Synthetic lubricating oils

A synthetic lubricating oil comprising as a base oil a mixture of (i) at least one carbonic acid ester selected from the group consisting of:

• [I] a carbonic acid ester represented by the general formula (1) ##STR21## wherein R.sup.1 and R.sup.2 are identical with, or different from each other and are each a group selected from the group consisting of alkyl groups having 1-15 carbon atoms and dihydric alcohol residues having 2-12 carbon atoms, R.sup.3 is an alkylene group having 2-12 carbon atoms, and a is an integer of 1-30;
• [II] a carbonic acid ester represented by the general formula (2) ##STR22## wherein X.sup.1 is a hydrogen atom or a group represented by the general formula ##STR23## R.sup.5 and R.sup.6 are identical with, or different from, one another and are each a group selected from the group consisting of alkyl groups having 1-12 carbon atoms, cycloalkyl groups having 5-12 carbon atoms and neopentyl type polyol residues having 5-30 carbon atoms and 3-8 hydroxyl groups;
• R.sup.7 is an alkyl group having 1-6 carbon atoms;
• b is an integer of 1 or 2, c is an integer of 0 or 1 with the proviso that the sum of b and c equals to 2;
• d is an integer of 0-30, at least one of R.sup.4 and R.sup.5 indicating a neopentyl type polyol residue when d is 0;
• and e is an integer of 1-3;
• and
• [III] a carbonic acid ester other than said carbonic acid esters [I] and [II], which is prepared from a source of carbonic acid moieties and the following alcoholic components:
• (A) a monohydric alcohol,
• (B) a dihydric alcohol, and
• (C) a neopentyl type polyol having 5-7 carbon atoms and 3-4 hydroxyl groups, or a dimer or trimer of the polyol, and
• (ii) at least one oil selected from the group consisting of
• (a) a polyoxyalkylene glycol or an ether thereof represented by the general formula (3) ##STR24## wherein R.sup.8 and R.sup.9 are each a hydrogen atom or an alkyl group having 1-18 carbon atoms, R.sup.10 is an alkylene group having 2-4 carbon atoms, and f is an integer of 5-70.
• (b) a polyoxyalkylene glycol glycerol ether represented by the general formula (4) ##STR25## wherein R.sup.11 -R.sup.13 are each a hydrogen atom or an alkyl group having 1-18 carbon atoms, R.sup.14 -R.sup.16 are each an alkylene group having 2-4 carbon atoms, and g-i are each an integer of 5-7.
• (c) an ester represented by the general formula (5) ##STR26## wherein X.sup.2 is a group represented by the general formula --OR.sup.19 or ##STR27## X.sup.3 is a group represented by the general formula ##STR28## R.sup.17 and R.sup.23 are each an alkylene group having 1-8 carbon atoms, R.sup.18 and R.sup.20 are each an alkylene group having 2-16 carbon atoms, R.sup.19 and R.sup.24 are each an alkyl group having 1-15 carbon atoms, R.sup.21 and R.sup.22 are each an alkyl group having 1-14 carbon atoms, j and k are each an integer of 0 or 1 and .rho. is an integer of 0-30.
• (d) a polyol ester represented by the general formula ##STR29## wherein X.sup.4 is a group selected from the group consisting of methyl group, ethyl group, propyl group and groups represented by the general formula ##STR30## R.sup.25 -R.sup.28 may be identical with, or different from, each other and are each a group selected from the group consisting of straight-chain alkyl groups having 3-11 carbon atoms, branched-chain alkyl groups having 3-15 carbon atoms and cycloalkyl groups having 6-12 carbon atoms, the straight-chain alkyl groups being present in a ratio of not more than 60% of the total alkyl groups, and m is an integer of 1-3, and
• (e) a polyol dicarboxylic acid ester represented by the general formula (7) ##STR31## wherein X.sup.5 and X.sup.6 may be identical with, or different from, each other and are each a group selected from the group consisting of methyl group, ethyl group, propyl group and groups represented by the general formula ##STR32## R.sup.29 -R.sup.33 may be identical with, or different from each other and are each an alkyl group having 3-15 carbon atoms, R.sup.34 is a divalent hydrocarbon group having 1-8 carbon atoms, and n is an integer of 1-5.