Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-10-06
2001-09-04
Dawson, Robert (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C508S108000, C523S458000, C523S459000
Reexamination Certificate
active
06284322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low-friction coating composition, and more particularly to a low friction coating composition, comprising an admixture of (1) a high temperature epoxy, (2) molybdenum disulfide powder, and (3) a polyimide powder. The present invention is also directed to a substrate coated with the low-friction coating composition of the invention, and a method of coating a substrate with the low-friction coating composition of the invention.
2. Brief Description of the Art
Low-friction coatings are useful in a wide variety of industrial applications to provide movable linkages or reciprocating parts with a low friction interface without the need for lubrication by grease, oil, or other lubricant. Low-friction coating compositions also provide high load capability with lower resistance than exhibited by metal/metal bearing contact, as well as having a relatively long life. In particular, low friction coatings have proven useful in aircraft and other industrial equipment, where severe operating conditions can occur. For example, aircraft fuel and oil pump mechanisms require repair because their gear drive bushings wear away during use. This wear (called “galling” or “scoring” or “gear wiping”) limits the longevity of the pump mechanism and results in costly rebuilding, repair, or replacement of the moving components of the mechanisms. Low-friction coating compositions have also been used on reciprocating parts, such as engine pistons, where a low-friction interface between the reciprocating part and its housing is required for optimum performance.
Under extreme conditions, the wear resistance of a low-friction or self-lubricating coating composition becomes a key factor in how that coating composition performs in any particular application. Many low-friction or self-lubricating compositions available today do not have the wear resistance properties that are required for modern high-performance machinery parts made under close tolerances. Lack of wear-resistant properties in commercially available low friction coating compositions frequently results in premature degradation of the low-friction or self-lubricating coating. Without a wear resistant low friction coating, moving parts and/or linkages suffer accelerated wear which can result in costly replacement or complete failure of the parts. Therefore, efforts have been made to improve the wear resistance of low-friction or self-lubricating coatings.
U.S. Pat. No. 4,996,085 discloses coating a pump housing surface with a composition comprising a hardenable epoxy resin, a reinforcing filler, and an agent having a lower coefficient of friction than the epoxy resin. Graphite may function as the reinforcing filler, and the frictional reducing agent may be either graphite, in fibrous or granulated form; fluorinated carbon (i.e., —(CF
x
)—wherein x<2); or molybdenum disulfide. Further, the preferred class of epoxy resin is a diglycidyl ether of a dihydric phenol (e.g., the diglycidyl ether of bisphenol A).
U.S. Pat. No. 5,316,790 discloses a lubricative coating and filler material for restoring metal surfaces that have become scratched, scored, grooved, or otherwise damaged to a functional condition. This coating and filler material is a mixture of an epoxy resin, tungsten disulfide, and isopropyl alcohol in a ratio of 9:1:1.6.
U.S. Pat. No. 5,554,020 to Rao et al. discloses a high efficiency pump having relatively-moving parts constituted of a light weight material and a coating on at least one of the parts. The coating is comprised of solid lubricants in a polymer resin matrix stable up to 700° F. The solid lubricant may be graphite, molybdenum disulphide, boron nitride, tungsten disulphide, or polytetrafluoroethylene (PTFE). The resin matrix may be one of polyimides, epoxy, or polyaryl sulphone.
U.S. Ser. No. 09/183,859 discloses a curable composition useful as a self-lubricating coating and comprising an admixture of:
(1) 40-60 wt % of a first one-component epoxy resin composition, comprising:
(a) about 10-30% by weight of 4-gylcidyloxy, n,n-diglycidyl aniline;
(b) about 30-60% by weight of an epoxy resin (an epichlorohydrin ether of bisphenol A); and
(c) about 3-7% by weight of strontium chromate;
(2) 5-20 wt % of a second one-component epoxy resin composition, comprising:
(a) about 50% to about 90% by weight of an epoxy resin (a diglycidyl ether of bisphenol A);
(b) about 5% to about 25% by weight of diethylene glycol monoethyl ether acetate; and
(c) about 5% to about 25% by weight of p-t-butylphenyl glycidyl ether;
(3) 2-30 wt % of di-epoxide reactive diluent;
(4) 2-20 wt % polytetrafluoroethylene;
(5) 2-20 wt % molybdenum disulfide; and
(6) 0.5-13 wt % mica.
The preferred self-lubricating composition disclosed by U.S. Ser. No. 09/183,859 comprises: (1) about 40% to about 60% by weight of HYSOL EA 929NA epoxy resin composition; (2) about 5% to about 20% by weight HYSOL SR1000 high solids epoxy resin/solvent mixture; (3) about 2% to about 30% by weight of ARALDITE RD-2 di-epoxide reactive diluent; (4) about 2% to about 20% of ZONYL MP1000 polytetrafluoroethylene powder; (5) about 2% to about 20% by weight molybdenum disulfide powder; and (6) and about 0.5% to about 13% H360 wet ground mica.
Copending U.S. Ser. No. 08/568,114 discloses a curable composition useful for repairing worn surfaces on housings comprising an admixture of (1) a mixture of (a) at least one one-component epoxy resin, (b) at least one solvent and (c) at least one reactive diluent, wherein the epoxy resin is present in a major (i.e., at least 50% by weight) amount in the mixture; (2) graphite powder; and (3) polytetrafluoroethylene powder.
While these coating materials may be satisfactory for certain applications, there is still need for improved low-friction coating compositions that have high wear resistance, and that are useful for a wide variety of applications including pump housings and mechanisms, pistons, or other types of reciprocating parts where high wear resistance is required. The present invention is believed to be an answer to that need.
BRIEF SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a low friction coating composition, comprising:
A. about 60 wt % to about 95 wt % of a high temperature epoxy, comprising
1. about 30 wt % to about 60 wt % of N,N′-m-phenylene dimaleimide;
2. about 30 wt % to about 60 wt % of bisphenol epoxy resin; and
3. about 1 wt % to about 5 wt % of amorphous silicon dioxide;
B. about 1 wt % to about 30 wt % of molybdenum disulfide; and
C. about 1 wt % to about 20 wt % of polyimide powder.
In another aspect, the present invention is directed to a substrate coated with the low friction coating composition of the invention.
In yet another aspect, the present invention is directed to a method of coating a substrate with a low-friction coating composition, comprising the steps of (A) coating a substrate with the above low-friction coating composition; and (B) curing the low-friction coating composition onto the substrate at a temperature of between 350 and 500° F. for 0.5-5 hours.
These and other aspects will become apparent from the following written description.
DETAILED DESCRIPTION OF THE INVENTION
The present invention offers a solution to the problem of low-friction coating compositions with insufficient wear resistance. The present inventors have unexpectedly found that a low-friction coating composition made from a combination of a high temperature epoxy resin, molybdenum disulfide, and polyimide powder provides excellent wear resistance as well as a low-friction interface between parts. The improved wear resistance exhibited by the low-friction coating composition of the invention reduces premature degradation of the low-friction or self-lubricating coating, and thereby improves the longevity of the coating.
As mentioned above, the present invention is a low-friction coating composition, comprising (A) about 60 wt % to about 95 wt % of a high temperature epoxy component, (B) about 1 wt % to about 30 wt % of
Greenberg Glen
Nazaryan Nikolay
Orkin Stanley S.
Aylward D.
Dawson Robert
Garabedian Todd E.
Simons William A.
Turbine Controls, Inc.
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