Process for providing coatings on a metallic surface

Details Process for providing coatings on a metallic surface Process for providing coatings on a metallic surface

2000-10-06

2002-12-03

Barr, Michael (Department: 1762)

Coating processes

Applying superposed diverse coating or coating a coated base

Synthetic resin coating

C427S318000, C427S327000, C427S407100, C427S419100, C427S421100, C427S428010, C427S430100, C427S385500, C148S243000, C148S247000, C148S250000, C148S253000, C148S275000

Reexamination Certificate

active

06488990

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for forming a coating and an organic coating.
The invention is particularly concerned with at least two different coatings on metallic surfaces and preferably on aluminum, copper, iron, magnesium, zinc or of an alloy containing aluminum, copper, iron, magnesium and/or zinc.
BACKGROUND OF THE INVENTION
The term “conversion coating” is a well known term of the art and refers to the replacement of native oxide on the surface of a metallic material by the controlled chemical formation of a film on the metallic surface by reaction with chemical elements of the metallic surface so that at least some of the cations dissolved from the metallic material are deposited in the conversion coating. Other coatings are formed on the surface of the metallic material without or without significant deposition of constituents dissolved by chemical reactions with the metallic material.
In the search for alternative, less toxic coatings than chromium containing coatings, research has been conducted on non-conversion coatings and on conversion coatings based e.g. on zirconium and/or titanium as well as fluoride containing aqueous solutions instead of chromium bearing solutions.
However, there is considerable room for improvement in the adhesion and corrosion protection properties of prior titanium/zirconium-fluoride based coatings. The need for improvement is particularly true for coatings on certain metal alloys, such as 1000, 2000, 3000, 5000 and 6000 series aluminum alloys, which coatings can have variable adherence or no adherence.
Over the years there have been numerous attempts for the replacement of chromating chemicals by ones less hazardous to the health and the environment. Their major disadvantage is that they either form coatings with poor paint adhesion properties or there are working concentrations required showing a risk of blue discoloration which does not disturb performance but makes the process undesirable in the eyes of the users. Zirconium and titanium based coating processes have found some applications in certain market niches, but they have failed in the past 25 years to replace chromating as a pretreatment prior to painting especially of aluminum, magnesium, zinc or their alloys.
Accordingly, it is an object of the present invention to provide a surface treatment process for the surface of a metallic material which overcomes, or at least alleviates, one or more of the disadvantages or deficiencies of the prior art. It is also an object of the present invention to provide an aqueous, titanium/zirconium-fluoride containing coating solution for use especially together with a further organic coating or paint. Specifically, it was an object of this invention to propose such a process to suit industrial requirements of short time formation of the coating and of near-ambient operating temperature.
It has been discovered that the combination treatment of a titanium/zirconium-fluoride treatment with an application of self assembling molecules can greatly promote corrosion resistance and paint adhesion of the coating.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a process of treating metallic surfaces showing at least two separate steps for applying two different coatings one after the other, whereby the metallic surfaces are contacted at a temperature in the range of from 10 to 100° C. first with an aqueous solution A and later on with an aqueous solution B or vice versa characterized in that the solution A contains an effective amount of zirconium, hafnium, titanium, silicon and/or boron as well as of fluoride in the form of ions and/or complex ions able to pickle the metallic surface and to generate a coating on the pickled metallic surface and that the solution B contains an effective amount of one or more compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X*, where Y is an organic group with 2 to 50 carbon atoms, where X as well as Z is a group—each same or different—of OH—, SH—, NH
2
—, NHR′—, CN—, CH═CH
2
—, OCN—, CONHOH— (=hydroxamic), COOR′ (=alkyl ester), acrylamide-, epoxide-, CH
2
═CR″—COO—, COOH—, HSO
3
—, HSO
4
—, (OH)
2
PO—, (OH)
2
PO
2
—, (OH)(OR′)PO—, (OH)(OR′)PO
2
—, SiH
3
—, Si(OH)
3
—, where R′ is an alkyl group with 1 to 4 carbon atoms, where R″ is a hydrogen atom or an alkyl group with 1 to 4 carbon atoms, and where the groups X and Z are each bound to the group Y in their terminal position, where Y* is an organic group with 1 to 30 carbon atoms, where X* as well as Z* is a group—each same or different—of OH—, SH—, NH
2
—, NHR′—, CN—, CH═CH
2
—, OCN—, CONHOH— (=hydroxamic), COOR′ (=alkyl ester), acrylamide-, epoxide-, CH
2
═CR″—COO—, COOH—, HSO
3
—, HSO
4
—, (OH)
2
PO—, (OH)
2
PO
2
—, (OH)(OR′)PO—, (OH)(OR′)PO
2
—, SiH
3
—, Si(OH)
3
—, >N—CH
2
—PO(OH)
2
—, —N—[CH
2
—PO(OH)
2]
2
-where R′ is an alkyl group with 1 to 4 carbon atoms, where R″ is a hydrogen atom or an alkyl group with 1 to 4 carbon atoms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process according to the invention may be characterized in that the metallic surfaces consist essentially e.g. of aluminum, copper, iron, magnesium, zinc or of an alloy containing aluminum, copper, iron, magnesium and/or zinc. p In the following it is not distinguished between the metallic surfaces and the already coated metallic surfaces, especially, if both possibilities may be possible at the same time, e.g. with reaction products and deposited compounds of the solution A not to make the text too complicate as the expert in the art knows what is meant. Furtheron, it is not distinguished by this term, if there is a very thin “natural” oxide and/or hydroxide layer. This oxide and/or hydroxide layer is typically extremely thin, mostly of few nm thickness. The solution A according to the invention may react chemically with the metallic surface by depositing cations in the coating being dissolved from the metallic material, but must not. Therefore, the coating is not generally called a conversion coating, although this may be in some cases a conversion coating.
Further on, it is preferred to have in the solution A concerning the fluoride content of the solution a high or very high percentage of complex fluoride and no or a low percentage of fluoride ions. In the case that in the same solution A titanium and zirconium would be present, it is preferred that the content of titanium is higher than the content of zirconium. On the other hand, it may be often preferred to have a content mainly or only of zirconium referring to chemical elements selected from the group of titanium, zirconium, hafnium, silicon and boron. Normally, no further additive is necessary for the use of solution A; in the case that a further additive is necessary, then surfactants, acids, or alkaline materials may be added. The coating formed by contacting the metallic surface may be a conversion or may be a non-conversion coating, depending on the type of metallic surface and on the contacting conditions. This coating is favorably located directly on the very thin oxide/hydroxide layer formed on the metallic surface or even directly on the metallic surface and contains often titanium, zirconium, hafnium, silicon and/or boron as well as hexafluoride and/or oxide/hydroxide. In the process according to the invention, the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* used in the solution B may preferably show a group Y with 3 to 30 carbon atoms, more preferred with 4 to 20 carbon atoms, much more preferred with 4 to 16 carbon atoms, especially preferred with 9 to 14 carbon atoms as well as a group Y* with 2 to 24 carbon atoms, more preferred with 3 to 20 carbon atoms, much more preferred with 4 to 16 carbon atoms, especially preferred with 9 to 14 carbon atoms. It is preferred that the groups X* and Z* of the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* are each bound to the group Y* in their terminal posi

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