JP2625498B2 - Hot-dip aluminized steel sheet for can lid with excellent corrosion resistance - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip aluminized steel sheet for a can lid having excellent corrosion resistance.

2. Description of the Related Art In the field of beer / carbonated beverages or general beverage cans, metal cans are widely used because they have many advantages such as preservability of contents, toughness, beautiful appearance, and price. Above all, an easily openable container lid which can easily open a part of the can lid by a human hand is essential in the field of beverage cans which are often consumed outdoors.

This easy-open container lid (hereinafter abbreviated as EOE: Easy Open End) is manufactured by various methods, but the score method is most frequently used in Japan. What is the scoring method?
This shows a method in which a notch that forms a part to be opened is put in a lid material, and the part is opened by tearing the part by human power. In order to tear by human power, a handle (hereinafter referred to as a tab) for applying force is required, and a rivet method is employed to fix the tab to the can lid. The rivet method means a method of mechanically swaging a tab.

Currently, materials used for EOE include aluminum and tinplate (tin-plated steel). These materials are subjected to EOE molding after an organic coating of about 5 microns on both sides, but scoring or riveting is a very severe process, and defects occur in the thin coating applied before processing. The corrosion resistance of the material is important.

On the other hand, aluminum-plated steel sheets have excellent heat resistance and corrosion resistance, and have been conventionally manufactured by a hot-dip plating method.
In conventional hot-dip aluminized steel sheets, the hot-dip aluminum reacts with the iron in the base steel sheet to produce a considerably thick iron-aluminum alloy layer. Was not used as a container material because of the peeling. The alloy layer has developed to a thickness that can be sufficiently observed at a magnification (× 500) of the order of an optical microscope, and the base material surface is completely covered with the alloy layer.

As a method of suppressing alloy layer growth, there is a method of adding about 10% of silicon to aluminum. Further, as a method of performing pre-plating before hot-dip plating to reduce the amount of the alloy layer formed between the base steel sheet and the aluminum plating layer, for example, JP-A-57-76176 and JP-A- 57-1
No. 40864, JP-A-56-33463, JP-A-57-1146
No. 50, JP-A-57-70268 and the like have been proposed.

However, in any of these methods, the reduction of the alloy layer is insufficient, and even if the thickness is thin, the surface of the base material is completely covered with the alloy layer, so that a steel sheet having good workability is obtained. It is difficult to do so, and there is no example applied as a can lid for containers or even EOE.

Problems to be Solved by the Invention In the case of tinplate, since the plating thickness is very thin, in the score-processed portion or the rivet-processed portion, the coating film often causes defects and the base material of the base material is often exposed, resulting in high acidity. When a beverage is used as a content, the beverage has a weak defect that tends to cause a decrease in taste and flavor due to iron elution in the base steel sheet. Therefore, in order to improve the corrosion resistance, the score-processed portion and the rivet-processed portion have to be painted again with the organic paint after the EOE molding.

In addition, in the case of tinplate, the adhesion of the organic paint is generally not good, so the inner surface of the can cover winding portion (hereinafter CS: Countersink)
(Referred to as “parts”), coating film defects are likely to occur, and taste and flavor problems due to iron elution tend to occur.

In the case of aluminum, the material itself has a relatively strong property to the organic acid that affects the corrosiveness of the contents, so even if the coating film has defects in the score processing part and the rivet processing part, it is necessary to perform repair painting. Has no advantages.

The present invention is to provide a hot-dip aluminized steel sheet for a can lid having excellent corrosion resistance, utilizing the high corrosion resistance of aluminum and eliminating the need for repair painting, in order to eliminate the disadvantages of tinplate as described in detail above. It was made for the purpose.

It is another object of the present invention to provide an aluminum-plated steel sheet which can be applied to a can lid by solving the drawbacks of the conventional aluminum-plated steel sheet in workability.

Means for Solving the Problems In order to achieve the above object, the present invention is to improve the point that the Fe-Al alloy layer of the conventional aluminum-plated steel sheet completely covers the steel sheet surface of the base material, -Partially destroyed the Al alloy layer, forming the presence and absence of the Fe-Al alloy layer between the base steel sheet and the aluminum plating film, and coating the outermost layer with a chromium compound. There is a feature.

That is, the present invention relates to a method of manufacturing a steel
-Al alloy layer, and on its surface Al film or Al alloy film,
In addition, at least the outermost layer on the surface is 5
A molten aluminum-plated steel sheet for a can lid having a film made of chromium compounds of to 50 mg / m ^2, there portion and absence of said Fe-Al alloy layer is formed on the substrate surface,
A hot-dip aluminized steel sheet for a can lid excellent in corrosion resistance, characterized in that the non-existent portion of the alloy layer is at least 10% of the surface of the base material.

Operation Hereinafter, the present invention will be described in detail.

One of the features of the present invention resides in that the bonding form between the base material and the aluminum or aluminum alloy film as the plating metal is changed. As described above, in the conventional hot-dip aluminized steel sheet, the entire surface of the base steel sheet is always covered with the alloy layer, and although there is a slight difference in workability depending on the thickness, the strength such as score processing or rivet processing is used. When it is subjected to the above-mentioned processing, peeling of the plating film occurs due to the destruction of the alloy layer, and it cannot be used as a steel sheet for EOE.

The present invention secures a non-existent portion of the Fe-Al alloy layer at a certain limit or more between the base steel sheet and the plating film in order to obtain the processing adhesion of the plated metal. The non-existent portion of the Fe-Al alloy layer referred to here indicates a state in which substantially no alloy layer is present at the interface between the base steel sheet and the plating film, for example, when a metal is plated by electroplating. Is similar to the interface between the steel sheet and the plated metal.

The proportion of the non-existing portion of the alloy layer in the present invention, by observing the cross section of the hot-dip aluminum-plated steel sheet with a microscope,
The sum of the length of the broken line portion (the portion where the alloy layer is broken) with respect to the entire length of the alloy layer portion observed linearly (the entire observation visual field) is also expressed as a percentage.

The present invention is a hot-dip aluminum plating that can withstand EOE processing by partially destroying the alloy layer without peeling the plating layer and having a non-existent part of the alloy layer over a certain limit on the base steel sheet I found a steel plate. The cold rolling method is most suitable for destroying the alloy layer without peeling off the plating layer.However, processing with excessive strength degrades the mechanical properties of the base material and poses a problem in the workability of the steel sheet itself. Occurs. The adhesion of the plating film is improved as the rolling reduction of the cold rolling is increased, but the mechanical properties of the base material are deteriorated, so that an appropriate rolling reduction must be set. As a method of applying cold rolling, when performing multi-pass rolling, it is possible to obtain better adhesion by adopting a high-pressure reduction in the preceding stage.

The total reduction is 5% to 50%, and more preferably 10% to 50%.
The 30% rolling reduction is necessary to improve adhesion.
% Or more of the iron-aluminum alloy layer must be generated and the mechanical properties of the base material must be ensured.

The thickness of the alloy layer where the alloy layer is present is desirably as thin as possible, and it is important that the thickness be 3.0 microns or less, and preferably 1.5 microns or less.

By such a method, it is possible to obtain a hot-dip aluminized steel sheet having excellent work adhesion, but it is not sufficient in performance alone for a can lid, and the aluminum surface must be coated with an organic coating film. . At that time, the processing adhesion and coating corrosion resistance of the organic coating film are extremely important factors, and at least the presence of a chromium compound film on the outermost layer is necessary.

According to the findings of the present inventors, as an example of forming a film having a chromium compound on at least the outermost layer, by performing cathodic electrolytic treatment in a chromic acid solution containing some anions, Electrolytic formation of a film having a two-layer structure of metallic chromium and hydrated chromium oxide film, or by performing cathodic electrolysis treatment in a dichromate compound solution to electrolyze a film mainly composed of hydrated chromium oxide Was effective.

At this time, the amount of chromium film
If it is less than g / m ² , the effect on the processing adhesion and coating corrosion resistance of the organic coating film is weak, and if it is more than 50 mg / m ² , the effectiveness is saturated and coloring by the chromium film occurs, which is not preferable.

A particularly desirable chromium coating amount is 15 to 30 mg / m ² .

The method of forming the chromium film is not limited to the electrolytic method, and sufficient performance can be obtained even with a chromium compound film formed by a chemical reaction. For example, in a processing solution containing chromic acid, phosphoric acid and hydrofluoric acid as main components,
By causing the phosphate chrome surface 5 to 50 mg / m ² formed,
Extremely good processing adhesion and coating corrosion resistance of the organic coating film can be obtained.

The aluminum alloy in the present invention refers to an alloy obtained by mixing silicon, manganese, magnesium, iron, or the like with aluminum and alloying it.

The present invention is based on a hot-dip aluminum or hot-dip aluminum alloy-plated steel sheet, and has a certain or more portion where the iron-aluminum alloy layer is not present on the base steel sheet, so that the plating adhesion is excellent, and the surface is coated with an organic coating film. By producing a score type EOE, it is possible to obtain extremely excellent processing adhesion and coating corrosion resistance of the organic coating film, so that sufficient corrosion resistance can be obtained without performing repair coating to maintain corrosion resistance after molding. Can be done.

With such an effect, good corrosion resistance can be expected for other uses, for example, for general lid production.

Example 1 Both sides of a thin steel plate having a thickness of 0.25 mm were plated with aluminum (containing 10% silicon) having a total of 30 μm on both sides. After the plating, the steel sheet was rolled to 0.22 mm by cold rolling to obtain a hot-dip aluminum-plated steel sheet having a 15% alloy free layer on the surface of the base steel sheet. This steel sheet was immersed in a chemical conversion treatment solution containing chromic acid, phosphoric acid, and hydrofluoric acid as main components, and was subjected to 25 mg / m ²
Of chromium phosphate was obtained.

5μ of epoxyphenol paint is applied on one side of this steel plate.
m, after applying 5 μm of vinyl paint on the other side,
EOE molding was performed.

The EOE was formed by a score method, and the vinyl-based paint surface was formed so as to be the outer surface of the can so that the steel thickness of the score portion was 65 μm. After peeling off the coating film on the inner surface of the score portion of the formed EOE, the plating surface was examined in detail, and there was no place where the substrate surface was exposed. The degree of exposure of the substrate surface was determined based on whether or not iron was detected on the surface by an X-ray microanalyzer. Further, the adhesion of the aluminum film in the rivet processing portion was extremely excellent, and there was no peeling of the film.

Example 2 Both sides of a 0.30 mm-thick thin steel plate were plated with aluminum (containing 10% silicon) having a total of 50 μm on both sides. After the plating, the steel sheet was rolled to 0.24 mm by cold rolling to obtain a hot-dip aluminum-plated steel sheet having a ratio of 40% without an alloy layer on the surface of the base steel sheet. This steel sheet was subjected to cathodic electrolysis in a solution mainly containing sodium bichromate to obtain an 8 mg / m ² hydrated chromium oxide film.

One surface of this steel plate was coated with an epoxy phenol-based paint, and the other surface was coated with a vinyl-based paint.

After the lid-forming process, the epoxyphenol-based paint on the inner surface was solvent-peeled, and the adhesion and uniformity of the aluminum film were examined. As a result, there was no film peeling and no exposure of the substrate surface.

Comparative Example 1 Both sides of a 0.18 mm-thick thin steel plate were plated with aluminum (containing 10% silicon) having a total of 40 μm on both sides. An alloy layer having a thickness of about 3 μm was present on the entire surface of the base material between the base material and the aluminum film in the plated steel sheet, and the non-existent portion of the alloy layer was 0%.

After the surface of this steel sheet was subjected to chromate treatment and coating in the same manner as in Example 1, score-type EOE molding was performed. As a result, aluminum was peeled off at the rivet portion, and the steel sheet had no practical performance.

Effect of the Invention As described above, the plated steel sheet of the present invention has workability,
It has excellent adhesion and corrosion resistance and is useful for can lids.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-298142 (JP, A) JP-A-58-224159 (JP, A) JP-A-57-126960 (JP, A) 83457 (JP, U)

Claims (1)

(57) [Claims] An iron-aluminum alloy layer on the surface of a thin steel sheet as a substrate, an aluminum film or an aluminum alloy film on the surface, and at least the outermost layer on the surface has a chromium equivalent of 5 to 50 mg / mm. a molten aluminum-plated steel sheet for a can lid having a film made of chromium compounds of m ^2, wherein the iron to the substrate surface - the presence portions and absence of the aluminum alloy layer is formed, non of the alloy layer Hot-dip aluminized steel sheet for can lids with excellent corrosion resistance, characterized in that the existing part is at least 10% of the surface of the base material.