Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Patent
1993-07-19
1995-07-04
Padgett, Marianne
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
427566, 427250, B05D 306, C23C 1600
Patent
active
054298431
DESCRIPTION:
BRIEF SUMMARY
This is a filing under 35 U.S.C. 371 of PCT/JP92/01511, filed on Nov. 19,1992.
The present invention relates to a method of forming a vapor deposition plating layer excellent in adhesiveness, corrosion resistance, conformability to paint film on the surface of a substrate steel without deteriorating the properties of the steel material.
BACKGROUND OF THE INVENTION
A material such as a steel sheet is coated with a Zn plating layer and then with paint, in order to improve the corrosion resistance of a building or structrual material in various fields of use. The material after being coated with a Zn plating layer is usually subjected to phosphating treatment before paint application. A film composed of fine phosphate crystals is formed on the surface of the substrate material by the phosphating treatment. The phosphate film effectively improves the adhesiveness of a paint film to the surface of the substrate steel, so that the obtained product is excellent in corrosion resistance and weatherability.
Corrosion resistance required for building and structural materials has become more severe, as the environment is getting worse in corrosive condition. In this regards, a material coated with a Zn or Zn alloy plating layer does not exhibit sufficient corrosion resistance, so that corrosion is often observed under the paint film. In addition, a brittle alloyed layer is likely to be formed between the plating layer and the steel substrate. The brittle alloyed layer would cause the formation of various defects such as flaking and powdering in the plating layer, when the coated steel sheet is worked to an objective shape.
In order to acquire enough endurance against the severer environment for use, there have been proposed various improvements such as the selection of substrate steel, the modification of the plating layer in composition and the change of a plating method to improve corrosion resistance. For instance, a stainless steel is used as a substrate to be coated with a Zn plating layer. The Zn-coated stainless steel exhibits extremely excellent corrosion resistance owing to the co-operative effect of the stainless steel with the Zn plating layer.
Vapor depostion plating has been noted in recent years as a substitution for conventional hot-dip or electrolytic plating. According to the vapor deposition, it is possible to obtain a plating layer having a composition, which can not be formed by the conventional method, with the high degree of freedom. For instance, Japanese Patent Application Laid-Open 63-247353 discloses a vapor deposition plating method for forming a Zn-Al alloy plating layer on the surface of a steel sheet. In this method, Zn and Al are independently evaporated from different vessels, and Zn and Al are simultaneously deposited from the vapor phase on the surface of the steel sheet.
The vapor deposition plating layer adheres onto the surface of the steel substrate without substantial reaction between the plating layer and the substrate steel, so that the coated steel sheet exhibits excellent workability as compared with a Zn alloy-coated steel sheet manufactured by a hot-dip plating method or the like. In addition, the coated steel sheet is excellent in corrosion resistance, too, due to Al contained in the plating layer.
However, during the formation of a vapor deposition plating layer, there is a possibility that the plating layer would be formed in a state which has poor adhesiveness and defects such as pores would be involved in response to the surface conditions of the material such as a steel sheet to be coated. In order to improve the adhesiveness of the vapor depostion plating layer, there has been proposed a pretreatment for activating the surface of the steel sheet by electron beam heating, gas reduction or the like before the vacuum deposition of a plating metal on the surface of the steel sheet.
When the surface of the steel sheet is activated by electron beam heating, it is necessary to elevate the surface temperature of the steel sheet at the begining of vapor deposition. For ins
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Fukui Yasushi
Masaki Katsuhiko
Miyake Hideo
Morita Yukihiro
Saito Minoru
Nisshin Steel Co. Ltd.
Padgett Marianne
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