JPS61264195A - Production of tin-free steel for retort can - Google Patents

Abstract

PURPOSE:To produce a tin-free steel having excellent retort treatment resistance by subjecting a steel sheet to a cathodic treatment in an electrode for reverse electrolysis, Cr plating treatment, reverse electrolytic treatment and electrolytic Cr acid treatment. CONSTITUTION:The steel sheet as a cathode is subjected to the cathodic treatment at 7A/dm<2> current density in an aq. Cr acid soln. in the electrode for the reverse electrolytic treatment. The cold rolled steel sheet is successively immersed for 10sec in a 5% NaOH soln. at 70 deg.C and 8A/dm<2> current density and is then washed. Such steel sheet is subjected to the cathodic treatment for 1.2sec in a plating soln. contg. CrO3 and H2SO4 at 80A/dm<2> and further the steel sheet as an anode is subjected to the reverse electrolytic treatment for 0.2sed at 3.5A/dm<2> and is then immersed in a plating soln. contg. CrO3 and is electrolytically treated with the Cr acid by the cathodic treatment at 10 Coulomb/dm<2> quantity of electricity. The steel sheet is cathodically treated for the cathodic treatment and is used as the electrode for the reverse electrolysis for the anodic treatment in the electrode for the reverse electrolysis for the cathodic treatment, by which the uniform Cr oxide film is formed and the tin-free steel having the stable quality is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a tin-free steel plate having a lower layer of metallic chromium and an upper layer of chromium water-containing oxide on the surface of the steel plate, particularly a retort-resistant steel plate for adhesive cans.

<Prior art and its problems> Recently, electrolytic chromate-treated steel sheets, called tin-free steel chromium type (hereinafter abbreviated as TFS), have been recognized for their properties as a material for cans that can replace tinplate. Applications are expanding not only to low-temperature packs, where the contents are sterilized at low temperatures, but also to so-called hot bags, in which the contents are sterilized at high temperatures before being filled, and can materials, which require retort processing, in which sterilization is performed at high temperatures after packaging. It became so.

With the expansion of this use, the problem has arisen that when TFS is manufactured into cans, the can body is generally bonded with a polyamide adhesive, which causes the can body to break.

The tearing of the can body after each adhesion occurs due to peeling from the paint film-TFS interface, and the decrease in adhesion between the paint film and TFS has traditionally been caused by chromium plating baths,
Wtt-1411cif! by eutectoiding of sulfuric acid added to the electrolytic chromium bath into the hydrated chromium oxide film! +-1, +-*1.1τso'xNi&+)tFIl, b-*
Methods that do not add it to the bath have been proposed. However, chromium plating baths without sulfuric acid have low plating efficiency.
This method is unfavorable in terms of quality stability, as it reduces production efficiency and does not provide stable chromium plating, and many problems remain from an industrial perspective.

Therefore, as a method to solve these drawbacks, it has been proposed to perform reverse electrolysis using the steel plate as an anode in an aqueous chromic acid solution after chromium plating, and then to perform electrolytic chromic acid treatment in an aqueous chromic acid solution (patent application). (See No. 5.6-62766).

However, when reverse electrolysis is applied continuously to the steel plate as an anodizing process between the chromium plating process and the electrolytic chromic acid treatment process, the bath voltage in the chromium bath where the reverse electrolysis electrode is located increases, and the reverse electrolysis This causes the precipitation of metallic chromium and the generation of hydrogen gas on the surface of the electrode, making the reverse electrolytic treatment uneven.
The effect of reverse electrolytic treatment will not be fully exerted. Furthermore, if the effect of reverse electrolytic treatment is insufficient, the properties of the surface layer of the steel sheet will change due to the reverse electrolytic treatment applied after plating, using the steel sheet as an anode, and this will affect the formation of a chromium hydrated oxide film in the subsequent electrolytic chromic acid treatment. This may cause a chromium hydrated oxide film to be formed non-uniformly, leading to a decrease in product quality stability.

<Purpose of the Invention> The present invention provides a method for effectively applying reverse electrolytic treatment to a steel plate without using expensive gold or platinum electrodes for reverse electrolytic treatment for anodizing after chromium plating. Before carrying out the chromium plating process including reverse electrolytic treatment in which the steel plate is anodized in the solution - reverse electrolytic treatment - electrolytic chromic acid treatment, cathodic treatment is performed for several hours at the electrode for reverse electrolytic treatment.

An object of the present invention is to provide a method for manufacturing tin-free steel for retort cans, which can uniformly form a chromium hydrated oxide film by using it as an electrode for anodizing.

<Structure of the Invention> The present invention performs electroplating mainly consisting of metallic chromium by cathodic treatment of a thin steel plate in an aqueous solution containing chromium, followed by anodization in the solution, and then further plating. In order to produce tin-free steel with excellent retort resistance by performing electrolytic chromic acid treatment in an aqueous solution containing chromium, the electrodes used for anodizing are first cathodized, and then the electrodes for anodizing are The present invention provides a method for manufacturing tin-free steel for retort cans, which is characterized in that it is used as a retort can.

The present invention will be explained in more detail below.

According to the present invention, tin-free steel is manufactured by a process using reverse electrolytic treatment using a steel plate as an anode.
In advance, cathode treatment is performed using a steel plate as a cathode in an electrode for reverse electrolytic treatment to stabilize the electrode properties, and then this process is performed, and one side of the thin steel plate is plated with metal chromium at a concentration of 50 to 200 mg/m2, and this metal 5 to 30 mg on the surface of the chromium layer
The objective is to obtain a TFS in which a chromium hydrated oxide film of /m2 is formed.

Even if it exceeds 200 mg/ra2, no improvement in corrosion resistance can be expected, so normal TFS is 50 to 200 mg/s2 (
7) Contains metallic chromium.

On the other hand, if the amount of chromium water-conserving oxide film is less than 5 mg/112, the desired paint adhesion cannot be obtained;
Exceeding this value may result in poor appearance or cracks in the chromium water-retaining oxide film during processing, making it impractical.

Normally, when reverse electrolytic treatment is performed in a chromium plating solution using a steel plate as an anode, for example with a lead-based anode, a yellow scale (PbCrO2) with high electrical resistance is formed on the electrode surface, reducing the electrical conductivity of the anode. It gets worse. The generation of scale impairs electrical conductivity, resulting in non-uniform reverse electrolytic treatment.

Further, this scale forms on the electrode surface and corrodes the electrode to the extent that it crumbles and falls off, making the distance between the electrode and the steel plate unstable.

Therefore, one aspect of the present invention is to minimize the formation of lead dioxide (pbo2) scale, which has good electrical conductivity and is hard and dense, on the node surface by cathodic treatment before scale (PbCr02) is formed on the electrode surface. It is about providing.

By preventing corrosion of the reverse electrolysis electrode in this way,
The effect of the reverse electrolytic treatment becomes uniform, promoting the formation of a stable chromium water-retaining oxide film, and making it possible to produce tin-free steel with excellent retort treatment resistance.

<Example> Hereinafter, the present invention will be specifically explained with reference to examples.

(1) Cathode treatment in the electrode for reverse electrolysis treatment in the chromic acid aqueous solution in the electrode for reverse electrolysis treatment at 7 A/
Cathode treatment was performed for 1 hour using a steel plate as a cathode at a current density of dm2.

Subsequently, a cold-rolled steel plate (T4-CA) with a thickness of 0.22 mm was electrolytically degreased with a 5% NaOH solution at 70°C at a current density of 8 A/dm2 (7) for 10 seconds, and after washing with water, it was degreased with 3% H2
After immersing in SO4 for 5 seconds and washing with water, the steel plate was subjected to the following treatment.

(2) Chromium plating treatment plating solution composition CrO: + 180 gel Solution temperature 5
0°C H2SO40, 75g/I Ha2SiF68 gel Plating conditions: Cathode treatment was performed at a current density of 80 A/da2 for 1.2 seconds.

(3) Reverse electrolytic treatment A reverse electrolytic treatment was performed at 3.5 A/dm2 for 0.2 seconds using the steel plate as an anode.

(4) Electrolytic chromic acid treatment plating solution composition CrO3Go gel Solution temperature 50℃N
a25iFa 5tag/! ;L Plating conditions: Cathode treatment was performed with an amount of electricity of 10 coulombs/d112.

Regarding the case where the steel plate is subjected to the cathodic treatment using the reverse electrolysis electrode of (1) above (invention example) and the case where it is not applied (comparative example), the above (2) chromium plating treatment, (3) reverse TFS by combining electrolytic treatment and (4) electrolytic chromic acid treatment.
Figure 1 shows the variation over time in the amount of chromium water-retaining oxide coating in the width direction of the plate, which was analyzed using fluorescent X-rays.

As mentioned above, the effects of the present invention are as clarified through the embodiment shown in FIG. By using it as an electrode for reverse electrolysis, a uniform chromium oxide film is formed, and the quality stability of the product can be ensured.

[Brief explanation of drawings]

FIG. 1 is a graph showing the variation over time in the amount of chromium hydrated oxide coating in the width direction of the plate under constant current supply conditions. 22..., (Oshi1 yt:: - Tsukasa r M, l,. FIG, 1 Between the ends of use (H") A

Claims (1)

[Claims] Electroplating consisting mainly of metallic chromium is performed by cathodic treatment of a thin steel plate in an aqueous solution containing chromium, followed by anodization in the solution, and then electroplating of chromium in an aqueous solution containing chromium. A retort can characterized in that, in producing tin-free steel with excellent retort treatment resistance by acid treatment, the electrode used for anodization is previously subjected to cathode treatment and then used as an electrode for anodization. Manufacturing method for tin-free steel.