Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Ptfe
Reexamination Certificate
2001-03-14
2002-10-08
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Ptfe
C508S582000
Reexamination Certificate
active
06461998
ABSTRACT:
The present invention relates to the use as lubricants having a low friction coefficient and an improved noise reduction among moving mechanical parts, preferably mechanical parts in polymer material, of concentrated dispersions dilutable with water.
More specifically the present invention relates to concentrated dispersions dilutable with water comprising a lubricant having a (per)fluoropolyether structure, a (per)fluoropolymer, water, a surfactant and optionally a fluorinated solvent, and to the above dispersions when they are used for the above application. Said dispersions can be used, even in very thin layers, for the lubrication for example of miniaturized gears, flat surfaces both in plastomer and metal material, surfaces in plastic material in contact with painted surfaces, seal gaskets, moulds for moulding plastomer and elastomer materials, lubrication of hinges in plastic or metal material.
The concentrated dispersions in order to be applied in a thin layer require a dilution with water: the usable dispersions according to the invention must therefore be dilutable with water and therefore they must be continuous in water. The non dilution with water would lead to biphasic systems unsuitable to give continuous liquid layers on the substrata to be lubricated.
The treatment of surfaces and articles with dispersions of PTFE as dry lubricant is known in the prior art, applying said dispersions and evaporating the solvent, leaving as a result an uniform layer of PTFE at a dry state. Dispersions in water or in organic solvents (for example isopropanol), for example Vydax®, are marketed; they contain PTFE having a low molecular weight at a concentration in the range 20-30% by weight. These dispersions in order to be used must be diluted at about 2% of dry product. A solvent used for this purpose was CFC 113 for its high volatility. However it is well known that CFCs cannot be used any longer according to the Montreal Protocol due to their environmental impact.
A partial solution to these drawbacks has been obtained by adding to said dispersions hydrochlorofluorocarbons (HCFC), such as for example 141b, alone or in combination with (per)fluorocarbons. This solution, as said, is partial since also HCFCs are subjected to restrictions according to the Montreal Protocol and later amendments due to their impact on the atmospheric ozone. A solution to this problem has been suggested in U.S. Pat. No. 5,532,310, which relates to dispersions of fluoropolymers in (per)fluorinated liquids, wherein the (per)fluorinated liquids are included in the continuous phase. The dispersions have sufficient stability to be used for preparing coatings. This patent relates also to the preparation of emulsions of (per)fluorinated liquids and polar solvents. The dispersions of the patent are formed by four main components: a (per)fluorinated solvent, a polar solvent (including water and polar organic solvents), a (per)fluoropolymer under the form of dispersed particles, typically PTFE, and a surfactant selected from specific classes. Typically the system comprises as main component the (per)fluorinated solvent. The teaching of this patent relates to the preparation of a (per)fluoropolymer coating such as for example PTFE to be used as dry lubricant, starting from an emulsion of fluorinated solvents and polar hydrogenated solvents or water.
The drawback of the PTFE-based dispersions used as dry lubricant resides in that the lubricant properties are not very high since the friction coefficient is rather high and there is not a meaningful noise reduction.
The use of greases formed by mixtures of PTFE and (per)fluoropolyether (PFPE) oils as lubricants for bearings, sliding surfaces, etc. is also known in the prior art. These greases are viscous systems and are not substantially suitable to be used as lubricants in thin films.
It is known that dispersions of fluorinated PFPE oils in water have low stablity. It has been recently found by the Applicant, see EP 894,838, that dispersions having improved stability to separation during the time, comprising (per)fluorinated solvents and (per)fluorinated polymers, specifically PTFE, can be prepared by mixing a fluoropolymer in polar solvent water and/or alcohol, with a fluorinated liquid having a (per)fluoropolyether or (per)fluorocarbon structure, in the presence of specific surfactants. The dispersions comprise from 0.1 to 30% by weight of PTFE, 50-99% by weight of fluorinated liquid, from 0.01 to 5% by weight of a surfactant selected from particular classes and polar solvent complement to 100% by weight. The fluorinated liquids are (per)fluoropolyethers having a number average molecular weight 250-5,000, preferably 350-1,000, or liquid (per)fluorocarbons or mixtures thereof. These dispersions can be obtained in various ways and using various starting components. The preparation of the dispersions can be carried out by a process comprising the following steps. One starts from dispersions of fluorinated polymers in polar solvent water and/or alcohol (step a′)), surfactants are added (step b′)) and subsequently a (per)fluoropolyether or (per)fluorocarbon liquid such that the ratio by weight polymer/(per)fluorinated liquid is lower than 0.7 (step c′)). The (per)fluoropolymer dispersions in polar solvent used in a′) are the (per)fluoropolymer dispersions in alcohol or the latexes directly obtained from polymerization processes using water. The concentration of (per)fluorinated polymers in the latexes ranges from 20 to 50% by weight. Said latexes can optionally be concentrated up to 60-75% by weight of (per)fluoropolymer. The (per)fluoropolymer/polar solvent system of step b′) is obtained by a gelification process of the aqueous latexes of step a′), neutralization and dispersion of the gel. In the gelification process high yields of transfer of the PTFE polymer from the polar solvent to the fluorinated organic phase, are obtained. In most Examples wherein the gel formation process is used, a PTFE dispersion in the fluorinated organic liquid containing a very low amount of water, of the order of some percent by weight, for example 2-7%, is therefore obtained. In the Examples wherein the gelification process is not used but a simple mixing of the phases, i.e. by directly using the initial dispersion of the (per)fluoropolymer, a biphasic system can be obtained consisting of a (per)fluoropolymer dispersion in fluorinated solvent having a very low water content, lower than about 20% by weight, and of an aqueous phase which substantially comprises most part of the (per)fluoropolymer and the surfactant, wherein the fluorinated solvent is practically absent.
In the Examples in which the (per)fluoropolymer is used under the form of concentrated latex, stabilized by non ionic surfactants such as for example Triton® X100, the system obtained by the process is formed by a mixture comprising water in a percentage in the range 10-20% by weight and (per)fluoropolymer in the range 15-25% by weight. The remaining part of the mixture is formed by (per)fluoropolyether solvents. In the reported application Example (Example 21) a coating formed by a continuous polymer film of (per)fluoropolymer is described, obtained from this dispersion through the complete evaporation of all the solvents (water and fluorinated solvents).
From the prior art no indication is available about the preparation of aqueous dispersions of (per)fluoropolyether lubricants dilutable with water to give a continuous phase and especially of dispersions able to give lubricant films having a low friction coefficient and an improved noise reduction among moving mechanical parts, preferably mechanical parts in polymer material.
The need was felt to have available stable dispersions of fluorinated oils in aqueous medium in order to minimize the environmental impact of solvents and to improve the performances of the applications of lubricant having the combination of the indicated properties in thin films for the lubrication for example of miniaturized gears, flat surfaces both in plastom
Carignano Gabriella
Lenti Daria
Arent Fox Kintner Plotkin & Kahn
Ausimont S.p.A.
McAvoy Ellen M.
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