JPH04235295A - Steel sheet for di can excellent in printability on the outside face of can and rusting resistance - Google Patents

Abstract

PURPOSE:To offer a steel sheet for a can body manufactured particularly by drawing and ironing and excellent in printing properties and rusting resistance as for a metallic can vessel, particularly for an internal pressure vessel. CONSTITUTION:At least on one face of a steel sheet, two-layer plated films of zinc on the lower layer and of tin on the upper layer are formed, the total of the coating weight of zinc and tin is regulated to >=5.0g/m<2> and the ratio of the coating weight of zinc to the total coating weight is regulated to >=75% to obtain excellent printability on the outside face of a can and rusting resistance. By furtermore eutectically precipitating fluororesin into the zinc plated layer as the lower layer, its DI lubricity can be improved.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to metal can containers, particularly steel plates for internal pressure containers such as containers for beer, carbonated drinks, juice, etc. or aerosol cans, and particularly relates to steel sheets for internal pressure containers such as containers for beer, carbonated drinks, juice, etc.
The objective is to provide a steel plate for can bodies that is manufactured by a method called molding (referred to as molding) and has excellent printability and rust resistance.

0002

[Prior Art] The method for manufacturing DI cans involves obtaining a relatively shallow cup-shaped molded product by drawing twice, and then stretching the side wall of the cup thinly by multi-stage ironing.
The first step is to form it into a long and narrow container. In the second stage, the lubricating oil used during processing is removed, and the subsequent surface treatment for painting and printing (formation of a chemical conversion film) is performed. After that, the third step is to perform external printing and internal painting, and finally neck-in (reducing the diameter of the upper part of the can).
Processing and flanging (edging for sealing the lid) are performed to complete the manufacture of the can body.

Materials for DI cans must have excellent processing lubricity and corrosion resistance, and aluminum and tinplate (tin-plated steel sheets) have been put into practical use. In the case of aluminum, an alloy system containing small amounts of Mn, Mg, Fe, Cu, etc. is used, and in the case of tinplate, a tin-iron alloy layer is not formed, and 2 to 6
Electroplated tin-plated steel sheets with a coating weight of approximately g/m2 are used.

The DI can is used as a container for beer, carbonated drinks, juice, etc. or as an internal pressure container such as an aerosol can, but the amount of processing during DI molding naturally differs depending on the purpose. In the case of aerosol cans, the pressure inside the can is very high;
Since it is necessary to ensure a sufficient thickness of the side wall of the can, the degree of processing of the side wall (reduction rate of plate thickness) is approximately 50 to 60%.
Approximately 70% of containers for beer, carbonated drinks, juice, etc. are processed.

[0005]

[Problem to be Solved by the Invention] In the manufacturing process of such DI cans, printing on the outside of the can is the face of the product, and along with accurate display of contents, it influences the impression of the product and promotes sales promotion. It has important aspects. Therefore, the finished appearance of the outer surface printing is one of the very important performances of a container, and the material also needs to have excellent characteristics.

However, when using tinplate with a steel plate as a substrate, DI
When used as a material for cans, problems with appearance may occur in the finish of external printing. That is, the outer surface of the can after molding was dark, resulting in a poor printing finish, and it was necessary to apply a white paint as a base coat to erase the blackness of the base before printing. The work of undercoating with this white paint was considered to be a very big drawback when using tinplate as a material for DI cans, since it not only caused problems in terms of cost but also hindered productivity.

On the other hand, the bottom of a DI can is designed to have a shape that takes into consideration pressure resistance against the contents and stacking, and has a convex portion on the outside of the can. This part has a disadvantage in that it rubs against other objects during transportation of the can, damages the rust-preventing coating or plating film, and tends to cause red rust. The present invention was made in order to solve the problem of the finished appearance of the outer surface printing of DI cans and the problem of occurrence of red rust, which were considered to be disadvantages of tinplate.

[0008]

[Means for Solving the Problems] The gist of the present invention is as follows. (1) A surface-treated steel sheet having a two-layer plating film of zinc on the lower layer and tin on the upper layer on at least one side of the steel sheet,
DI with excellent can external printability and rust resistance, characterized in that the total amount of zinc and tin deposited is 5.0 g/m2 or more, and the ratio of zinc deposit to the total amount of deposit is 75% or more
Steel plate for cans.

(2) 0.1-10V in the galvanized layer
The steel sheet for DI cans having excellent can external printability and rust resistance as set forth in the preceding item 1, characterized in that the lower layer is a composite galvanized layer containing a fluororesin and the upper layer is a tin plating film. It is well known that the metal tin currently used in tinplate has excellent ductility and lubricity, and is applied in extremely thin coatings. It is said that when this tinplate is used as a material for DI cans, the printing appearance is not good.

In the case of tinplate, the iron surface is completely covered with tin when it is manufactured as a steel plate, and when it is painted, a good color tone can be obtained. The fact that when this tinplate is molded into a DI can, the color tone after printing is inferior is presumed that the surface changes due to DI molding and the printability deteriorates. As a result of various investigations into the cause, it was found that the main cause was that a considerable amount of iron surface was exposed on the tin plate surface during the DI molding process.

In other words, since iron itself has a low spectral reflectance and absorbs light, if the exposed area ratio of iron is large, the total spectral reflectance of the can surface decreases and the printed appearance becomes black. The present invention was achieved by elucidating this fact and studying various countermeasures. The spectral reflectance here means the reflectance in the entire wavelength range of visible light.

[0012] When examining the spectral reflectance of metals alone, it was found that iron, chromium, etc. have low reflectance in the entire visible region, and when directly printed on these metals, the color tone tends to be dark. On the other hand, silver, tin, aluminum, etc. have excellent spectral reflection characteristics, and when printing on these metal surfaces, extremely excellent color tones can be obtained. This thing is
It also suggests an extremely important technological direction when improving the printed color tone of DI cans, and it is important to expose as little iron as possible on the can surface after DI forming in DI cans that use steel plates as a substrate. It's coming. One possible way to prevent the iron from being exposed is to re-plating after processing, but if it is possible to do this with the material before processing, it is preferable as it is an extension of the conventional technology and does not require the introduction of a new process. .

[0013] When processing a plated steel sheet, the most effective way to prevent the base iron from being exposed is to increase the amount of plating, but simply increasing the amount of plating increases manufacturing costs and is not practical. It has aspects that are not. Therefore, it is necessary to determine the mutual effect between the material and the can body that can achieve the maximum effect with the minimum amount of plating deposited. The can body design differs depending on the application, and the material design will change accordingly, but the most important thing in doing so is to consider the minimum plating thickness and composition of the plating film that will not adversely affect printability. be.

Based on this idea, we investigated the relationship between the iron surface exposure rate and printed appearance on the DI can body, and found that at least 90% of the outer surface of the can body is coated with plated metal, and the iron surface is coated with plated metal. It has been found that a can body with an exposed area ratio of 10% or less has excellent printing characteristics. At that time, the plating metals include tin, zinc,
Although it is possible to use one or more of aluminum and nickel, in view of the spectral reflection characteristics of the metal itself, a plating film in which tin or aluminum is the outermost surface is desirable.

In the case of aluminum, it is difficult to perform electroplating in an economical manner, and it is necessary to employ a plating bath based on an organic solvent or a molten salt, and is therefore outside the scope of the present invention. On the other hand, tin plating can be easily electroplated using an aqueous solution, and an industrial manufacturing method has been established, but tin plating is an expensive metal with few resources, and there are problems in applying thick plating. Furthermore, even if thick tin plating is applied, some iron exposure cannot be avoided after DI processing, and red rust is likely to occur.

[0016] As a measure to prevent the occurrence of red rust and also reduce the iron exposure rate after DI processing, a two-layer plated steel plate with zinc on the lower layer and tin on the upper layer is adopted. The tin/zinc double-layer plated steel sheet itself is well known, but in the present invention, by specifying the amount of coating and the ratio of the plating layer, we have achieved particularly excellent external printability and rust resistance as a steel sheet for DI cans. It is something to be acquired.

That is, the present invention provides a surface-treated steel sheet having a two-layer plating film of zinc on the lower layer and tin on the upper layer on at least one side of the steel sheet, wherein the total amount of zinc and tin deposited is 5.
The present invention provides a steel sheet for DI cans having excellent can external printability and rust resistance, characterized in that the zinc adhesion amount is 0 g/m2 or more and the ratio of zinc adhesion amount to the total adhesion amount is 75% or more. The reason why the total amount of zinc and tin deposited was set at 5.0 g/m2 or more was because, as mentioned above, in order to obtain excellent printability, the lower limit of the deposit amount was set to keep the iron exposure rate to 10% or less. be. Although the upper limit is not specified, it is probably around 20 g/m2 considering economic efficiency, productivity, etc.

The reason for adopting the two-layer plating structure of zinc for the lower layer and tin for the upper layer is from the point of view of DI moldability. If zinc is used as the upper layer, problems will occur in DI molding lubrication, and "galling" will occur in a short period of time, making continuous molding impossible. Next, in the present invention, it is essential that the ratio of the amount of zinc deposited to the total amount of deposited zinc be 75% or more. In the DI can making process, as mentioned above, after DI molding there are steps such as degreasing, chemical conversion, external printing, and internal painting, and each time the can body is exposed to considerably high temperatures (200 to 220°C). The alloying reaction of the two-layered tin-zinc plating progresses. In this case, the tin-zinc ratio becomes an extremely important factor. That is, as the tin-zinc alloying reaction progresses, a low melting point alloy layer is formed, and when the zinc ratio is small, most of the material becomes the low melting point alloy layer, and a spangle pattern of molten metal is generated on the can surface. . This not only impairs the printed appearance, but also causes problems such as build-up of molten metal on the can holder in the heating furnace, which is a major problem.

[0019] The ratio of the amount of zinc deposited to the total amount of deposited is 75
% or more, the amount of tin-zinc low melting point alloy layer formed is drastically reduced and the above-mentioned problem hardly occurs, but it is desirable that the ratio of the amount of zinc deposited is 85% or more. In this case, in order not to deteriorate the continuous DI formability, it is necessary to ensure the absolute amount of tin deposited, and it is necessary to increase the total deposited amount as the ratio of zinc deposited amount increases.

An increase in the total coating weight is economically undesirable, and in order to avoid this, it is necessary to improve the lubricity of the underlying galvanized layer. Various measures can be taken to improve the lubricity of the galvanized layer, but the lubricity can be improved by eutectoiding a fluororesin into the galvanized layer, and by tin plating the upper layer, it is possible to improve the lubricity of the composite plating film. It can be expected to improve the appearance and assist in lubrication.

Examples of the fluororesin to be dispersed in the plating layer include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. combination, tetrafluoroethylene-ethylene copolymer, chlorotritetrafluoroethylene-alkylene copolymer, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-chlorotritetrafluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene Examples include copolymers, fluorinated ethylene propylene ether resins, and mixtures of two or more thereof.

[0022] No matter which of the above fluororesins is used, a plating film having excellent DI lubricity and rust resistance can be obtained. The amount of fluororesin to be eutectoid is 0.1 to 10.0v
ol% range, more preferably 2 to 8% range. The lower limit value is the limit at which the effect can be expected, and the upper limit value is the limit at which the effect is saturated, and was set from an economic standpoint. In the case of two-layer plating, which has a galvanized layer with a fluororesin eutectoid on the lower layer, the amount of tin plating on the upper layer can be small;
Considering the print appearance, it is desirable that the amount is within the range of 0.5 to 2.0 g/m2. In this case as well, it is necessary to keep the ratio of the amount of zinc deposited to the total amount of deposited to be 75% or more.

[0023]

[Example 1] Steel plate with a thickness of 0.28 mm (surface roughness Ra:
Zinc plating was performed on one side of the sheet (1.5 μm) at a coating weight of 8.5 g/m 2 using an acidic zinc plating bath. After that, 1.8 g/g was applied on the zinc plating using a tin pyrophosphate plating bath.
m2 tin plating was performed. At that time, the other side of the steel plate was plated with tin at a coating weight of 2.8 g/m2.

Starting from a blank size of 139 mm, 1
A cup with a diameter of 85 mm was obtained by drawing in the first stage, and a cup with a diameter of 65 mm was formed in a second stage, and the thickness of the side wall was reduced to 0.085 mm by ironing a total of three times. After degreasing and chemical conversion treatment, white ink was printed on the outer surface of the can, and the color was measured using a color meter, and it was confirmed that the printed appearance was much whiter than that of conventional tin DI cans (Table 1) .

[0025]

[Table 1]

An epoxy paint was spray applied to the inner surface of the can after the outer surface was printed, and baked at 210.degree. C. for 10 minutes. There was no occurrence of spangle patterns or the like, and no change in the printed appearance was observed. When the unpainted bottom of the can was immersed in tap water and a rust resistance test was conducted, no red rust was observed for 4 days.

[0027]

[Example 2] Steel plate with a thickness of 0.50 mm (surface roughness Ra:
0.8 μm) surface, zinc plating was performed on only one side with a coating amount of 5.0 g/m2 using a normal sulfuric acid bath, and then 1.5 g/m2 (per single side) of tin was applied in a tin pyrophosphate plating bath. Plating was performed on both sides of the steel plate. A DI molded can with a side wall thickness of 0.22 mm was produced by drawing twice and ironing twice so that the tin-zinc two-layer plating surface of this steel plate became the outer surface of the can.

After degreasing and chemical conversion treatment, this can was printed with white ink and its surface appearance was measured, and it was confirmed that it had an excellent white printed appearance (Table 1). A polyester paint was spray applied to the inner surface of the can after the outer surface was printed, and baked at 210.degree. C. for 10 minutes. There was no occurrence of spangle patterns or the like, and no change in the printed appearance was observed.

When a rust resistance test was conducted by immersing the unpainted bottom of the can in tap water, no red rust was observed for 4 days.

[0030]

[Example 3] As in Example 1, one side of a steel plate with a thickness of 0.28 mm (surface roughness Ra: 1.5 μm) was coated with zinc at a coating weight of 6.5 g/m2 using an acidic zinc plating bath. I did it. At that time, PTF with a particle size of 0.02 μm was added to the plating bath.
E-resin was dispersed and eutectoided at 4.6 vol% into the galvanized layer. Thereafter, 0.8 g/m2 of tin plating was performed on the zinc plating using a tin pyrophosphate plating bath. At that time, the other side of the steel plate was plated with tin at a coating weight of 2.8 g/m2. Starting from a blank dimension of 139 mm, so that the tin-zinc double-layer plated surface of this steel plate becomes the outer surface of the can,
The cup was formed into a cup with a diameter of 85 mm in the first stage of drawing, and a cup with a diameter of 65 mm in the second stage.The thickness of the side wall was reduced to 0.085 mm by ironing a total of 3 times, but "galling" occurred. Continuation D without any problems such as
It showed moldability.

After degreasing and chemical conversion treatment, white ink was printed on the outer surface of the can, and the color was measured using a color meter. It was confirmed that the printed appearance was much whiter than that of conventional tin DI cans (Table 1). ). Spray epoxy paint on the inside of the can after printing on the outside and heat for 10 minutes at 210℃.
Baking was performed for 1 minute. There was no occurrence of spangle patterns or the like, and no change in the printed appearance was observed.

When a rust resistance test was conducted by immersing the unpainted bottom of the can in tap water, no red rust was observed for 4 days.

[0033]

[Comparative example] Steel plate with a thickness of 0.28 mm (surface roughness Ra: 1
．． Zinc plating was carried out on one side of the sheet (5 μm) at a coating weight of 4.5 g/m 2 using an acidic zinc plating bath. After that, 2.8g/m on the zinc plating using a tin pyrophosphate plating bath.
2. Tin plating was performed. At this time, the other side of the steel plate was also plated with tin at a coating weight of 2.8 g/m2.

This steel plate was subjected to drawing twice and ironing three times in the same manner as in Example 1, so that the side wall thickness was 0.085.
It was molded into a DI molded can of mm. After degreasing and chemical conversion treatment, this can was printed with white ink and its surface appearance was measured, and it was found to be excellent in terms of appearance evaluation. When baking was carried out for 10 minutes in a vacuum cleaner, a spangled pattern was generated due to the formation of a zinc-tin low melting point alloy, deteriorating the printed appearance and lowering the commercial value (Table 1).

In the rust resistance test on the bottom of the can, no red rust was observed for 4 days.

[0036]

[Comparative Example 2] A thin steel plate with a thickness of 0.26 mm was degreased and pickled, then galvanized with a coating weight of 2.0 g/m2 and a coating weight of 2.0 g.
A double-layer plated steel plate having a tin plating of /m2 was obtained. This steel plate was subjected to an appearance evaluation test after DI processing and printing in the same manner as in Example 1. The appearance evaluation results were inferior to those of the present invention (Table 1).

[0037]

[Effects of the invention] The tin-zinc double-layer plated steel sheet having the above film structure has excellent external printability and rust resistance,
Although it exhibits excellent performance as a steel plate for DI cans, the steel plate of the present invention can be used not only for DI cans, but also for drawing cans, 5-gallon cans, general cans,
It goes without saying that it can be effectively utilized in applications where rust resistance is particularly required, such as can lids or steel plates for welded cans.

Claims (2)

[Claims] 1. A surface-treated steel sheet having a two-layer plating film of zinc on the lower layer and tin on the upper layer on at least one side of the steel sheet, the total amount of zinc and tin deposited being 5.0 g/m2 or more, The ratio of zinc adhesion to total adhesion is 75%
A steel plate for DI cans having excellent can external printability and rust resistance, which is characterized by the above properties. [Claim 2] 0.1 to 10 vol in the galvanized layer
2. The steel sheet for DI cans having excellent can external printability and rust resistance according to claim 1, characterized in that the lower layer is a composite galvanized layer containing 50% of fluororesin, and the upper layer is a tin plating film.