Title of Invention

BASE OIL FOR LUBRICATING COMPOSITION OIL FOR TWO-CYCLE GASOLINE ENGINES, AND LUBRICATING OIL COMPOSITION

Abstract

Base oil for lubricating oils for two-cycle gasoline engines, having as main component a base oil of a kinematic viscosity of from 4 to 20 mm<sup>2</sup>/s at 100º C and a viscosity index of 75 or more, a condensed polycyclic aromatic hudrocarbon (DMSO extract) content of less than 1.0% wt and a sulphur content of 1.0% wt or less; lubricating oil composition for two-cycle gasoline engines, comprising a base oil of a kinematic viscosity of from 4 to 20 mm<sup>2</sup>/s 100ºC, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon (DMSO extract) content of less than 1.0% by weight and a sulphur content of 1.2% wt or less, and (B) from 0.1 to 2.0 parts by weight of phenolic antioxidant per 100 parts by weight of base oil.

Full Text

The present invention relates to a base oil for lubricating oils for two-cycle gasoline engines, and to a lubricating oil composition comprising a base oil. Two-cycle gasoline engines in small two-wheeled vehicles and the like generally differ from other four-stroke engines in that they do not have a moving valve-type mechanism, and so they are advantageous in that they are small, have a large output with respect to the amount of exhaust gas, and have low production costs. However, two-cycle gasoline engines are ^;Lsadvantageous in that both fuel and lubricating oil "^are aspirated into the combustion chamber and combusted, and so uncombusted fuel and combusted residue from lubricating oil that has been incompletely combusted in the combustion chamber readily builds up in the piston ring grooves and piston skirts, and a decreased engine output and ignition plug contamination become more likely as these combustion chamber deposits increase. (Reference literature: Tribologist, S^A No.2, p. 101, 1993). Therefore, in order to maintain the performance of a two-cycle gasoline engine over long periods, it is important that the two-cycle gasoline engine oil can clean the engine. Mineral oil-based base oils are generally used as base oil compositions used for two-cycle gasoline engines. Examples of various mineral oil-based base oils which can be solvent-purified or lightly hydrogen-purified include saturated hydrocarbons such as paraffins and naphthenes, and aromatic compounds. Moreover, it is known that components of the aromatic compounds which can be used as base oils include i? condensed polycyclic aromatic hydrocarbon (DMSO extj compounds, ,^t Sulphur compounds in which sulphur atoms are bound to the various abovementioned hydrocarbon compounds are V^ also included in mineral-based base oils. Examples «, . ,,.>../ include benzothiophenes and carbazoles. CP .•^ Japanese Patent no. 2520923_[xegistered 17 May /^ ^"^^ Cf 1996) suggests improving the cleaning properties and /x^ ^ seizure resistance of lubricating oil base oils used in two-cycle gasoline engines. This patent discloses a two-cycle gasoline engine oil having as its main component a base oil with a kinematic viscosity of from 2 to 20, a viscosity index of 75 or more, an aromatic content of 5% or less and a sulphur content of 0.1% or less. It has been found that, contrary to the technology disclosed in the abovementioned Japanese Patent No. 2520923, the most important factor for improving the cleaning properties of two-cycle gasoline engines is not the aromatic component of the base oil, but the amount of condensed polycyclic aromatic hydrocarbon (DMSO extract). Specifically, the monocyclic component in the aromatic component of base oil is effective at dissolving sludge and cleaning inside the engine, and is an important component of the base oil in that it improves the cleaning properties of two-cycle gasoline engine oils. However, the condensed polycyclic aromatic hydrocarbons in base oil have a higher molecular weight, a higher boiling point and a higher degree of unsaturation within the molecule than other components contained in the base oil. Because a large amount of oxygen is required in order to achieve complete combustion in a short time, the condensed polycyclic aromatic hydrocarbons readily form partially oxidized uncombusted compounds. It has been found that these partially oxidized uncombusted condensed polycyclic aromatic hydrocarbons stick to the insides of the engine combustion chamber, resulting in a deterioration in the engine cleaning properties an increase in the amount of exhaust smoke produced, and a decrease in the engine output as they are deposited in the piston ring grooves in the engine. The components of common lubricating oils for two-cycle gasoline engines can be divided into base oil, diluents and additives, as described above. Two-cycle gasoline engine oils differ from lubricating oils for internal combustion engines such as four-cycle gasoline engines in that because the engine oil is mixed with fuel and lubricates each part, and because a mixed gas comprising air and fuel containing some of the two-cycle engine oil is combusted, they do not contain substances which are not readily combustible or substances which combust to form ash, such as the antioxidant zinc dialkyldithiophosphate (ZnDTP) or other organometallic phosphates or oil-soluble molybdenum compounds. By way of exception, metallic cleaning agents are commonly used. However, the metallic compound content is generally limited because these compounds contaminate the electrodes of ignition plugs which emit electric sparks to the mixed gas to achieve combustion. Two-cycle gasoline engine oils also differ from four-cycle gasoline engine oils and the like in that they are usually stored in lubricating oil tanks at room temperature and so it is not necessary to consider engine oil deterioration at high temperatures. As a result, it is not thought necessary to add ash-free antioxidants or the like. The present invention aims to provide a two-cycle gasoline engine oil that can maintain two-cycle gasoline engines at high performance levels over long periods due to its excellent cleaning properties. As a result of diligent research into developing engine oils with good cleaning properties, the present inventors found that, contrary to the technology disclosed in the abovementioned Japanese Patent No. 2520923, the important factor for improving cleaning properties with respect to two-cycle engines is not the aromatic component of the base oil, but the amount of condensed polycyclic aromatic hydrocarbons (DMSO extract) contained therein. Consequently, the present inventors perfected the present invention. The present invention relates to a base oil for lubricating oils for two-cycle gasoline engines, having as main component a base oil of a kinematic viscosity of from 4 to 20 mm^/s at 100°C, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon (DMSO extract) content of less than 1,0% by weight and a sulphur content of 1.0% or less, .- The present invention further relates to a lubricating oil composition for two-cycle gasoline engines characterized by comprising (A) a base oil of a kinematic viscosity of from 4 to 20 mm^/s at 100°C, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon (DMSO extract) content of less than 1.0% by weight and a sulphur content of 1.2% "or less, and (B) from 0.1 to 2.0 parts by weight of phenolic antioxidant per 100 parts by weight of base oil. The base oil used in the present invention can be obtained by the distillation of crude oil followed by purification or ultrafiltration. The base oil of the present invention must have a kinematic viscosity at 100°C of from 4 to 20 mm^/s, preferably from 8 to 13 mm^/s. If the kinematic viscosity at 100°C is less than 4 mm^/s, the lubricating properties and seizure resistance deteriorate and if it exceeds 20 mm^/s, considerable amounts of exhaust smoke are produced and clogging of the engine exhaust pipe occurs. The viscosity index is 75 or more, preferably 80 or more. If the viscosity index is less than 75, the kinematic viscosity at low temperatures is high and so starting properties deteriorate, and this is not appropriate for the target base oil for two-cycle gasoline engine oils. There are no particular limitations regarding the aromatic content of the base oil used in the present invention, according to ring analysis (n-d-Method: disclosed in Japanese Patent No. 2520923), and it is not difficult to achieve the aims of the present invention with a base oil having an aromatic content (CA%) of 5% wt or more. In order to improve the cleaning properties, lubrication properties, seizure resistance (scuffing resistance) between the piston and the cylinder, and the like, the aromatic content (CA%) is preferably from 5 to 30% wt. This is because the monocyclic aromatic component has better sludge-dissolving properties and lubricating properties than paraffin-based hydrocarbons. However, when the condensed polycyclic aromatic hydrocarbon (DMSO extract) content in the aromatic hydrocarbon component of the base oil is 1.0% by weight or more per 100% by weighs or tne tiase oil, the engine-cleaning properties deteriorate considerably and large amounts of exhaust smoke are produced, so this is not appropriate for target base oil for two-cycle gasoline engine oils. Methods for measuring the condensed polycyclic aromatic compound (DMSO extract) content include the DMSO (dimethyl sulphoxide) extraction method stipulated in UK Petrochemical Society Methods IP346. The sulphur content in the base oil of the present invention is 1.0% by weight or less, preferably 0.7% by weight or less. If the sulphur content exceeds 1.0% by weight, engine-cleaning properties deteriorate and large amounts of exhaust smoke are produced, which is not suitable for the aims of the present invention. This is thought to be because when sulphur-containing hydrocarbons are combusted, sulphate soot and sulphite compounds are formed, and they stick inside the engine resulting in a deterioration in the engine-cleaning properties and an increase in the amount of exhaust smoke produced. In the further embodiment of the present invention, the action of the antioxidant inhibits deterioration due to the combustion of sulphur compounds, and it becomes possible to achieve engine-cleaning properties using the base oil having a sulphur content of 1.2% by weight or less, preferably 0.8% by weight or less. Mineral oils, hydrocarbon-based synthetic oils, gasoline-propylene copolymers and aliphatic ester-based synthetic oils can be used as the base oil in the present invention provided that they have the abovementioned properties. It is also possible to use a mixture comprising the abovementioned mineral oils and the synthetic oils described below, in suitable proportions. Phenolic antioxidants that are used in internal combustion engine lubricating oils are suitable for use in the present invention. Examples include 4,4"-methylenebis(2,6-di-t-butylphenol) and 2,6-di-t-butyl-4-methylphenol. It should be noted that sulphurated phenolic antioxidants and amine-based antioxidants which are also generally used in internal combustion engine lubricating oils can increase the amount of sulphite gas and nitrogen oxide gas in the exhaust gas emitted after combustion, and are undesirable. In practice, base oils of the present invention are preferably mixed with suitable amounts of polybutene, kerosene or synthetic saturated hydrocarbon-based diluents, detergent dispersants and other various additives, if necessary. Examples of cleaning agents which can be present are detergents and dispersants, can include metallic detergent dispersants such as sulphonates, phenates and salicylates, and ashless dispersants such as succinimide, succinic acid esters and gasoline-propylene oxide copolymers. Of these, sulphonate detergents, succinimide and combinations of salicylate detergents and succinimide are particularly suitable. Figure 1 is a graph showing the sulphur content and the condensed polycyclic aromatic hydrocarbon (abbreviated to PCA) contents of some base oils. Figure 2 is a graph showing the sulphur content and the condensed polycyclic aromatic hydrocarbon content of some engine oil compositions (product). Tne present invention is described in more detail below by means of working examples and comparative examples. EXAMPLES Test oils were prepared by mixing the various base oils shown in Table 1 and 2 with the kerosene, detergent dispersant, polybutene and pour point lowering agent shown in Table 3 according to the proportions shown in Tables 4 and 5, and the resulting various two-cycle gasoline engine oil compositions were subjected to cleaning property tests according to the two-cycle gasoline engine lubricating oil cleaning property test method stipulated in JASO M341-92. The results are shown in Tables 4 to 7. Table 1 Base oil 1 Base oil 2 Base oil 3 Base oil 4 Kinematic viscosity 40°C, min^/s 105.7 104.5 107.2 98.9 Kinematic viscosity 100°C, mm^/s 11.5 11.1 11.0 11.0 Viscosity index 95 96 85 95 Sulphur content % by weight *1 1.2 1.2 0.8 0.5 Condensed polycyclic aromatic 1.4 0.8 1.3 0.5 hydrocarbon content % by weight *2 CA% *3 6.2 5.9 5.7 6.1 CN% *3 25.6 30.9 35.8 30.3 CP% *3 68.2 63.2 58.5 63.6 Purification method Solvent Solvent Solvent Solvent purification purification purification purification *1: *2 The sulphur content was measured by the radiation excitation method of JIS-K2541-95(6). The condensed polycyclic aromatic hydrocarbon (DMSO extract) was measured by the DMSO (dimethyl sulphoxide) extraction method stipulated in the UK Petrochemical Society Method IP346-92. Ring analysis results were obtained by the ASTM D 3238-90, n-d-M method. CA% represents the aromatic component, CN% represents the naphthene component and CP% represents the paraffin component. Table 2 Base oil 5 Base oil 6 Base oil 7 Base oil 8 Kinematic viscosity 40°C mm"^/s 100.0 99.2 66.0 85.5 Kinematic viscosity 100°C mm^/s 11.2 11.2 10.1 12.5 Viscosity index 97 98 138 143 Sulphur content % by weight *1 0.5 0.5 0.0 0.0 Condensed polycyclic aromatic hydrocarbon content % by weight *2 0.4 0.5 0.0 0.0 CA% *3 2.6 2.8 - - CN% *3 27.5 28.5 - - CP% *3 69.9 68.7 - - Purification method Solvent purification Light hydrogen treated oil Solvent purification Solvent purification Other comments Base oil 2 lightly hydrogentreated Poly-a-olefin synthetic base oil Synthetic aliphatic ester *1: *2: *3 The sulphur content was measured by the radiation excitation method of JIS-K2541-95(6) The condensed polycyclic aromatic hydrocarbon (DMSO extract) was measured by the DMSO (dimethyl sulphoxide) extraction method stipulated in the UK Petrochemical Society Method IP346-92. Ring analysis results were obtained by the ASTM D 3238-90, n-d-Method. CA% represents the aromatic component, CN% represents the naphthene component and CP% represents the paraffin component. Table 3 Poly- Poly- Kerosene Detergent Pour point butene A butene B dispersant lowering agent Kinematic viscosity 40°C, inm"^/s 9610 650 1.2 - - Kinematic viscosity 100°C, mm^/s 223 31 - 78.2 - Number average molecular weight *4 1130 650 - - - Elemental analysis results Sulphur mass% >0.001 >0.001 0.002 0.06 >0.001 Nitrogen mass% >0.001 >0.001 >0.001 0.12 >0.001 Ca mass% >0.001 >0.001 >0.001 0.05 >0.001 Other compounds Isobuty- Isobuty- JIS K220 Mixture Poly- lene lene 3-1992 comprising methacrylate- copoly- copoly- JIS 1 succinimide-based based mer mer kerosene dispersant and calcul sulfonate-based detergent copolymer pour point lowering agent 4: Molecular weight measurement conditions: Column: Toso G2000H*L*1, G3000H*L*1, G4000H*L*1, G5000H*L*1 Solvent used: THF, flow rate 1.0 mm/min, temperature 40°C, Detector: R.I., Integrator: Chromatopac C-R4A (Shimadzu) Table 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Base oil 1 %wt 84.0 50.0 Base oil 2 %wt 84.0 Base oil 3 %wt 84.0 Base oil 4 %wt Base oil 5 %wt 34.0 Base oil 6 %wt Base oil 7 %wt Base oil 8 %wt Phenolic antioxidant A *5 %wt Polybutene A %wt Polybutene B %wt Kerosene (kerosene JIS No. 1) %wt 8.3 8.3 8.3 8.3 Detergent dispersant %wt 7.3 7.3 7.3 7.3 Pour point lowering agent %wt 0.4 0.4 0.4 0.4 Test oil properties Kinematic viscosity 100°{mm^/s) 8.7 8.4 8.4 8.6 Cleaning properties test results *6 Cleaning property index 75 77 79 77 Table 5 Comparative example 5 Comparative example 6 Base oil 1 %wt 50.0 50.0 Base oil 2 %wt Base oil 3 %wt Base oil 4 %wt Base oil 5 %wt Base oil 6 %wt Base oil 7 %wt Base oil 8 %wt Phenolic antioxidant A *5 %wt Polybutene A %wt 15.0 10.0 Polybutene B %wt 7.3 32.3 Kerosene (kerosene JIS No. 1) %wt 20.0 25.0 Detergent dispersant %wt 7.3 7.3 Pour point lowering agent %wt 0.4 0.4 Test oil properties Kinematic viscosity 100°C mm^/s 8.5 8.6 Cleaning properties test results *6 Cleaning property index 80 85 "5: 4,4"-Methylenebis(2,6-di-t-butylphenol) was used as the phenolic antioxidant A *6: The cleaning property tests were performed according to the cleaning property test method for two-cycle gasoline engine lubricating oils Automobile Standard JASO M 341-92, of the Automobile Technology Corporation. Lubricating oils having a cleaning property index less than 80 according to the Automobile Standard JASO M 345-93 for two-cycle gasoline engine lubricating oils were deemed to have not met this standard for two-cycle engine oil performance, and were deemed unsuitable as two-cycle lubricating oils. Lubricating oils having a high cleaning performance index according to the Automobile Standards JASO M 341-92 and JASO M 345-93 exhibited good engine-cleaning properties. Table 6 Working example 1 Working example 2 Working example 3 Working example 4 Base oil 1 %wt Base oil 2 %wt Base oil 3 %wt Base oil 4 %wt 84.0 50.0 Base oil 5 %wt 84.0 Base oil 6 %wt 84.0 Base oil 7 %wt Base oil 8 %wt Phenolic antioxidant A *5 %wt Polybutene A %wt 15.0 Polybutene B %wt 7.3 Kerosene (kerosene JIS No. 1) %wt 8.3 8.3 8.3 20.0 Detergent dispersant %wt 7.3 7.3 7.3 7.3 Pour point lowering agent %wt 0.4 0.4 0.4 0,4 Test oil properties Kinematic viscosity 100°C, mmVs 8.3 8.4 8.4 8.2 Cleaning properties test results *6 Cleaning property index 95 97 94 101 Table 7 Working example 5 Working example 6 Working example 7 Working example 8 Base oil 1 %wt Base oil 2 %wt Base oil 3 %wt Base oil 4 %wt Base oil 5 %wt Base oil 6 %wt Base oil 7 %wt Base oil 8 %wt Phenolic antioxidant A *5 %wt Polybutene A %wt Polybutene B %wt Kerosene (kerosene JIS No. 1) %wt Detergent dispersant %wt Pour point lowering agent %wt 25.0 10.0 32.3 25.0 7.3 0.4 83.5 0.5 8.3 7.3 0.4 83.5 0.5 8.3 7.3 0.4 37.7 10.0 10.0 10.0 10.0 15.0 7.3 Test oil properties Kinematic viscosity 100°C mm^/s 8.3 8.5 8.6 8.2 Cleaning properties test results *6 Cleaning property index 105 90 106 99 / Comparing working examples 1, 2 and 3 with comparative examples 1, 2, 3 and 4 shows that when a mineral oil-based base oil containing less than 1.0% by weight of condensed polycyclic aromatic hydrocarbons (DMSO extract) and 1.0% by weight or less of sulphur per 100% by weight of base oil is used, the cleaning properties are improved. Working example 1 shows that when a mineral oil-based base oil containing less than 1.0% by weight of condensed polycyclic aromatic hydrocarbons (DMSO extract) and 1.0% by weight or less of sulphur per 100% by weight of base oil is used, the use of the base oil having an aromatic content (CA%) of 5% or more according to the n-d-Method does not result in a deterioration in cleaning properties but actually improves them. Comparing working examples 4 and 5 with comparative examples 5 and 6 shows that even when the proportions of the base oil contained in the product are altered, if a mineral oil-based base oil containing less than 1.0% by weight of condensed polycyclic aromatic hydrocarbons (DMSO extract) and 1.0% by weight or less of sulphur per 100% by weight of the base oil is used, the cleaning properties are improved. Comparing working examples 6 and 7 with comparative example 2 shows that combining a mineral oil-based base oil containing less than 1.0% of condensed polycyclic aromatic hydrocarbons (DMSO extract) and 1.2% by weight or less of sulphur with a phenolic antioxidant improves the engine-cleaning properties considerably. Working example 8 shows that the present aims can be achieved even when a mixture comprising suitable proportions of synthetic oil and mineral oil-based base oil containing less than 1.0% by weight of condensed polycylic aromatic hydrocarbons (DMSO extract) and 1.0% by weight or less of sulphur per 100% by weight of base oil is used. Lubricating oil base oils of the present invention exhibit excellent cleaning properties when used as the lubricating oil for two-cycle gasoline engines, and they are effective as lubricating oils for various high-output, high-performance two-cycle gasoline engines. WE CLAIM; 1. A base oil for lubricating oils for two-cycle gasoline engines, having as main component a base oil of a kinematic viscosity of from 4 to 20 mm1/s at 100°C, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon (DMSO extract) content of less than 1.0% and a sulphur content of 1.0% wt or less. 2. The base oil according to Claim 1, wherein said base oil is obtained by the distillation of crude oil followed by purification or ultrafiltration. 3. The base oil according to Claim 1 or 2, wherein said base oil has a kinematic viscosity at 100°C of from 8 to 13 mm1/s. 4. The base oil according to any one of Claims 1 to 3, wherein said base oil has a viscosity index of 80 or more. 5. The base oil according to any one of Claims 1 to 4, wherein said base oil has an aromatic content (CA%) of from 5 to 30% wt. 6. The base oil according any one of Claims 1 to 5, wherein said base oil has a sulphur content of 0.7% by weight or less. 7. A lubricating oil composition for two-cycle gasoline engines characterized by comprising (A) a base oil of a kinematic viscosity of from 4 to 20 mm1/s at 100°C, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon (DMSO extract) content of less than 1.0% by weight and a sulphur content of 1.2% wt or less, and (B) from 0.1 to 2.0 parts by weight of phenolic antioxidant per 100 parts by weight of base oil. 8. The lubricating oil composition according to Claim 7, wherein the base oil has a sulphur content of 0.8% by weight or less. 9. The lubricating oil composition according to Claim 7 or 8, wherein the antioxidant is selected from 4,4"methylenebis(2,6-di-t-butylphenol) and 2,6-di-t-butyl- 4-methylphenol. 10. A base oil for lubricating oils for two-cycle gasoline engines substantially herein described with reference to the accompanying drawing. 11. A lubricating oil composition for two-cycle gasoline engines substantially herein described with reference to the accompanying drawing.

Documents:

0780-mas-1999 abstract duplicate.pdf

0780-mas-1999 abstract.pdf

0780-mas-1999 claims duplicate.pdf

0780-mas-1999 claims.pdf

0780-mas-1999 correspondence-others.pdf

0780-mas-1999 correspondence-po.pdf

0780-mas-1999 description (complete) duplicate.pdf

0780-mas-1999 description (complete).pdf

0780-mas-1999 drawings duplicate.pdf

0780-mas-1999 drawings.pdf

0780-mas-1999 form-1.pdf

0780-mas-1999 form-19.pdf

0780-mas-1999 form-26.pdf

0780-mas-1999 form-3.pdf

0780-mas-1999 form-4.pdf

0780-mas-1999 form-5.pdf

0780-mas-1999 others.pdf

0780-mas-1999 petition.pdf