JPS6014117B2 - Surface treatment method for aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel surface treatment method for producing a film with a beautiful striped pattern on the surface of aluminum or aluminum alloy (hereinafter simply referred to as aluminum) by an electrochemical method. .

This type of pattern forming method using electrochemical surface treatment is described in Tsubakiiso Sho 50-136485 and Special Collection Sho 51-27556, which the present inventors previously developed and successfully put into practical use.
If this invention is applied to the surface treatment of aluminum, a pattern can be created on the surface of the object to be treated using the conventional embossing method, printing method, etching method using partial masking, or photoetching method. This process does not require special equipment or mechanical equipment such as molds or plates, and can form vertical stripes on the surface of aluminum using ordinary electrochemical processing equipment. This method is attracting attention as a promising and innovative method for producing decorative aluminum materials because it is simple, allows for cost savings, and has excellent weather resistance.

The method of the invention includes a pre-treatment step: First, oil and dirt adhering to the surface of the object to be treated are removed.

Pattern forming process: Next, the pattern is inert in an electrolytic bath consisting of an aqueous solution to which an alkali or alkali metal hydroxide or a salt thereof, or an organic or inorganic acid that easily forms a barrier film is added thereto. AC electrolysis is performed using the material as a counter electrode, and a film with a vertical striped pattern is formed on the surface of the object by the action of bubbles generated during AC electrolysis.

1. Pattern coloring step: The striped pattern film in the step [o] is vividly colored by a known metal salt electrolytic coloring method or coloring treatment by immersion in dyes or pigments, or the striped pattern film in the step After forming a protective film by oxidation treatment and improving the corrosion resistance and abrasion resistance of the film, the cotton pattern subjected to the above-mentioned coloring treatment is vividly colored.

0 Post-treatment process: Finally, sealing with steam or heated water, or coating with transparent resin.

It consists of the above-mentioned steps, all of which consist of electrochemical steps such as immersion in a processing bath, energization, and heating.

The most important process among these is the pattern formation process by AC electrolysis of {o}, and the reaction mechanism for the appearance of the pattern is estimated from observation of the cross section of the film using an electron microscope. A part of the mold film is destroyed, and many bubbles rise from this part along the surface of the workpiece to the surface of the electrolyte, and at this time, the bubbles float up along a nearly constant trajectory. These bubbles create a large difference in electrolytic action between the traced area and other areas, and many pores are generated in the area where the bubbles pass, causing the general electrolytic action to flow through the bubbles at the beginning of electrolysis. This is thought to be due to focusing on one part.

In other words, the part through which the bubbles pass becomes the "streak" part of the striped pattern, and the density and shape of this part have a great influence on the decorative effect of the design on the pattern formation of the final product. In actual production, variations in pattern formation from production lot to production lot cannot be tolerated, and this point is especially important when using different parts such as aluminum extrusion molds. It's coming. Therefore, the present inventors conducted intensive research in order to stabilize production site operations by preventing variations in pattern shape from production lot to production lot and maintaining the reproducibility of pattern appearance. The surface condition of the object to be treated at the end of the pretreatment process is significantly involved in determining the state of bubble generation in the initial stage of electrolysis in the alternating current electrolytic pattern formation process, which is thought to have an impact. I discovered that.

That is, in the early stages of AC electrolysis, the surface of the object to be treated is first covered with a uniform thin barrier-type film (the thickness of which is estimated to be several tens of amperes to several hundreds of amperes) as soon as the current is started, and then this thin film A particularly weak part of the is destroyed and the current is concentrated in that part, and bubbles are concentrated from this part and this becomes the starting point of the "streaked" part of the vertical striped pattern. In the areas traced by air bubbles rising to the surface, the reaction of film formation → dissolution or bubble generation → dissolution is accelerated and progresses more than in other areas, resulting in the formation of a vertical striped pattern. Therefore, in order to maintain the reproducibility of the appearing state of the vertical striped pattern, it is necessary to make the distribution state of the parts with different electrical characteristics constant, since they are first destroyed and become the point of concentrated generation of bubbles. Pretreatment conditions are desirable. This difference in electrochemical properties is caused by particularly sharp convexities among the convexities and convexities on the surface of the workpiece after the pretreatment is completed.
In other words, it is thought that the protrusions are large enough to affect the film thickness of several tens of amperes to several hundreds of amperes at the initial stage of turtle scales.
This can be easily deduced from the fact that there is a starting point for the "streak".

In normal cases, the pretreatment for removing dirt such as oil adhering to the surface of aluminum materials is a combination of a degreasing process using a detergent or organic solvent and an alkaline etching process. Alkaline etching does not have a particular function of geometrically smoothing the surface of the object to be processed, and depending on the selection of processing conditions, may conversely increase the surface roughness. For example, if an aluminum mold with a surface with partially different thermal histories is etched with a high-temperature caustic soda aqueous solution, the areas with coarse grains will be visible to the naked eye. When applying , the difference between coarse and fine grains is
The degree of surface organization is markedly different, and therefore the shape of the cotton pattern formed on the surface of the treated product is also different. For this reason, there is no problem when making a single product using only the above-mentioned materials, but when used in combination with other materials, the decorative effect may be impaired. This is extremely inappropriate. However, if the causes of these problems can be clearly clarified as mentioned above, it is possible that the crystallographic characteristics of the crystal grains and crystal faces on the aluminum surface have a decisive influence on the surface finish. Instead of an etching process that may cause damage, electrolytic polishing or chemical polishing can dissolve the convex parts of the fine irregularities on the surface of the workpiece more quickly than the concave parts, making the surface geometrically smooth. This problem can be solved by employing surface smoothing processing.

The present invention has succeeded in developing a new aluminum surface treatment method focusing on the above points,
When forming a colored film with a cotton pattern on the surface of aluminum, the surface is first smoothed by electrolytic polishing or chemical polishing as a pretreatment, and then treated with an alkali or alkaline metal hydroxide or a salt thereof. Alternatively, alternating current electrolysis is applied to this in an electrolytic bath made of an aqueous solution containing an organic or inorganic acid that tends to form a barrier-type film, and the surface of the object to be treated has a vertical striped pattern due to the action of bubbles generated during alternating current electrolysis. After forming a film, this film is subjected to AC electrolysis treatment in a bath containing metal salts or coloring treatment by bonding with dyes or pigments, or the surface of the vertically striped film is anodized before that. The method is characterized in that after a protective coating is applied to the object, the coloring treatment described above is applied to sharpen the pattern, thereby obtaining a beautiful striped colored coating on the surface of the object to be treated.

In addition, in each of the above treatment steps, if it is necessary to perform electrolytic polishing or chemical polishing after removing relatively rough surface irregularities in the pretreatment step of the object to be treated, degreasing treatment must be performed first. After that, it is preferable to perform etching and then electrolytic polishing or chemical polishing.

At that time, electrolytic polishing uses perchloric acid grade or phosphoric acid grade, but phosphoric acid grade is suitable for on-site production because of its good operational stability. Chemical polishing methods include phosphoric acid-nitric acid system, phosphoric acid-sulfuric acid-nitric acid system, phosphoric acid monohydrogen peroxide system,
Although there are hydrofluoric acid-nitric acid systems, phosphoric acid-sulfuric acid-nitric acid systems are preferred from the viewpoint of smoothness of the polished surface and operational stability. In addition, when performing anodizing treatment prior to pattern coloring, lightly etching the object to be treated with an aqueous solution of sodium hydroxide or sodium carbonate before treatment will result in a more vivid colored pattern in the subsequent coloring treatment. can be done.

According to the method of the present invention, the pattern formation in the pattern forming process using AC electrolysis is stabilized compared to the case where surface smoothing processing is not performed, and the luster of the parts other than the "streaks" of the pattern is increased, so that the coloring is improved. The clarity is improved and a colored surface with an overall polished appearance is obtained.

Furthermore, the method of the present invention has the characteristic that the outline of the wood grain becomes clear and the way the "streaks" grow is stiff and linear, so it is an advantageous method when you want to strongly express the straight-grained wood grain. be. Next, the embodiments of the present invention will be specifically described with reference to typical examples of the present invention.

Example 1 105 aluminum plates were degreased by a conventional method, and then treated with 800 cc of phosphoric acid (d=1.74) and sulfuric acid (d
= 1.80) Electrolytic polishing was performed for 10 minutes at 40°C and 30V in 200cc of chromic acid and 50 days of moat passing,
Next, after washing this with water, sodium metashelate was added for 0.3 h.
When an alternating current with a frequency of 60 Hz was applied for 18 minutes at 30 y using a stainless steel plate as a counter electrode in an aqueous solution of 0.1 mol of shelf acid/the aluminum plate, a wood grain pattern appeared on the surface of the aluminum plate.

Further, this was immersed for 2 minutes in a sodium carbonate aqueous solution at 450 m/m, then anodized for 30 minutes at 16 V in a sulfuric acid bath for 150 m/m, and then immersed in an aqueous solution containing nickel sulfate. When the electrolytic coloring treatment was applied, the "streak" part of the wood grain was darkly colored, and the parts other than the "streak" were shiny and beautiful aluminum plates were obtained. Finally, a transparent resin was coated with lightning to complete the process. Example
2 Degrease 14 pieces of 1050P aluminum plate per day by a conventional method, and then degrease at 85°C in a mixed solution of 800cc of phosphoric acid (d=1.74), 200cc of sulfuric acid (d=1.80), and 10% by weight of nitric acid. 1. Apply a special chemical polishing.

After washing this with water, in an aqueous solution containing 0.3 mol of sodium metashelfate and 0.1 mol of shelactic acid, the aluminum plate A wood grain pattern appeared on the surface. Further, this was immersed in a sodium carbonate aqueous solution of 4yC for 40 nights for 2 minutes, then anodized at 16V for 3 minutes in a sulfuric acid bath of 150 nights, and then in an aqueous solution containing nickel sulfate. When subjected to AC electrolytic coloring, the "streaks" of the wood grain are colored darkly, and the "streaks"
A beautiful aluminum plate with a glossy finish was obtained. Finally, the transparent resin was coated with a lightning coat to complete the process.
Example 3 A 606$-T5 aluminum profile was electrolytically polished in the same manner as in Example 1, and then polished with boric acid for 15 days/night and sodium hydroxide for 1 night/day in a immersion bath using stainless steel as the counter electrode. When AC current was applied at 35 V for 10 minutes, a straight-grained silver-gray pattern was formed on the surface of the profile.

This profile is then treated with an inorganic colored oxide containing stannous sulfate (
70qC) and finally coated with a transparent resin paint, a beautiful aluminum shape with only the wood grains colored was obtained. Example 4 Aluminum profile 6
06$-T5 was electrolytically polished in the same manner as in Example 1, and then an alternating current was applied at a current density of 2.0 using stainless steel as the counter electrode in a 0.3 hol/trisodium phosphate bath.
When electricity was applied for 15 minutes at A/d, a straight-grained silver-gray pattern was formed on the surface of the treated material.

Next, this shape was immersed in a sodium hydroxide solution (concentration: 30°C, temperature: 600°C) for about 1 minute, and after washing with water, the temperature was 15°C.
Current density: 1.2A in a sulfuric acid bath at a temperature of 20°C
/d for 3 minutes to form an anodized film about 1 inch thick on the surface of the profile. After washing with water, an aqueous solution of ferric ammonium oxalate (pH 4.5) was added.
When the material was colored by immersing it in water (at a temperature of 60° C.) for 5 minutes, a clear colored wood grain pattern was developed on the surface of the shape. Finally, it was immersed in boiling water for about 3 minutes to perform a pore-sealing treatment to obtain a beautiful aluminum profile with a pale yellow plain wood-like pattern.

Example 5 An aluminum profile 606$-T5 was electrolytically polished in the same manner as in Example 1, and then calcium hydroxide 0.3
In the evening, when alternating current was applied for 15 minutes at a current density of 2.0 A/d using stainless steel as the counter electrode, a straight-grained silvery-gray pattern was formed on the surface of the treated material.

Thereafter, the material to be treated was subjected to anodizing treatment and coloring treatment in the same manner as in Example 4, and an aluminum material having a clear colored pattern was obtained. As described above,
When the method of the present invention is applied to the surface treatment of aluminum, when a colored film with excellent film characteristics and a beautiful striped pattern is produced on the surface of the object to be treated using an electrochemical method,
In the pretreatment process, the surface is smoothed by electrolytic polishing or chemical polishing, which is applied before the colored striped pattern film treatment process to adjust the surface condition of the object to be treated. This method not only makes it possible to obtain an aluminum material with a remarkable shine and excellent decorative effect, but also greatly contributes to improving the quality of products and stabilizing operations at production sites.

Claims (1)

[Claims] 1. A workpiece made of aluminum or an aluminum alloy is first subjected to surface smoothing processing by electrolytic polishing or chemical polishing as a pretreatment, and then treated with an alkali or alkaline earth metal hydroxide, a salt thereof, or a barrier thereto. AC electrolysis is performed in an electrolytic bath using an aqueous solution containing an organic or inorganic acid that tends to form a mold film, and a film with a vertical striped pattern is formed on the surface of the workpiece by the action of bubbles generated during AC electrolysis. Then, this film is subjected to AC electrolysis treatment in a bath containing metal salts or coloring treatment by immersion in dyes or pigments, or, before that, a protective film treatment is applied to the surface of the vertical striped pattern film by anodizing treatment. 1. A method for surface treatment of aluminum or aluminum alloy, which comprises applying the coloring treatment described above to sharpen the pattern and obtain a beautiful striped colored film on the surface of the treated object.