NO174348B - Lubricant and method of increasing the flowability of a lubricant - Google Patents

Description

The present invention relates to a lubricant which has improved low and high temperature properties as well as a method for increasing the fluidity of a lubricant.

Lubricants are often used in applications that require satisfactory performance at both hot and cold temperature extremes. Examples of such applications include slewing gears on mining buckets, large open gears on ball mills, etc. A main objection from users of this type of product is that it becomes very brittle at cold temperatures and has a tendency to "run off" at warmer temperatures.

Various combinations of additives have been proposed to correct this problem. E.g. US patent 3,705,853 describes a lubricating grease comprising a lubricating oil, a thickener and an ethylene terpolymer having a melt index in the range of 0.5-200. Although viscosity index agents may be present, it is not mentioned that the lubricating grease contains an ethylene copolymer (see also US patent 3,904,534).

However, ethylene copolymers have been incorporated into a variety of different compositions. E.g. US patent 4,115,343 describes that the storage stability and antifoam tendency of organosiloxane polymers in mineral oils can be improved by adding ethylene-vinyl acetate copolymer (EVA) to the dispersion. As another example, US patent 3,250,714 discloses that EVA is a viscosity index improver (VI improver) for mineral lubricating oils. However, nothing is mentioned about the melt index of the polymer. In US patent 3,947,368, EVA with a melting index of 5-580 is used as a pour-point depressant in waxy lubricating oils. However, there is no mention of a thickener being present.

Therefore, these references neither teach nor suggest a lubricant having the excellent low temperature slumpability and high temperature adhesion of the agent described below.

According to the present invention, a lubricant is provided which is characterized in that it includes:

(a) from over 50 to 90 wt-# of a lubricating oil,

(b) 1-15 wt-# of a thickener based on an aluminum soap, a barium soap, a calcium soap, a lithium soap, a sodium soap or their complexes, (c) 5-40 wt-# of a VI improver which is a polymer of isobutylene or a copolymer of ethylene, propylene, butene or isobutylene with a C3-C30 olefin, and (d) 1-20 wt-56 of a copolymer of ethylene, with at least one compound selected from the group of vinyl acetate, alkyl acrylate or alkyl methacrylate, where the copolymer has a melt index of at least 40 g/10 min. and a vinyl acetate, alkyl acrylate or alkyl methacrylate content between 10 and 40 wt.

Said melt index is preferably between 40 and 10,000, more preferably between 40 and 5,000, and most preferably between 40 and 2,500, g/10 min.

Furthermore, according to the invention, a method is provided for increasing the flowability of a lubricant at temperatures below -20°C and for increasing its adhesion at temperatures above +20°C, where the agent contains:

(a) from over 50 to 90 wt-# of a lubricating oil,

(b) from 1 to 15 wt-# of a thickening agent, and (c) from 5 to 40 wt-# of a VI improver, and this process is characterized by adding from 1 to 20 wt-# of a copolymer of ethylene with at least one compound selected from the group of vinyl acetate, alkyl acrylate or alkyl methacrylate, where the copolymer has a melt index of at least 40 g/10 min. and a vinyl acetate, alkyl acrylate or alkyl methacrylate content of between 10 and 40% by weight of the agent.

A number of different lubricating oils can be used in the preparation of the present agent. Accordingly, the lubricating oil base material may be any of the conventionally used mineral oils, synthetic hydrocarbon oils or synthetic ester oils. Generally, these lubricating oils will have a viscosity in the range of 5 to 10,000 cSt at 40°C, although typical applications will require an oil having a viscosity varying from 10 to 1,000 cSt at 40°C. Mineral lubricating oil base materials used in the manufacture of the lubricant may be any conventional refined base materials derived from paraffinic, naphthenic and mixed base crude oils. Synthetic lubricating oils which may be used include esters of dibasic acids such as di-2-ethylhexyl sebacate, esters of glycols such as an 0^3 oxyacid 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 2-ethylhexanoic acid. Other synthetic oils that may be used include synthetic hydrocarbons such as poly-alpha-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 condensation of butyl alcohol with propylene oxide); and carbonate esters (e.g., the product of reaction of C 6 oxo alcohol with ethyl carbonate to form a half-ester followed by reaction of the latter with tetraethylene glycol, etc.). Other suitable synthetic oils include the polyphenyl ethers, e.g. those having from 3 to 7 ether linkages, and from 4 to 8 phenyl groups

(cf. US patent 3,424,678, column 3). Normally, the lubricating oil will make up a major amount of the lubricant. Typically, the amount of lubricating oil will vary from over 50 to 90% by weight, preferably from 70 to 85% by weight, of the lubricant.

The lubricant will also contain a thickener dispersed in the lubricating oil to form a base lubricating grease. The particular thickener used is not critical, however, and can vary greatly. For example the thickener may be based on aluminum, barium, calcium, lithium, sodium soaps or their complexes. Soap thickeners can be obtained from a number of different animal oils, vegetable oils, and fats as well as the fatty acids derived therefrom. These materials are well known in the art, and are described in e.g. C. J. Boner, Manufacture and Application of Lubricating Greases, Chapter 4, Robert E. Krieger Publishing Company, Inc., New York 1971). Carbon black, silicon dioxide and clays can be used as well as dyes, polyurea compounds and other organic thickeners. Pyrrolidone-based thickeners can also be used. 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 the soaps. Particularly preferred thickeners are based on lithium soap, calcium soap, aluminum soap, their complexes or mixtures thereof. More preferred thickeners are based on lithium soap, calcium soap, their complexes, or mixtures thereof. Most preferred is a lithium or lithium complex thickener which includes a hydroxy fatty acid with 12-24 (preferably 16-20) carbon atoms. A preferred hydroxy fatty acid is a hydroxystearic acid (eg a 9-hydroxy or a 10-hydroxystearic acid) of which 12-hydroxystearic acid is most preferred (see US patent 3,929,651). The amount of thickener in the lubricant will typically vary from 1 to 15% by weight. For most purposes between 1 and 10% by weight, preferably between 2 and 5% by weight, of the thickener will be present in the composition.

A VI improver will also be present in the lubricant. Viscosity modifiers are long chain, generally high molecular weight polymers (including polyesters) that provide high and low temperature operability to the lubricant by allowing it to remain relatively viscous at elevated temperatures and fluid at low temperatures. Viscosity improvers can also be derivatized to give them other properties or functions, such as adding dispersibility properties. Water-soluble viscosity-modifying polymers useful in the present invention will generally have number average molecular weights from 300 to 10<6>, preferably from 500 to 10<4>, and more preferably from 1000 to 2000. The amount of VI-f improvers present in the lubricating composition will vary depending on the particular VI enhancer used, its molecular weight, etc. Typically, however, from 5 to 40 wt-# (preferably from 10 to 30 wt-#) of the lubricant will be VI improvers.

Suitable VI improvers can be based on hydrocarbon polymers, polyesters, or mixtures thereof. Examples of suitable hydrocarbon polymers-VI enhancers include homopolymers and copolymers of two or more monomers of c2~c30 (eg, C2~Cg) olefins, including both alpha-olefins and internal olefins which may be straight or branched, aliphatic, aromatic , alkylaromatic, cycloaliphatic, etc. Often the VI improver will be a polymer of isobutylene or a copolymer of ethylene, propylene, butene or isobutylene with a C3-C30 olefin. A polymer of isobutylene or a copolymer of butene and isobutylene is preferred, a polymer of isobutylene being particularly preferred. Other polymers which may be used include homopolymers and copolymers of Cf, and higher alpha-olefins; atactic polypropylene; hydrogenated polymers, copolymers and terpolymers of styrene (e.g. with isoprene and/or butadiene and hydrogenated derivatives thereof). The molecular weight of the polymer can be reduced by grinding, extrusion, oxidation, thermal decomposition, etc., and can contain oxygen.

Suitable VI improvers also include polyester VI improvers, which are generally polymers of esters of ethylenically unsaturated C3-C8 mono- and dicarboxylic acids such as methacrylic acid and acrylic acid, maleic acid, maleic anhydride, fumaric acid, etc. Examples of unsaturated esters that can be used, includes those of aliphatic, saturated monoalcohols with at least one carbon atom and preferably with 12-20 carbon atoms, such as decyl acrylate, 1-auryl acrylate, stearyl acrylate, decyl methacrylate, diamyl fumarate, cetyl methacrylate, etc., and mixtures thereof. Other esters include the vinyl alcohol esters of C2-C22 fatty or monocarboxylic acids such as vinyl acetate, vinyl laurate, vinyl stearate, and the like, and mixtures thereof. Preferably, said C2-C22 fatty or monocarboxylic acids are saturated. Copolymers of vinyl alcohol esters with unsaturated acid esters, such as the copolymer of vinyl acetate with dialkyl fumarates, can also be used.

The lubricant will also contain 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 from 10 to 40 wt-#, preferably from 10 to 30 wt-5é. Preferably, the melt index should range from 40 to 10,000, more preferably from 40 to 5,000, and most preferably from 40 to 2,500, g/10 min. The amount of copolymer added should vary from 1 to 20% by weight (preferably from 1 to 10% by weight-56) based on the total weight of the agent.

The particular VI enhancers and polymers used are readily available on the market from various chemical suppliers. Thus, the method of their manufacture is well known to those skilled in the art.

The lubricant may also contain small amounts of supplementary additives including, but not limited to, anti-corrosion agents, high-pressure anti-wear agents, pour-point depressants, tackifiers, oxidation inhibitors, dyes, etc., which are incorporated for special purposes. The total amount of these additives will typically vary from 2 to 5 weight-5é based on the total weight of the lubricant. In addition, such solid lubricants as molybdenum disulfide and graphite may be present in the agent typically from 1 to 5 wt-# (preferably from 1.5 to 3 wt-#) for molybdenum disulfide and from 3 to 15 wt-# (preferably from 6 to 12 weight-#) for graphite.

One or more solvents (typically from 10 to 40 weight-#) may be added to the lubricant as a diluent to improve its delivery properties. Suitable solvents include pure hydrocarbon solvents, mixed hydrocarbon solvents, chlorohydrocarbon solvents, or mixtures thereof, which will typically have an atmospheric boiling point of between 30 and 300°C.

Suitable pure hydrocarbon solvents include toluene, ortho-xylene, meta-xylene, mesitylene, ethylbenzene, butylbenzene, hexane, heptane, octane, isooctane, etc., or mixtures thereof. Typically, these solvents will have a solid (or melting) point below approx. -25°C (preferably below -40°C). Suitable mixed hydrocarbon solvents include kerosene, spring sun, naphtha, etc., or mixtures thereof. Typically, these solvents will have a solidification point below -25°C, preferably below -40°C.

Suitable chlorohydrocarbon solvents include n-propyl chloride, isopropyl chloride, n-butyl chloride, iso-butyl chloride, sec-butyl chloride, pentyl chloride, hexyl chloride, dichloromethane, dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane, trichloroethylene, chlorobenzene, etc., and their mixtures, 1,1,1-trichloroethane being particularly preferred.

The lubricant according to the invention is usually prepared by first dispersing or "mixing" the thickener in the lubricating oil for from 1 to 8 hours or more (preferably from 1 to 4 hours) followed by heating at an elevated temperature (e.g. from 60 to 260° C depending on the particular thickener used) until mixtures thicken. The mixture is then cooled to ambient temperature (typically about 25°C) during which time the VI improver, ethylene copolymer and other additives are added. Although the VI improver and ethylene copolymer may are added together or separately in any order, it is preferred that they be added as described below to obtain a lubricant having the desired low temperature and high temperature properties.

As the mixture cools, it is preferred to add the ethylene copolymer (eg EVA) at a temperature between 120 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 and 190°C. Additional lubricating oils can also be added within the latter temperature range to achieve the desired lubricating grease consistency and oil viscometric properties. Other additives (such as the supplementary additives and solid lubricants mentioned above) are normally added at a temperature between 50 and 100°C. Finally, at a temperature between ambient temperature and 50°C (preferably between 25 and 40°C) a solvent is added to the mixture to provide the necessary delivery capability. Lower temperatures are preferred for solvent addition to avoid excessive evaporation. Normally, the agent will be mixed while adding its components.

The components of the lubricant can be mixed or ground in a number of different ways that can be easily selected by those skilled in the art. Suitable devices include external mixers, roller mills, internal mixers, Banbury mixers, screw extruders, screw mixers, colloid mills, homogenizers, and the like.

The present lubricant can be suitably used in just about any application that requires good lubrication at both high and low temperatures. Examples of such applications include open gears, rollers, bearings, bar downs, cables, etc. However, the agent is particularly suitable for use as a lubricant in open gears.

Example 1 - Production of base lubricating grease

Base grease was prepared in an Eobart mixer. The open mixing vessel was equipped with heat "tracing" and thermal insulation. The vessel was charged with 300 g of 12-hydroxystearic acid and 915 g of 100 STJS (at 37.8°C) hydrotreated naphthenic distillate (commercially available from Exxon oil 1502), and the mixture was heated to 70°C with constant stirring. At 70°C, the mixture was neutralized by slowly adding 45 g of LiOH-EgO in 150 g of water over a period of 1 hour, during which time the temperature was maintained between 70 and 110°C. After the alkali addition was complete, the temperature was increased to 150°C and held at this temperature until dehydration was complete. The alkali content was determined by acid titration to be 0.2 mass-# (expressed as NaOH equivalent), indicating complete neutralization. The temperature of the mixture was then increased to between 190 and 200°C and held in this range for approx. 30 min. After this "boiling out", the mixture was then cooled to approx. 120°C by slow addition of 500 g of Pennsylvania resin (2600 SUS at 98.9°C) and 500 g of polybutene (800 cSt at 100°C), followed by addition of 345 g of Penn resin and 86 g of polybutene to obtain of the desired oil viscosity (approx. 1000 cSt at 40°C). Additional oil

(3000 g) was then added in six 500 g aliquots, each containing 195 g of 1502 oil, 180 g of Penn resin, and 125 g of polybutene to achieve a softer grease consistency while maintaining the desired ratio of mineral oil to VI improver. Oil additions were made slowly to avoid formation of a separate oil phase. The fat was then passed once through a Charlotte colloid mill. The milled product had a cone penetration of 298 mm/10 as determined by ASTM D217.

A 3000 g aliquot of the 298 mm/10 penetration product was returned to the mixing vessel and six additional 500 g aliquots of the 1502/Penn resin/polybutene mixture were added. Because the mixing vessel was too small to obtain a base grease of the correct consistency, 1000 g of product was removed from the mixing vessel and a further 500 g aliquot of the mixture was added to the remaining product. The resulting final base grease had a consistency of 367 mm/10 as determined by ASTM D217 and the following composition: Lithium hydroxide.HgO 0.25 wt-# 12-hydroxystearic acid 1.69 wt-#

100 SUS at 37.8°C hydrogen treated

naphthenic distillate 38.22% by weight

Pennsylvania resin (2600 SUS

at 98.g^) 35.31 wt-# Polybutene (800cSt at 100°C) 24.53 wt-#

The lubricants used in Examples 2 and 3 (below) were prepared from this base grease as follows. About 400 g of base grease was mixed with the required amount of each of the following commercially available polymers at 125°C. The penetration achieved by impact with 60 blows for each mixture was then measured according to ASTM D217. The mixtures were then cooled and mixed with trichloroethane to obtain of a final solvent concentration of 25 wt-# in the agents tested.

Example - 2 - Effect of different polymers on low temperature flowability

The tendency of each polymer modified agent prepared in Example 1 to flow ("slump") was determined from the cone flow value. To determine the cone flow, a round container with a diameter of 9 mm and a depth of 60 mm was filled with a sample of each agent and the surface was smoothed with a spatula (if necessary). Ever sample was subjected to cold exposure for 4 hours at -40°C and then the penetration was determined with a standard grease penetrometer, a description of which is given in ASTM D217. For this measurement a special right-wound cone was used with a base of 62 mm. The total weight of the cone and shaft was 66.7 g. The penetration at -40°C was measured after 10 seconds instead of after 5 seconds as used in the usual test with the standard cone. The measurement was made during 1 minute from the removal of the sample from the cold box to avoid unnecessary heating of the sample.

The cone flow value was calculated from the penetration at -40°C using the following formula:

Previous experience has shown that cone flow values of less than 80 are characteristic of lubricants with good flowability.

The cone flow value for each sample was determined and the results obtained are listed in Table 2.

The data in Table 2 showed that the samples containing polymers A-F have good flowability at -40°C and a concentration of 2 wt-#. However, at a concentration of 6 wt-#, the sample containing polymer E had poor flowability, 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 plates. The plates were then suspended vertically in a circulation oven for 24 hours at 65°C. The change in weight of each plate was then calculated, and a solvent-free basis and degree of surface coverage determined visually. The results of these experiments are shown in Table 3.

The data in Table 3 show that the samples containing 2500 MI EVÅ's (Polymers A and B) showed good performance at concentrations of 2 and 6 wt-S6, with observed weight losses varying from 48 to 49%>. Of greatest importance, however, is that at the end of the test the remaining agent formed an evenly distributed adhesive coating on the plate without any visible bare surface. The sample containing polymer D (39 MI EVA) also showed good performance at a concentration of 2 wt #. Both samples containing SBS 416 (Polymer E) and the LLDPE polymer (Polymer F) showed poor performance, with large bare areas visible at the end of the test period. Only a lubricant containing the polymers A, B and D thus gave good adhesion at 65°C.

The data in Tables 2 and 3 show that both good adhesion at high temperature and good flowability at low temperature are achieved for the samples containing polymers A, B and D, i.e. ethylene vinyl acetate copolymers which have a melt index of at least 40 g/min .

(most preferably from 40 to 2500 g/10 min.) and containing between 10 and 40 wt-#, (preferably between 10 and 30 wt-#) vinyl acetate.

Claims (11)

1. Lubricant, characterized in that it includes: (a) from over 50 to 90 wt-# of a lubricating oil, (b) 1-15 wt-56 of a thickener based on an aluminum soap, a barium soap, a calcium soap, a lithium soap, a sodium soap or their complexes, (c) 5-40 wt-# of a VI improver which is a polymer of isobutylene or a copolymer of ethylene, propylene, butene or isobutylene with a C3-C30 olefin, and (d) 1- 20 wt-# of a copolymer of ethylene, with at least one compound selected from the group of vinyl acetate, alkyl acrylate or alkyl methacrylate, where the copolymer has a melting index of at least 40 g/10 min. and a vinyl acetate, alkyl acrylate or alkyl methacrylate content between 10 and 40 wt. 2. Lubricant according to claim 1, characterized in that the copolymer in (d) has a melt index varying from 40 to 10,000 g/10 min. 3. Lubricant according to claim 2, characterized in that the copolymer in (d) has a melt index varying from 40 to 2500 g/10 min. 4. Lubricant according to claim 1, characterized in that the thickener is based on an aluminum soap, a calcium soap, a lithium soap, their complexes, or mixtures thereof. 5 . Lubricant according to claim 4, characterized in that the thickener is based on a calcium soap, a lithium soap, their complexes or mixtures thereof. 6. Lubricant according to claim 5, characterized in that the thickener is a lithium soap or a lithium complex soap based on a hydroxy fatty acid having 12-24 carbon atoms. 7 . Lubricant according to claim 6, characterized in that the hydroxy fatty acid comprises a hydroxystearic acid. 8. Lubricant according to claim 7, characterized in that the hydroxystearic acid comprises 12-hydroxystearic acid. 9. Lubricant according to claim 1, characterized in that the copolymer in (d) comprises ethylene-vinyl acetate. 10. Lubricant according to claim 9, characterized in that the vinyl acetate content is between 10 and 30% by weight. 11. Process for increasing the fluidity of a lubricant at temperatures below — 20°C and for increasing its adhesion at temperatures above +20°C, where the agent contains: (a) from more than 50 to 90 wt-# of a lubricating oil, (b ) from 1 to 15 wt-# of a thickener, and (c) from 5 to 40 wt-# of a VI improver, characterized by adding from 1 to 20 wt-5é of a copolymer of ethylene with at least one compound selected from the group of vinyl acetate, alkyl acrylate or alkyl methacrylate, where the copolymer has a melt index of at least 40 g/10 min. and a vinyl acetate, alkyl acrylate or alkyl methacrylate content of between 10 and 40% by weight of the agent.