Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-08-02
2001-08-07
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C106S014110, C106S014210, C106S014410, C106S014440, C427S487000, C427S515000, C427S517000, C428S331000, C428S341000, C428S450000
Reexamination Certificate
active
06270884
ABSTRACT:
BACKGROUND OF THE INVENTION
A variety of at least substantially resin-free, chromium-containing coating compositions for protecting ferrous substrates are known. Of special interest are those which contain particulate metal. Representative coating compositions of this type that were initially developed could be quite simplistic, such as compositions containing essentially chromic acid and particulate metal in an alcohol medium, as disclosed in the U.S. Pat. No. 3,687,738.
A later development of particular effectiveness for providing a corrosion-resistant coating on metal substrates was the more complex composition such as shown in U.S. Pat. No. 3,907,608. The composition comprised chromic acid, or equivalent, a particulate metal of mainly zinc or aluminum, wetter and a liquid medium comprising water plus high-boiling organic liquid. The composition had very desirable coating characteristics when including a viscosity modifier such as a water-soluble cellulose ether, as disclosed in U.S. Pat. No. 3,940,280.
The coating could be especially useful as an undercoating. Thus it has been taught to use such a more complex coating composition as an undercoating over ferrous surfaces. The coating is then provided with a silicate topcoating, as disclosed in U.S. Pat. No. 4,365,003. Another topcoating that could be utilized is a weldable primer, most notably a zinc-rich primer, which may be typically applied before electrical resistance welding of the substrate, as discussed in the hereinbefore mentioned U.S. Pat. No. 3,940,280.
It has been known that where coating compositions could contain the particulate metal as untreated aluminum flake, such flake can be unstable in water-based coating compositions. In such water-based coating compositions, standard aluminum flake will react with water in the composition to form hydrogen gas. One approach for avoiding this problem has been to coat the aluminum flake. One such coating is an acrylic coating formed by reacting mono-ethylenically unsaturated silane with acrylic monomers having amine hydroxyl or epoxy groups, as disclosed in U.S. Pat. No. 4,213,886. However, these products are specialty items tailored to provide a coating of good glamour appearance and have not found a wide acceptance.
Another approach to improving the coating composition was to consider the chromic acid constituent. As taught in U.S. Pat. No. 4,266,975 this constituency can be partially replaced by boric acid component. However, some chromic acid for the constituency is retained.
For coating compositions for providing corrosion-resistance to metal substrates, which compositions are of the particular type referred to as “wash primers”, such have conventionally contained zinc chromate pigment. Attempts have been made with these primers to provide anti-corrosion primers free from chromium, thus reducing potential pollution problems. There has been proposed, as disclosed in U.S. Pat. No. 4,098,749, a coating composition containing a polyvinyl butyral resin, an organofunctional silane, a borate or polyphosphate compound and phosphoric acid. The composition may contain a metal powder as an optional ingredient and usually a phenolic resin. Such compositions, however, are not suitable as replacements for the above-discussed complex compositions of pulverulent metal and chromium-providing substance, owing in part to their resin content.
There has also been proposed the preparation of coating compositions that contain hydrolyzed organotrihydrocarbonoxy silane and a particulate metal. These compositions, such as disclosed in U.S. Pat. No. 4,218,354, can provide corrosion protection to a coated substrate. However, the silanes utilized are not water-reducible. Rather, they react with water and may readily form a gel, unless the reaction takes place in the presence of organic liquid. The compositions can thus have limited utility.
More recently, it has been taught in U.S. Pat. No. 5,868,819 that composition substituents which are epoxy functional silanes, and which are water-reducible, can be useful in forming compositions for coating metal substrates. The compositions rely on a variety of ingredients to provide for a chrome-free system.
As mentioned hereinabove, corrosion-resistant coatings can be combinations of undercoatings and topcoatings. The topcoatings can be solvent-based weldable zinc-rich primers. For the topcoatings, such as these zinc-rich primers, it has been proposed, as disclosed in U.S. Pat. No. 4,476,260, to enhance primer corrosion-resistance by formulating a primer to contain zinc pigment, a thermoplastic or thermosetting resin, an organosilane, and optionally aluminum trihydrate with one or more dispersing agents. Such compositions, however, are not suitable as replacements for the complex undercoating compositions, and would be useful in the combination of coatings as the zinc-rich topcoating.
It would, therefore, be desirable to provide a coating composition which could have the wide acceptance of the complex undercoating compositions. It would further be desirable to provide such compositions, which would avoid the pollution problems associated with the compositions which contain hexavalent chromium, as well as avoid compositions which are solvent-based.
SUMMARY OF THE INVENTION
The present invention offers a water-reducible coating composition, generally referred to herein as a water-based coating composition, having highly desirable characteristics such as providing a coating offering desirable corrosion-resistance on coated steel parts. In addition to corrosion-resistance, the deposited film has desirable coating adhesion on the substrate. For small, threaded parts, such as threaded fasteners, the coating can be a non-thread filling coating. The composition is chrome-free in addition to being water-reducible. Coating application equipment can thereby be readily cleaned and the cleaning liquid can be easily and economically disposed. The coating composition of the present invention can virtually always readily be a one-package composition, thereby providing ease of preparation, storage and transport as well as use. The composition lends itself to extended storage stability and offers enhanced flexibility in choice of ingredients for preparing a most economical and efficient composition.
In one aspect, the invention is directed to a chrome-free, stable and water-reducible coating composition for application to, and heat curing on, a substrate for providing corrosion protection thereto, which composition comprises:
(A) water in an amount supplying from about 20 to about 70 weight percent of the coating composition;
(B) low-boiling organic liquid;
(C) particulate metal;
(D) water-reducible, organofunctional silane binding agent containing alkoxy groups, which binding agent contributes from about 3 to about 20 weight percent of the total composition weight; and
(E) wetting agent;
and with the proviso that the coating composition has a molar ratio of water to silane alkoxy groups above 4.5:1.
In another aspect, the invention is directed to the above-noted coating composition additionally containing one or more of typically boric acid component and/or corrosion-inhibiting substituent.
Another aspect of the invention is directed to a coated substrate protected with a chrome-free, corrosion-resistant coating of the deposited and cured film from the herein-described coating composition. In another aspect, the invention is directed to a method of preparing a corrosion-resistant coated substrate by applying the herein described coating composition to the substrate in an amount to provide at least about 500 milligrams per square foot (mg/ft
2
) of coating on the substrate upon curing the applied composition on the substrate at a temperature up to about 650° F. for a time of at least about 5 minutes.
In a still further aspect, the invention is directed to preparing the coating composition by premixing silane binding agent with aqueous medium, or organic liquid, or both aqueous medium and organic liquid, and then using the resulting premix in subsequent processing compris
Dorsett Terry E.
Germano Victor V.
Guhde Donald J.
Gunn Walter H.
Maze Etienne
Freer John J.
Le Hoa T.
Metal Coatings International Inc.
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