EP0757712A1

EP0757712A1 - Lubricant composition

Info

Publication number: EP0757712A1
Application number: EP95916764A
Authority: EP
Inventors: Andrew Jonathan Markson; John William Anthony Pragnell; Mark Anthony Edwards
Original assignee: Castrol Ltd
Current assignee: Castrol Ltd
Priority date: 1994-04-26
Filing date: 1995-04-25
Publication date: 1997-02-12
Anticipated expiration: 2015-04-25
Also published as: CN1043053C; GB9408235D0; JPH10503535A; JP3780323B2; AU695511B2; PT757712E; EP0757712B1; ATE190997T1; DE69515861T2; DE69515861D1; KR100339777B1; DK0757712T3; NZ284520A; CN1151174A; WO1995029214A1; AU2313595A; GR3033741T3; CA2188936A1; ES2148513T3

Abstract

A lubricant composition suitable as a helicopter transmission lubricant comprises a synthetic base stock of viscosity in the range 5.0 to 10.0 cSt at 100 DEG C, an antioxidant component, a neutral organic phosphate component, a dicarboxylic acid component, a monocarboxylic acid component, a triazole component and a phosphorus containing extreme pressure additive.

Description

LUBRICANT COMPOSITION

This invention relates to a lubricant composition and is particularly concerned with a transmission lubricant suitable, for example, for helicopter transmission systems.

The development of new transmission systems, for example, for helicopters, has led to the requirement for dedicated lubricants for such purposes which can meet demanding load carrying and corrosion protection criteria. Specifications put forward by, for example, the U.K. Ministry of Defence and the United States Navy, pose requirements to be met by new dedicated helicopter transmission lubricants that cannot be fulfilled by existing aviation turbine engine lubricants. There is thus a need for the development of new and improved lubricant compositions for such purposes. The present invention seeks to fulfil this need.

Accordingly, the present invention provides a lubricant composition comprising:

a) a base component comprising one or more synthetic base stocks, which base component has a viscosity in the range of from 5.0 to 10.0 cSt at 100°C;

b) at least one antioxidant selected from aromatic amines and hindered phenolics;

c) at least one neutral organic phosphate of the formula (R'θ)₃PO where R¹ is a tolyl, phenyl, xylyl, alkyl or cycloalkyl group, the alkyl or cycloalkyl group having up to 10 carbon atoms; d) at least one saturated and/or unsaturated dicarboxylic acid of the general formula

H R.

I 2 1 I ->

Rr- • C) ^• C) -COOH i * 1 y 1

R_ H

3 R •,

wherein x+y+z is an integer in the range from 2 to 22 inclusive and where at least one of the groups R, to R₅ is a carboxylic acid group and the remaining groups R, to R₅ are selected from alkyl, hydroxy, nitro, amino, carboxyl, hydrogen or alkyl derivatives thereof, where alkyl is a short chain of up to 5 carbon atoms; and/or a dicarboxylic acid of one of the three formulae

wherein R_t is -COOH, alkyl, hydroxy, nitro, amino, hydrogen or alkyl derivatives thereof; R is -COOH; and n is an integer from 1 to 4 inclusive when R is -COOH or an integer from 2 to 4 inclusive when R, is not -COOH.

e) at least one straight and/or branched chain saturated or unsaturated monocarboxylic acid which is optionally sulphurised in an amount which may be up to 35% by weight; and/or an ester of such an acid; and f) at least one triazole of the formula:

where R, is -COOH or alkyl derivatives thereof, or short chain alkyl of up to 5 carbon atoms; n is zero or an integer between 1 and 3 inclusive; and Rf is hydrogen, moφhilino, alkyl, amido, amino, hydroxy or alkyl or aryl substituted derivatives thereof; or a triazole selected from 1,2,4 triazole, 1,2,3 triazole, 5-anilo- 1,2,3, 4-thiatriazole, 3-amino- 1,2,4 triazole, 1 -H-benzotriazole- 1 -yl-methylisocy anide, methylene-bis-benzotriazole and naphthotriazole; and

g) at least one phosphorus containing extreme pressure additive.

In component (d) above the bicyclic structural formula is intended to indicate that the group(s) R₂ may be attached to either or both aromatic rings.

At least one base stock of the base component, is preferably a synthetic ester base stock, especially a polyol ester base stock. The synthetic polyolester which preferably forms a base stock of the lubricating composition of the present invention may be made from C₅ to C,₂ monocarboxylic acids esterified with polyols or polyol ethers such as neopentylglycol, dimethylolpropane, trimethylolpropane, pentaerythritol or dipentaerythritol. These are conventional synthetic ester base stocks. Preferred esters are those which are described in U.S. Patent 4826633. The viscosity may be adjusted to lie within the required range by inclusion of one or more viscosity index improvers.

For adequate performance as a transmission lubricant, the base component preferably has a viscosity in the range of 8.5 to 9.5 cSt, more preferably 8.75 to 9.25 cSt at 100°C. The base component may comprise a single polyol ester but is more usually a mixture of polyol esters, for example, a mixture of a polyol ester having a viscosity of about 4.0 cSt at 100°C with a polyol ester having a viscosity of about 12.0 cSt at 100°C. Preferred synthetic polyol esters are reaction products of pentaerythritol and/or trimethylolpropane and an acid mixture comprising C₅ to C_I0 straight and branched chain acids.

The antioxidant component b) may be a hindered phenolic antioxidant such as butylated hydroxytoluene, suitably present in an amount of 0.01 to 5%, preferably 0.4 to 0.8%, by weight of the lubricant composition. Alternatively, or in addition, component b) may comprise an aromatic amine antioxidant such as mono-octylphenylalphanapthylamine or p,p-dioctyldiphenylamine, used singly or in admixture. The amine anti-oxidant component is suitably present in a range of from 0.01 to 5% by weight of the lubricant composition, more preferably 0.5 to 1.5%.

The neutral organic phosphate which forms component c) of the formulation may be present in an amount of 0.01 to 4%, preferably 1.5 to 2.5% by weight of the composition. The neutral organic phosphate is also a conventional ingredient of lubricating compositions and any such neutral organic phosphate falling within the formula as previously defined may be employed. Tri-cresyl phosphate is a preferred phosphate for use in the present invention. Components d), e) and f) are intended to provide a corrosion inhibiting three component system. The combination has been found to enable the provision of lubricant compositions capable of passing United States Navy corrosion inhibition requirements (Ball Corrosion Test - ARP 4249) in which a result of 50% non corroded specimen is deemed a satisfactory corrosion protection requirement.

The dicarboxylic acid forming the first component of the anti-corrosion combination may be any dicarboxylic acid falling within the definition given hereinbefore. The dicarboxylic acid may be present in a proportion of up to 0.15% by weight of the composition. It should be noted however, that it is desirable that sebacic acid or an equivalent thereof should always be present in the composition even if another dicarboxylic acid falling within the above definition is present because sebacic acid or an equivalent of it may be necessary to meet parts of the specification other than the ball corrosion test, for example, for satisfactory lead corrosion resistance.

Examples of dibasic acids, other than sebacic acids, which may be used in the present invention, are adipic acid, azelaic acid, dodecanedioic acid, 3-methyladipic acid, 3-nitrophthalic acid, 1,10-decanedicarboxylic acid, and fumaric acid.

The second component of the anti-corrosion combination is a straight or branch-chained, saturated or unsaturated monocarboxylic acid or ester thereof which may optionally be sulphurised in an amount up to 35% by weight. Preferably the acid is a C₄ to C₂₂ straight chain unsaturated monocarboxylic acid. The preferred concentration of this additive is from 0.001% to 0.35% by weight of the total lubricant composition. The preferred monocarboxylic acid is sulphurised oleic acid. However, other suitable materials are oleic acid itself; valeric acid and erucic acid.

The third component of the anti-corrosion combination is a triazole as previously defined. The triazole should be used at a concentration from 0.005% to 0.25% by weight of the total composition. The preferred triazole is benzotriazole.

Component g) of the composition comprises at least one phosphorus containing extreme pressure additive. Examples of such additives are amine phosphate extreme pressure additives such as that known under the trade name IRGALUBE 349 and/or triphenyl phosphorothionate extreme pressure/anti-wear additives such as that known under the trade name IRGALUBE TPPT. Such amine phosphates are suitably present in an amount of from 0.01 to 2%, preferably 0.2 to 0.6% by weight of the lubricant composition while such phosphorothionates are suitably present in an amount of from 0.01 to 3%, preferably 0.5 to 1.5% by weight of the lubricant composition. Preferably, a mixture of an amine phosphate and phosphorothionate is employed.

For the provision of a helicopter transmission lubricant the amounts of the additive are selected so as to comply with the United States Navy requirement for the Ryder gear test, conducted at 100°C, (average of 6 runs) of 200 (relative rating, % Herco A as reference fluid).

The following example is intended to illustrate a preferred lubricant composition in accordance with the invention. % bv weight

mono-octylphenylalphanaphthylamine 0.5% butylated hydroxy toluene 0.5% benzotriazole 0.1% sulphurised oleic acid 0.05% sebacic acid 0.01% tri-cresyl phosphate 2.0% amine phosphate 0.4% triphenyl phosphorothionate 1.0% silicone antifoam agent 2ppm base synthetic ester fluid mixture to give a viscosity for the composition of 8.75 to 9.25 cSt 95.44%

The resulting composition was found to give a value of 204.7 in the Ryder gear test, 100°C (as relative rating, % Herco A) and pass rating in the Ball Corrosion Test (in accordance with ARP method 4249).

Claims

„CLAIMS

1. A lubricant composition comprising:

c) at least one neutral organic phosphate of the formula (R'0)₃PO where R¹ is a tolyl, phenyl, xylyl, alkyl or cycloalkyl group, the alkyl or cycloalkyl group having up to 10 carbon atoms;

d) at least one saturated and/or unsaturated dicarboxylic acid of the general formula

^R2 ^{H R}-

R₅ H ₄

wherein x+y+z is an integer in the range from 2 to 22 inclusive and where at least one of the groups R, to R₅ is a carboxylic acid group and the remaining groups R^ to R₅ are selected from alkyl, hydroxy, nitro, amino, carboxyl, hydrogen or alkyl derivatives thereof, where alkyl is a short chain of up to 5 carbon atoms; and/or a dicarboxylic acid of one of the three formulae

wherein R is -COOH, alkyl, hydroxy, nitro, amino, hydrogen or alkyl derivatives thereof; R is -COOH; and n is an integer from 1 to 4 inclusive when R is -COOH or an integer from 2 to 4 inclusive when R, is not -COOH.

e) at least one straight and/or branched chain saturated or unsaturated monocarboxylic acid which is optionally sulphurised in an amount which may be up to 35% by weight; and/or an ester of such an acid; and

f) at least one triazole of the formula:

where R, is -COOH or alkyl derivatives thereof, or short chain alkyl of up to 5 carbon atoms; n is zero or an integer between 1 and 3 inclusive; and R^is hydrogen, moφhilino, alkyl, amido, amino, hydroxy or alkyl or aryl substituted derivatives thereof; or a triazole selected from 1,2,4 triazole, 1,2,3 triazole, 5-anilo- 1,2,3, 4-thiatriazole, 3-amino- 1,2,4 triazole, 1 -H-benzotriazole- 1 -yl-methylisocyanide, methylene-bis-benzotriazole and naphthotriazole; and

g) at least one phosphorus containing extreme pressure additive.

2. A lubricant composition according to claim 1 wherein at least one base stock of the base component is a polyol ester.

3. A lubricant composition according to claim 2 wherein the polyol ester base stock comprises one or more C₅ to C₁₂ monocarboxylic acids esterified with one or more polyols or polyol ethers.

4. A lubricant composition according to anyone of claims 1 to 3 wherein the base component has a viscosity in the range of from 8.5 to 9.5 cSt at 100°C.

5. A lubricant composition according to any one of the preceding claims wherein the antioxidant comprises a hindered phenolic antioxidant present in an amount of 0.4 to 0.8% by weight of the composition.

6. A lubricant composition according to anyone of the preceding claims wherein the antioxidant comprises an aromatic amine antioxidant present in an amount of 0.5 to 1.5% by weight of the composition.

7. A lubricant composition according to any one of the preceding claims wherein the neutral organic phosphate is present in an amount of 1.5 to 2.5% by weight of the composition.

8. A lubricant composition according to any one of the preceding claims wherein the saturated and/or unsaturated dicarboxylic acid component (d) is present in an amount of up to 0.15% by weight of the composition.

9. A lubricant composition according to any one of the preceding claims wherein the saturated and/or unsaturated dicarboxylic acid component (d) comprises sebacic acid.

10. A lubricant composition according to any one of the preceding claims wherein the monocarboxylic and component (e) is present in an amount of from 0.001 to 0.35% by weight of the composition.

11. A lubricant composition according to any one of the preceding claims wherein the monocarboxylic acid component (e) comprises sulphurised oleic acid.

12. A lubricant composition according to any one of the preceding claims wherein the triazole component (f) is present in an amount of from 0.005 to 0.25% by weight of the composition.

13. A lubricant composition according to any one of the preceding claims wherein the triazole component (f) comprises benzotriazole.

14. A lubricant composition according to any one of the preceding claims wherein the extreme pressure additive component (g) comprises an amine phosphate extreme pressure additive present in an amount of from 0.2 to 0.6% by weight of the composition.

15. A lubricant composition according to any one of the preceding claims wherein the extreme pressure additive component (g) comprises a phosphorothionate extreme pressure additive present in an amount of from 0.5 to 1.5% by weight of the composition.

16. A helicoptor transmission lubricant comprising components (a) to (g) as defined in any one of the preceding claims.

17. A helicoptor transmission lubricant according to claim 16 wherein components (b) to (g) are present in amounts selected so as to comply with the United States Navy requirement for the Ryder gear test, conducted at 100°C, of 200 (relative rating, % Herco A as reference fluid).