LUBRICATING OIL COMPOSITION

Abstract: The present invention provides a lubricating oil com­ position comprising 97 to 60% by weight of mineral oil and 3 to 40% by weight of polyester, said mineral oil having a dynamic viscosity at 100°C of 2 to 50 centistokes, a pour point ( as determined by JIS K-2269) of -5 to -30°C, a viscosity index (as determined by JIS K-2283) of not less than 80 and % C A of not more than 3. This lubricating oil composition is suitable for lubrication of parts including a wet brake and a wet clutch, such as automatic transmissions and tractors. The lubri­ cating oil composition of the present invention has a suitable viscosity at high temperatures and further is low in low temperature viscosity. Furthermore the lubricating oil com­ position of the present invention is excellent in friction characteristics, oxidation stability and also in seal rubber compatibility.

Description: The present invention relates to a lubricating oil composition for wet brake and wet clutch and more particularly to a lubricating oil composition for wet brake and wet clutch of automatic transmissions and tractors, the lubricating oil composition containing a combination of a mineral oil having a low pour point, a high viscosity index and an aromatics content C A of not more than 6 % with a polyester. Lubricating oil compositions for wet brake or wet clutch which are used in lubrication of parts including a wet brake and a wet clutch are required to be low in low-temperature viscosity in view of starting performance. In general, the low-temperature viscosity of a lubricating oil composition can be easily decreased by decreasing the viscosity of the total base oil. In this case, however, the viscosity of the lubricating oil composition is too low at high temperatures, thereby producing a problem that the lubrication performance is decreased and the lubricating oil composition is unsuitable for practical use. Therefore a method of compounding viscosity index improvers such as polymers to the low viscosity base oil has been widely used. This method, however, fails to solve the above problem because such polymers undergo viscosity reduction under shearing. From GB-A-1 092 008 a lubricating oil composition is known which is to be used for heavy duty uses such as engine oils, gear oils, transformer oils or machine oils. This known lubricating oil composition comprises a combination of paraffin base oil and naphthene base oil wherein said paraffin oil is defined for a specific cloud point and viscosity index. The pour point, the kinematic viscosity and the aromatics content (A) of this known lubricating oil composition are not defined. However, this known lubricating oil composition is not suitable for lubrication of wet brakes and wet clutches because of its high low-temperature viscosity and its low oxidation stability. The same applies to the lubricating oil compositions already known from FR-A-2 195 674 which are to be used to particular bearing and which comprise minor amounts of an anti-wear agent, an antioxidant and a viscosity index improver, and a major amount of a blend of 20 to 50 parts by volume of a petroleum oil having a kinematic viscosity at 38°c of from 7 x 10⁻⁶ to 7 x 10⁻⁴ m²/s (7 - 700 cSt ). Although it is described therein that paraffinic lubes having pour points of -15°C or lower can be used as the base oil, actually, a base oil having a pour point of -18°C is used. As can be seen from a comparison between example 1 and comparative example 12 following below, mineral oils as used in FRA-2 195 674 are not suitable for lubrication or parts including a wet brake and a wet clutch of automatic transmissions and tractors because of their high low-temperature viscosity and their insufficient oxidation stability and friction characteristics. Therefore it is the object of the present invention to provide a lubricating oil composition which is suitable for lubrication of a wet brake and a wet clutch and which holds a constant viscosity at high temperatures as one of the characteristics thereof and which is low in its low-temperature viscosity and which exhibits an excellent oxidation stability and excellent friction characteristics. The present invention provides a lubricating oil composition for wet brake and wet clutch containing a combination of a mineral oil having a low pour point, a high viscosity index and an aromatics content C A of not more than 6 % with a polyester, which is characterized in that it comprises 97 to 60 % by weight of a mineral oil been subjected to high refining comprising a first hydrogenation treatment optionally followed by an alkali distillation or sulfuric acid washing; or a first and a second hydrogenation treatment optionally followed by an alkali distillation or sulfuric acid washing; or a first, a second and a third hydrogenation treatment; and having a kinematic viscosity at 100°C of from 2.10⁻⁶ to 50.10⁻⁶ m²/s. (2-50 cSt), a pour point of from -5 to -30°C, a viscosity index of not less than 80, and a C A of not more than 3 %, and 3 to 40 % by weight of a polyester which is a hindered ester or dicarboxylic acid ester. The lubricating oil composition of the present invention has a suitable viscosity at high temperatures and further is low in low-temperature viscosity. In addition, it exhibits excellent friction characteristics and is excellent in oxidation stability and also in seal rubber compatibility. Therefore, the lubricating oil composition of the present invention is suitable as a lubricant additive for parts including a wet brake and a wet clutch. For example, it can be used as a lubricant additive for automatic transmission fluids and tractor oils. The mineral oil component of the lubricating oil composition of the present invention preferably has a sulfur content of not more than 0,01 % by weight, especially not more than 0,001 % by weight. According to a further preferred embodiment of the present invention the mineral oil component of the lubricating oil composition has a kinematic viscosity at 100°C of from 5 x 10 ⁻⁶ to 30 x 10 ⁻⁶ m²/s (5 - 30 cSt). According to another preferred embodiment of the present invention the mineral oil component of the lubricating oil composition has a pour point of from -7,5 to -30°C, preferably not more than -30°C. The viscosity index of the mineral oil of the lubricating oil composition of the present invention preferably has a viscosity index of not less than 85. The mineral oil preferably has a C A of not more than 1 %. According to another preferred embodiment of the present invention the mineral oil component of the lubricating oil composition has a kinematic viscosity at 100°C of from 5 x 10⁻⁶ to 30 x 10⁻⁶ m²/s (5 - 30 cSt), a pour point of from -7,5 to -30°C, a viscosity index of not less than 85 and a C A of not more than 1 %. The mineral oil as the major component of the lubricating oil composition of the present invention has a kinematic viscosity at 100°C of from 2 x 10⁻⁶ to 50 x 10⁻⁶ m²/s (2 to 50 cSt), preferably 5 x 10⁻⁶ to 39 x 10⁻⁶ m /s (5 to 30 cSt), a pour point of -5 to -30°C, preferably -7,5 to -30°C, a viscosity index of not less than 80, preferably not less than 85, and a C A of not more than 3 %, preferably not more than 1 %. If the above physical values are not within the above defined ranges, the desired lubricating oil composition cannot be obtained. From a viewpoint of oxidation stability, a mineral oil having a sulfur content of not more than 0,01 % by weight, especially not more than 0,001 % by weight is preferred. A mineral oil having the properties as described above can be obtained by refining to a high extent a distillate (having a boiling point under atmospheric pressure of 250 to 450°C) which has been obtained by distilling a paraffin crude oil or an intermediate crude oil. The distillate means an oil obtained either by atmospheric distillation of crude oil or by vacuum distillation of residual oil resulting from atmospheric distillation of crude oil. The used method of high refining is not critical, and any of the methods (1) to (5) as described below can be employed: (1) the distillate is subjected to a hydrogenation treatment or alternatively, after the hydrogenation treatment, the distillate is subjected to an alkali distillation or sulfuric acid treating; (2) the distillate is subjected to a solvent refining treatment, or alternatively, after the solvent refining treatment, the distillate is subjected to an alkali distillation or sulfuric acid treating; (3) the distillate is subjected to a hydrogenation treatment followed by a second hydrogenation treatment; (4) the distillate is subjected to a hydrogenation treatment, then to a second hydrogenation treatment, and further to a third hydrogenation treatment; (5) the distillate is subjected to a hydrogenation treatment followed by a second hydrogenation treatment, and further to an alkali distillation or sulfuric acid treating. One of the above methods will hereinafter be explained. A crude starting material for lubricating oil is produced from paraffin or intermediate crude oil by the usual method and then is subjected to a severe hydrogenation treatment. In this treatment, undesirable components, such as aromatics, for the lubricating oil fraction are removed or converted into useful components. Almost all of sulfur and nitrogen components are removed at the same time. Such fractional distillation as to obtain the necessary viscosity is carried out by vacuum distillation. Then, a known solvent dewaxing treatment is carried out so as to dewax to the pour point of a usual paraffin base oil, that is, about -15 to -10°C. After the dewaxing treatment, if necessary, a hydrogenation is carried out to hydrogenate the major portion of aromatic components into saturated components, thereby increasing thermal and chemical stability of the base oil. Then, to obtain the desired pour point, a dewaxing treatment is applied. For this treatment, a solvent dewaxing method and a deep dewaxing method can be employed. The conditions for the hydrogenation treatment vary with the properties of the feed oil. The reaction temperature is usually 200 to 480°C and preferably 250 to 450°C, the hydrogen pressure is usually 0,5 to 30 MPa (5 to 300 kg/cm²) and preferably 3 to 25 MPa (30 to 250 kg/cm²), and the amount of hydrogen introduced (per 1 000 1 of the fed distillate) is 30 to 3 000 Nm³ and preferably 100 to 2 000 Nm³. In this hydrogenation treatment, there are used catalysts which are prepared by depositing catalyst components such as groups VI, VIII group metals, preferably cobalt, nickel, molybdenum and tungsten on supports such as alumina, silica, silica alumina, zeolite, active carbon and bauxite. It is preferred that the catalyst be previously subjected to a preliminary sulfurization. As described above, after the hydrogenation treatment, the distillate is subjected to various treatments. When a second hydrogenation treatment or further a third hydrogenation treatment is applied, the treatment may be carried out under conditions falling within the ranges as described above. The conditions at first, second and third stage hydrogenation treatments may be the same or different. Usually the second hydrogenation treatment is carried out under more severe conditions than the first stage hydrogenation treatment, and the third stage hydrogenation treatment, under more severe conditions than the second stage hydrogenation treatment. An alkali distillation is a step where small amounts of acidic substances are removed to improve the stability of distillate. In this alkali distillation, alkalis such as NaOH and KOH are added and a vacuum distillation is conducted. A sulfuric acid treating is generally carried out as a finishing step of oil products, in which aromatic hydrocarbons, especially polycyclic aromatic hydrocarbons, olefins and sulfur compounds, are removed to improve the characteristics of distillate. For example, 0,5 to 5 % by weight of concentrated sulfuric acid is added to the distillate, the treatment is carried out at a temperature ranging between room temperature and 60°C, and thereafter a neutralization using NaOH, for example, is applied. The aforementioned methods (1) to (5) to be employed in the treatment of distillate comprise combinations of the operations as described above. Of these methods, the methods (1), (3) and (4) are particularly suitable. Polyesters which are used as the other component in the present invention include hindered esters and dicarboxylic acid esters. Hindered esters having a pour point of not more than -30°C, preferably not more than -40°C are used. Those having a pour point exceeding-30°C are not preferred because they increase the low temperature viscosity. From viewpoints of kinematic viscosity, viscosity index and pour-point, the following hindered esters are preferred. Polyols in which the β-carbon of alcohol is quaternary, such as neopentyl glycol, trimethylolpropane, trimethylolethane and pentaerythritol are used as the polyol component constituting the hindered esters. As fatty acids which form hindered esters in combination with the above polyols, straight chain or branched fatty acids having 3 to 18 carbon atoms, expecially 4 to 14 carbon atoms, especially branched fatty acids are preferred. Representative examples are straight chain fatty acids such as hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and decanoic acid, and branched fatty acids such as 2-ethylhexanoic acid, isooctanoic acid, isononanoic acid and isodecanoic acid. In addition, mixed fatty acids composed mainly of fatty acids having 4 to 14 carbon atoms are preferably used. These branched fatty acids and mixed fatty acids increase low temperature fluidity. As dicarboxylic acid esters, those having a pour... point of not more than -30°C, preferably not more than -40°C are used. Dicarboxylic acid eaters having a pour point of more than -30°C are not preferred because they increase the low temperature viscosity. From viewpoints of kinematic viscosity, viscosity index and pour point, the following dicarboxylic acid esters are preferred. Branched alcohols having 3 to 18 carbon atoms, especially 4 to 13 carbon atoms are preferred as the alcohol component to form dicarboxylic acid eaters. Representative examples are isobutyl alcohol, isoamyl alcohol, isohexyl alcohol, isooctyl alcohol, isononyl alcohol, isodecyl alcohol and isotridecyl alcohol. As dibasic acids to form dicarboxylic acid esters in combination with the above alcohols, dibasic acids having 4 to 16 carbon atoms can be used. Representative examples are adipic acid, azelaic acid, sebacic acid and dodecane dicarboxylic acid. The lubricating oil composition of the present invention comprises the aforementioned mineral oil and polyester. The lubricating oil composition comprises 97 to 60% by weight of mineral oil and 3 to 40% by weight of polyester, and preferably 90 to 70% by weight of mineral oil and 10 to 30% by weight of polyester. If the proportion of the polyester is less than 3% by weight, the effects resulting from addition of the polyester cannot be obtained. On the other hand, if the proportion of the polyester is in excess of 40% by weight, seal rubber compatibility and friction characteristics are undesirably decreased. To the lubricating oil composition of the present invention, if desired, additives such as an antioxidant, a detergent-dispersant, a viscosity index improver, a defoaming agent, an extreme pressure agent and a pour point decreasing agent can be added. When the lubricating oil composition of the present invention is used as a lubricating oil for use in lubricating parts including a wet brake or wet clutch, a friction modifier such as reaction products of fatty acids and amines can be added thereto. As the antioxidant, those commonly used such as phenol compounds, amine compounds and zinc dithiophosphate can be used. Representative examples are 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 4,4'-methylenebis(2,6-di-tert-butylphenol), phenyl-∝-naphthylamine, dioctyldiphenylamine, zinc di-2-ethylhexyldithiophosphate, zinc diamyldithiocarbamate, and pinene pentasulfide. Detergent-dispersants which can be used include an ashless dispersant and a metal-based detergent. For example, alkenylsuccinic acid imide, sulphonates and phenates are preferred. Representative examples of such preferred compounds are polybutenylsuccinic acid imide, calcium sulphonate barium sulphonate, calcium phenate, barium phenate and calcium salicylate. Viscosity index improvers which can be used include polymethacrylate and polybutene. The present invention is described in greater detail with reference to the following examples. EXAMPLES 1 TO 6, AND COMPARATIVE EXAMPLES 1 TO 11 Mineral oils having the properties shown in Table 1 and polyesters having the properties shown in Table 2 were mixed in the ratios shown in Table 3 to prepare lubricating oil compositions. These lubricating oil compositions were evaluated and the results are shown in Table 3. The testing methods are as follows. (1) Kinematic Viscosity Measured according to JIS K-2283. (2) Brookfield (BF) Viscosity Measured according to ASTM D2983-80. (3) ISOT (Test for Oxidation Stability of Lubricating Oil for Internal Combustion Engine) Measured according to JIS K2514 (165.5°C x 48 hours) (4) SAE No. 2 Friction rest Friction characteristics were evaluated by the use of a SAE No. 2 friction tester (produced by Greening Co., U.S.A.) under the following conditions: Disc : Three paper discs for an automatic transmission made in Japan Plate: Four plates made of steel for an automatic transmission made in Japan Number of revolutions of motor: 3,000 rpm Oil Temperature: 100°C µ 1200 means a dynamic friction coefficient at a number of rotations of 1,200 rpm and µ 0 means a static friction coefficient at the time that the motor is stopped. (5) Aniline Point Measured according to JIS k-2256. (6) Seal Rubber Dipping Test Measured according to JIS K-6301 under the following conditions. Rubber: Acrylonitrile-butadiene rubber (A727 produced by Japan Oil Seal Co., Ltd.) Oil Temperature: 150°C Test Duration: 170 hours COMPARATIVE EXAMPLE 12 Commercially available paraffin-based solvent refining oils were evaluated in the same manner as in Example 1. The results are shown in Table 3. *1 Mineral oil obtained in the following manner was used. Kuwait crude oil was subjected to atmospheric distillation followed by vacuum distillation. A fraction resulting from deasphalting of the fraction and residual oil as obtained above was used as the feed stock and was subjected to hydrogenation treatment under such severe conditions that the viscosity index of the dewaxed oil product (after the first dewaxing treatment) reached about 100. The product obtained by the above method was fractionated to produce two distillates having viscosities at 100°C of 2,3,10⁻⁶ m²/s (2.3 cSt) and 5,6,10⁻⁶ m²/s (5.6 cSt). These two distillates were further subjected to solvent dewaxing treatment. Conditions for this treatment were such that the pour point of dewaxed oil was -15°C. Then the above dewaxed oil was further subjected to hydrogenation treatment so that the aromatic content (as measured by the n-d-M-method) was not more than 1.5% by weight. *2 Paraffin base solvent refining oil *3 Paraffin base solvent refining oil *4 Naphthene based oil *5 Naphthene based oil *1 Package type additive containing a detergent-dispersant, an antioxidant, a friction modifier and a defoaming agent. *2 Polymethacrylate type viscosity index improver *3 Not more than room temperature *4 Commercially available oil The following can be seen from the results shown in Table 3. In Comparative Examples 1, 2 and 5 the low temperature viscosities (@ -40°C) were 23,8 Pa·s (23,800 cp), 36,9 Pa·s (36,900 cp) and 78,7 Pa·s (78,700 cp), respectively; that is, the requirement that the low temperature viscosity is not more than 20,0 Pa·s (20,000 cp) is not satisfied. In Comparative Examples 2 and 5, an increase in total acid number of ISOT is large, showing that the deterioration is seriously large. In Comparative Examples 3 and 4, and Comparative Examples 6 and 7, the total actid number of ISOT is large and further the low temperature viscosity is low. However, the requirement in practical use that the low temperature viscosity is not more than 20,0 Pa·s (20,000 cp)is not satisfied. In Comparative Examples 8 and 9, the aniline point is low, and the weight and volume change ratios of rubber are large, demonstrating that the swelling and softening is large. In Comparative Examples 10 and 11, the formulations are not within the range defined in the present invention. If the proportion of polyester is too small as in Comparative Example 10, the requirement in practical use that the low temperature viscosity (@ -40°C) is not more than 20,0 Pa·s (20,000 cp)is not satisfied. On the other hand, if the proportion of polyester is too large as in Comparative Example 11, the aniline point is low and further the weight and volume change ratio of rubber is large, demonstrating that the swelling and softening is large. If commercially available oil is used as in Comparative Example 12, the low temperature viscosity (@ -40°C) is 42,0 Pa·s (42,000 cp,) which fails to satisfy the requirement in practical use. Furthermore, friction characteristics are not sufficiently satisfactory. On the contrary, in Examples 1 to 6, the low temperature viscosity is not more than 20,0 Pa·s (20,000 cp,) and oxidation stability (ISOT) and seal rubber compatibility are good. Furthermore, friction characteristics are excellent. INDUSTRIAL APPLICABILITY The lubricating oil composition of the present invention is suitable as a lubricant additive for parts including a wet brake and a wet clutch. For example, it can be used as a lubricant additive for automatic transmission fluid and a tractor oil. In addition, the lubricating oil composition of the present invention can be used as a power stearing oil, an hydraulic oil or an internal combustion engine oil because it is low in low temperature viscosity and is good in oxidation stability and seal rubber compatability.

Claims: A lubricating oil composition for wet brake and wet clutch containing a combination of a mineral oil having a low pour point, a high viscosity index and an aromatics content C A of not more than 6% with a polyester, characterized in that it comprises 97 to 60% by weight of a mineral oil having been subjected to high refining comprising a first hydrogenation treatment optionally followed by an alkali distillation or sulfuric acid washing; or a first and a second hydrogenation treatment optionally followed by an alkali distillation or sulfuric acid washing; or a first, a second and a third hydrogenation treatment; and having a kinematic viscosity at 100°C of 2 . 10⁻⁶ to 50. 10⁻⁶ m²/s (2-50 cSt), a pour point of -5 to -30°C, a viscosity index of not less than 80, and a C A of not more than 3%, and 3 to 40% by weight of a polyester which is a hindered ester or dicarboxylic acid ester. The composition as claimed in claim 1 wherein the mineral oil has a sulfur content of not more than 0,01% by weight. The composition as claimed in claim 2 wherein the mineral oil has a sulfur content of not more than 0,001% by weight. The composition as claimed in any of claims 1 to 3 wherein the mineral oil has a kinematic viscosity at 100°C of 5 . 10⁻⁶ to 30 . 10⁻⁶ m²/s (5-30 cSt). The composition as claimed in any of claims 1 to 4 wherein the mineral oil has a pour point of -7,5° to -30°C. The composition as claimed in any of claims 1 to 5 wherein the mineral oil has a viscosity index of not less than 85. The composition as claimed in any of claims 1 to 6 wherein the mineral oil has a C A of not more than 1%. The composition as claimed in any of claims 1 to 7 wherein the mineral oil has a kinematic viscosity at 100°C of 5 . 10⁻⁶ to 30 . 10⁻⁶ m²/s (5-30 cSt), a pour point of -7,5° to -30°C, a viscosity index of not less than 85 and a C A of not more than 1%. The composition as claimed in any of claims 1 to 8 wherein the polyester has a pour point of not more than -30°C.

Inventors: SEIKI, HIROMICHI
Applicants: IDEMITSU KOSAN COMPANY LIMITED
Application year: 1987
Main classification: C10M111
IPC codes: C10M169, C10M111, C10N20, C10N40, C10N30