JPH0832966B2 - Aluminum alloy coating plate for can lid and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an aluminum alloy coating plate for a can lid,
The present invention relates to an aluminum alloy coating plate for a can lid that requires particularly excellent feathering resistance.

[Prior Art] Conventionally, as a material for a can lid, Al-Mg-based JIS5052,50
Aluminum alloy plates such as 82,5182 are used, and are coated to maintain the flavor of the contents of the can and prevent corrosion of the lid material.

Then, in such coating, first a predetermined aluminum alloy plate is subjected to degreasing and etching treatment, and then phosphoric acid chromate treatment is performed, and then a vinyl chloride organosol-based, epoxyurea-based, or epoxyphenol-based resin coating is applied. 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 that a film residue of the coating film on the inner surface of the lid called feathering occurs at the opening when the lid is opened. This phenomenon tends to occur when a vinyl chloride organosol-based paint is applied to a pressure film of 10 g / m ² or more in order to deal with a more corrosive content, and has become a serious problem.

This became a serious problem when trying to increase the weight of the coating film in order to deal with more corrosive contents, for example, a container containing a large amount of salt, which was a big problem.
Therefore, the countermeasure against feathering is a major technical problem in the field of the present aluminum coating material, but as a solution to this feathering, by improving the adhesion between the coating film and the aluminum alloy plate, It was known to be preventable.

As a measure for preventing feathering, for example, JP-A-1-
In the technology disclosed in No. 230787, the adjustment of the composition of the phosphoric acid chromate treatment liquid and the temperature of the aluminum alloy plate at 20 to 50 ° C.
Heat treatment is performed to improve adhesion. However, strict control of the liquid composition is difficult, and the occurrence of feathering occurs even in the case of manufacturing in the summer when the temperature is high, so it is unlikely that low-temperature heating is sufficiently effective.

In the technique disclosed in JP-A-64-79400, the phosphoric acid anodizing treatment is performed instead of the phosphoric acid chromate treatment to improve the adhesion. However, phosphoric acid is extremely corrosive to conductive metal materials and structural steel materials. In addition, a high voltage of 100 V or more is required to perform anodization at a high current density for processing in a short time, which makes industrialization difficult.

[Problems to be Solved by the Invention] Although the phosphoric acid chromate treatment, which has been most widely used as a conventional base treatment method for aluminum plates, is found to be effective in improving adhesion, a degreasing bath, an etching treatment bath, and a chemical conversion treatment bath. Since a large number of processing tanks are required, the production line becomes long and the equipment cost increases. Further, since several kinds of treatment liquids have to be controlled separately, the quality tends to be unstable, and it is often impossible to stably improve the adhesion.

Particularly, the biggest problem is that the adhesion between the coating film and the aluminum alloy plate is insufficient as a material for a can lid.

Further, since the degreasing power is inferior only by electrolytic oxidation with an acidic aqueous solution of phosphoric acid, sulfuric acid, etc., it is necessary to provide a separate degreasing step, and in addition, a thick barrier layer of an oxide film is likely to be formed during electrolysis, and therefore it is necessary to process in a short time In addition, there is a problem that a very high DC electrolysis voltage is required for electrolysis at a high current density. Further, it has a basic problem that it has a strong corrosiveness with respect to conductive metal materials and structural steel materials.

The present invention effectively solves the above problems, can stably secure the adhesion between the coating film and the aluminum alloy plate, does not require a long time for the treatment, and is a low-cost can lid. It is an object of the present invention to provide an aluminum alloy plate for use and a manufacturing method thereof.

[Means for Solving the Problems] The present invention is an aluminum alloy for can lids, in which an oxide film having a film thickness of 500 to 5000Å is formed by an alternating current electrolytic treatment in an alkaline aqueous solution, which is excellent in coating film adhesion. Another object is to provide an aluminum alloy coating plate for a can lid.

Further, the aluminum alloy coating plate for a can lid excellent in the coating film adhesion is an aluminum alloy plate having a film thickness of 500 to 5000 Å
So that the oxide film is formed in an alkaline aqueous solution at a bath temperature of 40 to 90 ° C and a current density of 4 to 50 A / dm ^{2 with an} electric quantity of 80 c / dm ²
For a period of time that exceeds the above, which can be obtained by a method for producing an aluminum alloy coating plate for a can lid excellent in coating film adhesion, which is characterized by performing an alternating current electrolytic treatment, and is a subject of the present invention for feathering resistance. Not only manufacturing aluminum alloy coating plates for can lids with excellent properties, but also processing in a short time,
The present invention also provides a manufacturing method that requires low cost.

In the present invention, the oxide film obtained by the AC electrolytic treatment in the alkaline aqueous solution is formed to have a film thickness of 500Å to 5000Å, whereby the adhesion of the coating film of the vinyl-based coating applied thereon can be remarkably improved. If the thickness of the oxide film is less than 500Å, the thickness of the porous oxide film grown on the dense barrier layer will be insufficient, and the adhesion of the coating film formed on it will not be sufficient. Needless to say.

On the other hand, the upper limit of the thickness of the oxide film is 5000 Å, the effect of the present invention can be enjoyed by increasing the thickness, and there is no particular obstacle, but this degree is the upper limit of the thickness obtained under normal conditions, It is considered that there is no particular advantage even if the thickness is further increased.

The alkaline aqueous solution used in the present invention does not seem to be particularly limited, and is usually an aqueous solution of sodium pyrophosphate, sodium carbonate, potassium carbonate, sodium hydroxide, sodium phosphate, or the like, or a mixed solution of two or more thereof. Is preferable, and a surfactant may be contained in order to improve degreasing property.

The desirable hydrogen ion exponent (pH) of the electrolytic solution is 9 to 13.5, preferably pH 10 to 12.

If the pH is less than 9, the degreasing property is poor and the rolling oil and oxide film on the surface of the aluminum alloy plate cannot be dissolved and removed. Also, the bath voltage rises and uneven electrolysis tends to occur, which is not preferable.
On the other hand, if the pH exceeds 13.5, the solubility is too strong, and the resulting dissolved residue is not sufficiently removed by the bubbles, and a porous oxide film having excellent adhesiveness cannot be formed.

The temperature of the alkaline solution bath during electrolysis is usually 40-
Within the range of 90 ℃. If the temperature is lower than 40 ° C, the degreasing / cleaning effect tends to be insufficient, while if it exceeds 90 ° C, the solubility is too strong, and it becomes difficult to obtain an anodized film having a required thickness. In addition, even in the range of 40 to 90 ° C., particularly preferably in the range of 60 to 80 ° C.

The maximum current density in both polarities during AC electrolysis is 4 ~
It is 50 A / dm ² , preferably 5-30 A / dm ² . If it is less than 3 A / dm ² , the amount of bubbles generated during electrolysis is insufficient, the cleaning effect on the surface is poor, and the formation of a porous oxide film having excellent adhesion is insufficient, which is not preferable.

If it exceeds 50 A / dm ² , not only is the electrolytic voltage too high and it is easy for leakage to occur, but also uneven appearance such as “burning” due to reaction heat is likely to occur, which is not preferable.

AC electrolysis must be carried out for a time such that the total amount of electricity exceeds 80 c / dm ² . If the total amount of electricity is 80 c / dm ² or less, the porous oxide film will not be formed to a predetermined thickness, and therefore the adhesion with the coating film formed thereon will be insufficient. As the current density is higher, sufficient coating film adhesion can be obtained in a shorter time, but since the voltage is higher, a large power source is required.
The polarity must be an alternating waveform.

[Operation] In the present invention, electrolytic treatment is carried out using an 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 washed, and at the same time, an anodized film having excellent coating adhesion is produced.

That is, first of all, regarding the degreasing / cleaning action, in addition to the alkaline solution having degreasing properties by itself,
Due to the high temperature, the degreasing property is stronger. Moreover, in the electrolysis by alternating current, oxygen gas is generated during the anode reaction, while hydrogen gas is generated during the cathode reaction, so the degreasing / cleaning action by the oxidation of organic substances adhering to the plate surface works during the anode reaction, and during the cathode reaction. A mechanical cleaning action works by the expansion of hydrogen bubbles on the plate surface. Therefore, according to the AC electrolysis treatment in a high temperature alkaline solution, the above-mentioned respective functions synergistically exert a strong degreasing / cleaning effect, and adversely affect the coating adhesion in a very short time. It completely removes the rolling oil on the surface of the aluminum alloy sheet and the thermal oxide film formed in a lump, and at the same time forms a porous oxide film with a clean surface and a film thickness of 500 to 5000Å with excellent coating adhesion. is there.

Furthermore, since electrolytic treatment is performed by alternating current, rough skin is unlikely to occur, and a large amount of electric current can be applied in a short time without causing rough skin, thus significantly reducing the processing time and improving workability. You can

That is, in the conventional general electrolytic treatment with direct current, if a large amount of electricity is applied in a short time (therefore,
When electrolyzing at a high current density), the bath voltage is likely to rise rapidly, and thus non-uniform electrolysis is likely to occur, but electrolysis with an AC waveform does not cause this and a large amount of electricity can be generated in a short time without causing skin roughness. A large amount of electrolysis, that is, electrolysis at high current density can be performed, and a film having excellent adhesion can be efficiently produced.

Further, in the present invention, as described above, degreasing / cleaning and formation of an anodized film having excellent adhesion are carried out by the same treatment in the same tank, so that when anodizing in another tank after degreasing, Differently, the stains do not adhere between the steps, and the anodic oxide film is generated while the plate surface remains activated, so that a film of uniform quality can be obtained and stable and excellent adhesion can be exhibited. .

Therefore, it is considered that the anodized film formed in this way has significantly improved adhesion to the coating film as compared with the oxide film formed by the conventional method.

Also, degreasing / cleaning and anodized film formation are performed by the same electrolytic treatment in the same tank, and the electrolysis time is also short, so the overall work time is significantly shortened compared to conventional production. And the facility cost will be significantly reduced.

[Embodiment] Aluminum metal plate for can lid (JIS5052, thickness 0.3 mm ^t )
Using Examples, the electrolytic treatment shown in Examples and Comparative Examples is performed, followed by washing with water and drying, and then applying a vinyl chloride organosol paint (KAN-COATI8-D374 manufactured by Kansai Paint Co., Ltd.) in a hot air drying oven at 280 ° C. It was baked for 30 seconds. The thickness of the coating film was 15 g / m ² as the coating film.

The aluminum alloy coated plate thus obtained was cut into 50 mm × 50 mm pieces and retort treated (6
After treatment for 0 minutes, feathering was generated by the Alcoa method (Note) to evaluate the coating adhesion, and the maximum width was measured.

 The results are shown in Table 1.

(Note) As shown in FIG. 1, make a cut of about 5 mm with a 1/2 inch width in the middle of one side of a painted aluminum plate of 1 to 2 inch square, and bend it in the direction opposite to the painted surface.

This in hot water at 100-121 ℃ for a predetermined time (30-60 minutes)
Immediately after immersing and taking out, pinch it with a vise and pull off the bent part with pliers. The maximum width of the remaining coating film at the fractured part of the remaining aluminum piece is measured.

Example 1 In an aqueous solution of 2% Na ₄ P ₂ O _{7 having} a bath temperature of 70 ° C. and a pH of 10.5,
Electrolytic treatment was performed for 23.6 seconds (total electricity amount: 150 c / dm ² ) at an alternating current density of 10 A / dm ² (sine waveform, 50 Hz).

(Example 2) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at an alternating current electrolytic density of 20 A / dm ² for 11.8 seconds.

(Example 3) 10 A / dm in an aqueous solution of 2% Na ₂ CO _{3 having} a pH of 12 at a bath temperature of 40 ° C.
^The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at ² for 23.6 seconds.

(Example 4) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at an alternating current electrolytic density of 40 A / dm ² for 4.7 seconds.

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

(Example 6) The same process as in Example 1 was performed except that the electrolytic treatment was performed at an alternating current electrolytic density of 40 A / dm ² for 7.9 seconds.

(Example 7) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at an AC electrolytic density of 7 A / dm ² for 22.4 seconds.

Comparative Example 1 The same process as in Example 1 was performed except that the current density was 3 A / dm ² .

(Comparative Example 2) The same treatment as in Example 1 was performed except that the total amount of electricity was 80 c / dm ² .

(Comparative Example 3) After degreasing with an alkaline degreasing agent and washing with water,
Phosphoric acid chromate treatment was performed so that the Cr amount was 30 mg / m ² .

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

[Effects of the Invention] The aluminum alloy coating plate for a can lid of the present invention has significantly improved feathering resistance as compared with the currently practiced phosphorous chromate-treated aluminum alloy coating material for a can lid. In addition, since an alkaline aqueous solution is used, corrosiveness to equipment materials such as steel materials can be greatly reduced, and it is easy to reduce the voltage because it is an AC electrolysis method. It has advantages that it can form an oxide film and that it can achieve degreasing and cleaning and formation of an oxide film (anodic oxidation treatment) by the same treatment in the same apparatus, which is far superior to the conventional method.

[Brief description of drawings]

 FIG. 1 shows a feathering measurement method by the Alcoa method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 64-79400 (JP, A) JP-A 52-150751 (JP, A) JP-A 48-47448 (JP, A) JP-B 55- 36718 (JP, B2) JP 54-25502 (JP, B2) JP 57-4716 (JP, B2)

Claims (2)

[Claims] 1. An aluminum alloy plate for a can lid, having a film thickness of 500 to 5000Å by an alternating current electrolytic treatment in an alkaline aqueous solution.
Aluminum alloy coating plate for can lids, which has excellent oxide film adhesion and has an oxide film formed on it. 2. An aluminum alloy plate for a can lid having a film thickness of 500 to 5
The amount of electricity is 8 at a bath temperature of 40 to 90 ° C and a current density of 4 to 50 A / dm ² in an alkaline aqueous solution so that an oxide film of 000 Å is formed.
A method for producing an aluminum alloy coating plate for a can lid, which is excellent in coating film adhesion, characterized by performing an alternating current electrolytic treatment for a time that exceeds 0 c / dm ² .