Compositions: coating or plastic – Coating or plastic compositions – Metal-depositing composition or substrate-sensitizing...
Patent
1995-10-10
1997-04-29
Klemanski, Helen
Compositions: coating or plastic
Coating or plastic compositions
Metal-depositing composition or substrate-sensitizing...
106 112, 106 127, 148259, 148261, 148262, C23C 2207
Patent
active
056244800
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an acidic substitutional plating bath composition, also called a "bath" herein for brevity, for application to zinciferous surfaces, particularly to steel sheet plated with zinc-containing metal (hereinafter referred to as zinciferous metal-plated steel sheet), and to processes for using such a composition to treat metals. More specifically, the present invention relates to an acidic substitutional plating bath composition that can be continuously employed for long periods of time while maintaining its initial performance and that, upon contact with the surface of zinciferous metal-plated steel sheet, forms thereon a heavy metal film that contributes to the formation of a paint undercoat that is very strongly adherent for paint films. This acidic substitutional plating bath composition can also improve the black rust resistance of the unpainted sheet.
As used herein, the term "zinciferous metal-plated steel sheet" encompasses steel sheet plated with zinc or a zinc alloy. Said zinc alloys encompass, for example, zinc-aluminum alloys, zinc-nickel alloys, and zinc-iron alloys.
BACKGROUND ART
In order to increase the adherence of zinciferous metal-plated steel sheet to paint or other types of dryable films coated thereon, treatment of zinciferous metal-plated steel sheet with an acidic aqueous solution (particularly aqueous phosphate solutions) is widely used in industry in order to form a paint undercoat film on the sheet. Paint films laid down on such a phosphate film layer perform well when the treatment has been managed so as to give appropriate film weights and crystal dimensions. Since these physical parameters must be adjusted into appropriate ranges, it therefore becomes necessary to vary the conversion treatment conditions as a function of the type of plating on the steel sheet and the steel sheet line speed and to frequently remove the sludge that is generated in the treatment bath.
In the case of low-lead hot-dip galvanized steel sheet (with a lead content in the zinc plating layer reduced from that in conventional hot-dip galvanized steel sheet), it has already been discovered that corrosion inhibition is obtained due to the absence of lead segregation at the grain boundaries of the crystals in the plating layer and at the interface between the plating layer and alloy layer. Low-lead hot-dip galvanized steel sheet is, as a consequence, widely used in various industrial sectors. However, unlike the conventional hot-dip galvanized steel sheet, low-lead hot-dip galvanized steel sheet resists cracking during bending processes, with the result that shear stresses become concentrated in the phosphate film positioned between the steel sheet and paint film. This produces cohesive failure in the phosphate film, which in turn causes facile delamination of the paint film.
In order to avoid the problems described above, application-type chromate treatments that include hexavalent chromium and trivalent chromium are in use as paint undercoat treatments in place of phosphate treatments. The treatment bath composition in this type of process is easily maintained and managed. Moreover, this type of process can easily respond to many different types of plating and to line speed variations, and the treatment effluent in this case poses few environmental problems. However, the paint adherence of these chromate films is not as good as that of the phosphate films, and in particular delamination of the paint film occurs quite easily during strong flexural working involving pressure contact.
In order to improve the paint adherence of such application-type chromate films, i.e., in order remediate the problem of facile delamination, (1) Japanese Patent Publication Number Sho 43-12974 [12,974/1968], (2) Japanese Patent Publication Number Sho 52-22618 [22,618/1977], (3) Japanese Patent Publication Number Sho 52-43171 [43,171/1977], and (4) Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 61-69978 [69,978/1986]propose methods for improving the paint ad
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Murasawa Yoshiyuki
Tsuda Shotaro
Yoshitake Noriaki
Henkel Corporation
Jaeschke Wayne C.
Klemanski Helen
Szoke Ernest G.
Wisdom, Jr. Norvell E.
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