Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Graphite – coal – or elemental carbon
Reexamination Certificate
2002-03-29
2004-02-24
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Graphite, coal, or elemental carbon
C508S126000, C508S129000, C508S169000, C508S173000, C508S212000, C427S387000, C427S407100, C427S419100, C428S447000, C428S688000, C428S689000, C428S697000, C428S699000
Reexamination Certificate
active
06696392
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to dry film lubricants, and more particularly to dry film lubricants for coating metal-alloy substrates such as steel-, titanium-, nickel-, or aluminum-alloy substrates. The inventive dry film lubricants can also be applied to non-metals such as plastics, organic matrix composites, and ceramic matrix composites.
BACKGROUND OF THE INVENTION
Liquid lubricants, including petroleum-based lubricants, vegetable oil and animal oil-based lubricants do not perform well under a variety of environmental conditions such as high temperature applications, vacuum applications, nuclear radiation applications, and aerospace applications. Moreover, such lubricants, due to their nature, require additives such as oxidation inhibitors, or pour-point depressants that increase the viscosity of the lubricant at elevated temperatures.
Attempts to obtain a more versatile lubricant have resulted in the development of solid film lubricants. Solid film lubricants are typically thin films of a single solid or a combination of solids. Such lubricants perform well under the extreme pressures and temperatures required in applications where petroleum-based lubricants are less effective.
Some solid film lubricants that include line earth metals that may be mixed with a binder system are known. For example, a solid film lubricant including alkaline earth metal fluorides and an aluminum phosphate binder system is known. However, phosphate binders are acidic and may react with the fluorides and coagulate the lubricant. The coagulation of the lubricant makes it difficult to apply the lubricant to the desired surface. If the phosphate binder is neutralized so that it no longer reacts with the alkaline earth metal fluorides, the adhesive properties of the lubricant are either lost or diminished. Moreover, the range of temperatures that such a dry film lubricant can windstand are limited.
A need therefore exists for a dry film lubricant that is easy to apply to a surface, has a substantially neutral pH and can withstand higher temperatures compared to other bonded mixed fluoride systems. The present invention addresses this need.
SUMMARY OF THE INVENTION
Briefly describing one aspect of the present invention, there is provided a dry film lubricant coating comprising an alkaline earth metal fluoride and a silicone resin binder. The dry film lubricant coating is preferably applied as an aqueous coating composition comprising 10-70% alkali earth metal lubricant, 5-40% silicone resin binder (preferably an emulsion of about 50% resin and 50% water), and water. A wetting agent, an anti-rust agent, a porosity-inducing agent, and minor amounts of a solvent may also be included, either individually or in combination.
In another aspect of the invention the dry film lubricant coating can be applied as a solvent based system comprising 10-70% alkali earth metal fluoride, 5-40% silicone resin binder, and an organic solvent. A wetting agent and/or a porosity-inducing agent (preferably glycerine), may also be included, either individually or in combination.
In a further aspect of the invention a multi-layer, dry film lubricant coating is provided. The multi-layer coating has a basecoat layer comprising an alkaline earth metal fluoride and a silicone resin binder system, and a topcoat layer comprising a layer-lattice solid and a topcoat binder. The layer-lattice solid preferably includes graphite, and/or molybdenum disulfide, and/or tungsten disulfide. The topcoat binder preferably includes either a silicone resin (either in a solvent or as an aqueous emulsion), an aluminum phosphate, or an alkali metal silicate.
Articles coated with the inventive coatings, and methods of coating articles with the inventive dry film lubricant coatings, are also disclosed.
One object of the present invention is to provide superior dry film lubricant coatings capable of operating at a temperature of up to 2000° F. with good load bearing capability.
Further objects and advantages of the present invention will be apparent from the following description.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications of the invention, and such further applications of the principles of the invention as illustrated herein, being contemplated as would normally occur to one skilled in the art to which the invention relates.
As briefly described above, the present invention provides a system for producing single- or multi-layer dry film lubricant coatings on metallic or non-metallic substrates. Referring first to the single-layer, dry film lubricant coatings, one aspect of the present invention provides an aqueous coating composition for producing such coatings. The aqueous coating composition generally includes one or more alkaline earth metal fluorides, a silicone resin binder system, and water. An anti-rust agent, a wetting agent, a porosity inducing agent, and some solvent are also preferably included.
As to the alkaline earth metal fluorides used in the inventive coating compositions, calcium fluoride, barium fluoride, magnesium fluoride and/or cerium fluoride are preferably used, independently or in combination. All of these alkaline earth metal fluorides, and others, may be obtained commercially or may be prepared by methods known to the art.
The alkaline earth metal fluorides are generally present in the aqueous composition in amounts ranging up to 70% each. For example, BaF
2
is preferably present in amounts ranging from 10-70%, with 5% to 50% BaF
2
being more preferred, and 15-40% being most preferred. CaF
2
is preferably present in amounts ranging from 2% to 70%, with 3% to 50% CaF
2
being more preferred, and 3-30% being most preferred. MgF
2
and/or CeF
2
are preferably present in amounts ranging from 1% to 70%, with 2% to 20% being more preferred, and 3-10% being most preferred.
In certain preferred embodiments BaF
2
and CaF
2
are used in combination. Preferably, the amounts of those alkali metal fluorides range from 18-27% for BaF
2
, and from 10-18% for CaF
2
when those to metal fluorides are used in combination. In general, when barium fluoride and calcium fluoride are used together, those components are preferably included in a ratio of about 1:9 to about 9:1 by weight.
In other preferred embodiments the alkali metal fluoride comprises either BaF
2
or CaF
2
used alone. In those embodiments the amounts preferably range from 28-50% for the metal fluoride used.
In other preferred embodiments the alkali metal fluoride comprises 24-32% BaF
2
, 3-10% CaF
2
, and 3-8% magnesium and/or cerium fluoride. Most preferably, 4-6% magnesium and/or cerium fluoride is used in such compositions.
As described above, the dry film lubricant compositions also include a silicone resin. That resin may be provided as a silicone resin emulsion, or it may be provided in an appropriate solvent system.
Most preferably, the silicone resin is an alkyl silicone resin emulsion in water, such as Silres M50E or Silres MP42E, both from Wacker Chemie GmbH. The preferred emulsions have a silicone resin content of between about 35% and about 60%, with about 40-50% silicone resin being most preferred. As is known to the art, minor amounts of emulsifying agents may be included in the aqueous silicone resin emulsions. Also, an aqueous emulsion may be made from powdered alkyl silicone resin, such as MK resin from Wacker Chemie GmbH, if commercially available aqueous silicone resin emulsions are not used.
Alternatively, the silicone resin binder may be provided as a solvent-based system, either by using a commercially available silicone resin/solvent system, or by making one from powdered alkyl silicone resin such as MK resin. In solvent-based systems the solvent may be an organic solvent such as xylene,
Barber Michael J.
Klotz James M.
Naik Subhash K.
Medley Margaret
Rolls-Royce Corporation
Woodard Emhardt Moriarty McNett & Henry LLP
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