Lubricating oil composition

Abstract: The present invention relates to a lubricating oil composition comprising a mineral oil, an ethylene-α-olefin copolymer, a polymethacrylate and common additives, characterized in that it comprises (A) a mineral oil having a kinematic viscosity at 100°C of 1 . 10⁻⁶ to 50 . 10⁻⁶ m²/s (1 -50 cSt) and a viscosity index of at least 60, (B) 0,5 to 20% by weight based on the total weight of the composition of an ethylene-α-olefin copolymer having a number average molecular weight of 800 to less than 5 000, (C) 0,05 to 20% by weight based on the total weight of the composition of polymethacrylate having a number average molecular weight of 10 000 to 250 000 or a mixture of said polymethacrylate and an olefin copolymer, having a number average molecular weight of 10 000 to 250 000 selected from the group consisting of an ethylene-propylene copolymer and an ethylene-styrene copolymer, and (D-II)0,5 to 20% by weight based on the total weight of the composition of at least one member selected from the group consisting of a extreme pressure agent, an anti-wear agent and an oiliness agent.

Description: BACKGROUND OF THE INVENTION The present invention relates to a lubricating oil composition and more particularly to a multi grade lubricating oil composition which is excellent in shear stability. One embodiment of the present invention relates to a multi grade engine oil composition and more particularly to a multi grade engine oil composition which is excellent in shear stability and engine cleanliness. This multi grade engine oil composition can be used as an internal combustion engine oil for a gasoline engine, a diesel engine, a gas engine and other special engine, and further as a compressor oil. This embodiment is the subject-matter of the parent EP-application 88 102 657.9. Another embodiment of the present invention relates to a high viscosity index lubricating oil composition containing a mineral oil as a major component, and more particularly to a lubricating oil composition which has a particularly high viscosity index, is excellent in shear stability and further in extreme pressure properties and anti-wear properties, and thus which can be used as an oil for cars and industrial gears, a power stearing oil, a tractor oil, a shock absorber oil, a hydraulic fluid, a door check oil, a bearing oil and so on. A mineral oil with high molecular weight polymers compounded thereto has heretofore been used as a high viscosity index lubricating oil. However, since this lubricating oil contains a relatively large amount of high molecular weight polymers, its shear stability is seriously poor; when subjected to mechanical shear, it suffers from disadvantages in that viscosity is markedly decreased, initial performance cannot be satisfied, and abrasion is increased. Thus the lubricating oil is unsuitable for practical use. SUMMARY OF THE INVENTION The present invention is intended to overcome the above problems and an object of the present invention is to provide a lubricating oil composition which has a high viscosity index and which is excellent in shear stability and further in extreme pressure and anti-wear properties. The present invention provides a lubricating oil composition comprising: a mineral oil, an ethylene-α-olefin copolymer, a polymethacrylate and common additives, characterized in that it comprises (A) a mineral oil having a kinematic viscosity at 100°C of 1 . 10⁻⁶ to 50 . 10⁻⁶ m²/s (1 - 50 cSt) and a viscosity index of at least 60, (B) 0,5 to 20% by weight based on the total weight of the composition of an ethylene-α-olefin copolymer having a number average molecular weight of 800 to less than 5 000, (C) 0,05 to 20% by weight based on the total weight of the composition of polymethacrylate having a number average molecular weight of 10 000 to 250 000 or a mixture of said polymethacrylate and an olefin copolymer, having a number average molecular weight of 10 000 to 250 000 selected from the group consisting of an ethylene-propylene copolymer and an ethylene-styrene copolymer, and (D-II) 0.5 to 20% by weight based on the total weight of the composition of at least one member selected from the group consisting of a extreme pressure agent, an antiwear agent and an oiliness agent, provided that 1 to 20% by weight based on the total weight of the composition of a detergent-dispersant and/or an antioxidant is excluded. DETAILED DESCRIPTION OF THE INVENTION In the present invention, as the component (A), a mineral oil having a kinematic viscosity at 100°C of 1x10⁻⁶ to 50x10⁻⁶ m²/S (1 to 50 centistokes (cSt)) and a viscosity index of at least 60, preferably at least 80 is used. The present invention, as the component (A), mineral oil having a kinematic viscosity at 100°C of 1x10⁻⁶ to 40x10⁻⁶ m²/S (1 to 40 cSt) is more preferable. The pour point of the mineral oil is not more than -5°C and preferably not more than -10°C. This mineral oil is a base of the lubricating oil composition of the present invention. If the kinematic viscosity of the mineral oil is less than 1x10⁻⁶ m²/S (1 cSt), evaporation loss is large, which is unsuitable for practical use. On the other hand, it is in excess of 50 cSt, the viscosity at low temperatures is high, effect of increasing the viscosity index is poor and thus a large amount of a polymer is needed, which is undesirable because of a reduction in second performance. This mineral oil is obtained by the known lubricating oil purification methods, for example, by purifying a lubricant fraction obtained by ordinary distillation or vacuum distillation, by techniques such as solvent purification and hydrogenation purification. More specifically, fractions such as 70 Neutral, 100 Neutral, 150 Neutral, 300 Neutral, 500 Neutral, Bright Stock, and mixtures of the fractions can be used. In the present invention, as the component (A), a synthetic oil can be used in place of the above mineral oil. However, since the synthetic oil is low in an ability to dissolve additives, exerts adverse influences on anti-sealing properties and is expensive, it is prefered to be used in combination with a mineral oil. In the present invention, as the component (B), an ethylene-α-olefin copolymer having a number average molecular weight of from 800 to less than 5,000 and preferably from 2,000 to 4,000 is used. If the number average molecular weight of the ethylene-α-olefin copolymer is less than 800, the effect of increasing the viscosity.index is poor. On the other hand, it is in excess of 5,000, the shear stability is undesirably reduced. This ethylene-α-olefin copolymer is a cooligomer of ethylene and α-olefin having 3 to 20 carbon atoms, such as propylene, 1-butene and 1-decene, and is a hydrocarbon-based synthetic oil not having a polar group. The above component (B) is compounded in a proportion of 0.5 to 20% by weight based on the total weight of the composition. If the proportion of the component (B) compounded is less than 0.5% by weight, the effect of increasing the viscosity index is undesirably poor. On the other hand, if it is in excess of 20% by weight, the viscosity at low temperatures is increased and the object of the multi grade cannot be attained. In the present invention, component (B) is compounded in a proportion of 2 to 20% by weight and preferably 3.0 to 15% by weight based on the total weight of the composition. In the present invention, as the component (C), polymethacrylate having a number average molecular weight of 10,000 to 250,000, preferably 20,000 to 200,000 is used. If the number average molecular weight is less than 10,000, the viscosity index is not increased. On the other hand, it is in excess of 250,000, the shear stability is undesirably reduced. The component (C) is compounded in a proportion of 0.05 to 20% by weight, by weight based on the total weight of the composition. If the proportion of the component (C) compounded is less than 0.05% by weight, low temperature fluidity is undesirably low. On the other hand, it is in excess of 20% by weight, shear stability and engine cleanliness are undesirably reduced or the viscosity at low temperature is high. The component (C) acts to increase the viscosity index of the lubricating oil composition and to lower the pour point thereof. In the present invention, component (C) is preferably compounded in a proportion of 0.1 to 15% by weight based on the total weight of the composition. In combination with the polymethacrylate, an olefin copolymer having a number average molecular weight of 10,000 to 250,000, preferably 50,000 to 200,000 can be used as the component (C) of the present invention. Use of the olefin copolymer in combination increases the engine cleanliness. Examples of the olefin copolymer include an ethylenepropylene copolymer and an ethylene-styrene copolymer. In the present invention, as the component (D-II), at least one member selected from the group consisting of a extreme pressure agent, an anti-wear agent and an oiliness agent is used. As the extreme pressure agent, various compounds can be used. More specifically, sulfur-containing extreme pressure agents such as sulfides, sulfoxides, sulfones, thiosulfinates, thiocarbonates, olefinic sulfides; sulfurized fats and oils; phosphorus-containing extreme pressure agents such as phosphoric acid esters, phosphorous acid esters, and phosphoric acid ester amine salts; halogen-containing extreme pressure agents such as chlorinated hydrocarbons; organic metal-containing extreme pressure agents such as thiophosphoric acid salts, e.g., zinc dithiophosphate, and thiocarbamic acid salts; and the like can be used. As the anti-wear agent, organomolybdenum compounds such as MoDTP and MoDTC; organoboric compounds such as alkylmercaptyl borate; solid lubricant-based anti-wear agents such as graphite, molybdenum disulfide, antimony sulfide, boron compounds and polytetrafluoroethylene; and the like can be used. As the oiliness agent, higher fatty acids such as oleic acid and stearic acid; higher alcohols such as oleyl alcohol; amines; esters; chlorinated fats and oils; and the like can be used. In the present invention, as the component (D-II), a extreme pressure agent, an anti-wear agent and an oiliness agent as described above are used alone or as mixtures comprising two or more thereof. As the component (D-II), sulfur-containing extreme pressure agents such as sulfurized fats and oils, and olefinic sulfide, phosphorus-containing extreme pressure agents such as phosphoric acid esters, phosphorous acid esters and their amine salts, and zinc dithiophosphate, Mo compounds such as MoDTP and MoDTC, and boron compounds are preferably used alone or as mixtures comprising two or more thereof. The component (D-II) is compounded in a proportion of 0.5 to 20% by weight, preferably 0.5 to 10% by weight based on the total weight of the composition. If the proportion of the component (D-II) compounded is less than 0.5% by weight, extreme pressure and anti-wear properties are undesirably low. On the other hand, if it is in excess of 20% by weight, corrosion is sometimes caused. The lubricating oil composition of the present invention contains the components (A) to (DII) as described above. In addition, if necessary, the lubricating oil composition may contain additives such as a defoaming agent, a rust preventing agent, a corrosion inhibitor and a color additive. As the defoaming agent, silicone-based defoaming agents such as dimethylsiloxane and a silica gel dispersion; alcohol-based defoaming agents; ester-based defoaming agents; and the like can be used. As the rust-preventing agent, carboxylic acids, carboxylic acid salts, sulfonic acid salts, esters, phosphoric acid, phosphoric acid salts, and the like can be used. As the corrosion inhibitor, benzotriazole and its derivatives, thiazole compounds and the like can be used. In accordance with the present invention, there can be obtained a lubricating oil composition having a viscosity index of at least 140 and a high viscosity index. Moreover, the lubricating oil composition of the present invention has a pour point of not more than -30°C and a Brookfield viscosity at -26°C of not more than 150,000 cp, and thus it is excellent in low temperature characteristics. Furthermore, the lubricating oil composition of the present invention is excellent in shear stability and also in extreme pressure properties. Accordingly the lubricating oil composition of the present invention can be used as an oil for car and industrial gears, a power stearing oil, a tractor oil, a shock absorber oil, a hydraulic fluid, a door check oil, a bearing oil and so on. The following examples are given to illustrate the present invention, although the present invention is not limited thereto. Examples 1 to 2 and Comparative Examples 1 to 7 The lubricating oil composition shown in Table 1 were subjected to various tests and their physical properties were evaluated. The results are shown in Table 1. The following can be understood from the results of Table 1. The lubricating oil compositions obtained in Examples 1 and 2 have a viscosity index of at least 140, a pour point of not more than -30°C and a Brookfield viscosity at -26°C of not more than 150,000 cp. Furthermore, the extreme pressure performance as determined by the Four ball test is superior to those of the comparative examples. Thus the lubricating oil compositions are satisfactory as a 80W/90 multi grade gear oil. Comparative Example 1 is an example in which the component (B) is not used and as the component (C), polymethacrylate having a number average molecular weight of 21,000 which is most rarely subject to shear is used. This oil composition, however, is poor in shear stability and furthermore its extreme pressure performance is very low. Comparative Example 2 is an example in which the component (C) is not used. This oil composition is poor in low temperature fluidity and thus cannot be used as a 80W/90 gear oil. Comparative Example 3 is an example in which polybutene is used in place of the component (B). Even though a large amount of polybutene is used, the viscosity increasing effect can be obtained only insufficiently, and moreover low temperature fluidity is poor. Thus this oil composition cannot be used as a 80W/90 gear oil. Comparative Example 4 is an example in which the proportion of the component (B) compounded is small. Although pour point is decreased, shear stability and extreme pressure properties are markedly poor. Comparative Example 5 is an example in which the components (B) and (C) are not used and an ethylene-propylene copolymer having a number average molecular weight of 100,000 was used. This oil composition has a pour point of -20°C and its shear stability is markedly poor. Comparative Examples 6 and 7 are examples in which ethylene-a-olefin copolymer (oligomer) having a number average molecular weight of 10,000 is used in place of the component (B). In Comparative Example 6, although shear stability is good, low temperature viscosity become undesirably high and thus this oil composition cannot be used as 80W/90 gear oil. In Comparative Example 7, although low temperature viscosity is good, shear stability undesirably drops.

Claims: A lubricating oil composition comprising a mineral oil, an ethylene-α-olefin copolymer, a polymethacrylate and common additives, characterized in that it comprises (A) a mineral oil having a kinematic viscosity at 100°C of 1 . 10⁻⁶ to 50 . 10⁻⁶ m²/s (1 - 50 cSt) and a viscosity index of at least 60, (B) 0,5 to 20% by weight based on the total weight of the composition of an ethylene-α-olefin copolymer having a number average molecular weight of 800 to less than 5 000, (C) 0,05 to 20% by weight based on the total weight of the composition of polymethacrylate having a number average molecular weight of 10 000 to 250 000 or a mixture of said polymethacrylate and an olefin copolymer, having a number average molecular weight of 10 000 to 250 000 selected from the group consisting of an ethylene-propylene copolymer and an ethylene-styrene copolymer, and (D-II)0,5 to 20% by weight based on the total weight of the composition of at least one member selected from the group consisting of a extreme pressure agent, an anti-wear agent and an oiliness agent, provided that 1 to 20% by weight based on the total weight of the composition of a detergent-dispersant and/or an antioxidant is excluded. The composition according to claim 1, characterized in that the component (A) is a mineral oil having a kinematic viscosity at 100°C of 1 . 10⁻⁶ to 40 . 10⁻⁶ m²/s (1 - 40 cSt) and a viscosity index of at least 80. The composition according to claim 1 or 2, characterized in that the component (A) is a mineral oil having a pour point of not more than -5°C. The composition according to any of claims 1 to 3, characterized in that the component (B) is an ethylene-α-olefin copolymer having a number average molecular weight of 2 000 to 4 000. The composition according to any of claims 1 to 4, characterized in that the polymethacrylate has a number average molecular weight of 20 000 to 200 000. The composition according to any of claims 1 to 5, characterized in that the extreme pressure agent is at least one member selected from the group consisting of a sulfur-containing extreme pressure agent, a phosphorus-containing extreme pressure agent, a halogen-containing extreme pressure agent and an organic metal-containing extreme pressure agent. The composition according to any of claims 1 to 6, characterized in that the anti-wear agent is at least one member selected from the group consisting of an organomolybdenum compound, an organoboric compound and a solid lubricant-based anti-wear agent. The composition according to any of claims 1 to 7, characterized in that the oiliness agent is at least one member selected from the group consisting of a higher fatty acid, a higher alcohol, an amine, an ester and a chlorinated fat and oil. The composition according to any of claims 1 to 8, characterized in that the component (B) is compounded in a proportion of 3,0 to 15% by weight based on the total weight of the composition. The composition according to any of claims 1 to 9, characterized in that the component (C) is compounded in a proportion of 0,1 to 15 % by weight based on the total weight of the composition. The composition according to any of claims 1 to 10, characterized in that the component(D-II)is compounded in a proportion of 0,5 to 10% by weight based on the total weight of the composition.

Inventors: ICHIHASHI TOSHIHIKO C O IDEMIT, TAMOTO YOSHITAKA C O IDEMITSU, ICHIHASHI, TOSHIHIKO, C/O IDEMITSU KOSAN CO. LTD., TAMOTO, YOSHITAKA, C/O IDEMITSU KOSAN CO. LTD.
Applicants: IDEMITSU KOSAN CO, IDEMITSU KOSAN COMPANY LIMITED
Application year: 1991
Main classification: C10M169
IPC codes: C10M169