JPH059780A - Surface-treated steel sheet for container excellent in corrosion resistance and appearance - Google Patents

Abstract

PURPOSE:To provide a surface-treated steel sheet for container have excellent corrosion resistance, appearance and high-temp. coating and baking property to be used as a material for a two-piece can (for drawing and ironing (e.g. DI can)). CONSTITUTION:This surface-treated steel sheet for container has plating layers on the surface corresponding to the outer surface of a can to be produced. These layers are a lower layer consisting of 0.5-20g/m<2> zinc-iron alloy plating layer containing 0.5-30% iron, and 0.5-10g/m<2> tin plating layer as an upper layer, and if necessary, a chromate film having 1-50mg/m<2> chromium deposition is formed as the outermost layer. Thus, excellent corrosion resistance, print finishing property and high-temp. coating and baking property can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet for containers, which is used as a material for two-piece cans (drawing and ironing (for example, DI cans)) and has excellent rust resistance and appearance and high-temperature paint baking properties. is there.

[0002]

2. Description of the Related Art In recent years, a can making method (for example, a DI processed can making method) by squeezing and ironing mainly for beverage cans has been remarkably developed, and there is a great demand for a surface-treated steel sheet for containers having higher performance than ever before. strong.

Conventionally, as a surface-treated steel sheet for DI cans, for example, "a steel sheet for a seam welded can having a Sn plating layer and a Ni plating layer formed thereon (Japanese Patent Publication No. 63-18676)", "Sn for steel sheet" Plated layer, steel plate for seam welded can with chromate treatment on it (Japanese Patent Publication No. Sho 63-30998), "Electroplated steel plate for seam can containing P in the Sn plating layer film (Japanese Patent Publication No. 1- No. 32308) ”, and many tinplates with good DI moldability have been used, but the following are major problems on the outer surface side of the can.

Rust is likely to occur on the outer surface of the can, and when immersed in tap water, river water, or salt water, rust is generated in a short time at the bottom portion and the flawed portion.

[0007] Tin has a problem in print finish after the DI molding, because the outer surface side of the can becomes glossy and the appearance after printing becomes dark.

After the DI molding, the base metal is exposed, which causes variations in the chemical conversion treatment, resulting in a problem of uniform printability.

At present, these problems can be dealt with by increasing the coating film thickness of the undercoating performed before printing.

If the coating film thickness is increased and the coating film having no coating defects is applied on the outer surface of the can, good print finish and uniform printability can be secured.

However, this method cannot deal with the problem of rusting at the damaged portion of the coating film, that is, at the scratched portion on the outer surface of the can.

Further, if the coating film thickness is increased, the coating cost is high and it is economically disadvantageous.

[0011]

DISCLOSURE OF THE INVENTION The present invention exhibits excellent rust resistance on the outer surface of a can, has good can-making processing characteristics (particularly DI moldability), and has good print finish after DI molding. The object of the present invention is to provide a surface-treated steel sheet for a container which has good uniform printability and is economically compatible.

[0012]

That is, the gist of the present invention is that 0.5 to 30% of Fe is added to the side of the steel plate corresponding to the outer surface of the can.
Zn-Fe alloy plating layer containing 0.5 to 20 g / m
² and then 0.5 to 10 g / m ² of Sn plating layer on it, or 1 to 50 mg in terms of chromium conversion
The present invention provides a surface-treated steel sheet for containers, which has a chromate film of / m ² and has excellent corrosion resistance and appearance.

[0013]

The present invention will be described in detail below.

In the present invention, as a plating original plate, a plating original plate having a material suitable for a use as a steel plate for a container is used.

The method for producing the plated original sheet is not particularly limited, and it is produced from the ordinary billet producing step through steps such as hot rolling, pickling, cold rolling, annealing and temper rolling.

The Zn-Fe alloy plating is applied to the surface of the thus-prepared original plating plate corresponding to the outer surface of the can, and then the Sn plating is applied.

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

The purpose of applying the Zn--Fe alloy plating to the lower layer of the steel sheet on the side corresponding to the outer surface of the can is to ensure good rust resistance and good appearance.

That is, in the conventional steel DI can, the Sn plating layer is damaged by DI processing and the base iron is exposed. When water is present on the surface of the DI can, the base iron has a lower potential than Sn. As a result, the ground iron corrodes.

However, on the surface of the DI can, Zn-
The presence of the Fe alloy prevents the corrosion of the base iron by the sacrificial anticorrosion action of the Zn-Fe alloy on the base iron to ensure good rust resistance, and also to ensure a good appearance after DI processing. -The amount of Fe alloy plated must be 0.5 g / m ² or more.

As described above, the conventional steel DI can has a dark appearance and poor print finish because the base metal is exposed after DI processing.

However, the lower layer has a Zn content of 0.5 g / m ² or more.
By providing the Fe alloy plating layer, the bare iron after DI processing is prevented from being exposed, and the appearance is whitish and the print finish is good.

In addition, to increase the Zn-Fe alloy plating layer,
The print finish is improved, but when the amount exceeds 10 g / m ² , this effect reaches the saturation range. Therefore, economically, the plating amount of Zn—Fe alloy is 10 g / m ² or less.

In order to obtain the effect of such a Zn--Fe alloy plating layer, the Fe content in the plating layer is 0.5%.
The above is necessary.

That is, with a small Fe content of less than 0.5%, when the temperature of the plating layer rises to 198 ° C. or higher during coating baking in the can manufacturing process after DI processing, the contact surface between Sn and Zn may be affected. There is a problem that the plating layer melts and the appearance deteriorates.

This is because the Sn—Zn alloy has a eutectic point at 198 ° C., which lowers the melting point of the plating layer.

However, Zn containing 0.5% or more of Fe
When the --Fe alloy is plated in the lower layer, Zn is alloyed with Fe even when the Sn plating is applied to the upper layer, so that the Sn--Zn alloy layer is not generated and high temperature and high speed coating baking is possible.

If the Zn-Fe alloyed plating layer exceeds 30%, even if Sn is plated on the upper layer, the drawing and ironing workability deteriorates significantly.

This is because when the Fe content exceeds 30%, Zn
This is because the Fe alloy becomes harder than pure Zn and the lubricity required for drawing and ironing is lost.

Therefore, it is necessary to regulate the Fe content contained in the Zn--Fe alloy to 0.5 to 30%.

Further, Sn plating on the upper layer is carried out by using Zn-- on the lower layer.
It imparts good DI processability to the Fe alloy plating layer, and a basis weight of 0.5 g / m ² or more is required.

If the Sn plating amount is less than 0.5 g / m ² , the lubricity at the time of DI processing becomes insufficient, and "galling" in which the plating layer is damaged by the die becomes large.

However, the Sn plating layer having a plating amount of more than 10 g / m ² is economically disadvantageous because the effect of improving DI processability is saturated. Therefore, the Sn plating amount of the upper layer is 0.
It was set to 5 to 10 g / m ² .

The lower layer Zn— having such excellent characteristics
The plating bath for forming the Fe alloy plating layer and the upper Sn plating layer is not particularly limited, and the lower Zn-
For Fe alloy plating, a sulfuric acid bath, a pyrophosphoric acid bath, a cyanide bath, and a chloride bath are used. The Fe% in the alloy plating layer is mainly controlled by the balance of the metal ion amount in each bath, and the alloy plating amount is also electrolyzed. It can be obtained by controlling the number of coulombs required for.

For the Sn plating, a pyrophosphoric acid bath, a cyanide bath, a sulfuric acid bath, a chloride bath or a ferrostane bath is used, and the plating amount is controlled by the Coulomb number required for electrolysis.

(Chromate) Further, in the present invention, as described above, for a plated steel sheet having a Zn—Fe alloy plating layer as a lower layer on the outer surface and an Sn plating layer as an upper layer,
Chromate treatment is performed as necessary for the purpose of preventing discoloration of the plating layer due to air oxidation.

For the chromate treatment, an aqueous solution of chromic acid sodium salt, potassium salt or ammonium salt is generally used, and the treatment method is not particularly limited, but for example, dipping treatment,
Spray processing and electrolytic processing.

The amount of chromate adhered by the chromate treatment needs to be 1 mg / m ² or more in terms of the amount of metal chromium.

This is because a chromate coating formed by the chromate treatment cannot completely cover the plated steel sheet with a small amount of deposited chromium of less than 1 mg / m ^{2, and} therefore discoloration due to air oxidation cannot be prevented.

If the amount of deposited chromium exceeds 50 mg / m ² , it is economically disadvantageous.

Thus, a slight amount of chromate film is effective for preventing air oxidation of the plating layer.

Further, after the DI molding, a chromate treatment or a phosphoric acid treatment is applied as a chemical conversion treatment in order to improve the coating performance and the corrosion resistance after the coating. In the present invention, these treatment methods and treatment conditions after the DI molding are described. However, there is no particular restriction, and a commonly used treatment method is applied.

[0043]

EXAMPLES Examples of the present invention will be described below. The results are shown in Table 1.

After cold-rolling and annealing processes, the plating base plate adjusted to the material and plate thickness according to the purpose of DI can is electrolytically degreased and washed in 5% caustic soda, and electrolytically pickled in 10% sulfuric acid to be surface activated. , (1)-(a) on the surface corresponding to the inner surface of the can,
Sn plating was performed under the conditions shown in (b), or an organic film was laminated under the conditions shown in (2), and then the conditions shown in (3)-(a) and (b) were applied to the lower layer of the surface corresponding to the outer surface of the can. Zn-Fe plating is carried out with (1)-
Sn plating was performed under the conditions shown in (a) and (b).

When performing the chromate treatment,
It carried out on the conditions shown in (4).

(1) Sn plating conditions (a) Sulfuric acid bath plating bath composition Stannous sulfate 10 g / l Sodium sulfate 300 g / l Plating bath temperature 55 ° C. Current density 10-30 A / dm ² (electrolysis time depends on the plating amount Adjust)

(B) Pyrophosphate plating bath composition Stannous pyrophosphate 50 g / l Potassium pyrophosphate 100 g / l Plating bath temperature 50 ° C. Current density 10 to 30 A / dm ² (electrolysis time is adjusted according to the plating amount)

(2) Organic film laminating conditions Polyethylene terephthalate film having a film thickness of 40 μm,
Laminate at 200 ° C for 1 second

(3) Zn-Fe alloy plating conditions (A) Pyrophosphoric acid bath plating bath composition Zinc pyrophosphate 10-150g / l (for alloy composition
Adjusted accordingly) Iron pyrophosphate 20-100g / l (for alloy composition
Adjusted accordingly) Potassium pyrophosphate 250g / l Plating bath temperature 50 ℃ Current density 10-30A / dm² (Electrolysis time
Is adjusted according to the plating amount)

(B) Sulfuric acid bath plating bath composition Zinc sulfate 30-250g / l (Depending on alloy composition
Adjust) Iron sulfate 10 to 100 g / l (depending on alloy composition
Adjust) Sodium sulfate 80g / l Plating bath temperature 55 ℃ Current density 20-40A / dm² (Electrolysis time fit
(Adjust according to the amount)

(4) Chromate treatment conditions Bath composition Sodium dichromate 24g / l pH 4.5 Plating bath temperature 45 ℃

Treatment Conditions Immersion Treatment The above treated materials were tested for the following items (A) to (D) to evaluate their performance.

(A) DI moldability Using a water-soluble emulsion type coolant, blank size 136 mm
Can manufacturing speed from φ to 65.9 mmφ 110 cans /
DI can be molded under the molding conditions of min, and DI of various treated materials
The moldability was evaluated. The evaluation criteria are as follows.

⊚: DI moldability is extremely good. ○: Some galling occurs on the outer surface during ironing, but DI
Good molding. Δ: DI molding is possible, but strength galling occurs on the outer surface during ironing, resulting in poor DI moldability. ×: The material was broken during the DI molding process and DI molding was impossible.

(B) Print Finishability after DI Molding A DI can was prepared under the condition of (A), and inks for can outer surfaces of red, white, and yellow were printed at a film thickness of 5 μ, and the print finish was visually observed. It was judged. The judgment criteria are as follows.

◯: Appearance after printing is whitish, and print finish is very good. Δ: The appearance after printing is slightly glossy, and the print finish is slightly inferior. ×: A gloss similar to that of tinplate was observed in the appearance after printing,
Poor print finish.

(C) Rust resistance on the outer surface side The rust resistance on the outer surface side of the DI printing can prepared under the conditions (A) and (B) was evaluated by the following evaluation test. In addition, the evaluation material evaluated the part where the wall part was flawed and the bottom part.

Tap Water Immersion Test: The evaluation material was immersed in tap water at room temperature for 3 days, and the rust rate of the evaluated portion was measured.

Freezing cycle test: The evaluation material was kept in a freezer at -15 ° C for 30 minutes, and immediately after that, 49 ° C and 98% relative humidity.
After putting it in the above humidity tank for 60 minutes, put it in the room at room temperature.
The test was continued for 15 cycles, with one cycle being left for a period of time, and the rusting rate of the evaluation evaluation part was measured.

Humidity tank test: Stored in a humidity tank at 49 ° C. and a relative humidity of 98% or more for 2 weeks, and the rust rate of the evaluated portion was measured.

The evaluation criteria of rust resistance in each test are as follows: ⊚ No rust was found at all, and rust resistance was extremely good. ◯: Rust resistance is 5% or less and good rust resistance. Δ: Rust resistance is 5 to 30%, and rust resistance is slightly inferior. X: Rust resistance is 30% or more, and rust resistance is inferior to tin plate.

(D) Plating Layer Melting Test A DI can prepared under the conditions of (A) was placed in a drying oven at 230 ° C. for 1 hour.
After holding for 0 min, the melting of the plating layer on the outer surface of the can was visually observed. The judgment criteria are as follows.

O: No melting of the plating layer is observed. Δ: Melting of the plating layer is slightly observed. X: Melting of the plating layer is observed in the entire can.

[0064]

As is apparent from the above test results, the formability and print finish of the plated steel sheet obtained by the method of the present invention are higher than those of the plated steel sheet presented as a comparative material which deviates from the scope of the present invention. , Shows stable and excellent performance.

[0065]

[Table 1]

[0066]

[0067]

[0068]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadaaki Ochiai             Futtsu City Shintomi 20-1 Shin Nippon Steel Co., Ltd.             Central Research Division

Claims (2)

[Claims] 1. Fe is added in an amount of 0.5 to 3 on the side of the steel plate corresponding to the outer surface of the can.
0.5-20 g of Zn-Fe alloy plating layer containing 0%
/ M ² applied, excellent container for surface treated steel sheet corrosion resistance and appearance characterized over that which has been subjected to Sn plating layer 0.5 to 10 g / m ² thereon. 2. Fe of 0.5 to 3 is provided on the side of the steel plate corresponding to the outer surface of the can.
0.5-20 g of Zn-Fe alloy plating layer containing 0%
/ M ² applied, thereon subjected to Sn plating layer 0.5 to 10 g / m ^2, and further 1 to 50 mg / m in terms of chromium coating weight
^A surface-treated steel sheet for containers with excellent corrosion resistance and appearance, which is characterized by applying the chromate film of ² .