US 3384582 A
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United States Patent 3,334,582 DISPERSIONS AND GREASES Aleksauder Jerzy Groszek, Ealing, London, England, as-
signor to The British Petroleum Company Limited, London, England, a corporation of England No Drawing. Filed Sept. 21, 1966, Ser. No. 580,868 Claims priority, application Great Britain, Sept. 24, 1965, 40,699/ 65 9 Claims. (Cl. 252-) This invention relates to novel lubricating greases and to dispersions with improved lubricating properties.
It is known to incorporate molybdenum disulphide into dispersions. Up to the present it has not been possible to obtain stable dispersions containing more than a small proportion of molybdenum disulphide without the use of surface active agents as stabilisers. F ur-thermore, it has not been possible to prepare greases containing molybdenum disulphide.
It has now been found that greases can be prepared using molybdenum disulphide as thickener.
It has now been found also that very stable dispersions can be prepare-d with excellent lubricating properties using molybdenum disulphide alone.
A lubricating composition according to the invention is provided which is based on a mineral or synthetic lubrieating base oil and contains an oleophilic molybdenum disulphide, as hereinafter defined.
OLEOPHILIC MOLYBDENUM DISULPHIDE The oleophilic molybdenum disulphide used as the thickening agent in the dispersions or greases according to the invention is prepared by grinding natural or synthetic molybdenum disulphide in a low viscosity, low surface tension organic liquid. For convenience, molybdenum disulphide product prepared in this Way will hereinafter be called oleophilic molybdenum disulphide to distinguish it from the untreated starting material. Oleophilic molybdenum disulphide has a considerable tendency to absorb ndotriacontane in preference to n-butanol in contrast to the untreated starting material. Both natural and synthetic molybdenum disulphide are well-known and readily available. One example of a natural molybdenum disulphide product is that supplied by Acheson Colloids, Dag 325.
Satisfactory products can be obtained by grinding in most organic liquids, but it is desirable to use one the bulk bulk of which can be easily removed from the oleophilic molybdenum disulphide. Those liquids distilling below 500 C. and having a viscosity below 600 centistokes at 100 F. (38 C.) are therefore preferred. Liquids having a surface tension below 72 degrees/cm, preferably from 10 to 40 degrees/cm, at 25 C. are preferred.
Suitable organic liquids are lower molecular weight hydrocarbons, including straight-chain or branched-chain, saturated or unsaturated alkyls, saturated or unsaturated, substituted or unsubstituted, cycloalkyls, and substituted or unsubstituted aromatic compounds. Examples of such compounds are n-heptane, octene-Z, 2,2,4-trimethylpentane, cyclohexane benzene or toluene. Branched alkyl compounds are particularly preferred. Other suitable organic liquids are those compounds which contain fluorine, chlorine, or phosphorus and chlorine, for example, carbon tetrachloride.
Other suitable organic liquids are the polar oxygen compounds such as isopropyl alcohol. Silicone fluids can also be used.
For best results, the amount of molybdenum disulphide in the molybdenum disulphide/organic liquid mixture should not exceed wt.; preferably it should be from 2 to 20% wt.
The grinding may be carred out in any suitable grinding mill or device and it is desirable to continue the grinding until an oleophilic molybdenum disulphide having a Patented May 21, 1958 ICC surface area (as determined by nitrogen adsorption) of from 10 to 400, preferably from 30 to 200, square metres per gram is obtained. Usually this can be achieved by grinding at normal temperatures for the required period but the temperature of the mixture may be artificially increased if desired, for example, up to 400 C. In this case, liquids which have viscosities up to 600 centistokes at F. (38 C.) may be used, for example, mineral lubricating oils, ranging from spindle oils to bright stocks.
One of the quickest and most effective techniques is to carry out the grinding in a vibratory ball mill.
It is desirable to exclude air so far as possible during the grinding operation and this can be most easily achieved by filling the mill with the organic liquid first, followed by the balls and molybdenum disulphide. A suitable procedure is to fill the mill with the liquid, add half the balls, then the molybdenum disulphide and finally the rest of the balls.
When using a ball mill, it is of course desirable to use bails made of a material which does not react with the graphite and which does not wear unduly during the grinding. Vibratory ball mills usually contain steel balls and these are suitable for the present purpose. It is preferred to use a hard grade of steel for the balls.
A magnetic filter can be used to remove small steel particles from the slurry. A circulatory system can also be used wherein the slurry is pumped through an internal magnetic filter and then return to the mill.
A suitable vibratory ball mill is sold under the trade name Megapact, manufactured by Pilamec Limited. The grinding effect is produced by the impact of the balls upon the molybdenum disulphide and upon each other.
The slurry of oleophilic molybdenum disulphide can be separated from the balls by sieving or by displacement by another liquid and sieving.
If a relatively high boiling organic liquid is used for grinding it is preferred to displace this liquid by a low boiling liquid. This liquid can then be removed by boiling. It is preferred to use vigorous boiling.
It is also possible to filter the slurry to obtain a filter cake of oleophilic molybdenum disulphide.
In either case it is preferred to remove the last traces of solvent by heating the filter cake in a vacuum oven for several hours, for example, at 100 C. and at 1 mm. mercury.
THE BASE OIL The lubricating base oil may be a mineral oil or a synthetic oil.
Suitable mineral oils are refined mineral oils obtained from petroleum, for example, those having a viscosity at 210 F. within the range from 2 to 50 centistokes, preferably from 4 to 40 centistokes.
Synthetic lubricating oils include organic esters, polyglycol ethers, polyphenyl ethers, fluorinated hydrocarbons, silicate esters, silicone oils and mixtures thereof.
The most important class of synthetic oils are the organic liquid polyesters, particularly the neutral polyesters, having a viscosity at 210 F. within the range from 1 to 30 centistokes. The expression polyester is used to mean esters having at least two ester linkages per molecule. The expression neutral is used to mean a fully esterified product. Examples of suitable polyesters include liquid diesters of aliphatic dicarboxylic acids and monohy-dric alcohols (for example, dioctyl sebacate, dinonyl sebacate, octyl nonyl sebacate, and the corresponding azelates and adipates), liquid diesters of aliphatic dicarboxylic acids and phenols (for example, those described in copending US. patent application Ser. No. 382,964, filed July 15, 1964, UK. patent application 19,687/63, US. patent application Ser. No. 400,243, filed Sept. 29, 1964, US. patent application Ser. No. 434,-
3 094, filed Feb. 19, 1965 and U.K. patent application 31,249/ 65 and more complex polyesters (for example,
THE GREASES ACCORDING TO THE INVENTION The amount of oleophilic molybdenum disulphide required to thicken the base oil will depend on the nature of the oil and the consistency of grease required. For most purposes an amount up to 50% wt., based on the final grease, will be used, generally 40% wt.
The oleophilic molybdenum disulphide can be incorporated into a grease by a numberof methods. It is preferred to incorporate the oleophilic molybdenum disulphide into a grease, immediately after grinding. However, if the oleophilic molybdenum disulphide is prepared some time before incorporation into the grease, it is preferred to store the oleophilic molybdenum disulphide in an airtight container to prevent deterioration.
The slurry of ground oleophilic molybdenum disulphide can be converted into a grease by, for example:
(a) The grinding fluid is filtered oil". The resulting filter cake is ground by, for example, feeding the cake through a colloid mill and stirring the resulting powder into the oil. The resulting grease is finished by colloid milling.
(b) The grinding fluid is boiled olf rapidly to avoid the formation of a molybdenum disulphide cake and the resulting powder is stirred into the oil and the grease finished by colloid milling.
(0) Oil is added to the slurry of molybdenum disulphide and the grinding fluid distilled 01f.
d) Oil is added to the slurry of molybdenum disulphide and the mixture circulated through a homogeniser (for example, of the Manton-Gaulin type) so that temperatures up to or exceeding 140 C. are produced. The temperature must be high enough to drive off the grinding fluid.
(e) Molybdenum disulphide might also be ground directly in the base oil for the grease. For example, a low boiling point, low viscosity, low surface tension mineral lubricating oil with a viscosity up to 600 centistokes at 100 F. (38 C.) can be used. Elevated temperatures up to 400 C. can be used during the grinding.
Methods (c), (d) and (e) are particularly preferred. In general, the oleophilic molybdenum disulphides can be incorporated into the base oil either at ambient temper-atures or, if desired, example, up to 400 C.
The greases according to the invention have remarkably high drop points. When their drop points are measused according to the IP or ASTM standard methods, they are found to be above 400 C.; such greases are described as infusible and are diffi'cult to produce by conventional methods. By using carefully selected base oils, for example, synthetic oils with high oxidation and thermal stability, greases having a unique combination of properties can be produced.
In certain circumstances it may be advantageous to add dispersants to the molybdenum disulphide either before grinding or after grinding to oleophilic molybdenum disulphide. In this way the dispersion of the oleophilic at elevated temperatures, for
improv ers, metal deactivators, anti-corrosion agents, antioxidants etc. can also be added to the greases. Loadcarrying additives can also be added to the greases according to the invention.
' PROPERTIES OF THE GREASES ACCORDING TO THE INVENTION The greases according to the invention have been found to be infusible, that is, they show no dropping point at temperatures up to 400 C. (using either the IP 31 test or the ASTM Method D566-42). The combination of temperature-stable synthetic base oils, for example, the polyphenyl others, with oleophilic molybdenum disulphide has been found to show remarkable high temperature DISPERSIONS Oleophilic molybdenum disulphide can be incorporated into base oils in quantities up to 30% wt., based on the total wt., generally 130%, to form dispersions with surprisingly good lubricating properties. The dispersions are remarkably stable even without the dispersants usually employed to stabilise the dispersion. However, surface active agents etc. can in some cases be added to the oleophilic molybdenum disulphide either during or after grinding and the ease of dispersion of the oleophilic molybdenum disulphides might, thereby, be increased The dispersions can be formed quite simply by stirring the oleophilic molybdenum disulphide into the base oil. Alternatively, a mechanical aid to dispersion such as a colloid mill can be used.
The base oils used for the dispersion are the same as those used for grease and described above. Usually 2 to 20% wt. M08 will be used.
PROPERTIES OF THE DISPERSIONS ACCORDING TO THE INVENTION The properties of lubricating dispersions can conveniently be evaluated in the well-known Four Ball EP Lubricant Test Machine. The method of test isas prescribed in US. Federal Test Method Standard No. 791a Method 6503.1. The load-carrying properties of the dispersions according to the invention are conveniently evaluated by measuring the wear scar diameters on the balls of this ma chine when lubricated by the dispersions under various loads and after known time intervals.
The load-carrying properties of the dispersions according to the invention are found to be considerably superior to those of suspensions of air-ground molybdenum disulphide.
Dispersions of molybdenum disulphides which have been ground in solvents such as fiorinated or chlorinated hydrocarbons, or solutions of chlorinated hydrocarbons, or sulphur-containing or phosphorus-containing compounds in hydrocarbons, for example, carbon tetrachloride, have improved load-carrying properties.
Further details regarding the preparation and properties of the oleophilic molybdenum disulphide may be found in our copending U.S. patent application Ser. No. 586,346, filed Sept. 21, 1966.
The following examples serve to illustrate the invention.
EXAMPLE 1 The properties of two greases according to the invention prepared using oleophilic molybdenum disulphide are molybdenum disulphide may .be aided. Viscosity index given in Table I below.
TABLE I Grease A Grease B Thickener 33% wt. oleophilic MOS: pre- 33% wt. oleophilic MoS; prepared by grinding in n-heppared by grinding in n-heptane for 4 hours. tane for 8 hours. 01L Light medicinal paraifin oil- B G 150/75. Penetration, unworked-.- 380 298.
Penetration, worked 391 317. Bleed, percent oil 5.2 Drop point Above 300 C B G 150[75 refers to a basic grade mineral oil having a Redwood I Viscosity of 150 seconds (36.4 centrstokes) at F. (60 0.) and a viscosity index of 75.
Grease A was prepared by stirring the oleophilic molybdenum disulphide into the base oil at room temperature, followed by passing the mixture through a colloid mill. Grease B was prepared by adding the oils to the slurry of molybdenum disulphide in n-heptane and distilling off the latter.
TABLE 4 Nature and composition of MOS: dispersion Four Ball Machine Results (Wear sear, mm., 60 secs.)
Friction-Wear Balance Rig, Scar Surface, min.
50 kg. 100 kg. 150 kg. 200 kg.
Base oil plus 5% M08: commercial, A (fine) 0. 40 0.77 1. 44 2. 29 3. 07/3. 6 Base oil plus M032 commercial, A (fine) 0.39 0.74 1. 66 1. 71 2. 57/2. 63 Base oil plus 5% MoS; commercial, A (very fine). 0. 38 0. 68 1. 68 1. 93 3. 3/3. 2 Base oil plus 10% M082 commercial, A (very fine)- 0. 41 0. 69 1. 84 1. 79 2. 60/2. 80 Base oil plus 10% M082 commercial, B 0.59 2. 08 2. 11.4/12. 1 Base oil plus 2% MOSz commercial, 0 0. 45 0. 73 1. 22 1. 83 2.46/2. 53 Base oil plus 4% M082 commercial, 0.. 0. 45 0. 73 0.82 2. 09 2. 53/2. 13 Do 0. 39 0.71 0. 84 1.74 2. 33/2. 5 Base oil plus 5% oleophilic MOSz (average of 3 results) 0. 41 0. 60 0. 00 2. 3/2. 4
1 The base oil was a mineral lubricating oil, Redwood I viscosity at 140 F. (60 C.) of100 seconds and a VI 2 I he oleophilic MOS: was ground in -heptane for 8 hours.
EXAMPLE 2 The properties of dispersions prepared using 5% wt. oleophilic molybdenum disulphide are given in Table 2.
The superiority of the oleophilic M05 dispersion is clearly shown, particularly at higher loads. The Friction- TABLE 2 Mean Initial 2% sec. Welding Number of Dispersion of molybdenum disulphide Hertz Seizure Seizure Load, Experiment in base 011 Load, Load, Delay Load, in kg.
111 kg. in kg. in kg.
1 Medicinal parafim oil 19 centistokes at 100 F. 14 10.5
(35 0.) [MP0]. 2 Commercial MoSz in MP0 36 200 Olcophilic MoS; in MP0 67 5O 45 370 4.. .dc. 80 65 420 5 Naphthenic plus paraflinic frac.ion of mineral 17 60 110 oil, [NPF] 265 centistokes at 100 F. (38 0.). 6 Commercial MoS in NPF 35 220 7 Oleophilic M082 in NPF 53 300 8 Oleophilic M082 in an SAE 90 base oil 47 250 9 Polar M082 in MP0 3 38 70 250 10. oleophilic MOS; in an SAE 30 base oil 4 66 60 500 11 Commercial MoS in an SAE 30 base oil 44 00 280 1 MDS: ground in n-heptane for 4 hours.
2 M08: ground in medieinai parafiitn oil for 6 hours. 3 M08: ground in air for 4 hours.
4 Most ground in n-heptane for 16 hours.
Wear Balance Rig is also known as the Reichert Friction- Wear Balance.
EXAMPLE 5 The effectiveness of oleophilic molybdenum disulphide dispersions when used in the FZG Gear Machine is shown by the data in Table 5.
TABLE 5 Lubricating composition Initial Seizure Total Wear,
Load step mg.
Base o il (Medicinal paraffin oil) 18 Mediclnal parafiin oil plus 5% oleophilic 1 Ground for 8 hours in n-heptane.
. Wear scars, 1 min. tests, Wear scar Welding Initial Additive in a base oil of viscosity Redwood I in mm. 60 min test load, in seizure viscosity at F. (00 C.) 160 secs., VI 95 at 15 kg., kg. load, in
100 kg. kg. 200 kg in mm. kg.
None 2. 50 0. 79 13-5 00 6% oleophilic M052 1 0.77 1. 05 1. 35 0.31 250 60 5% oleophilic MoSz plus 1% tricresylphospha l 0. 92 1. 25 1. 70 0. 29 320 60 5% oleophilic M052 plus 1% zinc dithiophosphate 1. 70 2. 0 2. 20 0. 30 450 85 5% oleophilic MoS2plus 3% phosphosuliurised terpcne l 1. 40 1. 60 1. 80 0. 88 470 85 The FZG Gear Machine is described in the Journal of the Institute of Petroleum, 52, No. 507, March 1966.
EXAMPLE 6 In this example the effect of the base oil on the loadcarrying properties of dispersions of commercial molybdenum disulphide and dispersions of oleophilic molybdenum disulphide was investigated. The results are given in Table 6 below:
in the molybdenum disulphide/organic liquid mixture during grinding is 2 to 20% wt.
TABLE 6 Wear scar diameters, in Base 011 Type of molybdenum mm. for l min. tests disulphide 100 kg. 150 kg. 200 kg.
Medicinal paraffin oil wt. of commercial 0. 70 1. 70 2.00
product, X. Mineral oil (B G 160/95), 0.77 1. 1. 90
Redwood I viscosity at 140 F. (60 C.) 160 secs, VI at 95. SAE nil do 1.25 1. 1. 90 Medicinal parailin oil 5% wt. of oleophilic MoS J. 0. 0. 1. 00 B G /95 do. 0. 72 0. 98 1. 16 SAE 50 oil d0. 0. 83 1. 15 1. 40 B G 160/95 5% wt. of commercial 2. 25 2. 40 Weld product, Y.
1 Ground for 8 hours in n-heptane.
From this table it appears that the nature of the base oil does not affect the superiority of olcophilic molybdenum disulphide over commercial molybdenum disulphide dispersions.
1. A lubricating composition which is based on a lubricating base oil and containing an elfective amount of an oleophilic molybdenum disulphide having a surface area of 10 to 400 square metres per gram and prepared by grinding natural or synthetic molybdenum disulphide in an organic liquid distilling below 500 (3., having a viscosity below 600 centistokes at 38 C. and having a surface tension below 72 degrees/ cm. at 25 C.
2. A lubricating composition as claimed in claim 1, which comprises up to 50% by weight of oleophilic molybdenum disulphide, based on the total weight of composition.
3. A dispersion of an oleophilic molybdenum disulphide in a lubricating oil as claimed in claim 1, which comprises 1 to 30% by weight of oleophilic molybdenum disulphide.
4. A lubricating composition as claimed in claim 1, wherein the lubricating oil is a mineral oil.
5. A lubricating composition as claimed in claim 1, wherein the lubricating oil is a synthetic lubricating base oil.
6. A lubricating composition as claimed in claim 1, in which the organic liquid is selected from the group consisting of n-heptane, octene-2, 2,2,4-trimethylpentane, cyclohexanc, benzene, to toluene, carbon tetrachloride and isopropyl alcohol.
7. A lubricating composition as claimed in claim 1, in which the amount of molybdenum disulphide present 8. A method of preparing a lubricating composition comprising forming a mixture which consists of less than 50% by weight of natural or synthetic molybdenum disulphide and an organic liquid distilling below 500 C., having a viscosity below 600 centistokes at 38 C. and having a surface tension below 72 degrees/cm. at 25 C., grinding the molybdenum disulphide in the organic liquid until the molybdenum disulphide becomes oleophilic and has a surface area of 10400 square meters per gram, separating the oleophilic molybdenum disulphide from the organic liquid, stirring an eflective amount of the olcophilic molybdenum disulphide into a lubricating base oil, and finishing the resultant composition by' colloid milling.
9. A method of preparing a lubricating composition comprising forming a mixture which consists of less than 50% by weight of natural or synthetic molybdenum disulphide and a lubricating base oil distilling below 500 C., having a viscosity below 600 centistokes at 38 C. and having a surface tension below 72 degrees/cm. at 25 C., and grinding the molybdenum disulphide in the lubricating base oil until the molybdenum disulphide becomes oleophilic and has a surface area of 10-400 square meters per gram.
References Cited UNITED STATES PATENTS 3,059,769 10/1962 Frost 252-25 3,338,822 8/1967 Groszek 252-25 DANIEL E. WYMAN, Primary Examiner.
IRVING VAUGHN, Assistant Examiner.