Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
1999-01-22
2002-05-07
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S259000, C148S260000, C106S014120, C106S014440, C106S014450, C252S384000, C252S393000
Reexamination Certificate
active
06383307
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous autodepositable composition that is useful as a metal surface treatment.
It is well-known that metal surfaces are subject to corrosive and chemical degradation. This degradation has been combated by the application of various treatments to the metal surface. Conversion coating of the metal sur face is one such treatment. Conversion coating generally involves treating the surface with chemicals that form a metal phosphate and/or metal oxide conversion coating on the metal surface. The conversion coating provides protection against corrosion and can enhance adhesion of any subsequent coatings. Phosphatizing is a well-established conversion process. However, phosphatizing suffers from several drawbacks. It is a complex multistep process that is capital intensive, requires close monitoring and can generate significant amounts of waste sludge. In addition, phosphatizing requires oxidative accelerators that promote corrosion and thus must be removed by multiple rinsing steps. Conventional inorganic phosphate conversion coatings are also very brittle and thus can fracture. A seal coat also is typically applied for good corrosion resistance that often includes hexavalent chrome which presents considerable environmental problems.
It is also generally known that the corrosion resistance or metal substrates can be improved by coating the substrate with an autodeposition composition that generally comprise an aqueous solution of an acid, an oxidizing agent and a dispersed resin. Immersion of a metallic surface in an autodeposition composition produces what is said to be a self-limiting protective coating on a metal substrate. The general principles and advantages of autodeposition are explained in a multitude of patents assigned to Parker Amchem and/or Henkel (see, for example, U.S. Pat. Nos. 4,414,350; 4,994,521; 5,427,863; 5,061,523 and 5,500,460).
U.S. Pat. No. 5,691,048 includes phosphoric acid in a list for possible acids in an autodepositing composition, but hydrofluoric acid is the preferred acid. This patent also lists hydrogen peroxide, chromic acid, potassium dichromate, nitric acid, sodium nitrate, sodium persulfate, ammonium persulfate, sodium perborate and ferric fluoride as possible oxidizing agents. Hydrogen peroxide and ferric fluoride are preferred.
Phosphatizing is also a well-known conversion treatment for providing corrosion resistance to metal surfaces. U.S. Pat. No. 5,011,551 relates to a metal conversion coating composition that includes an aliphatic alcohol, phosphoric acid, an alkali nitrate, tannic acid and zinc nitrate. U.S. Pat. No. 4,293,349 relates to a steel surface protective coating composition that includes pyrogallic acid glucoside, phosphoric acid, phosphates of bivalent transition metals such as Zn or Mn, Zn or Mn nitrate, and, optionally, formaldehyde.
An environmentally acceptable, user-friendly metal treatment with superior corrosion resistance and fracture toughness would be very desirable.
SUMMARY OF THE INVENTION
According to the present invention there is provided an aqueous metal surface treatment composition that includes (A) an aqueous dispersion of a phenolic novolak resin that includes water and a reaction product of a phenolic resin precursor, a modifying agent and a multi-hydroxy phenolic compound wherein the modifying agent includes at least one functional moiety that enables the modifying agent to react with the phenolic resin precursor and at least one ionic moiety, (B) an acid and, optionally, (C) a flexibilizer. According to one embodiment the modifying agent is ail aromatic compound. According to another embodiment the ionic moiety of the modifying agent is sulfate, sulfonate, sulfinate, sulfenate or oxysulfonate and the dispersed phenolic resin reaction product has a carbon/sulfur atom ratio of 20:1 to 200:1.
The metal treatment composition preferably is applied to electrochemically active metals such as steel. This treatment improves adhesion of subsequent coatings such as primers and adhesives to the metal surface and it improves corrosion resistance. Since this treatment requires only a minimum number of coatings—typically less than three and often only a single coating—it is much more user friendly than conventional phosphatizing and eliminates the need for a seal coat. In addition, the metal treatment generally does not require any rinsing steps subsequent to application of the metal treatment composition. A unique feature of the invention is that the metal treatment composition is autodepositable.
It has also been discovered that metal substrates treated with the compositions of this invention may require sitting at ambient conditions (approximately 25° C.) for an extended time period after autodepositing and drying (approximately 2 to 24 hours after drying) and prior to application of a subsequent coating of a different composition. This intermediate time period is referred to herein as the “ambient staging period”. Without this ambient staging period the corrosion resistance of the final product was inconsistent for certain demanding commercial applications. In addition, formation of a uniformly thick metal treatment coating is required for superior corrosion resistance. Too thin or too thick a coating also can be detrimental to corrosion protection.
Addition of a control agent to autodeposition compositions has been found to dramatically improve uniform coating formation on more complex surface topography and enhance the autodeposition of subsequently-applied compositions thus improving corrosion resistance and overall robustness. The protective coating formed by the composition of the invention is particularly useful for providing corrosion resistance to metal substrates that are subjected to significant stresses and/or strains causing significant flexing or movement of the substrate surface. Due to the improved deposition caused by the control agent, the concentration of active ingredients in an autodepositable composition that includes the control agent can be reduced. Another advantage of the invention is that there is no need to post-rinse the treated surface in order to remove only control agent residue. Furthermore, the control agent eliminates or substantially eliminates the ambient staging period thus improving process efficiency.
Accordingly, a further embodiment of the invention provides an aqueous autodeposition composition that includes an autodepositable component and a control agent, preferably an organic nitro material. The autodepositable component preferably is an aqueous phenolic resin dispersion, particularly the aqueous novolak dispersion mentioned above. The autodeposition composition is particularly useful as a metal treatment composition that also includes an acid, especially phosphoric acid.
According to another embodiment of the invention there is provided a method for treating a metal surface that includes applying to the surface an aqueous autodeposition composition that includes an autodepositable component and the control agent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Unless otherwise indicated, description of components in chemical nomenclature refers to the components at the time of addition to any combination specified in the description, but does not necessarily preclude chemical interactions among the components of a mixture once mixed.
Certain terms used in this document are defined below.
“Primer” means a liquid composition applied to a surface as an undercoat beneath a subsequently-applied covercoat. The covercoat can be an adhesive and the primer/adhesive covercoat forms an adhesive system for bonding tab two substrates together.
“Coating” means a liquid composition applied to a surface to form a protective and/or aesthetically pleasing coating on the surface.
“Phenolic compound” means a compound that includes at least one hydroxy functional group attached to a carbon atom of an aromatic ring. Illustrative phenolic compounds include unsubstituted phenol per se, substituted phenols such as alkylated phen
He Yuan
Kucera Helmut W.
Dearth Miles B.
Lord Corporation
Oltmans Andrew L.
Sheehan John
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