JPH0474889A - Surface treated steel sheet for container having excellent rust resistance and appearance - Google Patents

Abstract

PURPOSE:To provide the surface treated steel sheet for containers adequate as a material for two-piece cans having excellent rust resistance and appearance by applying a lower layer plating of Zn on the outside surface side of the cans and applying an Sn-Zn alloy plating contg. a specific ratio of Zn on the upper layer thereof. CONSTITUTION:The Zn plating layer of 0.5 to 20 g/m<2> is formed on the lower layer of the surface corresponding to the outside surface side of the cans and the Sn-Zn alloy plating layer of 1.0 to 20 g/m<2> contg. 5 to 97.5% Zn is formed on the upper layer thereof. A chromate film of 1 to 50 mg/m<2> deposition in terms of chromium is otherwise formed further on the extremely outer surface layer on the surface of the steel sheet corresponding to the outside surface side of the cans. The exposing of the base iron after DI working is prevented and the whitish appearance is obtd. by applying the Zn plating of >=0.5 g/m<2> on the lower layer. The finishing quality of printing is thereby improved. The purpose of applying the Sn-Zn alloy plating at 1.0 to 20 g/mm<2> on the upper layer is to improve the DI workability of the Zn plated steel sheet of the lower layer.

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 with excellent rust resistance and appearance.

(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 has been a strong demand for surface-treated steel sheets for containers with higher performance than ever before. Strong against Conventionally, as a surface treated mesh plate for DI cans, JP-A-5
Tinplates with good DI formability, such as those described in Publication No. 1-43324 and Japanese Patent Application Laid-open No. 139694/1983, have been used, but the following are major problems on the outside 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 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 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 film is thick and a coating film with no 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 processing properties (particularly DI moldability), and has good printing finish after DI molding. It is an object of the present invention to provide a surface-treated copper plate for containers which has good uniform printability and is economically suitable.

(Means for Solving the Problems) That is, the gist of the present invention is to apply a Zn plating layer of 0.5 to 20 g/n (0.5 to 20 g/n) on the lower layer of the surface corresponding to the outer surface of the can, and to apply a Zn plating layer of 5 g/n on the upper layer. ~97.5% containing 1, 0-2
A surface-treated plate for containers with excellent rust resistance and appearance characterized by being coated with a S n, -Z n alloy coating layer of 0 g/n (S n, -Z n), or a surface of the steel plate corresponding to the outer surface of the can. A surface-treated steel sheet for containers having excellent rust resistance and appearance, characterized in that the outermost layer is coated with a chromate film with a coating weight of 1 to 50 cm/bo in terms of chromium conversion.

(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. The manufacturing method of the plated original plate is not particularly regulated, and the plated original plate is manufactured through the usual steps of manufacturing a steel piece, such as hot rolling, pickling, cold rolling, annealing, and temper rolling. Zn plating is applied to the surface corresponding to the outer surface of the can of the plated original sheet manufactured in this way to ensure good rust resistance and good appearance.

The surface corresponding to the inner surface of the can is not particularly limited, and may be plated with ordinary tinplate or laminated with an organic film, for example.

In conventional steel DI cans, the Sn plating layer is damaged due to DI processing and the base metal is exposed, so if moisture is present on the DI can surface, the potential of the base metal becomes base compared to Sn, so the base metal is exposed. Corrode. However, according to the present invention, since a Zn layer that is more base than the base metal exists on the surface of the DI can, corrosion of the base metal can be prevented by sacrificial corrosion protection against the ZnO base metal. In order to ensure good rust resistance and a good appearance after DI processing, the amount of Zn plating in the lower layer must be 0.5 g/rd or more. By applying Zn coating of 0.5 g/m2 or more to the lower layer, exposure of the base metal after DI processing is prevented,
The appearance becomes whitish and the print quality improves. However, if the amount of Zn plating exceeds 20 g/n (20 g/n), the effect of improving printing finish reaches saturation and is economically disadvantageous. Therefore, the amount of Zn plating in the lower layer is set to 20 g/n (20 g/n) or less.

Next, the effects of the upper layer Sn--Zn alloy plating will be described. 160~20g/Sn-Zn alloy plating on the upper layer
n (The purpose of applying this is to improve the DI workability of the lower layer Zn-plated steel sheet.The Sn-Zn alloy plating layer is 1.
If it is less than 0 g/m2, the alloy plating layer will not be able to exhibit its good workability improvement effect;
If the Sn--Zn alloy plating layer exceeds rd, the effect of improving DI workability is saturated, which is economically disadvantageous.

Furthermore, in order to improve the rust resistance of the Sn-Zn alloy plating layer, it is necessary to control the Zn content in the plating layer to 5 to 97.5%. After DI processing of a copper plate with Zn on the lower layer and Sn-Zn alloy plating on the upper layer, the can wall has a base iron part and Z
There is an n plating layer and an Sr+-Zn alloy plating layer. When a steel plate in this state is immersed in an electrolytic solution such as water or salt water, a potential difference is generated between the upper Sn-Zn alloy plating layer and the lower Zn plating layer, creating a local battery and reducing the electrical potential. The Zn plating layer is eluted and the rust resistance deteriorates. Therefore, in order to make this potential difference as small as possible, Sn - Z
By increasing the Zn content in the n-alloy plating layer, the potential is increased to Z
It is necessary to make it close to n plating. In this case, SnZn
If the Zn content in the alloy plating layer is less than 5%, the effect of improving the external rust resistance of the steel plate cannot be obtained for the above-mentioned reasons. On the other hand, S
When the Zn content in the n-Zn alloy coating layer exceeds 97.5%, the lubricity of the Sn-Zn alloy plating layer deteriorates, and the degree to which the outer plating layer is damaged by the die during DI forming, that is, the "galling J" Therefore, it is necessary to create an appropriate Sn-Zn compound that ensures good rust resistance on the outer surface of the DI can and does not cause deterioration of DI formability. Zn in the gold plating layer is 5
~97.5% is required.

The plating baths and controls for forming the lower Zn plating layer and the upper Sn-Zn alloy plating layer with such excellent properties are not particularly regulated, but for Zn plating, sulfuric acid bath, pyrophosphate bath, etc. It is best to control the plating amount by the number of coulombs required for electrolysis using a cyanide bath, chloride bath, etc., and for Sn-Zn alloy plating, use a pyrophosphate bath, cyanide bath, sulfuric acid bath, chloride bath, etc. It is preferable that the amount of alloy plating is controlled by the number of coulombs required for electrolysis, and the Zn content in the alloy plating layer is controlled mainly by the balance of the amount of metal ions in each bath.

Furthermore, in the present invention, in order to prevent discoloration of the plating layer of the plated net plate as described above due to air oxidation, the plated mesh plate may be subjected to chromate treatment as necessary before use. Chromate treatment is generally performed using the sodium salt of chromic acid,
An aqueous solution of potassium salt or ammonium salt is used, and the treatment method is not particularly regulated, but may be, for example, immersion treatment, spray treatment, or electrolytic treatment. The amount of chromate deposited by the chromate treatment is required to be 1 to 50 .mu./bo in terms of the amount of metallic chromium. If the amount of chromium deposited is less than 1 .mu./m.sup.2 drop, the chromate film produced by the chromate treatment cannot completely cover the plated mesh plate, and therefore discoloration due to air oxidation cannot be prevented. Furthermore, even if the amount of chromium deposited exceeds 50 cm/bo, the effect is small and economically disadvantageous. In the present invention, after the plated steel sheet as described above is formed by DI, it may be subjected to a chromate treatment or a phosphoric acid treatment as a chemical conversion treatment in order to further improve painting performance and post-painting corrosion resistance. In the present invention, these processing methods and processing conditions after DI molding are not particularly regulated;
Normally used processing methods can be used.

(Example) Examples of the present invention will be described below. Table 1 shows the results of performance evaluation test pieces of Examples and Comparative Examples.

Through cold rolling and annealing processes, the plated original plate was adjusted to the material and thickness suitable for DI can use and can lid use. After electrolytic degreasing and water washing in 5% caustic soda, it was electrolytically pickled in 10% sulfuric acid to achieve surface activation. After oxidation, S was applied to the surface corresponding to the inner surface of the can under the conditions shown in (1).
Zn plating or lamination with an organic film under the conditions shown in (2), followed by Zn plating on the lower layer of the surface corresponding to the outer surface of the can under the conditions shown in (3)-(), (3)-(o).
Plating is applied, and the upper layer is (4) - (a), (4) - (n
) Sn-Zn alloy plating was performed under the conditions shown in (). Then, one that was subjected to chromate treatment under the conditions shown in (5) and one that was not subjected to chromate treatment were prepared.

(1) Sn plating conditions Plating bath composition: tin sulfate 20-30g/f additive 1-5g
/f Plating bath temperature 50"C Current density 15-25A/d Bo (electrolysis time is adjusted according to the amount of Sn plating) (2) Organic film lamination conditions Polyethylene terephthalate film with film thickness 40j!rn, 200"C at 11 seconds Lamination (3) Zn plating conditions (a) Pyrophosphate bath Plating bath composition Zinc pyrophosphate 10-150g//! zinc sulfate
20-100 g/i! .

Potassium birophosphate 250g/A plating bath temperature
50°C current density 10
~30A/dm2 (electrolysis time is adjusted according to the amount of Zn) (b) Sulfuric acid bath Plating bath composition Zinc sulfate 30~250g/f! Sodium sulfate 80g/ff plating bath temperature
55°C current density 20-40 A
/dm2 (electrolysis time is adjusted according to the amount of Zn plating) (4
) Sn-Zn alloy plating conditions (a) Birophosphate bath Plating bath composition Tin birophosphate 10-50 g/1 (adjusted according to alloy composition) Zinc sulfate 20-100 g/f (adjusted according to alloy composition) ) Mu 250g/i! .

50°C 10-30A/dm" Adjusted according to the amount of alloy coating) Potassium pyrophosphate plating bath temperature Current density (Electrolysis time is Sn-Zn (b) Sulfuric acid bath Plating bath composition Stannous sulfate Zinc sulfate Soda sulfate plating bath temperature Current density 10-60 g/1 (adjusted according to alloy composition) 30-150 g/ff (adjusted according to alloy composition) 300 g/1 55°C 10-30 A/dm2 (electrolysis time depends on the amount of Sn-Zn alloy loading (adjust accordingly) (5
) Chromate treatment conditions Bath composition NaCrz03 24 g/'
pH 4,5 Bath temperature 45°C Treatment conditions Immersion treatment The above-mentioned treated materials were tested for items (A) to (C) 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 anφ under molding conditions of a can making speed of 110 cans/min, and DI of various treated materials was molded. The moldability 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.

△;D■ Forming is possible, but strong galling occurs on the outer surface during ironing, and DI formability is poor.

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

(B) Printing finish after DI molding A DI can was created under the conditions of (8), red, white, and yellow ink for the outside of the can was printed in 5 film thicknesses, 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) 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 -I5°C for 3
After holding at 0m1n, immediately put the test piece in a humidity chamber at 49 °C and relative humidity of 98% or higher for 60ff+in, and then leave it indoors at room temperature for 22 hours.The test was continued for 15 cycles, and the rusting rate of the relevant part was evaluated. It was measured.

Humidity tank test: The product was stored in a humidity tank at 49°C and a relative humidity of 98% or higher 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.

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

Δ; Rust resistance is slightly inferior with a rusting rate of 5 to 30%.

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

As a result, as is clear from various performance evaluation tests, the plated steel sheets of the present invention exhibit superior properties than the plated steel sheets of comparative examples that deviate from the scope of the present invention, and have excellent rust resistance and appearance. It can be evaluated as follows.

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

Claims (2)

[Claims] (1) 0.5 to 20g/
A Zn plating layer of m^2 is applied, and 5 to 9 Zn is applied on the top layer.
Sn-Zn of 1.0-20g/m^2 containing 7.5%
A surface-treated steel sheet for containers with excellent rust resistance and appearance, featuring an alloy plating layer. (2) The outermost layer of the surface-treated steel sheet for containers according to claim 1, which corresponds to the outer surface of the can, has a coating weight of 1 to 50 m in terms of chromium.
A surface-treated steel sheet for containers with excellent rust resistance and appearance, characterized by being coated with a chromate film of g/m^2.