JPH059782A - Surface-treated steel sheet for containers with excellent rust resistance and appearance - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a surface-treated steel sheet for a container, which is used as a material for a two-piece can (drawing and ironing, for example, a DI can) and has excellent rust resistance, appearance, and high-temperature paint baking property. provide. [Composition] Chromium is added to the bottom of the surface corresponding to the outer surface of the can in an amount of 0.0
It has a zinc-chromium alloy plating layer of 0.5 to 20 g / m ² containing 3 to 7%, and then zinc 5 to 97.5 as an upper layer.
% Of 1 to 20 g / m ² of tin-zinc alloy plating layer, and depending on the case, it may be 1 in terms of chromium equivalent deposition amount on the outermost layer.
The surface-treated steel sheet for containers having a chromate coating of up to 50 mg / m ² can ensure excellent rust resistance, print finish, and high temperature paint bakeability.

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. .

[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. Therefore, conventionally, as a surface-treated steel sheet for a DI can, for example, a steel sheet is coated with a Sn plating layer, and then a Ni plating
Steel plate for seam welding cans with a plated layer (Japanese Patent Publication No. 63-1
No. 8676), a steel sheet having an Sn plating layer, and a chromate-treated steel sheet for a seam welding can (Japanese Patent Publication No. 63-30).
998), an electroplated steel sheet for seam cans containing P in the Sn plating layer film (Japanese Patent Publication No. 1-232308).
Although many tinplates having good DI moldability have been used, 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 part and the scratched part. After DI molding, the tin plate has a glossy appearance on the outer surface side of the can, resulting in a dark appearance after printing, which causes a problem in print finishability. Since the base metal is exposed after DI molding, the chemical conversion treatment varies, and there is a problem in uniform printability. Currently, it is possible to deal with these problems by increasing the coating film thickness of the undercoating performed before printing. Certainly, if the coating thickness is increased 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 secured. However, this method cannot deal with the problem of rusting on the damaged portion of the coating film, that is, the flawed portion on the outer surface of the can.
Further, if the coating film thickness is increased, the coating cost will be high and it will be economically disadvantageous.

[0003]

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

[0004]

That is, the gist of the present invention is that 0.03 to 7% of Cr is present on the side of the steel plate corresponding to the outer surface of the can.
Zn-Cr alloy plating layer containing 0.5 to 20 g / m
² applied, containing 5 to 97.5% of Zn thereon Sn-
A surface-treated steel sheet for containers excellent in rust resistance and appearance in which a Zn alloy plating layer is applied in an amount of 1 to 20 g / m ² or a chromate film having a chromium conversion amount of 1 to 50 mg / m ² is applied. Is.

[0005]

The present invention will be described in detail below. In the present invention, a plating original plate having a material suitable for a use as a steel plate for a container is used as the plating original plate. 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-Cr alloy plating is applied to the surface of the thus-produced plating original plate corresponding to the outer surface of the can, and then the Sn-Zn alloy 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—Cr 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 to expose the base iron, and when water is present on the surface of the DI can, the base iron has a lower electric potential than Sn, so Corrodes. However, if a Zn-Cr alloy, which is less base metal than the base metal, is present on the surface of the DI can, Zn-C
The sacrificial anticorrosion effect of the r alloy on the base iron ensures good rust resistance to prevent the corrosion of the base iron, and further, in order to secure a good appearance after DI processing, the Zn-Cr alloy plating amount is set to 0. It is necessary to make it more than 0.5 g / m ² . 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, by applying a Zn-Cr alloy plating layer of 0.5 g / m ² or more to the lower layer, it is possible to prevent the base metal from being exposed after DI processing, to give a whitish appearance and a good print finish. Further, the print finish is improved by increasing the Zn-Cr alloy plating layer, but when the amount exceeds 20 g / m ² , this effect reaches the saturation region. Therefore, economically Zn-Cr
The alloy plating amount is preferably 20 g / m ² or less.

Further, in order to obtain the effect of such Zn--Cr alloy plating, the Cr content in the plating layer must be 0.03% or more. That is, when the Cr content is as low as less than 0.03%, when the plating layer temperature rises to 198 ° C or higher during coating baking in the can manufacturing process after DI processing, S
There is a problem that the plating layer melts at the contact surface between n and Zn 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, when a Zn-Cr alloy containing 0.03% or more of Cr is plated on the lower layer, Z is plated even if Sn is plated on the upper layer.
Since n is alloyed with Cr, a Sn—Zn alloy layer is not generated and high temperature and high speed coating baking is possible. Further, if the plating layer formed by Zn—Cr alloying exceeds 7%, even if an Sn—Zn alloy plating layer is applied as an upper layer, the drawing and ironing workability is significantly deteriorated. This has a Cr content of 7
This is because the Zn-Cr alloy becomes harder than pure Zn when the content exceeds%, and the lubricity necessary for drawing and ironing is lost. Therefore, Cr contained in the Zn-Cr alloy
It is necessary to regulate the content rate to 0.03 to 7%. Furthermore, the Sn-Zn alloy plating layer of the upper layer is Zn-Cr of the lower layer.
It gives good DI processability to the alloy plating layer.
A basis weight of 0 g / m ² or more is required. Plating amount is 1.
If it is less than 0 g / m ² , good DI processability of the Sn—Zn alloy plating, that is, sufficient lubricity between the material and the mold during DI process cannot be imparted. However, the Sn-Zn alloy plating layer having a plating amount of Sn-Zn alloy plating exceeding 20 g / m ² is economically disadvantageous because the effect of improving DI workability is saturated.

Further, in order to obtain the effect of such a Sn--Zn alloy plating layer, Zn in the plating layer must be contained at 5 to 97.5%. A steel sheet having a Zn-Cr alloy plating as a lower layer and a Sn-Zn alloy plating as an upper layer has a Sn-Zn alloy plating portion and a Zn A local battery is created between the -Cr alloy plated parts, and Zn-C, which is base in terms of potential, is used.
The r alloy plating layer is eluted. Since the elution rate of the Zn-Cr alloy depends on the potential difference between the Zn-Cr plating layer and the Sn-Zn alloy plating layer, it is necessary to make this potential difference as small as possible in order to ensure good rust resistance after DI processing. There is. Although the potential of the Sn-Zn alloy plating layer is considerably noble as compared with that of the Zn-Cr plating layer, the potential is changed to Z by increasing the content of Zn in the Sn-Zn alloy plating layer.
Close to n-plating. Therefore, if the Zn content in the Sn-Zn alloy plated layer is a small content of less than 5%,
For the above reason, the effect of improving the outer surface rust resistance of Zn-Cr is not sufficiently recognized. When the Zn% in the Sn-Zn alloy plating layer exceeds 97.5%, the lubricity is reduced and the outer plating layer is damaged by the die during DI molding, that is, "galling" occurs. Becomes larger, DI
Moldability deteriorates. That is, the Zn content in the Sn—Zn alloy plating layer is 5% to 97% as a proper amount that ensures good rust resistance on the outer surface side of the DI can and does not cause deterioration of DI moldability. Specified as 0.5%. Thus, the lower layer Zn-Cr alloy plating layer and the upper layer Sn-Z having such excellent characteristics
The plating bath for forming the n alloy plating layer is not particularly limited, and a lower layer Zn-Cr alloy plating may be a sulfuric acid bath, a pyrophosphoric acid bath, a cyan bath, or a chloride bath. The Cr content can be controlled mainly by the balance of the amount of metal ions in each bath, and the amount of alloy plating can also be controlled by the Coulomb number required for electrolysis. Upper layer Sn
-Zn alloy plating is carried out with pyrophosphoric acid bath, cyan bath, sulfuric acid bath,
A chloride bath is used, the Zn content in the alloy plating layer is controlled mainly by the balance of the amount of metal ions in each bath, and the amount of alloy plating can also be controlled by the Coulomb number required for electrolysis.

(Chromate) Further, in the present invention, as described above, the plating layer of air is used for the plated steel sheet having the Zn--Cr alloy plating layer as the lower layer and the Sn--Zn alloy plating layer as the upper layer as the outer surface. If necessary, chromate treatment is performed to prevent discoloration due to oxidation. As the chromate treatment, an aqueous solution of chromate sodium salt, potassium salt, or ammonium salt is generally used, and the treatment method is not particularly limited, but examples thereof include dipping treatment, spraying treatment, and electrolytic treatment. The amount of chromate deposited by the chromate treatment needs to be 1 mg / m ² or more in terms of the amount of metallic chromium. This is because a small amount of deposited chromium less than 1 mg / m ² cannot completely cover the plated steel sheet with the chromate film formed by the chromate treatment, so that discoloration due to air oxidation cannot be prevented. Also, the amount of chromium deposited is 50 mg /
If it exceeds m ² , it is economically disadvantageous. Thus, a small amount of chromate film is effective for preventing air oxidation of the plating layer. Further, after DI molding, chromate treatment or phosphoric acid treatment is applied as chemical conversion treatment in order to improve coating performance and post-coating corrosion resistance. In the present invention, these treatment methods and treatment conditions after DI molding are particularly restricted. However, the usual processing method is applied.

[0009]

EXAMPLES Examples of the present invention will be described below. The results are shown in Table 1. The inner surface of the can is subjected to electrolytic degreasing and water washing in 5% caustic soda, electrolytic pickling in 10% sulfuric acid, and surface activation of the original plating plate whose material and thickness have been adjusted by cold rolling and annealing to suit the DI can application. The surface corresponding to (1) is Sn-plated under the conditions shown in (1), or the organic film is laminated under the conditions shown in (2), and then (3)-(a), ( Zn-
Cr plating was performed, and Sn-Zn alloy plating was applied to the upper layer under the conditions shown in (4)-(a) and (b). In addition, the chromate treatment was performed under the conditions shown in (5). (1) Sn plating conditions 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 is adjusted according to plating amount) (2) Conditions for laminating organic film Polyethylene terephthalate film having a film thickness of 40 μm,
Laminated at 200 ° C for 1 second (3) Zn-Cr alloy plating conditions (a) Pyrophosphoric acid bath Plating bath composition Pyrophosphorous acid salt 10 to 150 g / l (adjusted according to alloy composition) Chromium chloride 20 to 100 g / l ( Adjusted according to alloy composition) Potassium pyrophosphate 250 g / l Plating bath temperature 50 ° C Current density 10-30 A / dm ² (electrolysis time is adjusted according to plating amount) (b) Sulfuric acid bath plating bath composition Zinc sulfate 30-250 g / L (adjusted according to alloy composition) Chromium sulfate 10 to 100 g / l (adjusted according to alloy composition) Sodium sulfate 80 g / l Plating bath temperature 55 ° C Current density 20-40 A / dm ² (electrolysis time depends on the plating amount) (4) Sn-Zn alloy plating conditions (a) Pyrophosphate bath plating bath composition Stannous pyrophosphate 10-50 g / l (adjusted according to alloy composition) Zinc sulfate 20-100 g / l ( And adjustment) Potassium pyrophosphate 250 g / l plating bath temperature 50 ° C. according to the gold composition current density 10~30A / dm ² (electrolysis time is adjusted depending on the coating weight) (ii) sulfuric acid bath plating bath composition stannous 10 sulfate -60 g / l (adjusted according to alloy composition) Zinc sulfate 30-150 g / l (adjusted according to alloy composition) Sodium sulfate 300 g / l Plating bath temperature 55 ° C Current density 10-30 A / dm ² (electrolysis time is plating (5) Chromate treatment condition Bath composition Sodium dichromate 24g / l pH 4.5 Plating bath temperature 45 ° C Treatment condition Immersion treatment

Regarding the above-mentioned treated material, the following (A) to
The item (D) was tested to evaluate its performance. (A) DI moldability Using a water-soluble emulsion type coolant, blank size 136 mmφ to can diameter 6
DI cans were molded under a molding condition of a can manufacturing speed of 110 cans / min up to 5.9 mmφ, and the DI moldability of various treated materials 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 moldability. 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) A DI can was prepared under the conditions of print finish (A) after DI molding, and red, white, and yellow can outer surface inks were printed at a film thickness of 5 μ, and the print finish was visually determined. The judgment criteria are as follows. ◯: Appearance after printing is whitish and print finish is extremely good. Δ: Appearance after printing is slightly glossy and print finish is poor. ×: 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 rusting rate of the evaluated portion was measured. Refrigeration cycle test: Evaluate materials in a freezer at -15 ° C for 30
Immediately after holding for min, put it in a humidity tank with a relative humidity of 98% or more at 49 ° C for 60 min and leave it for 22 hours at room temperature for 22 hours to continue the 15-cycle test, and measure the rust rate of the evaluation part. did. Humidity tank test: Stored in a humidity tank of 49 ° C. and a relative humidity of 98% or more for 2 weeks, and measured the rust rate of the evaluation applicable part. The evaluation criteria for rust resistance in each test are as follows: No rust was observed and rust resistance was extremely good. ◯: Rust resistance is 5% or less and good rust resistance. Δ: The rust rate is 5 to 30%, and the rust resistance is slightly inferior. X: Rust resistance is 30% or more, and rust resistance is inferior to tin plate. (D) The DI can prepared under the conditions of the plating layer melting test (A) was placed in a drying oven at 230 ° C.
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. As is clear from the above experimental results, the formability and print finish of the plated steel sheet obtained by the method of the present invention are stable and excellent in performance as compared with the plated steel sheet deviated from the present invention presented as a comparative material. Indicates.

[0011]

[Table 1A]

[0012]

[Table 1B]

[0013]

As described above, the steel sheet obtained by the present invention exhibits extremely excellent performance in formability and print finish, and particularly when used as a can material, it has excellent resistance to the outer surface of the can. Demonstrates rust and has good can-making properties, and DI
The printed finish after forming is good, the uniform printability is also good, and it makes a great industrial contribution as an economically matched surface-treated steel sheet for containers.

Claims (2)

[Claims] 1. A steel plate having a steel outer surface corresponding to a can outer surface containing Cr in an amount of 0.03 to 0.03.
0.5-20 g of Zn-Cr alloy plating layer containing 7%
/ M ² applied, and S containing 5 to 97.5% of Zn thereon
A surface-treated steel sheet for containers excellent in rust resistance and appearance, characterized by being coated with an n-Zn alloy plating layer in an amount of 1 to 20 g / m ^2. 2. A steel plate containing 0.03% to 0.03% of Cr on the outer surface side of the can.
0.5-20 g of Zn-Cr alloy plating layer containing 7%
/ M ² applied, and S containing 5 to 97.5% of Zn thereon
n-Zn alloy plating layer 1-20 m ² subjected, further rust resistance and appearance excellent in container surface treated steel sheet, characterized in that subjected to chromate film of 1 to 50 mg / m ² in terms of chromium coating weight .