JPH0633506B2 - Method for producing surface-treated steel sheet with excellent weldability and paint adhesion - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a surface-treated steel sheet for a welding can, which is suitable for various foods, beverages, and other filling preservation.

BACKGROUND ART Tin and tin-free steel sheets are generally used as materials for containers used in foods and beverages, and recently, thin tin-plated steel sheets with reduced tin plating (to ensure weldability) , Some have Ni plating on the base), and nickel-plated steel sheets are also used for the purpose of reducing material costs.

In terms of cost, tin-free steel sheets are extremely superior to tin-plated steel sheets and nickel-plated steel sheets, not to mention tinplate. Also, the tin-free steel sheet is very excellent in terms of paint adhesion and corrosion resistance after painting, and the fact that these characteristics are excellent is also the reason why the demand for the tin-free steel sheet is increasing.

However, this tein-free steel sheet has a very big defect that the weldability is poor, and at present, it is exclusively made by a bonding method or welded after grinding and removing metal chromium and chromium oxide layers on the surface layer. Cans are manufactured by the can manufacturing method. Therefore, improving the weldability of the tin-free steel sheet has great industrial significance. Various attempts have been made to improve the weldability of thetain-free steel sheets, and the following are listed, for example.

(1) JP-A-62-124296, JP-B-61-1518, JP-A-56-127776, and JP-A-56-44793 are examples of Sn-plated lower layers of the chrome-plated layer to improve weldability.

(2) JP-A-62-40396, JP-A-62-107097, JP-A-61-91393, and JP-A-62-205297, which are Ni-plated under the chromium-plated layer to improve the weldability.

(3) JP-A-62-20529 discloses that the chrome plating layer itself has been devised (often, the chrome plating is made to have a protruding shape or discontinuous to reduce the resistance during welding).
7, JP-A-62-99497, JP-A-63-35797, JP-A-62-6367
8, JP-A-61-281899 and JP-A-61-213399. All of them are intended to improve the weldability by improving the insulating properties of the chromium plating layer and the hydrated chromium oxide layer.

Problems to be Solved by the Invention (1) has a large amount of base Sn plating required to reduce the contact resistance, and, like the thin Sn plated steel sheet, the original tin-free steel sheet for improving weldability. Sacrifices the characteristics of. That is, although the weldability of the tin-free steel sheet is improved, the original excellent characteristics of the tin-free steel sheet, such as metallic luster appearance, excellent paint adhesion, and corrosion resistance after painting, are sacrificed. Therefore, it cannot be said that it is an excellent surface-treated steel sheet for cans.

The present invention is a metal luster appearance, which is a characteristic of an excellent tein-free steel sheet, paint adhesion, without impairing corrosion resistance after painting,
It is intended to provide a surface-treated steel sheet that is cheaper than tin plate, has improved weldability, and is capable of high-speed can making.

MEANS FOR SOLVING THE PROBLEM The present invention is directed to “grains of tin to be plated after degreasing and pickling on a steel plate surface, using an acidic tin plating bath containing no additive as a commonly used brightener. Divalent tin ion concentration 2 to 20 g /, acid concentration 10 to 50 g / so that the diameter becomes 0.2 to 1.5 μ
(Sulfuric acid conversion), plating current density within the range of ^{2 to} 15 A / dm ² is selected, and tin plating of ²⁰ to 200 mg / m ² is performed,
After that, 30 to 150 mg / m ² of metallic chrome by ordinary chrome plating or chrome plating and chromate treatment,
A method for producing a surface-treated steel sheet having excellent weldability and paint adhesion, which is characterized by coating ^{2 to} 40 mg / m ² of chromium oxide as chromium ”.

Hereinafter, the present invention will be described in detail. The present invention is a tin plating bath in which the base tin plating is not an ordinary tin plating bath, but a tin plating bath from which an additive called a brightening agent which is usually added to a tin plating bath is removed, and the plating conditions are selected to perform tin plating. A very small amount of tin plating is applied so that the particle size of 0.2 to 1.5μ. After performing a very small amount of granular tin plating, a conventional chromium plating bath and a chromate treatment bath are used to form a metallic chromium layer and a chromium oxide layer.

Regarding whether seam weldability is significantly improved by applying a tin plating layer obtained from a tin plating bath containing no brightening agent to the lower layer, tin plating obtained from a tin plating bath containing no brightening agent is It is presumed that by selecting the particles, the particles have a particle size of 0.2 to 1.5 μm, and this granular tin acts as a conductor in the initial stage of seam welding.

That is, the seam weldability of the TEIN FREE steel plate is inferior because the surface layer is uniformly covered with a metal chromium or chromium oxide layer, the electric insulation of these layers is high, and the welding current during seam welding is applied. It is presumed that this is due to inhibition of However, if granular tin is present in the lower layer, it is presumed that this granular tin serves as a current-carrying part, so that current can be smoothly conducted during seam welding.

FIG. 1 shows a schematic view (assuming drawing) of the coating film cross section of the product manufactured by the method of the present invention. The steel plate 1 has a roughness (0.2 μRa), and the metal chromium and the chromium oxide layer 3 have When considering the thickness and the like, it can be sufficiently assumed that the tin particles 2 of 0.2 to 1.5 μm act as a conductor. (A = 0.01-0.03μ, b
(0.2-1.5μ, c = 0.1-0.3μ) Incidentally, JP-A-62-124296 also suggests that tin plating undercoating improves the weldability of a tin-free steel sheet. The contents of the invention differ greatly in the following points.

First of all, the concentration of divalent tin ions in the tin plating bath is 2 to 20 g / in the present invention.
In 62-124296, the normal tin plating concentration range is 30 to 80 g /. Although the concentration of divalent tin ions in the tin plating bath is a major factor in determining the tin plating state, granular tin can be obtained within the scope of the present invention.
With 296, it is difficult to obtain granular tin.

The second difference is whether or not an additive is added to the plating bath. In the present invention, since it is important to first deposit 0.2 to 1.5μ of granular tin on the steel sheet, it is an essential condition that no additive is added. That is, when an additive (a brightening agent added to a tin plating bath such as ethoxylated α-naphthol and ethoxylated α-naphthol sulfonic acid) is used in the present invention, it is difficult to obtain granular tin and seam weldability is improved. I can't improve. Of course, in the range of thin tin plating, even if an additive is added, partial tin plating will result and the exposed state of the steel plate will remain, but even in this case, the tin will have a planar shape (or small unevenness). It is not granular and has no surface irregularities sufficient to improve weldability.

As described above, the plating layer structure is similar to that of the present invention.
6 and the difference between the present invention and the present invention, but in summary, the purpose of the present inventors is to obtain 0.2-1.5μ granular tin, and improve the conductivity (weldability improvement) with this granular tin. The aim of the inventors of JP-A-62-124296 is the same in terms of "improving the conductivity by the tin plating layer", but the inventors of the present invention aim at the deposition state of tin plating. It's very different.

FIG. 2 shows the appearance of granular tin (a) obtained in the plating bath without the addition of the brightening agent of the present invention (a) and the appearance of tin plating obtained from the tin plating bath in which the usual brightening agent is added (b). Scanning electron micrograph (×
5,000). The plating conditions at this time were the same except that a phenol sulfonic acid bath was used, with or without a brightener, and the divalent tin ion concentration was 10 g / and the acid concentration (as sulfuric acid) was 50.
g /, current density 5 A / dm ² , tin plating amount 100 mg / m ² .

The contents of the present invention and the reasons for limitation will be described in more detail below.

First, regarding the divalent tin ion concentration in the tin plating bath,
The reason for limiting the amount to 20 g / is that if it is less than the lower limit value, the precipitation current efficiency of tin plating is 50% or less, which hinders high productivity, and if it exceeds the upper limit value, no matter how the plating conditions are selected, it is 0.
This is because granular tin plating having a size of 2 μ or more cannot be obtained.

Fig. 3 shows the relationship between the average particle size of granular tin obtained by plating at a current density of ² to 5 A / dm ² and the concentration of divalent tin ions in the tin plating bath. Granular tin becomes smaller as the concentration increases, and at 20 g /, 2 A / dm ²
Even if plated with, it will be less than 0.2μ.

Next, for the reason for limiting the current density, the applicable current density differs depending on the concentration of divalent tin ions, and in order to obtain granular tin plating, it is necessary to set ² to 15 A / dm ² . The lower limit is the current density at which the target granular tin is obtained when the divalent tin ion concentration is 20 g /, and the upper limit is the tin of the target particle size when the divalent tin ion concentration is 2 g /. The current density at which plating is obtained.

Next, the limitation of the acid concentration (sulfuric acid conversion) to 10 to 50 g / shows only the optimum range for stably allowing the divalent tin ion to exist. That is, when the acid concentration of divalent tin is in an inappropriate range (when the acid concentration is lower than that of divalent tin ion), the divalent tin ion is oxidized to form tetravalent tin ion, which is a normal acid tin. It precipitates as a hydroxide in the plating bath. This 2
It is necessary to keep the acid concentration appropriate for the purpose of preventing the oxidation of valent tin ions to tetravalent tin ions. When the concentration of divalent tin ions is low, the acid concentration may be low, and conversely, when the concentration of divalent tin ions is high, it is necessary to increase the acid concentration. Further, when the acid concentration is higher than necessary, the deposition current efficiency of tin plating decreases, so the upper limit is determined.

In the present invention, the tin plating amount is suitably ²⁰ to 200 mg / m ² , and preferably 80 to 150 mg / m ² . The lower limit of tin plating is determined from the viewpoint of ensuring weldability. If it is less than 20 mg / m ² , weldability cannot be ensured, so the lower limit is 20 mg / m ² . on the other hand,
The upper limit is determined in order to secure the properties of the tin-free steel plate, specifically, the properties such as surface appearance (color tone), paint adhesion, and coating corrosion resistance. That is, although the tin plating amount increases, the characteristics of the tin-plated steel sheet appear and the excellent performance of the tin-free steel sheet is impaired, however, the upper limit is set to 200 mg / m ² . Therefore, the optimum amount of tin plating should be the above-mentioned 20 from the required weldability, paint adhesion, coating corrosion resistance, etc.
It may be appropriately determined within the range of up to 200 mg / m ² .

Next, the chrome plating and the chromate treatment method will be described. In the present invention, these chrome plating and chromate treatment methods are not particularly limited.
That is, according to a method for producing a normal tin-free steel plate, chromium plating and chromate treatment may be performed,
The area ratio occupied by granular tin is 20% or less, and if chromium plating and chromate treatment are performed by a normal method, metallic chromium and a chromium oxide layer are formed on the exposed portion of the steel sheet, and the characteristics are the same as those of ordinary tin-free steel sheets. Will be shown.

Depending on the plating conditions, metallic chromium does not precipitate on the granular tin and a chromium oxide layer is exclusively formed, or vice versa, but within the range investigated by the present inventors,
The precipitation of chromium on the granular tin is slightly less than that on the exposed portion of the steel sheet. Further, even if chromium is deposited on the granular tin, the lower layer tin has a thickness of 0.2 μ or more, which is presumed to contribute to the reduction of contact resistance. Therefore, in the present invention, the state of chromium deposition on tin plating is not particularly limited,
It is essential that the exposed portion of the steel plate forms the original chromium plating layer and chromium oxide layer.

Therefore, the chromium plating layer of the surface-treated steel sheet of the present invention, the amount of the chromium oxide layer, the range of general Tein-free steel sheet metal chromium 30 ~ 150 mg / m ² , chromium oxide layer chromium 2 ~ 40 mg. Limited to / m ² (metal chrome equivalent). Generally, chromium of chromium oxide is required to be 10 mg / m ² or more, but this is to secure the adhesive force in the adhesive can manufacturing method and to secure general paint adhesion. Is 2
About mg / m ² is sufficient, and the thickness of the chromium oxide layer that adversely affects seam weldability is preferably as small as possible. In the present invention, the lower limit amount of chromium (chromium oxide layer) is set slightly lower. Therefore, the amount of metallic chromium and the amount of chromium oxide are
It may be appropriately selected within the above range depending on the can manufacturing method, contents and the like.

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. Example 1 Low carbon cold-rolled steel sheet having a thickness of 0.23 mm which was cold-rolled, continuously annealed, and temper-rolled by a conventional method. And normal degreasing (Na
OH 50g /, 60 ℃, current density 10A / dm ² for 1 second cathodic electrolysis treatment, pickling (sulfuric acid 50g /, 30 ℃, current density 10A / dm ² 1
Second cathodic electrolysis treatment), and then tin plating and chromium plating under the following treatment conditions. Examples 1 to 5 shown in Table 1, Comparative examples 1 to 2 and then Conventional Examples 1 to 5 Create
The evaluation results are summarized in Table 1.

1. Tin plating [Tin plating conditions for Examples and Comparative Examples] (1) Bath conditions Sn ²⁺ 10 g / phenol sulfonic acid 30 g / (H ₂ SO ₄ conversion) Bath temperature 40 ° C (2) Plating conditions Current density 3 A / dm ² Electricity 0.5 to 5.0 C / dm ² (Coulombs / dm ² ) [Tin plating conditions of the conventional example] (1) Bath conditions Sn ²⁺ 10 g / phenol sulfonic acid 30 g / (sulfuric acid conversion) ethoxy α-naphthol 2g / (with brightener) Bath temperature 40 ℃ (2) Plating condition Current density 3A / dm ² Electricity 0.5 to 5.0C / dm ² 2. Chromium plating (1) Bath conditions CrO ₃ 100 g /, H ₂ SO ₄ 1.2 g / bath temperature 50 ° C (2) Plating conditions Current density 50 A / dm ² Electricity 50 C / dm ² 3. Evaluation (1) Coating adhesion Epoxyphenol-based paint (Kansai Paint Co., Ltd. SJ-6256) was applied on the test material, and after baking (coating amount 50 mg / dm ² ), 3.0
After performing retort treatment at 110 ° C. for 60 minutes in a NaCl solution, a flaw was inserted into a cross board with a knife and a tape peeling test was performed.

(10 (good) ← → 1 (poor)) (2) Adhesion of paint After epoxy-based paint (Kansai Paint Co., Ltd. SJ-6256) was applied and baked on the test material (coating amount 50 mg / dm ² ), 1.5% NaCl, 1.5% after cross-cutting with a knife
Dip in a citric acid solution (40 ° C) for 4 days, and then perform a tape peeling test on the cross-cut part for evaluation. (5 (good) ←
→ 1 (poor) (3) Contact resistance After the sample material was first heat-treated at 210 ℃ for 30 minutes, 50mm
Cut into squares, stack these two test pieces, and electrode diameter is 4.5mm
Insert between φ electrodes. Then, a pressure of 50 kgf was applied between the electrodes, and the contact resistance was measured. (The current flowing between the electrodes is 10
00mA) 500μΩ or less is acceptable (weldability is good) (4) Evaluation of tin-plated grains The sample material is observed with a scanning electron microscope at a magnification of 5000 to 10,000 times. The size of a representative tin grain was measured.

(5) Evaluation of product appearance Evaluation was performed based on the appearance of thetain-free steel sheet.

◎: Equivalent to tein-free steel plate 〇; Almost equivalent to tein-free steel plate ×; Different from tein-free steel plate Example 2 Cold-rolled, continuous-annealed, and temper-rolled low-carbon cold 0.23 mm thick by the usual method Normal degreasing (Na
OH 50g /, 60 ℃, current density 10A / dm ² for 1 second cathodic electrolysis treatment, pickling (sulfuric acid 50g /, 30 ℃, current density 10A / dm ² 1
Second cathodic electrolysis treatment), followed by tin plating, chromium plating, and chromate treatment under the following treatment conditions, and Examples 1 to 6 shown in Table 2 were carried out, followed by Comparative Examples 1 to 3.
Next, Conventional Examples 1 to 3 were prepared, and the evaluation results are summarized in Table 2.

1. Tin plating (1) Bath condition [Example] Bath condition A Sn ²⁺ 5g / H ₂ SO ₄ 30g / bath temperature 40 ° C Bath condition B Sn ²⁺ 15g / H ₂ SO ₄ 30g / bath temperature 40 ° C [Comparative example] ] Bath conditions C Sn ²⁺ 25 g / H ₂ SO ₄ 30 g / bath temperature 40 ° C. [Conventional example] Bath conditions D Sn ²⁺ 30 g / phenol sulfonic acid (H ₂ SO ₄ conversion) 30 g / ethoxy α-naphthol sulfone Acid (brightener) 2 g / bath temperature 40 ° C (2) Plating conditions Current density 5 A / dm ² Electricity 0.5 to 5.0 C / dm ² 2. Chromium plating (1) Bath conditions CrO ₃ 100 g /, H ₂ SO ₄ 1.2 g / bath temperature 50 ° C (2) Plating conditions Current density 50 A / dm ² Electricity 50 C / dm ² 3. Chromate treatment (1) Bath conditions CrO ₃ 50 g /, H ₂ SO ₄ 0.1 g / bath temperature 50 ° C (2) Treatment conditions Current density 10 A / dm ² Electricity 10 C / dm ² Effects of the Invention As described in detail above, first tin-plated in granular form,
After that, by providing metallic chromium and chrome oxide layers in the same manner as the ordinary tein-free steel plate, the excellent appearance, paint adhesion, and corrosion resistance after painting of the tain-free steel plate are maintained, and yet high-speed seam welding is performed. A surface-treated steel sheet having excellent properties was obtained.

According to the present invention, high-speed seam welding, which was conventionally possible only with tinplate, ultra-thin tin-plated steel sheets, and nickel-plated steel sheets, is now possible with surface-treated steel sheets having substantially the same characteristics as ordinary tin-free steel sheets.

[Brief description of drawings]

FIG. 1 is a schematic view of a coating cross section of a surface-treated steel sheet manufactured by the method of the present invention, and FIGS. 2 (a) and 2 (b) are metal structures after tin plating obtained in a tin plating bath with or without a brightening agent added. FIG. 3 is a drawing-substituting photograph showing the appearance of the above with a scanning electron microscope, and FIG. 3 is an explanatory view of the relationship between the concentration of divalent tin ions in the tin plating bath and the average particle diameter of tin particles with the current density as a parameter. 1 ... Base iron, 2 ... Granular tin, 3 ... Metal chrome, chrome acid layer.

Claims (1)

[Claims] 1. After degreasing and pickling on the surface of a steel sheet, a generally used acidic tin plating bath containing no additive as a brightener is used, and the tin particle size is 0.2 to 1.5 μm. So that the concentration of divalent tin ion is 2 to 20 g /, and the concentration of acid is 10 to 50 g /
(Sulfuric acid conversion), plating current density within the range of ^{2 to} 15 A / dm ² is selected, and tin plating of ²⁰ to 200 mg / m ² is performed,
After that, 30 to 150 mg / m ² of metallic chrome by ordinary chrome plating or chrome plating and chromate treatment,
A method for producing a surface-treated steel sheet having excellent weldability and paint adhesion, which comprises coating ^{2 to} 40 mg / m ² of chromium oxide as chromium.