JPH03274296A - Aluminum alloy material to be painted for deep drawing and its production - Google Patents

Abstract

PURPOSE:To produce an Al alloy material having tight adhesion of a coating film even when deep-drawn after painting and baking by forming an oxide film of a specified thickness on an Al alloy material by AC electrolysis in an alkaline aq. soln. CONSTITUTION:An oxide film of 500-5,000Angstrom thickness is formed on an Al alloy material by AC electrolysis in an alkaline aq. soln. of pH9-13 contg. sodium pyrophosphate, etc., at 35-85 deg.C and 4-50A/dm<2> current density for such a time that the quantity of electricity exceeds 80c/dm<2>. Since the oxide film is porous and has a clean surface, adhesion to a resin painting film is remarkably improved when the Al alloy material is painted and tight adhesion of the coating film is maintained even after the painted material is deep-drawn.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an aluminum alloy coating material, and in particular, when the aluminum alloy material is coated with a synthetic resin paint and then deep drawn and used as a food container. The present invention relates to an aluminum alloy coating material for deep drawing, which has excellent adhesion between an aluminum alloy material and a resin coating film, and has high corrosion prevention properties for aluminum alloy containers, and a method for producing the same.

[Prior Art] In recent years, in order to meet the demands for aesthetic appearance, weight reduction, and easy opening of containers for food and beverages, aluminum alloys that have been left in this field have begun to be put into practical use.

In order to improve productivity by simplifying and speeding up the production line, in order to manufacture can products, especially aluminum alloy container can bodies, aluminum alloy strips that have been baked with a resin coating are used, which are then deep-drawn. It is often molded by

In this case, the resin coating and the aluminum alloy plate must be firmly adhered even during deep drawing. Many of the contents to be filled are high in salt, and these can products are heated and sterilized after being filled into containers and stored for long periods of time, so poor adhesion to the resin can cause damage. Corrosion of real aluminum alloy containers occurs depending on the location, and the contents also become contaminated and deteriorate.

Currently, vinyl-based paints containing modified vinyl are often used as paints for such aluminum alloy containers and cans. However, although vinyl paints have good processability, they have the disadvantage that they have poor adhesion, resulting in insufficient coating film adhesion and many restrictions on the contents of containers and cans.

Conventionally, aluminum alloy materials, which are deep-drawn after the resin paint is baked, are treated with phosphoric acid chromate as a pre-painting treatment, and the phosphoric acid chromate coating formed on the surface of the aluminum alloy material improves paint film adhesion. This aims to improve the corrosion of aluminum alloy containers, thereby preventing corrosion of aluminum alloy containers.

Furthermore, in the technique disclosed in JP-A-1-114435, instead of the phosphoric acid chromate treatment, the adhesiveness with the resin coating is improved by "forming a composite film of a specific resin and a transition metal compound."

In the phosphoric acid chromate treatment method, which is widely used as a base treatment for aluminum alloy materials, the treatment solution mainly consists of chromate, phosphate, hydrofluoric acid, etc., and these are extremely harmful to the human body, so they require a huge amount of treatment. This requires investment in wastewater treatment equipment, and chromium-free treatment is desired from the perspective of environmental conservation. In addition, the phosphoric acid chromate film produced by phosphoric acid chromate treatment is prone to cracking due to heating and deep drawing during paint baking, so the adhesion of the paint film may decrease in these areas, and the drawing ratio It was unsuitable for deep drawing processing with a high degree of oxidation or as a container material for storing food contents containing a large amount of salt.

In addition, the method of forming a resin film as an adhesive brimer after degreasing and cleaning aluminum alloy materials not only increases costs due to the addition of the resin itself, but also requires a separate paint baking process, which reduces productivity. There is.

[Problems to be solved by the invention] The present invention has the following advantages: no environmental pollution, the base is stable even after deep drawing, a base with high coating film density can be obtained, and the freedom to select the resin. The advantages of conventional The present invention was completed by providing an extremely high-performance aluminum alloy material that differs from surface treatment and by researching a method for manufacturing it.

[Means for Solving the Problems] The present invention provides a deep drawing product characterized in that an aluminum alloy material is subjected to AC electrolysis treatment in an alkaline aqueous solution to form an oxide film with a thickness of 500 to 5,000. Our objective is to provide aluminum alloy coating materials.

Furthermore, the aluminum alloy coating material for deep drawing is prepared by coating the aluminum alloy material in an alkaline aqueous solution with a pH of 9 to 13 and a bath temperature of 35 to 85°C at a current density of 4 = 50 A/d m.
The method of producing an aluminum alloy coating material for deep drawing, which is characterized by performing an AC electrolytic treatment for a time such that the amount of electricity exceeds 80 c/dm2 at The purpose of this invention is to provide not only a method for manufacturing an aluminum alloy material that has excellent adhesion to a certain resin coating, but also a manufacturing method that requires only a short time, a minimum number of processing steps, and a low cost.

The aluminum alloy to which the present invention is applied is not particularly limited as long as it can be deep drawn, and can be applied to all JIS or AA standard alloys. In particular, 1100 alloy, 3003003 alloy 04004 alloy 05005 alloy 52052 alloy 83083 alloy, 99 alloy
% or more of pure aluminum-based aluminum-manganese,
It is preferable to apply it to an aluminum-magnesium alloy.

In the present invention, the oxide film obtained by alternating current electrolytic treatment in an alkaline aqueous solution is formed to have a thickness of 500 to 5000 Å. This oxide film is extremely porous and has a clean surface, which can significantly improve the adhesion with the resin coating applied thereon.

In addition, since this oxide film has a thin porous structure, cracks do not occur even when the paint is heated or deep drawn with a high drawing ratio, so the paint film remains strong even after deep drawing of the painted material. You can maintain your sexuality.

Note that if the thickness of the oxide film becomes thinner than 500A, the coating film formed thereon will not have sufficient density.

On the other hand, the upper limit of the thickness of the oxide film is 5000A, and although the effect of the present invention can be enjoyed by increasing the thickness and there is no particular problem, this is the upper limit of the thickness that can be obtained under normal processing conditions. , there is no particular advantage in making it thicker than this.

There seems to be no particular limit to 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 two types thereof. It is desirable to use the above mixed solution, and a surfactant may be included in order to improve degreasing properties.

Further, the desirable hydrogen ion index (pH) of the electrolytic solution is 9 to 13, preferably pH 10 to 12.

If the pH is less than 9, the degreasing property is poor, rolling oil and oxide film on the surface of the aluminum alloy plate cannot be dissolved and removed, and the bath voltage increases and uneven electrolysis tends to occur, which is not preferable.
On the other hand, if the pH exceeds 13, the solubility is too strong and the removal of the generated dissolved residue by bubbles is insufficient, and a porous oxide film with excellent adhesion will not be formed, so it should be avoided.

Regarding the bath temperature of the alkaline solution during electrolytic treatment, a bath temperature of about 20° C. is generally employed in anodizing treatment to form an oxide film. This is because if the temperature is higher than this, the amount of oxide film dissolved will increase, making it difficult to form a thick oxide film.

However, in the present invention, the amount of dissolved oxide film is increased and a thin porous oxide film is required, so the bath temperature is usually 35-35°C.
It is within the range of 85°C. At low temperatures below 35°C, the degreasing and cleaning effects tend to be insufficient, while at temperatures above 85°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 35 to 85 °C, especially 60 to 80 °C
It is preferably within the range of °C.

4 to 5 at the maximum current density in both polarities during AC electrolysis.
0 A/dm 2. Preferably 5-30A/dm
If it is less than 4 A/dm, the amount of bubbles generated during electrolysis will be insufficient, the surface cleaning effect will be poor, and the formation of a porous oxide film with excellent adhesion will be insufficient, which is not preferable.

If it exceeds 50 A/dm, the electrolytic voltage becomes too high, which not only makes it easy to cause electrical leakage, but also causes "burning" due to reaction heat.
This is not preferable because it tends to cause unevenness in appearance.

AC electrolysis must last for an order of magnitude in which the total amount of electricity exceeds 80 c/dm2. Total electricity amount is 80
If it is less than c / d m 2, the porous oxide film will not be formed to the specified thickness, and the adhesion with the coating film formed thereon will not be sufficient. Although it is possible to obtain good coating film adhesion, a large power source is required due to the high voltage. The polarity must be an AC waveform.

Note that when processing materials with a thick natural oxide film on the surface, such as 5182 alloy, l! It is effective to extend the life of the electrolyte if the electrolytic treatment is carried out after the natural oxide film of the i-type aqueous solution is dissolved and removed.

Cleaning treatment before electrolysis can be performed as necessary.

The aluminum alloy plate treated as described above has good adhesion to vinyl paint, PVC paint, P8 hardened epoxy paint, epoxy-phenol paint, and epoxy-urea paint, and is suitable for food containers. It is extremely useful as a material.

[Function J] In this invention, electrolytic treatment is performed using alternating current in an alkaline solution at a high temperature of 35 to 85°C.

By such electrolytic treatment, as described in detail below, the surface of the aluminum material is strongly degreased and cleaned, and at the same time, a porous 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, the degreasing and cleaning effects are activated by the oxidation of organic matter attached to the surface of the aluminum alloy material, and the cathode During the reaction, 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. Completely removes rolling oil and thermal oxidation film formed in lumps on the surface of the aluminum alloy plate, and at the same time maintains a clean surface with a film thickness of 500 to 500.
It forms a porous oxide film with excellent coating adhesion of 0^.

Furthermore, in the present invention, electrolytic treatment using alternating current is performed in a high-temperature alkaline aqueous solution.

Electrolysis at high current density becomes possible, and chemical reactions occur at high speed.

That is, the dissolution reaction of the oxide film by the high-temperature alkaline aqueous solution and the formation reaction of the oxide film at the anode polarity occur at high speed. The oxide film produced by the dissolution reaction on the surface of the oxide film and the intermittent growth of the oxide film due to alternating current is extremely porous compared to the oxide film anodized by direct electrolysis in a numerically acidic aqueous solution. It will be Chino.

The formation of this porous oxide film can only be realized by alternating current electrolytic treatment in an alkaline aqueous solution.

That is, in electrolytic treatment using a numerical direct current, the bath voltage rises rapidly, making it impossible to conduct electrolysis at the high current density necessary for forming an oxide film. In addition, acidic aqueous solutions such as phosphoric acid and sulfuric acid, which are generally used to form anodized films,
Because a barrier-type acidic film is likely to form, industrialization is extremely difficult because a voltage five times higher than that for alkaline aqueous solutions is required for short-time treatment with high current density electrolysis. This is because

The oxide film formed by AC electrolysis treatment in an alkaline aqueous solution has a clean surface and a very porous structure, which can significantly improve adhesion to resin coatings. Moreover, since paint baking does not cause cracks even when subjected to heating or deep drawing at a high drawing ratio, strong paint film adhesion can be maintained even after deep drawing of the coating material.

Furthermore, since degreasing and cleaning and the generation of a porous oxide film are carried out in the same tank through the same electrolytic treatment, and the electrolytic time is short, the overall working time is significantly shortened compared to conventional methods, improving productivity. Equipment costs are also significantly lower. In addition, since it does not use substances harmful to the human body such as chromium, it has great advantages in terms of operation and environmental protection.

[Example] JTSA5052-819 alloy plate, thickness 0.26mm"
Using the paint base treatment shown in Examples and Comparative Examples,
After washing with water and drying, coated with modified vinyl resin N (KAN-COA manufactured by Kansai Paint Co., Ltd.) on each base-treated aluminum alloy material.
T 5J-9009-90: ] ) was applied to the container at a rate of 10g/m'', baked at 200°C x 10m1n, and drawn so that the painted surface became the inner surface, and then the durability of the container was examined. .

Durability evaluation was performed by filling the prepared container with an aqueous solution containing 5% salt and 0.5% citric acid with a pH of 3.0, retorting it (121°C x 3 m1n), and then leaving the container as it was at 50°C for 1 month. After storage, durability was evaluated based on the occurrence of blisters in the resin coating. The results are shown in Table 1. The drawing ratio is blank diameter/punch diameter.

(Example 1) 2% Na s P z O? with a bath temperature of 70°C. pH of 1
Electrolytic treatment was performed in an aqueous solution of No. 05 for 295 seconds at an alternating current density of 8 A/dm" (sine waveform of 50 Hz). (Total electricity amount: 150 c/dm") (Example 2) ．． 6 seconds (total electricity amount 100c/dm
”) The same process as in Example 1 was performed except that

(Example 3) 9.8 seconds at an alternating current density of 24 A/dm (total amount of electricity 15
The same treatment as in Example 1 was performed except that electrolytic treatment (0 c/dm'') was performed.

(Example 4) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at an alternating current density of 7 A/dm'' for 22.4 seconds (total electricity amount 100 c/dm'').

(Example 5) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed in an aqueous solution of 2% Na a COs with a pH of 12 at a bath temperature of 40°C.

(Comparative Example 1) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed for 15.7 seconds (total amount of electricity: 80 c/dm'').

(Comparative Example 2) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed in an aqueous solution at a bath temperature of 90°C.

(Comparative Example 3) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed in an aqueous solution of 2% NaOH with a pH of 14 at a bath temperature of 40°C.

(Comparative Example 4) After degreasing with an alkaline degreasing solution and washing with water, chromate treatment was performed so that the amount of chromium in the film was 30 mg/m2.

(The following is a margin) [Effects of the invention] The aluminum alloy coating material for deep drawing of the present invention has strong coating film adhesion even after the resin coating is formed by post-deep drawing processing, and is suitable for food contents with high salt content. The durability of the container is no longer impaired even when it is filled, heat sterilized, and stored at high temperatures.

In addition, unlike the conventional phosphoric acid chromate treatment, it does not use romic acid, which is extremely harmful to the human body, so it has the advantage of being easy to industrialize.

Claims (2)

[Claims] (1) An aluminum alloy coating material for deep drawing, characterized in that an aluminum alloy material is subjected to AC electrolysis treatment in an alkaline aqueous solution to form an oxide film with a thickness of 500 to 5000 Å. (2) Aluminum alloy material, pH 9 to 13, bath temperature 35
In alkaline aqueous solution at ~85°C, current density 4~50A/
A method for producing an aluminum alloy coating material for deep drawing, characterized in that AC electrolytic treatment is performed at dm^2 for a time such that the amount of electricity exceeds 80 c/dm^2.