JPS6014119B2 - Method of forming opaque white film on aluminum surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to aluminum or an aluminum alloy (hereinafter referred to as aluminum).

) relates to a method for forming an opaque white film on the surface of Many methods have been proposed to give a transparent white finish to the surface of aluminum by two-stage electrolysis. Namely, (1) A method in which an anodic oxide film is formed on the surface of aluminum by primary electrolysis, and then an opaque milky white film is formed by performing secondary electrolysis in an electrolytic solution of a chromium compound (Tokukan Sho 35-114519).

■ After forming an anodized film on the surface of aluminum by primary electrolysis, spots containing inorganic acids such as phosphoric acid or organic acids 1
A method of forming an opaque milky white film by performing secondary electrolysis in the aqueous solution of ~6.

(Hakama Kosho 55-121838).

In both of these methods, aluminum with an anodized film formed thereon is treated in a specific aqueous solution (e.g., inorganic acid such as chromic acid, phosphoric acid, oxalic acid, or organic acid) under specific treatment conditions (e.g., solution temperature, solution concentration). , pH, voltage, etc.) to form an opaque milky white film on the aluminum surface.

However, method (2) uses substances harmful to the human body, such as chromic acid, which poses problems in terms of working environment and wastewater treatment.

In addition, according to the method (2), especially the technique disclosed in Example 1 of the specification, a low concentration aqueous solution of phosphoric acid (1g') is relatively inexpensive and has the effect of roughening the anodic oxide film. In this process, aluminum is electrolytically treated under high temperature conditions.

However, when electrolytic treatment is repeated many times in such a low concentration electrolyte, impurities such as aluminum phosphate accumulate in the solution as aluminum is eluted, and phosphoric acid A sudden change in concentration occurs, making it impossible to maintain uniformity of the liquid composition.

If the concentration of the liquid composition changes rapidly, the quality of the resulting film will naturally become non-uniform, and there is a problem in that it requires a great deal of effort to manage the liquid in order to prevent such a situation. In addition, since the treatment temperature is high (70o○), it has the advantage of promoting whitening of the anodic oxide film, but electrolytic treatment under such high temperature conditions may cause the film to melt due to the high temperature and cause a powder blowing phenomenon. However, there is also the problem that the purulent membrane obtained becomes brittle and the membrane quality is poor.

On the other hand, when phosphoric acid is conventionally used as an electrolyte to form an opaque white film, when the aluminum surface is treated at a relatively low temperature, the powder blowing phenomenon does not occur compared to the above-mentioned high temperature treatment, and the film is uniform. Although a hard film can be obtained, the desired opaque white film cannot be obtained.

Therefore, conventionally, it has not been possible to obtain a hard, uniform, opaque white film by treating aluminum in an electrolytic solution using phosphoric acid at relatively low temperatures. The present invention has been made through intensive research to overcome the drawbacks of the conventional methods described above, and to develop a method that is fully satisfactory in terms of whitening effect, uniformity of the treated surface, various physical properties, etc., and is suitable for practical use due to simple operating conditions. As a result, an anodic oxide film is formed on the aluminum surface, which is then electrolytically treated in a specific aqueous solution to produce a transparent silvery white color that is slightly whiter than the silvery white color obtained with normal sulfuric acid alumite treatment. After obtaining the desired color tone, the present invention was completed based on the finding that aluminum with an opaque white film that gives a pleasant feeling can be obtained by applying a resin coating to the treated surface using an electrophoretic coating method according to a conventional method.

That is, the present invention provides aluminum having an anodic oxide film formed thereon by a conventional method, in pH 1000. 3
~3.5 in an aqueous solution containing no coloring metal, at a voltage of 1
0-20V, current density 0.5-1. I/dwa, time 5~
After 10 minutes of alternating current electrolysis or connecting the aluminum to the anode, the voltage was 15 to 35 V and the current density was 0.2 to 1.
This is a method of forming an opaque white film on the aluminum surface by applying a transparent resin coating to the aluminum using a dew electrophoresis coating method after direct current electrolysis at 0 A/d for 5 to 10 minutes. I will explain this in detail below,
In the method of the present invention, aluminum is first degreased in a conventional manner, etched as necessary, and smut removed, and then anodized using a conventional method in a sulfuric acid bath or a mixed acid bath (primary electrolysis) using the aluminum as an anode. to form an anodic oxide film on the aluminum surface.

Next, secondary electrolysis is performed, and the aqueous solution for secondary electrolysis is a mixed aqueous solution of one or more of phosphoric acid, phosphorous acid, or salts thereof.

The amount added is more than log/log, preferably 20 g/~saturation amount, and the final pH is adjusted to 0.3~3.5. Examples of phosphates include ammonium salts, sodium salts, potassium salts, and aluminum salts of phosphoric acid, and specifically, ammonium monophosphate, ammonium daniphosphate, tertiary ammonium phosphate, monobasic sodium phosphate, and dibasic ammonium phosphate. Examples include sodium phosphate, sodium tertiary phosphate, potassium phosphate, magnesium phosphate, and ammonium magnesium phosphate.

In addition, phosphites include ammonium salts, sodium salts, potassium salts, magnesium salts, etc. of phosphorous acid.
Specifically, there are ammonium phosphite, sodium hydrogen phosphate, potassium phosphite, potassium hydrogen phosphite, magnesium phosphite, and the like.

Setting the content of phosphoric acid, etc. in the secondary electrolyte to more than the log' limit eliminates the above-mentioned drawbacks in the case of a low concentration, and facilitates liquid management.

Also, the reason why the pH of the secondary electrolyte is limited to 0.3 to 3.5 is that if the pH exceeds 3.5, the opaque whiteness of the final product will be insufficient. If it is less than this, the anodic oxide film will be violently dissolved, the film quality will become brittle, and a film that can withstand practical use cannot be obtained.

When the pH after secondary electrolysis is high, use organic acids such as oxalic acid, acetic acid, maleic acid, citric acid, lactic acid, and phenolsulfonic acid, or inorganic acids such as sulfuric acid, chromic acid, shelf acid, nitric acid, and hydrochloric acid. Adjust the pH using

If the pH is within the range of 0.3 to 3.5 and it is desired to increase it, the pH can be adjusted using a base such as sodium, potassium, ammonium, or amine.

Further, an alkali metal salt, an alkali metal salt, an amino salt, or an imino salt of the acid mentioned above may be added to the electrolytic solution in order to impart a pH buffering effect or conductivity. Color-forming metal salts (nickel, nickel,
If salts of tin, cobalt, iron, manganese, copper, zinc, selenium antimony, lead, etc. are present, for example, when secondary electrolysis is performed with alternating current, a so-called electrolytic coloring reaction will occur on the surface of aluminum, causing the surface of aluminum to become Since it is colored, it is necessary to use the aqueous solution for secondary electrolysis that does not contain such coloring metal salts.

The non-color forming metal salts used in the present invention include lithium,
There are salts of sodium, potassium, magnesium, aluminum, etc. In addition, the higher the temperature of the secondary electrolyte, the faster the reaction and the shorter the processing time. .

The aluminum is subjected to alternating current electrolysis in the electrolytic solution described above, or direct current electrolysis is carried out by connecting aluminum to an anode (secondary electrolysis).

The point is that there is only time for aluminum to be applied positively. These electrolytic conditions are determined in consideration of economic efficiency and productivity, etc.
ACIO~20V, 0.5~1. Set to 15 to 35 V DC, 0.2 to 1.0 A/d, 5 to 1 minute.

The aluminum surface obtained by this electrolytic treatment exhibits a transparent silver-white metallic luster with a slight whitish tinge.

Then, by lightning electrophoresis coating method, the aluminum is coated with
By applying a transparent resin paint, the strong silvery-white metallic luster characteristic of aluminum disappears, revealing an opaque white aluminum surface that looks very pleasing as if it had been painted over.A detailed theory of this phenomenon is needed. The rationale is unclear.

The above-mentioned transparent resin paint may be any conventionally known resin paint, such as acrylic, alkyd, acrylic alkyd, epoxy, or modified maleinated oil, etc. Paint resin is dissolved in water or an organic solvent. This is what I did. Further, if necessary, a neutralizing agent and a crosslinking agent such as melamine or phenol may be added to these aqueous solutions. In addition, the reason why we limited the painting method to lightning electrophoresis is that when used with methods such as electrostatic painting, spraying, and brush painting, an opaque white film is not formed, but a transparent silvery white film is formed. It is from. As described above, the present invention comprises: (1) Aluminum on which an anodic oxide film has been formed by a conventional method; (2) Contains phosphoric acid or phosphorous acid or one or more of their salts in a log/saturation amount; and ■ pH 0. 3 to 3.5 in an aqueous solution containing no color-forming metal at a voltage of 10 to 20 V and a current density of o. 5-1.
AC electrolysis or the above aluminum was connected to the anode under conditions of 5 to 1 minutes at a voltage of 15 to 35 V,
After direct current electrolysis at a current density of 0.2 to 1.0 A/d and a time of 5 to 1 powder, a transparent resin paint is applied using the electrophoretic coating method to make the aluminum surface opaque. This method forms a white film.

As described above, the present invention is comprised of the above six requirements, and as will become clear from the comparative examples described below, the present invention particularly requires the above-mentioned requirements An excellent opaque white coating can only be obtained if the requirements are combined.

According to the present invention, it is possible to form an opaque white film uniformly over the aluminum surface, and the obtained film quality performance is sufficiently satisfactory in terms of various physical properties.

In addition, liquid management is easy, and an opaque white film can be formed on the aluminum surface under relatively low voltage, room temperature, and short electrolysis conditions, so it is economical. below,
Examples of the present invention will be explained by giving comparative examples.

Example 1 Aluminum (A-606$-T5) was degreased, etched, and smutted in a conventional manner, and then electrolytically treated under the following conditions to form an anodized film.

Electrode ratio 1:1 (counter electrode aluminum) electrolyte
10% sulfuric acid, liquid temperature 20oo current density 1
．． After rinsing with water, 45 g of sulfuric acid was added to the aqueous solution of phosphoric acid, and the pH was adjusted to 0.
42 secondary electrolytes were prepared and electrolytically treated under the following conditions.

Pole ratio 1:1 (versus pole -bon) voltage
DC I9V, current density 0. Ship/mooring time
8 minutes, liquid temperature: 33 qo As a result, the surface of the aluminum exhibited a silvery white color with a slightly whitish transparent metallic luster, and the color was far from opaque white.

However, after washing the aluminum with water, electrophoresis coating was applied using a transparent water-soluble resin paint mainly composed of acrylic-melamine at a voltage of 170 V, a liquid temperature of 200 V, and a time of 3 minutes. When baked and dried, a uniform opaque white film appeared on the aluminum surface.

Example 2 Secondary electrolyte composition Sulfuric acid 3 groups/Sophosphoric acid
4 Demons/Diammonium phosphate
3 females/phenolsulfonic acid 5g
'The secondary electrolyte was configured as above, the voltage was AC14V, and the current density was 0. Carp/Landmine clearing time
When the same operating conditions and method as in Example 1 were used except that the conditions were 6.5 minutes and pH 0.8, a uniform opaque white film was similarly obtained.

Example 3 The same operating conditions and methods as in Example 2 were used, except that the secondary electrolysis conditions in Example 2 were changed to a voltage of 25 V DC, a current density of 0.2 I/O electrolysis time of 9 minutes, and the results were the same. A uniform opaque white film was obtained.

Example 4 An anodic oxide film was formed on aluminum under the same conditions as in Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition Oxalic acid 2'
Diammonium diammonium phosphate 4-female/diammonium diammonium phosphate 3-female/so-pole ratio 1:1 (contrary to carbon), pH 2.90 Voltage AC 15V
, current density o. Ship/enemy electrolysis time
9 minutes, liquid temperature: 34qo At this time, the aluminum surface had a silvery white color with a slightly whitish transparent metallic luster, but after washing with water, it was coated with haze electrophoresis using the same method and treatment conditions as in Example 1. According to the law, transparent water lagoon resin paint is applied to
When dried by baking at a temperature of 0.00, a uniform opaque white film was obtained on the aluminum surface.

Example 5 An anodic oxide film was formed on aluminum under the same conditions as Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition: sulfuric acid, diacid/phosphorous acid
4 bets/ammonium sulfate 8g/sopol ratio 1
:1 (opposite), pH 0.55, pressure 15
V, current density: 1.1 A/0, electrolysis time: 1 ratio, solution temperature: °C At this time, the aluminum surface had a silvery white color with a transparent metallic luster tinged with a slight whitish color, but after washing with water, Example 1 A transparent water-soluble resin paint was applied using the haze electrophoresis method using the same method and treatment conditions as described above and dried under sintering at 180 qo. A uniform opaque white film was obtained on the aluminum surface.

Example 6 An anodic oxide film was formed on aluminum under the same conditions as in Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition Phosphoric acid 45g' Tertiary magnesium phosphate 2 female/Sulfuric acid
20g/electrode ratio 1:1 (opposite electrode), pH 0.95, voltage AC18V, current density 1. M/Crucumber electrolysis time: 8 minutes, liquid temperature: 33 qo At this time, the aluminum surface had a silvery white color with a slightly whitish transparent metallic luster, but after washing with water, Example 1
When a transparent water-soluble resin paint was applied using the same method and treatment conditions as described above and baked and dried at 180oC, a uniform opaque white film was obtained on the aluminum surface.

Example 7 An anodic oxide film was formed on aluminum under the same conditions as in Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition phosphoric acid 70g/sulphuric acid
35g/Kipoku ratio 1:1
(opponent), pH O. 45 voltage DC22
V, current density: 1.0 A/electrolysis time: 5 minutes, liquid temperature: 33 oo At this time, the aluminum surface had a silvery white color with a slightly whitish transparent metallic luster, but after washing with water, it was the same as Example 1. When a transparent water-borne resin paint was applied using the same method and treatment conditions using the lightning electrophoresis coating method and then blotted and dried at 180°C, a uniform opaque white film was obtained on the aluminum surface.

Example 8 An anodic oxide film was formed on aluminum under the same conditions as in Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition Phosphoric acid 60g/Soichi 2S
04 45g/ and ammonium phosphate 2 female/other ratio 1:1 (contrary to carbon), PH O. 55 voltage AC17V,
Current density 1.0A/geolysis time 9 minutes 3 sand, liquid
At this time, the aluminum surface had a silvery white color with a slightly whitish transparent metallic luster, but after washing with water, it was made transparent by dew electrophoresis painting using the same method and treatment conditions as in Example 1. When a water-soluble resin paint was applied and baked and dried at 180°C, a uniform opaque white film was obtained on the aluminum surface.

Example 9 An anodic oxide film was formed on aluminum under the same conditions as in Example 1, and after washing with water, a secondary electrolytic treatment was performed under the following treatment conditions.

Secondary electrolyte composition Sulfuric acid 22
g/phosphoric acid 45g'diammonium phosphate 4sagi'sogoku ratio 1:
1 (opposite power), pH 1.55 voltage AC4
5V, current density 0.8 matsuno c, electrolysis time 6 minutes, 3 Tochisand, liquid temperature 33 oo At this time, the aluminum surface had a silvery white color with a transparent metallic luster, but after washing with water. When a transparent water-repellent resin paint was applied using the haze spray coating method using the same method and treatment conditions as in Example 1,
A uniform opaque white film was obtained on the aluminum surface.

Comparative Example 1 (Other than ED) This was carried out under the same operating conditions and method as in Example 2, except that this spray coating method was used instead of the haze electrophoresis coating method, and the final color tone was transparent. It had a silvery white color with a metallic feel, and was far from opaque white.

Comparative Example 2 (Large PH) Ammonia water was added to the secondary electrolyte of Example 2 to make a barrier 4.5, and the rest was carried out under the same operating conditions and method as in Example 2. As a result, silver with a transparent metallic feel was obtained. A white tone was obtained, far from being an opaque white.

Claims (1)

[Claims] 1 Aluminum on which an anodic oxide film has been formed by a conventional method in an aqueous solution containing no coloring metal and adjusted to pH 0.3 to 3.5 and containing phosphoric acid, phosphorous acid, or one or more of these salts in a saturated amount of 10 g/l to 3.5. Then, under the conditions of voltage 10 to 20 V, current density 0.5 to 1.5 A/dm^2, time 5 to 10 minutes, AC electrolysis or the above aluminum was connected to the anode, voltage 15 to 35 V, current density 0 .2~1.0A/
After direct current electrolysis under the conditions of DM^2 and time of 5 to 10 minutes,
A method of forming an opaque white film on the aluminum surface by applying a transparent resin coating to the aluminum using an electrophoretic coating method.