DE68902115T2 - LUBRICANT MIXTURE. - Google Patents

Description

This invention relates to a lubricant composition having improved high temperature and low temperature properties, the manner of its preparation and its use, particularly as a lubricant for open gears.

Lubricant compositions are more often used in applications that require satisfactory performance at both extremely high and extremely low temperatures. Examples of such applications include swing gears in mine bucket blades, large open gears in ball mills, and the like. A major complaint among users of such products is that they become very brittle at colder temperatures and "run away" at warmer temperatures.

Various combinations of additives have been proposed to solve this problem. For example, US-A-3,705,853 describes a grease composition containing a lubricating oil, a thickener and an ethylene terpolymer having a melt index in the range of 0.5 to 200. Although viscosity index agents may be present, there is no mention of the grease containing an ethylene copolymer. (see also US-A-3,904,534).

Ethylene copolymers have been incorporated into a variety of lubricant compositions. For example, US-A-4,115,343 describes that the shelf life and antifoaming properties of organosiloxane polymers in mineral oil can be improved by adding ethylene vinyl acetate polymer (EVA) to the dispersion. In another example, US-A-3,250,714 describes EVA as a VI improver for mineral lubricating oils. The melt index of the polymer is not mentioned. In US-A-3,947,368, EVA with a melt index of 5 to 580 is used as a pour point depressant in paraffin-containing lubricating oils. The presence of a thickener is not mentioned.

None of these references teaches or suggests a lubricant composition with such excellent low-temperature worked penetration and high-temperature adhesion as the composition described below.

This invention, in its broadest form, relates to a lubricant composition having improved low temperature and high temperature properties. More specifically, it has been found that a lubricant composition comprising (1) a lubricating oil, (2) a thickener, (3) a VI improver, and (4) a copolymer of ethylene with at least one member selected from the group consisting of vinyl acetate, alkyl acrylate, and alkyl methacrylate has both excellent high temperature adhesion and low temperature work penetration. The ethylene copolymer used in the invention must have a melt index of at least 40 g/min and should contain 10 to 40 weight percent vinyl acetate, alkyl acrylate, or alkyl methacrylate. Preferably, the melt index should be between 40 and 10,000, preferably between 40 and 5,000, and most preferably between 40 and 2,500 g/10 min. The VI improver is either an isobutylene polymer or a copolymer of ethylene, propylene, butene or isobutene with a C3 to C30 olefin.

In another embodiment, this invention relates to a method for increasing the worked penetration of a lubricant composition at temperatures below -20°C and its adhesiveness at temperatures above +20°C.

In another embodiment, this invention relates to the use of the above polymer as an additive in a lubricant composition to improve the low temperature work penetration and the high temperature adhesion of the lubricant composition.

Various lubricating oils can be used to prepare the composition of the invention. Therefore, the lubricating oil base can be any of the commonly used Mineral oils, synthetic hydrocarbon oils or synthetic ester oils. Generally, these lubricating oils have a viscosity in the range of 5 to 10,000 cSt at 40ºC, although typical applications require an oil having a viscosity in the range of 10 to 1,000 cSt at 40ºC. Mineral lubricating oil bases used to prepare the lubricant blend can be any conventional refined bases prepared from paraffinic, naphthenic and mixed feedstocks. Synthetic lubricating oils which can be used include esters of dibasic acids such as di-2-ethylhexyl sebacic acid, esters of glycol such as a C₁₃ oxoacid diester of tetraethylene glycol or complex esters such as the ester formed from 1 mole of sebacic acid, 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Other synthetic oils which may be used include synthetic hydrocarbons such as poly-alpha-olefins, alkylbenzenes (e.g., alkylated bottoms from the alkylation of benzene with tetrapropylene, or copolymers of ethylene and propylene silicone oils, e.g., ethylphenylpolysiloxanes, methylpolysiloxanes, etc.), polyglycol oils (e.g., obtained from the condensation of butyl alcohol with propylene), and carbonate esters (e.g., the product of the reaction of a C8 oxo alcohol with ethyl carbonate to form a half-ester, followed by reaction thereof with tetraethylene glycol, etc.). Other useful synthetic oils include polyphenyl ethers, e.g., those having 3 to 7 ether linkages and 4 to 8 phenyl groups (see U.S. Patent 3,424,678, column 3). Normally, the lubricating oil comprises the majority of the lubricant composition. Typically, the proportion of lubricating oil is in the range of over 50 to 95 wt.%, preferably 70 to 85 wt.% of the lubricant composition.

The lubricant composition also contains a thickener dispersed in the lubricating oil to form a base lubricant. However, the particular thickener used is not critical and can be varied within wide limits. For example, the Thickeners are based on aluminum, barium, calcium, lithium or sodium soaps or complexes thereof. Soap-based thickeners are derived from a wide range of animal oils, vegetable oils and fats, and fatty acids derived therefrom. These materials are known to those skilled in the art and are described, for example, in CJ Boner, Manufacture and Application of Lubricating Greases, Chapter 4, Robert E. Krieger Publishing Company, Inc., New York (1971). Carbon black, silicon dioxide and clay can be used, as well as dyes, polyureas and other organic thickeners. Preferred thickeners are based on clay, a pyrrolidone, an aluminum soap, a barium soap, a calcium soap, a lithium soap, a sodium soap or complexes of these soaps. Particularly preferred thickeners are based on lithium soap, calcium soap, aluminum soap, complexes thereof or mixtures thereof. More preferred thickeners are based on lithium soap, calcium soap, complexes thereof or mixtures thereof. Most preferred is a lithium or lithium complex thickener incorporating a hydroxy fatty acid having from 12 to 24 (preferably from 16 to 20) carbon atoms. A preferred hydroxy fatty acid is a hydroxystearic acid (e.g. a 9-hydroxy or a 10-hydroxystearic acid), with 12-hydroxystearic acid being most preferred (see US-A-3,929,651). The amount of thickener in the lubricant composition is typically in the range of 1 to 15% by weight. For most uses, between 1 and 10% by weight, preferably between 2 and 5% by weight, of thickener is included in the composition.

A VI improver is also included in the lubricant composition. Viscosity modifiers are long-chain, usually high-molecular polymers that make the lubricant composition usable at high and low temperatures by remaining relatively viscous at elevated temperatures and flowable at low temperatures. Viscosity modifiers can also be derivatized to provide other properties. or to include functions such as additional dispersion properties. Oil-soluble viscosity modifying polymers useful in this invention have number average molecular weights of from 300 to 106 , preferably from 500 to 104 , and most preferably from 1000 to 2000. The amount of VI improver included in the lubricant composition will depend on which particular VI improver is used, its molecular weight, etc. Typically, from 5 to 40 weight percent (preferably from 10 to 30 weight percent) of the lubricant composition will consist of VI improver.

The VI improver is an isobutylene polymer or a copolymer of ethylene, propylene, butene or isobutylene with a C3 to C30 olefin. An isobutylene polymer or a copolymer of butene or isobutylene is preferred, with an isobutylene polymer being particularly preferred. The polymer may have a molecular weight reduced by mastication, extrusion, thermal degradation, etc. and may contain oxygen.

The lubricant mixture also contains a copolymer of ethylene with at least one compound selected from the group of vinyl acetate, alkyl acrylate or alkyl methacrylate. Vinyl acetate is the preferred ethylene copolymer. The copolymer must have a melt index of at least 40 g/10 min and should have a copolymer content of 10 to 40 wt.%, preferably 10 to 30 wt.%. Preferably the melt index is in the range of 40 to 10,000, more preferably 40 to 5,000 and most preferably 40 to 2,500 g/10 min. The content of added copolymer should be in the range of 1 to 20 wt.%, preferably 1 to 10 wt.%, based on the total weight of the composition.

The special VI improvers and polymers used can be purchased on the market from various chemical dealers. Processes for their production are known to those skilled in the art.

The lubricant composition may also contain small amounts of additional additives including, but not limited to, anti-corrosion agents, extreme pressure anti-wear agents, pour point depressants, adhesion agents, oxidation inhibitors, colorants, and the like, which are incorporated for specific uses. The total amount of these additives is typically in the range of 2 to 5 wt.%, based on the total weight of the lubricant composition. Additionally, solid lubricants such as molybdenum disulfide and graphite may be included in the mixture, typically in the range of 1 to 5 wt.% (preferably 1.5 to 3 wt.%) for molybdenum disulfide and 3 to 15 wt.% (preferably 6 to 12 wt.%) for graphite.

One or more solvents (typically 10 to 40 wt.%) may be added to the lubricant composition as a diluent to improve its dispersion properties. Useful solvents include pure hydrocarbon solvents, mixed hydrocarbon solvents, chlorinated hydrocarbon solvents or mixtures thereof, typically having a boiling point at atmospheric pressure between 30°C and 300°C.

Useful pure hydrocarbon solvents include toluene, ortho-xylene, meta-xylene, mesitylene, ethylbenzene, butylbenzene, hexane, heptane, octane, isooctane, or mixtures thereof. Typically, these solvents have a solidifying point (or melting point) below about -25ºC (preferably below -40ºC).

Useful mixed hydrocarbon solvents include jet fuel (kerosene), varsol and naphtha, and mixtures of these. Typically these solvents have a pour point below about -25°C, preferably below about -40°C.

TEXT MISSING rid, sec-butyl chloride, pentyl chloride, hexyl chloride, methyl chloride, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, trichloroethylene, chlorobenzene and mixtures thereof, with 1,1,1-trichloroethane being particularly preferred.

The lubricant composition of this invention is usually prepared by first mixing or dispersing the thickener with the lubricating oil for 1 to 8 hours or longer (preferably 1 to 4 hours) and subsequently heating to an elevated temperature (e.g., 60°C to 260°C, depending on the thickener used) until the mixture thickens. The mixture is then cooled to room temperature (typically about 25°C), during which time VI improver, ethylene copolymer and other additives are added. Although the VI improver and ethylene copolymer can be added together or individually in any order, it is preferable that they be added as described below to obtain a lubricant composition having the desired high and low temperature properties.

It is preferred to add the ethylene copolymer (e.g. EVA) while cooling the mixture at a temperature between 120°C and 180°C. Although the ethylene copolymer can be added at a temperature outside this range, the copolymer will tend to coalesce at lower temperatures and not be properly dispersed in the mixture. At higher temperatures, the copolymer may be thermally unstable. Preferably, the VI improver is added at a temperature between 80°C and 190°C. Additional lubricating oil can also be added in the latter temperature range to obtain the desired consistency of the grease and viscometric properties of the oil.

Other additives (such as the additional additives and solid lubricants mentioned above) are usually added at a temperature between 50ºC and 100ºC. Finally, at a A solvent is added at a temperature between room temperature and 50ºC (preferably between 25ºC and 40ºC) to achieve the required dispensing suitability (handling). Lower temperatures are preferred for solvent addition to avoid losses due to evaporation. Normally the composition is blended or mixed during addition of its components.

The components of the lubricant composition can be mixed, blended or milled by any means readily selected by one skilled in the art. Useful means include external mixers, roller mills, internal mixers, Banbury mixers, screw extruders, screw presses, colloid mills, homogenizers and the like.

The lubricant composition according to the invention can be suitably used in any application requiring good lubrication at high and low temperatures. Examples of such applications are open gears, rollers, bearings, wire ropes and cables. However, the composition is particularly well suited for use as a lubricant for open gears.

In another embodiment, this invention relates to a method for increasing the work penetration of a lubricant composition at temperatures below about -20°C and increasing the adhesion at temperatures above about +20°C, wherein the composition

(a) a lubricating oil,

(b) a thickener,

(c) a VI improver which is an isobutylene polymer or a copolymer of ethylene, propylene, butene or isobutylene with a C₃ to C₃₀ olefin,

wherein the process comprises adding a copolymer of ethylene with at least one compound selected from the group consisting of vinyl acetate, alkyl acrylate or alkyl methacrylate, a melt index of at least 40 g/10 min (preferably 40 to 10,000, more preferably 40 to 5,000, most preferably 40 to 2,500 g/10 min) and a vinyl acetate, alkyl acrylate or alkyl methacrylate content of between 10 and 40 wt.%, preferably 10 to 30 wt.%, to the composition.

This invention will be better understood by reference to the following examples, which, however, are not intended to limit the scope of the claims.

Example 1 - Preparation of the base grease composition

The base grease composition was prepared in a Hobart mixer. The open mixing vessel was equipped with temperature control and thermal insulation. The vessel was charged with 300 g of 12-hydroxystearic acid and 915 g of 100 SUS naphthenic distillate (commercially available as Exxon Oil 1502) hydrotreated at 37.8ºC (100ºF) and the mixture was heated to 70ºC with constant agitation. At 70ºC the mixture was neutralized by slowly adding 45 g of LiOH H₂O in 150 g of water over one hour, during which time the temperature was maintained between 70ºC and 110ºC. After the alkali addition was complete the temperature was increased to 150ºC and maintained until dehydration was complete. The alkali content was determined by titration with acid and was found to be 0.2 mass % (expressed as NaOH equivalent), indicating that neutralization was complete. The temperature of the mixture was then raised to between 190ºC and 200ºC and maintained in this range for 30 minutes. After this "boil-out" the mixture was cooled to about 120ºC by slow addition of 500 g of Pennsylvanian resin (2600 SUS at 98.9ºC (210ºF)) and 500 g of polybutene (800 cSt at 100ºC), followed by the addition of 345 g of Penn. resin and 86 g of polybutene to obtain the desired oil viscosity (about 1000 cSt at 40ºC). Additional oil was added in 6 500 g aliquots, each containing 195 g 1502 oil, 180 g Penn. resin and 125 g polybutene to obtain a softer grease consistency while maintaining the desired ratio of mineral oil to VI improver. The oil was added slowly to avoid the formation of a separate oil phase. The composition was then passed through a Charlotte colloid mill. The milled product had a cone penetration of 298 mm/10 according to ASTM D217.

A 3000 g aliquot of the 298 mm/10 penetration product was returned to the mix tank and 6 additional 500 g aliquots of 1502/pen. resin/polybutene blend were added. Because the mix tank was too small to obtain a base grease of the correct consistency, approximately 1000 g of product was removed from the mix tank and another 500 g aliquot of the blend was added to the remaining product. The resulting finished base grease had a consistency of 367 mm/10 per ASTM D217 and the following composition:

Lithium hydroxide H₂O 0.25 wt.%

12-Hydroxystearic acid 1.69 wt.%

100 SUS 100ºF Hydrotreated Naphthenic Distillate 38.22 wt%

Penn. Resin (2600 SUS at 98.9ºC (210ºF)) 35.31 wt.%

Polybutene (800 cSt at 100ºC) 24.53 wt.%

The lubricant composition used in Examples 2 and 3 (see below) was prepared from the base grease as follows. Approximately 400 g of base grease was mixed with the required amount of each of the following commercially available polymers at 125ºC. The penetration after 60 strokes in the grease mixer according to ASTM D217 was determined for each mixture. Table 1 Polymer Description Melt index g/10 min Ethylene vinyl acetate, 14% VA Ethylene vinyl acetate, 28% VA Ethylene vinyl acetate, 12% VA Ethylene vinyl acetate, 28% VA Styrene butadiene styrene, 70% butadiene/30% styrene (SBS) MW 160 000 Linear low density polyethylene (LLDPE)

The mixtures were then cooled and mixed with trichloroethane to obtain a final solvent concentration of 25 wt.% in the tested composition.

Example 2 - Effect of different polymers on the low temperature work penetration

The tendency of each of the polymer-modified compositions prepared in Example 1 to sink (i.e., flow) was determined by the cone flow value. To determine the cone flow, a round container with a diameter of 90 mm and a depth of 60 mm was filled with a sample of each mixture and the surface was smoothed with a spatula if necessary. Each sample was cooled at -40ºC for 4 hours and then the penetration was measured with a standard grease penetrometer, a description of which is given in ASTM D217. A special rectangular cone with a diameter of 62 mm at the base was used for this measurement. The total weight of the cone and stem was 66.7 g. The penetration at -40ºC was determined after 10 seconds instead of the 5 seconds used in the usual test with the standard cone. The measurement was taken within one minute of removing the sample from the freezer to avoid unnecessary heating of the sample. The cone flow was calculated from the penetration at -40ºC using the following formula:

Cone flow at -40ºC = (weight of cone and shaft) π(pen at -40ºC /100)²

Previous experiments have shown that cone flow values of less than 80 are characteristic of lubricants with good worked penetration.

The cone flow value of each sample was determined and the results obtained were summarized in Table 2. Table 2 Polymer conc., wt.% Cone flow g/cm² MI = melt index (1) 60 strokes in the grease kneader before solvent addition (2) Penetration at -40ºC in the final product (3) Average of two samples, which gave values of 34 and 43. (4) Sample could not be prepared because the polymer could not be dispersed in the base grease.

The values in Table 2 show that the samples containing polymers A to F have a good work penetration at -40ºC and a concentration of 2 wt.%. However, at a Concentration of 6 wt.% the sample containing polymer E had poor worked penetration and the sample containing polymer F could not be prepared.

Example 3 - Effect of different polymers on high temperature adhesion

The adhesion of the samples prepared in Example 1 was determined by spreading 10 g of each sample on separate aluminum panels. The panels were then hung vertically in a convection oven at 65ºC for 24 hours. The weight change of each panel was then calculated on a solvent-free basis and the degree of surface coverage estimated visually. The results of these tests are shown in Table 3. Table 3 Polymer conc., wt.% Weight loss wt.%(2) uncovered surface, area% uncovered area evenly covered (1) Values from Table 2 (2) Weight loss based on the trichloroethane-free product MI = melt index

The data in Table 3 show that the samples containing EVA's with a melt index of 2500 (Polymers A and B) performed well at concentrations of 2 wt% and 6 wt%, with observed weight losses ranging from 48% to 69%. Most importantly, however, at the end of the test, the remaining composition forms a uniformly distributed, adherent coating on the panel with no exposed areas visible. The sample containing Polymer D (EVA with melt index of 39) also performed well at a concentration of 2 wt%. Both samples containing SBS 416 (Polymer E) and LLDPE (Polymer F) performed poorly, with large exposed areas visible at the end of the test period. Therefore, only the lubricant compositions containing Polymers A, B and D show good adhesion at 65ºC.

The data in Tables 2 and 3 show that both good adhesion at high temperatures and good worked penetration at low temperatures are obtained for the samples containing Polymers A, B and D, which are ethylene-vinyl acetate copolymers having a melt index of at least 40 g/min (most preferably 40 to 2500 g/10 min) and containing between 10 and 40 wt% (preferably between 10 and 30 wt%) vinyl acetate.

Claims (10)

1. Lubricant composition, a) lubricating oil, b) thickeners, c) VI improver which is an isobutylene polymer or a copolymer of ethylene, propylene, butene or isobutene with a C₃ to C₃₀ olefin, and d) copolymer of ethylene with at least one compound selected from the group of vinyl acetate, alkyl acrylate and alkyl methacrylate, wherein the copolymer has a melt index of at least about 40 g/10 min. and a content of vinyl acetate, alkyl acrylate or alkyl methacrylate between 10 and 40 wt.%, contains. 2. Composition according to claim 1, which a) over 50 to 90 wt.% of the lubricating oil, b) 1 to 15 wt.% of the thickener, c) 5 to 40 wt.% of the VI improver, d) 1 to 20 wt.% of the copolymer contains. 3. A composition according to claim 1 or claim 2, wherein the thickener is based on clay, a pyrrolidone, an aluminium soap, a barium soap, a calcium soap, a lithium soap, a sodium soap, complexes of these soaps or mixtures thereof. 4. A composition according to claim 3, wherein the thickener is a lithium soap or a lithium complex soap based on a hydroxy fatty acid having 12 to 24 carbon atoms. 5. Composition according to claim 4, wherein the hydroxy fatty acid consists of a hydroxystearic acid. 6. A composition according to claim 5, wherein the hydroxystearic acid consists of 12-hydroxystearic acid. 7. Composition according to one of the preceding claims, in which the copolymer in d) has a melt index in the range from 40 to 10,000 g/10 min, preferably from 40 to 2500 g/10 min. 8. Composition according to one of the preceding claims, in which the copolymer in d) contains ethylene-vinyl acetate and the vinyl acetate content is between 10 and 30% by weight. 9. A method for increasing the work penetration of a lubricant composition at temperatures below about -20ºC and increasing the adhesion at temperatures of about +20ºC, wherein the composition a) more than 50 to 90 wt.% of a lubricating oil, b) 1 to 15 wt.% of a thickener, c) 5 to 40 wt.% of a VI improver which is a polymer of isobutylene, or a copolymer of ethylene, propylene, butene or isobutylene with a C₃ to C₃₀ olefin , wherein the process comprises adding from 1 to 20% by weight of a copolymer to the lubricating oil mixture, the copolymer consisting of ethylene with at least one compound selected from the group consisting of vinyl acetate, alkyl acrylate or alkyl methacrylate, the copolymer having a melt index of at least about 40 g/10 min and a content of vinyl acetate, alkyl acrylate or alkyl methacrylate of between 10 and 40% by weight. 10. Use of a copolymer of ethylene and at least one compound selected from the group consisting of vinyl acetate, alkyl acrylate and alkyl methacrylate, wherein the copolymer has a melt index of at least about 40 g/10 min and a vinyl acetate, alkyl acrylate or alkyl methacrylate content of between 10 and 40% by weight, as an additive in a lubricant composition for improving the low-temperature Work penetration and the high-temperature adhesion of the lubricant composition.