This invention relates to thickened functional fluids characterized by substantially improved wear properties.
It is known that antiwear additives such as zinc dialkyldithiophosphates reduce wear in thickened high-water hydraulic fluids. See for example U.S. Pat. No. 4,481,125. These fluids, however, are limited in their ability to operate in equipment, such as vane pumps, at pressures above 1,000 psi.
New associative thickeners have been developed that can be used to prepare high-water hydraulic fluids which will operate in vane pumps at pressures greater than 2,000 psi. The problem is that the wear rate at these pressures is too high (generally more than 8 mg/hr) even though the fluids contain a traditionally used antiwear additive such as a zinc dialkydithiophosphate.
The instant specification discloses that the addition of certain primary amine compounds will significantly reduce the wear rate.
British Pat. No. 1,409,157 discloses reacting a metal dialkyl dithiophosphate with an amine. However, the British patent relates to a completely non-analogous art, namely, vulcanization of synthetic elastomers and has nothing to do with functional fluids.
One group of useful primary amines is disclosed in U.S. Pat. No. 4,313,004. This patent describes certain diaminoalkoxy compounds having the following structural formula: ##STR1## wherein m and n are both numbers from 0 to about 25 and m+n equals at least 1 and R.sub.1 is selected from H and a lower alkyl group having from 1 to about 4 carbon atoms and R.sub.2 is selected from H and an alkyl group containing from 1 to 10 carbon atoms.
At column 6, lines 9-10, the patent indicates that these compounds are generally used as epoxy curing agents. Other uses for the compounds are listed at column 6, lines 9-19, of the patent. It is disclosed that they can be used as oil and fuel adductive intermediates; for the formation of diisocyanate compositions; and to form polyamides. The patent, however, does not teach or suggest that such compounds can be used to reduce the wear rate of thickened hydraulic fluids which contain an antiwear additive.