JPH0459993A - Surface-treated steel sheet for vessel having superior rust resistance and fine appearance - Google Patents

Abstract

PURPOSE:To improve rust resistance and suitability to working into a can and finishing by printing by subjecting one side of a steel sheet to tinning and Zn-Sn alloy plating and the other side to tinning and forming a chromate film on both the sides. CONSTITUTION:One side of a steel sheet corresponding to the outside of a can is tinned to form a lower Sn layer by 0.5-20g/m<2> and this layer is plated with 1-20g/m<2> Sn-Zn alloy contg. 5-97.5% Zn. The other side of the steel sheet corresponding to the inside of the can is tinned and a chromate film is formed on both the sides by 1-50mg/m<2> (expressed in terms of Cr).

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a two-piece can (drawing and ironing process (for example, DI can))
) This relates to a surface-treated steel sheet for containers that is used as a material for containers and has excellent rust resistance, appearance, and chemical conversion treatment properties.

(Prior art) In recent years, can manufacturing methods using drawing and ironing processes (for example, DI processing can manufacturing methods), mainly for beverage cans, have developed significantly, and there is a strong demand for surface-treated steel sheets for containers with higher performance than ever before. strong. Conventionally, JP-A-57 has been used as a surface-treated steel sheet for DI cans.
As introduced in many patent publications such as JP-A-67196 and JP-A-58-52495, tinplate with good DI formability has been used, but the major problems on the outside of the can are as follows. The following points can be mentioned.

■ Rust is likely to form on the outside of the can, and if it is immersed in tap water, commercial water, or salt water, rust will form in the bottom and scratched areas in a short period of time.

- After tinplate is DI molded, the outer surface of the can becomes glossy, resulting in a dark appearance after printing, which poses a problem in printing finish.

■ After DI molding, the base metal is exposed, causing variations in chemical conversion treatment and problems with uniform printing.

Currently, these problems can be addressed by increasing the thickness of the base coating applied before printing. It is true that good print finish and uniform printability can be ensured by increasing the coating thickness and applying a coating film free of coating defects to the outer surface of the can.

However, this method cannot deal with the problem of rust occurring in damaged parts of the paint film, ie, scratched parts on the outer surface of the can. Furthermore, increasing the coating thickness increases the coating cost and is economically disadvantageous.

(Problems to be Solved by the Invention) The present invention exhibits excellent rust resistance on the outer surface of the can, has good can processing properties (especially DI moldability), and has good printing finish after DI molding. It is an object of the present invention to provide a surface-treated steel sheet for containers that has good uniform printability and is economically suitable.

(Means for Solving the Problems) The gist of the present invention is to apply Sn plating to the lower layer of the surface corresponding to the outer surface of the can at an amount of 0.5 to 20 g/rd, and then apply Zn plating to the upper layer at an amount of 5 to 97.5 g/rd. % containing Sn-Zn alloy plating of 1.0 to 20 g/m2, Sn plating is applied to the surface corresponding to the inner surface of the can, and then a chromate film with a chromium equivalent coating weight of 1 to 50 g/m2 is applied to both sides. This is a surface-treated steel sheet for containers with excellent rust resistance and appearance.

(for production) The present invention will be explained in detail below.

In the present invention, as the plated original plate, a plated steel plate having a material suitable for the purpose of use as a steel plate for containers is used. There are no particular restrictions on the manufacturing method of plated original sheets, and there are various methods for manufacturing plated sheets, including hot rolling, pickling, cold rolling,
It is manufactured through processes such as annealing and temper rolling. S
After applying Sn plating to the surface corresponding to the outer surface of the can, or at the same time applying Sn plating to the surface corresponding to the inner and outer surfaces of the can.
After applying n-metal coating, Sn--Zn alloy plating is applied. The lower layer Sn plating on the inner and outer surfaces is not particularly limited, and for example, ordinary tinplate may be used.

The purpose of applying Sn plating to the lower layer on the outer surface of the can is to ensure good workability. In order to ensure good workability, the amount of Sn coating in the lower layer must be 0.5 g/nf or more. If the amount of Sn plating is less than 0.5g/rd, the lubricity in DI processing will be insufficient, and the upper layer Sn-Zn
The alloy plating layer or the underlying Sn plating layer may be damaged or partially scraped off. The scraped plating layer turns into powder and adheres to the punch or die of the DI processing machine, causing flaws during DI processing.

Furthermore, in the worst case, DI processing becomes impossible. However, if Sn plating is applied in a plating amount of 0.5 g/m2 or more, it is possible to ensure good lubricity, suppress scraping of the plated layer during DI processing, and ensure good I processability. but,
If the Sn plating amount exceeds 20 g/%, this effect will be saturated and it will be economically disadvantageous.

The upper layer of the Sn plating applied to the outer surface of the can is coated with Sn--Zn alloy plating in a plating amount of 1.0 to 20 g/rd to improve the rust resistance and appearance of the outer surface. The plating layer is
The thickness is reduced to about 1/3 or less by DI processing, and this plating layer is damaged by impact during processing, so the base iron is exposed in a plating layer with a plating amount of less than 1.0 g/rd. If a chemical conversion treatment is performed in this state, the plating layer and the base metal have different chemical conversion properties, which causes unevenness, spots, etc. to occur after painting or printing, causing problems in uniform printability. However, if the plating amount is 1.0 g/nf or more, exposure of the base iron can be prevented even if the plating layer is damaged. Furthermore, if the amount of plating exceeds 20 g/rd, the effect of preventing the bare metal from being exposed becomes saturated, which is economically disadvantageous. For this reason, the upper layer Sn-Z
The plating amount of the n-alloy plating layer was set to 1.0 to 20 g/bo.

Moreover, the Zn content in the Sn-Zn alloy plating layer is 5 to
It must be regulated to 97.5%. At a low Zn content of less than 5%, almost no effect of improving the external rust resistance is observed, and the rust resistance is only comparable to that of tinplate. In other words, if the Zn content is less than 5%, the potential of the Sn-Zn alloy plating layer will be a liability to the base steel, and when exposed to a corrosive environment, especially when the plating layer is damaged by DI processing etc. When there are plating defects such as pinholes in the layer, it is not possible to sacrificially protect the base steel from corrosion, as with tinplate.

However, when the Zn content in the alloy plating layer becomes 5% or more, the potential of the Sn--Zn alloy plating layer changes to be less noble due to the base Zn metal, and exhibits sacrificial corrosion protection against the base steel. In other words, plated steel sheets with a Sn-Zn alloy plating layer containing 5% or more of Zn in the alloy plating layer were exposed to a corrosive environment with sufficient presence of moisture and oxygen, resulting in machining damage and pinholes in the plating layer. Even in cases where rust is not observed from the base steel.

Furthermore, regarding the appearance after DI processing, if the Zn content in the Sn-Zn alloy plating layer is less than 5%, the appearance of the plating layer and the appearance of the outer surface after DI processing will be glossy like that of tinplate, and printing will be difficult. The finish is dark. However, Zn in the plating layer
If it exceeds 5%, the appearance of the outer surface after DI processing will lose its luster, but the appearance after printing will be whiter than that of tinplate, and the printing finish will be good.

Furthermore, Zn in the Sn-Zn alloy plating layer is 97.5%.
If the value exceeds 1, the degree to which the outer plated layer is damaged by the die during DI molding, that is, the occurrence of r-galling 1 increases, and good I-formability cannot be ensured. This is because when the Zn content in the Sn-Zn alloy plating layer exceeds 97.5%, the lubricity of the Sn-Zn alloy plating layer decreases, and D
This is because I-formability deteriorates.

Furthermore, when the Zn content in the plating layer exceeds 97.5%, the sacrificial corrosion protection effect on the base steel is sufficient;
The material itself begins to corrode and elute, making it easier for white rust to occur and deteriorating its corrosion resistance under printing ink.

In other words, the Zn content in the Sn-Zn alloy plating layer is set to 5 to ensure good rust resistance and appearance on the outer surface of the DI can, and to prevent deterioration of DI formability and white rust.
~97.5%.

Plating baths for Sn-Zn alloy plating layers with such excellent properties are not particularly regulated, but pyrophosphoric acid baths, cyanide baths, sulfuric acid baths, and chloride baths are used. The percentage can be controlled mainly by the balance of the amount of metal ions in each bath, and the amount of alloy plating can be controlled by the number of coulombs required for electrolysis.

Further, in the present invention, a plated steel plate having a Sn plating layer on the inner surface and a Sn--Zn alloy plating layer on the outer surface is subjected to chromate treatment in order to improve paint adhesion and post-painting corrosion resistance. In the chromate treatment, an aqueous solution of a sodium salt, potassium salt, or ammonium salt of chromic acid is generally used, and the treatment method is not particularly restricted, but examples include dipping treatment, spray treatment, and electrolytic treatment. The amount of chromate deposited must be at least 1 cm/bo in terms of the amount of metallic chromium. 1
If the amount of chromium deposited is less than 1/2, the chromate film cannot completely cover the plated steel sheet, so discoloration due to air oxidation cannot be prevented. In addition, the amount of chromium attached is 50
■Exceeding /bo is economically disadvantageous.

Furthermore, chromate treatment or phosphoric acid treatment is performed as a chemical conversion treatment to improve coating performance and post-painting corrosion resistance after DI molding, but in the present invention, these treatment methods and treatment conditions after DI molding are not particularly regulated. It is not necessary to do so, but the usual processing method will be applied.

(Example) Examples of the present invention will be described below. The plated original steel plate, which has been adjusted to the material and thickness suitable for DI can use and can lid use through cold rolling and annealing processes, is electrolytically degreased and washed with water in 5% caustic soda, and then electrolytically pickled in 10% sulfuric acid. After surface activation, Sn plating is applied to the surfaces corresponding to the lower layer of the inner and outer surfaces of the can under the conditions shown in (1), and then to the surfaces corresponding to the outer surface of the can under the conditions shown in (2)-(()(U). Sn--Zn alloy plating was applied in step (3), and a chromate treatment was performed under the conditions shown in (3).

(1) Sn plating conditions Plating bath composition Tin sulfate 20-30 g/l Additives 1-5 g/l Plating bath temperature 50°C Current density 15-25 A/dm" (Electrolysis time is adjusted according to the amount of Sn plating) (2) S
n-Zn alloy plating conditions (a) Pyrophosphoric acid bath Plating bath composition Tinn pyrophosphate 10 to 50 g/j2 (adjusted according to alloy composition) Zinc sulfate 20 to 100 g/f (adjusted according to alloy composition) Pyrophosphoric acid Potassium 250g//! Plating bath temperature 50°
C Current density: 10-308/d1 (Electrolysis time is adjusted according to the amount of S-low Zn alloy plating) (B) Sulfuric acid bath Plating bath composition: 10-60 g/i of stannous sulfate! , (adjusted according to alloy composition) Zinc sulfate 30 to 150 g/f (adjusted according to alloy composition) Sodium sulfate 300 g/42 Plating bath temperature 55°C Current density 10 to 30 A/dm2 (electrolysis time is (Adjusted according to the amount of gold plating) (3) Chromate treatment conditions Bath composition NaCrzOs 24 g / 1 pH 4
, 5 Bath temperature: 45°C Treatment conditions: Immersion treatment After the above-mentioned treated material was tested, the following items (A) to (D) were tested to evaluate their performance.

(A) DI moldability Using water-soluble emulsion type coolant, from blank size 136mmφ to can diameter 65,91+101
01 cans were molded under molding conditions of a can manufacturing speed of 110 cans/min up to φ, and the DI moldability of various treated materials was evaluated.

The evaluation criteria were as follows.

◎, DI moldability is extremely good.

○: Slight galling occurs on the outer surface during ironing, but DI
Good moldability.

△: DI molding is possible, but strong galling occurs on the outer surface during ironing, and DI moldability is poor.

×: The material broke during the D1 molding process, making DI molding impossible.

(B) Printing finish after DI molding A 01 can was prepared under the conditions of (A), red, white, and yellow ink for the outside of the can was printed at a film thickness of 5IITn, and the printing finish was visually judged. The judgment criteria are as follows.

O: The appearance after printing is whitish, and the printing finish is extremely good.

Δ: Slight gloss was observed in the appearance after printing, and the print finish was slightly inferior.

×: Appearance after printing has the same level of gloss as tinplate,
Poor print finish.

(C) Uniform printability after DI molding A 01 can was produced under the conditions of (A), the outer surface was printed under the conditions of (B), and the uniform printability was visually judged.

○: There are no printing unevenness or spots in the appearance after printing, and the uniform printability is extremely good.

Δ: Slight unevenness and scratches are observed in the appearance after printing,
Uniform printability is slightly inferior.

×: Printing unevenness and spots were observed in a considerable portion of the appearance after printing, and uniform printing performance was poor.

(D) Rust resistance on the outside surface side The rust resistance on the outside surface side of the DI printed cans prepared under the conditions (A) and (B) was evaluated using the following evaluation test.

In addition, the evaluation material was evaluated for the part where the wall part had scratches and the bottom part.

Tap water immersion test: The evaluation material was immersed in tap water at room temperature for 3 days, and the rusting rate of the portion to be evaluated was measured.

Refrigeration cycle test: Place the evaluation material in the freezer at -15°C for 3
Immediately after holding at 0 m1n, the test was continued for 15 cycles, with 60 m1n placed in a humidity chamber at 49 °C and a relative humidity of 98% or higher, and then left indoors at room temperature for 22 hours. It was measured.

Humidity tank test: The product was stored in a humidity tank at a relative humidity of 98% or higher at 49° C. for two weeks, and the rusting rate of the relevant parts was measured.

The evaluation criteria for rust resistance in each test are as follows.

◎: No rust was observed at all, and the rust resistance was extremely good.

O: Rust resistance is good with a rust occurrence rate of 5% or less.

Δ: Rust resistance is slightly inferior with a rust occurrence rate of 5 to 30%.

×; Rust resistance is inferior to that of tinplate when the rusting rate is 30% or more.

The results are shown in a table. That is, the present invention has extremely good rust resistance on the outer surface under various conditions, and is also excellent in formability and printability during DI can processing. On the other hand, comparative examples in which the Zn content or plating amount of the Sn-Zn alloy plating layer deviates from the limited range of the present invention have problems in either DI formability, printability, or rust resistance, and are not equivalent to the present invention. I can't get the properties.

(Effects of the Invention) The present invention exhibits excellent rust resistance on the outer surface of the can, has good can processing characteristics (particularly DI moldability), and has good printing finish after DI molding. Moreover, it provides a surface-treated steel sheet for containers that has good uniform printability and is economically suitable, so it is extremely useful industrially.

Claims (1)

[Claims] Sn plating of 0.5~2 on the lower layer of the surface corresponding to the outer surface of the can
0g/m^2, then 5-97.5% Zn on the top layer
Sn-Zn alloy plating containing 1.0-20g/m^
2 plating, Sn plating is applied to the surface corresponding to the inner surface of the can, and then a chromate film with a chromium equivalent adhesion amount of 1 to 50 mg/m^2 is applied to both sides.It has excellent rust resistance and appearance. surface-treated steel sheet for containers.