LUBRICATING OIL COMPOSITION

Abstract: Lubricating oil composition which comprises: lubricating base oil, (A) at least one organophosphorus compound represented by the general formula (I), (II), (III), (IV), (V), (VI), (VII) or (VIII) and (B) at least one organomolybdenum compound selected from the group consisting of molybdenum oxysulfide alkylphosphoro­ dithioates and molybdenum oxysulfide alkyldithiocarbamates. The lubricating oil composition is excellent in antiwear properties, anti-seizure properties, and corrosion resistance, and is suitable for gear oils, and bearing oils, also for internal combustion engine oils and automatic transmission fluids, and further for hydraulic fluids, metal working fluids.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to lubricating oil compositions. More particularly it relates to lubricating oil compositions that are excellent in antiwear properties, anti-seizure properties, and corrosion resistance, and are suitable for gear oils, and bearing oils, also for internal combustion engine oils and automatic transmission fluids, and further for hydraulic fluids, and metal working fluids. 2. Description of the Related Art Lubricating oils for various applications are generally required to have anti-seizure properties and antiwear properties for many situations. Especially, lubricating oils that require a high degree of anti-seizure property and antiwear property need incorporation of extreme pressure agents, which has resulted in increased corrosion of metals and posed a great problem in practice. Metal deactivators have been added to lubricating oils incorporated with extreme pressure agents to solve this problems, but has given rise to a question of decreasing antiseizure property and antiwear property as side effects. Recently there was a proposal for preparation of lubricating oil compositions with improved anti-seizure property and antiwear property by incorporating into the base oil organomolybdenum compounds in combination with mono-, di-substituted phosphates or mono-, di-substituted phosphites (JP-A-75995/1984). Furthermore, in EP-A-0 286 239 and EP-A-0 239 088 lubricating oils are described which besides a mineral oil or synthetic oil as base oil comprise an organophosphorus compound such as a trialkylphosphite, and an asymmetric organometallic compound, for example an organomolybdenum compound, such as a molybdenum dialkyldithiophosphate or molybdenum dialkyldithiocarbamate. Although the lubricating oil compositions described above have shown some extent of improvement in anti-seizure property and antiwear property they have still left the problem of failure in reducing metal corrosion unsolved. SUMMARY OF THE INVENTION The object of this invention is to provide lubricating oil compositions with further improved anti-seizure properties and antiwear property and with little metal corrosion. The present invention relates to a new lubricating oil composition comprising a lubricating base oil, an organophosphorus compound and an organomolybdenum compound, which is characterized in that it contains (A) as organophosphorus compound at least one organophosphine compound represented by the general formula (I), (II) or (III) R¹R²R³P (I) wherein R¹, R² and R³ are each an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 25 carbon atoms or a cycloalkyl group having 6 to 25 carbon atoms, R¹R²PPR³R⁴ (II) wherein R¹, R² and R³ are the same as defined above, and R⁴ is an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 25 carbon atoms or a cycloalkyl group having 6 to 25 carbon atoms, or R¹R²P(CH₂)nPR³R⁴ (III) wherein R¹, R², R³ and R⁴ are the same as defined above, and n is an integer of from 1 to 4, and (B) at least one organomolybdenum compound selected from the group consisting of molybdenum oxysulfide alkylphosphorodithioates(MoDTP) of formula (IX) and molybdenum oxysulfide alkyldithiocarbamates (MoDTC) of formula (X) wherein each of R¹⁸, R¹⁹, R²⁰ and R²¹ stands for alkyl having 1 to 30 carbon atoms, cycloalkyl having 6 to 30 carbon atoms or phenyl or alkylaryl; and a and b are positive real numbers but not necessarily integers, to hold a + b = 4. DESCRIPTION OF PREFERRED EMBODIMENTS A lubricating base oil, the principal component of lubricaring oil composition, used in this invention can be selected from a variety of mineral oils and synthetic oils without any special limitation as far as they are of a type of base oil used for conventional lubricating oils. Properties of the base oil such as kinematic viscosity, viscosity index, and pour point, may be suitably specified depending on the applications and required characteristics of the lubricating oil composition. Mineral oils which can be used as the base oil include a distillate oil obtained by atmospheric distillation of a paraffin base crude oil, an intermediate base crude oil or a naphthene base crude oil, or by vacuum distillation of a residual oil resulting from the above atmospheric distillation and a purified oil obtained by conventional method, such as solvent-refined oil, hydrogenated oil and dewaxed oil. Synthetic oils include polybutene, poly-α-olefin, polyglycol ether, polyphenylether, polyol ester, complex ester, alkylbenzene, alkylnaphthalene, dibasic acid ester, phosphoric acid ester, silicone oil, silicic acid ester, and alkyldiphenyl. In a lubricating oil composition of this invention, an aforementioned base oil is incorporated with (A) organophosphine compounds and (B) organomolybdenum compounds each as defined above. The organophosphine compounds, the (A) component used herein, are organophosphine compounds represented by the above general formulae (I)to (III). The organophosphine compounds are at least one type of compound from among: tri-substituted phosphines represented by general formula (I); tetra-substituted diphosphines represented by general formula (II); and bis(di-substituted phosphino)alkanes represented by general formula (III). In the general formulae (I) to (III), each of R¹, R², R³ and R⁴ as described previously represents an alkyl group having 1 - 18 carbon atoms, an aryl group having 6 - 25 carbon atoms, or a cycloalkyl group having 6 - 25 carbon atoms, and n denotes an integer of from 1 - 4. Examples of tri-substituted phosphines represented by the above general formula (I) include trialkylphosphine such as trimethylphosphine, triethylphosphine, tri-n-propylphosphine, tri-iso-propylphosphine, tri-n-butylphosphine, tri-iso-butylphosphine, tri-n-hexylphosphine, tri-n-octylphosphine, tri-2-ethylhexylphosphine; triarylphosphine such as triphenylphosphine, tri-o-tolylphosphine, tri-m-tolylphosphine and tri-p-tolylphosphine; alkyl(aryl)phosphine such as dimethyl(phenyl)phosphine and methyl(diphenyl)phosphine; and tricyclohexylphosphine. Tetra-substituted diphosphines represented by the above general formula (II) are, for example, tetraalkyldiphosphine such as tetramethyldiphosphine, tetraethyldiphosphine, tetrabutyldiphosphine and tetraoctyldiphosphine and also tetraphenyldiphosphine. Bis(di-substituted phosphino)alkanes represented by the above general formula (III) are, for examples, bis(diarylphosphino)alkanes such as bis(diphenylphosphino)methane, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)-propane, 1,4-bis(diphenylphosphino)butane and also bis(dibutylphosphino)methane. In this invention, the (A) component consists of a single compound or of a combination of two or more compounds selected from the organophosphine compounds with the above general formulae (I) to (III). The proportion of the (A) component is not limited and can be suitable selected, according to various conditions, but preferably 0.01 - 5 % by weight and the most preferably 0.1 - 2 % by weight of the whole composition. In this invention, organomolybdenum compounds used as the (B) component are incorporated into the lubricating base oil together with the above (A) component. The organic molybdenum compounds are one or more compounds selected from the group consisting of molybdenum oxysulfide alkylphosphorodithioates (MoDTP) represented by the following general formula (IX) and and molybdenum oxysulfide alkyldithiocarbamates (MoDTC) represented by the following general formula (X) In the general formula (IX), each of R¹⁸ and R¹⁹ stands for an alkyl radical having from 1 to 30 carbon atoms (e.g. a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-amyl, isoamyl, n-hexyl, 1-methylpentyl, 4-methylpentyl, 1,3-dimethylbutyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, 2-octyl, n-decyl, isodecyl, lauryl, tridecyl, myristyl, palmityl, stearyl and isostearyl radical), a cycloalkyl radical having from 6 to 30 carbon atoms (e.g. a cyclohexyl radical) or a phenyl radical or alkylaryl radical (e.g. p-amylphenyl, p-octylphenyl, p-nonylphenyl, p-dodecylphenyl and p-pentadecylphenyl radical). Here, a and b are positive real numbers but not necessarily integers, to hold a + b = 4. In general formula (X) R²⁰ and R²¹ represent individually the same radicals as R¹⁸ and R¹⁹ in formula (IX). Furthermore, a and b are the same as for the aforesaid general formula (IX). In this invention, the (B) component consists of a single compound or a combination of two or more compounds selected from organomolybdenum compounds represented by the aforesaid general formulas (IX) and (X). The proportion of the (B) component is not limited and can be suitably selected, according to various conditions; to be preferably 0.05 - 5 % by weight and most preferably 0.1 - 2 % by weight of the whole composition. In the compositions of this invention, the content ratio of organophosphine compounds, (A) component, and organomolybdenum compounds, (B) component, is not limited. The weight ratio of (A) component to (B) component is preferably 1:100 - 100:1, more preferably 1:10 - 10:1, and the most preferably 1:5 - 5:1. In preparing a lubricating oil composition of this invention, either a mixture Of aforesaid (A) component and (B) component can be added, or (A) component and (B) component can be separately added to the lubricating base oil. To this lubricating oil composition, antioxidants, detergent dispersants, rust inhibitors, viscosity index improvers, pour point depressants, extreme pressure agents, oilness agents, antifoamers, and others can be suitably added accordingly as needed. Examples of antioxidants include phenolbased antioxidants, amine-based antioxidants zinc dialkyldithiophosphates. Detergent-dispersants include sulfonate-, phenate-, salicylate-,naphthenate-, or phosphonate-detergents, and alkenylsuccinimide-, or benzylamine-dispersants. Furthermore, alkenylsuccinates may be available as rust inhibitors; polymethacrylates, polybutenes, ethylenepropylene copolymers, or styrene-butadiene copolymers as viscosity index improvers; polyacrylates and others as pour point depressants; and silicones and others as antifoamers. Lubricating oil compositions of this invention are excellent in antiwear property, anti-seizure property, and corrosion resistance, and therefore can be effectively used: for gear oils and bearing oils; also for internal combustion engine oils and automatic transmission oils; and further for hydraulic fluids, metal working fluids, and others. This invention now will be illustrated in more detail by the following examples and comparative examples. Example 1 - 5 and comparative example 1 - 5 Lubricating oil compositions were prepared by adding in predetermined proportion (A) organophosphorus compounds (organophosphines), (B) organomolybdenum compounds, and metal deactivators to predetermined mineral base oils. Then, copper-strip corrosion tests, seizure property tests, and antiwear property tests were carried out on these lubricating oil compositions. The results are shown in Table 1. Herein, the copper-strip corrosion tests were made according to JIS K 2513 with the conditions of 100°C and 3 hours; the seizure property tests by Falex test according to ASTM D 3233; and antiwear property tests by Falex test according to ASTM D 2670. The seizure property was evaluated in terms of the seizure load N (lbs), and the antiwear property was evaluated in terms of the wear amount (mg) of the pin after rubbing under a load of 1334 N (300 lbs) for 60 minutes. The following are found in Table 1. (1) In comparative examples 1 and 2, the compositions, not containing organophosphine compounds, are all poor in copper-strip corrosion being rated 3(3b) and show a large amounts of wear in antiwear property tests. (2) In comparative example 3, the composition, not containing (B) organomolybdenum compounds, shows a large amount of wear in the antiwear property test although is good in copper-plate corrosion with the rate 1(1a). (3) In comparative example 4, the composition, containing metal deactivators together with (B) organomolybdenum compounds but not containing (A) organophosphine compounds, shows a large amount of wear in the antiwear property test although is good in copper-strip corrosion with the rate 1(1a). (4) In comparative example 5, the composition, not containing (A) organophosphine compounds, is unsatisfactory in all of the tests for copper-strip corrosion, seizure property, and antiwear property.

Claims: Lubricating oil composition comprising a lubricating base oil, an organophosphorus compound and an organomolybdenum compound, characterized in that it contains (A) as organophosphorus compound at least one organophosphine compound represented by the general formula (I), (II) or (III) R¹R²R³P (I) wherein R¹, R² and R³ are each an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 25 carbon atoms or a cycloalkyl group having 6 to 25 carbon atoms, R¹R²PPR³R⁴ (II) wherein R¹, R² and R³ are the same as defined above, and R⁴ is an alkyl group having 1 to 18 carbon atoms, an aryl group having 6 to 25 carbon atoms or a cycloalkyl group having 6 to 25 carbon atoms, or R¹R²P(CH₂) n PR³R⁴ (III) wherein R¹, R², R³ and R⁴ are the same as defined above, and n is an integer of from 1 to 4, and (B) at least one organomolybdenum compound selected from the group consisting of molybdenum oxysulfide alkylphosphorodithioates(MoDTP) of formula (IX) and molybdenum oxysulfide alkyldithiocarbamates (MoDTC) of formula (X) wherein each of R¹⁸, R¹⁹, R²⁰ and R²¹ stands for alkyl having 1 to 30 carbon atoms, cycloalkyl having 6 to 30 carbon atoms or phenyl or alkylaryl; and a and b are positive real numbers but not necessarily integers, to hold a + b = 4.

Inventors: IGARASHI, HIDEO, SEIKI, HIROMICHI, Igarashi, Hideo, c/o Idemitsu Kosan Co. Ltd., Seiki, Hiromichi, c/o Idemitsu Kosan Co. Ltd.,
Applicants: IDEMITSU KOSAN COMPANY LIMITED
Application year: 1988
Main classification: C10M137
IPC codes: C10M141, C10M137