JPH0874092A - Manufacturing method of tin-plated steel sheet with excellent paint adhesion - Google Patents

Abstract

(57) [Summary] [Purpose] In the case of tin-plated steel sheets used for welding cans, there is a step of melting electrodeposited tin, and a tin oxide film is inevitably formed in this step. Since this tin oxide is mechanically brittle, when an external force is applied to the coating film after coating, the tin oxide undergoes cohesive failure, causing peeling of the coating film. It is an object of the present invention to provide a fundamental measure against poor paint adhesion of tin-plated steel sheets due to the presence of a tin oxide film. [Structure] A steel sheet having a tin plating film formed by an electroplating method is subjected to hot-melting tin treatment by resistance heating and / or induction heating, if necessary, and after water cooling, is immersed in an acidic solution of pH 4 or less and / or Electrolytic treatment, washing with water, cathodic electrolysis treatment in an aqueous solution containing chromic acid as a main component, and forming a chromate film on the tin plating film. Law.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel sheet having a tin-plated film, and industrially relates to a method for producing a product used in large quantities as a steel sheet for containers such as beverage cans and food cans. is there.

[0002]

2. Description of the Related Art Metal containers are roughly classified into three-piece cans consisting of a canopy, a canopy, and a can and two-piece cans in which the can body and the can are integrated. For both the three-piece can and the two-piece can, a product obtained by tin-plating a steel plate is used. In the case of a 2-piece DI can, it is drawn twice (Drawing) and ironed 2-3 times (Ir
oning). After the molding can is removed from the lubricating oil for molding with an alkaline degreasing agent, it is subjected to a coating base treatment with chromic acid, phosphate or the like to have excellent paint adhesion. The DI cans include beverage cans filled with beer, carbonated drinks, and aerosol cans filled with antiperspirant, shaving cream, and the like, and the number of manufactured cans is increasing year by year because they are containers closely related to daily life.

On the other hand, three-piece cans are currently represented by adhesive cans and welded cans, and tin-free steel (a steel plate having a two-layer structure film of metallic chromium and hydrated chromium oxide) is used for the adhesive cans. Tinned steel sheets are used for the cans. The tin-plated steel sheet used for the welding can is cold-rolled.
It is manufactured by cleaning the surface of the annealed and pressure-regulated steel sheet, then electroplating it in a tin plating bath, and heating and melting the electrodeposited tin by resistance heating and / or induction heating. This is necessary for forming a tin-iron alloy layer, adjusting the plating gloss, and the like, and is a major step for tinplate production. Then, chromate treatment is performed in a solution containing chromic acid or dichromate as a main component,
A film containing metal chromium and / or hydrated chromium oxide as a constituent is formed. By this treatment, oxidation resistance, paint adhesion, etc. are imparted and the product is obtained.

[0004]

In recent years, the main market of welded cans in Japan is beverage cans, and most of the cans are used after being internally coated. For the corrosion resistance on the inner surface of the can, in the past, there was a case where a tin coating film having a large basis weight was used in some cases, but recently, the corrosion resistance is ensured by an organic coating film. Therefore, if any defect occurs in the organic coating film on the inner surface of the can, tin or iron may be dissolved in the contents, and the taste, flavor, appearance, etc. may change, resulting in a defective product. If it is more violent, it becomes a perforated can, which may lead to an accident of leakage of the contents.

In the case of tin-plated steel sheets used for welding cans,
As described above, there is a step of melting the electrodeposited tin, and a tin oxide film is inevitably formed in this step. The produced tin oxide film remains on the surface of the steel sheet without being completely removed by the chromate treatment bath. Since this tin oxide is mechanically brittle, when an external force is applied to the coating film after coating, the tin oxide undergoes cohesive failure, causing peeling of the coating film. This phenomenon has been clarified by many researchers in the past. (For example, "Tintaki and Tin Free Steel" (Agne, 1970) 17
3 to 182). The present invention has been found as a result of various studies on various fundamental measures against the problem of poor paint adhesion of tin-plated steel sheets due to the presence of a tin oxide film.

[0006]

According to the present invention, a steel sheet having an electrodeposition tin film formed by an electroplating method is subjected to hot tin treatment by resistance heating and / or induction heating, if necessary, and then cooled to pH 4 after water cooling. It is characterized in that it is immersed or / and electrolytically treated in the following acidic solution, washed with water, and then subjected to cathodic electrolytic treatment in an aqueous solution mainly containing chromic acid to form a chromate film on the tin plating film. The present invention relates to a method for producing a tin-plated steel sheet having excellent paint adhesion. In view of the basic idea of the present invention, it is important to suppress the formation of the tin oxide film as much as possible, and it is advantageous to omit the hot-melting tin treatment. However, it is quite difficult to omit the hot-melting tin treatment in order to secure performance such as corrosion resistance, appearance, and weldability due to the formation of an alloy layer, etc. In many cases, the molten tin treatment is practically involved. Even if the hot tin treatment can be omitted, it is considered that the formation of the tin oxide film is unavoidable in the current line because the equipment is configured to dry once before the chromate treatment.

In the present invention, the tin-plated steel sheet after plating or molten tin treatment is immersed or / and electrolytically treated in an acidic solution having a pH of 4 or less to dissolve and remove the tin oxide film. As a method of dissolution removal, a method of reducing by cathodic electrolysis,
It can be divided into the method of melting the base material and removing the oxide. In the case of reduction by cathodic electrolysis, a method of performing high Coulomb treatment in an acidic solution having a pH of 4 or less in a high temperature bath of 40 to 80 ° C is effective. The acidic solution may be a solution of organic acids such as sulfuric acid, sulfate, phosphoric acid, phosphate, and citric acid, which may be used alone or as a mixed solution and has a pH of 4 or less, more preferably pH 2.5.
The following solutions are used. In particular, sulfuric acid or its salt is most recommended because of its excellent conductivity, economy, chemical dissolution ability, and the like. The amount of cathodic reduction electricity is 50 coulomb / m ² or more, preferably 500 to 5,000 coulomb / m ² .

There are two methods for dissolving the base material and removing the oxide. One is a promotion method by anodic electrolysis, and the other is a chemical dissolution method. The chemical dissolution method is a method of dipping and dissolving in an acidic solution, and acids having strong dissolving power of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and other halogen acids are used alone or in combination. The temperature is room temperature to 7
About 0 ° C is practical. A shorter immersion time is practically preferred, but about 0.2 to 4 seconds is a practical range. When the substrate is dissolved and oxides are removed by anodic electrolysis, 2
It is effective to pass an anode current of 0 coulomb / m ² or more. In this case, by adopting a liquid composition effective for chemical dissolution, the electrolysis and the chemical dissolution can proceed at the same time, and the treatment time can be dramatically shortened.
An effective effect can be expected with an electrolysis time of about 2.0 seconds. The treatment bath composition is sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid,
In addition, acids having a strong dissolving power such as halogen acids are used alone or as a mixture. A practical temperature range is room temperature to 70 ° C.

The acid treatment solution is removed from the surface-activated tin surface by washing with water and immediately introduced into the chromate treatment bath without drying. At that time, what is important is that the washing operation is performed within a short time so that the oxide film is not formed again. As the chromate treatment bath, a bath containing chromic acid as a main component (concentration of 30 to 150 g / l) and sulfuric acid or a fluorine compound as an auxiliary agent alone or mixed and added to about 1/30 to 1/300 with respect to chromic acid To use. At a bath temperature of 30 to 70 ° C., preferably 40 to 60 ° C., high current density electrolysis of 20 A / dm ² or more, preferably 30 A / dm ² is performed. On the tin surface from which the oxide film has been removed, it is better to carry out electrolysis at a higher current density than in the usual case. A chromate film containing metallic chromium is formed by high current density electrolysis, and even if coating baking is performed at a high temperature, the tin oxide film does not grow, and excellent paint adhesion can be maintained. As the chromium adhesion amount after the chromate treatment, good paint adhesion can be secured in the range of 0.2 to 30 mg / m ² of metallic chromium and 1 to 25 mg / m ² of hydrated chromium oxide (as chromium).

The embodiments of the present invention will be described in detail below.

【Example】

Example 1 A slab manufactured by continuous casting or ingot / slabbing by melting in a converter or an electric furnace is hot-rolled, pickled, cold-rolled, further annealed and temper-rolled to obtain a plate thickness of 0. A 19 mm steel plate was produced. The surface of the annealed and pressure-regulated steel sheet having a thickness of 0.19 mm was cleaned, and then electroplated with 2.8 g / m ² of electric tin using a phenol sulfonate tin plating bath. After washing and drying with water, the steel sheet was heated to 250 ° C. by electric heating, cooled immediately in water immediately after the plated tin was melted, and dried to obtain a tin plate with high gloss. Next, at room temperature, this steel sheet was immersed in a tank containing a sulfuric acid solution having a pH of 1.0 (temperature: 45 ° C.) and subjected to a cathodic electrolysis treatment at a current density of 20 A / dm ^{2 for} 1.2 seconds. After washing with water for a short time, a cathodic electrolysis treatment was carried out for 0.5 seconds at a current density of 35 A / dm ^{2 in} a chromate treatment bath (55 ° C.) containing 100 g / l of chromic acid and 1.0 g / l of sulfuric acid.

Example 2 It was manufactured by the same method as in Example 1 above. Thickness 0.19m
After cleaning the surface of annealed and pressure-controlled steel sheet of m,
1.4 g / m using tin ruphonate plating bath² Electric tin
Plated. After washing and drying, the steel sheet is heated by applying electricity.
Immediately after the plating tin is melted by heating to 250 ° C in water
After cooling and drying, a semi-gloss tin plate was obtained. Then always
Solution containing sulfuric acid solution (temperature 55 ° C) with pH = 0.8 at high temperature
This steel plate is dipped in the tank and the plating surface is 0.08g / m
² It melted to the extent that the tin in the melted. After washing with water for a short time,
Chromate treatment of 100 g / l of mumic acid and 1.0 g / l of sulfuric acid
Current density 35A / dm in bath (55 ℃) ² At 0.
The cathodic electrolysis treatment was performed for 5 seconds.

Example 3 The same method as in Example 1 was used. Thickness 0.19m
After the surface of the annealed and pressure-adjusted steel sheet of m was cleaned, 1.3 g / m ² of electric tin plating was performed using a tin phenol sulfonate plating bath. After washing and drying with water, the steel sheet was heated to 250 ° C. by electric heating, cooled immediately in water immediately after the plated tin was melted, and dried to obtain a semi-gloss tin plate. Next, at room temperature, this steel sheet was immersed in a tank containing a sulfuric acid solution having a pH of 0.5 (temperature: 45 ° C.), and anodically electrolyzed at a current density of 5 A / dm ^{2 for} 0.6 seconds. After washing with water for a short time, 0.5 g at a current density of 25 A / dm ^{2 in} a chromate treatment bath (55 ° C.) containing 100 g / l of chromic acid and 0.6 g / l of sulfuric acid.
Cathodic electrolysis treatment for seconds.

Example 4 The same method as in Example 1 was used. Thickness 0.19m
After cleaning the surface of annealed and pressure-controlled steel sheet of m,
1.3 g / m using tin ruphonate plating bath² Electric tin
Plated. After washing and drying, the steel sheet is heated by applying electricity.
Immediately after the plating tin is melted by heating to 250 ° C in water
After cooling and drying, a semi-gloss tin plate was obtained. Then always
A solution containing a hydrochloric acid solution (temperature: 45 ° C) having a pH of 0.8 at a temperature
This steel plate is dipped in the tank and the plating surface is 0.06g / m
² It melted to the extent that the tin in the melted. After washing with water for a short time,
Chromate treatment of 100 g / l of mumic acid and 0.6 g / l of sulfuric acid
Current density 25A / dm in bath (55 ℃) ² At 0.
It was subjected to cathodic electrolysis for 5 seconds.

Example 5 It was manufactured by the same method as in Example 1 above. Thickness 0.19m
After the surface of the annealed and pressure-adjusted steel sheet of m was cleaned, 1.3 g / m ² of electric tin plating was performed using a tin phenol sulfonate plating bath. After washing and drying with water, the steel sheet was heated to 250 ° C. by electric heating, cooled immediately in water immediately after the plated tin was melted, and dried to obtain a semi-gloss tin plate. Then, at room temperature, the steel sheet was immersed in a tank containing a mixed solution of sodium sulfate having a pH of 0.8 (temperature: 45 ° C.) to obtain a current density of 3
A cathodic electrolysis treatment was carried out for 1.2 seconds at 0 A / dm ² . After washing with water for a short time, a current density of 30 A / in a chromate treatment bath (55 ° C.) of chromic acid 100 g / l and sulfuric acid 1.0 g / l
It was subjected to cathodic electrolysis treatment for 0.5 seconds at dm ² .

Comparative Example 1 The same method as in Example 1 was used. Thickness 0.19m
The surface of the annealed and pressure-controlled steel sheet of m was cleaned, and then electroplated with 2.8 g / m ² of electric tin using a tin phenol sulfonate plating bath. After washing and drying with water, the steel sheet was heated to 250 ° C. by electric heating, cooled immediately in water immediately after the plated tin was melted, and dried to obtain a tin plate with high gloss. Then
In a chromate treatment bath (55 ° C.) containing 100 g / l of chromic acid and 1.0 g / l of sulfuric acid, a cathodic electrolysis treatment was performed at a current density of 35 A / dm ^{2 for} 0.5 seconds.

Comparative Example 2 The same method as in Example 1 was used. Thickness 0.19m
After the surface of the annealed and pressure-adjusted steel sheet of m was cleaned, 1.3 g / m ² of electric tin plating was performed using a tin phenol sulfonate plating bath. After washing and drying with water, the steel sheet was heated to 250 ° C. by electric heating, cooled immediately in water immediately after the plated tin was melted, and dried to obtain a semi-gloss tin plate. Then, in a chromate treatment bath (55 ° C.) containing 100 g / l of chromic acid and 0.6 g / l of sulfuric acid, a cathodic electrolysis treatment was performed at a current density of 25 A / dm ^{2 for} 0.5 seconds.

Epoxyphenol resin was applied to the steel sheet prepared by the above method and baked at 210 ° C. for 10 minutes. After that, the coated surfaces are heat-bonded and water-cooled with a nylon adhesive, and after standing for 24 hours, the T-peel strength (one steel plate adhered to the chuck of the tensile tester is sandwiched by the tensile tester and adhered to the other chuck). The other steel plate was sandwiched and pulled up and down to measure the peel strength of the adhesive surface). The results are shown in Table 1. Comparative example is 3
In contrast to the strength of around kg / cm, all the examples of the present invention showed a peel strength of 6 kg / cm or more, which proved to have excellent paint adhesion.

[0018]

[Table 1]

[0019]

By applying the manufacturing method of the present invention,
Since a steel sheet having extremely excellent paint adhesion can be obtained, various effects are expected in the production of welded cans. The first is to improve corrosion resistance. In the can manufacturing process, even if various external forces are applied to the coating film surface, excellent coating adhesion does not generate coating film defects, so good corrosion resistance is secured. The second effect is workability. When performing necked-in processing (processing for reducing the can diameter) for attaching a lid with a small can diameter after welding, there is no processing problem due to peeling of the coating film, and smooth processing is possible.

Claims (2)

[Claims] 1. A steel sheet having a tin-plated film formed by electroplating is immersed in an acidic solution having a pH of 4 or less and / or electrolytically treated, washed with water, and then subjected to cathodic electrolysis in an aqueous solution containing chromic acid as a main component. A method for producing a tin-plated steel sheet having excellent paint adhesion, which comprises performing a treatment to form a chromate film on the tin-plated film. 2. A steel sheet having a tin plating film formed by an electroplating method is subjected to hot-melting tin treatment by resistance heating and / or induction heating, cooled with water, and then immersed in an acidic solution having a pH of 4 or less and / or Electrolytic treatment, washing with water, cathodic electrolysis treatment in an aqueous solution containing chromic acid as a main component, and forming a chromate film on the tin plating film. Law.