Engine oil composition

Abstract: The invention provides an engine oil composition characterized by containing a major amount of lubricating base oil and (a) about 0.01 to 30 % by weight of an overbasic oil-soluble metal salt prepared by use of an alkaline-earth metal borate, (b) about 0.01 to 5 % by weight of a friction modifier, (c) about 0.01 to 5 % weight of an antioxidant as essential components, on the basis of the total amount of the composition.

Description: Background of the Invention (1) Field of the Invention This invention relates to an engine oil composition, and more particularly to an engine oil composition useful as a lubricating oil for gasoline engine, diesel engine, and the like. (2) Description of the Prior Art Because of increased concern regarding the energy-saving measures to counter oil shocks, the research for a fuel-saving internal combustion engine lubricating oil has been recently intensified. As measures for fuel-saving by use of lubricating oil to meet such situation, the following measures are now under review among business circles: (a) Lowering viscosity of lubricating oil with the intention of reducing engine friction loss under hydrodynamic lubricating conditions, and (b) Addition of friction reducers with the intention of reducing engine friction loss under mixed and boundary lubrication. Addition of friction modifiersto lubricating oil is indispensable especially in latest fuel-saving lubricating oil, and many compounds have been heretofore been found to be useful. However, it has been observed that even though these compounds possess a high fuel-saving effect on the fresh lubricating oil, they gradually lose said effect in the aged lubricating oil due to degradation during engine operation. While many antioxidants have widely been used heretofore and proved to be effective to some extent for preventing the degradation, they could not necessarily provide satisfactory results in view of their lubricating performance. The present invention is based on a discovery whereby excellent fuel-saving effect can be attained by combining a specific overbasic metallic detergent comprising an alkaline earth metal and being prepared by use of boric acid or boric acid anhydride as reactant with a molybdenum compound as friction modifier and an antioxidant, as defined hereinafter. The present invention therefore provides an engine oil composition having a specific combination of lubricating additives and having an excellent fuel-saving effect over a long period of time. 3. Summary of the Invention It is an object of the subject invention to provide a fuel-saving engine oil composition comprising a major amount of a lubricating base oil and as essential components (a) about 0.01 to 30% by weight of an overbasic oil-soluble metal salt which is the reaction product of an oil-soluble metal salt with an alkaline earth metal oxide or hydroxide in the presence of boric acid or boric acid anhydride, (b) about 0.01 to 5% by weight of a molybdenum compound friction modifier, and (c) about 0.01 to 5% by weight of an antioxidant selected from the group consisting of phenol type, amine type, sulfur type, zinc thiophosphate type and phenothiazine type antioxidants, calculated on the basis of the total amount of the composition. EP-A-0 317 354 discloses an improved lubricant composition for enhanced fuel economy which comprises four essential components A to D. Component A is comprised of a mixture of a calcium overbased detergent inhibitor and of a magnesium-overbased detergent inhibitor, such overbased products being prepared by carbonating fully neutralized sulfonic and/or carboxylic acids with CO₂. Inter alia there can be used Mg borate to neutralize such acids. However, it will be shown later that such carbonated overbased products cannot be used within the context of the present invention. Furthermore, DE-OS 2 028 703 discloses antioxidant mixtures for luboils comprising an oil dispersion of a metal borate, like Ca(BO₂)₂, and an aromatic compound with an OH-group or a mercapto group bound directly to the aromatic ring structure. Preferably the metal borate is prepared by reacting a metal alcoholate with a boric acid, an anhydride, or an ester of such acid. 4. Detailed Description of the Invention Either mineral oils or synthetic oils may be used as the lubricating base oils of the instant invention. Any paraffinic or naphthenic lubricating base oils may be acceptable wherein said base oils are manufactured by a process consisting mainly of topping crude oil followed by vacuum distillation to give a lubricating oil fraction, and refining said lubricating fraction by a process selected from the group consisting of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydro-refining, sulfuric acid treating, and clay treating. The synthetic oils of the present invention include, α-olefin polymers (polybutenes, octene-1 oligomers, decene-1 oligomers, and the like), alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-3-ethylhexyl sebacate, and the like), polyol esters (trimethylolpropane caprilate, trimethylolpropane pelargonate, pentaerythritol- 2-ethyl hexanoate, pentaerythritol pelargonate, and the like), polyoxyalkylene glycol, polyphenyl ether, silicon oils, perfluoroalkyl ethers, and mixtures thereof. Preferred kinematic viscosity of these lubricating base oils is in a range of about 3 to 20.10⁻⁶ m²/s at 100°C. The overbasic oil-soluble metal salts (a) of the present invention are prepared by a reaction of an oil-soluble alkaline-earth metal salt such as an oil-soluble alkaline-earth metal sulfonate, alkaline-earth metal salicylate, alkaline-earth metal pheneate or an alkaline-earth metal phosphonate, with an oxide or hydroxide of an alkaline-earth metal in the presence of boric acid or boric acid anhydride. Among oil-soluble alkaline-earth metal salts, alkaline-earth metal salicylates are most appropriate. Generally, the overbasic oil-soluble metal salts (a) of the present invention have a total base number of about 100 or more, and preferably 170 or more, and a particle size of less than about 0.1 µ m, and preferably less than about 0.05 µ m. Any methods for preparing the overbasic metal salts may be acceptable. For example, a method has been known which comprises reacting an oil-soluble metal salt as aforesaid, a hydroxide or an oxide of alkaline-earth metal, and boric acid or boric acid anhydride in the presence of water, an alcohol such as methanol, ethanol, propanol, or butanol, and a diluent such as benzene, toluene or xylene at a temperature of about 20 to 200 °C for about 2 to 8 hours, heating the mixture at about 100 to 200 °C to remove water, followed by removing the alcohol and the diluent if necessary, to give an overbasic metal salt. The reaction conditions may be employed suitably depending on raw material type, the amount of reactants and the like. Typical of such prior art practices are those disclosed in Japanese patent Publications Nos. 116688 /60 and 204208 /61. Such an overbasic alkali-earth metal salt prepared according to the present invention is present in an amount of 0.01 to 30 % by weight, and preferably of 0.05 to 5 % by weight, on the basis of the total amount of the composition. A content of less than 0.01 % by weight is not to be recommended because of the insufficient realisation of the fuel-saving effect of the overbasic metal salt, especially since the effect can not be maintained over a long period of time. Inversely, when it is in excess of 30 % by weight, there is no additional merits due to the excessive addition. Other overbasic oil-soluble metal salts, such as those prepared by use of alkaline-earth-metal carbonates can not provide an engine oil composition which can persistently maintain the fuel-saving effect throughout the engine operation. As friction modifiers(b) there are employed in the present invention molybdenum compounds. Typical friction modifiers include molybdenum sulfide diethyldithiophosphate, molybdenum sulfide dipropyldithiophosphate, molybdenum sulfide dibutyldithiophosphate, molybdenum sulfide dipentyldithiophosphate, molybdenum sulfide dihexyldithiophosphate, molybdenum sulfide dioctyldithiophosphate, molybdenum sulfide didecyldithiophosphate, molybdenum sulfide didodecyldithiophosphate, molybdenum sulfide di(butylphenyl) dithiophosphate, Molybdenum sulfide di(nonylphenyl) dithiophosphate, oxymolybdenum sulfide diethyldithiophosphate, oxymolybdenum sulfide dipropyldithiophosphate, oxyolybdenum sulfide dibutyldithiophosphate, oxymolybdenum sulfide dipentyldithiophosphate, oxymolybdenum sulfide dihexyldithiophosphate, oxymolybdenum sulfide dioctyldithiophosphate, oxymolybdenum sulfide didecyldithiophosphate, oxymolybdenum sulfide didodecyldithiophosphate, oxymolybdenum sulfide di(butylphenyl) dithiophosphate, oxymolybdenum sulfidedi(nonylphenyl) dithiophosphate, molybdenum sulfide diethyldithiocarbamate, molybdenum sulfide dipropyldithiocarbamate, molybdenum sulfide dibutyldithiocarbamate, molybdenum sulfide dipentyldithiocarbamate, molybdenum sulfide dihexyldithiocarbamate, molybdenum sulfide dioctyldithiocarbamate, molybdenum sulfide didecyldithiocarbamate, molybdenum sulfide didocecyldithiocarbamate, molybdenum sulfide di(butylphenyl) dithiocarbamate, molybdenum sulfide di(nonylphenyl) dithiocarbamate, oxymolybdenum sulfide diethyldithiocarbamate, oxymolybdenum sulfide dipropyldithiocarbamate, oxymolybdenum sulfide dibutyldithiocarbamate, oxymolybdenum sulfide dipentyldithiocarbamate, oxymolybdenum sulfide dihexyldithiocarbamate, oxymolybdenum sulfide dioctyldithiocarbamate, oxymolybdenum sulfide didecyldithiocarbamate, molybdenum sulfide didocecyldithiocarbamate, oxymolybdenum sulfide di(butylphenyl) dithiocarbamate and oxymolybdenum sulfide di(nonylphenyl) dithiocarbamate. The content of the friction modifier (b) of the present invention is in the range of 0.01 to 5 % by weight, and preferably 0.05 to 2 % by weight, on the basis of the total amount of the composition. A content of less than 0.01 % by weight is not recommended because of the insufficient realisation of the friction reducing effect. Inversely, when it is in excess of 5 % by weight, there is no additional merits due to the excessive addition. As antioxidants (c) there are employed such of the phenol type, amine type, sulfur type, zinc thiophosphate type, and phenothiazine type. Typically, they include diphenylamine, p,p′-dioctyl diphenylamine, p,p′-dinonyl diphenylamine, p,p′ -didodecyl diphenylamine, phenyl- α-naphthylamine, p-octylpenyl-α-naphthylamine, p-nonylphenyl-α-naphthylamine, p-dodecylphenyl-α-naphthylamine, 2,6-di-tert.-butylphenol, 2,6-di-tert.-butyl-p-cresol, 2,6-di-tert.-butyl-4-ethylphenol, 2,2′-methylene-bis(4-methyl-6-tert.-butylphenol), 2,2′-methylene-bis(4-ethyl-6-tert.-butylphenol), 4,4′-methylene-bis (2,6-di-tert.-butylphenol), 4,4′-bis (2,6-di-tert.-butylphenol), 4,4′-thio-bis (6-tert.-butyl-o-cresol), zinc dialkyl dithiophosphate, phenotiazine, and mixtures thereof. dithiophosphate, phenotiazine, and mixtures thereof. The content of the antioxidant (c) of the present invention is in the range of 0.01 to 5 % by weight, and preferably 0.1 to 2 % by weight, on the basis of the total amount of the composition. A content of less than 0.01 % by weight is not recommended because the antioxidation effect can be realized only for a short period if time. Inversely, when the amount is in an excess of 5 % by weight, there is no additional merits due to the excessive addition. In the present invention, the following conventional lubricating oil additives can be additionally used to improve further the performance of the present composition if necessary, in so far as they do not deviate from the gist of the present invention. Examples of these additives include extreme pressure additives such as tricresyl phosphate, triphenyl phosphate, zinc dithiophosphates,; rust preventives such as petroleum sulfonates, dinonyl naphthalene sulfonates and the like; metal deactivating agents such as benzotriazole and the like; metal-based detergents such as alkaline-earth metal sulfonates, alkaline-earth metal salicylates, alkaline-earth metal pheneates, alkaline-earth metal phosphonates and the like; ashless dispersants such as succinimide, succinic esters, benzylamine and the like; defoamers such as silicon oils and the like; viscosity index improvers and pour point depressants such as polymethacrylates, polyisobutylenes and polystyrenes and the like; and mixture thereof. Generally, the content of the viscosity index improver is in the range of about 1 to 30 % by weight, the defoamer is in the range of about 0.0005 to 1 % by weight, the metal deactivating agent is in the range of about 0.005 to 1 % by weight, and other additives are used in amounts of about 0.1 to 15 % by weight respectively on the basis of the total amount of the composition. The engine oil compositions of the present invention are suitable for two stroke and four stroke gasoline engine oils, diesel engine oil for land use, marine diesel engine oil, and the like. While the advantages of the compositions according to the present invention will be described in detail hereinbelow in conjunction with the following examples, it is to be noted that the scope of the present invention should not be limited to these examples. Examples and Comparative Examples According to the indications in Table 1, an engine oil composition of the present invention and two comparative compositions were prepared. Performance tests were conducted with respect to these compositions by the following method. (LFW friction test) LFW friction test is carried out on both oxidation degraded samples and freshly prepared samples. The test conditions are as follows: The oxidation degraded sample oils were prepared by oxidizing new sample oils under the following conditions on the basis of " the method for testing oxidaton stability of lubricating oil" prescribed by JIS K 2514 3.1: Table 1 shows the test results. As is apparent from the results shown in Table 1, the engine oil composition according to the present invention has excellent performance as an engine oil in which the fuel-saving effect can be maintained persistently throughout the engine operation because of the synergism of each component. On the contrary, when the compositions of Comparative Examples 1 and 2 in which an overbasic oil-soluble metal salt prepared by use of calcium carbonate instead of an overbasic oil-soluble metal salt (a) prepared by use of an alkaline-earth metal borate is used, or the antioxidant of component (c) of the present invention is omitted, are compared with those of Example respectively, the friction coefficient increases after oxidation degradation in both cases, and the time during which the fuel-saving effect may be maintained is shorter in both cases.

Claims: An engine oil composition comprising a major amount of lubricating base oil and as essential components (a) 0.01 to 30% by weight of an overbasic oil-soluble metal salt which is the reaction product of an oil-soluble metal salt with an alkaline-earth metal oxide or hydroxide in the presence of boric acid or boric acid anhydride, (b) 0.01 to 5% by weight of a molybdenum compound friction modifier, and (c) 0.01 to 5% by weight of an antioxidant, selected from the group consisting of phenol type, amine type, sulfur type, zinc thiophosphate type and phenothiazine type antioxidants calculated on the basis of the total amount of the composition. The engine oil composition claimed in claim 1, wherein the alkaline-earth metal is calcium and the antioxidant is a combination of phenol and amine type antioxidants. The engine oil composition claimed in claims 1 or 2, wherein the amount of the overbasic oil-soluble metal salt is 0.05 to 5% by weight, the amount of molybdenum compound is 0.05 to 2% by weight and the amount of antioxidants is 0.1 to 2% by weight. The engine oil composition claimed in claims 1, 2 or 3, wherein the overbasic oil-soluble metal salt has a base number of at least about 100 and a particle size of less than about 0.1 µm. The engine oil composition claimed in claims 1, 2 or 3, wherein the overbasic oil-soluble metal salt has a base number of at least about 170 and a particle size of less than about 0.05 µm.

Inventors: HIRATA MASAKUNI, IGARASHI JIICHI, INOUE KIYOSHI, ISHIMARU MITUAKI, KAGAYA MINEO, HIRATA, MASAKUNI, IGARASHI, JIICHI, INOUE, KIYOSHI, ISHIMARU, MITUAKI, KAGAYA, MINEO
Applicants: NIPPON OIL CO LTD, NIPPON OIL CO., LTD.
Application year: 1991
Main classification: C10M141
IPC codes: C10N30, C10N10, C10N60, C10N40, C10M159, C10M163, F02B3