US2639266A - Lubricating grease comprising a complex ester base and sodium myristate - Google Patents

Description

Patented May 19, 1953 UNITED a misc J 011 P, CDHWEU! rles 4 k ll, N-

ssianor to The To Ne york; 1 a orp-9mm e GREA E. oMrn siNe A rna BASE AND s-onrcm 19 maime- I 1 The present invention relates to a Wide pera-ture range ball and roller bearing grease. More particularly it relates to a lubricating grease composition comprising as the oil component complex polyester of the type obtained by ester- 5 ifying a dicarboxylic acid with both a mcnohy dric alcohol and a dih-ydric ether alcohol thickening agent comprising sodium myristate. There is a rapidly growing demand, particularly by aircraft engineers and by the manuiacr iturers of 'prepackeci bearings, for lubricating greases which will provide good lubrication 'for .anti friction bearings over a wide temperature range, such as from about Ts5=o F. or lower up to about 200 F. .or higher. Bali and roller bear:- 5 ing greases oi the usual type, comprising mineral oil fractions thickened with various fatty acid soaps, are unsuitable for use under conditions invoiving'wide variations in temperature specause of the changes in texture and consistency which they undergo with changes in temperature. Recently has been iounol that all or a part of the mineral oil base .of such greases fbB replaced :by non-hydrocarbon oils such as war.- iOus esters, polymerized ethers and like, with considerable improvement in the low tempera.- ture torque characteristics ,of the greasfifi. E-ice esters .of aliphatic .dibasic acids have been .recommended particularly for this purpose because of Ltheir hi h boiling points, z-lo-w pour minis and high viscosity indexes, However, it has been found that t me improved low temperature characteristics :of these rsoecalled synthetic greases of the type l c ifiilo- :iore proposed are obtained at the expense .oifoth- 3;, er lubricating properties. particular they are unsuitable :ior the long time lubrication :of anti-friction bearings at ordinary or elevated temperatures.

It is a principal object of this invention to pro- 5 0 vc ki ce ix m fining rom i to 1.2

al hatic other group eoniaioing from 4 to 12 carbon atoms, R1 is an alizyl g 0 1p cont inin mm 1 1 9 12 carbo atoms Rags an a torn and a i n nteger f m t Pref rably R is an a iphat ether group w. o i a .i ie 6 t :12

atom ranch d a n co al- 4 s a alkyl vs onr c n ainin I iQ IQarL-QP atoms 12 is {an alkyl sroup con ainin irprc 1 9 i9 oar-boa ca ms branched hain rr e meo and x is 1 or 2. This ester may corn e irgrn abou 2.0% 1. 9 9 1 9% o t e in common. of the easemei rably it comp ises rom an i9 9 c th e campme The rem nr o .ih oilc mponezi su tabl be a 91 mecca 47 i hlnd$ c c n .162 et e este w th other es s, with pol me ic .e ilie t are wi h a l a hon me liial 9 e, ad e ibea ice e e a vv iie icicice. are no; obtainabl by es mnpei he et ore propqse iii .y a I 3 9 mica??? $9h by a e eiabal t c {9.136

e t rs ides nibed-abore Whi hLQ Hi- E e the 9 componectoi 1 'Q W co cal "by-re ctin to et r si c nbcziil' a xiii slibyslric ethe el idl mo olixerip alc hols;

or suitable derivatives thereof according to any of the known methods for producing esters. They may conveniently be prepared by heating together a suitable dicarboxylic acid, dihydric ether alcohol and monohydric alcohol at about 150-- 200 0., preferably in the presence of an esterification catalyst such as a sulfonic acid or zinc chloride, and of a volatile solvent such as benzene, toluene, xylene, etc. A suitable ester of this type may be produced, for example, by heating together under reflux a mixture comprising dipropylene glycol, sebacic acid and 2-ethylhexanol in a 1:222 mol proportion respectively, with benzene as the solvent and with about 0.5 per cent of a sulfonic acid as the esterification catalyst. The reaction is continued until an amount of water equivalent to a mol proportion of 4 with reference to the weight of the reactants is collected and the neutralization number of the product is approximately zero. The mixture is then neutralized with a mild basic reagentsuch as sodium bicarbonate and distilled under vacuum, removing the volatile solvent and traces of water and any excess of monohydric alcohol. As an alternate method, a polyhydric ether alcohol and dicarboxylic acid, in a 1:2 mol proportion respectively, may be permitted to react completely before the monohydric alcohol is added and'the esterification then continued until all the acid groups have been esteriried.

The acids which may be employed in the esterification are the saturated aliphatic dicarboxylic acids containing from 3 to 14 carbon atoms. As examples of such acids there may be mentioned particularly malonic, succinic, isosuccinic, glutaric, ethyl malonic, pyro tartaric, adipic, pimelic, suberic, azelaic and sebacic. Of these, azelaic and sebacic are particularly suitable. Mixtures of such acids may also be used.

I The dihydric ether alcohols used are most suitably polyalkylene glycols containing up to 12 carbon atoms obtained by condensation in the known manner of 1,2 diols containing from 2 to 6 carbon atoms. Of these, the polypropylene glycols, particularly dipropylene glycol and tripropylene glycol, are especially suitable. Instead of a single glycol, mixtures of the above glycols may be employed.

The monohydric alcohols employed are saturated aliphatic alcohols containing from '1 to 9 carbon atoms. They are preferably branched chain non-tertiary alcohols containing from 4 to 9 carbon atoms. Suitable alcohols of this type which may be mentioned are Z-butanol, 2-ethylbutanol, Z-pentanol, 2-'nethylpentanol, i-methylpentanol, 2,3-dimethylbutanol, '2=hexanol, 2.- ethylhexanol, Z-heptanol, 3-heptanol, 2,3-dimethylpentanol, '4-methyl-2-pentanol, 2-octanol, z-methyloctanol, 2-nonanol, 3-nonanol, and so forth. Such alcohols may be used either singly or as mixtures in the esterification reaction.

The sodium myristate soap which is employed as the thickening agentmay be prepared by fatty acids comprising at least 70%, and preferably at least 90% by weight, of myristic acid and/or the glycerides of such acidswith caustic soda or other suitable sodium compound, preferably employing a small excess of the-alkali sufficient to provide an excess of about 0.1 to "about 1% of free alkali in the finished grease. In addition to this soap the greasemay contain minor amounts of other thickening agents such as other metal soaps, polymeric materials, etc. The grease may suitably contain from about"% 4 to about by weight of the sodium myristate soap or of the sodium myristate soap and other thickening agents.

The greases of this invention may be prepared by conventional grease making procedures. In making a grease in which a mineral oil fraction comprises a portion of the oil base, the grease may advantageously be made by forming the soap in situ with the saponification carried out in the presence of the mineral oil component, and then finishing off with the ester component. Greases for the lubrication of high speed bearings are preferably prepared by the method described in -Patent No. 2,542,570, dated February 20, 1951.

In accordance with the method of said patent, a myristic acid mixture is saponified with a small excess of sodium hydroxid in the presence of small amounts of mineral oil and water, the resulting soap base dehydrated at a temperature in the range 295-320 F. and suificient synthetic oil added to obtain the desired consistency, the

- synthetic oil addition being carried out in two saponifying a mixture of low molecular weight stages so that a total amount of oil equal to at least twice the weight of the fatty acids initially charged is added before the temperature of the mass is allowed to drop below 260 F.

Various addition agents may be added in accordance with common practice in the compounding of lubricating greases, such as antioxidants and other stabilizing agents, corrosion inhibitors, extreme pressure agents, and so forth. Suitable stabilizing agents include various amines, alkylated phenols, beta-naphthol and phosphorusand sulfur-containing compounds such as alkyl and aryl thiophosphates and their metal salts. N,N' diphenyl p-phenylene diamine has been found to be particularly effective for this purpose. It may suitably be employed in amounts ranging from about 0.1% to about 8%, and preferably from about 0.5% to about 5% by weight based on the weight of the grease. This compound may be added to the grease by any of the methods commonly employed for incorporating additives such as by adding it in the form of a slurry in a portion of the lubricating oil base or in solution in a volatile solvent, which is later flashed off. A particularly convenient method comprises adding it to the grease in the form of a solution in tricresyl phosphate. The latter serves as a solubilizing agent and carrier for the diphenyl p-phenylene diamine in addition to imparting its known anti-wear properties to the grease. A suitable composition for addition to the grease, comprising the amine and tricresyl phosphate in a ratio of about 1 to 3 by weight, may be obtained by heating them together at about 200 F.

The following example is presented to illustrate the preparation of a representative grease falling within the purview of our invention. It is understood, however, that this example is merely illustrative and not intended to limit the scope of the invention in any way.

EXANIPLE I A small pestle stirred kettle was charged with 400 grams of myristic acid having a neutralization number of 240, a saponification number of 241, and a titer, 0., of 41.8, 300 grams of water and 24.0 grams of lubricating oil obtained by clay and solvent refining a paraiiinic distillate oil. The charge was heated to -l90 F. and 144 grams of a 50.3% aqueous sodium hydroxide, sufficient to give a slight excess, was added with stirring. "After saponification the temperature was maintained at 295-320 F. for two hours to" efiect dehydration while the stirring was con tinued. The temperature was then allowed to decrease gradually while 1620 grams of an ester were added which was -.obtained by reacting to- .gether seba'cic acid, dipropylene glycol and 2- -ethylhexanol according to the method described above for obtaining complex ether esters. Analysis showed this ester to be predominantly The physical tests on this ester and on the mineral oil are as follows:

Ester gg 465 455 535 525 240 332 Viscosity, SUS, at 210 F. 55 55 Viscosity Index 140 103 Pour, F -65 Neutralization number 0. 11 Saponification number. 277

The temperature or the mass was controlled during the addition of the ester so that approximately .1200 grams of the latter was added while the mass was at 'a temperature above 260 F. and the remainder added while the mass was at a temperature below 260 F. .At a temperature below about 250 F. 23.9 grams of N,N' diphenyl paraphenylene diamine was added in the form of a solution of 67 grams of tricresyl phosphate. The product obtained was a tan short fiber grease having the following calculated composition:

Per cent Sodium myristate 18.4v Mineral oil 10.0 Ester 67.7 Excess NaOI-I 0.1 NN diphenyl p-phenylene diamine 1.0 'I'ricresyl phosphate 2.8

The following table shows some of the properties of the foregoing grease comparatively with those of a sodium myristate grease of similar preparation and composition containing in place of the ester a mineral lubricating oil of the type commonly used in compounding ball and roller bearing greases. This mineral oil was a mixture of distillate and residual parafiinic oils having an 8135 viscosity at 210 F. of 100.0, a viscosity index of 92, a flash point, COC of 520 and a. fire point, COC, of 585.

Seconds/revolution at 0 F Seconds/revolution at F Seconds/revolution at F Seconds/revolution at F 1. Seconds/revolution at F. 3. 3. gecongslrevoluumtion a: -23: gun econ srevo one Seconds/revolution at 70 F 120 120 The dynamic shear test of the foregoing table is a measure of the resistance of the grease to texture change when worked under high shearing stress, the test being carried out as described in U. S. 2,450,219, column 5, lines 6-19. A small change in miniature penetration of the sample after the test in comparison with the original is indicative of excellent texture stability under high shearing stress. The miniature penetration test is described in Ind. Eng. Chem, analytical edition, volfII, page 108, February 15, 1939.

The low temperature torque test of the tore-v going table is essentially a measure of the resistance of the grease to congealing and of its ability to afiord proper lubrication under extremely low temperature conditions, such as are encountered in aircraft at Very high altitudes. The apparatus employed for the test consists essentially of a vertically mounted hollow spindle with a No. 204K Conrad type 8-bal1 bearing mounted on the bottom, and a drum on which is wrapped a coiled line for applying torque mounted on the top. The bearing, packed with a 60% capacity charge of the grease to he tested, is clamped at the inner race to the spindle, while the outer race is clamped immovably to a stationary cup within which the bearing is inserted. The assembly is inserted with the lower bearing end in a low temperature bath containing isopropyl alcohol, and the desired temperature of the bath and bearing is attained by dropping Dry Ice in the bath. The drum and drum extension carried at the upper end of the hollow spindle and protruding from the bath are held in vertical position by a tapered roller bearing. The line coiled around the drum extends over a pulley to a container into which the desired weights are added to apply the torque load to the hollow spindle to thereby cause rotation of the spindle and inner race of the bearing with respect to the fixedouter race. A time of not less than two hours is utilized to cool the bearing to the test temperature, and an additional soaking period at the test temperature is permitted such that the test is not run until three hours from the start of cooling. When the desired bearing temperature and soaking period are attained, a 2000 gram-centimeter torque load is applied in both clockwise and counter-clockwise directions, and the number of seconds for one rotation in each direction is observed. The values obtained with rotation is clockwise and counter-clockwise directions are given separately in the table under the headings cw. and. cow, respectively.

The foregoing table shows that the ester base grease combines a high dropping point equivalent to that of the mineral oil base grease with good low temperature torque characteristics. In addition the ester base grease has a greatly improved resistance to shear as compared with the mineral oil base grease, and equally satisfactory oxidation stability, water resistance and anti-corrosiveness.

The following table shows the high temperature properties of ester base greases of this invention as compared with those of other ball and roller bearing greases containing different oil bases. soaps and additives. I

Table II .--H2'gh temperature performance test 300 F. and 10,000 R. 'P. M.]

Hours to Soap Base 011 Component Additive Failure Na Myristate Mineral Oil None 219 ..--.do -.do 1% Diphenylarm'ne 392 1% Triphenylguam'dine-.. 452 1% Diphenyl p-phenylene l, 056

diamine. 1% Diphenyl p-phenylene 1,308

diamine +28% tricresyl 1 phosphate. 6 Na 4:1 Stearic acid: Ta1l0w.... None 273 Li 3:1 Hydrogenated castor oil: .....(10 -.do 144 Triple pressed stearic acid. Na 3:1 Menhaden oil: Snodotte ...-.do 1% Diphenylamine 254 acids 5% Al Stearate. Sulfonic acids. Li Hydrogenated Fish Oil Silicone fluid. 262 10.. Na Myristate Butyl stearate.... 264 11.. .do Tetradecyl sebacate..- .---.do 572 12.. do Dioctyl phthalate --do.... 396 13.. Polymerized ether ..do 156 14.. Chlorinated diphenyl. 2.8% Diphenylamine. 61 1% Diphenylamine 843 0.9% Triphenylguanidine... 1,106 1% Diphenyl p-phenylene 2, 376

diamine +28% tricresyl phosphate.

All Of the sodium myristic greases of the above table were prepared according to the procedure described in Example I. Grease No. 17 is the grease prepared in Example I, and Greases No. 15 and 16 differ from this grease only in the additives employed. Grease No. 5 is the mineral oil base grease of Table I. Grease No. 9 is a commercial grease generally rated as a very superior grease for the lubrication of high speed ball bearings over a wide temperature range. Analysis of this grease indicates that it is composed of 23% of a lithium soap of hydrogenated fish oil fatty acids, 0.2% free fatty acid and a silicone fluid of an SUS viscosity of 330 at 100 F. This grease has a dropping point of 422 F. and gave 33.4 seconds/ revolution at l0 F. in the low temperature torque test.

The high temperature performance test of the foregoing table is a test for determining the performance characteristics of greases in anti-friction bearings at elevated temperatures and high rotative speeds. Thev test unit consists essentially of a steel spindle supported on ball bearings in an electrically heated housing and driven by an electric motor connected into an electric cirouit containing a low amperage fuse 0.1 ampere below that required for full load running. The bearings are Norma-Hofifman ABEC No. 3 grade, and are mounted on the spindle approximately 5%. inches apart. A thrust load of 17.5 pounds is, applied to the bearings. One bearing is used for test purposes and the second bearing,'which is not heated, is used as a guide bearing. The test consists of operating the test bearing for twenty-four hours at 10,000 R. P. M. and at a temperature of 300 F. followed by a shut down and cooling period of two hours, and repeating this cycle until the lubricant fails, which is indicated by rupture of the low amperage fuse in the motor circuit. In starting up the test, three grams of the test grease are charged to the test bearing and worked into and around the races and balls. The bearing is next rotated both clockwise and counterclockwise for one minute each at 200 R. P. M. and assembled into the test unit. The heaters and the motor are then started and the test bearing brought up to the test temperature as rapidly as possible, which requires 1.0 to 1.25 hours, while the spindle is rotated at a speed of 10,000 E. P. M. After 24 hours of operation the heaters and motors are shut off for 2 hours, during which the temperature of the test bearing drops to a minimum of -130 F. The total hours of operation, excluding the two hour shutdown periods, to the failure point is recorded as the hours to failure. A grease giving satisfactory lubrication for 1000 hours at 300 F. under the conditions of-this test is considered a very superior lubricant for the lubrication of anti-friction bearings at elevated temperatures and at high rotative speeds.

As shown in the tables, the greases of our invention are markedly superior in both high and low temperature properties to greases comprising other soap and oil base combinations, including the usual types of soaps with mineral oils, and sodium myristate with both mineral oils and with other types of synthetic non-hydrocarbon oils such as have been proposed heretofore as lubrieating oil bases. More particularly, the greases of our invention are superior for lubricating small, light, high speed bearings, such as those used in aircraft gyroscopes, over a wide range of temperatures.

Obviously many modifications andvariations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

l. A wide temperature range ball and roller bearing grease consisting essentially of an oleaginous liquid lubricating base and a thickening agent comprising in major proportion sodium myristate, said oleaginous liquid lubricating base comprising in substantial proportion a complex polyester of lubricating characteristics represented by the general formula wherein R is an aliphatic ether group containing from 4 to 12 carbon atoms, R1 is an alkyl group containing from 1 to 12 carbon atoms, R2 is an alkyl group containing from 1 to 12 carbon atoms and :r is an integer from 1 to 5.

2. The grease composition of claim 1 wherein the complex polyester is represented by the general formula wherein R is an aliphatic ether group containing 9 from 6 to 12 carbon atoms in branched chain arrangement, R1 is an alkyl group containing from 7 to 8 carbon atoms, R2 is an alkyl group containing from 4 to 9 carbon atoms in branched chain arrangement and a: is an integer from 3. The grease composition of claim 1 wherein the complex polyester is a compound having the formula (iso-C Hu)OOC(CH2) COO(iso-CaH6)O 4. The grease composition of claim 1 containing a small amount of free alkali.

5. The grease composition of claim 1 in which the complex polyester is obtained by reacting together under esterification conditions a polypropylene glycol containing from 6 to 9 carbon atoms, sebacic acid and 2-ethyl hexanol.

6. The grease composition of claim 1 containing 0.18% by Weight of N,N' diphenyl paraphenylene diamine.

7. The grease composition of claim 1 containing 0.5-% by weight of N,N diphenyl paraphenylene diamine.

8. The grease composition of claim 1 in which the oleaginous liquid lubricating base comprises a minor proportion of a mineral oil of lubricating characteristics.

9. The grease composition of claim 1 containing 03-15% by weight of tricresyl phosphate.

10. A lubricating grease consisting essentially of an oleaginous liquid lubricating base, about 10 15-25% by weight based on the grease of a sodium soap of a soap-forming fatty material containing at least based on the fatty material of myristic acid, 0.5-5% by weight of N,N diphenyl p-phenylene diamine, 15-15% by weight of tricresyl phosphate and ill-1.0% of free alkali,

said oleaginous liquid lubricating base comprising in minor proportion a mineral lubricating oil and in major proportion a complex polyester of lubricating characteristics obtained by reacting together under esterification conditions a polypropylene glycol containing from 6 to 9 carbon atoms, sebacic acid and 2-ethyl hexanol.

JOHN P. DILWORTH.

CHARLES H. CULNANE.

References Cited in the file of this patent UNITED STATES PATENTS from Aliphatic Diesters, article in Industrial and Eng. Chem., vol. 39, pp. 500-506, April 1947.

Claims (1)

10. A LUBRICATING GREASE CONSISTING ESSENTIALLY OF AN OLEAGINOUS LIQUID LUBRICATING BASE, ABOUT 15-25% BY WEIGHT BASED ON THE GREASE OF A SODIUM SOAP OF A SOAP-FORMING FATTY MATERIAL CONTAINING AT LEAST 70% BASSED ON THE FATTY MATERIAL OF MYRISTIC ACID, 0.5-5% BY WEIGHT OF N,N'' DIPHENYL P-PHENYLENE DIAMINE, 1.5-15% BY WEIGHT OF TRICRESYL PHOSPHATE AND 0.1-1.0% OF FREE ALKALI SAID OLEAGINOUS LIQUID LUBRICATING BASE COMPRISING IN INOR PROPORTION A MINERAL LUBRICATING OIL AND IN MAJOR PROPORTION A COMPLEX POLYESTER OF LUBRICATING CHARACTERISTICS OBTAINED BY REACTING TOGETHER UNDER ESTERIFICATION CONDITIONS A POLYPROPYLENE GLYCOL CONTAINING FROM 6 TO 9 CARBON ATOMS, SEBACIC ACID AND 2-ETHYL HEXANOL.