JPH02175145A - Steel sheet for can excellent in corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To obtain a steel sheet for a can excellent in corrosion resistance and weldability by forming metallic chromium on the surface of the steel sheet and forming chromium oxide on the top layer thereof and furthermore forming a resin layer on the top layer thereof. CONSTITUTION:For example, metallic chromium is deposited by electrolytic treatment while utilizing a steel sheet as a cathode in a plating bath contg. ordinary CrO3 as a main agent. Chromium oxide simultaneously formed on the top layer of metallic chromium is removed by washing of water. As the amount of metallic chromium, 20 - 150mg/m<2> generally used as the steel sheet for a can is secured. It is preferable that chromium oxide formed on the top layer thereof is completely removed but this is difficult in the actual operation. Chromium oxide is removed at the amount less than 5mg/m<2>. When chromium oxide is regulated to the amount less than 5mg/m<2>, corrosion resistance is impaired. Corrosion resistance is secured and also deterioration of weldability resulting from chromium oxide is prevented by forming a resin layer on the metallic chromium layer. In other words, when an electrode is pressurized and press-fixed at a time of welding, a crack is caused in the resin film and the electrode can be brought into contact with metallic chromium and electrification is made sure. At this time, when the residual amount of chromium oxide is regulated to the amount less than 5mg/m<2>, power conduction is not kindered and weldability can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steel sheet for cans that has excellent corrosion resistance and weldability.

[Prior Art and Problems to be Solved by the Invention] As is well known, chrome-plated steel sheets for cans have a drawback in weldability. In particular, chromium oxide is formed on the upper layer of the metal chromium layer to improve corrosion resistance, but this chromium oxide inhibits electrical conductivity and is a main factor in reducing weldability.

In order to solve such difficulties, for example, Japanese Patent Application Laid-Open No. 61-2
Publication No. 13399. Japanese Unexamined Patent Publication No. 61-281899 discloses a method in which the surface of metallic chromium is made uneven, the chromium oxide is broken by the convex parts by the pressure of the electrode during welding, and the weldability is improved by contact between the electrode and the metallic chromium. It is disclosed that

However, it is difficult to reliably improve weldability even in such a rommetically plated steel plate.

[Problem to be solved by the invention]

The present invention has been made to advantageously solve these difficulties.

[Means to solve the problem]

The gist of the present invention is as follows.

(1) Metallic chromium 20 to 150 cm/h on the surface of the steel plate.

A steel sheet for cans having excellent corrosion resistance and weldability, characterized in that a resin layer is formed on the upper layer of a metal chromium-plated steel sheet containing less than 5 mg/m2 of chromium oxide.

(2) Metallic chromium 20 with surface irregularities formed on the surface of the steel plate
-150■/bo, chromium oxide on top layer 5■/rrf
A steel sheet for cans with excellent corrosion resistance and weldability, characterized by forming a resin layer on the upper layer of a metal chromium-plated steel sheet consisting of:

The present invention will be explained in detail below.

In the present invention, for example, metallic chromium is deposited by electrolytic treatment using a steel plate (strip) as a cathode in a plating bath mainly containing C, O, etc., and at the same time, chromium oxide produced on the upper layer of the metallic chromium is removed by washing with water, etc. Remove by.

In other words, it is preferable to secure the amount of metallic chromium of 20 to 150 μ/rrf, which is generally used for steel sheets for cans, and to completely remove the chromium oxide that forms in the upper layer, but this is difficult in actual operation. and is removed to less than 5 mg/m2.

As described above, when the content of chromium oxide is less than 5 mg/rrf (including 0), corrosion resistance is significantly deteriorated.

Therefore, in the present invention, a resin layer is formed on top of the metal chromium layer. As such a resin, for example, a polyethylene-based, polyester-based, polypropylene-based, or saran-based resin can be used, and the appropriate coating amount is 20 to 200 μ/rrf. That is, 2
If it is less than 0 .mu./bo, corrosion resistance may be poor, which is not preferable. If it exceeds 200 .mu./rrf, the corrosion resistance will be further improved, but the weldability will be poor, which is not preferable.

That is, by forming the resin, corrosion resistance due to chromium oxide is ensured, and deterioration of weldability due to chromium oxide is prevented. In other words, if the resin is applied as described above and the electrode is pressure-bonded during welding, unlike chromium oxide, the resin film (layer) will crack.
This allows contact between the electrode and metal chromium, ensuring electrical conduction and improving weldability. As mentioned above, chromium oxide
Even if a small amount of oxide remains, less than mg/m2, this level of oxide hardly hinders current flow and can improve weldability. Further, by forming irregularities on the surface of the metal chromium of such metal plating wJFi, weldability can be further improved reliably. That is,
When the pressurizing electrode comes into contact with the convex part, the resin film (layer) is reliably broken, and the metallic chromium convex part comes into contact with the electrode, ensuring electrical conduction, thereby improving weldability.

Conditions for forming unevenness on the metal chromium surface include, for example, a convex diameter of 10 to 200 nm and a number of convex portions of 1.2X10'' to 1.0X.
10" pieces/pot is sufficient, and the forming method is, for example, after metal chromium plating, the plated steel strip is energized as an anode in a plating bath to remove the upper layer of chromium oxide, and then the plated steel strip is plated with electricity. Irregularities can be formed by further applying chromium plating on the metal chromium plating layer as a cathode.Also, unevenness can be formed by applying metal chromium plating to the plated original plate surface which has been dulled to have an uneven surface.

Furthermore, in order to further improve weldability, weldability can be improved by substantially uniformly dispersing and mixing other conductive substances such as graphite powder into the resin film (layer).

The above-mentioned resin can be applied to the surface of a metal chromium-plated steel plate by, for example, processing the resin into a film and pressing it, applying the resin in a molten state using a roll coater, spraying, dipping, or the like. By forming a resin layer in this manner, corrosion resistance and weldability can be improved, and when used, the surface is painted in the conventional manner to form a steel sheet for cans.

〔Example〕

Next, Table 1 lists examples of the present invention along with comparative examples.

Note 1: The steel plate has a plate thickness of 0.17 mm and has a normal tone 2 = The chrome plating in the example uses ordinary C70 as the main agent, and is plated by cathode treatment in a bath using sulfuric acid as a catalyst, and then post-dipped in the plating bath. , chromium oxide was removed. In a comparative example, chromium oxide was newly generated in an electrolytic treatment bath containing C, On as the main ingredients after the metal chromium plating was performed and washed with water.

The unevenness of the metallic chromium was formed by anodizing the metallic chromium plating, followed by chromium plating.

Note 3: Corrosion resistance was determined by applying 50 mg/drrf of epoxy phenol can paint to the test material, baking it, and sealing the end surface.
Scratch with a utility knife until you reach the base (5cm)
x5ca+), then 1.5% citric acid, 1.5%
It was immersed in a saline solution (50°C) for 3 days, and the coating was removed using cellophane tape, and the peeling width was measured. (Peeling width 0
．． Less than 1 rtm O10, 1-0.2 mmΔ, 0.2
(exceeding mm ×) Note 4: Weldability was evaluated using a seam welding machine using a copper wire as an intermediate electrode.

The test material was preheated at 210°C for 20 minutes.

Welding conditions were as follows: lap width Q: 5 mm, pressing force: 40 kgf, speed F: 50 mpm, and current frequency: 400 H2. The evaluation criteria are determined by the width of the appropriate current range, and the lower limit is the weld strength,
The upper limit was determined based on the occurrence of dust (molten iron protruding like a splash). (The appropriate current range was 200 A or more without any practical problems.) Note 5: Resin formation was performed using a roll coater.

(Effects of the Invention) According to the present invention, a chromium-plated steel sheet for cans can be provided with excellent corrosion resistance and weldability, and therefore the present invention is extremely useful industrially.

Claims (2)

[Claims] (1) Metallic chromium 20 to 150 mg/m^ on the steel plate surface
2. A steel sheet for cans having excellent corrosion resistance and weldability, characterized in that a resin layer is formed on the upper layer of a metallic chromium-plated steel sheet containing less than 5 mg/m^2 of chromium oxide. (2) Metallic chromium 20 with surface irregularities formed on the surface of the steel plate
~150mg/m^2, 5mg of chromium oxide on top layer
A steel sheet for cans having excellent corrosion resistance and weldability, characterized in that a resin layer is formed on the upper layer of a metal chromium-plated steel sheet consisting of less than /m^2.