EP0686690B1

EP0686690B1 - Gear and transmission lubricant compositions of improved sludge-dispersibility.

Info

Publication number: EP0686690B1
Application number: EP94304031A
Authority: EP
Inventors: Shoji Takigawa
Original assignee: Sanyo Chemical Industries Ltd
Current assignee: Sanyo Chemical Industries Ltd
Priority date: 1994-06-06
Filing date: 1994-06-06
Publication date: 2002-11-13
Anticipated expiration: 2014-06-06
Also published as: DE69431710D1; EP0686690A1; DE69431710T2

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to gear and transmission lubricant compositions, having improved sludge-dispersibility, particularly, those useful for automotive gear and transmission fluids.

2. Description of the Prior Art:

Heretofore, in order to improve anti-wear or lubricating qualities and sludge-dispersibility, required for automotive gear and transmission fluids, there have been known those containing added thereto anti-wear or lubricating agents comprising phosphorus-containing organic compound, such as phosphate or phosphite esters or amine salts thereof, together with lower molecular weight dispersants, such as succinimides and benzyl amine. For example, US Patent 4,800,029 discloses an automatic transmission fluid (ATF) comprising a solvent-purified 150 neutral oil, containing added thereto an oleamide phosphate as anti-wear agent and polybutenyl succinimide as dispersant.
These fluids containing added thereto phosphorus-containing organic compounds together with lower molecular weight dispersants, however, have drawbacks, such that dispersabilities become insufficient under severe service conditions likely to form larger sludge, encounterd with friction or wear, accompanied with recent tendency of miniturization and output power up of automobiles; and it is desired to improve the dispersibility.
US-A-3640872 describes an automatic transmission fluid comprising a major proportion of a mineral lubricating oil and a zinc di (alkylphenoxypolyalkoxyalkyl) dithiophosphate and which is said to have a long friction-stable life. The anti-rust and corrosion inhibiting properties of the transmission fluid are improved by optionally including an additive which contains alkyl phosphoric acid esters.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a gear or transmission lubricant composition having improved sludge-dispersibility.
It is another object of this invention to provide a gear or transmission lubricant composition capable of providing reduced sludge formation.
It is still another object of the invention to provide a gear or transmission lubricant composition capable of maintaining good sludge-dispersibility even at severe service conditions.
It is yet another object of the invention to provide a gear oil or a transmission fluid, particularly ATF, having improved sludge-dispersibility.
According to the present invention, these and other objects have been attained by a gear or transmission lubricant composition which comprises a major portion of mineral base oil, having a viscosity of 1-50 cSt. at 100°C and having a viscosity index of at least 60; containing, based on the weight of the composition,
0.1-3% of (A) at least one phosphorus-containing metal-free organic compound, selected from the group consisting of compounds represented by any of the following formulae (1), (2), (3) and (4): O=P(OR)_p(OH)_3-p O=P(OR)_q(OH)_3-q NH_rR¹ _3-r P(OR)_p(OH)_3-p P(OR)_q(OH)_3-q NH_rR¹ _3-r wherein p is an integer of 1-3; q and r are independently integers of 1 or 2; R and R' are independently selected from the group consisting of saturated or unsaturated alkyl groups containing at least 4 carbon atoms, aryl groups and alkyl-substituted aryl groups;
and 1-30% of (B) at least one oil-soluble copolymer containing 92-99%_, preferably 94-98%, by weight of monomer units of (a) alkyl acrylate or methacrylate, preferably containing 1-24 carbon atoms in the alkyl group, and 1-8%, preferably 2-6%, by weight of monomer units of (b) N,N-dialkylaminoalkyl acrylate or methacrylate.
[In the above and hereinafter, (meth)acrylate represents acrylate and/or methacrylate; and similar expressions are used hereinafter].

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Base Oil

Suitable base oils used in the present invention are mineral oils, having a viscosity of 1∼50 cSt (centistokes), preferably 2∼30 cSt at 100°C. Base oils having a viscosity higher than 50 cSt give rise to energy loss because of too high viscosity resistance. Oils of less than 1 cSt are liable to result in evaporation during use at elevated temperature and to cause seizing on account of shortage of oil film exposed to extreme pressure at lubricating parts. Viscosity index (hereinafter referred to as VI) of base oils is at least 60, preferably at least 70. Oils of VI less than 60 do not provide satisfactory viscosity-temperature properties. Illustrative of suitable base oils are 100 neutral oil, 150 neutral oil, 300 neutral oil, 500 neutral oil, 150 bright stoch and the like.

(A) Phosphorus-containing Organic Compound

Suitable phosphorus-containing metal-free organic compound (A) are phosphate esters, phosphite esters, phosphonate esters, and amine salts of these esters; as well as mixtures of two or more of these compounds; as represented by any of the following formulae (1), (2), (3) and (4). O=P(OR)_p(OH)_3-p O=P(OR)_q(OH)_3-q· NH_rR' _3-r P(OR)_p(OH)_3-p P(OR)_q(OH)_3-q· NH_rR' _3-r
In the formulae (1), (2), (3) and (4), p is an integer of 1, 2 or 3; q and r are independently integers of 1 or 2.
R and R' are independently selected from the group consisting of saturated or unsaturated alkyl groups containing at least 4 carbon atoms, aryl groups and alkyl-subsituted aryl groups. Examples of R and R' include straight-chain or branched, saturated or unsaturated alkyl groups (aliphatic hydrocarbyl groups) containing 4∼30 or more, preferably 4∼20 carbon atoms, such as n-, iso-, sec- and t-butyl, hexyl, octyl, 2-ethylhexyl, decyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl, eicocyl, and oleyl groups; aryl groups, such as phenyl and naphthyl groups; and aryl groups subsituted substituted with one or more alkyl groups containing 1∼20, preferably 1∼10 carbon atoms in the alkyl group, such as tolyl group. These alkyl, aryl and alkyl-substituted aryl groups may be ether group-containing ones, such as lauroxyethyl, lauroxypropyl, oleoxyethyl groups.
Illustrative examples of these compounds of the following formulae (1), (2), (3) and (4) are as follows:
(1) mono-, di- and tri-alkyl and/or aryl phosphates, such as mono-oleyl phosphate, tricrezyl phosphate, and dibutyl lauroxypropyl phosphate;
(2) salts of mono- or di-alkyl and/or aryl phosphates as above, with mono- or di-alkyl amine, such as di-2-ethylhexyl amine;
(3) mono-, di- and tri-alkyl and/or aryl phosphites, such as di-n-butyl phosphite, tributyl phosphite,
(4) salts of mono- or di-alkyl and/or aryl phosphites as above, with mono- or di-alkyl amine, such as di-2-ethylhexyl amine.
Phosphorus-containing compounds, as written in C.J.Boner "Gear and Transmission Lubricants" (1964 Reinhold Publishing Corp.), page 94, Table 3.8, may also be used.
Among these phosphorus-containing metal-free organic compound (A), preferred are those of the formula (1), particularly alkyl phosphate containing 4∼18 carbon atoms in the alkyl group. The most preferred is mono-oleyl phosphate.
The amount of the phosphorus-containing metal-free organic compound (A) is 0.1∼3 %, based on the weight of the lubricant composition.

(B) Oil-soluble Copolymer

Suitable alkyl (meth)acrylates (a), constituting said oil-soluble copolymer (B), are ones containing 1∼24 carbon atoms in the alkyl group; and include, for example: (a₁) C8∼20 alkyl (meth)acrylates, such as octyl, decyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl and eicocyl (meth)acrylates; (a₂) C1∼4 alkyl (meth)acrylates, such as methyl, ethyl, propyl and butyl (meth)acrylates; (a₃) C5∼7 alkyl (meth)acrylates, such as pentyl, hexyl and heptyl (meth)acrylates; (a₄) C21∼24 alkyl (meth)acrylates, such as Nafol 20+ and Nafol 22+ (produced by Kondea-Chemie); and combinations of two or more of them.
Among these, preferred are (a₁) (particularly decyl methacrylate and dodecyl methacrylate), and combinations thereof with (a₂) (particularly methyl methacrylate).
Suitable N,N-dialkylaminoalkyl (meth)acrylate (b), constituting said oil-soluble copolymer (B), include one by the following formula (5):
wherein R₁ and R₂ are the same or different alkyl groups containing not more than 10 carbon atoms, R₃ is an alkylene group containing 2∼10 carbon atoms, and R₄ is hydrogen atom or methyl group.
Illustrative of (b) are N,N-dimethylaminoethyl (meth)acrylates, N,N-diethylaminoethyl (meth)acrylates, N,N-diethylaminohexyl (meth)acrylates, N,N-dimethylaminopropyl (meth)acrylates, N,N-dibutylaminooctyl (meth)acrylates, and mixtures of two or more of them. Among these, preferred are N,N-dimethylaminoethyl methacrylate and N,N-diethylaminoethyl methacrylate.
Said oil-soluble copolymer (B) may contain monomer units of (c) one or more of N-vinyl-pyrrolidone and morpholinoalkyl (meth)acrylates, to improve sludge dispersibility. Suitable morpholinoalkyl (meth)acrylates include ones containing 2∼4 or more carbon atoms in the alkylene, such as morpholinoethyl and morpholinopropyl (meth)acrylates. Among these, preferred is N-vinyl-pyrrolidone.
Said copolymer (B) may further contain monomer unis of (d) one or more additional monomers. Exemplary of additional monomers (d) are aromatic vinyl compounds, such as styrene and vinyltoluene; esters (such as alkyl esters containing not more than 20 carbon atoms in the alkyl group) of unsaturated dicarboxylic acid (such as maleic, fumaric and itaconic acids), for example, dibutyl, dioctyl and dilauryl maleates, and dihexyl, dihexadecyl and dioctadecyl fumarates; and vinyl esters (ones containing not more than 5 carbon atoms in the alkyl group), such as vinyl acetate and vinyl propionate; and so on. Among these, preferred is styrene, in view of VI and bodying effects.
The contents of these monomers units of (a), (b), (c) and (d) in said oil-soluble copolymer (B) are as follows:

Usually preferably

(a) 92∼99 % 94∼98 %

(a₁) 52∼99 % 64∼93 %

(a₂) 0∼40 % 5∼30 %

(b) 1∼8 % 2∼6 %

(c) 0∼10 % ∼ %

(d) 0∼30 % 0∼20 %
In the above and hereinafter, % represents % by weight.
Copolymer (B) can be produced by usual polymerization techniques, for instance, by radical polymerization of (a) and (b) with or without (c) and/or (d), within a solvent, such as mineral oil. There may be used any polymerization catalysts, for example, azo compounds, such as azobis-isobutyrenitrile (hereinafter referred to as AIBN) and azobis-valeronitrile, and peroxides, such as benzoyl peroxide, cumyl peroxide and lauryl peroxide, with or without chain transfer agents, such as mercaptans (lauryl mercaptan and the like).
Said copolymer (B) is oil-soluble and is effective as a VI improver in addition to dispersant. To attain these effects, (B) has a weight-average molecular weight (hereinafter referred to as Mw), as measured by GPC (gel permeation chromatography) using calibration curve of polystyrene, of generally 20,000∼200,000, preferably 30,000∼150,000. Polymer of too high molecular weight causes degradation to form shorter chain polymer when subjected to shearing and cannot maintain necessary viscosity and VI for a long period of time. Polymer of too low molecular weight is to be used in a larger amount in order to attain sufficient viscosity.
The gear or transmission lubricant composition of the present invention contains, as a practical use level of the lubricant, 0.1 - 3 %, more preferably 0.1∼2 %, of said phosphorus-containing organic compound (A) and 1∼30 %, preferably 2∼25 %, more preferably 3∼20 %, of said oil-soluble copolymer (B).
Concentrate containing (A) and/or (B) in higher concentration than the above range may be prepared, and this is diluted to the level of practical use.
The composition of this invention may further contain one or more additives, usually used in gear and transmission lubricants. Such additives include, for example, detergents, such as sulfonates, salicylates, phenates and naphthenates; dispersants, such as alkenylsuccinimides and Mannich condensates; anti-oxidants, such as thiophosphates, amines and hindered phenols; oiliness additives, such as fatty acids and esters thereof; antiwear agent, other than (A), such as molybdenum dithiophosphate and molybdenum carbamate; and extreme pressure agents, such as sulfur-containing compounds, phosphorus-containing compounds and chlorine-containing compounds. These additives can be used in such amounts : 0∼10 % of the detergent, 0∼10 % of the dispersant, 0∼5 % of the anti-oxidant, 0∼3 % of the oiliness additive, 0∼ 10 % of the antiwear agent, and 0∼10 % of the extreme pressure agent.
Compositions of the invention, containing said phosphorus-containing organic compound (A) and said oil-soluble copolymer (B), are useful as gear and transmission lubricants, particularly automotive gear lubricants. Excellent effects can be attained especially when used as automatic transmission fluid for torque converters.
Having generally described the invention, a more complete understanding can be obtained by reference to certain specific examples, which are included for purposes of illustration only and are not intended to be limiting unless otherwise specified.
In the following examples, parts represents parts by weight.

Preparation of Copolymers

Into a reaction vessel equipped with a stirrer, a thermometer and a condensor, 150 parts of a mineral oil (100 neutral oil) were charged and heated to 70°C under an atmosphere of nitrogen. Then, thereto were added dropwise the monomers (parts) written in Table 1 together with 1.7 parts of AIBN and 2.0 parts of lauryl mercaptan over 2 hours at the temperature, followed by heating to 100°C for 3 hours to complete the polymerization to obtain a solution of copolymer having Mw as written in Table 1.

Copolymer	B1	B2	B3	B4	B5	b1	b2	b3
Lauryl methacrylate	250	150	150	246	250	250	261	226
Hexadecyl methacrylate	―	―	85	―	―	―	―	―
Octadecyl methacrylate	23	23	―	23	23	23	27	23
Decyl acrylate	―	96	―	―	―	―	―	―
Methyl methacrylate	70	―	70	70	55	70	70	70
Butyl methacrylate	―	70	―	―	―	―	―	―
Dimethylaminoethyl methacrylate	18	―	―	―	15	―	3	42
Diethylaminoethyl acrylate	―	22	―	―	―	―	―	―
Dibutylaminoethyl methacrylate	―	―	18	―	―	―	―	―
Dimethylaminopropyl methacrylate	―	―	―	15	―	―	―	―
Morpholinoethyl methacrylate	―	―	―	7	―	18	―	―
N-vinyl-pyrrolidone	―	―	―	―	18	―	―	―
Styrene	―	―	30	―	―	―	―	―
Mw , × 10³	40	61	100	90	88	73	100	98

Examples 1 to 10, and Comparative Examples 1 to 6

According to the following Formulation I or II (%), mineral oil compositions were prepared.

Formulation	I	II
Each copolymer solution	10	18
Oleyl amine salt of dilauryl phosphate	1	―
Octyl amine salt of dioleyl phosphate	―	1
Polybutenylsuccinimide (Hitec E638)	3	―
Polyolefin sulfide (TLA369, produced by Texaco)	―	5
Perbasic calcium sulfonate (Hitec E611)	1	1
Dialkylzinc dithiophosphate (Amoco 194)	0.3	―
Dialkylzinc dithiophosphate (Amoco 198)	―	0.5
2,6-di-tert-butyl-p-crezole (Lubrizol 817)	0.2	―
A mineral oil (100 neutral)	84.5	74.5

Resistance to oxidation of each composition was evaluated in accordance with JIS K2514, measuring the amounts of sludge (pentane-insuluble matter, %) of Methods A and B. Method A represents the amount of sludge obtained by centrifuging the oil after the test, and Method B represents the amount of sludge obtained by centrifuging the oil to which a flocculant was added after the test. The amounts of Methds A and B show resistance to oxidation, and the difference between the amounts of Methods A and B means sludge dispersability.

The results were as shown in Table 2.

Example No.	Example	Comparative Example
	1	2	3	4	5	1	2	3
Copolymer	B1	B2	B3	B4	B5	b1	b2	b3
Formulation	I	I	I	I	I	I	I	I
Resistance to Oxidation	Method A	0.02	0.02	0.05	0.03	0.05	0.91	1.08	2.96
Method B	0.33	0.32	0.49	0.35	0.38	0.95	1.13	3.01
Difference	0.31	0.30	0.44	0.32	0.30	0.04	0.05	0.05
Example No.	Example	Comparative Example
	6	7	8	9	10	4	5	6
Copolymer	B1	B2	B3	B4	85	b1	b2	b3
Formulation	II	II	II	II	II	II	II	II
Resistance to Oxidation	Method A	0.05	0.03	0.06	0.03	0.05	0.90	1.23	2.99
Method B	0.35	0.32	0.36	0.39	0.35	0.94	1.28	3.05
Difference	0.30	0.29	0.30	0.36	0.30	0.04	0.05	0.06

As apparent from Tables 1 and 2, compositions of the present invention provided extremely small amount of sludge and showed excellent sludge dispersibility and resistance to oxidation.
Compositions of this invention, when used as gear and transmission lubricants, particularly automatic transmission fluid for torque converters, can attain excellent sludge dispersibility with remarkably reducing sludge formation.

Claims

A gear or transmission lubricant composition which comprises a major portion of mineral base oil, having a viscosity of 1-50 cSt. at 100°C and having a viscosity index of at least 60; containing, based on the weight of the composition,
0.1-3% of (A) at least one phosphorus-containing metal-free organic compound, selected from the group consisting of compounds represented by any of the following formulae (1), (2), (3) and (4): O=P(OR)_p(OH)_3-p O=P(OR)_q(OH)_3-q NH_rR¹ _3-r P(OR)_p(OH)_3-p P(OR)_q(OH)_3-q NH_rR¹ _3-r wherein p is an integer of 1-3; q and r are independently integers of 1 or 2; R and R' are independently selected from the group consisting of saturated or unsaturated alkyl groups containing at least 4 carbon atoms, aryl groups and alkyl-substituted aryl groups;
and 1-30% of (B) at least one oil-soluble copolymer containing 92-99%, preferably 94-98%, by weight of monomer units of (a) alkyl acrylate or methacrylate, preferably containing 1-24 carbon atoms in the alkyl group, and 1-8%, preferably 2-6%, by weight of monomer units of (b) N,N-dialkylaminoalkyl acrylate or methacrylate.
A composition according to Claim 1, wherein the monomer (a) comprises (a₁) alkyl acrylate or methacrylate containing 8-20 carbon atoms in the alkyl group, and optionally (a₂) alkyl acrylate or methacrylate containing 1-4 carbon atoms in the alkyl group.
A composition according to Claim 2, wherein said copolymer contains 52-99%, preferably 64-93%, by weight of monomer units of (a₁), and 0-40%, preferably 5-30%, by weight of monomer units of (a₂).
A composition according to Claim 2 or Claim 3, wherein (a₂) is methyl methacrylate.
A composition according to any one of Claims 1 to 4, wherein said copolymer further contains up to 10% by weight of monomer units of (c) at least one monomer selected from the group consisting of N-vinyl-pyrrolidone, morpholinoalkyl acrylate and morpholinoalkyl methacrylate; and/or up to 30% by weight of monomer units of (d) at least one monomer selected from the group consisting of aromatic vinyl compound, alkyl esters of unsaturated dicarboxylic acid containing not more than 20 carbon atoms in the alkyl group, and vinyl esters.
A composition according to any one of Claims 1 to 5, wherein said copolymer has a weight-average molecular weight of 20,000-200,000.
A composition according to any one of Claims 1 to 6, which further contains one or more additives as follows:

1) detergent preferably selected from sulfonates, salicylates, phenates and naphthenates;

2) dispersant preferably selected from alkenylsuccinimides and Mannich condensates;

3) anti-oxidant preferably selected from thiophosphates, amines and hindered phenols;

4) oiliness additive preferably selected from fatty acids and esters thereof;

5) antiwear agent preferably selected from molybdenum dithiophosphate and molybdenum carbamate; and

6) extreme pressure agent preferably selected from sulfur-containing compounds, phosphorus-containing compounds and chlorine-containing compounds.
A composition according to Claim 7, which contains said additive in such amounts as follows:

1) 0∼10% by weight of said detergent,

2) 0∼10% by weight of said dispersant,

3) 0∼5% by weight of said anti-oxidant,

4) 0∼3% by weight of said oiliness additive,

5) 0∼10% by weight of said antiwear agent, and

6) 0∼10% by weight of said extreme pressure agent.
A gear oil, particularly an automatic transmission fluid, comprising the composition according to any one of Claims 1 to 8.
A torque converter which has contained therein the automatic transmission fluid according to Claim 9.