JPH0570996A - Production of tin-free steel plate - Google Patents

Abstract

PURPOSE:To provide the process for production of the TFS steel which has excellent secondary adhesion of a coating material and has color tones uniform even in the transverse direction of a strip. CONSTITUTION:This process consists in continuous production of the tin free steel plate by subjecting the steel plate to a cathodic electrolysis in a chromium plating bath after degreasing and pickling to form metallic chromium and chromium oxide films, then subjecting the steel plate to a reverse electrolytic treatment in the same chrome plating bath, sufficiently rinsing the steel plate and, succession, subjecting the steel plate to the cathodic electrolysis in an electrolytic chromic acid treating bath to form the chromium oxide films. The steel plate is subjected to the initial electrolysis by alternating currents consisting of the continuous repetition of the anodic electrolysis and the cathodic electrolysis in the above-mentioned electrolytic chromic acid treating bath before the execution of the cathodic electrolysis in the electrolytic chromic acid treating bath.

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 tin-free steel sheet which is excellent in secondary adhesion of paint and has a uniform appearance.

[0002]

2. Description of the Related Art Tin-free steel plate (hereinafter referred to as TFS)
As a method of joining the can bodies of cans that use as a can body, a method of joining with an adhesive (adhesion method) has become widespread, but with the expansion of applications, the secondary adhesion of TFS paint is improved. The demand for was increased. Many TFS manufacturing methods have been investigated to meet these requirements. Among them, JP-A-57-177998 "TFS production method"
(Reverse electrolysis method) is excellent. This reverse electrolysis method provides excellent secondary coating adhesion by forming a chromium oxide film in the electrolytic chromic acid treatment bath after chrome plating in the chrome plating bath, followed by immediate reverse electrolysis in the same bath, washing with water. Can be produced.

[0003]

In the production of TFS by such a reverse electrolysis method, if the cathodic treatment is carried out as it is in the electrolytic chromic acid treatment bath after the reverse electrolysis treatment, the edge in the width direction of the strip (steel strip) is obtained. There is a problem that the color tone up to 50 mm is different from the color tone of the strip center portion.

[0004]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method for producing a TFS having excellent secondary adhesion of a paint and having a uniform color tone in the strip width direction.

[0005]

SUMMARY OF THE INVENTION That is, according to the present invention,
After degreasing and pickling the steel sheet, and then performing cathodic electrolysis in a chromium plating bath to form metallic chromium and a chromium oxide film, subsequently perform reverse electrolysis treatment in the same chromium plating bath, thoroughly wash with water, and continue electrolysis. A method for continuously producing a tin-free steel sheet for forming a chromium oxide film by performing cathodic electrolysis in a chromic acid treatment bath, wherein the electrolytic chromic acid treatment bath is used before cathodic electrolysis in the electrolytic chromic acid treatment bath. In the above, there is provided a method for producing a tin-free steel sheet (TFS), which comprises performing initial electrolysis on a steel sheet by an alternating current consisting of continuous repetition of anodic electrolysis and cathodic electrolysis.

[0006] TFS produced by the method of the present invention is usually metallic chromium 20 to 200 mg / m ^2, chrome oxide layer is in a range of 5 to 50 mg / m ² reckoned as metal chromium metal in the lower layer of chromium, the upper layer Has a two-layer structure having a chromium oxide film on the steel sheet, after applying a coating material for a can to the inner and outer surfaces,
The can body is formed by adhering the can body via a nylon-based adhesive, and one side of the can body is heated at a temperature of 80 to 95 ° C. after the contents of food and the like are closed after the can lid is wound. For cans that are either hot-packed or hot-packed as the next step, and then the contents are sealed in the cans by wrapping the can body and then heat sterilized (retort treatment) at a high temperature of 100 ° C or higher for sterilization. In the application, even after the retort treatment following the above hot pack, the adhesive strength of the can body joint is sufficiently high, and TF
No peeling (breakage) of the adhesive portion due to a decrease in adhesion between S and the paint, that is, excellent secondary adhesion of the paint and a uniform color tone in the strip width direction.

The present invention will be specifically described according to manufacturing steps. The cold-rolled steel sheet is degreased and pickled, and then subjected to cathodic electrolysis in a chromium plating bath, and metallic chromium is inevitably deposited together with a small amount of chromium oxide film. The chromium plating bath is a normal aqueous solution containing chromic acid as a main component and further containing an appropriate amount of an additive such as sulfuric acid, fluoride or silicofluoride in order to increase the deposition efficiency of metallic chromium. After chrome plating, reverse electrolysis is carried out immediately in the same chrome plating bath. Reverse electrolysis is performed using a DC power supply or an AC power supply, and the chromium oxide film on the steel plate is removed.

Subsequently, the electrolytic chromic acid treatment tank is entered through the dragout tank and the water washing tank. According to the conventional method, cathodic electrolysis is performed by a DC power source, but in the method of the present invention, a power source capable of supplying a current (AC in a broad sense) having current components having different polarities is used. Initial electrolysis is performed before cathodic electrolysis with a DC power supply.

The formation and removal of the chromium oxide film is repeated by such an initial electrolysis to form a dense chromium oxide film in advance, and the desired cathode oxide amount is obtained by the conventional cathode treatment. Here, the electrolytic chromic acid treatment bath is a bath containing chromic acid as a main component and an additive such as sulfuric acid, fluoride or silicofluoride added as an auxiliary agent for increasing the deposition efficiency of the chromium oxide film.

The current having different polarities is preferably an alternating current having a cycle sufficiently repeated within an electrolysis time determined by the moving speed (line speed) of the steel plate and the length of the electrode plate, and is practically 20 msec. The following cycle (Fig. 1
And has a current corresponding to the value of t ₁ -t ₂ ). The subsequent next step is washing with water or washing with hot water, followed by drying.

The TFS thus produced has a uniform appearance and is excellent in the secondary adhesion of the paint.

Although the reason why the uneven color tone in the width direction is eliminated by the present invention is not clear, it is considered to be an action caused by repeating the generation and removal of the chromium oxide film in any case.

[0013]

The present invention will be described in more detail with reference to the following examples and comparative examples. In the following examples and comparative examples, the TFS (Examples 1 to 4) obtained according to the present invention and the conventional method were used. The obtained TFS (Comparative Example 1) was visually observed to evaluate the uniformity of color tone, and the T-peel peel test was performed to evaluate the secondary adhesion of the paint.

(Examples 1 to 4) A cold rolled steel sheet having a thickness of 0.22 mm was continuously produced at a line speed of 200 mpm in a 5% NaOH solution at 85 ° C. at a current density of 10 A / dm ² and 10 After electrolytic degreasing for 2 seconds, wash with water and
It was dipped in 0% H ₂ SO ₄ for 4 seconds, washed with water, and then subjected to chromium plating and reverse electrolysis under the following conditions. Chromium plating conditions Bath composition CrO ₃ 200 g / l + H ₂ SO ₄ 2
g / l Bath temperature 50 ° C. Electrolysis conditions 50 A / dm ² × 1.0 seconds Reverse electrolysis treatment conditions 2 A / dm ² × 0.5 seconds After the above chromium plating treatment and reverse electrolysis treatment, washed with water,
Immediately, electrolytic chromic acid treatment was performed under the following conditions. Electrolytic Chromic Acid Treatment Conditions Bath Composition CrO ₃ 60g / l + F ^- 0.1g
/ L Bath temperature 40 ° C Initial electrolysis condition Anode effective current density for steel sheet 2 A / dm ² (constant) Cathode effective current density for steel sheet 0.1-15 A / d
m ² Electrolysis time 0.5 seconds Cathodic treatment condition 7 A / dm ² × 1.0 seconds

(Comparative Example 1) In the same manner as in Example 1, after performing chrome plating and reverse electrolysis, conventional cathode treatment was performed without initial electrolysis. However, the cathode treatment condition is 10 A / dm ² ×
It was set to 1.0 second. Then, it was washed with water and treated in the same manner as in Example to obtain TFS.

Table 1 shows the results obtained by examining the uniformity of the color tone of the TFS according to the method of the present invention (Examples 1 to 4) and the conventional TFS (Comparative Example 1) and the secondary adhesion of the coating material. From these results, it was confirmed that the TFS according to the method of the present invention has a uniform appearance with no difference in color tone in the width direction of the plate and has a good secondary adhesion property of the coating.

[0017]

[0018]

INDUSTRIAL APPLICABILITY The present invention provides a TFS having no color difference in the plate width direction by using an alternating current as initial electrolysis in electrolytic chromic acid treatment after plating and reverse electrolysis in the method for producing TFS by the reverse electrolysis method. It became possible to manufacture stably.

[Brief description of drawings]

FIG. 1 is a graph showing an example of a waveform of a current used in an initial electrolytic treatment in an electrolytic chromic acid treatment bath of the present invention.

Claims (1)

[Claims] 1. A steel plate is degreased and pickled, and then cathodic electrolyzed in a chromium plating bath to form metallic chromium and a chromium oxide film, followed by reverse electrolysis in the same chromium plating bath, followed by thorough water washing. In a method for continuously producing a tin-free steel sheet for forming a chromium oxide film by continuously performing cathodic electrolysis in an electrolytic chromic acid treatment bath, before performing cathodic electrolysis in the electrolytic chromic acid treatment bath, A method for producing a tin-free steel sheet, which comprises performing initial electrolysis on a steel sheet in an electrolytic chromic acid treatment bath by alternating current consisting of continuous and repeated anodic electrolysis and cathodic electrolysis.