Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2002-04-02
2004-12-14
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S523000, C106S014050, C106S287220, C523S440000, C523S442000, C523S445000, C523S454000, C523S457000, C523S459000, C508S110000, C525S405000
Reexamination Certificate
active
06830815
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to surface coatings for surfaces of low softening point materials that reduce the wear and friction of the surface and, more particularly, to anti-friction and anti-wear coatings compositions and methods for coating articles made of low softening point materials, such as high density polyethylene (HDPE), and to coated articles made of low softening point materials.
2. Background Art
The bearing surface of many parts in the automotive and other industries are subject to friction and wear as a result of their bearing surface rubbing against a counter surface. Because of the wear and stress associated with these parts, these parts are typically made of relatively high softening point materials, such as stainless steel and the high temperature polyester Hytrel®, which have softening points above about 450° F. These relatively high softening point materials typically are relatively heavy. Prior art anti-friction and anti-wear coatings have been used with great regularity to coat these parts to help prevent wear and friction to extend the parts lives.
In an effort to reduce the weight and cost of many articles, an effort has been underway to replace parts that typically have been made of relatively high softening point materials with parts made of lighter weight materials such as HDPE. While the aforementioned relatively high softening point materials typically have softening points above about 450° F., the lighter weight materials (HDPE) typically have softening points of less than about 300° F. While many parts that have typically been made of relatively high softening point materials have been replaced over the years with parts made of lower softening point materials, such as HDPE parts, replacing parts made with relatively high softening point materials that are subject to wear and friction at their interfaces with parts made of relatively low softening point (lightweight) materials have not been met with great success. This is because the anti-wear and anti-friction coatings that coat the parts made of relatively high softening point materials typically have curing temperatures above 350° F., well in excess of the softening temperatures of the lighter weight material (HDPE) parts. As such, the anti-friction and anti-wear coatings that have typically been used to coat the higher softening point metals would not be acceptable for coating the lighter weight lower softening point material parts.
Accordingly, it would be desirable to provide an anti-wear and anti-friction coating composition that would be suitable for use with parts made of materials such as HDPE that are relatively lightweight and have relatively low softening points.
SUMMARY OF INVENTION
The present invention relates to an anti-friction and anti-wear coating composition for use with parts made of materials that have softening points below about 300° F. The coating composition comprises a mixture of (i) solid lubricants comprising boron nitride, graphite and molybdenum disulfide, (ii) one or more thermoset resins, (iii) catalyst for curing the resin, and (iv) a solvent system comprising highly volatile solvents.
The present invention also relates to a method of coating high density polyethylene (HDPE) parts and parts made from other low softening point materials with an anti-friction and anti-wear coating composition that comprises a mixture of (i) solid lubricants comprising boron nitride, graphite and molybdenum disulfide, (ii) one or more thermoset resins, (iii) catalyst for curing the resin, and (iv) a solvent system comprising highly volatile solvents.
The present invention also relates to articles made of low softening point materials that are coated with the cured product/coating of the coating composition described herein.
DETAILED DESCRIPTION
The present invention relates to a liquid anti-friction and anti-wear coating composition that can be readily deposited at low temperatures (i.e., from room temperature to about 200° F.) in a thin film that presents a low coefficient of friction, and that is curable to form a coating that has durability at high temperatures (i.e., 400° to 700° F.) and has good load bearing capabilities. The coating composition is relatively low in viscosity and preferably has a viscosity of between about 5 to 75 centipoise at 25° C., more preferably between about 10 and 60 centipoise at 25° C., and most preferably between about 15 to 50 centipoise at 25° C.
The coating composition is comprised of a mixture of solid lubricants comprising boron nitride, graphite and molybdenum disulfide, one or more thermoset resins, catalyst for curing the resin, and a solvent system comprising highly volatile solvents.
Preferably, the solid lubricant mixture is present in the composition in an amount of about 12 to 35 weight percent of the total weight of the composition, more preferably about 15 to 28 weight percent, and most preferably about 20 to 23 weight percent. Preferably, the thermoset resins are present in the composition in an amount of about 15 to 30 weight percent of the total weight of the composition, more preferably about 18 to 26 weight percent, and most preferably about 21 to 24 weight percent. Preferably, the solvent system is present in the composition in an amount of about 35 to 75 weight percent of the total weight of the composition, more preferably about 45 to 65 weight percent, and most preferably about 52 to 58 weight percent.
The solid lubricants should preferably constitute about 30-70% by weight of the cured coating. The graphite should preferably constitute about 25-58% by weight of the solid lubricants, the molybdenum disulfide (MoS
2
) should preferably constitute about 25-58% of the solid lubricants and the boron nitride (BN) should preferably constitute about 7-16% of the solid lubricants. The solid lubricants can also comprise about 5-20% by weight of LiF, CaF
2
WS
2
, a eutectic of LiF/CaF
2
or LiF/NaF
2
.
Particle sizes of the individual solid lubricant mixture ingredients may be as follows: graphite is introduced into the mixture in the range of about 0.5-45 microns, molybdenum disulfide in the range of about 0.3-45 microns, and boron nitride at about five microns. The mixture is typically ball-milled to produce an average particle size of about 0.3-10 microns.
The mixture provides for a temperature stability up to temperatures as high as about 700° F., load bearing capacities well above about 10 psi, and excellent oil attraction capability. The mixture of graphite, molybdenum disulfide and boron nitride provides a coefficient of friction which is in the range of about 0.07-0.08 at room temperature and a coefficient of friction as low as about 0.03 at about 700° F.
The thermoset resin is an organic material that has been selected to yield high molecular weight polymer and a tendency to flow on stress before being polymerized. The thermoset resin is advantageously an epoxy, such as bisphenol A, because of enhanced oil affinity properties and higher load bearing capabilities (about 6 psi), phenol formaldehyde, urea formaldehyde, melamine formaldehyde, alkyd polyester, or epoxy. Other resins, such as vinyl butyryl, can also be present. Preferably two or more of the above resins are present and more preferably an epoxy resin and a vinyl butyryl resin are present. The carrier for such polymer or resin may be mineral spirits or butyl acetate.
The composition also preferably contains a curing agent present in an amount of 1-5 wt. % of the composition such as dicyanidimide. Tertiary amine catalyst may also be preferably present in an amount of 0.1-0.8 wt. % of the composition. The composition may also contain a dispersing agent present in an amount of 0.3-1.5 wt. % such as 2, 4, 6 tri dimethlamino ethyl phenol.
The solvent system comprises one or more highly volatile solvents such as methyl ethyl ketone, mineral spirits, 2-propoxy ethanol, xylene and diacetone alcohol. Preferably, the solvent system has an evaporation/boiling point below about 165° F. and more preferably below about 150° F. w
Brooks & Kushman P.C.
Dawson Robert
Feely Michael J.
Ford Motor Company
Porcari Damian
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