Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1998-06-08
2001-02-20
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S472300, C106S014210, C106S014440, C106S014120
Reexamination Certificate
active
06190780
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a surface treated metal material having a coating layer with working-follow-up properties and excellent corrosion resistance and containing absolutely no hexavalent chromium, as well as to a surface treatment agent therefor.
BACKGROUND ART
Coating of chromate films on surfaces as a corrosion resistance treatment for cold-rolled steel sheets, zinc-plated steel sheets and zinc-based alloy plated steel sheets, aluminum-plated steel sheets, etc. conventionally used for automobiles, household electrical appliances, construction materials and the like, is a common technique. In addition to steel sheets, chromate films are also widely used for petroleum transport pipes and other steel pipes, and for wires and other wiring materials. Aluminum and its alloy surfaces are covered with natural oxides which protect the materials from many types of corrosive environments, but anodic oxidation and chromate treatment are carried out on structural materials for aircraft and the like which require more excellent corrosion resistance and coating adhesion.
Chromate treatment often used for such metal materials includes electrolytic chromate and application-type chromate. Electrolytic chromate treatment has been carried out by cathodic electrolytic treatment of metal sheets using baths containing, for example, chromic acid as the main component, in addition to sulfuric acid, phosphoric acid, boric acid, halogens and various other anions. Application-type chromate treatment, which has been associated with the problem of elution of chromium from the chromate treated metal sheets, has been carried out by first adding an inorganic colloid or inorganic anion to a solution wherein a portion of the hexavalent chromium has been reduced to trivalent, or a solution with a specified hexavalent chromium and trivalent chromium ratio, to prepare the treatment solution, and then dipping the metal sheet therein or spraying the metal sheet with the treatment solution.
Among chromate films, those coating layers formed by electrolysis cannot be said to have sufficient corrosion resistance despite the low elution of hexavalent chromium, and their corrosion resistance is particularly low when considerable film damage occurs during working, etc. On the other hand, metal sheets coated with application-type chromate films have high corrosion resistance, and especially excellent worked portion corrosion resistance, but extensive elution of hexavalent chromium from the chromate film becomes a problem. Although elution of hexavalent chromium is controlled considerably by coating with an organic polymer, it is not sufficient. A method generally known as the resin chromate method, such as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-230666, gives an improvement in the control of elution of hexavalent chromium, but it is still impossible to avoid elution of trace amounts.
As a coating method which forms films having the same functions as conventional chromate films but containing absolutely no chromium ions, there is known a method for obtaining a corrosion resistant coating layer of a cerium-containing hydroxide while generating hydrogen gas, by dipping an Al sheet in an acidic aqueous solution of about pH 1 to 3 containing cerium ions, which method is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-502655, a double-salt film of cerium ions, zirconium ions, phosphate ions and fluorine ions on aluminum, which method is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-25579, and a zinc phosphate film formed in a zinc ion, phosphate ion and lanthanum compound treatment bath, which method is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-331658; however, none of these have adequate working-follow-up properties and sufficient corrosion resistance.
It is an object of the present invention to provide a novel technique for surface treated metal materials having corrosion-resistant coating layers with working follow-up properties and excellent corrosion resistance and employing absolutely no hexavalent chromium.
DISCLOSURE OF THE INVENTION
According to a first aspect of the invention, as a result of much diligent research aimed at designing general use films which have been subjected to conversion treatment instead of the existing chromate treatment, in systems containing absolutely no hexavalent chromium, the present inventors have successfully obtained novel and revolutionary inorganic-based chemically treated films which exhibit the unique functions of the individual components, by converting a rare earth element and/or a group IVA element to an oxyacid compound (which term includes hydrogen oxyacid compounds) in the form of a paste to give the working-follow-up properties, to thus suppress corrosion by its barrier effect, inhibit cathodic reaction by the rare earth element ion and/or group IVA element ion, and induce oxyacid salt-type film passivation and oxide film-type passivation by creating an excess of the oxyacid, to inhibit anodic reaction.
According to a second aspect of the invention there is provided a surface treated metal material with an inorganic/organic composite film having an enhanced working-follow-up property and corrosion resistance, by addition of a resin to the aforementioned inorganic-based chemical treatment film.
According to a third aspect of the invention there is provided a surface treated metal material with an organic-based corrosion resistant film with an excellent working-follow-up property, by using as a corrosion resistant coating layer a film containing in a resin matrix the above-mentioned oxyacid compound, hydrogen oxyacid compound or other compound of a rare earth element and/or Group IVA element which is effective as an anticorrosion agent.
According to a fourth aspect of the invention there is provided a surface treated metal material with improved corrosion resistance, as well as increased functionality and aesthetic quality if desired, by further formation of a film composed mainly of a resin on the corrosion resistant coating layer of any of the aforementioned different surface treated metal materials.
The elements of the gist of the present invention are as follows.
(1) A surface treated metal material characterized by having a corrosion resistant coating layer composed mainly of an oxyacid compound or hydrogen oxyacid compound of a rare earth element and/or group IVA element, or a mixture thereof, on the surface of a metal material.
(2) A surface treated metal material according to (1) above, wherein the rare earth element is yttrium, lanthanum and/or cerium.
(3) A surface treated metal material according to (1) above, wherein the group IVA element is zirconium.
(4) A surface treated metal material according to (1), (2) or (3) above, wherein the anion species of the oxyacid compound and the hydrogen oxyacid compound is a polyvalent oxyacid anion.
(5) A surface treated metal material according to any of (1) to (4) above, wherein the anion species is phosphate ion, tungstate ion, molybdate ion and/or vanadate ion.
(6) A surface treated metal material according to (1) above, wherein the corrosion resistant coating layer is composed mainly of a phosphate compound or hydrogen phosphate compound of yttrium, lanthanum and/or cerium, or a mixture thereof.
(7) A surface treated metal material according to (6) above, wherein the phosphate compound or hydrogen phosphate compound is an ortho-(hydrogen)phosphate compound, meta-phosphate compound or poly-(hydrogen)phosphate compound, or a mixture thereof.
(8) A surface treated metal material according to any of (1) to (7) above, wherein the corrosion resistant coating layer further contains as an added component one or more compounds selected from among oxides, hydroxides, halides and organic acid compounds of rare earth elements.
(9) A surface treated metal material according to (8) above, wherein the rare earth element of the added component is cerium.
(10) A surface treated metal material according to (9) above, wherein the
Kaneda Yoshihiro
Sakashita Masao
Sakon Tadashi
Shoji Hiromasa
Tadokoro Kenichiro
Jones Deborah
Kenyon & Kenyon
Nippon Steel Corporation
Stein Stephen
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