JP2000309882A - Surface treating method for magnesium material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the quality such as corrosion resistance, decorativeness, or the like, by allowing this method to have an electrodeposition treating stage in which voltage is applied on a work of a magnesium material as an anode in an electrolytic soln. contg. an anionic electrodeposition coating material to form a coating film on the surface of its member. SOLUTION: It is also preferable that this method has a coating film forming stage in which at least one of a chemical coating film and an anodically oxidized coating film is formed on the surface of a member prior to an electrodeposition treating stage. It is possible that the method has a degreasing stage in which a work of a magnesium material is subjected to electrolytic degreasing prior to the coating film forming stage. Moreover, in the case of forming an anodiacally oxidized coating film also in the coating film forming stage, the formation of the anodically oxidized coating film to the work as an anode in any of an acidic soln. of ammonia fluoride, an acidic soln. of potassium fluoride, an acidic soln. of sodium fluoride, a soln. of potassium fluoride and a soln. of sodium fluoride is furthermore suitable. It is moreover preferable that the surface of the coating film formed by the electrodeposition treating stage is further applied with coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of a magnesium material, and more particularly to a technique for improving quality such as corrosion resistance and decorativeness.

[0002]

2. Description of the Related Art Magnesium material (in this specification, unless otherwise specified, "magnesium material" is a general term for magnesium and alloys containing magnesium) formed on the surface in a dry state. It is generally known that the metal oxide is a highly corrosive metal that has a small change in corrosion or the like in the oxide film to be formed, but rapidly progresses when the humidity increases.

[0003] In addition, there is one side of low acid resistance, which reacts violently with most inorganic acids and organic acids other than fluoride, and is the metal with the lowest potential among practical metals. It is also known to cause corrosion.

[0004] As a method of compensating for such disadvantages, a treatment in which several kinds of chemicals such as sodium dichromate, chromic anhydride, ammonium acid fluoride, hydrofluoric acid and its salts, nitric acid, phosphoric acid and its salts, etc. are mixed at a high concentration is used. The formation of a chemical conversion film by immersion in a liquid (chemical conversion film treatment) or the formation of a film by anodic electrolysis (anodic oxidation treatment) with a positive member is performed to improve the corrosion resistance and the adhesion of the coating as a pretreatment of the coating.

[0005] Examples of conventional treatment methods are as follows: <Conversion coating treatment> Example 1) 180 g / l of sodium dichromate, nitric acid (6
0%) composition of 260 g / l, 20-30 ° C, 30-1
Soak for 20 seconds.

Example 2) As a first step, immersion was carried out at 20 to 30 ° C. for 30 to 120 seconds at a composition of 180 g / l of sodium dichromate and 260 g / l of nitric acid (60%). It is immersed in a boiling solution having a composition of 130 g / l calcium fluoride and 2.5 g / l for 30 seconds.

Example 3) Hydrofluoric acid (4
6%) 248 g / l, liquid temperature 20-30 ° C, 30-300
For 2 seconds, and as a second step, 50 g of sodium acid fluoride, calcium acid fluoride or ammonium acid fluoride
Then, the substrate is immersed in a boiling liquid having a composition of 130 g / l sodium bichromate and 2.5 g / l calcium fluoride for 30 seconds as a third step.

<Anodizing treatment> Example 1) 30 g / l of ammonium sulfate, 30 g / l of sodium bichromate, 2.5 ml of aqueous ammonia (28%)
/ L composition, liquid temperature 50-60 ° C, current density 0.1-2A /
The treatment is performed at dm ^{2 for} an electrolysis time of 10 to 30 minutes.

Example 2) Caustic soda 240 as the first step
g / l, ethylene glycol or diethylene glycol 83 g / l, sodium oxalate 2.5 g / l, liquid temperature 75-80 ° C., current density 1-2 A / dm ² , electrolysis time 1
The treatment is carried out for 5 to 25 minutes, and as a second step, sodium dichromate 50 g / l and sodium acid fluoride 50 g / l
Treat with composition.

[0010] These treatment methods use sodium dichromate, nitric acid, fluoride, phosphoric acid and salts thereof, so that sufficient measures are taken in terms of environmental protection, working environment, and wastewater (waste liquid) treatment. Needless to say, it is necessary to maintain the processing facilities and work environment.

For this reason, costs are incurred.

However, in the case of the above-described conventional surface treatment, the following problems have occurred.

(1) It is difficult to maintain the dimensional accuracy of the magnesium material due to the acid treatment with high solubility.

(2) Since chemicals such as chromium compounds, nitric acid and the like are used, it is necessary to very carefully deal with environmental protection, working environment, waste water (waste liquid) treatment, etc. Become.

(3) It is difficult to satisfy the requirements for exterior members and eyeglass frames of daily necessities, which require beauty and design, by using only the chemical conversion coating treatment and the anodic oxidation treatment alone. is there.

(4) It has been considered to apply a coating after a chemical conversion coating treatment or an anodic oxidation treatment, but the quality sufficient for practical use has not been obtained.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a surface treatment method for a magnesium material capable of improving the quality such as corrosion resistance and decorativeness. To provide.

[0017]

Means for Solving the Problems In order to achieve the above object, a method for surface treating a magnesium material according to the present invention comprises:
The method is characterized by having an electrodeposition treatment step of applying a voltage to a work of a magnesium material as an anode in an electrolytic solution containing an anionic electrodeposition paint to form a coating film on the member surface.

Before the electrodeposition treatment step, it is preferable that the method further comprises a film formation treatment step of forming at least one of a chemical conversion film and an anodic oxide film on the surface of the member.

It is preferable that the method further includes a degreasing process for performing electrolytic degreasing of the work of the magnesium material before the film forming process.

When forming the anodic oxide film in the film forming process, any one of an acidic ammonium fluoride solution, an acidic potassium fluoride solution, an acidic sodium fluoride solution, a potassium fluoride solution, and a sodium fluoride solution may be used. It is also preferable to form an anodic oxide film using the work as an anode.

It is also preferable to further apply a coating to the surface of the coating film formed by the electrodeposition process.

According to the present invention, the magnesium material is provided with an electrodeposition treatment step of performing electrodeposition coating with an anionic electrodeposition coating material. In the case where the step includes an electrolytic degreasing step, a chemical conversion treatment step or an anodic oxidation treatment step before the step, In addition, by forming a coating film by an electrodeposition process after forming the coating film, a more durable surface treatment can be obtained.

In the electrodeposition treatment step, since the workpiece is used as an anode, the electrodeposition paint is adhered to the same state as the anodic oxidation while adhering. Therefore, the components for forming the oxide film are added to the solvent of the anionic electrodeposition paint. It can also be contained.

However, since it is difficult to perform an effective anodic oxidation treatment step by the electrodeposition treatment step itself, it is necessary to combine it with the electrolytic degreasing step and to carry out the conversion coating treatment step or the anodic oxidation treatment step before the electrodeposition treatment step. By doing in advance,
A high quality surface treatment method having more corrosion resistance and decorativeness can be obtained.

Although the electrodeposition coating can be finished as it is, a higher quality surface treatment can be obtained by applying a finish coating thereon.

Compared to spray coating, powder coating, etc.,
Another advantage of electrodeposition coating is that it is easy to paint shadows and invisible gaps, which leads to improved quality.

[0027]

(Example 1) An eyeglass frame member (surface area 60 cm) made of a magnesium material and a magnesium alloy AZ-91D
² work (non-processing object))
0 g / l, trisodium phosphate 10 g / l electrolytic degreasing solution, at a liquid temperature of 70 ° C., 5 A / dm ² , using a work as a cathode while conducting electricity (electrolytic degreasing) for 4 minutes, then commercially available melamine-based curing Electrodeposition coating was performed using a work as an anode with an electrodeposition liquid at 22 ° C. containing 12% of an acrylic anion electrodeposition coating material using an agent.

The electrodeposition coating was performed at 150 V for 90 seconds with the workpiece plus and the opposite electrode plate minus, and baked at 180 ° C. for 20 minutes after predrying at 50 ° C. for 20 minutes.

The work is held by using a jig made of the same magnesium material as the work, and hooking the work into a holding hole for obtaining electrical connection with the work.

As a quality test, a glossy coating film without any peeling was obtained in an adhesion test by taping a 1-mm square grid cut. Further, a boiling water test was conducted using this sample. The condition was an adhesion test by taping after immersion for 1 minute, and the test was repeated 10 times, but there was no peeling of the grid cut surface.

At this time, the thickness of the coating film was 23 μm. Regarding the dimensional change, peel off the coating with an organic solvent,
When measured with a gauge capable of measuring in units of 1/000 millimeter, a change of several microns was observed, but it was within the range of measurement error, and it was confirmed that there was almost no effect.

Examples of the anionic electrodeposition paint include, in addition to the acrylic anion electrodeposition paint, modified paints such as an acrylic anion electrodeposition paint incorporating fluorine, and an aminoalkyd electrodeposition paint represented by a melamine resin. Can be used, and formally, all anionic electrodeposition paints can be selected.

(Embodiment 2) After electrodeposition coating under the same conditions as in Embodiment 1, it was further painted in a brown color with a commercially available acrylic spray paint, and subjected to the same quality test (adhesion) as in Embodiment 1. Test and boiling water test), but no peeling of the coating film was observed.

The heat treatment conditions for spray coating are 175 ° C. and 6
It was baked for 0 minutes.

The coating includes powder coating, spray coating,
A commonly used coating method such as dip coating or brush coating can be appropriately employed.

Example 3 60 g of sodium hydroxide /
l, trisodium phosphate 10 g / l electrolytic degreasing solution, a liquid temperature of 70 ° C., 5 A / dm 2, and treating for 4 minutes using the work as a cathode, then performing electrodeposition coating and spray coating finishing under the same conditions as in Example 2, The same quality test as in Example 1 was performed, but no abnormality was found. In addition, Cass test 48
As a result of performing the time, several spots due to the corrosion of the magnesium alloy were confirmed in the finished sample of the electrodeposition coating alone.
However, no corrosive substance was blown out on the surface of the coating film.
No corrosion was observed on the sample which was spray-painted for the finish, and the sample showed extremely excellent corrosion resistance.

(Embodiment 4) The conditions for electrodeposition coating in Example 2 were 70 V for 90 seconds, 100 V for 60 seconds, and 150 V for 3 seconds.
Three types of electrodeposition coating were performed at 0 seconds, and an acrylic spray coating was applied as a finish. A confirmation test was conducted by taping a 1 mm square board with a mesh cut and tapping after immersion in boiling water for 1 minute. An adhesion test was performed to return the circuit.

As a result, in the adhesion test using boiling water, a peeling of about 5% was confirmed in the sample at 70 V for 90 seconds under the condition, but it was proved that the adhesion was good as a whole.

Casing test 48 was performed on a sample prepared under the same conditions.
We performed for a while, but there was no swelling or corrosion in any of the materials,
No difference due to the difference in electrodeposition coating conditions was confirmed.

(Embodiment 5) The electrodeposition conditions were 70 V and 300
, Two types of electrodeposition coating with 150V for 300 seconds,
For the purpose of examining the change in the corrosion resistance of the Mg base material, the coating film was dissolved with an alkaline stripping solution before the baking coating, and the cast test was performed for 1 hour using three types of samples that were degreased only.

The results are better at 300 V for 150 V with a large amount of electric current.
Samples at 0 V for 300 seconds provided intermediate corrosion resistance.

(Example 6) 60 g of sodium hydroxide /
After treating the work as a cathode at a liquid temperature of 70 ° C. under an electrolysis condition of 5 A / dm ² for 4 minutes with an electrolytic degreasing solution of 10 g / l of trisodium phosphate, 20 g / l of ammonium acid fluoride was applied as a film forming treatment step. In the added aqueous solution at 25 ° C., the members were made positive, and anodizing treatment at 100 V for 4 minutes was performed in the pretreatment, and then an acrylic anion electrodeposition coating at 100 V for 90 seconds was performed.

The subsequent processing steps and processing conditions are the same as those in Example 1
Same as 2, spray coating was applied as the final finish.
The quality of this sample was confirmed by the same boiling water test and cas test as in Example 4, but no defects such as peeling and corrosion were observed.

The members spray-coated directly by the anodic oxidation treatment under the same conditions had blisters on the entire surface, demonstrating that the effect of the anion electrodeposition coating was great.

Here, the anodic oxidation treatment includes, in addition to the aqueous ammonium acid fluoride solution, an acidic potassium fluoride solution, an acidic sodium fluoride solution, a potassium fluoride solution,
It is also possible to use any of the sodium fluoride solutions or a mixed solution thereof.

[0046]

According to the surface treatment method for a magnesium material described above, it is possible to enhance the quality such as corrosion resistance and decorativeness.

Claims (5)

[Claims] 1. A surface of a magnesium material, comprising an electrodeposition treatment step of applying a voltage as a positive electrode to a work of the magnesium material in an electrolyte solution containing an anionic electrodeposition paint to form a coating film on the surface of the member. Processing method. 2. The magnesium material according to claim 1, further comprising a coating forming step of forming at least one of a chemical conversion coating and an anodic oxide coating on the member surface before the electrodeposition processing step. Surface treatment method. 3. The method for treating a surface of a magnesium material according to claim 1, further comprising a degreasing step of performing electrolytic degreasing of a work of the magnesium material before the step of forming the film. 4. When forming an anodic oxide film in the film forming treatment step, an acidic ammonium fluoride solution;
Potassium acid fluoride solution, sodium acid fluoride solution,
The surface treatment method for a magnesium material according to claim 2, wherein the anodic oxide film is formed using the work as an anode in one of a potassium fluoride solution and a sodium fluoride solution. 5. The surface treatment method for a magnesium material according to claim 1, wherein a coating is further applied to a surface of the coating film formed in the electrodeposition process.