JPH03229895A - Aluminum alloy sheet to be coated for can lid and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an aluminum alloy coating board for can lids, which is applied to aluminum alloy coatings for street use and requires particularly excellent feathering resistance. .

[Prior Art] Conventionally, Al2-Mg based JIS materials have been used as materials for can lids.
Aluminum alloy plates such as 5052.5 (182 and 5182) are used, and are painted to preserve the flavor of the contents of the can and to prevent corrosion of the lid.

In such painting, a predetermined aluminum alloy plate is first degreased and etched, then subjected to phosphoric acid chromate treatment, and then coated with a resin paint such as vinyl chloride organosol, epoxy urea, or epoxy phenol. It is painted and then baked.

By the way, if the adhesion of the coating film formed in this way is insufficient, there is a problem in that when the lid is opened, the coating film on the inner surface of the lid remains at the opening, which is called feathering. This phenomenon tends to occur when a vinyl chloride organosol paint is made into a thick film of 0g7m'' or more in order to cope with more corrosive contents, and has become a serious problem.

This became a major problem when trying to increase the weight of the coating to deal with more corrosive contents, such as contents containing a lot of salt, and this was a major problem. Countermeasures against feathering are considered to be a major technical issue in the field of aluminum coating materials, but it is known that this feathering can be prevented by improving the adhesion between the coating film and the aluminum alloy plate. was.

As a measure to prevent feathering, for example, Japanese Patent Application Laid-Open No. 1-2
In the technique disclosed in No. 30787, the composition of the phosphoric acid chromate treatment solution is adjusted and the
Heat treatment at ~50°C is performed to improve adhesion. However, it is difficult to strictly control the liquid composition, and feathering occurs even when manufactured in the hot summer months, so it is difficult to imagine that low-temperature heating is sufficiently effective.

In the technique disclosed in JP-A-6-4-79400, phosphoric acid anodic oxidation treatment is performed instead of phosphoric acid chromate treatment to improve adhesion. However, phosphoric acid is highly corrosive to conductive metal materials and structural steel materials. Further, in order to carry out anodic oxidation at a high current density in order to perform the process in a short time, a high voltage of 100 V or more is required, making it difficult to commercialize the process.

[Problems to be Solved by the Invention] Phosphoric acid chromate treatment, which is the most widely used base treatment method for conventional aluminum plates, is effective in improving adhesion, but it is difficult to use in degreasing baths, etching treatment baths, and chemical conversion treatment baths. Since a large number of processing tanks are required, the production line becomes long and the equipment cost increases.

Furthermore, since several types of treatment liquids must be controlled separately, the quality tends to be unstable, and it is often not possible to stably improve adhesion.

The biggest problem in particular is that there are complaints that the adhesion between the paint film and the aluminum alloy plate used as a material for can lids is insufficient.

In addition, electrolytic oxidation using an acidic aqueous solution such as phosphoric acid or sulfuric acid alone has poor degreasing power, so a separate degreasing process is required.Furthermore, a thick barrier layer of oxide film tends to form during electrolysis, so it is necessary to process in a short time. However, there is a problem in that a very high DC electrolysis voltage is required for electrolysis at high current density. Furthermore, it has fundamental problems such as being highly corrosive to conductive metal materials and structural steel materials.

This invention effectively solves the above-mentioned problems, and can stably ensure adhesion between the coating film and the aluminum alloy plate, and can lids that do not require long processing times and are inexpensive in terms of equipment. The object of the present invention is to provide an aluminum alloy plate for use in aluminum alloys and a method for manufacturing the same.

[Means for Solving the Problems] The present invention is characterized in that an aluminum alloy plate is subjected to AC electrolysis treatment in an alkaline aqueous solution to form an oxide film with a thickness of 500 to 5,000. To provide an aluminum alloy coating plate for can lids which is excellent in quality.

Furthermore, the aluminum alloy coating plate for can lids with excellent coating film adhesion can be coated with an aluminum alloy plate having an electrical charge of 80 c at a current density of 4 to 50 A/dm2 in an alkaline aqueous solution.
/ d m'', which can be obtained by a method for manufacturing an aluminum alloy coating plate for can lids with excellent coating film adhesion, which is characterized by performing AC electrolytic treatment for a time exceeding The object of the present invention is not only to manufacture an aluminum alloy coating plate for can lids with excellent feathering resistance, but also to provide a manufacturing method that requires only a short processing time and at low cost.

In the present invention, the oxide film obtained by alternating current electrolytic treatment in an alkaline aqueous solution is formed to a thickness of 500 to 5,000 coats, which can significantly improve the adhesion of the vinyl paint film applied thereon. be. If the thickness of the oxide film becomes thinner than 500, the thickness of the porous oxide film grown on the dense barrier layer will be insufficient, and the adhesion of the coating film formed thereon will not be sufficient. Needless to say, it will disappear.

On the other hand, the upper limit of the thickness of the oxide film is 5,000 people, and although the effects of the present invention can be enjoyed by increasing the thickness and there are no particular problems, this is the upper limit of the thickness that can be obtained under normal conditions. , it is thought that there is no particular advantage in making it thicker than this.

There seems to be no particular restriction on the alkaline aqueous solution used in the present invention, and it is usually an aqueous solution of sodium birophosphate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, sodium phosphate, etc., or aqueous solutions thereof. It is desirable to use a mixed solution of two or more types, and a surfactant may be included in order to improve the degreasing property.

Further, the desirable hydrogen ion index (pH) of the electrolytic solution is 9 to 13.5, preferably pHto to 12.

If the pH is less than 9, the degreasing property is poor and rolling oil and oxide film on the surface of the aluminum alloy plate cannot be dissolved and removed. It is also undesirable because the bath voltage increases and non-uniform electrolysis tends to occur.
On the other hand, if the pH exceeds 13.5, the solubility is too strong, and the removal of the generated oxidation residue by bubbles is insufficient, and a porous oxide film with excellent adhesion is not formed, so it should be avoided.

The bath temperature of the alkaline solution during electrolytic treatment is usually 40~
It is within the range of 90°C. At low temperatures below 40°C, the degreasing and cleaning effects tend to be insufficient, while at temperatures above 90°C, the solubility is too strong and it becomes difficult to obtain an anodic oxide film of the required thickness. In addition, even within the range of 40 to 90°C, especially 60 to 80°C
It is preferably within the range of °C.

The current density during AC electrolysis is 4 to 50 A in both polarities.
/dm”, preferably 5-30 A/dm
If it is less than 3 A/d m, the amount of bubbles generated during electrolysis is insufficient, the surface cleaning effect is poor, and the formation of a porous oxide film with excellent adhesion is insufficient, so it is not preferable. .

If it exceeds 50 A/dm2, the electrolytic voltage becomes too high, which is not preferable because it not only tends to cause electrical leakage but also tends to cause uneven appearance such as "burning" due to the heat of one reaction.

The alternating current electrolysis must be of a temporal nature such that the total amount of electricity exceeds 80 c/dm 2 . Total electricity amount is 80
If it is less than c/d m 2 , a porous oxide film will not be formed to a predetermined thickness, and the adhesion to the coating film formed thereon will not be sufficient. The higher the current density, the more sufficient coating film adhesion can be obtained in a shorter time, but the higher the voltage, the greater the need for a large power source. The polarity must be an AC waveform.

1. In this invention, electrolytic treatment is performed using alternating current in an alkaline solution at a high temperature of 40 to 90°C.

By such electrolytic treatment, as described in detail below, the surface of the aluminum plate is strongly degreased and cleaned, and at the same time, an anodic oxide film with excellent coating film adhesion is generated.

That is, first of all, speaking of the degreasing and cleaning effects, the alkaline solution has degreasing properties by itself, and because of the high temperature, the degreasing properties are stronger. Moreover, in electrolysis using alternating current, oxygen gas is generated during the anode reaction, while hydrogen gas is generated during the cathode reaction. Therefore, during the anode reaction, degreasing and cleaning effects occur due to the oxidation of organic matter attached to the plate surface, and during the cathode reaction, the degreasing and cleaning effects are activated. A mechanical cleaning action occurs due to the expansion of hydrogen bubbles on the plate surface. Therefore, when AC electrolytic treatment is performed in a high-temperature alkaline solution, the above-mentioned effects function synergistically to produce a strong degreasing and cleaning effect, and in an extremely short period of time, there is no adverse effect on paint film adhesion. Rolling oil on the aluminum alloy plate surface, giving
At the same time as completely removing the thermal oxide film that has formed in lumps,
It forms a porous oxide film with a clean surface, a film thickness of 500 to 5,000 people, and excellent film adhesion.

Furthermore, because electrolytic treatment is performed using alternating current, it is difficult to cause skin roughness, and a large amount of current can be applied in a short period of time without causing skin roughness, which significantly shortens treatment time and improves workability. I can do it.

In other words, in conventional general electrolytic treatment using direct current, if a large amount of current is applied in a short period of time (therefore,
If electrolysis is carried out at a high current density), the bath voltage tends to rise rapidly, which tends to cause non-uniform electrolysis, but this does not occur with electrolysis using an AC waveform, and large amounts of electricity can be generated in a short time without causing skin irritation. By electrolyzing at a high current density, it is possible to efficiently produce a film with excellent adhesion.

Furthermore, in this invention, as described above, degreasing/cleaning and formation of an anodic oxide film with excellent adhesion are performed in the same process in the same tank, so it is possible to perform anodization in a separate tank after degreasing. Unlike this, dirt does not adhere during the process, and an anodic oxide film is generated while the board surface remains activated.
A film of uniform quality can be obtained, and it can exhibit stable and excellent adhesion.

For this reason, it is believed that the anodic oxide film formed in this manner has significantly improved adhesion to the paint film compared to the oxide film formed by the conventional method.

Furthermore, since degreasing/cleaning and the formation of an anodized film are performed in the same electrolytic treatment in the same tank, and the electrolytic time is short, the overall working time is significantly shortened compared to conventional methods, and productivity is increased. In addition to improving the performance, equipment costs are also significantly reduced.

[Example] Metal plate such as five-piece aluminum (JIS5052, thickness 0.
After washing and drying, a vinyl chloride organosol paint (manufactured by Kansai Paint Co., Ltd., KANCOAT l 8-D37) was applied.
4) was applied and baked at 280° C. for 30 seconds in a hot air drying oven.

The thickness of the coating film was 15 g/m2.

The aluminum alloy coated plates thus obtained were each cut into 50mm x 50mm pieces and subjected to retort treatment (12
After treatment in water at 1° C. for 60 minutes, feathering was generated using the Alcoa method (Note) to evaluate coating film adhesion, and the maximum value of its width was measured.

The results are shown in Table 1.

(Note) As shown in Figure 1, approximately 5 m in inch width is placed in the middle of one side of a 1 to 2 inch square painted aluminum plate.
Make a notch in M and fold it in the opposite direction to the painted surface.

This is placed in hot water of 100-121'C for a specified time (30-121'C).
Soak for 60 minutes), then take it out, immediately put it in a vise, and pull the bent part with pliers to tear it off. The maximum width of the remaining paint film at the broken part of the remaining aluminum piece is 111
Set.

(Example 1) In an aqueous solution of 2% Na4Pz Ot with a bath temperature of 70°C and a pH of 1O65, electrolytic treatment was performed for 23.6 seconds at an alternating current density of 10 A/dm" (sine waveform, 50 Hz) (total electricity amount 150
c/d m2) electrolytic treatment was performed.

(Example 2) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 11.8 seconds at an AC electrolytic density of 2 OA/d m''.

(Example 3) Same as Example 1 except that electrolytic treatment was performed at 10 A/d m2 for 23.6 seconds in an aqueous solution of 2% Na2Co3 with a pH of 12 and a bath temperature of 40°C. Processed.

(Example 4) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 4.7 seconds at an AC electrolytic density of 40 A/dm2.

(Example 5) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 7.9 seconds at an AC electrolytic density of 20 A/d m 2 .

(Example 6) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 7.9 seconds at an AC electrolytic density of 40 A/dm2.

(Example 7) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 22.4 seconds at an AC electrolytic density of 7 A/dm2.

(Comparative Example 1) Except that the current density was 3 A/d m2,
The same treatment as in Example 1 was performed.

(Comparative Example 2) The same process as in Example 1 was performed except that the total amount of electricity was 8.0076 m2.

(Comparative Example 3) After degreasing with an alkaline degreaser and washing with water, C in the film was removed.
Phosphate chromate treatment was performed so that rM was 30 mg/m''.

The results of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1.

(Leaving space below) Table 1: Evaluation of paint film adhesion [Effects of the invention J] The aluminum alloy coating plate for can lids of the present invention is comparable to the aluminum alloy coating material for can lids that is currently being treated with phosphoric acid chromate. This method significantly improves the feathering resistance, and since it uses an alkaline aqueous solution, it can significantly reduce the corrosivity to equipment materials such as steel, and because it uses an AC electrolytic method, it is easy to lower the voltage. , the ability to form the necessary oxide film in a short time with high current density, and the ability to perform degreasing, cleaning, and oxide film formation (anodization treatment) in the same equipment, making it significantly superior to conventional methods. has excellent advantages.

[Brief explanation of drawings]

FIG. 1 shows the feathering measurement method using the Alcoa method.

Claims (2)

[Claims] (1) For aluminum alloy coating for can lids with excellent coating adhesion, characterized by subjecting an aluminum alloy plate to AC electrolysis treatment in an alkaline aqueous solution to form an oxide film with a thickness of 500 to 5000 Å. Board. (2) An aluminum alloy plate is heated to an electric capacity of 80 c/dm at a current density of 4 to 50 A/dm^2 in an alkaline aqueous solution.
A method for producing an aluminum alloy coating plate for can lids with excellent coating film adhesion, characterized by performing AC electrolytic treatment for a time exceeding ^2.