The problems associated with the lubrication of gears such as utilized in automotive transmissions and axles are well known to those skilled in the art. In the lubrication of automatic transmissions, proper fluid viscosity at both low and high temperatures is essential to successful operation. Good low temperature fluidity eases cold weather starting and insures that the hydraulic control system will properly "shift gears". High viscosity at elevated temperatures insures pumpability and the satisfactory operation of converters, valves, clutches, gears and bearings.
It also is well known that the high pressure which occurs in certain types of gears and bearings may cause rupture of lubricant films with consequent damage to the machinery. Because of the severe conditions under which they are used, industrial and automotive gear lubricants ordinarily must contain additives which maximize their capability of functioning under extreme pressure conditions. It has been suggested that certain compounds of metal-reactive elements, such as compounds of chlorine, sulfur, phosphorus and lead impart extreme pressure properties to various lubricants. Among the various compositions known to serve this purpose are various phosphorus- and sulfur-containing compositions, chiefly salts and esters of dialkylphosphorodithioic acids, and sulfurization products of various aliphatic olefinic compounds. These two types of compositions have been used in combination in lubricants of this type, and they serve to increase the effectiveness of the lubricant under conditions of extreme pressure.
In addition to extreme pressure agents, lubricating compositions useful as gear lubricants generally will contain one or more of the following: dispersants, detergents, pour point depressants, oxidation inhibitors, corrosion inhibitors, foam inhibitors, friction modifiers and viscosity improvers.
Lubricating and industrial oil compositions contain dispersants which are capable of dispersing sludge and other deposits formed in the oil compositions in use. Unless maintained in fine suspension (i.e., dispersed in the lubricating or industrial oil) the sludge deposits on gears, bearings and seals where it eventually interferes with equipment operation. Dispersants which have been used extensively in lubricants and functional fluids include the so-called ashless dispersants. These dispersants are referred to as being ashless because they do not ordinarily contain metal and therefore do not yield a metal-containing ash on combustion. Many types of ashless dispersants are known in the art, and they are described more fully below.
It is well known that water is an undesirable contaminant in lubricants and functional fluids. Water not only reduces the effectiveness of the lubricant or fluid, it tends to form deleterious by-products, particularly in relation to the metal parts in contact with or utilizing the lubricant or functional fluid. For example, water present in a lubricant is responsible for the formation of objectionable mayonnaise-like sludge which in turn promotes the formation of hard-to-remove deposits from various parts of the machinery being lubricated. Presumably, the formation of the sludge is preceded by the water forming an emulsion with the lubricant oil. While water should be separable from an oil or functional fluid due to immiscibility, some of the additives in the lubricants or functional fluids may have water-solubility sufficient to form emulsions which are difficult to remove. Also, the presence of additives such as ashless dispersants and detergents facilitate the formation and increase the stability of emulsions thereby making it difficult to separate the water from the oil or functional fluid. Therefore, it is important to minimize the presence of water in lubricating compositions and functional fluids to reduce or eliminate the formation of such emulsions.
Obviously, lubricants having minimum contact with water will not present serious problems of water-oil emulsions. However, it is difficult to eliminate contact with water, particularly during storage, handling, and/or use (e.g., in a steel mill environment).
Demulsifiers have been suggested and used in the prior art. Primarily, these demulsifiers have comprised compositions such as polyoxyalkylene glycols and polyoxypolyamines. It has been observed, however, that these glycols and polyamines have not been entirely satisfactory because of their limited use and inability to function except in specific lubricants or functional fluids.
U.S. Pat. No. 4,129,508 describes a demulsifier additive composition for lubricants and fuels which comprises (A) one or more reaction products of a hydrocarbon-substituted succinic acid or anhydride with one or more polyalkylene glycols or monoethers thereof, (B) one or more organic basic metal salts, and (C) one or more alkoxylated amines.
The use of various derivatives of imidazolines as friction-reducing additives in lubricating compositions is described in U.S. Pat. Nos. 4,406,802; 4,298,486; and 4,273,665. The '802 patent describes the use of mixed borated alcohol-amines, alcohol-amides, alcohol-ethoxylated amines, alcohol-ethoxylated amides, alcohol-hydroxy esters, alcohol-imidazolines and alcohol-hydrolyzed imidazolines and mixtures thereof as friction-modifying agents in various organic media. The borated derivatives include those derived from hydroxy alkyl or hydroxy alkenyl alkyl or alkenyl imidazolines and/or the hydrolysis products of the imidazolines. The '486 patent describes boric acid salts and borate esters of hydroxyethyl alkyl imidazolines whereas U.S. Pat. No. 4,273,665 describes the use of hydrolysis products of 1-(2-hydroxyalkyl)-2-alkyl or alkenyl imidazolines and borated adducts of hydrolyzed 1-(2-hydroxyethyl)-2-alkyl imidazolines as friction modifiers for lubricating oils. In addition to exhibiting friction-reducing properties, the imidazoline derivatives described in the above patents are reported to provide the lubricant with copper anticorrosion and antioxidant properties.