Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
1999-08-13
2001-06-05
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S256000, C148S259000, C148S270000, C427S344000, C427S419500, C106S014120
Reexamination Certificate
active
06241830
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing a metal material or steel plated with metal from the formation of white rust, a primary anticorrosion, and a pollution-free anticorrosive treatment as a primer coating without a chromate.
An anticorrosive treatment for zinc or aluminum plated steel sheet or non-plated steel has been researched and actually used for a long time. As conventional anticorrosive coatings chromate-based anticorrosive coatings are exemplified typically in Japanese Patent Application KOKAI No.131370/1991 in which anticorrosive coatings containing aqueous resins and chromate are disclosed. Such chromate-based anticorrosive coatings, however, are restricted in use because of the high toxicity and the carcinogenicity. In addition, the corrosion resistance is insufficient in some cases.
Alternatively, various kinds of chromium-free, so-called non-chromium type anticorrosive coatings have been developed recently. Non-chromium type anticorrosive coatings containing a compound having a carbodiimide bonding, an organo-silicate and silica particles are disclosed in Japanese Patent Application KOKAI No. 221595/1997, which relates to a multi-layer film, and is insufficient in the corrosion resistance as a single layer.
Generally, the non-chromium treatment using non-chromium type anticorrosive coatings has a problem that the adhesion after applying is not always sufficient. When a paint is applied on a chromate film, a strong adhesion is achieved between a chromate film and a topcoat paint film, as a chromium ion in the interface is used for the cross-linking of the paint resin in the chromate treatment. On the contrary, in the case of the non-chromium treatment, such a strong adhesion can be hardly attained.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a non-chromium anticorrosive treatment, which is more excellent in anticorrosive property and adhesion of topcoat film, and to provide a metal material or steel plated with metal that is treated an-icorrosively thereby. The present invention is relates to a method of preventing corrosion of a metal material or steel plated with metal, which comprises contacting a metal material or a steel plated with metal with an aqueous solution containing one or more kinds of compounds containing a phosphorus ion (The term “phosphorus ion” means acid ions containing at least one of a phosphorus atom in the present specification), washing the treated sheet if desired, and then applying anticorrosive coatings containing one or more kinds of sulfur compounds and a water dispersible silica in a composition containing aqueous resins and water.
Further, the present invention relates to a metal material or steel plated with metal treated anticorrosively with the method mentioned above.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is relates to a method of preventing corrosion of metal, which comprises contacting a metal material or steel plated with metal with an aqueous solution containing one or more kinds of compounds containing a phosphorus ion, washing the treated sheet with water if desired, and then applying anticorrosive coatings containing one or more kinds of sulfur compounds and a water dispersible silica in a composition containing aqueous resins and water.
In the present specification the term “metal material” includes steel, titanium, aluminum, copper sheet or the like and a metal material plated by galvanizing, fused metal plating and the like. As the steel cold-rolled steel, hot-rolled steel, stainless steel and the like are exemplified.
In the present specification the term “steel plated with metal” means steel which is plated with metal such as Zn, Al, Ni, Cr, Sn, Pb, Fe, Co, Mg, Mn, Ti and the like, or an alloy of the above metals. A metal that is alloyed by a heat treatment after the plating is also included. A small amount of another metal such as Co, Mo, W, Ni, Ti, Cr, Al, Mn, Fe, Mg, Pb, Sb, Sn, Cu, Cd, As and the like as a hetero-metal or an impurity, and/or a metal material in which at least one of inorganic compounds such as silica, alumina, titania and the like are dispersed, or a plating containing any ingredients other than Fe-P. The plating may contain plural layers.
The method of plating may include electro-galvanizing, hot dip-plating, fused metal plating deposition, injection and the like.
The typical examples of the steel plated with metal are zinc-plated steel and aluminum plated steel, on which an excellent anticorrosive effect is achieved by the anticorrosive coatings of the present invention.
When a metal material or steel plated with metal is treated with an aqueous solution comprising compounds containing phosphorus ion such as phosphoric acid ion, condensed phosphoric acid ion, phytic acid ion phosphinic acid ion or phosphonic acid ion, such ions are adsorbed on the zinc plated surface and an amorphous thin film of the compounds containing a phosphorus ion is formed. It is considered that this film not only lowers the oxygen reduction current density so as to improve the anticorrosion property, but also improves the adhesion between the metal and an organic compound film when the organic film is formed thereon when the phosphorus ion exists on the surface of the metal as known in the case of zinc phosphate treatment. Therefore, in the present invention where a metal material or steel plated with metal is pre-treated with an aqueous solution of the compound containing a phosphorus ion and then the resin type anticorrosive coating is applied thereon, the adhesion between the metal material or steel plated with metal and the anticorrosive film is improved, so that the impregnation of corrosion factors such as water or ions into the interface is prevented and the anti-corrosive property improves moreover.
The defect of the adhesion of the top coat which may happen when the top coat is applied on the metal treated with anticorrosive coatings of the present invention is mostly due to the defect of the adhesion between anticorrosive film and zinc plated surface, and the adhesion between the anticorrosive film and the top coat film is good in general. Such defect of the adhesion often happens when a phosphorus ion is removed out of an anticorrosive coatings. On the other hand, when the phosphorus ion exists in anticorrosive coatings, particularly when a water dispersible silica is additionally used, the anticorrosive coatings are apt to gel and the storage stability becomes deteriorated. Thus, the presence of a phosphorus ion will be often inconvenient.
In the present invention a metal material or steel plated with metal is pre-treated with aqueous solution containing the phosphorus ion, a conversion film is formed by said ion on its surface, and then anticorrosive coating not containing a phosphorus ion is applied. Therefore, the adhesion between the anticorrosive film and the zinc plated surface increases and the adhesion of the topcoat increases as well as the storage stability of the anticorrosive coatings is improved.
According to the present invention the anticorrosive effect is achieved by the adsorption of a sulfur atom of sulfur compounds selected from sulfides, sulfur powder, triazinethiol compounds, thiocarbonyl group-containing compounds, thiosulfuric acid, thiosulfates, persulfuric acid, persulfates, and sulfur oxides in the anticorrosive coatings on the surface of zinc plated steel treated with the compounds containing phosphorus ion. Further, though its reason is not sure, when compounds containing a phosphorus ion exist on the zinc plated surface, the adsorption of the sulfur atom is promoted. In addition, this effect is increased by the pre-treatment of a metal material or steel plated with metal with the aqueous solution of the compounds containing a phosphorus ion acid.
In the present invention, examples of the compounds which can generate the phosphorus ion in water include phosphoric acid; phosphates represented by Na
3
PO
4
, Na
2
HPO
4
, NaH
2
PO
4
; condensed phosphoric acids, for example polyphosp
Shimakura Toshiaki
Yamasoe Katsuyoshi
Nippon Paint Co. Ltd.
Oltmans Andrew L.
Sheehan John
Wenderoth , Lind & Ponack, L.L.P.
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