JPH09195084A - High corrosion resistance tin-plated steel sheet manufacturing method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To control the formation of an alloy layer and establish a technique for producing a highly corrosion-resistant tin-plated steel sheet. SOLUTION: In an acidic tin plating solution having a Sn ²⁺ ion concentration of 10 to 40 g / l and a solution pH of 0.5 to 1.5, a steel sheet to be plated is used as a cathode, a cathode current density of 100 A / dm ² or more, and a current efficiency of 5 A tin pre-plating is performed under a condition of -30%, and then a target plating amount of tin plating is performed in an acidic tin plating solution, and then a melting treatment is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion resistance having a dense alloy layer of tin and iron, which secures the properties of a tin plate material used in an unpainted state, in particular, corrosion resistance and improves high-speed productivity. The present invention relates to a method for manufacturing a tin-plated steel sheet.

[0002]

2. Description of the Related Art AT is used as an index of tinplate corrosion resistance.
C (Alloy Tin Couple), ISV (lron Solution Valu
e), TC (Tin Crystal), PL (Pickle Lag Time)
It has been known. In particular, the ATC value has a good correlation with the life of the can material using tinplate, as shown in FIG.
Material manufacturers often use this ATC value as a quality control index.

As a method for reducing the ATC value, it is known to control an alloy layer (FeSn ₂ ) of tin and an iron base formed by performing a melting process after tin plating.

However, when tinplate is manufactured in the usual process, pinholes may occur in the tin plating layer or the tin-iron alloy layer, and the pinholes cause corrosion.
Therefore, in order to suppress the occurrence of pinholes, it has been considered to suppress the occurrence of pinholes by, for example, generating a large amount of alloy layer and improving the continuity of the alloy layer. However, the formation of a large amount of alloy layers is not a good solution, because it involves a risk that the metal tin plating layer having excellent corrosion resistance is reduced and the alloy layer is hard so that sufficient processing characteristics cannot be obtained.

Therefore, various studies have been made so far, and a method for controlling the alloy layer formation has been proposed.

For example, as seen in Japanese Patent Laid-Open Nos. 62-284086 and 57-108291,
It has been reported that tin plating is performed after pre-plating such as Ni plating and Fe plating, and a melting treatment is performed to densify the alloy layer, suppress pinholes, and improve corrosion resistance. Ni plating is a well-known technique for densifying an alloy layer or improving wettability with a plating metal, and is a widely used alloy layer control technique, but it is brought into the post-process of the Ni plating solution. It is economically difficult to provide a water washing step in order to prevent Ni from being mixed into the tin plating solution.

The function of Fe plating is to keep the surface layer of the steel sheet in a state close to that of pure iron to uniformly generate nuclei for the tin-iron alloy layer formed by the melting process. That is, normally, on the iron surface that has been degreased and pickled,
Since iron-based oxide films and hydroxide films are generated, and there are some parts that are too large, even if a melting process is applied after tin plating in that state, the formation of the alloy layer in that part is delayed, and There was a concern that it would create holes.

Fe plating is considered to be an effective means for removing iron oxides and the like. However, it was necessary to take appropriate measures and investment such as preventing contamination of the tin plating solution by bringing it into the post-process of the iron plating solution and increasing the washing process after the iron plating.

[0009]

Therefore, the present invention prevents the tin plating solution from being contaminated and controls the formation of the alloy layer.
An object of the present invention is to provide a method for producing a highly corrosion-resistant tin-plated steel sheet excellent in TC value with high productivity.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made earnest studies as to whether or not the above-mentioned alloy layer control effect can be obtained by the metal constituting tin, that is, tin, and as a result, tin having excellent corrosion resistance is obtained by the following means. Enables the manufacture of plated steel sheets.

Sn ²⁺ ion concentration 10 to 40 g / 1, liquid P
In an acidic tin plating solution of H 0.5 to 1.5, with a steel sheet to be plated as a cathode, under conditions of a cathode current density of 100 A / dm ² or more and a current efficiency of 5 to 30%, the tin plating amount ≦ 0.56 g /
Highly corrosion-resistant tin plating characterized by forming a dense alloy layer of tin and iron by applying a target tin plating amount in a tin plating solution after performing m ² plating and performing a melting treatment. Steel plate manufacturing method.

The reason why the tin plating conditions are limited in the present invention will be described below.

First, the Sn.sup.2 ⁺ ion concentration was set to the same level as that of a commonly used phenol sulfonic acid type bath, or set to a high concentration in order to cope with high current density electrolysis. This aim is that, when considering a production system pursuing high productivity in recent years, the same plating amount can be secured at a higher speed than in the conventional case with high current density electrolysis. The Sn ²⁺ ion concentration may be determined according to the current density. That is, as the current density increases, the Sn ²⁺ ion concentration may be increased in order to obtain a sound plating layer, but if it is too large, the economical efficiency is impaired. That is, if the plate is passed at high speed, the plating solution is often taken out of the system and is wasted. The appropriate Sn ²⁺ ion concentration is considered to be 10 to 40 g / l from the viewpoint of economical efficiency and ensuring the soundness of plating under high current density.

Next, the pH of the solution must be controlled to 0.5 to 1.5. If it is less than 0.5, the pickling effect is too strong to effectively carry out tin electrodeposition, and the appearance of electrodeposition is poor. On the other hand, if it exceeds 1.5, the electric fold appearance is black.
No good plating appearance was obtained.

Next, the current density during electrolysis is 100 A / d.
It was set to m ² or more. It is well known that high current density electrolysis densifies a plated crystal, and it is considered that a dense crystal of pre-tin plating, which becomes a nucleus for generating an iron-tin alloy layer, is generated. However, due to the high current density, it should be noted that when the flow rate of the plating solution is low, a phenomenon such as plating burn that deteriorates the soundness of the plating occurs.

Next, it is necessary to control the plating current efficiency within a certain range. This aim is for the following reasons. It is important to remove the iron-based oxides and hydroxides generated on the steel plate to be plated, that is, the iron surface, and it was considered to utilize the cleaning effect of hydrogen gas generated from the iron surface during electrolysis. However, at the same time as gas generation and iron surface cleaning, it is necessary to form nuclei for generation of an alloy layer on the iron surface, that is, to cause tin electrodeposition. The current efficiency is 5 to 30 as the distribution of the amount of electricity so that the gas generation and the tin electrodeposition can occur simultaneously and efficiently
% (Amount of electricity used for tin electrodeposition).

The Sn ²⁺ ion concentration, the current density, the flow rate of the plating solution, and the current efficiency are closely related to each other.
It may be determined in consideration of plating equipment and the like.

Next, regarding the tin plating amount, 0.56
When the amount exceeds g / m ² , the alloy layer forming effect is saturated and it is not necessary to perform further plating.

The stipulations of the numerical values of the present invention are determined for the above reasons.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In order to clarify the effects of the present invention, Table 1 shows manufacturing conditions of some Examples and Comparative Examples.

That is, a steel sheet degreased and pickled according to a conventional method was subjected to pre-electrolytic tin plating using the steel sheet as a cathode under the conditions shown in Table 1, followed by final tin plating and a known melting treatment.

Next, Table 2 shows the performance characteristics of the tin-plated steel sheet produced under the conditions.

As shown in Table 2, all of No. 1 to 5 within the conditions of the present invention are Sn-Fe alloy layer amount and ATC.
The value was satisfactory. On the other hand, No. 6 of the comparative example is an example in which normal tin plating is applied without pre-tin plating. In this case, the Sn—Fe alloy layer and A
The TC value was a normal value and was not satisfactory. Comparative examples No. 7 and No. 9 are S of the pre-tin plating solution.
When the values of the n-ion concentration and the cathode current density deviate from the values specified in the present invention and are lowered, No. 8 of the comparative example has a high Sn-ion concentration value of the pre-tin plating solution, and the cathode current density is Although an example in which is set low is shown, the Sn-Fe alloy layer amount and the ATC value are inferior to those of the present invention.

The performance evaluation was carried out according to the following method.

Evaluation criteria for the amount of Sn-Fe alloy layer formation ⊚: 70% or less of the normal process ○: 70 to 90% of the normal process Δ: Equivalent amount to the normal process Evaluation standard of ATC value measurement ◎: 70% of the normal process Hereafter, ◯: 70 to 90% of the normal process Δ: Equivalent amount to the normal process Here, the normal process is to deposit a predetermined amount at a time in the acidic tin plating solution, and to perform the pretreatment as in the present invention. It means a process without plating.

From these results, the tin-plated steel sheet obtained by the production method of the present invention has a low ATC value, though the amount of Sn-Fe alloy layer is smaller than that in the usual process.
That is, it has good corrosion resistance, or the ATC value is reduced even when the alloy layer amount is equivalent.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

According to the manufacturing method of the present invention, a tin-plated steel sheet having excellent corrosion resistance can be obtained. In addition, since an ATC value lower than that in the normal process can be obtained with a small amount of alloy layer, the production rate can be increased, and the ATC value equivalent to that in the normal process can be obtained with a smaller amount of alloy layer.
The condition for obtaining the TC value can also be set, and the present invention is a technique that also leads to improvement in high-speed productivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an ATC value and a can life.

Claims (1)

[Claims] 1. An acidic tin plating solution having a Sn ²⁺ ion concentration of 10 to 40 g / l and a solution pH of 0.5 to 1.5, with a steel sheet to be plated as a cathode, a cathode current density of 100 A / dm ² or more and a current efficiency. Under conditions of 5-30%, tin plating amount ≤ 0.56g
Of a high corrosion-resistant tin-plated steel sheet having a dense alloy layer of tin and iron, which is characterized by performing a target plating amount in a tin plating solution and performing a melting treatment after pre-tin plating of 1 / m ² / m ^2. Production method.