JPS5821546B2 - Surface treatment method for aluminum castings - Google Patents

Description

[Detailed Description of the Invention] Aluminum castings (including die-cast products) are used in aircraft,
It is used in a wide range of applications, from parts for automobiles to general household items such as pots and frying pans.

The present invention relates to a method for surface treating IJ products for the purpose of corrosion resistance, decoration, non-adhesion, etc.

Aluminum castings have poor corrosion resistance due to their composition and structure compared to general aluminum plate materials, and may be subjected to surface treatments such as anti-corrosion painting and anodizing treatment.

In addition, there are kitchen utensils, industrial parts, etc. that require not only corrosion resistance but also non-adhesive properties and are coated with fluorocarbon resin such as tetrafluoroethylene resin.

The present invention thus relates to a method for surface treatment of aluminum castings, and it has been discovered that by adjusting the chemical components of the casting, etc., it is possible to perform surface treatment with excellent adhesion to fluorocarbon resin.

Normally, for fluorine resin-coated bases of aluminum castings, the base material surface is degreased and washed, and then the resin coating is applied as is.If the adhesion of the resin to the base material is weak, the coated surface may be roughened by methods such as blasting. The roughened surface is then coated with a resin, or the roughened surface is coated with a primer, which is an adhesion aid, and after drying, a predetermined resin is coated thereon.

The method of the present invention is particularly suitable for coating resins that are difficult to adhere to substrates, such as tetrafluoroethylene resins.

Taking aluminum casting steel coated with tetrafluoroethylene resin as an example, the coated base material surface is usually roughened mechanically by sandblasting etc. as described above, and then a primer resin is coated and baked. is used as an adhesive layer, and a tetrafluoroethylene resin is coated on the adhesive layer.

On the other hand, for pots and pots made from aluminum wrought materials, the process of roughening, priming, and finishing coating is performed in the same way as for castings.

However, in the case of aluminum wrought materials, it is possible to prepare the surface with fine irregularities by using electrical or chemical etching methods that are superior to sandblasting or other methods of burying the base, so it is possible to prepare the surface with fine irregularities, so it is possible to prepare the surface with only a finishing coat without using a primer. A coating film with stronger adhesion can be obtained.

However, since the manufacturing method for aluminum castings is completely different from that of wrought materials, the metal structure on the surface of the casting is completely different from that of wrought materials.

Furthermore, aluminum castings generally contain relatively large amounts of Si, Cu, and Mg in order to improve the flowability of molten aluminum.

For these reasons, it is very difficult to perform etching on aluminum castings, and it has not been possible to provide a base treatment that is effective for adhesion with fluorocarbon resin.

Therefore, the inventors of the present invention investigated the details of both the alloy composition of aluminum castings and the etching conditions in order to enable etching treatment of aluminum castings and obtain coatings with strong adhesion to fluorocarbon resin. As a result of extensive research, the present invention was completed.

In other words, in the present invention, an aluminum casting having an aluminum purity of 94% or more and a silicon content of 4% or less is used as an aluminum casting, and this is electrolytically etched in an aqueous solution of chlorides. After treatment or chemical etching with hydrochloric acid or the like, this surface is coated with fluorocarbon resin.

The surface roughness of the unevenness after etching is the 10-point average roughness R
z) (defined in JISB-0601) Must be 8μ or more.

If the unevenness is smaller than this, the adhesion between the fluorocarbon resin and the casting will be insufficient.

Further, in etching, it is more desirable to perform mechanical cutting or polishing, or chemical degreasing and polishing as a pretreatment.

This is because the casting surface is affected by the attachment of mold release agent during molding, the influence of the mold surface, and even the thermal influence during cooling, and the casting surface has adhesion of impurities and uneven structure. It is.

Furthermore, in the case of kitchen appliances, etc., it is effective to perform etching, then anodize the surface, and then coat the surface with furan resin to improve corrosion resistance and abrasion resistance.

The present invention will be described in more detail below based on examples.

Example 1 Aluminum castings having different chemical compositions as shown in Table 1-1 were produced.

A test piece of 100 m x 50 x m x 5 mm was cut out from this material, and after degreasing and cleaning the surface with 5% NaOH, electrolytic etching was performed in a 5% NaCl aqueous solution with an electric charge of 50 Q/cd using the test piece as an anode. .

After removing the smut, a polytetrafluoroethylene resin dispersion was applied to a thickness of about 20 μm and dried to a thickness of 38 μm.
Coating was performed by heating at 0° C. for 10 minutes.

In order to evaluate the adhesion of this fluorocarbon resin coating, a cross-cut test was conducted.

In this test, 100 gobbles with a width of 1 mm reaching the base aluminum are made on the resin surface using a sharp knife, cellophane tape is pressed onto the gobbles, and the tape is immediately removed.

This operation was repeated 10 times, and the number of peeled pieces out of 100 pieces was counted, and the adhesive strength was evaluated based on this number.

The results are shown in Table 1-2 below.

This shows that when the Si content was 4% or more, even if etching was performed, the fine irregularities necessary for adhesion with the fluorocarbon resin could not be obtained.

Furthermore, the same was true for those in which the Si content was 4% or less, as well as those in which the content of other components such as Cu was high and the Al purity was 94% or less.

Therefore, the chemical composition of aluminum castings is that the purity of aluminum is 94% or more and the content of Si is 4%.
% or less.

Such aluminum castings are relatively special and have considerably higher purity than those commonly used.

Example 2 The relationship between the treatment conditions of electrolytic etching and chemical etching and the adhesive strength of the Zutsuso resin-coated plate was investigated.

Furthermore, a comparison was made with the conventional one-primer type.

As the aluminum casting, the same Si as in Example 1-2 was used.
A material containing 2% of was used.

First, this aluminum casting was cleaned and degreased with 5% NaOH, and then etched.

For electrolytic etching, a 5% NaCl aqueous solution was used and the processing conditions were changed by changing the amount of electricity applied.

In electrolytic etching, the amount of electricity applied determines the unevenness of the surface of the rib, which determines the adhesive strength with the fluorocarbon resin.

After etching, the surface roughness was measured, and in the same manner as in Example 1, a polytetrafluoroethylene resin dispersion was applied to a thickness of about 20μ, and then sintered at 380°C to test the adhesive strength by cross-cutting. It was evaluated by the chest test.

These results are summarized in Table 2-1 below.

In Table 2-1, the average roughness is expressed as the 10-point average roughness Rz defined in JISB-0601.

As a result, in the case of electrolytic etching, in order to obtain sufficient adhesive strength, an uneven surface with a 10-point average roughness Rz) of 8 μm or more is required.

If this is considered as the amount of electricity for etching, an amount of electricity of 30 galon or more is required.

(In the case of normal wrought aluminum, a considerable amount of adhesive force can be obtained even with an electric charge of about 10 coulombs and 1 crrr, and in the case of such castings, a considerably large throughput is required compared to wrought aluminum.) Table 2-2 shows the processing conditions, surface roughness after etching, and adhesive strength with fluorocarbon resin when chemical etching with hydrochloric acid was performed.

The casting material and pretreatment used were the same as in Example 1.2.

Looking at this, as in the case of electrolytic etching, a surface roughness of 8μ or more is required.

Further, as shown in Comparative Example 2-10, a conventional tetrafluoroethylene resin primer was applied and sintered, and then a tetrafluoroethylene resin enamel was further coated and sintered.

The adhesive force of this method was considerably lower than that of the etching method.

As mentioned above, as a method for coating aluminum castings with fluorocarbon resin, the chemical composition of aluminum castings is limited,
Further, if electrolytic etching or chemical etching is performed to obtain a surface roughness Rz) of 8 μ or more, and this surface is coated with fluorocarbon resin, a fluorocarbon resin coating with strong adhesive properties can be obtained.

Example 3 The following experiment was conducted to examine how the adhesion between the base material and the resin changes depending on the surface treatment of the base material before etching.

The base material is shown in Example 1-2.

An aluminum casting containing 2% Si was used, and its surface was subjected to mechanical and chemical pretreatment as shown in Table 3-1 below.

This surface was immersed in a 5% NaCl aqueous solution with an electric charge of 50Q/crA.
Electrolytic etching was performed.

After removing smut, a polytetrafluoroethylene resin dispersion was applied to a thickness of about 20 μm, dried, and
Coating was done by heating at 80°C for 10 minutes.

Adhesion was evaluated by a cross-cut test in the same manner as in Example 1.

The results are shown in Table 3-1.

As described above, pretreatment removes surface dirt, impure structures, oxide films, and other surface layers that adversely affect the etching process that occur during casting molding, and makes the unevenness caused by etching more uniform. It can be done.

It has become clear that this can strengthen the adhesion to the fluorocarbon resin.

Of course, methods for removing this surface layer include all methods such as chemical degreasing and polishing, mechanical cutting, and polishing, and are not limited to the four methods shown in the examples.

As described above, the present invention provides a surface treatment method for extremely firmly adhering fluorocarbon resin, which has non-adhesive properties and a low coefficient of friction, to the surface of aluminum castings.
It is extremely useful for various kitchen appliances and mechanical parts.

Claims (1)

[Claims] 1. As an aluminum casting, aluminum purity is 94.
% or more and whose silicon content is 4% or less, and perform electrolytic etching treatment in an aqueous halide solution or chemical etching treatment to create irregularities with a surface roughness of 8μ or more. A method for surface treatment of aluminum castings, characterized in that the surface of the aluminum casting is coated with a fluorocarbon resin. 2. The method for surface treatment of aluminum castings according to claim 1, wherein the surface is mechanically cut and polished or chemically degreased and polished in advance during the etching treatment. 3. The method for surface treatment of aluminum castings according to claim 1, characterized in that the etched surface is anodized and then coated with fluorocarbon resin.