JPH04120295A - Surface-treated steel sheet for vessel having superior rust resistance and fine appearance - Google Patents

Abstract

PURPOSE:To produce a surface-treated steel sheet for cans having superior rust resistance, fine appearance and superior chemical treatability by plating one side of a steel sheet for two-piece cans corresponding to the outsides of the cans with an Sn-Zn alloy and tinning the other side corresponding to the insides of the cans. CONSTITUTION:When an annealed cold rolled steel sheet is drawn and ironed to produce drink cans such as two-piece cans, one side of the steel sheet corresponding to the outsides of the cans is plated with 8.4-40g/m<2> Sn-Zn alloy consisting of 5-97.5% Zn and the balance Sn. The other side corresponding to the insides of the cans is tinned. A surface-treated steel sheet for cans used as the material of two-piece cans and having superior rust resistance and fine appearance is obtd.

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 invention relates to a surface-treated steel sheet for containers that has excellent rust resistance, appearance, and chemical conversion treatment properties and is used as a material for containers.

(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.

■Tinplate 0■ After molding, 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 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 if the coating thickness is increased and a coating film without coating defects is applied to the outer surface of the can, good print finish and uniform printability can be ensured.

However, this method cannot deal with the problem of rust occurring in damaged parts of the paint film, that is, in flawed parts on the outer surface of the can. Furthermore, increasing the coating thickness increases the coating cost (which is also 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 manufacturing processing characteristics (particularly DI moldability), and has excellent 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 compatible.

(Means for Solving the Problems) That is, the gist of the present invention is to provide Sn containing 5 to 97.5% Zn at least on the surface corresponding to the outer surface of the can.
- A surface-treated steel sheet for containers with excellent rust resistance and appearance, which is coated with 8.4 to 40 g of Zn alloy plating and Sn plating is applied to the surface corresponding to the inner surface of the can.

(Function) 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 plating is applied to the surface corresponding to the inner surface of the can, and Sn--Zn alloy plating is applied to the surface corresponding to the outer surface of the plated original plate thus manufactured. Incidentally, the amount of Sn plating on the inner surface of the can is not particularly limited, and may be as long as, for example, that of ordinary tinplate.

Next, the effects of the Sn--Zn alloy plating on the outer surface, which is a feature of the present invention, will be described. The amount of Sn-Zn alloy plating is required to be 8.4 g/nf or more. The reason for this will be explained below. Generally, the plating layer is approximately 1 due to DI processing.
The thickness shall be less than /3. Furthermore, this plating layer is damaged by impact during processing, so the amount of plating is 8.4g/
Below rrf, the base metal is exposed. 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, the amount of plating is 8.4g/n? By doing so, even if the plating layer is damaged, the bare metal can be prevented from being exposed.

Furthermore, if the amount of plating exceeds 40 g/rrT, the effect of preventing the bare metal from being exposed will be saturated and it will be economically disadvantageous, so the amount of plating should be 40 g/n? There is no need for more. From the above results, it can be seen that the amount of plating is 8.4 to 40g1rd.

Moreover, the Zn content in the Sn-Zn alloy plating layer is 5 to 9.
It must be regulated at 7.5%. Zn content is 5
If the amount is less than %, almost no effect on improving the external rust resistance is observed, and the rust resistance is only comparable to that of tinplate.

This is because when the Zn content 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. Alternatively, if there are plating defects such as pinholes in the plating layer, it is not possible to sacrificially protect the base steel from corrosion in the same way as with tinplate.

However, when the Zn content exceeds 5%, 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, plated steel sheets with a Sn-Zn alloy plating layer with a Zn content of 5% or more are exposed to a corrosive environment with sufficient moisture and oxygen, and even if there is machining damage or pinholes in the plating layer, the plated steel sheet will No rust is observed from the iron.

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 be as shiny as tinplate. The print quality is dark. However, when the Zn content in the plating layer is 5% or more, the appearance of the outer surface after DI processing loses its luster, and the appearance after printing becomes whitish compared to that of tinplate, resulting in a good printing finish.

Moreover, the Zn content in the Sn-Zn alloy plating layer was 97.
If it exceeds 5%, the degree to which the outer plated layer is damaged by the die during DI molding, that is, the occurrence of galling 1, increases, making it impossible to ensure good concave moldability.

This is because the Zn content in the Sn-Zn alloy plating layer is 97%.
．． This is because if it exceeds 5%, the lubricity of the Sn--Zn alloy plating layer decreases and DI formability deteriorates. Furthermore, if the Zn content exceeds 97.5%, the sacrificial corrosion protection effect on 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, and under printing ink. In other words, proper Sn-Zn alloy plating is required to ensure good rust resistance and appearance on the outer surface of the can, and to prevent deterioration of DI formability and white rust. It can be seen that the Zn content in the layer is 5-97.5%.

The plating bath for forming the Sn-Zn alloy plating layer with such excellent properties is not particularly regulated, but pyrophosphate 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.

(Example) Examples of the present invention will be described below, and the results are shown in Table 1. Through cold rolling and annealing processes, the plated original plate is adjusted to the material and thickness suitable for DI cans and can lids, and is then electrolytically degreased and washed with water in 5% caustic soda, and then electrolytically pickled in 10% sulfuric acid for surface activation. After that, 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 (n). provided.

(1) Sn plating condition Plating bath composition Tin sulfate 20-30g/f Additive 1
~5g#2 Plating bath temperature 50°ct flow density 15~25
A/dm” (the solution time is adjusted according to the amount of Sn plating) (
2) Sn-Zn alloy plating conditions (a) Pyrophosphoric acid bath Plating bath composition Pyrophosphoric acid 10-50 g/l (adjusted according to alloy composition) Zinc stannous sulfate 20-100 g/l (adjusted according to alloy composition) Plating bath temperature 50°C (b) Sulfuric acid bath Plating bath composition Stannous sulfate 10 to 60 g/l (Adjusted according to alloy composition) Zinc sulfate 30 to 150 g/l (Adjusted according to alloy composition) Sodium sulfate 300 g / 1 Plating bath temperature 55°C The above-mentioned treated material was tested for the following items (^) to (D) to evaluate its performance.

(A) DI moldability Using a water-soluble emulsion type coolant, DI cans were molded from a blank size of 136 mφ to a can diameter of 65.9 mm under molding conditions of a can manufacturing speed of 110 cans/win, and various treatments were carried out. The DI formability of the material was evaluated.

The evaluation criteria were as follows.

O11 moldability is extremely good.

Slight galling occurs on the outer surface when machining OWL, but DI
Good moldability.

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

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

0 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 DI can was created under the conditions of (A), the outer surface was printed under the conditions of CB), and the uniform printability was visually judged.

O: The appearance after printing had no unevenness or gaps, and the uniform printability was 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 CB) 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
After holding for 0.0 in, immediately put 60ml in a humidity chamber at 49℃ and relative humidity of 98% or more, and then leave the test indoors at room temperature for 22 hours.The test was continued for 15 cycles, and the rusting of the relevant parts was evaluated. The rate was measured.

Humidity chamber test: 2 times in a humidity chamber at 49℃ and relative humidity of 98% or higher.
It was stored for a week and the rusting rate of the part concerned was measured.

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

O: No rust was observed, and the rust resistance was extremely good.

○: 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%.

×: The rusting rate is 30% or more, and the rust resistance is inferior to that of tinplate.

As is clear from the above test results, the present invention is superior to the comparative example in all aspects such as DI formability and outer surface rust resistance.

(Effects of the Invention) According to the present invention, it is possible to provide a surface-treated steel sheet for containers that is excellent in rust resistance and appearance and is used as a material for two-piece cans.

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 surface-treated steel sheet for containers with excellent rust resistance and appearance, characterized by having been subjected to Sn plating on the surface corresponding to the inner surface of the can.