JPH0459994A - 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 plating one side of a steel sheet with an Sn-Zn alloy under prescribed conditions, tinning the other side and forming a chromate film. CONSTITUTION:One side of a steel sheet corresponding to the outside of a can is plated with 8.4-40g/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 by 1-100mg/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, tinplate with good DI formability has been used as a surface-treated steel sheet for DI cans, but the following are major problems with the outer surface of the can.

■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 DI molding, tinplate becomes glossy on the outside of the can, 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 the chemical conversion treatment and causing problems in 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. The present invention aims 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 provide Sn-Zn containing 5 to 97.5% Zn at least on the surface corresponding to the outer surface of the can.
Rust resistance characterized by applying alloy plating at 8.4 to 40 g/rd, applying Sn plating to the surface corresponding to the inner surface of the can, and then having a chromate coating with a coating amount of 1 to 100 mg/m2 in terms of chromium. This is a surface-treated steel sheet for containers that has an excellent appearance.

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

In the present invention, as the plated original plate, a plated original 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 the plated original plate, and it is manufactured through a normal steel billet manufacturing process such as hot rolling, pickling, cold rolling, annealing, and temper rolling. Sn plate was applied to the surface corresponding to the inner surface of the can of the metal plate produced in this way.
The surface corresponding to the outer surface of the can is coated with Sn--Zn alloy metal. There are no particular restrictions on the inner surface; for example, ordinary tinplate may be used.

In the present invention, the amount of Sn--Zn alloy plating on the outer surface side must be 8.4 g/rd or more. Generally, the thickness of the plating layer is reduced to about 1/3 or less by Dr processing, and this plating layer is damaged by the impact during processing.
If the plating amount is less than 8.4 g/n'r, the bare metal will be exposed.

If chemical conversion treatment is performed in this state, the chemical conversion properties differ between the plating layer and the base metal, resulting in unevenness, spots, etc. occurring after painting or printing, causing problems in uniform printability. Therefore, when the amount of plating is 8.4 g/% or more, exposure of the base iron can be prevented even if the plating layer is damaged. In addition, the amount of plating is 40g
If the plating amount exceeds 40 g/rd, the effect of preventing the bare metal from being exposed becomes saturated and is economically disadvantageous, so the amount of plating does not need to be greater than 40 g/rd. For the above reasons, Sn-Z
The amount of n-alloy plating is defined as 8.4 to 40 g/m2.

Moreover, the Zn content in the Sn-Zn alloy plating layer is 5 to 9.
It must be regulated at 7.5%. 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. This is Z
If n is less than 5%, the potential of the Sn-Zn alloy plating layer is a liability to the base steel, and when exposed to a corrosive environment, especially when the plating layer is damaged by DI processing, etc. If there are plating defects such as pinholes, it is not possible to sacrificially protect the base steel from corrosion, just like 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 effect of Zn, which is a base metal, and it begins to exhibit sacrificial corrosion protection against the base steel. . In other words, even if a plated steel sheet with a Sn-Zn alloy plating layer containing 5% or more of Zn in the alloy plating layer is exposed to a corrosive environment where moisture, oxygen, etc. are sufficiently present,
Even if there is processing damage or pinholes in the plating layer, no rust is observed from the base metal.

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 will hardly change, and the appearance of the outer surface after DI processing will exhibit a gloss similar to that of tinplate. The print finish is dark.

However, if the Zn content in the plating layer is 5% or more, the appearance of the outer surface after DI processing will lose its luster, and the appearance after printing will be whitish compared to 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 bottom molding, that is, the occurrence of "r galling" 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.
This is because DI moldability deteriorates. Furthermore, when the Zn content in the plating layer exceeds 97.5%, the sacrificial corrosion protection against the base steel is sufficient, but the Zn itself in the plating layer begins to corrode and elute, making white rust more likely to occur. Or, the corrosion resistance under the printing ink deteriorates.

In other words, an appropriate amount of Zn in the Sn-Zn alloy plating layer that ensures good rust resistance and appearance on the outer surface of the DI can and does not cause deterioration of DI formability or white rust is 5 to 97.
It is necessary to be 5%.

The plating bath for forming the Sn-Zn alloy plating layer with such excellent properties is not particularly regulated, but birophosphate baths, cyanide baths, sulfuric acid baths, and chloride baths are used. The Zn% in the layer 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.

The above-mentioned plated steel sheets, that is, the plated steel sheets that have a Sn plating layer on the inner surface and a Sn-Zn alloy plating layer on the outer surface, are subsequently subjected to chromate treatment for the purpose of improving paint adhesion and post-painting corrosion resistance. administer. In the chromate treatment, an aqueous solution of sodium salt, potassium salt, or ammonium salt of chromic acid is generally used, and the treatment method is not particularly limited, but examples thereof include dipping treatment, spray treatment, and electrolytic treatment. The amount of chromate deposited by the chromate treatment is required to be 1 mg/m2 or more in terms of the amount of metallic chromium.

This is because if the amount of chromium deposited is less than 1/n, the chromate film produced by the chromate treatment cannot completely cover the plated steel sheet, making it impossible to prevent discoloration due to air oxidation.

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, and the results are shown in Table 1. The plated original 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 for surface activation. After oxidation, Sn plating was applied to the surface corresponding to the inner surface of the can under the conditions shown in (1), and then Sn-Zn alloy plating was applied to the surface corresponding to the outer surface of the can under the conditions shown in (2)-(a) and (b). was applied. Then, a product was prepared which was subjected to chromate treatment under the conditions shown in (3).

(1) Sn plating conditions Plating bath composition: 20-30 g/l of tin sulfate.

Additive 1 to 5 g/l Plating bath temperature 50°C Current density 15 to 25 A/dm2 (Electrolysis time is adjusted according to the amount of Sn plating) (2) Sn-Zn alloy plating conditions (a) Pyrophosphoric acid bath Plating bath Composition: Tin-pyrophosphate 10-50g/1 (adjusted according to alloy composition) Zinc sulfate 20-100g/Il (adjusted according to alloy composition) Potassium pyrophosphate 250g/j! Plating bath temperature
50'C Current density 1 (1 to 30 A/dmt (electrolysis time is adjusted according to the amount of Sn-Zn alloy plating) (b) Sulfuric acid bath Plating bath composition Stannous sulfate 10 to 60 g/l (depending on the alloy composition) Adjustment) Zinc sulfate 30-150g/42 (Adjusted according to alloy composition) Sodium sulfate 300g/f Plating bath temperature 55°C Current density 10-30A/dm" (Electrolysis time adjusted according to the amount of Sn-Zn alloy plating ) (3) Chromate treatment conditions Bath composition NaCrzOs 24 g/Itpo
4.5 Bath temperature 45°C Treatment conditions Immersion treatment The above-mentioned treated materials were tested for items (A) to (D) shown below to evaluate their performance.

(A) DI moldability Using a water-soluble emulsion type coolant, DI cans were molded from a blank size of 136 mmφ to a can diameter of 65.9-φ under molding conditions at a can manufacturing speed of 110 cans/mtn. DI moldability was evaluated. The evaluation criteria were as follows.

◎; D■ Moldability is extremely good.

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

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

X; D! The material breaks during the molding process, making DI molding impossible.

(B) Printing finish after DI molding DI cans were prepared under the conditions of (A), red, white, and yellow inks for external surfaces were printed with a film thickness of Sn, 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 DI cans were created under the conditions of (A), outer surface printing was performed under the conditions of (B), and uniform printability was visually judged.

○: Appearance after printing has no unevenness or gaps, and uniform printability is extremely good.

Δ: Appearance after printing shows slight printing unevenness and spots, and uniform printing performance 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 one cycle consisting of placing the product in a humidity chamber at 49 °C and relative humidity of 98% or higher for 60 min, then leaving it indoors at room temperature for 22 hours. The rate was measured.

Humidity chamber test: The specimens were stored in a humidity chamber at 49° C. and a relative humidity of 98% or higher for two weeks, and the rusting rate of the evaluated 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.

As is clear from the above test results, the present invention has excellent DI molding properties and rust resistance, and these properties are also stably obtained compared to the comparative examples.

(Effects of the Invention) According to the present invention, the can exhibits excellent rust resistance on the outer surface side, has good can making processing characteristics (especially DI moldability), and has good printing finish after DI molding. It is possible to provide a surface-treated steel sheet for containers that has good uniform printability and is economically compatible.

Claims (1)

[Claims] Z of 5 to 97.5% on at least the surface corresponding to the outer surface of the can
8.4~40g/N-containing Sn-Zn alloy plating
A container with excellent rust resistance and appearance, characterized by having Sn plating applied to the surface corresponding to the inner surface of the can, followed by a chromate coating with a coating amount of 1 to 100 mg/m^2 in terms of chromium. Surface treated steel plate for use.