JPH0433871B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for surface treatment of aluminum or aluminum alloy (hereinafter referred to as aluminum material). [Conventional technology] Conventionally, aluminum materials used for various purposes such as sash and entrance doors are generally treated by degreasing, washing with water, etching, washing with water, neutralization, anodizing, washing with water, electrolytic coloring, washing with water, washing with pure water, and liquid treatment. Cutting, electrodeposition painting, washing,
The surface is treated through a series of steps of draining and baking and drying, and is usually electrolytically colored to a reddish bronze color, and then a clear coat is applied by electrodeposition. [Problem to be solved by the invention] In recent years, user needs regarding the color tone of products have diversified, and the traditional reddish bronze color of aluminum building materials tends to become boring. There is an increasing demand for an amber color with a tinge of color. For this reason, there is a need to respond to high-mix, low-volume production in the surface treatment process, and it is desired to be able to perform electrolytic coloring from dark colors to light colors using a single electrolytic solution. However, in electrolytic coloring, it is actually difficult to perform electrolytic coloring in two or more different colors using an electrolytic solution having one composition. On the other hand, in the conventional surface treatment method for aluminum materials, after electrolytic coloring, washing is performed with water, followed by washing with pure water (semi-sealing), and the inside of the micropores of the anodic oxide coating is removed.
Remove miscellaneous ions such as SO ₄ ^2- and S ^2- as much as possible,
Electrodeposition painting is performed, but these miscellaneous ions are not sufficiently discharged and remain in the micropores, causing changes in adsorbed substances (Ni ²⁺ , Sn ^2+, etc.) during electrolytic coloring, and
It acts as a promoting medium for decolorization in electrodeposition coating (because aluminum is an anode in electrodeposition coating, and metals, metal hydroxides, etc. precipitated in the micropores of the anodic oxide film try to elute), It also causes milky whitening of the film, and the overall color tone is unstable, making it difficult to obtain a constant quality. To prevent this,
Although the pure water washing temperature was raised to the limit that would not cause cracks in the anodic oxide film, and the cleaning time was maintained for a relatively long time (complete sealing), the above problem could not be completely covered, and this may be the cause of color blurring. It's summery. Therefore, an object of the present invention is to solve the above-mentioned problems, and to use an electrolytic coloring bath with a certain composition, for example, even when electrolytically colored to a bronze color, it is possible to control the coloring to an amber color. The object of the present invention is to provide a method for surface treatment of aluminum material, which can produce colored products of stable quality. [Means for Solving the Problems] The method for surface treatment of aluminum materials according to the present invention involves electrolytically coloring an aluminum material that has been subjected to anodization treatment in an electrolytic solution containing a metal salt, and then applying electrodeposition coating to the surface of the aluminum material. The treatment method is characterized in that a heat treatment is performed at a temperature of at least 100°C or higher after the electrolytic coloring and before the electrodeposition coating. [Operation and mode of the invention] According to the research of the present inventors, ordinary anodic oxidation
In the case of electrolytic coloring-electrodeposition coating, it has been found that other color tones can be controlled without changing the conditions in the film treatment process, especially by simply inserting a hot air heating process after electrolytic coloring and washing with pure water. That is, when electrolytically colored a reddish bronze color using an electrolytic coloring bath of a certain composition, the color changes to a yellowish amber color by simply heating the color with hot air to 100°C or higher. It has been found that the color tone obtained is also stable, and that decolorization and blurring of coloring during subsequent electrodeposition coating can be prevented. Although the cause of this has not necessarily been clarified, miscellaneous ions such as SO ₄ ^2- and S ^2- that remain free in the micropores of the anodic oxide film after electrolytic coloring can be removed as much as possible by washing with water or hot water with pure water. By removing it and then heating it at a high temperature, the remaining miscellaneous ions such as SO ₄ ^2- and S ^2- , the colored adsorbate such as Ni ²⁺ and Sn ²⁺ due to electrolytic coloring, and the anodic oxide film pore walls react. It becomes a compound that is difficult to ionize and stabilizes, and the color tone changes.
It is thought that the decoloring effect in the subsequent electrodeposition coating is suppressed. The heat treatment temperature needs to be at least 100°C or higher, and the higher the temperature, the more yellow the amber color becomes. However, if the temperature exceeds 240°C, the aluminum material becomes over-aged and becomes soft, making it impossible to obtain the desired hardness, which is not preferable. However, there are cases where strength is not an issue, and the invention is not limited to this. Also, the heat treatment time is at least 5
It is necessary to make the heating time more than 1 minute, and the higher the heating temperature, the shorter the time can be. The conditions of the above heat treatment process are shown in the accompanying drawings. The shaded area A indicates the range where the effect of the above heat treatment process is clearly recognized, and the shaded area B
indicates an industrially preferable range. As the surface treatment method for aluminum materials of the present invention, conventionally known surface treatment methods can be applied as they are, except that a heat treatment step is added after electrolytic coloring and before electrodeposition coating. That is, first, the aluminum material is subjected to appropriate pretreatment such as degreasing, etching with water, washing with water, and neutralization, and then subjected to a well-known anodic oxidation treatment to form an anodic oxide film. That is, electrolytes containing well-known inorganic acids and/or organic acids, such as sulfuric acid, chromic acid, phosphoric acid, etc., mixed acids thereof, oxalic acid, malonic acid, etc., or mixed acids of these or with inorganic acids, etc. The aluminum material is anodized in an electrolyte using direct current, alternating current, or a similar current waveform. The applied voltage, application time, etc. for the anodic oxidation treatment are sufficient as usual. Next, the anodized aluminum material is washed with water if necessary, and then subjected to a known electrolytic coloring treatment in an electrolytic solution containing a metal salt. There are various metal salts used in electrolytic coloring solutions, but examples include nickel, cobalt,
Inorganic acids such as nitrates, sulfates, phosphates, hydrochlorides, chromates of metals like chromium, copper, magnesium, iron, cadmium, titanium, manganese, molybdenum, calcium, vanadium, tin, lead, zinc etc. There are salts, organic acid salts such as oxalates, acetates, and tartrates, and these are used selectively. Preferably, when two or more of these metal salts are used in combination, and more preferably three or more types are used in combination, the degree of coloring progress and spreading properties are significantly improved.
In addition, a strong reducing compound may be added to two or more metal salts for the purpose of improving the degree of coloring and improving coverage. Examples of such strong reducing compounds include dithionite salts such as sodium dithionite, zinc dithionite, and ammonium dithionite;
Thiosulfates such as ammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, iron thiosulfate,
Examples include thioglycolic acid salts such as thioglycolic acid, ammonium thioglycolate, and sodium thioglycolate (see Japanese Patent Publication No. 54-23661). The electrolysis conditions are the same as before, e.g.
AC electrolysis is performed using an applied voltage of 15 V or less, preferably 5 to 14 V, using an AC or a waveform having an equivalent effect. Thereafter, after washing with water and hot water with pure water, and draining the liquid if necessary, the heat treatment described above is performed according to the present invention. Next, after cooling, electrodeposition coating is performed according to a conventional method, followed by washing with water, draining liquid, and baking drying to obtain an aluminum product. [Example] Hereinafter, the present invention will be specifically described with reference to Examples. 17.5W/V of extruded aluminum A6063S that has been degreased, etched, and smutted using conventional methods.
% sulfuric acid aqueous solution to serve as an anode and an aluminum cathode provided as a counter electrode, a 15 V DC current was applied at a current density of 1.2 A/dm ² for 35 minutes.
An anodized film of approximately 12 microns was formed on its surface. This was washed with water. Then, length 300mm, width
A container with a length of 100 mm and a height of 150 mm is used as a coloring electrolysis device, and a counter electrode is placed in one place.
The material to be treated is 70 mm wide and 1.3 mm thick with a distance of 250 mm.
mm, immersed in an electrolytic solution with the following composition at a temperature of 20°C, and subjected to AC electrolysis at an applied voltage of 12.5 V for 3 minutes.
A uniform reddish bronze coloring was obtained on the non-opposite surface. Colored electrolyte composition: Nickel sulfate (hexahydrate) 25g / Magnesium sulfate (heptahydrate) 10g / Ammonium thiosulfate 1.0g / Ammonium sulfate 30g / DL-malic acid 0.5g / Boric acid 10g / pH 5.6 The above colored film was soaked in pure water. After washing with hot water, heat treatment was performed under various conditions shown in Table 1 below. Table 1 also shows the results of visual judgment of the color tone of products subjected to various heat treatments relative to products not subjected to heat treatment (control).

〔Effect of the invention〕

As described above, according to the surface treatment method for aluminum materials of the present invention, by performing heat treatment at a temperature of at least 100°C or higher after electrolytic coloring and before electrodeposition coating, the same equipment, electrolyte, and method as before can be used. For example, by adding the above heat treatment step to the step of obtaining a reddish bronze colored film, a yellowish amber colored film can be obtained. The color tone can also be controlled by changing the heat treatment conditions. Furthermore, the influence of miscellaneous ions such as SO ₄ ^2- and S ^2- remaining in the micropores of the anodic oxide film on the electrodeposition coating film is also suppressed, and the coating performance is improved and stabilized. Moreover, the above-mentioned effects can be achieved in a relatively short heat treatment time.
It is possible to create a line with the heating space required for each cycle, and it is easy to apply to existing production lines. Therefore, the needs for high-mix, low-volume production can be satisfactorily met.

[Brief explanation of drawings]

The attached drawing is a graph showing the range of conditions for the heat treatment process of the present invention.

Claims (1)

[Claims] 1. In a surface treatment method in which anodized aluminum or aluminum alloy is electrolytically colored in a metal salt-containing electrolyte and then electrocoated, at least
A method for surface treatment of aluminum or aluminum alloy, characterized by heat treatment at a temperature of 100°C or higher.