DE69524412T2 - GREASE COMPOSITION - Google Patents

Description

Background of the invention 1. Field of the invention

This invention relates to lubricating grease compositions having improved noise reduction properties and high dropping points.

2. Description of related technology

The bearings in modern automobiles and electrical equipment are typically sealed bearings. Greases for sealed bearings must provide lubrication for the life of the bearing, which places high demands on greases used for these purposes. Greases for sealed bearings must meet numerous performance requirements, including extending bearing life, high temperature performance, high dropping point, low oil separation, oxidation resistance, protection against vibrational wear, and noise reduction.

Recently, greases based on lithium complex soap have been used in sealed bearing applications. These greases offer long operating times at high temperatures, but generally suffer from higher noise levels than greases based on simple lithium soaps.

It would be desirable to have a grease for sealed bearings that contains a lithium complex soap that does not lead to increased noise levels in sealed bearings. To improve high temperature serviceability, it is also desirable to improve the dropping point of the grease.

Summary of the invention

This invention relates to a lubricating grease composition with improved noise reduction properties and a dropping point of more than 270ºC according to the standard test ASTM D566, the composition

a) a larger quantity of a lubricating base oil,

b) 2 to 30% by weight, based on the grease composition, of a lithium soap complex thickener and

c) 0.1 to 10% by weight, based on the grease composition, of a polyalkenylsuccinic anhydride, a polyalkenylsuccinic acid or a mixture thereof, wherein the polyalkenyl group has an average molecular weight (number average) of 300 to 4000.

The lubricating greases according to the invention provide a long bearing life and a high dropping point, while at the same time ensuring low bearing noise.

Detailed description of the invention

Many different lubricating base oils can be used to prepare the grease compositions of the present invention. Accordingly, the lubricating oil base stock can be any of the conventionally used mineral oils, synthetic hydrocarbon oils or synthetic ester oils or mixtures thereof, depending upon the particular grease being prepared. Generally, these lubricating oils have a viscosity in the range of about 5 to about 400 cSt at 40°C, although typical applications require an oil having a viscosity in the range of about 10 to about 200 cSt at 40°C. Mineral lubricating oil base stocks used to prepare the greases can be any of the conventionally refined base stocks derived from paraffinic, naphthenic and mixed base crude oils. Useful synthetic lubricating oils include esters of glycols such as C₁₃-oxo acid diesters of tetraethylene glycol, or complex esters such as that formed from 1 mole of sebacic acid and 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Other useful synthetic oils include synthetic hydrocarbons such as poly-α-olefins, alkylbenzenes, e.g. alkylate residues from the alkylation of benzene with tetrapropylene, or the copolymers of ethylene and propylene, silicone oils, e.g. ethylphenylpolysiloxanes, methylpolysiloxanes, etc., polyglycol oils, e.g. those obtained by condensing butyl alcohol with propylene oxide, carbonate esters, e.g. the product of reacting C8 oxo alcohol with ethyl carbonate to form a half ester followed by reacting the latter with tetraethylene glycol, etc. Other suitable synthetic oils include the polyphenyl ethers, e.g. those having about 3 to 7 ether linkages and about 4 to 8 phenyl groups. The amount of lubricating oil in the grease can also vary widely but typically ranges from about 50% to about 98%, preferably about 75% to about 95%, by weight of the grease.

The grease composition contains a thickener dispersed in the lubricating base oil to form a grease. Preferred thickeners are lithium soap complex thickeners containing a lithium soap of a C12 to C24 hydroxy fatty acid and a second lithium salt compound which is a lithium salt of a C2 to C12 aliphatic or cycloaliphatic dicarboxylic acid, a lithium salt of a C3 to C14 hydroxycarboxylic acid in which the hydroxy group is separated from the carboxyl group by six or fewer carbon atoms, or a mixture thereof. As a third thickener component, the lithium salt of boric acid can be added. Preferred hydroxy fatty acids include hydroxystearic, hydroxyricinoleic, hydroxybehenic and hydroxypalmitic acids. Particularly preferred is 12-hydroxystearic acid. The second lithium salt compound is preferably an aliphatic C6 to C10 dicarboxylic acid, in particular azelaic or sebacic acid, especially azelaic acid. The hydroxycarboxylic acid is preferably lactic acid, salicylic acid or other hydroxybenzoic acids, in particular salicylic acid. The amount of lithium soap complex thickeners is preferably 5 to 20% by weight, based on the lubricating grease. The ratio of hydroxy fatty acid to aliphatic dicarboxylic acid and/or hydroxycarboxylic acid is 10:0.5 to 10:15, preferably 10:1.5 to 10:6.

The grease composition further contains a polyalkenylsuccinic anhydride, a polyalkenylsuccinic acid or a mixture thereof as a dispersant. The polyalkenyl group has a number average molecular weight of 300 to 4000, preferably 400 to 2500. Preferred polyalkenyl groups are poly-C3 and poly-C4 olefins, especially polyisobutylene. Polyisobutylene succinic anhydride and/or acid are hereinafter referred to collectively as PIBSA. The amount of dispersant is preferably 0.1% to 5% by weight, based on the lubricating grease.

Lithium complex soap greases are prepared by heating hydroxy fatty acid and base oil and adding a concentrated aqueous solution of lithium hydroxide. It is further heated to an elevated temperature to remove most of the water. The reaction mixture is then cooled to about 100°C and dicarboxylic acid is added, followed by a second portion of the concentrated lithium hydroxide. This mixture is again heated to an elevated temperature to again remove water. After heating is complete, the grease mixture is cooled, remaining oil and any other additives are added, and the grease is reconditioned using conventional techniques. It can also be prepared in a one-step process by heating base oil, fatty acid and dicarboxylic acid, then adding lithium hydroxide solution, followed by dehydration and addition of the remaining oil.

The grease composition may contain minor amounts of supplementary additives including, but not limited to, anti-corrosion agents, extreme pressure anti-wear agents, pour point depressants, tackifiers, antioxidants, colorants, and the like, added for specific purposes. The total amount of these additives typically ranges from about 2% to about 10% by weight based on the total weight of the grease composition.

The invention is further explained with reference to the following examples, which include a preferred embodiment of the invention.

example 1

This example illustrates the preparation of a low noise grease. A laboratory kettle was charged with 700 g of refined paraffinic base oil having a viscosity of 90 cSt at 40°C, 139.2 g of 12-hydroxystearic acid, 69.5 g of azelaic acid and 12.0 g of PIBSA having a polyisobutenyl moiety with a number average molecular weight of 950. The resulting mixture was heated with stirring until the temperature reached 90°C. At this point, heating was stopped and 345 g of 15% solution of lithium hydroxide (heated to 90°C) was added with stirring. When the addition of the lithium hydroxide solution was complete, heating was resumed to remove water. During the dehydration process, an additional 100 g of oil was added to counteract hardening of the grease. It was heated to a temperature of 210ºC, at which point heating was stopped and an additional 128 g of oil was added. The heated mixture was allowed to cool slowly to a temperature of 70ºC or less. The cooled greases were ground with 0.005 inch gaps and deaerated. The grease samples described in Table 1 of Example 3 were prepared by this procedure. The component amounts were varied as described in Samples 1 through 3 and Comparative Samples 4 through 14.

Example 2

Grease noise was measured according to the following method, which is described in more detail in Japanese Patent 53-2357. Solid particles in grease cause vibrations, which can be converted into an electrical signal. After correcting for the running noise of the bearings under standard conditions, the electrical signal due to solid particles including soap particles in the grease can be measured according to the following method. A vibration detection device was attached to the outer ring of the bearings. The detection device converts the vibrations into an electrical signal, which is amplified and fed to a waveband filter. The waveband filter compares the amplified signal received from the bearings with the known vibration frequency of the bearings alone, filters out the vibration frequencies from the bearings, and sends the filtered electronic signal through an amplifier to an amplitude limiting circuit. The amplitude limiting circuit "cuts off" the electrical signal from the amplifier at a given intensity. This intensity is set so that only peak voltages corresponding to particulate noise from particles in the grease are measured. The cutoff height is set to a value above the peak value corresponding to the running noise from the bearings.

Example 3

This example compares the noise properties and dropping point of a grease formulated with polyisobutenyl succinic anhydride/polyisobutenyl succinic acid dispersant according to the invention with polyisobutenyl succinimide type dispersants described in Japanese Patent A2 58125794. Greases were formulated according to the procedures of Example 1. Noise was tested according to the procedure of Example 2 and dropping point was measured according to test method ASTM D566. The results are presented in Table 1. Table 1

Remarks:

(1) 80 wt.% solution of

in refined mineral oil, average molecular weight of PIB is 950.

(2) 50 wt.% solution of

in refined mineral oil, average molecular weight of PIB is 950.

(3) 52 wt.% solution of

in refined mineral oil, average molecular weight of PIB is 950.

(4) 60 wt.% solution of borated

in refined mineral oil, average molecular weight of PIB is 950.

(5) Single pulses/120 seconds, determined according to the procedure in Example 2

(6) Commercial sample lithium complex grease

Greases prepared with polyisobutenyl succinic anhydride/polyisobutenyl succinic acid dispersants (Samples 1 to 3) exhibited significantly better noise properties and higher dropping point compared to a lithium complex grease formulated without dispersants (Sample 4). Samples 1 to 3 also exhibited consistently higher dropping points compared to greases prepared with polyisobutenyl succinimide dispersants (Comparative Samples 5 to 13). A commercial lithium complex grease (Sample 14) exhibited significantly worse noise properties compared to inventive Samples 1 to 3.

Claims (8)

1. A lubricating grease composition having improved noise reduction properties and a dropping point of more than 270ºC according to the standard test ASTM D566, the composition a) a larger quantity of a lubricating base oil, b) 2 to 30% by weight, based on the lubricating grease composition, of a lithium soap complex thickener and c) 0.1 to 10% by weight, based on the grease composition, of a polyalkenylsuccinic anhydride, a polyalkenylsuccinic acid or a mixture thereof, wherein the polyalkenyl group has an average molecular weight (number average) of 300 to 4000, contains. 2. A grease composition according to claim 1, wherein the lithium soap complex thickener contains a lithium soap of a C₁₂ to C₂₄ hydroxy fatty acid and a lithium salt of a C₂ to C₁₂ aliphatic or cycloaliphatic dicarboxylic acid, a lithium salt of a C₃ to C₁₄ hydroxycarboxylic acid or a mixture thereof. 3. A grease composition according to claim 2, wherein the lithium soap complex thickener contains a lithium soap of 12-hydroxystearic acid and a lithium salt of azelaic acid and/or lithium salt of salicylic acid. 4. A lubricating grease composition according to claim 2 or 3, wherein the ratio of hydroxy fatty acid to aliphatic or cycloaliphatic dicarboxylic acid and/or hydroxycarboxylic acid is 10:0.5 to 10:15. 5. A grease composition according to any one of the preceding claims, wherein the polyalkenyl moiety in the polyisobutenylsuccinic anhydride and/or polyisobutenylsuccinic acid has a number average molecular weight of 400 to 2500. 6. A method for improving noise reduction and providing a dropping point of greater than 270ºC (ASTM D566) in a grease comprising incorporating into a base oil 2 to 30% by weight of the grease of a lithium soap complex thickener and 0.1 to 10% by weight of the grease of a polyisobutenyl succinic anhydride, a polyisobutenyl succinic acid or a mixture thereof, wherein the polyalkenyl group has a number average molecular weight of 300 to 4000. 7. Use of a polyalkenyl succinic anhydride, a polyalkenyl succinic acid or a mixture thereof, wherein the polyalkenyl group has a number average molecular weight of 300 to 4000, in an amount of 0.1 to 10% by weight, based on the grease, in a grease composition containing 2 to 30% by weight, based on the grease, of a lithium soap complex thickener, for improving the noise reduction properties of the grease composition. 8. Use of a polyalkenylsuccinic anhydride, a polyalkenylsuccinic acid or a mixture thereof, wherein the polyalkenyl group has an average molecular weight (number average) of 300 to 4000, in an amount of 0.1 to 10% by weight, based on the lubricating grease, in a lubricating grease composition containing 2 to 30% by weight, based on on the lubricating grease, of a lithium soap complex thickener, to improve the dropping point of the lubricating grease composition.