JPS63247378A - Post treatment after mechanical plating - Google Patents

Abstract

PURPOSE:To enhance the corrosion preventing effect of a plated layer formed on a product by mechanical plating by immersing the product in a specified chromating soln. so as to sufficiently chromate even the insides of the micropores in the plated layer. CONSTITUTION:A product coated with a film of a corrosion preventing metal by mechanical plating is immersed in a chromating soln. consisting of water, a sexivalent chromium compd. and an alcohol penetrant. Through the film formed by the mechanical plating has micropores, even the insides of the micropores can be sufficiently chromated and the corrosion resistance of the film can be improved. The corrosion preventing metal is Zn, Al, a Zn-Al alloy or mixture, an alloy or mixture of Zn and/or Al with Sn. Chromic anhydride, chromate, dichromate or a mixture of two or more kinds of such compds. is desirably used as the sexivalent chromium compd. Tert, butanol is preferably used as the alcohol penetrant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to post-treatment of mechanically plated metal products, and particularly relates to chromate treatment of mechanically plated metal products.

[Prior art and its problems]

It has been known for a long time that materials and products made of zinc, aluminum, tin, cadmium, or their alloys, or materials and products coated with them, can be treated with chromate to improve their corrosion resistance. It is also widely practiced commercially.

In this case, -i is carried out by chemical conversion treatment of the surface using an aqueous solution containing a hexavalent chromium compound and a small amount of acid as a catalyst.

On the other hand, there is a mechanical plating method called mechanical plating. That is, the object to be plated, glass beads as an impact medium, water, gold accelerator, and powder of the metal to be plated are placed in a barrel, and by rotating the barrel, the metal powder is coldly applied onto the object to be plated. This method involves crimping and forming a film.

The mechanical energy generated by the rotation of the barrel becomes the kinetic energy of the glass beads, and when the glass beads collide with the object to be plated, the metal powder present between them is compressed, forming a strong coating. The metal to be plated may be a single metal, or may be an alloy or a mixture of two or more metals to form a film. Furthermore, it is also possible to increase the adhesion between the metal particles in the film by adding a tin compound to the plating promoter and causing substitutional precipitation between the tin compound and the zinc powder. In this case, the coating consists of metal added as a powder,
Alternatively, it forms a structure in which a mixture of the alloy and tin, or a part thereof is alloyed with tin.

In addition, although there is no strict definition, in a narrow sense, mechanical plating generally refers to the formation of a film with a thickness of several micrometers to more than ten micrometers, and the plating metal is zinc or an alloy or mixture mainly composed of zinc. The case where the thickness of the film is more than the above-mentioned thickness is called mechanical galvanizing.

In a broad sense, all of these are referred to as mechanical plating, and the description here will be based on a broad interpretation.

By the way, since this mechanical plating is mechanical plating as mentioned above, fine voids are formed in the film that is formed, and only the surface layer is chemically treated using a normal water-based chromate solution as mentioned above. Even if processing is performed using
Corrosion progresses from the voids where the chromate film is not formed, and the expected corrosion protection effect cannot be obtained.

As one way to improve this, JP-A-60-
Publication No. 245785 (Japan Dacroshamrosoku/Dowa Iron Powder) describes a baking-type chromate treatment method in which a composition is immersed in a composition consisting of a water-soluble chromium compound and a reducing agent, pulled up, and then fired to form a chromate film. It has been disclosed that an excellent anticorrosion effect can be achieved by combining this method with a blast zinc coating method. However, when an aqueous chromate treatment liquid is used, it generally has low permeability into fine voids, and baking is performed to compensate for this drawback, which has the disadvantage of being laborious and costly.

Another method is to apply a non-aqueous chromate treatment method as disclosed in JP-A-61-67773 (Nippon Dacro Shamrock/Douwa Iron Powder). That is, it is a method in which treatment is performed with a composition containing a chromic acid compound, an organic solvent such as a halogenated hydrocarbon, and an alcohol as a solubilizer, and optionally a stabilizer and a reaction accelerator. It is also said that it exhibits an excellent anti-corrosion effect when combined with the blast zinc coating method.

Treatment with this non-aqueous chromate solution does not require treatment of wastewater containing harmful hexavalent chromium, so it is not only applied to mechanical plating films (but also applied to general plating films). Since it is also advantageous in cases where the organic solvent and the type of acid used as a catalyst are considered,
In addition to the above-mentioned applications, Japanese Patent Publication No. 42-3363 (DuPont), Japanese Patent Application Publication No. 55-97476 (Nippon Paint),
JP-A-56-1) 2479 (Nippon Paint), JP-A-56-139679 (Nippon Paint), JP-A-56-
62970 (Tokuyama Soda), JP-A-61-67773
(Japanese Dakuroshamurotsuta) etc. However, although non-aqueous chromate solutions are preferable from the perspective of not requiring wastewater treatment, they require closed treatment equipment or exhaust equipment because the solvent vapor is generally toxic, and compared to aqueous chromate solutions, they require closed treatment equipment or exhaust equipment. There are also factors that are not necessarily favorable for commercial operation, such as the high cost of treatment liquid.

However, the reason why non-aqueous chromate has a good effect on films with fine voids formed by mechanical plating is explained in the above-mentioned Japanese Patent Laid-Open No. 61
Although there is no clear explanation in Kowa No. 67773 (Japan Dacroshamrosoku/Dowa Iron Powder), the non-aqueous chromate solution has a stronger ability to penetrate into minute voids than the aqueous chromate solution, so This is presumably due to the fact that even the surface of the metal particles is covered with a chromate film.

[Purpose of the invention]

This invention was proposed in view of the above-mentioned conventional circumstances, and is a mechanical plating method using an easy-to-handle and inexpensive water-based treatment liquid, and a chromate liquid that has high permeability into minute voids. The present invention provides a method for post-processing.

[Means to achieve the purpose]

In order to achieve the above object, the present invention employs the following means. That is, after forming a film of a mixture of zinc or aluminum, an alloy or mixture thereof, or one or more of them and tin on the surface of the workpiece by a mechanical plating method, water, a hexavalent chromium compound, and a tertiary chromium compound are applied. The chromate treatment is performed using a treatment liquid consisting of butanol.

The hexavalent chromium compound mentioned above is chromic anhydride.

Chromic hydrochloric acid, dichromic hydrochloric acid, or a mixture thereof is used. More specifically, preferred for commercial use are the sodium or potassium salts of chromic acid or dichromate, or chromic anhydride. The concentration of hexavalent chromium is preferably in the range of 1 to 40 g/L in terms of chromic anhydride; anything less than 1 g/L does not provide the performance that satisfies the purpose of the present invention, which is to impart high corrosion resistance. Moreover, if the concentration is 40 g/L or more, not only will the appearance of the chromate film become uneven, but if the concentration of the alcohol penetrant is high, the ignitability will be high, which is dangerous. Furthermore, even if it is added at a concentration of 40 g or more, the performance of the treated film will not be improved compared to when the concentration is lower than that, so it is economically meaningless to increase the concentration.

As the penetrant used in the present invention, tertiary butanol ((CH3)2C(OH)) is preferably used.

If we focus only on permeability, alcohols with 1 to 6 carbon atoms will exhibit this effect, but alcohols with 1 to 3 carbon atoms and primary and secondary butanol will be more effective than hexavalent chromium. There is a problem with the stability of the processing solution. Also, alcohols with 5 or more carbon atoms are more expensive than tertiary butanol;
Not suitable for commercial operation. Examples of alcohol added to the chromate treatment solution include the above-mentioned Japanese Unexamined Patent Publication No. 6
1-67773 (Japanese Dacro Siamlotus, Dowa Iron Powder) or JP-A-61-34184 (Japanese Dacro-Shamro-Ivy, Dowa Iron Powder), JP-A-42-3363 (DuPont), JP-A-55-97476 (Nippon Paint) ), JP-A-56-1) 2479 (Nippon Paint), JP-A-Sho 5
6-139679 (Nippon Paint), JP-A-56-62
970 (Tokuyama Soda) etc., there are examples where chromium compounds are dissolved in non-aqueous solvents and used as solubilizers to prepare non-aqueous chromate solutions.
There are no examples of its application to an aqueous chromate treatment solution as a penetrating agent for porous films.

The addition of tertiary butanol to the aqueous chromate solution to impart permeability is effective at a concentration of 10% or more by volume relative to water. Further, even if the concentration is 80% or more, it can be used from the viewpoint of permeability, but if the concentration of the chromium compound is high, the flammability becomes high, so it is not suitable for commercial use.

Furthermore, the chromate treatment solution of the present invention contains sulfuric acid, which is contained in a general aqueous chromate treatment solution.

It is also possible to add an acid catalyst such as nitric acid, phosphoric acid, hydrofluoric acid, or acetic acid to make the appearance uniform after treatment.

Therefore, the present invention should not be limited to using treatment liquids that do not contain these acid catalysts. however,
The difference in corrosion resistance due to the presence or absence of the addition of an acid catalyst is only a slight difference compared to the dramatic improvement in corrosion resistance due to carbonization of tertiary butanol, and the addition is not necessarily necessary.

The present invention will be illustrated in detail by examples below, but the present invention should not be limited to the examples.The present invention is not limited to the examples. The composition of the liquid and the immersion and drying conditions can be changed as desired.

[Example ■]

Chromate treatment solution tertiary butanol 300ml water
700ml chromic anhydride
20g Mechanical plating treatment agent (trade name SC-M) commercially available from Nippon McDermind Co., Ltd.
.

5C-G, MGI 50), 20. cz(7)
A dry wall screw with mechanical zinc plating was immersed in the above chromate treatment solution for 3 minutes, followed by centrifugal dehydration and natural drying.

At the same time, a salt spray test was conducted on five samples each, along with a sample that was subjected to mechanical plating but not subjected to chromate treatment. All samples that were not subjected to chromate treatment developed red rust within 600 hours, whereas samples that were chromate treated with the above treatment solution showed 1.
No red rust was observed within 700 hours.

[Example ■]

Chromate treatment liquid tertiary butanol 200mt! water
800 m + 30 g of potassium dichromate By the method described above, a dry wall screw mechanically plated with zinc to a thickness of 50 μm was immersed in the above chromate treatment solution for 5 minutes, followed by centrifugal dehydration and natural drying. At the same time, a salt spray test was conducted on five trees each along with a sample that was mechanically plated but not chromate treated. All samples that were not subjected to chromate treatment developed red rust within 800 hours, whereas no red rust was observed within 3700 hours for the samples that were chromate treated with the above treatment solution. .

[Example ■]

Chromate treatment liquid tertiary butanol 100mj! water
900ml chromic anhydride 1g 6μ by the method described above
A washer with aluminum mechanical plating to a thickness of 100 ml was immersed in the above chromate treatment solution for 1 minute, and then dried in a dryer at 40°C. At the same time, a salt spray test was conducted on two of each sample along with a sample that was mechanically plated but not chromate treated. Both samples that were not subjected to chromate treatment were 1
The generation of red rust was observed within 300 hours, whereas the generation of red rust was not observed within 300 hours in the sample subjected to chromate treatment with the above treatment liquid.

[Example ■]

Chromate treatment liquid tertiary butanol 800ml water
200ml chromic anhydride
40 g of a dry wall screw mechanically plated with zinc to a thickness of 20 μm was immersed in the above chromate treatment solution for 4 minutes using the method described above, followed by centrifugal dehydration and natural drying. At the same time, a salt spray test was conducted on five samples each, along with a sample that had been mechanically plated and colored chromate treated with a normal aqueous chromate solution. All of the samples treated with the aqueous chromate solution showed red rust within 300 hours, whereas the samples treated with the above treatment solution showed 1.
No red rust was observed within 900 hours.

[Example ■]

Chromate treatment liquid tertiary butanol 350m6 water
650ml sodium chromate
20g aluminum to a thickness of 15μ by the method described above,
A washer mechanically plated with a tin-zinc alloy (composition ratio 15:0.5: balance) was immersed in the above chromate treatment solution for 1 minute, then centrifugally dehydrated and air-dried. At the same time, a salt spray test was conducted on five samples each, along with a sample that was subjected to mechanical plating but not subjected to chromate treatment. Red rust was observed on the shoulder of the washer within 50 hours of the sample that was not subjected to chromate treatment, whereas no red rust was observed within 700 hours of the sample that was chromate treated with the above treatment solution. There wasn't.

〔Effect of the invention〕

As explained above, this invention uses an aqueous chromate treatment solution, which is inexpensive and easy to handle, and furthermore, it does not contain tertiary butanol, which has a strong penetration effect into micropores. Since it is mixed in a fixed amount, it has the effect of sufficiently performing chromate treatment within the fine particles.

Procedural amendment June 15, 1986 1.Display of the incident 1986 Patent Application No. 81809 2. Name of the invention Mechanical plating post-processing method 3. Person who makes corrections Relationship to the case Patent applicant Address: 402 Ko, Shirahama-cho, Himeji City 4. Agent none 6. Subject of correction Processing method.

1. r Scope of Patent Claims” will be amended as follows.

(1) A mechanical plating post-treatment method characterized by immersing a product coated with a rust-preventive metal coating by mechanical plating in a chromate treatment solution consisting of water, a hexavalent chromium compound, and an alcohol penetrant.

(2) Claim No. 1, wherein the rust-preventive metal is zinc or aluminum, an alloy or mixture thereof, or an alloy or mixture of one or more of them and tin.
) Mechanical plating post-processing method described in section 2.

(3) The hexavalent chromium compound is chromic anhydride, chromium chloride 1
The mechanical plating post-treatment method according to claim 1, which is a modified dichromium salt, or a mixture of two or more thereof.

(4) Hexavalent chromium compound is 1 to 1 in terms of chromic anhydride
Claim No. (3)J whose concentration is 40 g/L or less
After the mechanical plating described in Section L, ■, the "Detailed Description of the Invention" is amended as follows in Claim No. (
1) Mechanical plating post-processing method described in ffi.

(6) The mechanical plating post-treatment method according to claim (5), wherein the ratio of water to tertiary butanol is 10 to 80% by volume of butanol.

1. In the 4th line of page 6 of the specification, the section ``On a mechanical plating film...'' was changed to ``...on a porous film formed by mechanical impact plating such as blast zinc coating method...''·"will do.

2. In the 1st and 2nd lines of page 7 of the specification, the part ``Where, non-water is applied to the film with fine voids formed by mechanical plating'' is changed to ``Where, where, the blast zinc coating method is applied. "Non-aqueous" as opposed to porous films formed by mechanical impact plating, such as "non-aqueous".

3. The third line from the bottom of No. 10 of the specification states ``Due to carbonization...''
・” should be replaced with “Due to the addition of...”.

4. In the 4th line of page 1) of the specification, the phrase "The above-mentioned purpose of carrying out a chemical conversion treatment..." is replaced with "The above-mentioned purpose of carrying out a chemical conversion treatment of..."·"will do.

−1 above

Claims (6)

[Claims] (1) A mechanical plating post-treatment method characterized by immersing a product coated with a rust-preventive metal coating by mechanical plating in a chromate treatment solution consisting of water, a hexavalent chromium compound, and an alcohol penetrant. (2) Claim No. 1, wherein the rust-preventive metal is zinc or aluminum, an alloy or mixture thereof, or an alloy or mixture of one or more of them and tin.
) Mechanical plating post-processing method described in section 2. (3) The mechanical plating post-treatment method according to claim 1, wherein the hexavalent chromium compound is chromic anhydride, chromic hydrochloric acid, dichromic hydrochloric acid, or a mixture of two or more thereof. (4) Hexavalent chromium compound is 1 to 1 in terms of chromic anhydride
The mechanical plating post-treatment method according to claim 3, wherein the concentration is 40 g/L or less. (5) The mechanical plating post-treatment method according to claim 1, wherein the alcohol penetrant is tertiary butanol. (6) The mechanical plating post-treatment method according to claim (5), wherein the ratio of water to tertiary butanol is 10 to 80% by volume of butanol.