1. Field of the Invention
This invention concerns esters of benzenepolycarboxylic acids with branched aliphatic alcohols and their use as hydraulic fluid, lubricants or cosmetic additives.
2. Description of the Prior Art
Esters have long been known as lubricants. They are used on a large scale as lubricating oils and greases for aircraft engines, for example. Mainly the reaction products of simple monocarboxylic acids with C8 through C10 alcohol mixtures such as those obtained in oxo synthesis, hydrogenation or aldol condensation are used. Complex esters obtained by esterification with dicarboxylic acids and/or glycols are added to the simple ester oils to improve their viscosity, shear stability and lubricant behavior. Ester oils are also used in lubricant greases such as metal soaps or silicones.
The alcohols typically used for esterification are available by oxo synthesis, for example. These alcohols are not chemically uniform and are in the form of isomer mixtures.
Ester oils are characterized by low vapor pressures, a high oxidation stability, good temperature-viscosity characteristics and high aging stability. For certain applications, they must have good miscibility with the desired operating medium. The operating medium may be, for example, pure hydrocarbons, fluorochlorocarbons or fluorocarbons. The ester may also be optimized with regard to low temperature behavior (solubility, pour point) and with regard to heat stability (flash point). Additional requirements are necessitated for compatibility with contact materials such as plastics, metals or paint coatings as required for the application. Ester oils usually have a good high-pressure capacity and load-bearing capacity.
Ester oils of aromatic polycarboxylic acids are known per se. European Patent Application 0 157 583-A2 describes the use of trimellitic acid esters synthesized from linear and/or branched primary alcohols, especially C8 through C10 alcohols. According to European Patent Application 0 157 583-A2 exclusive use of branched alcohols leads to an undesirably high viscosity and a low oxidation stability.