JPS63178039A - Surface-treated aluminum plate having excellent color fastness - 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 a surface-treated aluminum plate, and particularly to a surface-treated aluminum plate used for applications in which the plate comes into contact with high-temperature water and high-temperature steam containing impurity ions.

Note that the term "aluminum plate" is a general term for industrial pure aluminum plates and aluminum alloy plates.

(Conventional technology and problems to be solved) Aluminum and aluminum alloys generally have a highly protective oxide film formed on their surfaces, so they have practical corrosion resistance and are widely used in daily necessities, building materials, etc. This is where it is being done.

However, even if aluminum and aluminum alloys have such properties, they may turn black if exposed to high-temperature water containing impurity ions, especially high-temperature water of 50°C or higher, or may be exposed to high-temperature water vapor. If this happens, it may turn white.

Therefore, various surface treatments have been conventionally applied to the surfaces of aluminum and aluminum alloys in order to prevent such blackening and whitening.

- As an example, there is a surface treatment method in which the surface of an aluminum plate is subjected to phosphoric acid chromate treatment, which is widely used. However, if the amount of film on an aluminum plate subjected to this phosphoric acid chromate treatment is small, when exposed to high-temperature water or high-temperature steam containing impurity ions, the aluminum plate treated with phosphoric acid chromate will cause the same problem as an aluminum plate without such treatment. The surface may turn black or white. On the other hand, if the amount of the film is large, although the above-mentioned black change or white change does not occur, the workability becomes poor during press working with a mold, drawing work, etc., and this may cause problems in product processing.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art and to provide a surface-treated aluminum plate with excellent discoloration resistance that does not cause black discoloration or white discoloration even when exposed to high-temperature water or high-temperature steam. It is something to do.

(Means for Solving the Problems) In order to achieve the above object, the present inventor has conducted repeated experimental research on coating various water-soluble resins on aluminum alloy plates, taking into account manufacturing advantages. Films made of polyacrylic acid or polymethacrylic acid do not have this effect, but films obtained by crosslinking these with a specific water-soluble crosslinking agent have excellent blackening resistance, provided the film thickness is controlled. It was discovered that it exhibits white fastness deterioration.

That is, the present invention provides an epoxy group or an amino group on the surface of an aluminum or aluminum alloy plate by applying a water-soluble resin made of one or more of polyacrylic acid, polymethacrylic acid, and resins obtained by esterifying these. The film crosslinked with a water-soluble compound having two or more of
．． The gist of this invention is a surface-treated aluminum plate having a thickness of 0 μm and having excellent discoloration resistance against high-temperature water and high-temperature steam.

The present invention will be explained in detail below based on examples.

Polyacrylic acid, polymethacrylic acid, or resins obtained by esterifying these are water-soluble resins and have carboxyl groups (-COOH) or carbonyl groups (C=O), so they have epoxy groups (C, -, C :) Alternatively, water resistance can be improved by causing a crosslinking reaction with a compound having an amino group (-NH2).

That is, in polyacrylic acid, polymethacrylic acid, or a water-soluble resin obtained by esterifying these, carboxyl groups or carbonyl groups are crosslinked with each other via a crosslinking agent,
It forms a film in which polymer molecules are three-dimensionally crosslinked, and can improve water resistance.

Therefore, in the present invention, as a crosslinking agent, a water-soluble compound having two or more epoxy groups (water-soluble epoxy resin crosslinking agent) such as diglycerol polyglycidyl ether and sorbitol polyglycidyl ether, or an amino group such as melamine is used. This method uses a water-soluble compound (water-soluble amino resin cross-linking agent) having two or more of them.The water-soluble resin and cross-linking agent are mixed in appropriate amounts, diluted with water, and used as a treatment solution to treat the aluminum plate. A film is formed by painting and baking the surface.

However, in order to improve discoloration resistance such as blackening resistance and whitening resistance against high-temperature water and high-temperature steam, the film thickness should be set to 0.1~
It is necessary to keep it in the range of 2.0 μl.

If the film thickness is less than 0.1 μm, the film itself becomes discontinuous and cannot sufficiently prevent white discoloration or black discoloration. On the other hand, if the film thickness exceeds 2.0 μm, the film itself tends to discolor to white. Film thickness is 0.1-2.0
μI is preferably 0.3 to 1.0 μm.

In addition, points to note regarding the treatment method for forming the above-mentioned film are shown below.

First, the crosslinking agent shall be added in an appropriate amount to the water-soluble resin, and the amount added is 2.5 to 20% of the solid content of the resin.
．． It is desirable to set it to 0%. If it is less than 2.5%, the water-soluble resin will not be sufficiently crosslinked and good color fastness will not be obtained, but if it exceeds 20.0%, the effect of the crosslinking agent will be saturated and the color fastness will be even worse. Not only does it not improve, but also the discoloration resistance tends to decrease due to the unreacted crosslinking agent remaining.

Further, the baking temperature is preferably 100 to 250°C. 10
If the temperature is below 0℃, crosslinking will not occur sufficiently or it will take time for the crosslinking reaction to occur, resulting in a significant decrease in work efficiency, so the temperature should be 100℃ or higher. This is because there is a possibility that the material properties of the material will be adversely affected.

The baking time should be selected appropriately depending on the film thickness and baking temperature.
Sufficient color fastness can be obtained by baking for a few minutes. Regarding the baking time, when coating with a coil form, etc., it is possible to shorten the baking time by adding an appropriate catalyst to promote the crosslinking reaction.

In addition, since the film of the present invention is composed of a water-soluble resin and a water-soluble crosslinking agent, the film formation has the advantage of not requiring the exhaust equipment required when painting with a conventional solvent-based paint.

Next, examples of the present invention will be shown.

(Example) The various water-soluble resins and crosslinking agents shown in Table 1 were mixed in the proportions shown in the table, and the surface of the aluminum alloy plate was coated and baked in the manner described above to achieve the film thickness shown in the table. A film was formed.

The resulting film was examined for its resistance to blackening and whitening. The results are also listed in the same table. The blackening resistance was evaluated based on the degree of blackening after being immersed in boiling water (tap water) for 30 minutes. Moreover, the white change resistance was evaluated by the degree of white change after exposure to water vapor at 120° C. for 30 minutes.

For comparison, the aluminum plate was left degreased (Comparative Example 1), and the amount of chromium deposited was reduced by phosphoric acid chromate treatment (Comparative Example 2).

Painted and baked with only water-soluble resin (Comparative Example 3.4)
The discoloration resistance was similarly investigated for those with thin film thickness and those with thick film thickness (Comparative Examples 5 and 6) when a crosslinking agent was added to the water-soluble resin.

As is clear from the table, all of the surface-treated aluminum plates of the invention examples have excellent resistance to blackening and whitening, whereas in the comparative examples, those treated with phosphoric acid chromate have slightly less resistance to blackening. All of them are inferior in blackening resistance and whitening resistance, except for the one with (Comparative Example 2). In addition, Comparative Example 5 has the same film structure as the present invention example but the film thickness is not appropriate.
．． It can be seen that in No. 6, the blackening resistance and whitening resistance were deteriorated.

[Blank 1 (Effects of the Invention) As detailed above, according to the present invention, a film in which a specific water-soluble resin is cross-linked with a water-soluble cross-linking agent is provided on the surface of an aluminum plate at a predetermined thickness. It does not turn black or white even when exposed to high-temperature water or high-temperature steam containing impurity ions, and has excellent color fastness, and can be used in various applications that take advantage of this excellent property. Furthermore, since no exhaust equipment or the like is required when forming the film, there is an advantage that it can be manufactured at low cost.

Claims (1)

[Claims] A water-soluble resin containing one or more of polyacrylic acid, polymethacrylic acid, and resins obtained by esterifying these is applied on the surface of an aluminum or aluminum alloy plate. 1. A surface-treated aluminum plate having excellent discoloration resistance against high-temperature water and high-temperature steam, characterized by having a film crosslinked with a chemical compound having a thickness of 0.1 to 2.0 μm.