and inevitable components, and forms a chromium-free film on the front and back surfaces of the steel sheet, preferably has hydroxyl groups. By forming hydrogen bonds between such hydroxyl groups and the hydroxyl groups and carbonyl groups of the polyester resin, the adhesion between the film layer can be improved.

[0033] In addition to the chromium-based tin-free steel and the chromium-free type tin-free steel as described above, examples of the base steel sheet 10 include a tin plate obtained by subjecting an electrolytic Sn-plated steel sheet to a chromate treatment, and a chromium-free tin plate having a chromium-free film as described above on an electrolytic Sn-plated steel sheet.

[0034] By using the steel sheet as described above as the base steel sheet 10, the adhesion with the film layer is improved, and it becomes easier to realize the peel strength as described above.

[0035] [Thickness of the base steel sheet] In the film laminate steel sheet 1 according to this embodiment, regarding the thickness of the base material steel sheet 10 as described above (the thickness d in FIG. 1 M ), there is no particular limitation as long as it can achieve the desired wall thickness of the can body after DI forming. The thickness of the base material steel sheet 10 may be, for example, about 0.15 to 0.26 mm.

[0036] In addition, in order to measure the thickness of the base material steel sheet as described above from the state of the already manufactured film laminate steel sheet 1, the following may be done. That is, the film laminate steel sheet is immersed in boiling hydrogen peroxide water to peel off the film (usually the film peels off within 30 minutes), and the thickness of the base material steel sheet after the film peels off may be measured with a micrometer.

[0037] [Surface roughness of the base material steel sheet] In general deep drawing forming, it is preferable that the surface roughness of the film of the laminate steel sheet is somewhat large and the state where the die surface and the film convex surface are in point contact has lower sliding resistance. However, in the case of DI forming focused on in this embodiment, even if the surface roughness of the film layer is increased, the film softens due to the increase in the steel sheet temperature during drawing and ironing forming, and the unevenness on the surface of the film layer is crushed. Therefore, regarding the sliding resistance during DI forming, it can be said that the influence of the surface roughness of the base material steel sheet 10 is greater than that of the surface roughness of the film layer.

[0038] Normally, in DI forming, after arranging ironing dies in multiple stages, the steel sheet used as a material is formed into a desired shape. When a film laminate steel sheet with too small a surface roughness of the base material steel sheet is DI formed, the surface of the film layer is smoothed when passing through the first-stage ironing die, and at the same time, the wax accumulated in the depressions caused by the concave portions of the base material steel sheet is also likely to fall off. As a result, when passing through the ironing dies in the second stage and later, the slidability of the film laminate steel sheet may decrease, and there is a possibility that the film layer is easily shaved.

[0039] On the other hand, when DI forming a film-laminated steel sheet with a surface roughness of the base steel sheet being too large, if the film layer softens due to heat generation of the steel sheet when passing through the first-stage pressing die, pinholes are likely to occur in the film layer existing on the convex portions of the base steel sheet.

[0040] The peeling of the film layer and the generation of pinholes in the film layer as described above are events related to the drawability during high-speed forming of DI cans, and both can occur in the can outer surface side film layer 21 shown in FIG. 1. Therefore, in the film-laminated steel sheet 1 according to the present embodiment, on the surface of the base steel sheet 10 on the side that becomes the can outer surface of the DI can (that is, the surface on the side where the can outer surface side film layer 21 is provided), the surface roughness is preferably 0.10 to 0.50 μm in terms of the arithmetic mean roughness Ra defined in JIS B0601:2013. By setting the surface roughness of the base steel sheet 10 on the side that becomes the can outer surface to be 0.10 to 0.50 μm in terms of Ra, it becomes possible to prevent peeling of the film and generation of pinholes even when performing DI forming at high speed. The surface roughness of the base steel sheet 10 on the side that becomes the can outer surface is more preferably 0.10 μm or more in terms of Ra. Also, the surface roughness of the base steel sheet 10 on the side that becomes the can outer surface is more preferably 0.30 μm or less in terms of Ra.

[0041] Further, in the film-laminated steel sheet 1 according to the present embodiment, when the surface roughness of the base steel sheet 10 on the side that becomes the can outer surface is 0.10 to 0.50 μm in terms of Ra and the thickness of the can outer surface side film layer 21, which will be described in detail below, is 12 to 40 μm, it becomes possible to further prevent peeling of the film and generation of pinholes as described above, and also to prevent the occurrence of pressing flaws in the can outer surface side film layer 21, which is even more preferable.

[0042] The surface roughness of the base material steel plate 10 as described above can be measured using a commercially available surface roughness meter (for example, SURFCOM 570A, a surface roughness and shape measuring machine manufactured by Tokyo Seimitsu Co., Ltd.) compliant with JIS B0601:2013. More specifically, from the film laminate steel plate 1 of interest, after peeling the wax layer and the film layer by immersion treatment using boiling hydrogen peroxide water to expose the base material steel plate 10, a measurement sample with a size of 200 mm × 200 mm is collected from an arbitrary location on the surface of the base material steel plate 10. Then, for any three locations of such a measurement sample, measurements are taken three times each along the rolling direction of the base material steel plate 10 and the direction orthogonal to the rolling direction, respectively. The average value of the measurement values obtained in this way may be taken as the surface roughness of the base material steel plate 10.

[0043] ≪Regarding the film layer≫ Subsequently, the film layer included in the film laminate steel plate 1 according to this embodiment will be described in detail.

[0044] In the film laminate steel plate 1 according to this embodiment, the film layer is a layer provided on the front and back surfaces of the base material steel plate 10, and is composed of a thermoplastic polyester film. Note that the above-mentioned "thermoplastic polyester" means "a thermoplastic polymer compound having an ester bond (-COO-).

[0045] [Regarding the melting point of the thermoplastic polyester constituting the film layer] ◇Film layer 21 on the outer surface side of the can As described above, when manufacturing a can by continuously subjecting a laminated steel sheet to DI forming, the temperature of the steel sheet rises to about 200°C at maximum. Therefore, if the melting point of the film layer on the side that becomes the outer surface of the can is low, the film softens during ironing forming and is easily scraped off. For this reason, the thermoplastic polyester film that constitutes the film layer on the side that becomes the outer surface of the can of the film-laminated steel sheet 1 (the film layer 21 on the outer surface side of the can in Fig. 1) is preferably a thermoplastic film that does not soften even at around 200°C. If the melting point is 215°C or higher, even when the temperature of the steel sheet reaches 200°C, the degree of film softening is small, and it becomes possible to suppress the occurrence of film scraping. From such a viewpoint, in the film-laminated steel sheet 1 according to the present embodiment, the melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can is preferably 215°C or higher. The melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can 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, when the melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can exceeds 260°C, the deformation resistance of the film is large in a state where the mold temperature is still low immediately after the start of DI forming, and the film may tear at portions where the bending strain is large, such as the punch shoulder and the ring processing portion of the can bottom. By setting the melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can to 260°C or lower, it becomes possible to prevent such tearing of the film, which is preferable. Further, as will be described below, the melting point of the thermoplastic polyester film that constitutes the film layer 22 on the inner surface side of the can is preferably 5°C or higher than the melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can. Considering such a difference in melting point, the melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can is preferably less than 255°C. The melting point of the thermoplastic polyester film that constitutes the film layer 21 on the outer surface side of the can is more preferably 240°C or lower, and even more preferably 235°C or lower.

[0047] ◇Film layer 22 on the inner surface side of the can Regarding the side that becomes the inner surface of the can of the film-laminated steel sheet 1, when the temperature of the steel sheet rises and the film layer softens, the film is likely to be adsorbed by the punch, resulting in a decrease in the punch-through property. As a result of the punch becoming difficult to pass through, the end of the can may be caught by the stopper provided in the mold, and the end of the can may be deformed. However, if the degree of softening of the film is smaller than that of the film layer on the outer surface side of the can, when the punch is pulled out, relatively, the slipperiness on the inner surface side of the can is better than that on the outer surface side of the can. From such a viewpoint, the melting point of the thermoplastic polyester film constituting the film layer on the inner surface side of the can of the film-laminated steel sheet 1 (that is, the film layer 22 on the inner surface side of the can in FIG. 1) is preferably higher than the melting point of the thermoplastic polyester film constituting the film layer 21 on the outer surface side of the can.

[0048] As a result of the inventors conducting detailed studies based on the above idea, it was found that when the melting point of the thermoplastic polyester film constituting the film layer 22 on the inner surface side of the can is 5°C or more higher than the melting point of the thermoplastic polyester film constituting the film layer 21 on the outer surface side of the can, the punch-through property becomes good.

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

[0050] On the other hand, in the film-laminated steel sheet 1, when the melting point of the thermoplastic polyester film constituting the inner can surface film layer 22 exceeds 260°C, similar to the case of the outer can surface film layer 21, the deformation resistance of the film is large when the mold temperature is still low immediately after the start of DI forming, and the film may be torn at portions where the bending strain is large, such as the punch shoulder and the ring processed portion of the can bottom. By setting the melting point of the thermoplastic polyester film constituting the inner can surface film layer 22 to 260°C or lower, it becomes possible to prevent such tearing of the film, which is preferable. The melting point of the thermoplastic polyester film constituting the inner can surface film layer 22 is more preferably 255°C or lower, and even more preferably 250°C or lower.

[0051] As described above, in the inner can surface film layer 22 according to the present embodiment, it is within the range of 220 to 260°C, and it is preferable to use a thermoplastic polyester film having a melting point that is 5°C or higher than the melting point of the thermoplastic polyester film constituting the outer can surface film layer 21. The difference in the melting points of the thermoplastic polyester films between the inner can surface side and the outer can surface side is more preferably 10°C or higher, and even more preferably 15°C or higher. Note that the upper limit value of the difference in the melting points of the thermoplastic polyester films between the inner can surface side and the outer can surface side is not particularly defined, but substantially about 30°C is the upper limit.

[0052] Here, in order to determine whether a polyester film is used as the film layer in the film-laminated steel sheet 1 from the state of the already manufactured film-laminated steel sheet 1, a sample may be taken from an arbitrary portion of the film layer in the film-laminated steel sheet 1 of interest, and the obtained sample may be analyzed, for example, by Fourier transform infrared spectroscopy (FT-IR). In such an analysis result, when a result indicating the presence of an ester bond is obtained, it can be determined that the film layer of interest is composed of a polyester film. Also, by checking whether the obtained sample softens when heated, it is possible to determine whether the resin constituting the film layer of interest is thermoplastic.

[0053] Also, regarding the melting point of the thermoplastic polyester film as described above, about 5 to 10 mg of samples may be collected from any location of the film layer in the target film-laminated steel sheet 1, and the obtained samples may be analyzed by differential scanning calorimetry (DSC), and the temperature giving the main endothermic peak may be confirmed from the analysis results. For example, using a commercially available differential scanning calorimeter (for example, DSC7030 manufactured by Hitachi High-Technologies Corporation), the obtained samples may be sealed in an aluminum pan and measured in the range of 50 to 350 °C at a heating rate of 10 °C / min.

[0054] [Regarding the details of the thermoplastic polyester film] In the film-laminated steel sheet 1 according to the present embodiment, the thermoplastic polyester film used for the film layer is preferably a film that does not elute resin components or adsorb flavor components into the contained food contents even when the can body is formed, baked, or retorted.

[0055] Also, the elongation of the thermoplastic polyester film used for the film layer is preferably 100% or more when the film is alone. When the elongation of the film is 100% or more when the film is alone, breakage of the film layer when the film-laminated steel sheet 1 is DI-formed can be further prevented.

[0056] ◇Film layer 21 on the outer surface side of the can In the film-laminated steel sheet 1 according to the present embodiment, in addition to the characteristics to the food contents and the elongation of the film as described above, the melting point of the thermoplastic polyester film constituting the film layer 21 on the outer surface side of the can is preferably 215 °C or higher as described above.

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

[0058] In particular, in the case of a copolymer resin of butylene terephthalate and ethylene terephthalate and / or polyethylene isophthalate terephthalate, it is particularly preferable that the polybutylene terephthalate is contained in an amount equivalent to 50% by mass or more. Further, in the case of a blend resin of polybutylene terephthalate resin and polyethylene terephthalate resin and / or polyethylene isophthalate terephthalate resin, it is particularly preferable that the polybutylene terephthalate resin is contained in an amount of 50% by mass or more, because it is easy to stretch and has a high breaking strength.

[0059] ◇Inner film layer 22 on the can inner surface side In the film-laminated steel sheet 1 according to the present embodiment, the thermoplastic polyester film constituting the inner film layer 22 on the can inner surface side preferably has a melting point that is 5°C or higher than the melting point of the thermoplastic polyester film constituting the outer film layer 21 on the can outer surface side, in addition to the characteristics with respect to the food content and the elongation of the film 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, a blend resin of polyethylene terephthalate resin and polyethylene terephthalate isophthalate copolymer resin, a blend resin of polyethylene terephthalate and polybutylene terephthalate resin, a blend resin of polyethylene terephthalate isophthalate copolymer resin and polyethylene terephthalate butylene terephthalate copolymer resin, a stretched film or an unstretched film of a blend resin of the above resins, and the like.

[0061] In the film-laminated steel sheet 1 according to the present embodiment, the thermoplastic polyester film used for the film layer may be a stretched film or an unstretched film. However, since it is better to pay attention to the elongation of the film in DI molding, when using a stretched film, the stretching ratio is preferably 3 or less.

[0062] Also, within the range that satisfies the above characteristics, the film used for the film-laminated steel sheet 1 may be a multi-layer film of 2 to 3 layers.

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

[0064] The elongation of the thermoplastic polyester film as described above can be specified by measuring in accordance with JIS K7161-1:2014 and JIS K7127:1999. Specifically, after removing the wax layer of the film-laminated steel sheet 1 of interest with hexane, a tensile test piece may be sampled from an arbitrary location of the film layer in accordance with the above standards. The obtained tensile test piece may be set on a tensile testing machine and a tensile test may be performed at a measurement temperature of 23 to 25°C.

[0065] [Regarding the thickness of the film layer] ◇Film layer 21 on the outer surface of the can In the DI forming that is focused on in the present embodiment, the film layer (i.e., the film layer 21 on the outer surface of the can) on the side that becomes the outer surface of the film-laminated steel sheet 1 is subjected to a strong shearing force particularly by ironing forming. Therefore, when the thickness of the film layer 21 on the outer surface of the can is too thin, the surface of the film layer may be scraped, and pinholes are likely to occur. On the other hand, when the thickness of the film layer 21 on the outer surface of the can is too thick, the film may shear and shift when passing through the ironing die, resulting in the surface of the film layer being scraped, and it is likely that pressing defects and streak-like defects due to the generated scrap will be formed.

[0066] According to the detailed study by the present inventors, when the thickness of the film layer 21 on the outer surface of the film-laminated steel sheet 1 (the thickness d in FIG. 1 Fo ) is 12 μm or more, it has been clarified that even if a strong shearing force is applied to the surface of the film layer in DI forming, the generation of pinholes can be more suppressed. The thickness of the film layer 21 on the outer surface of the can is more preferably 15 μm or more.

[0067] On the other hand, according to the detailed study by the present inventors, when the thickness of the film layer 21 on the outer surface of the film-laminated steel sheet 1 is 40 μm or less, it is possible to prevent the film layer from being scraped when passing through the ironing die, and it has been clarified that the formation of pressing defects and streak-like defects can be more suppressed. The thickness of the film layer 21 on the outer surface of the can is more preferably 35 μm or less.

[0068] ◇Film layer 22 on the inner surface of the can In the film-laminated steel sheet 1 according to the present embodiment, the thickness of the film layer (i.e., the film layer 22 on the inner surface of the can) on the side that becomes the inner surface of the can may be appropriately set to a thickness that can obtain sufficient retort corrosion resistance according to the corrosiveness of the can contents. For example, for contents such as general boiling in water or oil immersion where the pH is not a low value, the thickness of the film layer 22 on the inner surface of the can (the thickness d in FIG. 1 FiBy setting [[ID=]] to 10 μm or more, good retort corrosion resistance can be obtained. Also, since canned contents with a low pH value exhibit strong corrosiveness, it is preferable to make the thickness of the film layer 22 on the inner surface side of the can as thick as possible. For example, by setting the thickness of the film layer 22 on the inner surface side of the can to 20 μm or more, it becomes possible to ensure good retort corrosion resistance even when containing canned contents with strong corrosiveness.

[0069] However, when the thickness of the film layer 22 on the inner surface side of the can exceeds 100 μm, the film may adhere tightly to the punch during DI forming, making it difficult to slide, and there is a possibility that the punch-through property may deteriorate. Therefore, by setting the thickness of the film layer 22 on the inner surface side of the can to 100 μm or less, it becomes possible to suppress the deterioration of the punch-through property while ensuring good retort corrosion resistance. The thickness of the film layer 22 on the inner surface side of the can is more preferably 50 μm or less.

[0070] In addition, in order to measure the thickness of the film layer as described above from the state of the already manufactured film laminate steel sheet 1, the following may be done. First, a plurality of sample pieces with a size of 100 × 100 mm are collected from an arbitrary position of the sheet-like or coil-like film laminate steel sheet 1. When measuring the thickness of the film layer 21 on the outer surface side of the can for the obtained sample pieces, first, after shaving the side of the film layer 22 on the inner surface side of the can with sandpaper or the like, the film laminate steel sheet 1 is immersed in hydrochloric acid of 17% to 35% to dissolve the base steel sheet, and only the film layer 21 on the outer surface side of the can is peeled and extracted. Then, the thickness of the film layer 21 on the outer surface side of the can may be measured at three arbitrary points using a micrometer while changing the position. The average value of the three obtained measurement values is taken as the thickness of the film layer 21 on the outer surface side of the can. Also, when measuring the thickness of the film layer 22 on the inner surface side of the can, for the obtained sample pieces, after shaving the side of the film layer 21 on the outer surface side of the can with sandpaper or the like, the film laminate steel sheet 1 is immersed in hydrochloric acid of 17% to 35% to dissolve the base steel sheet, and only the film layer 22 on the inner surface side of the can is peeled and extracted. Then, the thickness of the film layer 22 on the inner surface side of the can may be measured at three arbitrary points using a micrometer while changing the position. The average value of the three obtained measurement values is taken as the thickness of the film layer 22 on the inner surface side of the can.

[0071] <<Regarding the wax layer>> Next, the wax layer included in the film laminate steel sheet 1 according to the present embodiment will be described in detail.

[0072] As schematically shown in FIG. 1, the wax layer in the film laminate steel sheet 1 according to the present embodiment is a layer provided on the film layer as described above.

[0073] [Regarding the deposition amount of the wax layer] In the film laminate steel sheet 1 according to the present embodiment, the deposition amount of the wax layer has a great influence not only on the shaving and chipping of the film layer 21 on the outer surface side of the can during DI forming, but also on the ironing formability. Therefore, in order to maintain the punch-through property during DI forming and further improve the ironing formability, the deposition amount of the wax layer is an extremely important factor.

[0074] The wax layers provided on the inner surface side and the outer surface side of the can of the film laminate steel sheet 1 melt as the temperature of the steel sheet rises due to DI forming, and a lubricating film is formed on the surface of the laminate steel sheet (which can also be regarded as the surface of the film layer according to the present embodiment), thereby imparting good lubricity to the laminate steel sheet. Further, after the DI forming is completed, the wax that has melted during the DI forming may solidify again and remain on the surface of the film layer.

[0075] In the film laminate steel sheet 1 according to the present embodiment, the deposition amount of the wax layer is in the range of 0.030 to 0.120 g / m per side 2 and the deposition amount of the wax layer is different between the front side and the back side of the steel sheet. Note that the value of 0.030 g / m of the deposition amount per side 2 corresponds to the minimum value of the deposition amount of the wax layer on the side with less deposition amount, and the value of 0.120 g / m of the deposition amount per side 2 corresponds to the maximum value of the deposition amount of the wax layer on the side with more deposition amount.

[0076] Hereinafter, the adhesion amount of the outer can surface wax layer 31 and the adhesion amount of the inner can surface wax layer 32 will be described in detail respectively.

[0077] ◇ Outer can surface wax layer 31 In the film-laminated steel sheet 1 according to the present embodiment, the adhesion amount of the outer can surface wax layer 31 is more than the value of 0.030 g / m 2 mentioned above, and is 0.050 g / m 2 or more. When the adhesion amount of the outer can surface wax layer 31 is less than 0.050 g / m 2 , the frictional force during ironing forming becomes large, and there is a possibility that the film layer may be shaved or chipped at the ironed forming portion of the outer can surface, which is not preferable. By setting the adhesion amount of the outer can surface wax layer 31 to 0.050 g / m 2 or more, an increase in the frictional force during ironing forming can be suppressed, and shaving or chipping of the film layer at the ironed forming portion of the outer can surface can be prevented. The adhesion amount of the outer can surface wax layer 31 is preferably 0.060 g / m 2 or more, and more preferably 0.080 g / m 2 or more.

[0078] On the other hand, in the film-laminated steel sheet 1 according to the present embodiment, the adhesion amount of the outer can surface wax layer 31 is 0.120 g / m 2 or less. When the adhesion amount of the outer can surface wax layer 31 exceeds 0.120 g / m 2 , extra wax accumulates in the gap of the ironing die, and streaks or pressing marks are likely to be attached to the surface of the film layer at the portion where the wax accumulates thickly, which is not preferable. By setting the adhesion amount of the outer can surface wax layer 31 to 0.120 g / m 2 or less, the generation of streaks and pressing marks on the surface of the film layer can be prevented. The adhesion amount of the outer can surface wax layer 31 is preferably 0.110 g / m 2 or less, and more preferably 0.100 g / m 2 or less.

[0079] ◇ Inner can surface wax layer 32 Regarding the adhesion amount of the inner can surface wax layer 32 in the film-laminated steel sheet 1 according to the present embodiment, the present inventors have obtained the following findings. That is, during DI forming, if the slipperiness on the inner can surface is too good compared to the slipperiness on the outer can surface, the punch is likely to slip, and distortion concentrates and breaks at the portion where the punch shoulder of the can bottom hits, so-called "punch shoulder breakage" is likely to occur, which is not preferable.

[0080] On the other hand, during DI forming, if the slipperiness on the inner can surface is too poor compared to the slipperiness on the outer can surface, when the punch returns from the bottom dead center to the top dead center, it becomes difficult for the can body to come off the punch. As a result, when the punch retracts, the can body retracts together with the punch, and the can end strongly hits the stopper provided on the die side and is likely to be deformed. In some cases, the can body buckles and the can manufacturing has to be interrupted, which is not preferable.

[0081] Based on the above findings, as a result of further studies by the present inventors, the buckling of the can body as described above is likely to occur when the adhesion amount of the inner can surface wax layer 32 is too small compared to the adhesion amount of the outer can surface wax layer 31, and it has been found that the above punch shoulder breakage is more likely to occur as the adhesion amount of the inner can surface wax layer 32 approaches the adhesion amount of the outer can surface wax layer 31.

[0082] As a result of further detailed studies by the present inventors on this point, in the film-laminated steel sheet 1 according to the present embodiment, the adhesion amount of the inner can surface wax layer 32 (that is, the wax layer on the surface with less adhesion amount) is set within the range of 0.60 to 0.96 times the adhesion amount of the outer can surface wax layer 31 (that is, the wax layer on the surface with more adhesion amount), it has been found that can body buckling can be suppressed without reaching punch shoulder breakage. Here, the ratio obtained by dividing the adhesion amount of the wax layer on the surface with more adhesion amount by the adhesion amount of the wax layer on the surface with less adhesion amount is referred to as the "adhesion amount ratio". Then, the above range of 0.60 times to 0.96 times corresponds to the range of 1.04 (≈1.00 / 0.96) to 1.67 (≈1.00 / 0.60) in terms of the adhesion amount ratio.

[0083] Based on the above, in the film-laminated steel sheet 1 according to the present embodiment, the adhesion amount of the wax layer 31 on the outer surface side of the can is in the range of 0.050 to 0.120 g / m 2 within the range, and the adhesion amount of the wax layer 32 on the inner surface side of the can is within the range of 0.60 to 0.96 times the adhesion amount of the wax layer 31 on the outer surface side of the can (in other words, the adhesion amount ratio defined as above is within the range of 1.04 to 1.67). Thereby, in the film-laminated steel sheet 1 according to the present embodiment, while maintaining the punch-through property during DI forming, the ironing formability can be further improved. As a result, in the production of DI cans, further improvement in continuous can-making performance can be achieved.

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

[0085] In order to measure the adhesion amount of the wax layer as described above from the state of the 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 performed.

[0086] First, a plurality of sample pieces, for example, with a size of 200 mm × 200 mm, are collected from an arbitrary position of the sheet-like or coil-like film-laminated steel sheet 1. Then, in order to prevent the elution of wax from the wax layer on the side other than the side of interest, a tape seal is applied to the surface of the wax layer on the side not of interest. Next, a solvent (for example, n-heptane, etc.) capable of dissolving the wax is poured over the surface on the side where the tape seal is not applied to dissolve the wax layer. The poured solvent is collected in an aluminum foil case (for example, foil case S736210, deep mouth, 11 μm thick, mass: about 0.38 g, manufactured by Toyo Aluminum Eco Products Co., Ltd.) whose mass has been previously measured with a precision balance.

[0087] Subsequently, the aluminum foil case containing the solvent in which the wax has dissolved is placed in a constant temperature bath at 100°C for 30 minutes to completely volatilize the solvent. Then, the mass of the aluminum foil case from which the solvent has volatilized is measured with a precision balance. From the mass thus obtained, the mass of the wax can be calculated by subtracting the mass of the aluminum foil case before solvent recovery. By dividing the mass of the wax thus obtained by the area of the sample (converted to units of m 2 ), the adhesion amount of the wax layer on the surface of the side of interest can be specified.

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

[0089] When the penetration of the wax that constitutes the wax layer according to this embodiment is too small, especially at the molding start stage where the mold temperature has not fully risen, since the wax is in a hard state, the wax is likely to fall off in the squeezing molding part, and push marks caused by the generated wax chips are likely to occur. However, by using a wax with a penetration of 5 or more at a test temperature of 25°C, it is possible to prevent the wax from falling off at the molding start stage as described above. Therefore, in the wax layer according to this embodiment, the penetration of the wax that constitutes the wax layer at a test temperature of 25°C is preferably 5 or more. The penetration of the wax at a test temperature of 25°C is more preferably 10 or more.

[0090] On the other hand, if the penetration of the wax that constitutes the wax layer according to this embodiment is too large, it means that the viscosity of the wax is low. In this case, when continuous can manufacturing is carried out and the temperature of the mold increases, the lubricity of the wax decreases, and the film layer is likely to be scratched or chipped. However, by using a wax with a penetration of 20 or less at a test temperature of 25°C, it is possible to prevent the film layer from being scratched or chipped due to the viscosity of the wax as described above. Therefore, in the wax layer according to this embodiment, the penetration of the wax that constitutes the wax layer at a test temperature of 25°C is preferably 20 or less. The penetration of the wax at a test temperature of 25°C is more preferably 15 or less.

[0091] Note that the penetration of the wax as described above can be measured according to the above JIS K2235:2022.

[0092] [Regarding the melting point of the wax] In the wax layer 31 on the outer surface side of the can according to the present embodiment, if the melting point of the wax constituting the wax layer is too low, the melted wax will drip on the outer surface of the can wall during DI molding, and wax stains are likely to occur, which is not preferable. Also, in the wax layer 32 on the inner surface side of the can, if the melting point of the wax constituting the wax layer is too low, it becomes difficult to obtain appropriate lubricity during DI molding, and thus the film layer is likely to be scraped. However, when the melting point of the wax constituting the wax layer is 50.0 °C or higher, it becomes possible to further prevent indentation and wax stains on the outer surface side of the can, and scraping of the film layer on the inner surface side of the can. In the wax layer according to the present 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 wax layer 31 on the outer surface side of the can according to the present embodiment, if the melting point of the wax constituting the wax layer is too high, the wax will adhere and fall off around the squeezing die, and indentation is likely to occur on the surface of the outer surface side of the can, which is not preferable. Also, in the wax layer 32 on the inner surface side of the can, if the melting point of the wax constituting the wax layer is too high, it becomes difficult to obtain appropriate lubricity during DI molding, and thus the film layer is likely to be scraped. However, when the melting point of the wax constituting the wax layer is 70.0 °C or lower, it becomes possible to further prevent indentation on the outer surface side of the can and scraping of the film layer on the inner surface side of the can. In the wax layer according to the present embodiment, the melting point of the wax constituting the wax layer is more preferably 68.0 °C or lower.

[0094] Note that the melting point of the wax constituting the wax layer as described above 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 for the wax layer according to this embodiment is preferably selected in consideration of the removability of the wax after can manufacturing in addition to the above viewpoints. Examples of waxes with good removability of wax after can manufacturing include n-paraffin waxes having 24 to 32 carbon atoms and their urea adducts (for example, various paraffin waxes, candelilla wax, carnauba wax, etc.), micro waxes, mixtures of paraffin wax and micro wax, and the like.

[0096] In the wax layer according to this embodiment, in consideration of the removability of the wax after can manufacturing as described above, it is more preferable to select a wax having an appropriate penetration and melting point from among the waxes shown as specific examples above.

[0097] As described above, the film laminate steel sheet 1 according to this embodiment has been described in detail with reference to FIG. 1.

[0098] (Regarding the manufacturing method of the film laminate steel sheet) Subsequently, an example of the manufacturing method of the film laminate steel sheet 1 according to this embodiment will be described.

[0099] (Preparation of the base steel sheet) First, a steel sheet serving as the base material of the film laminate steel sheet 1 is prepared. Here, the manufacturing method of the steel sheet serving as the base material is not particularly limited, and it can be manufactured by various known methods. Also, in the surface conditioning rolling process when manufacturing the base steel sheet, it is possible to realize a desired surface roughness on the surface of the steel sheet by adjusting the surface roughness of the rolling roll used. Also, it is possible to purchase a commercially available steel sheet having desired characteristics and use it as the base steel sheet.

[0100] (Formation of the film layer) Next, the base steel plate thus obtained is subjected to various pretreatment processes as necessary, such as alkaline degreasing, water washing, pickling, etc., to obtain a clean steel plate surface. Then, a film layer is formed on the front and back surfaces of such a base steel plate using a thermoplastic polyester film.

[0101] Here, regarding the thermoplastic polyester film used for forming the film layer, one having desired properties may be manufactured by oneself based on various known manufacturing methods, or a commercially available one having desired properties may be purchased, or after purchasing a commercially available thermoplastic polyester film, various known treatment methods may be further applied to realize the desired properties.

[0102] Next, regarding the method of forming a film layer on the front and back surfaces of the base steel plate 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, an induction heating (IH) furnace, etc., and then a film is continuously fed from both sides of the steel strip and the film is pressed and fused onto the steel strip using a heat-resistant rubber roll. By using the thermal fusion method, it becomes possible to form a film layer with a more uniform thickness on the front and back surfaces of the base steel plate. At this time, by controlling the heating temperature of the base steel plate, the roughness of the roll surface of the film laminating roll, the temperature and pressing force of the roll surface, the thickness of the film layer and the surface roughness of the film layer can be controlled within a desired range.

[0104] Specifically, it is preferable that the base steel plate is heated to (film melting point + 15°C) or higher, and the surface temperature of the film laminating roll is within the range of not less than the glass transition point (Tg) of the film and not more than (film melting point + 30°C), and not more than (film glass transition point (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 quenched in a water cooling tank within 1 second after lamination in order to suppress spherulitization, which causes embrittlement of the film.

[0107] <Formation of wax layer> Subsequently, a wax layer is formed on the steel sheet on which the film layer has been formed. 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 its melting point to the surface of the film layer in a liquid state, or by preparing a wax solution in which wax is dissolved in a volatile solvent and applying the 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] (Manufacturing method for DI cans using film-laminated steel sheets) 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 can be 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. The film-laminated steel sheet is then subjected to DI forming. The conditions for DI forming are not particularly specified, and the film-laminated steel sheet can be subjected to DI forming under general conditions for DI forming.

[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 during DI forming are both ensured, and ironing formability is further improved. Therefore, DI forming can be performed without a coolant. Furthermore, when DI forming the film-laminated steel sheet 1 according to this embodiment, a coolant used in normal 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-molded can body is trimmed to the desired shape and then flanged up to obtain a DI can. When printing on the can body, the can end of a DI-molded can body is trimmed to the desired shape. Subsequently, the can body is printed using a curved printing machine with letterpress offset printing or flatbed offset printing, and the printing is baked. The can end is then flanged up to obtain a DI can. After filling the produced DI can with the contents, the DI can can be sealed by tightening the lid. [Example]

[0113] The following describes in detail the film-laminated steel sheet and the method for manufacturing DI cans according to this embodiment, using examples. 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 purpose. Therefore, the present invention can adopt various conditions, and all of these are included in the technical features of the present invention.

[0114] <Base material 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 △r = 0.00 to 0.40, on which a metallic chromium layer (adhesion amount: 80 mg / m per side) is applied. 2 ) and chromium hydrate oxide layer (adhesion amount: 10 mg / m per side) 2As shown in Table 1, M1 to M8 have different surface roughnesses of the steel sheets. M7 is a tin-plated steel sheet with a thickness of 0.24 mm, temper = T3, r value = 1.10, and Δr = 0.15. From the steel sheet side, a Sn-Fe alloy layer (Sn content: 1.3 g / m per side) is 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 ) is the so-called tinplate steel sheet (manufactured by Nippon Steel Corporation). M8 is a cold-rolled steel sheet with a thickness of 0.195 mm, temper = T3, r value = 1.00, and △r = 0.45. Zr hydroxide (Zr content: 60 mg / m per side) 2 This 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 both the coil longitudinal direction and the coil width direction using a Tokyo Seiki Co., Ltd. surface roughness and shape measuring instrument, Surfcom 570A. The average of the measurements was taken as the surface roughness Ra of each base steel plate. The results are shown in Table 1.

[0117] [Table 1]

[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 terephthalate dimethyl ester - 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 draw 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 draw 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 draw 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 draw 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 performed using a differential scanning calorimeter (DSC7030, Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min over the range of 50 to 350°C, and the temperature of the main endothermic peak was taken as the melting point of each resin film.

[0123] [Table 2]

[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 feeder, a metal heating hot press for heating the metal sheet, front and back film feeders, heat-resistant rubber laminating rolls (the rubber roll surface temperature was controlled by a metal heating backup roll), and a cooling water tank. Using this device, multiple steel sheets (200 mm wide x 200 mm long) with film layers formed thereon were produced at the levels shown in Tables 4-1 and 4-2 below.

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

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

[0127] Note that the penetration at 25°C of each of the above waxes was measured by an automatic penetration measuring device EX-210ED manufactured by Daiichi Rikagaku Co., Ltd. Also, the melting point of each of the above waxes was measured using 5 to 8 mg of a sample collected from each wax, in the same manner as for the resin film, with a differential scanning calorimeter (DSC7030 manufactured by Hitachi High-Technologies Corporation). The measurement conditions were a heating 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]

Table 3

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

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

[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 removed, and the opposite surfaces were brought together and resealed 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 removed, producing film-laminated steel sheets with different wax deposition amounts on the front and back surfaces. By repeating this process, 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] <Measuring the amount of wax layer adhesion> The amount of wax layer attached was measured as follows. First, for each level of film-laminated steel sheet (200 mm × 200 mm), the side on which the adhesion amount was not to be measured was sealed with commercially available tape that is insoluble in heptane. The tape sealing covered the side on which the adhesion amount was not to be measured and the side, and also covered the side on which the adhesion amount was to be measured within 5 mm of both ends in both the width and length directions. With this tape sealing, the size of the unsealed area on the side on which the adhesion amount was to be measured 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 thickness, 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 mass was calculated by dividing the resulting wax mass by the wax-applied area (190 mm x 190 mm, excluding the tape seal area).

[0136] The configurations of the film-laminated steel sheets produced as described above are shown in Tables 4-1 and 4-2 below.

[0137] [Table 4-1]

[0138] [Table 4-2]

[0139] <DI缶の成形> Each film-laminated steel sheet produced 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] [DI moldability evaluation] The DI formability was evaluated from the viewpoints of the "degree of can end deformation" and the "degree of cracking and necking at the bottom punch shoulder of the can." 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 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 acceptable.

[0143] [Evaluation of the degree of damage to the film surface on the outer surface of cans in can products] For the canned products produced as described above, the degree of damage to the film surface on the outer side of the can was evaluated by visual inspection of the appearance and by checking for the presence or absence of film pinholes using a pinhole tester. When there were no film flaws or indentation flaws on the film surface on the outer side of the can, the rating was "A". When there were independent minute indentation flaws on the film surface on the outer side of the can, or when, although no flaws were visible on the appearance, there were 5 or more pinhole reactions detected by the pinhole tester, the rating was "B". When there were scratching flaws on the film surface on the outer side of the can, or when indentation flaws causing the steel plate to dent were observed, the rating was determined to be "C". Ratings "A" and "B" were considered passing grades.

[0144] For the detection of pinhole defects using the pinhole tester, a pinhole tester (TRC-250A) manufactured by Sanko Electronics Laboratory Co., Ltd. was used. A carbon brush electrode was attached to the anode side of such a pinhole tester, and the ground side was attached to the part where a part of the film at the end of the can was scraped off with sandpaper, and the entire surface of the can wall was explored with the carbon brush electrode at 500V.

[0145] [Evaluation of the Degree of Damage to the Film Surface on the Inner Side of the Can in Canned Products] For the canned products, the determination of the degree of damage to the film surface on the inner side of the can was evaluated by performing a colored ERV (Enamel Rate Value) test on the canned products produced as described above. The determination was as follows: when there was no colored ERV reaction part on the film surface on the inner side of the can, the rating was "A"; when there were 5 or fewer independent dot-shaped colored ERV reaction parts per can on the film surface on the inner side of the can, the rating was "B"; when there were more than 5 independent dot-shaped colored ERV reaction parts per can, or when there were colored ERV reaction parts in a line - surface shape on the film surface on the inner side of the can, the rating was determined to be "C". Ratings "A" and "B" were considered passing grades.

[0146] The colored ERV test was performed as follows. First, the inner surface of the can was washed with hexane to remove wax, and then the can was filled with ERV test solution (ERV test solution composition: CuSO4·5H2O [50 g / L], NaCl [60 g / L]). Next, the positive electrode of a digital enamel rate meter (Digital Enamellator NDE-1200, manufactured by Nichia Instruments Co., Ltd.) was immersed and the negative electrode was connected to the can. A current of 6.3 V was applied for 15 seconds, depositing copper sulfate crystals on the exposed metal. The film surface on the inner surface of the can was then visually inspected for damage.

[0147] [Table 5-1]

[0148] [Table 5-2]

[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 buckle, 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 this time are illustrative in all respects and not restrictive. The above embodiments may be omitted, substituted, or changed in various forms without departing from the scope of the claims attached hereto and the gist and the configuration belonging to the technical scope of the present invention as described hereinafter. For example, the constituent elements of the above embodiments can be arbitrarily combined within a range not impairing their effects. Further, from such an arbitrary combination, the actions and effects of each of the constituent elements involved in the combination can be naturally obtained, and other actions and other effects obvious to those skilled in the art from the description of this specification can be obtained.

[0152] Also, the effects described in this specification are merely illustrative or exemplary and not limiting. That is, the technology according to the present invention can exhibit other effects obvious to those skilled in the art from the description of this specification, together with or instead of the above effects.

Description of Reference Numerals

[0153] 1 Film-laminated steel sheet 10 Base metal steel sheet 21 Film layer on the outer surface side of the can 22 Film layer on the inner surface side of the can 31 Wax layer on the outer surface side of the can 32 Wax layer on the inner surface side of the can

Claims

1. A steel sheet as a base material, film layers made of a thermoplastic polyester film provided on the front and back surfaces of the steel sheet, a wax layer provided on the film layer, and having, the adhesion amount of the wax layer is in the range of 0.050 to 0.120 g / m2 on one side of the steel sheet, and in the range of 0.030 to 0.120 g / m2 on the other side of the steel sheet, and the adhesion amount of the wax layer is different between the front side and the back side of the steel sheet, A film-laminated steel sheet, wherein the adhesion amount ratio obtained by dividing the adhesion amount of the wax layer on the side with the larger adhesion amount by the adhesion amount of the wax layer on the side with the smaller adhesion amount is in the range of 1.04 to 1.

67.

2. The melting point of the thermoplastic polyester film constituting the film layer on the side with the larger adhesion amount is 215°C or higher and less than 255°C, The melting point of the thermoplastic polyester film constituting the film layer on the side with the smaller adhesion amount is 220 to 260°C, and the melting point of the thermoplastic polyester film on the side with the smaller adhesion amount is 5°C or higher than the melting point of the thermoplastic polyester film on the side with the larger adhesion amount. The film-laminated steel sheet according to Claim 1.

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

4. The thickness of the film layer on the side with the larger adhesion amount is 12 to 40 μm. The film-laminated steel sheet according to Claim 1 or 2.

5. The thickness of the film layer on the side with the larger adhesion amount is 12 to 40 μm. The film-laminated steel sheet according to Claim 3.

6. The surface roughness of the steel sheet on the side with the larger adhesion amount is an arithmetic mean roughness Ra as defined in JIS B0601:2013 and is 0.10 to 0.50 μm. The film-laminated steel sheet according to Claim 1 or 2.

7. The surface roughness of the steel sheet on the side with the larger adhesion amount is an arithmetic mean roughness Ra as defined in JIS B0601:2013 and is 0.10 to 0.50 μm. The film-laminated steel sheet according to Claim 3.

8. The surface roughness of the steel sheet on the side with a larger amount of adhesion is an arithmetic mean roughness Ra defined in JIS B0601:2013 and is 0.10 to 0.50 μm. The film-laminated steel sheet according to claim 4.

9. A method for manufacturing a DI can using the film-laminated steel sheet according to claim 1 or 2, in the film-laminated steel sheet, the surface on the side with a larger amount of adhesion of the wax layer becomes the surface on the outer side of the DI can, and the surface on the side with a smaller amount of adhesion of the wax layer becomes the surface on the inner side of the DI can. The film-laminated steel sheet is arranged so that, A method for manufacturing a DI can, in which DI forming is performed on the film-laminated steel sheet.

Images