Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1996-04-29
1997-07-08
Silverberg, Sam
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148262, C23C 2218
Patent
active
056456506
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a conversion treatment bath composition (hereinafter usually called either "bath" or "composition", either of which in this context is to be understood as meaning "bath composition") that is suitable, either as such or after dilution with water, for improving the corrosion resistance and rust-inhibiting performance of, and the adherence of paint to, the surface of magnesium-containing metals by forming a conversion coating thereon by contact at suitable temperatures for suitable times. The invention also relates to a conversion treatment method that uses this bath and to objects to which this conversion treatment has been applied.
BACKGROUND ART
The conversion treatment of magnesium-containing metals is already known, for example, from JIS H-8651, MIL-M-3171, and so forth, and these conversion treatments have found practical application as underpaint coating treatments for magnesium-containing metals. However, all of these conversion treatment baths contain hexavalent chromium ions. Since hexavalent chromium ions are a pollution source, their presence is accompanied by a number of problems, for example, processing of the effluent from conversion treatment, management of the working environment, and the like.
These conversion treatments are also subject to other problems; for example, they require high treatment temperatures and long treatment times, and their treatment baths are very concentrated. Moreover, the conversion films produced by these conversion treatments have a strong tendency to be nonuniform.
Japanese Patent Publication Number Hei 3-6994 [6,994/1991] discloses a conversion treatment for magnesium-containing metals that does not use hexavalent chromium ions. This conversion treatment takes the form of a Cr.sup.6+ -free phosphate conversion treatment, which, however, is not sufficient to provide magnesium-containing metals with corrosion resistance. Specifically, after the phosphate treatment step, the overall treatment method of Japanese Patent Publication Number Hei 3-6994 teaches treatment with silicate and then silicone. The phosphate conversion coating by itself provides only a poor corrosion resistance and adherence when applied to the surface of magnesium-containing metals as an underpaint coating treatment. This treatment method also suffers from other problems; for example, it requires a multistep treatment process, high treatment temperatures, and long treatment times.
The use of treatment baths based on zinc phosphate, iron phosphate, zirconium phosphate, and so forth, is already known within the realm of phosphate-based conversion treatment methods, but these methods essentially can not provide the surface of magnesium-containing metals with a corrosion resistance satisfactory for practical applications.
A manganese phosphate treatment is reported in Section 7 of Japanese Industrial Standards ("JIS") H-8651, but this treatment bath is unsuitable for practical applications because it uses chromium, requires high treatment temperatures of 80.degree. C. to 90.degree. C., and requires long treatment times of 30 to 60 minutes.
DISCLOSURE OF THE INVENTION
Problems to Be Solved by the Invention
Thus, as described above, the following problems are associated with conversion treatment methods according to the prior art for magnesium-containing metals: has a corrosion resistance and paint adherence inferior to those obtained with the use of chromium; consistently obtain a uniform conversion coating; and
The invention was pursued in order to solve the problems listed above. The present invention takes as an object the introduction of a substantially chromium-free conversion treatment bath composition that is able to form a uniform, highly corrosion-resistant, highly rust-inhibiting, and strongly paint-adherent conversion film on the surface of magnesium-containing metals. An additional object of the invention is that said conversion film should be formed by a rapid, low-temperature, and low-cost method in which bath management is simple and whic
Ishizaki Sadao
Nishida Masahiko
Sato Yokichi
Henkel Corporation
Jaeschke Wayne C.
Silverberg Sam
Szoke Ernest G.
Wisdom, Jr. Norvell E.
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