JPS5912758B2 - Manufacturing method for colored light metal materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a colored light metal material having a transparent coating layer.

Colored light metals, especially colored aluminum materials, having a transparent or translucent coating layer (herein referred to as a transparent coating layer) have been developed using technology from the viewpoint of both improving the aesthetic appearance and protecting the base material by the coating layer. There is a strong need for development.

However, the conventionally used techniques have many drawbacks as described below and are not necessarily satisfactory. For example, there is a method of painting uncolored light metal substrates with anionic colored clear paints, but this method causes scratches and peeling of the paint film during construction, revealing the base metal color of the substrate, which is not aesthetically pleasing. In addition, there was a drawback that the film thickness of the coating film varied, causing color unevenness. As ten methods for improving this, a method has been proposed in which a coating layer is formed by electrocoating a light metal material that has been previously subjected to a coloring treatment using an anionic vehicle resin. This method has the following advantages: it is extremely easy to obtain a uniform coating layer, it can be mass-produced economically, and it is less likely to cause damage to the coating.Furthermore, it does not cause fading or bleaching of the colored substrate during electrodeposition. It comes with a fatal flaw. Attempts have been made to use a sealing treatment to improve this problem, but this has not been put to practical use. The present inventors have repeatedly conducted research on electrodeposition coating methods for colored substrates that do not fade, and have discovered that fading of colored substrates can be completely prevented by using a cationic water-dilutable coating composition. This research has led to the completion of the present invention.

That is, the present invention relates to a method for producing a colored light metal material having a transparent coating layer, which comprises cationically electrodepositing a previously colored light metal material in an electrodeposition bath containing a cationic water-dilutable coating composition. .

The light metal base materials according to the present invention include aluminum, aluminum alloys, aluminum composites, magnesium alloys, etc., and aluminum, its alloys, and composites are particularly suitable.

The light metal substrate is suitably colored in advance by conventional means. For the coloring treatment, any method such as a chemical conversion coloring method, an electrolytic coloring method, or a dyeing method may be used. Further, it may be colored in a light color of 35 due to boehmite processing. Preliminary means that the coloring treatment is performed in a process separate from the electrodeposition bath, as in the above-mentioned treatment, and does not include coloring treatment in the same bath as the electrodeposition bath in the process of the present invention. do not have.

The cationic water-dilutable coating composition may be any aqueous resin-containing composition used in ordinary anodic electrodeposition.

The composition resin may be an addition polymer of an unsaturated monomer containing 5 to 50 parts by weight of an amine compound, a polycondensation product of a polyfunctional amine such as polyamine or hydroxyalkylamine, and a polybasic acid or an epoxy resin. An example is resin. These resins may be modified with various forms of compounds as necessary, and many of those modified with aminoplasts, phenoplasts, proxisocyanates, etc. have favorable coating properties. In order to make the above resin dilutable with water, at least a portion of its amino groups are neutralized and cationized with an acid. Suitable acids include phosphoric acid,
These are inorganic acids such as boric acid, and organic substances such as formic acid, acetic acid, and lactic acid. Water dilutable means that in addition to being soluble in water, it may be of a dispersion type or emulsion type, and can be appropriately diluted with water. A small amount of organic solvent to stabilize the water-dilutable resin liquid.
Protective colloids, emulsifiers, etc. may be added to the extent that they do not impair the properties of the film. This electrodeposition composition is a painting finishing method that allows the coloring of the base material to be recognized, and is a so-called clear finish, so the composition must be transparent or translucent after coating. Finely dispersed pigments and dyes can be incorporated to an extent that does not significantly impair transparency, preferably about 2% or less based on the total solid weight.

Pigments such as mica, pearlescent pigments, etc. can be added in an amount of 2% or more if necessary. As the electrodeposition conditions employed in the present invention, conventional cathodic electrodeposition or AC electrodeposition conditions can be used as they are.

For example, a colored aluminum base material is used as a cathode, and a load voltage of 2~
What is necessary is just to carry out with 500V1 electric current application time about 15 to 300 seconds. The solid content of the electrodeposition bath is suitably in the range of 5 to 20%. The electrodeposited object to be coated is washed with water and cured by heating, if necessary.

The appropriate treatment temperature is 120 to 300°C and the time is 5 to 60 minutes, and an infrared furnace may also be used. Since the colored light metal material obtained by the production method of the present invention has a colored base material itself, it is not affected by scratches or peeling of the coating film, and can maintain a stable hue. In addition, by using a transparent or semi-transparent colored paint as a cationic paint as necessary, effects based on interaction with the color of the colored base material can be created, such as adding depth to the color tone or changing the hue. etc., which enables diversification of hue management.

Example 1 Degreased, etched, and neutralized aluminum material (JI
SA6O63) with 97.5 parts of deionized water (hereinafter referred to as parts by weight)
It is treated in a solution consisting of 2 parts of diethanolamine and 0.5 parts of nitric acid at 85°C for 3 minutes to obtain a golden colored aluminum base material 1.

Fill a stainless steel tank with an aqueous acrylic epoxy cation resin solution and stir with a magnetic stirrer.

The temperature of the bath is 30℃, pH 6.2, and conductivity 253μO/Cm.
, solid content was 7.2%. After the colored aluminum base material was immersed in this bath, a DC power source was used to connect the object to be coated to the cathode and the bath to the anode, and the bath was energized at 120 V for 3 minutes.

The object to be coated was taken out, washed with water, and heated at 190° C. for 25 minutes. The coated object retained the golden color of the base material, and a transparent coating film with a film thickness of 11μ and a pencil hardness of 2H was formed, and it passed the real alkaline test (5
%NaOH L. a. b. Display value -
Shown in 1. Example 2 A 52S aluminum plate is anodized in a 5% by weight (hereinafter referred to as % by weight) chromic acid solution for about 40 minutes according to a conventional method.

Next, a mixed solution of 2% each of ammonium oxalate and oxalic acid with 0.4% cobalt acetate added thereto was used as an electrolytic solution, and the above aluminum and carbon were used as both poles.
AC current was applied for 5 minutes to obtain a brown electrolytically colored aluminum base material (2). Thereafter, as a result of processing in the same manner as in Example 1, a good coated product was obtained. L. a. b. The values are shown in Table-1. Comparative Example 1 The colored aluminum materials used in Examples 1 and 2 were each electrodeposited in an acrylic melamine-based anionic electrodeposition clear paint, and heated and cured to form an L. a. b. As a result of measuring the value, extensive fading was observed.

The results are shown in Table-1. Example 3 Colored aluminum material 1 and coated colored aluminum material obtained in Example 1, colored aluminum material and coated colored aluminum material obtained in Example 2, and colored aluminum material 1 treated in Comparative Example 1. We conducted a performance test.

Coating film performance test (1) Alkali resistance: Ring method (5% Na
OHl2O°C, judgment after 72 hours).

Evaluation: x: Lots of corrosion, △: Lots of pitting, ○: No pitting. (
2) Pencil hardness: JIS-A-4706 (3) Cast test: JIS-H-8601 The results of each test are shown in Table-2.

Claims (1)

[Claims] 1. A method for producing a colored light metal material having a transparent coating layer, which comprises cationically electrodepositing a pre-colored light metal material in an electrodeposition bath containing a cationic water-dilutable coating composition. . 2. The method according to item 1 above, wherein the light metal base material is aluminum. 3. The method of claim 1 or 2, wherein the coating composition contains about 2.0% or less pigment based on the total weight of solids in the electrodeposition bath. 4. The method according to item 1 or 2 above, wherein the coloring treatment is conversion coloring. 5. The method according to item 1 or 2 above, wherein the coloring treatment is alternating current electrolytic coloring.