CA2077555A1

CA2077555A1 - Lubricating grease composition

Info

Publication number: CA2077555A1
Application number: CA002077555A
Authority: CA
Inventors: Wolfgang Mader; Georg Grun
Original assignee: Individual
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1990-03-07
Filing date: 1991-03-05
Publication date: 1991-09-08
Also published as: JP2964165B2; GB2241707A; DE69101376D1; GB9005104D0; DE69101376T2; JPH05504369A; WO1991013955A1; EP0523064B1; EP0523064A1

Abstract

A lubricating grease composition comprising a major proportion of a lubricating base oil, a lithium soap complex and an organic metal compound. The metal of the organic metal compound is selected from molybdenum, tungsten, vanadium, niobium and tantalum, and is preferably molybdenum. The grease can be used to lubricate mechanical parts such as antifriction bearings, and exhibits a long lifetime at high temperatures.

Description

WO91/13~5 ~ CT/E~1/~07 2077.~ ., 5 LUBRICATI~G GREASE COMPOSITIO~

This invention relates to a lubricating grease composition and, more especially, to grease compositions thickened wit~ lithium soap.

Lithium soap greases are well known and are used in the lubrication of many automotive and industrial applications, for example ~earings, gears and couplings. Whilst lithium soap greases, and particularly lithium soap complex greases, are often favoured for higher temperature applications, the greases have the disadvantage that they have a limited lifetime at temperatures exceeding about 120C as the oil tends to separate ("bleed") from the grease, and thus fre~uent reapplication of the grease is required.

The present invention provides a lithium complex grease with prolonged lifetime at high temperatures. More specifically the invention provides a lu~ricating grease composition comprising a major proportion of a lubricating base oil, a thickening amount of a lithium soap complex and an effective amount of an organic metal compound wherein the metal is selected from molybdenum, tungsten, vanadium, niobium and tantalum.

The grease according to the invention has the advantage that it has a significantly improved lifetime at high temperatures, the improvement being particularly evident at temperatures between about 120 and 160C. The grease has a lowe~ tendency to bleed oil compared with other lithium soap-containing greases. Thus by e~ploying the grease, the number of reapplications necessary to maintain satisfactory lubrication of the mechanical part to which the grease is applied can be considerably reduced. In some instances, where the mechanical part is enclosed in a sealed container, the grease can provi~e ~lifetime" lubrication, i.e. it need not be renewed for t~e lifetime of the mechanical part.

WO91/1395; PCT/E~l/~07 ~ r~ - 2 -Examples of such applicati~ns include automotiveantifriction bearings and sliding bearings.

The amount of lithium soap complex present in the grease is preferably from 2 to 30 wt %, preferably 5 to 20 wt % based on the total ~eight of the composition. It is preferred that the lithium complex soap comprises a lithium soap of a C12 to C24 hydroxy fatty acid and at least one other lithium compound. This other lithium compound is advantageously either a lithium soap of a C2 to C12 aliphatic dicarboxylic acid or a lithium salt of boric acid, or a mixture of both.

More preferably the lithium soap of the hydroxy fatty acid is a C16 to C20 hydroxy fatty acid. A particularly preferred hydroxy fatty acid is hydroxystearic acid, for example 9-hydroxy-, 10-hydroxy-, or 12-hydroxysteari~ acid, more preferably the latter. Ricinoleic acid, which is an unsaturated form of 12-hydroxystearic acid having a double bond in the 9-10 position, can also be used. Other suitable hydroxy fatty acids include 12-hydroxybehenic acid and lO-hydroxypalmitic acid.

Where the other lithium-containing compound is an aliphatic dicarboxylic acid, the proportion of dicarboxylic acid to hydroxy fatty acid employed is generally a weight ratio of between 0.05 and l, usually between 0.1 and 0.8, parts dicarboxylic acid per part hydroxy fatty acid. The dicarboxylic acid is preferably a C4 to Cl2, more preferably C6 to Clo, aliphatic dicarboxylic acid. Examples of suitable acids include oxalic, malonic, succinic, qlutaric, adipic, suberic, pimelic, azelaic, dodecanedioic and sebacic acids. Azelaic and sebacic acids are especially preferred.

WO91/1~955 PCT/E~1/00407 Where the other lithium-containing compound is the lithium salt of boric acid, t~e proportion of ~ydroxy fatty acid to boric acid employed is generally a weight ratio of between 3 and l00 parts, usually between S and 80 parts, hydroxy fatty acid per part boric acid.

The lithium soap complex may also include a second hydroxycarboxylic acid. This generally has 3 to 14 carbon atoms and an -OH group not more than 6 carbon at atoms away from the carboxyl group. This acid can be either an aliphatic acid such as lactic acid, 6-hydroxydecanoic acid, 3-hydroxybutanoic acid, l-hydroxycaproic acid, 4-hydroxybutanoic acid, 6-hydroxy-alpha-hydroxystearic acid, etc. or an aromatic acid such as parahydroxy-benzoic acid, salicylic acid, 2-hydroxy-4-hexylbenzoic acid, metahydrorybenzoic acid, 2,5-dihydroxybenzoic acid (gentisic acid); 2,6-dihydroxybenzoic acid (gamma resorcyclic acid);
4-hydroxy-4-methoxybenzoic acid, etc. or a hydroxyaromatic aliphatic acid such as orthohydroxyphenyl, metahydroryphenyl, or parahydroxyphenyl acetic acid. A
cycloaliphatic hydroxy acid such as hydroxycyclopentyl carboxylic acid or hydroxynaphthenic acid could also be used. Particularly useful hydroxy acids are lactic acid, salicylic acid, and parahydroxybenzoic acid.

Alternatively a lower alkyl ester, usually, a C1 to C4 alkyl ester of the above second hydroxycarboxylic acid can be used instead of the free acid. This is especially benericial when boric acid is employed as the ester aids dispersion of the insoluble salt. As example of a preferred ester is nethyl salicylate. When a second hydroxycarboxylic acid is employed in the grease composition, the proportion is generally a weight ratio of 0.1 to 10 parts, usually 0.5 to S parts, second ~ydroxycar~oxylic acid per part of the acid co~ponent of the said other lithium-containing compound, for example boric acid.

WO 91/13955 PCl/EP91/00407 .,.
The metal of the organic metal compound is preferably molybdenuz. The organic component of this compound is preferably a thiocarbamate or xanthate. Thus preferred organic metal compounds are molybdenum thiocarbamate and molybdenu~ xanthate compounds. Molybdenum dialXyldithiocarbamate and molybdenum oxysulphide dialkyldithiocarbamate.

The preferred amount of the organic metal compound present in the grease composition is from 0.1 to 10 wt ~, more preferably 0.5 to 5 wt %, based on the total weight of the composition. ~he organic metal compound acts as an antiwear agent and prolongs the high temperature lifetime of the grease.

In a preferred embodiment, the grease according to the invention also contains an antioxidant, which is generally present in an amount from 0.1 to 5 wt %, preferably 0.5 to 3 wt %, based on the total weight of the composition. The antioxidant employed is preferably an amine based antioxidant compound, an example being alXyldiphenylamine.

The lubricating base oil employed in the grease composition can be any of the conventionally used lubricating oils and is preferably a mineral oil or a blend of mineral and synthetic oils. In general these lubricating oils have a viscosity in the range of 35 to 300 SUS at 210F, and a viscosity index in the range of 30 to 170, preferably 30 to 140. Mineral lubricating oil base stocks used in preparing the greases can be any conventionally refined base stocks derived from paraffinic, naphthenic and mixed base crudes. Synthetic lubricating oils that can be used include esters of dibasic acids, such as a di-2-ethylhexyl sebacate, esters of glycols such as C13 oxo WO 91t13955 PCI/EP91/00407 - S - 2~77,-i''''.~' acid diester or tetraethylene glycol, or complex esters such as one formed from l mole of sebacic acid and 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid.
Other synthetic oils that can be used include synthetic hydrocarbons such as alkyl benzenes, e.g. alkylate bottoms from the alXylation of benzene with tetrapropylene, or the polymers and copolymers of alpha olefins; silicone oils, e.g. ethyl phenyl polysiloxanes, methyl polysiloxanes, etc.;
polyglycol oils, e.g. those obtained by condensing butyl alcohol ~ith propylene oxide; carbonate esters, e.g. the product of reacting Cg oxo alcohol with ethylcarbonate to form a half es~er followed by reaction of the latter with tetraethylene glycol, etc. Other suitable synthetic oils include the polyphenyl ethers, e.g. those having from about 3 to 7 ether linkages and about 4 to 8 phenyl groups (see US
Patent 3,424,678, column 3).

The grease according to the invention also has the advantage that the usual benefits associated with lit~ium complex greases may be retained, together with the additional benefit of prolonged lifetime at high temperatures. Usual benefits associated with lithium soap greases include good water resistance, high dropping point, and good mechanical and chemical stability. The grease according to the invention can also be employed in low temperature, as well as high temperature, applications.

The in~ention will ~ow be illustrated by the following Examples. All the greases of these Examples were made to a consistency of N~GI grade 2, i.e. all the greases have a 60-stroke vork penetration at 25C of 265-295, as determined by ASTM ~ethod D21~ or D2665.

W09l/13955 PCT/E~1/~07 " .

; ' Examples 1-4 Examples 1-3 demonstrate grease composition according to the invention based on lithium complexes comprising a lithium soap of a hydroxy fatty acid and a lithium soap of an aliphatic discarboxylic acid. Example 4 is comparative, using the same lithium soap complex.

The test results of Examples 1-4 are given collectively in Table 1.

Exam~le 1 A lithium complex grease was formulated with the following components:

Commonent Wt %

Paraffinic base oil 80.5%
(V40-l5omm2/s~ VI_g5)1 Lithium hydroxide monohydrate 2.5 12-Hydroxystearic acid 11.0 Azelaic acid 2.0 Molybdenum oxysulphide dialkyldithiocarbamate2 2.S
Alkydiphenylamine3 1.5 (1) V40 ~ viscosity at 40C, VI = Viscosity Index ~2) Supplied as Sakuralube 600 from Asahi Denka Rogyo KK.
(3) Supplied as Irganox L57 from Ciby-Geigy Limited.

WO91/13955 PCT/E~l/0~07 2Q77,;'~

The base oil and lit~ium soap complex components were formulated as described in Example 1 of GB Patent 1,384,904.
The molybdenum oxysulphide dialkyldithiocarbamate (MDDC) and the alkyldiphenylamine additives were then added to the grease, and the grease was milled using a conventional grease mill.

The lifetime of the grease at high temperature ~as measured according to the standard test DIN 51821 T2 A/1500/6000. In this test a set of five bearings is run under specified conditions of temperature, load and spee~.
When the required driving momentum becomes too high due to lubricant starvation, the alternator shuts down automatically. Five lubricant lifetimes are thereby obtained and the following data is calculated:

Flo which represents the time after which the first ten percent of the bearings are starved of lubricant; an~

Fso which represents the time after which fifty percen, of the bearings are starved of lubricant.

A grease ~hich has an Fso value of at least 100 hours at a given temperature is regarded as a lifetime lubricant at that temperature.

The results of the test are given in Table 1 below.

~x~mple 2 A grease composition was formulated as in Example 1 except that ~DDC employed was supplied as Molyvan A from Vanderbilt Company Inc.

The grease was tested as described in Example 1 and the results are given in Table 1 below.

WO 91/1395~ j PCT/E~1/~07 ~ 8 ExamDle 3 A grease composition was formulated as in Example 1 except that the alkyldiphenylamine was omitted and the amount of ~DDC increased to 3 wt %. The balance was made up by increasing the amount of base oil to 81.5 wt %.

The grease was tested as described in Example 1 and the results are given in Table 1 below.

Exam~le 4 The greases of Examples 1-3 were compared with a conventional lithium complex soap grease. This grease contained the same base oil and lithium complex as the above Examples, but contained no molybdenum compound nor alkyldiph~nylamine.

This comparative grease was tested as described in Example 1 and the results are given in Table 1 below.

Table 1 Grease Composition Lifetime Flo/Fso (hrs) Example No. 140C 150C 1600C

(Co~par~tive) 5 PCT/E~1/~7 _ g _ 2!J77;?,~

The results show that grease compositions according to the invention have significantly longer lifetime than zomparative greases using t~e same base oil and lithium complex. For example, at 140C Grease l has a lifetime over five times as great as comparative Grease 4.

Exam~les 5 & 6 These two examples demonstrate a qrease according to the invention based on a lithium complex comprising a lithium soap of a hydroxy fatty acid and the lithium salt of boric acid, and compare this grease with a conventional grease containing the same lithium soap complex. The results are given collectively in Table 2.

ExamDle 5 A grease composition was formulated with the following components:

ComDonent Wt Paraffinic base oil 78.3 (v4o_llOmm2/s~ VI_95)1 Lithium hydroxide monohydrate3,5 l2 - Hydroxystearic acid ll.0 Boric acid 0.9 Methylsalicylate 2.3 MDDC2 2.5 Alkydiphenylamine3 l.5 WO91/13955 PCT/EW1/~07 (l) V40 = viscosity at 40C, VI = Viscosity Index (2) Supplied as Sakuralube 600 from Asahi Denka Kogyo KR.
(3) Supplied as Irganox L57 from Ciby-Geigy Limited.

The base oil and lithium soap complex components were formulated as described in Example 2 of US Patent 3,758,497.
The MDDC and alkyldiphenylamine additives were then added, and the grease was milled using a conventional grease mill.

The grease was tested as described in Example l and the results are given in Table 2 below.

Exammle 6 A conventional lithium complex grease containing the same lithium soap complex as the grease of Example 5, but omitting the MDDC and alkyldiphenylamine was tested as described in Example l, for comparative purposes. The results are given in Table 2 below.

Table 2 Grease Composition Lifetime Flo/Fso (hrs) at 160C
Example No.

(Co:parative) WO 91/13955 PCI`/EP91/00407 These results show that, although the Flo lifetime at 160C are comparable at approximately 60 hours, the Fso lifetime of Grease 5, a grease according to the invention, is 1.7 ti~es greater than the Fso lifetime of comparative Grease 6.

ExamDle 7 A grease composition was formulated as in Example 2 except that the paraffinic base oil was replaced with a base oil blend of 28.5 wt %, based on the total grease composition, of a poly-alpha-olefin (V40_48mm2/s, Vloo -7.9mm2/s) and 52 wt ~, based on the total grease composition, of a paraffinic oil base (V4o-llomm2/s~ V10O_ 12mm 2/s). The blended base oil yielded the following viscosities:

V40_80 mm2/s, V10o-lo.3mm2/s~ VI_lll.

The grease was tested as described in Example 1 at 160C. The Flo result was 101 hours and the Fso result was 134 hours. Thus this grease also demonstrated long lifetime at high temperature.

Claims

1. A lubricating grease composition comprising a major proportion of a lubricating base oil, a thickening amount of a lithium soap complex and an effective amount of an organic metal compound wherein the metal is selected from molybdenum, tungsten, vanadium, niobium and tantalum.

2. A grease composition according to Claim 1 wherein the metal of the organic metal compound is molybdenum.

3. A grease composition according to Claim 1 or 2 wherein the organic component of the organic metal compound is a thiocarbamate or xanthate.

4. A grease composition according to any preceding claim wherein the organic metal compound is molybdenum oxysulphide dialkyldithiocarbamate.

5. A grease composition according to any preceding claim wherein the amount of the organic metal compound present in the composition is from 0.1 to 10 wt % based on the total weight of the composition.

6. A grease composition according to any preceding claim wherein the lithium soap complex comprises a lithium soap of a C12 to C24 hydroxy fatty acid and at least one other lithium-containing compound.

7. A grease composition according to Claim 6 wherein the other lithium-containing compound is a lithium soap of a C2 to C12 aliphatic dicarboxylic acid.

8. A grease composition according to Claim 6 wherein the other lithium-containing compound is a lithium salt of boric acid.

9. A grease composition according to any of Claims 6 to 8 wherein the lithium soap complex also comprises a lithium soap of C3 to C14 hydroxycarboxylic acid having an -OH group not more than 6 carbon atoms away from the carboxyl group.

10. A grease composition according to any preceding Claim wherein the amount of lithium soap complex present in the composition is from 2 to 30 wt % based on the total weight of the composition.

11. A grease composition according to any preceding claim which also comprises an antioxidant.

12. A grease composition according to Claim 11 wherein the antioxidant is alkyldiphenylamine.

13. A grease composition according to Claim 11 or 12 wherein the amount of the antioxidant present in the composition is from 0.1 to 5 wt % based on the total weight of the composition.

14. A grease composition according to any preceding claim wherein the base oil is a mineral oil or a blend of mineral and synthetic oils.

15. A lubricating grease composition substantially as hereinbefore described with reference to any of Examples 1-3, 5 or 7.