Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-02-28
2004-03-30
Sellers, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S065000, C525S113000, C525S526000
Reexamination Certificate
active
06713535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to self-lubricating coating compositions, and more particularly to self-lubricating coating compositions made from two specific resins and a specific aromatic amine, and wherein the composition is substantially free of chromate.
2. Brief Description of the Related 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.
Chromate is a know compound that is frequently used in self-lubricating compositions as a hardener or catalyst in the curing of epoxy resin systems at selected temperatures. However, chromate is also a known carcinogen, and efforts are being made to reduce or eliminate its use in epoxy resin systems. During preparation of a self-lubricating composition that contains chromate, it is possible that people may be exposed to the chromate, and could suffer toxic reactions. In addition, persons coming into contact with the self-lubricating coating after it has been applied are also susceptible to exposure to toxic chromate levels. U.S. Pat. No. 4,996,085 to Sievers 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 to Chan et al. 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 disulfide, boron nitride, tungsten disulfide, or polytetrafluoroethylene (PTFE). The resin matrix may be one of polyimides, epoxy, or polyaryl sulfone.
U.S. Pat. No. 6,090,869 to Orkin et al. 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-glycidyloxy 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 in U.S. Pat. No. 6,090,869 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.
U.S. Pat. No. 6,284,322 to Nazaryan et al. discloses a low friction coating composition, comprising (1) about 60 wt % to about 95 wt % of a high temperature epoxy; (2) about 1 wt % to about 30 wt % of molybdenum disulfide; and (3) about 1 wt % to about 20 wt % of polyimide powder, all based on the total weight of the coating composition.
U.S. Pat. No. 6,323,264 to Nazaryan et al. discloses a corrosion barrier coating composition, comprising an admixture of: (1) about 60 to about 95 wt % of a one-component epoxy resin composition comprising (a) about 10-30% by weight of 4-glycidyloxy, N,N-diglycidyl aniline; (b) about 30-60% by weight of an epoxy resin, wherein the epoxy resin is epichlorohydrin ether of bisphenol A; and (c) about 3-7% by weight of strontium chromate; (2) about 1 to about 30 wt % of polytetrafluoroethylene; and (3) about 1 to about 20 wt % of glass powder, all weight percents being based on the total weight of the composition.
Copending U.S. Pat. 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 the above 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. It is particularly desirable for a self-lubricating coating composition to be free of toxic chromate. The present invention is believed to be an answer to that need.
SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a low-friction coating composition, comprising: (a) about 10 to about 30 wt % of an epoxy resin composition consisting essentially of 4-glycidyloxy-N,N′-diglycidylaniline; (b) about 30 to about 60 wt % of an epoxide resin composition consisting essentially of bisphenol A diglycidyl ether polymer; and (c) about 20 to about 40 wt % of an aromatic
Greenberg Glenn
Orkin Stanley
Garabedian Todd E.
Sellers Robert
Turbine Controls, Inc.
Wiggin & Dana LLP
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