JPS601956B2 - Method of forming wood grain pattern on aluminum or aluminum alloy material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a wood grain pattern on the surface of aluminum or aluminum alloy (hereinafter referred to as aluminum material or treated material), and its purpose is to produce a wood grain pattern on the surface of aluminum or aluminum alloy (hereinafter referred to as aluminum material or treated material). It is an object of the present invention to provide a method for forming a highly decorative wood grain pattern on the surface of an aluminum material by an electrochemical method, without using such laborious and troublesome methods.

Conventionally, the patterning method for aluminum materials involves stamping patterns on the aluminum surface using wind pressure rolls or press molds.

'B} A method of etching patterns on the aluminum surface using chemicals using photolithography.

A method of printing colorants such as dyes on the aluminum surface using printing methods such as screen method and transfer method.

[D] Partially masking the surface of aluminum with a suitable shielding material and painting with an appropriate method, or chemically or electrolytically coloring; There are ways to attach it to the surface.

These middle-of-the-road methods apply strong pressure to the material with a die or mold to form patterns, so they can only be applied to flat aluminum materials, and like method {B), they cannot be applied directly to color I can't get a pattern.

}、' Although it is possible to add color patterns using the gong method,
All of them require troublesome processes such as plate making and masking, and are particularly unsuitable for creating wood grain patterns. Next, there is a problem with the durability of the pattern-forming film. These methods require special machines and equipment and are disadvantageous in terms of processing costs. In order to solve the problems of the above-mentioned methods, a method of electrolytically generating a wood grain pattern on the surface of an aluminum material has been proposed.

(Showa 52 Hand Patent Application Publication No. 6024). According to this method, aluminum material is subjected to alternating current electrolysis in an alkaline electrolytic bath to produce a barrier film with a wood grain pattern on the surface of the material to be treated, and then this material is treated with a sodium hydroxide aqueous solution. The next day after lightly etching with: AC electrolysis in an inorganic coloring bath containing metal salts, or 〇: inorganic acid,
Alternatively, after anodizing with an organic acid or a mixed acid thereof as an electrolyte, AC electrolysis is performed in an inorganic coloring bath containing a metal salt, or anodizing is carried out in an electrolytic bath of an inorganic acid, an organic acid, or a mixed acid thereof. After that, it is immersed in an inorganic coloring agent, dye, or pigment solution to which a metal salt has been added.
According to the description of this application, ``Hydrogen gas bubbles generated during the electrolytic treatment of hydrogen rise to the water surface from below along the surface of the material to be treated, and at this time, hydrogen gas traced by these bubbles There is a difference in electrolytic action between the surface of the material and other parts, and the part where the bubbles pass has more pores than other parts, and the surface is concave, so the shine differs from other parts. It is observed as a silver-gray wood grain pattern.

However, this wood grain pattern is essentially different in color from natural wood grain, and can be distinguished from other parts (ground) simply by the difference in luminance, so although it is a pattern, it lacks clarity. .

To compensate for this, following the processing of
■ Apply the treatment to complete the clear wood grain pattern. That is, a relatively large amount of the coloring component is deposited and adhered to the wood grain portion, which is more porous than the base portion. Although the known electrolytic woodgrain forming methods described above solve the problems associated with conventional non-electrolytic methods, they have serious deficiencies as described below.

In this method, a barrier film layer with wood grain-like streaks is first formed on the surface of the material to be treated using AC electrolysis, and then the material is colored to make the wood grain-like streaks darker than other parts. The wood is colored so that the wood grain pattern can be seen clearly.
Therefore, in the pattern obtained by this method, there is not much difference in color tone between the wood grain part and other parts (ground), and the pattern part always has a darker color than the ground color between the old wood grain part and the ground. It is difficult to obtain highly decorative aluminum materials due to constraints on color contrast. Furthermore, although metal salts are used in the steps M to (2), general metal salt coloring lacks uniformity, and disposal of the 9E solution also poses problems. Furthermore, since various processing liquids are used in each process, there are difficulties in managing these working liquids, and the operation of moving the material to be treated between electrolytic cells cannot be ignored, making it difficult to increase productivity.

As described above, the large number of steps and the large amount of processing liquid require large-sized equipment, which is also economically disadvantageous.

- The present invention was developed in order to solve the problems of the above-mentioned known electrolytic woodgrain pattern generation methods.

In particular, by selecting the color tone of the wood grain part and the color tone of the ground over a wide range, it is possible to create a wood grain pattern with a favorable contrast that could not be obtained with conventional electrochemical methods. Since an aluminum material with a bronze-toned wood grain pattern can be obtained, it can provide a method that can be widely used for manufacturing decorative parts such as panels and fittings. The method will be explained in detail below.

The method of the present invention consists of a first step in which an aluminum material is electrolytically treated in an electrolytic bath using a sacrificial waveform of pulses to form a barrier film having wood grain-like striations on its surface. .

'2}Next, a voltage lower than the peak voltage of the current used in the first step is applied to the treated material after the wood grain-like streaks have been formed in a flea scale bath mainly containing an organic acid that has a coloring effect. The second step is to generate a colored oxide film on the wood grain streaks.'3) Next, the treated material is treated with an organic acid that forms a complex salt with aluminum, such as oxalic acid and sulfosalicylic acid, and a mineral acid, such as sulfuric acid. Using a mixed aqueous solution as an electrolyte, electrolytic treatment is performed to elute and remove the barrier film present in areas other than the wood grain-like striations (concavities), generate an anodized film in those areas, and remove the wood grain-like striations. The third step is to form an oxide film also on the colored oxide film surface of the part. Each step will be explained in more detail below.

The materials used in this method include not only pure aluminum, but also Cu, Si, Fe, Mn, Mg, and Z.
An aluminum alloy containing n, Ti, Ni, Bi, Pb, etc. may be used. This method can be applied to extruded materials, thin materials, clad products, etc. Prior to the first step, the material to be treated is cleaned by a conventional pretreatment method. That is,
Degreasing with 10-30% nitric acid aqueous solution, washing with water, etching with 2-7% sodium hydroxide aqueous solution, washing with water, 10-
Desmutting with 30% nitric acid aqueous solution, washing with water, or desmatting with 50-80 qC in 10-15% sulfuric acid aqueous solution.
Degrease by soaking for ~10 minutes, or use an aluminum material as a cathode in a sulfuric acid aqueous solution of the same concentration, and 1~
Degreasing may be performed using direct current or pulse waveforms for 7 minutes. The electrolytes in the first step include (i) sodium silicate;
Electrolysis consisting of an alkaline electrolyte such as sodium phosphate, trisodium phosphate, or sodium carbonate, or (ii) an aqueous solution containing boric acid, tartaric acid, phthalic acid, malonic acid, etc., or a salt thereof, a so-called barrier-type film-forming electrolyte. liquid is used. In an exposure bath containing these, an aluminum material is electrolytically treated using a waveform having a peak voltage such as a pulse polarity conversion waveform. During this treatment, many large and small hydrogen gas bubbles are generated on the electrolytic surface of the aluminum material along the hanging direction, and as they move from the bottom to the top on the electrode surface, the formation phenomenon of the barrier film layer progresses. In this way, the surface of the material to be treated is coated with a barrier film layer having many wood grain-like striations (recesses) along the wake of the hydrogen gas bubbles. Incidentally, the concentration of (i) or (ii) in the electrolytic bath is preferably 5 to 100 m/m, but optimally 10 to 50 m/m.

In addition, in the case of a mixed solution of (i) and (ii), (l)
The range of :(ii)=10:1 to 5:1 is desirable. Practically, it is convenient for the temperature of the electrolyte to be 10 to 30 qo.
The first feature of the method of the present application is that in the first step, a pulse polarity conversion waveform is used. In other words, by appropriately converting the pass current, an electrolytic reaction accompanied by impact energy occurs, and the generation and movement of hydrogen gas bubbles on the electrode surface is activated, resulting in the formation of deep concave wood grains on the surface of the treated material. A barrier film layer with striations can be formed. Note that the deep wood grain-like streaks in the barrier film layer bring about a favorable effect in carrying out the next step of producing a colored oxide film. The second feature of the method of the present application is that, as will be described in detail later, by using a pulsed trough conversion waveform, the barrier film layer can be formed at a sufficiently high voltage in the first step. Practically speaking, the peak voltage of the pulse current is preferably 40 to 150V, preferably 40 to 6V.
0V is appropriate. Further, the pulse waveform may be either a regular rectangle or an asymmetric triangle.

For polarity conversion, after applying positive current, the polarity is changed and similarly negative current is applied. Alternatively, it may be a continuous waveform in which a positive energization consisting of a plurality of pulse waveforms is applied, the gutter properties are changed, and a negative energization is similarly conducted in a plurality of pulse waveforms. In short, any material that can perform electrolysis using a pulse polarity conversion waveform and form a barrier film on the surface of the treatment layer may be used. Following the first step, a second step is performed. That is, the material to be treated covered with the barrier film layer having wood grain-like streaks obtained in the first step is placed in an aqueous solution of an organic acid such as oxalic acid or sulfosalicylic acid, or a mixed aqueous solution of these organic acids and sulfuric acid. By anodizing using a DC waveform or a pulse waveform, an amber to bronze colored oxide film can be formed on the wood grain-like striations (recesses in the barrier layer). As an organic acid used for colored anodic oxidation of aluminum,
3-5% of the above oxalic acid, 5-10% of the sulfosalicylic acid
% aqueous solution, 5 to 15% aqueous solution of metacresol sulfonic acid or maleic acid, etc. are known, and of course, any of these can be used in the second step of the present application. In addition, 3 to 20% of the above organic acid and 1'10 to 1/5 of the organic acid.
Aqueous solutions containing amounts of inorganic acids, such as a mixture of 5% sulfuric acid and 3% cylic acid or 5% sulfosalicylic acid or 5% metacresol sulfonic acid, can also be used. The supplied electrolytic waveform may be a DC waveform, a rectangular waveform, a pulsating waveform, or a triangular pulse waveform. The peak voltage of the waveform used in the second step must be lower than the peak voltage used in the first step.

This is because, in general, if an aluminum material with a barrier film is anodized using a voltage higher than the voltage applied during the formation of the barrier film, the barrier film will be destroyed and an anodized film will be formed in that area. It is from. In the present invention, as mentioned above, the barrier film layer produced in the first step has wood grain-like striations (the barrier layer in this part is thinner than other parts), so the voltage during anodization is applied to the barrier film. Even if the applied voltage is lower than the applied voltage, the depressions in the barrier film with low withstand voltage will be eroded and the anodic oxide film will grow. An oxide film can be formed, but if the applied voltage is higher than the peak voltage of the pulsed current used in the first step, a colored oxide film will be formed in areas other than the wood grain-like streaks, which will not solve the purpose of the present application. The effect of this will be significantly reduced. Incidentally, organic acid anodic oxidation of ordinary flat surfaces yields only a monotonous color, but in the case of wood grain patterns, subtle changes in color appear, making it possible to obtain coatings that are highly decorative and have excellent corrosion and weather resistance. The applied voltage in the second step is preferably 10 to 30 V lower than the applied voltage in the first step.

Note that if the voltage difference is less than 10 V, the formation of an oxide film is insufficient, and if it is more than 3,000 V, a so-called fading phenomenon occurs. Actually, an applied voltage of 30 to 80 V is suitable.
The temperature of the electrolyte has an effect on the applied voltage, and generally there is an inversely proportional relationship between the normal temperature and the applied voltage. On the other hand, in the case of an electrolyte consisting of an organic acid or an organic acid and an inorganic acid in the method of the present application, the degree of coloring of the anodic oxide film becomes darker as the applied voltage is higher, and becomes lighter in the opposite case. Therefore, if a pattern similar to that of natural wood with dark wood grains is desired, it is preferable to lower the temperature and increase the applied voltage. In practice, 0 to 20:00 is used, but 5 to 1000 is optimal. Following the second step, the treated material is transferred to the third step.

In this process, the barrier film other than the wood grain area is removed and an anodized film is formed on that part, and an anodic production film is also formed on the wood grain area that has already been colored and anodized in the second process. It produces a beautiful and solid wood grain pattern finish, which is the goal of the law. For this purpose, anodization treatment may be performed using an aqueous solution of an organic acid that forms a complex salt with aluminum, such as oxalic acid or sulfosalicylic acid, as an electrolyte. That is, a 3-10% aqueous solution of an organic acid that combines with aluminum to form a complex salt, such as oxalic acid and sulfosalicylic acid, or an organic acid and 10-20% thereof.
We have discovered that when anodizing is carried out using a large amount of a mixed aqueous solution of inorganic acids such as sulfuric acid as the electrolyte, the seemingly contradictory phenomena of ``dissolution of barrier film'' and ``formation of anodic oxide film'' occur.
At this time, by appropriately determining the electrolytic conditions, the barrier layer present on the surface of the material to be treated after the second step is substantially removed as aluminum glazing salt, and an anodic oxide film is formed in its place. During this time, the anodic oxide film on the wood grain area obtained in the second step does not dissolve out, but on the contrary, as other areas are anodized, a slight oxide film is formed on this area as well. In the case of the third step as well, there is an inverse proportion between the applied voltage and the electrolytic overload, but in order to achieve the silver color unique to aluminum on a substrate other than wood grain, which is the first focus of this method, , set the temperature slightly higher, that is, 30 to 50%, and set the temperature to 10
It is better to apply ~25V.

In addition, as an application of this method, if you want a pattern in which the base material other than the wood grain is colored, for example, pale yellow or pale silver, you can lower the temperature to 15 to 30 qo and apply 30 to 70 V, and the barrier layer will be Since the anodic oxidation proceeds while slowly dissolving, the colored oxide film as described above is obtained. As described above, according to the method of the present application, a beautiful and robust wood grain pattern can be imparted to aluminum material by electrolytic method.
The number of processes is small, and the adjustment and management of electrolytic conditions are easy.

Furthermore, it is possible to easily form a silver pattern (yellow to amber color can also be applied) that is unique to aluminum, with the wood grain having an amber to freon color, which was considered difficult to form using conventional electrolytic methods. be. Examples will be described below.

Example: An extrusion mold made of aluminum A6063 was degreased by immersing it in a 10% nitric acid aqueous solution for 10 minutes at room temperature. After washing with water, it was soaked in 5% NaOH.
After being immersed in a 60 qo aqueous solution for 1 minute, etched and washed with water, it was immersed in a 10% nitric acid aqueous solution for 1 minute at room temperature, desmutted, and then washed with water.

1st step: The material to be treated is hung vertically with the extrusion direction perpendicular, sodium metaborate 15/day, boric acid 2/2.
The temperature is 20±2℃ when the electrolyte is an aqueous solution containing 50%
Then, the peak voltage of 60V in Figure 1 (t, = t2 = t', =
Electrolytic treatment was carried out for 25 minutes using a rectangular pulse waveform shown at t'2=1/6 $ec).

As a result, wood grain-like striations were formed on the surface of the treated wood. 2nd step: After washing the material to be treated with water, use it as an anode, and use an aqueous solution containing 5% of sulfosalicylic acid and 0.5% of sulfuric acid as a melting bath, and anode for 2 minutes using 50V DC at a temperature of 10%. Oxidized. The wood grain area of the treated material was colored a deep amber color. Third step: Using an aqueous solution containing 4% oxalic acid as an electrolytic solution, a direct current of 10,020 V was applied for 3 minutes to anodize the material to be treated.

A beautiful dark amber wood grain pattern was formed on the surface of the treated material.

[Brief explanation of drawings]

The figure is a diagram showing pulse waveforms used in Examples.

Claims (1)

[Claims] 1 A material to be treated made of aluminum or an aluminum alloy is electrolytically treated in an electrolytic bath consisting of an alkaline electrolyte or a barrier film-forming electrolyte containing an organic acid or a salt thereof using a pulse polarity conversion waveform having a peak voltage P_1 to form a barrier film. First step of forming a layer: After the first step, the treated material is placed in an electrolytic bath containing an organic acid having a coloring effect using a voltage 10 to 30 V lower than P_1 at an electrolytic bath temperature of 5 to 10°C. A second step of anodizing and after the second step, the material to be treated is oxidized in an electrolytic bath at a temperature of 30 to 50° C. containing an organic acid that forms a complex salt with aluminum as a main component.
A method for forming a wood grain pattern on aluminum or aluminum alloy material, comprising a third step of applying 0 to 70 V and anodizing the material.