CA1067887A - Hydrocarbon/silicone oil lubricating compositions for low temperature use - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A low temperature lubricant oil composition having improved viscosity-temperature properties, lubricating properties and pour point is described. The composition comprises a homogeneous mixture of from 1% to 50% by weight of poly(dimethylsiloxane) having an average viscosity at 100°F between 100,000 cs and 1,000,000 cs, the remainder of the mixture being a hydrocarbon oil selected from certain alkenes, isoparaffins and naphthenics.
The composition can also contain a foam inhibitor such as a perfluoroalkylpolyether.

Description

`" ~Ot;~7E~7 Thi8 inventlon relates to low tem~erature lubrlcant compos$tlons havlng lmproved vi9cosity-temperature propertles, lubricating propertie~, and pour point, contalning a 301vent oil, poly(dlmethylslloxane), and cert~in antiwear and foam inhlbitlng addltlve~.
Lubricatlng oll composltione are often employed a~ functional flulds, pGwer transmisslon fluids, or heat transfer flulds, such as in automatlc transmdsslons, pumps, and hydraullc equipment. Most equipment of thl~ sort is rendered inoperable if the vlscoslty of the functional fluid chan~s dramatically between extremes of operatlng temperature. The problem is partlcularly acute ln arctic regions where the amblent temperature can range from -75F to 100F, and the operatlng temperature of the equipment may vary from -75F to 300F; ~lmilar operational temperature ranges are frequently encountered ln heat exchange equipment.
In order to achieve ~he requlred vlsco~lty stability (high viscosity index) the flulds are p~cvided w~th addit~ve~ auch as polyalkyl methacrylate polymer~ and co-polymers, pol~i~obutylenes~ pol~alkyl styrenes, and co-polymers o~ methacrylates or fumaric.ac~d ester~ with polar monomers;
typical of the last type ~9 vinyl p~rrolidine. The~e additiYe~, ho~ever, are not alway3 completely sati~factor~ ln many cases thelr thermal stability, stabll~ty under lo~d~ or both, are incuf~icient to proYide the modified fluid with sn extended or u6eful li~e.
Where conventional vlaco~ity index improver~ have not been ~uccessful ~;
in providing adequate vi~cos~ty index along with other pr~perties, common practlce has been to operate equipment continually to mal~taln the operatlng temperature, or to frequently change the fluid to conform with~changlng ambient conditions and operating temperature. Clearly, such routes are economically and conaervationally unsound.
It is well known that certaln llquid poly(organoslloxanes) exhibit a very hlgh vlscoslty index which enables them to be u~ed aa functional fluid~ over a broat temperature range. Poly(dimethylsiloxane) in particular, ~hows a performance in thla srea whlch 1~ superlor to vlrtuslly all known '!
materlal~. Unfortunately, these ao-called slllcone 0119, especially poly-(dlmethyl~iloxane), are lncompatlble wlth most other materials and are econo~ically unattractlve; moreover, they have poor lubricstlng propertlea ~06788'7 when u~ed ~s lubricants for metal on metal, partlcularly ateel on steel applications. Their lncompatlbillty makes it dl~flcult to improve thelr perform~nce with additlves.
In order to take adv&ntagP of the good vlscoslty-temperature propertles of silicone 0119, lt 1~ desirable to di~solve them in lubricating oil carriers. Thls has been carried out wlth v~rlous poly(organo-slloxane~) aR descrlbed in Germnn Patent 1,806,445. However, the solublllty characterlstics of poly(dimethylsiloxane) generally prevent lts dlsperslon ln liquld medla, except wlth the ald of dispersing Rgents or emulslfler~, such as described in UOS. 3,445,385 and U.S. 2,466,642.
It ls well known ~hat the higher the molecular weight of the polymer or solvent, the m~re dlfficult lt becomes to effect dissolutlon. Thù~, ln those few cases where poly(dimethylslloxane) oll has been successfully A, lncorporated into a homogeneous compositlon, the molecular welght of the silicone ha~ been such that lts viscosity has been limited to around l,000 cs or less as shown ln U~S. 2,652,364 and U~S~ 2,618,601~ The solubility characterlstics, vlscosity-temperature behaylour, and lubricating propertles of such low molecular we~ght polymers of dimeth~lsiloxane are markedly different ~rom those exh~bited by the higher liquid polymers.
In fact, it is gene~ally accepted that hlgh polymexs of any polymeric material possess very d~f~e~ent properties from their lower molecular weight counterparts. Clearly, the behaviour of plastic polyethylene cannot be predicted from the properties of hexane or octane. It has been the experience of workers in the field that solutions of high viscosity (i.e; high molecular weight) poly(dimethylsiloxane~ are tem~erature sensitive, and solution components separate at temperatures s~gni~icantly~
above those at which lo~er polymers become incompatible. For this reason, it has, heretofore, been lmpos31ble to utilize hydrocarbon lubricants containing significant amounts of hlgh viscosity dimethyl silicone oil ln applications where even nomlnally l~w temperatures are encount~red.
It ls an obJect of this invention ~o provlde a l~w temperature lubricant oil composltion contalnlng poly(dlmethyl~iloxane) having a relatiyely high vlsco8ity, ~aId compo~ltlon exhibiting good lubricity and pour point characteri~tlc~.

- ~[)6'7887 In one aspect of this lnventlon there 19 provlded a homogeneous composltion comprising a hydrocarbon llquid and poly(dlmethyl~lloxane~
having a vl~co~ity between 10,000 c~ and 1,000,000 c~.
It i9 therefore an ob~ect of the inventlon to provide a lubricating oil compositlon comprlslng a homogeneous mlxture of from 1% to 50% by weight of (A) poly(dimethylslloxane) having the general formula:
R ~ R ~ R

R ~ Sl 0 Si 0 - Sl - R
R ~R ~ n ¦ :

When R is a methyl group ln essentlally all cases and n has a value such that the average vlscosity of the poly(dimethyl~iloxane) at 100F
is between 10,000 c~ and 1,000,000 cs9 and the remalnder of sald mixture consistlng of (B) hydrocarbon oll having a vlscosity of les~ than 40,000 c9 at -65F, and a flashpoint highe~ ~han 175F, and 3ald hydrocarbon oil being at least one selected from the group con~i~ting of (a~ alkenes, (b) isoparafflns, and (c) naE~hthenics havlng a ~lngle ring which has multiple alkyl ~ubstituents;ln the caae of (a) and (b), the longest carbon chaln, and in the caae of (c) any alkyl substituent in which the longest carbon chain exceeds flve carbon atom~, has multiple sub~tituent alkyl branches9 and it~ methyl branched homolog has a solubility parameter of less than 7.84 and said ~ub~tit~ent alkyl branches atom~
of four or more carbon/are themselveY branched, and where at least 50%
of said ~ub~tituent alkyl branches are bonded to carbons of the longes~
carbon chain which are lmmedlately adJacent, or separated by only one - ~.
carbon atom.
It 18 another ob~ect of the inventlon to provide a proce~ for effectlng movement of a movable member ~ithin an enclosing member ~hich compriae~ transmitting pressure to aald movable mem~er through a liquld ~-medium consistlng e~senelally of a lubricating oll compo~ltion as defined above.
It 1~ still another ob~ece of the inventlon to provide a process for tran~mittlng force ehroug~ a hgdraullc system having hydraulic activ~ting mean~, an hydraulic llne means connecting ~ald hydraullc actlvating means to an hydraulic actlvated mean~, ~hlch process comprises sub~tantially ~L0671~1~7 -filling ~aid hydraullc actlvating mean~, said hydraullc llne mean~ and ~aid hydraulic activated mean6 with a lubrlcatlng oil compo~ltlon as defined above.
The lubricating oil compo~itlons are a homogeneou~ admlxture contalnlng a hydrocarbon 11quid ant poly(dlmethyl~iloxane) in ~ufflclent quantity to give the de~lred viscosity. More ~pecifically, the homogeneou~ lubrlcatin~ compo~i~lon of the invention contains a hydrocarbon base oil, and from 1 to 50% by welght of a poly(dlmethyl~lloxane) of the ~enernl formula:
R / R \ R
R - Si - 0 ¢ ~1 - 0~ - Si 1 ~ I J R
where R i8 a me~hyl group ln essentlally all of the case~, and n has values such that the viscosity of the poly(dlmethylsiloxane) at 100F
i9 between 10,000 cs and 1,000,000 C8~ More preferably, R i~ alway~
a methyl group, and n has values such that the vl~c081ty of the poly(dimethylslloxane~ at 100F i9 between 1009000 cs and 500,000 c~ and the poly(dimethylslloxane) 1~ present in the composition in concentratlons from 2 to 15% by weight. It will be appreciated by those skilled ln the art of polymer chemlstry that ln polymer~ of the size described above, the poasiblllty exls~s that R might be other than a methyl group in one or more of the po~itions along the polymer chaln. Some slight deviation from R belng a methyl group in the poly(dimethylslloxane) would therefore be acceptable without departing from the present lnYentlon ~o long a~ ~ -the extent of devistion doe~ not algnificantly affect the viscosity, temr perature behavior9 or solubill~y. For thls reason the formula given above i~ de~cribed whereln R 1~ a methyl group ln "essentially" all of the cases.
The hydrocarbon oll of the invention may be of either synthetic or natural orlgin, and is selected from the classes known a~ naphthenic, paraffinic, alkene, or a comblnation of these. By naphthenic species, we mean any non-aromatic rlng ~tructure compri~ed solely of carbon ~nd hydrogen. By parsffinic ~pecles, we ~ean all those hydrocarbons that do not contain cycllc ~tructureff, or double or triple bond0. By alkene !
~67~87 species, we include only those hydrocarbons not containing cyclic structures, but which contaln non-conJugated double bonds.
The hydrocarbon olls of the invention should have a viscosity less than 40,000 cs at -65 F, and a flashpoint higher than 175 F.
More specifically, the paraffinic hydrocarbons mus~ be multi-branched hydrocarbons, commonly known as iso-paraffins, wherein at least 50% of the pri~ary branches are located on carbons which are immediately adjacent,-or separated by only one carbon. We have also discovered that the degree and type of b~anching is critical to the solvent power of the isoparafEins.
As a means of defining the degree of branching, the iso-paraffins must have a structure such that, if all the primary branches are methyl groups (methyl branched homologues), the compound would have a Hildebrand solubility parameter less than 7.84 as calculated by the method described by R. P. Fedors ln "Method for Estimating Both the Solubility Parameters and Molar Volume of Liquid" in the JPL Quarterly Technical Review Vol. 3, known in the art.
No. 1, April 1973, or as determined by experiment/ Uhile it is permissible for the primary branches to be higher alkyl groups, where they exceed ` 3 carbon atoms, they must also be branched, e.g. isobutyl radicals are acceptable, whereas n~butyl radicals are not. Examples of petroleum ~ dlstillates corresponding in large measure to this description include Esso Univolt 40~ and Imperial Oil Isopar M products.
The entire range of the above described paraffins may correspond identically to, and may be obtained directly by hydrogenation of polymers, oligomers, or copolymers of hydrocarbons of twelve carbons or less. Said small hydrocarbons include ethylene, propylene, butenes, pentenes, hexenes, et~., and their saturated analogues.
Following are examples of compositions which include the described paraffins.
EXAMPLE I
15% by weight of poly(dimethylsiloxane), having a viscosity of 750,000 cs at 100 F, was dissolved in Esso Univolt 40, a petroleum oil fraction very high ln iso--paraffin content, which has a flashpoint of 2]0F
and viscosities of 750 cs and 1.4 cs at -65F and 210F respectively.

~"Univolt 40" and "Isopar M" are trade marks ~6~8~7 The solubility parameter of the Univolt 40 was determined experi~entally ' to be 7.5. The resulting composition was homogeneous at -65F, and had ! viscosities of 8,792.2 cs and 53.9 cs at -65 F and 210 F

50% by weight of poly(dimethylsiloxane~, having a viscosity of 10,000 cs at 100F, was dissolved in Univolt 40. The resulting composltion was homogeneous at -65 F, and had viscosities of 17,000 cs and 187.5 cs at -65 F and 210 F respectively.
; EgAMPLE 3 10% by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cs at 100F was dissolved in 2,2,4,4,6,8,8 heptamethylnonane, a material obtainable by hydrogenating a random polymer of isobutylene.
Other methods for the synthesis of this hydrocarbon also exist of course and are known to those skilled in the art. Heptamethylnonane has a flashpoint of 240F, a solubility parameter of 7.42, and viscosities at -65 F and 210 F of 160 cs and 1.42 cs respectively. The resulting composition was homogeneous at -65F, and had viscosities of 750 cs and 12.5 cs at -65 F and 210 F respectively.

10g by weight of poly(dimethylsiloxane), having a viscosity of N 0,000 cs at 100 F, was dissolved in a cut of hydrogenated polyisobutylene t~at had a flashpoint of 260F, a solubility parameter of 7.34, and v~scosities at -65 F and 210 F of 1,150 cs and 1.8 cs respectively; the isobutylene polymer was formed exclusively by head to tail monomer addition. The resulting composition was homogeneous at -65 F, and had viscosities of 5,000 cs and 10.34 cs at -65F, and 210F respectively.
i FXAMPLE 5 1% by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cs at 100 F, was dissolved in Esso Univolt 40. The resulting composition was homogeneous at -65 F and had viscosities at -65 F and 210 F of 740 cs and 1.75 cs respectively.
The alkene hydrocarbons of the lnvention must have a structure such I that their saturated analogues correspond to the suitable paraffins ! deæcribed above. These alkenes may correspond identically to, and may ~; ~ "Univolt ~0"1s a trade mark.~ 6~
~ .
~, , . . . . ".,...... ,.,.. ,.. ,.. ~

s 1C1~71 3~37 be obtained dlrectly from polymers~ oligomers, or copolymers of hydrocarbons of twelve carbons or lesa. Such small hydrocarbons lnclude ethylene, propylene, bu~enes, pentenes, hexenes, etc.,and thelr ~aturated analogues.
An example of a compositlon that contain~ such an olefinlc compound follows.
EX~MPLE 6 10% by welght of poly(dlmethylslloxane), havlng a vl~coslty of lO0,000 cs at 100F, wa~ dl~solved ln polypropylene, a polymerlzatlon product having a f1ashpoint of 240F, and 8 vlscosity at -65F of 433 C9.

The solubility par~meter of the saturated analogue i8 7.6. The resultlng compos~tion was homogeneous at -65F and had vlscosltles of 1,624 C8 and 9.55 cs at -65 F and 210F respectively.
The naphthenics of the invention do not contain more than one ring;
furthermore, lt is desirable that the ring~ contaln ~ubstituent alkyl groups, and that where said substituent groups exceed four carbons, they mu3t corre~pond to structure0 deflned above for olefins or iso-parafflns.
An example of such 8 material follows.

10% by weight of poly(dimethylsilo~ane) having a Vi8c08ity of 100,000 cs a~ 100F was dis~olved in a cyclohexane ~tarted e~hy7ene oligomer having a fla~hpoint of 190F, and a viscoslty at -65F of 150 c~. The resulting compositlon was homogeneous at -65F and had vi~cosities of 921.6 cs and 17.1 C3 at -65F and 210F respectively. ~
To illu~trate the advantage of compositions of the invention over ~ -compositions comprising ~uantities of high molecular weight pol~(dimethyl-siloxane) and known ~olvent~ for low molecular weight poly(dimethylsiloxane),~
the following examples are offered. It i~ to be understood that Examples 8-ll are provlded for lllustratlve purposes, and ln no way con9titute or slmulate composltion~ of the invention~ ;

Trioctylpho~phate and trl~2-ethylhexyl phosphate (trialkyl phosphates employed ln U.S. 2,618,60i) were combined wlth 10% by welght of poly(dimethyl-~lloxane) havlng a vlscoslty at 100F of 100,000 cs. The admlxtures were non-homogeneou~ at temperature~ below 75~F. Analogous compositions utilizing - 6a .

,~;,`
i ~06~7887 poly(dimethylsiloxane) having a viscosity of 10 cs at 100F were homogeneous at temperatures above -40F.

A naphthenic oil, Sunoco Clrcosol 304, having a pour point of -50F
(i.e. a viscosity at -50F ~ 90,000 cs) was combined with 10% by weight of poly(dimethylsiloxane), having a viscosity at 100F of 100,000 cs.
The admixture was observed to separate at temperatures below 40F.
~XAMPLE 10 Polyisobutylene, of the type described in U.S. 2,446,642, having a flashpoint > 360 F, and viscosity at -65 F> 40,000 cs, was combined with 10% by weight of poly(dimethylsiloxane) having a viscosity at 100F of 100,000 cs. The admixture became non-homogeneous and separated at temperatures below 20F.

- -A highly reflned parafiin oll (Sunpar 106H) having a pour point of 15F, was cor~ined with 10% by weight of poly(dimethylsiloxane) having a YisCQsity at 100F of 100,000 cs. The admixture sepàrated at 75F~
To illustrate the great lmprovement in viscosity properties obtained ; when using poly(dimethylsiloxane) i~stead of another viscosity improver, the foll~wi.ng example is offered for comparison with Example 1.

Two compositions were prepared using quantities of poly(dimethylsiloxane) having a Yiscosity at 100F of 60~000 cs, and a commercial viscosity improver~
TLA-407, which when dissolyed in Uniyolt 40 gave initial viscosities which were approximately equal: 9.7 cs and 9.6 cs respectively at 100C. The viscosities of the same solutions at -67F were 990 cs and 1,390 cs respectively. The relative difference in viscosity change favours the use of the silicone viscosity improver by a wide margin~
It is a characteristic and great advantage of the compositions of the invention that they are compatible with many common antiwear additives.
Wear of system components moving with respect to, and in contact with each other is a serious problem and limits the life and usefulness of all "Circosol 304", "Sunpar 106H" and "Urlivolt 40" are trade mar];s ~L0678~'7 machlnery. Thus for lubrlcatlng flulds, utlllzed in envlronment~ where other than hydrodynamlc lubricatlon i8 requlred, commonly referred to a~ boundary or extreme pre~sure lubricatlon condltlon~, lndu~try and military Ypeciflcatlon~ have been ~et on the lubrlcatlng, or antiwear, or load bearlng propertles of the fluld. Under the~e ~o-called boundary or e~treme presHure condition~, one or more of the components - of the lubrlcant compositlon lnteract with each other and/or lnteract or chemlcally react with the ~urfaces to be lubrlcated to provide the fluld wlth certaln mea~urable and unique lubricatlng antlwear, and/or losd bearlng propertlesO Numerous example~ exi~t in the literature where so-called lubrlcity or antiwear addltlves have been lncluded ln lubrlcant compo~ltlons to provide the de~lred propertie~. Among the mor~ common antiwear additlves are: polyalkyl and polyaryl phosphate~ .b such as trlcresyl phosphate, organic acld~ such as adipic acld, various amines, die~ters, thlophosphates and thlocarbamates.
In some cases the effectivene~s of common lubriclty additive~ i~
dimlnished by thelr interaction with certain component~ of the fluld~
Specifically9 it i~ well documented that flulds contalnlng or comprised of liquld poly(organosiloxaneR), particularly poly(dimethyl~lloxane) 9 ~' inhlbit the action of such lubricity addltlves; example~ include 'IAntiwear and Antlfriction Propertles of Poly (organosiloxanes) and ~ ~
Their Mlxtures wlth Hydrocarbons", G.V. Vlnogradov et al, Paper No. ~ ; -64-Lub-8, Transactions of the ASME, 1964; "Influence of Additives on the Antiabra~ion and Antifrlction Propertie~ of Polysiloxane~", M,I. ~ -Nosov and GoV~ Vlnogradov, Khlm 1 Topllv i Masel, 9 (8), 50-3, (1964);
"Effects of Chemlcally Active Additives on Boundary Lubrication of Steel by Silicones", S.F. Murray, R.L. Johnson, Natl. Advisory Com~.
Aeronaut~ TechO Note 32579 ~1954)~ With these fluid compositions, it i8 neces~ary ~o utlllze exces~ive concentratlons of antiwear additlve~ or alternatively9 to u~e highly reactive material~ to replace ;common additive~ in order to provide wear protection meeting common ~tandard~. ~ither of the~e approache~ produce adver~e effect~g lncluding damaging corro~ion and/or decoMpo~itlon of the other materlal~ contained - . _.. , ._. !

--` 1(36'7~38'7 in the fluid. It is also known that additional problems are encountered ~hen using additives in fluids containing silicone oils. Poly (organo-si~oxane) molecules are sensitive to thé presence of certain chemical functionalities, most notably acids, which act to decompose the silicone molecule. Also, certain additives will cause silicone oil to be preci-pitated from solution, thereby degrading the properties of the fluid.
We have discovered that the inclusion of selected antiwear additives in the compositions of the invention overcomes the problems outlined above, and that said additives show unexpected and advantageous activity in the presence of silicone oil as found in said compositions.
- The additives are selected from three general classes, the first being certain ~etal salts of thiophosphates, corresponding to the general formuia: - -S S.
~ l .
~R - O - P - S - M - S ~ P - O - R
O O ~ . .
R R
... .. . . . .. . .. . . . . ...... . . . . : . ~ . .. :.
in which R is selected from the group consisting of an alkyl group and an aryl group and M is selected from among cadmium, lead, or zinc.
~ost preferably, R is an alkyl group of less than 20 carbons, and M
is zinc. The compositions contain said thiophosphate salts to the extent that the concentration of the metal in the final formulation is between 0.02 weight percent and 0~5 weight percent, and preferably ~etween 0.06 weight percent and 0.3 weight percent. These compounds are commonly referred to as æinc dialkyl dithiophosphates, and are well ~nown in the industry. Examples of effective dithiophosphate salts available in industry include: Lubrizol 1395, available from Lubrizol Corp.; Elco 116 and Elco 124, available from Elco Corp.;
- Oloa 267 and Oloa 269 available from the Oronite division of Chevron Chemical Co.; and Hitec E-522, available from Edwin Cooper Inc.

Additionally, it has been discovered that certain metal salts of ~i - thiocarbamdtes are also useful at normal levels in the presence of silicones. These are of the general formula:

"Lubri~ol 1395","Elco 116", "Elco 124", "Oloa 267", "Oloa 269" and "Hitec E-~' are trade marks g j:

~067~87 `

R S ~ S P~
/
N - C - S - M - S - C - N' R R

~n which R may be an alkyl group, an aryl group, or a hydrogen, and M is either antimony or cadmium. More preferably, R is an alkyl group, and most preferably R is a 5 carbon alkyl group, and M is cadmium.
' The compositions contain said thiocarbamate salts in concentra-tions such that the concentration of the metal in the final formulation ` is between 0.02 weight percent and 0.5 weight percent, and preferably between 0.06 weight percent and 0.3 weight percent. Examples of e~fective dithiocarbamate salts available in industry include: Cadmium '~
diamyl dithiocarbamate, marketed as Vanlube 61 ~and ~ntimony dialkyl dithiocarbamate marketed as Vanlube 73, both are available from the R.T. Vanderbilt Corp.
Further, for applications where corrosion is required to be - negligible, thus precludlng the use of sulphur, it hàs been discovered that, in contrast to the performance of other known organic esters~
certain alkyl esters of 4-isopropyl benzoic acid, commonly known as cumic acid, provide excellent antiwear properties when used in conjunc-- .
tion with silicone oils. These esters are of the general formula: -' `' - .

C13 ,, CH3 - C ~ C - O - R

where R is an alkyl group containing from 1 to 10 carbons and preferably from 3 to 5 carbons. Concentrations between 0.1 to 2% by 30- weight, and preferably 0.5 to 1% by weight of the named esters are required in the final formulation to meet rigorous industry specifi-cations.
An example of an e~fective ester is isobutyl cumate which has the structure:

-~ "Vanlube 61" and "Vanlube 73" ~r~Otrade marks .i 10 ............... , ~L~16~1 387 ", o C ~ ~ CH2 ~ CH - CH

".

WEAR ADDITIVE PRODUCT PERFORMANCE
Smnll concentratlons of the aboven~med anti-wear addltlve~ are effectlve ln maint~i~ing wear ~t or below common ~peclficatl~ns. The wear properties of lubricating fluids are commonly determined with a four-ball we~r tester. In this test, one steel ball is rotated in the interstice formed by three other immoblli2ed balls immersed in the oil. The wear scars on the three immobllized balls are measured to give an indication of ehe lubricating properties of the oil. One such test, described in the U. S. A. Milltary Specification Mil-H-5606 C and commonly utilized by ::~
, indu3try to approximats boundary or moderate E.P. condition~, (hence-forth referred to as test cond$tion A) is conducted under the following cond~ti~ns :

Test Contition A.

Temperature 75 C
Speed of Rotation of Ball 1200 RPM
Pressure 40 kg Time 1 hour .: ~
The average diameter of the we~r scar produced on the three immobili~.ed balls must be less than 1 mm for the lubricating fluid to p8S9 the specific~
ation. Examples which follow lllu~trate the superlor performance of anti- ~ :
wear additives of the invention when tested according to te~t condltion A.

A sllicone hydrocarbon composition was formulated a9 follows:
' J~ ,\
~0~78~3'7 Poly(dimethylsiloxa,ne) 100,000 cs 10% by weight Esso Univolt 40 ~ gO~ by weight This oil was ~ested in the four ball tester according to test condition A, and an average scar diameter of 1.16 mm was obtained.

The anti-wear additives were combined with a base oil described in Example 1. Since 9 with the exception of isobutyl cumate, they are available in industry in dilute form, higher concentrations of the diluted commercial products have been used in a manner consis-tent with the preceding discussion.

Wt % Blended With Average Example ~ Additive Base Oil oE Example 12 Wear Scar mm . ' ' .
14 ~ubrizol 1395 ~ 5% .61 Elco 116 5% .69 16 Elco 124 5% - .64 17 Oloa 267~Y - 5% .75 18 Oloa 269 ~ 5% ' .64 19 Hitec E-522 5% .62 ,Vanlube 61~ - 5% .78 : 21 Isobutyl Cumate 1% .82 The exceptional and surprising performance of the additives of the i~vention is appreciated by comparing their performance with that of other common additives of the eame general class which are shown to be ineffective~ Such a comparison is provided by examining the following data~
which were obtained from the testing of several common additives under conditions identical to Examples 14 - 21. It is to be understood that the antiwear additives described in Examples 22-28 are not included in ' the invention.

Wt % Blended With Average Example ~ Additive Base Oil of Example 12 Wear Scar mm 22 TCP 5% 1.07 "Iubrl ol 1395", "Elco 116" "Elco 124" "Oloa 267" "Oloa 2G9" "Hitec E-522"
and "Van].ube 61" are trade ma~ks ~3 ` ~67~387 23 ~on-~etallic (Van Lube - Thiophosphate 73) iti 5% Weld 24 Organic Acids Amines 5% 1.05 Zinc Dibutyl M thiocarbamate 1% - 1.08 26 Amine; Phosphate 5% 1.19 27 Sulphur (Elco 217)~ 5~ 1.01 28 Antimony Dialkyl (Oloa ~
Dithiophosphate 254) 3% 1.09 The concerltrations given in Examples 23, 27 and 28 refer to percentages of commercial products rather than pure active ingredient.
A significant aspect of the invention is the apparent comple-mentary action between silicone containing fluids and the antiwear compounds of the invention. Illustrative of this is the positive or neutral e~fect that antiwear additives of the invention have with respect to ~he antiwear properties of unimproved solutions of poly-(dimethylsilo~ane), as described in Example 13. It is well known that solutions of silicone oil show antiwear properties superior to ~i ~ those of either the silicone or the other component and publicationsdescribing this syner~istic phenomena are plentiful; examples include:
"Polysiloxanes as Additives for Increasing the Lubricating Action of Petroleum Oils and Hydrocarbons." M.I. Nosov; Teoriya Smaz. Deistviya ~i 1 Novye Msterialy, Akad. Nauk SSSX; 1965. 68-72. "Antiwear and Anti-friction Properties of Poly (organosiloxane)s and their Mixtures with Hydrocarbons." G.V. Vinogradov et al Wear, 8 (12), 92-lll, 1965.
T7ne conditions under ~hich this effect occurs are commonly encountered in industry, and they can be approximated by the following - four~ball test which is given in the Canadian Government Specification Board, specification 3 GP-59 (henceforth referred to here as test condition B):

Test Condition B

Temperature 75C
Speed of Rotating Ball 600 RPM
Pressure 15 kg Time 2 hours ,~- "Van Lube 73" "~lco 217" "and "Oloa 25~" are trRde rnarks l,7, /~ -- ~.3 --1'~ .

~67~

The solu~ion described in Example 13 was prepared and tested along with the individual components, according to test condition B.
EX~PLE # DESCRIPTION ~VEP~GE SCAR DI~I.
29 Solution described in .48 - Example 1 Univolt 40 ~ - .82 31 Poly(dimethylsiloxane) weld The following examples were tested on the four-ball tester according to test B. Many of the additiYes of the invention are not designed to ~mprove the lubricating properties under conditions as mild as those of ' tes~ B (e.g. Numbers 34 and 35), as is seen by the following examples.
Such limited usefulness with respect'to severity of conditions is common of many materials used by industry for antiwear additives. Nevertheless, , it is indicative of their utility in conjunction with silicone, that ¦ the additives of this invention do not adversely affect the antiwear action l ~ of silicone solutions, whereas other additives do. 'Comparing the following ~examples with Example 29 illustrates the neutral or beneficial effects of ' additives of the invention with regard to silicone induced antiwear scar ,diameters ~0.35 mm. - - , EXAMRLE # COMPOSITION AVERAGE SCAR DI~M.
32As descr;lbed in Example 14 .34 33As described in Example'15 .32 34As described in Example 19 .50 il . .
' 35As described in Example 20 .40 - 'EXAMPLES 36-42 ..
The effects of other additives on the antiwear action of silicone i solutions tested according to test B show marked contrast to t~ose of ,i the invention (examples 32-35~. Note also the deterioration occuring 30 in Examples 36-46 from the results of Example 29. It is to be -understood that the antiwear additives described in Examples 36-39 ' are not part of the invention.

"Univolt 40" is a trade mar~ 14 -'i i,' ~

67~387 ` l ` `

EXAMPLE ~ COM2OSITION~VERAGE SCAR DI~.
36 5~ TPSA in blend of Example 13 .62 - 37 As described in Example 22 .72 38 As described in Exsmple 24 .98 39 5% organic acids and esters in blend of Example 13 .75 As described in Exarnple 23 .78 41 As described in ~xample 25 .80 42 As described in Eximple 28 .88 The foregoi~g examples illustrate the exceptional antiwear . 1~
performance of lubricating compositions of the invention, including certain antiwear additives. The large wear scars observed for compositions containing common additives other than those of the inYenti~n lllustrate the urtexpected and important improve~ent realiæed by co~posltions oX the invention. To qualify silicone containing functional fluids for us~ under ex~reme pressure or boundary conditions requires improved perfor~ance such as that shown by compositions including - antlwear additives of the invention.
- It is a further adva~tage of compositions of the invention that they are compatible with many common additives such as pour point

2~
~ - depressants, e.g. low viscosity (~ 500 cs at 100F~ polydimethylsiloxane, j viscosity impro~ers, e.g polymethacrylates, oxidation or corrosion inhib~tors, and dyes. It is also a~ advantage of the invention that the ~ompositions may be diluted with materials whlch would not no~nally be . compatible with dimethyl ~ilicone oil. Such materials might include mineral oils, distillate products~ residues of petroleum oils, commoTl synthetic ~; - hydrocarbons, alcohols, and other common functional fluids. To illustrate the valuable compatibility characteristics9 the following ex.ample is

3 ofered.
, 1 ~1 30 EXAMPLE 43 A composition as described ln Example 3 WctS diluted with 20% by weight of Imperial H-515, a coTmr.ercial hydr~ulic fltlid. The mixture was compatible.
Poly(di~ethylsiloxane) having a viscosity of lOO,OOO cs at 100F is not miscible in H-515 alone. It' ls to be understood that the composi~.ion dcscribed in l~xampJe ~3 i8 not a part o~ the lnvontlon.
"Imperial ~-515" is a trade rnarklS

~7~ 7 It i~ an additional characteriBtic of compo~itions of the invention, particularly compositions containing ~dditives, that they are prone to foaming. This foamln~ la caused by the entr~inment and ~ub~equent relea~e of air from the liquid, a phenomenon which frequently occur~ ln conJunction wlth vigorou~
agitation, decompre~sion, or circulation of the lubrlcant. It i~
recognized throughout indu~try that foam in a functional fluid can be highly detrimentnl to the operation of an automatic transmission or hydraulic device; thus, in order to engure the commercial utility of composltions of the invention under such conditions, it was de~irable to identify a foam controlling additive.
The foaming tendency of many hydrocarbon fluids i9 controlled by the use of silicone oils, e.g. U.S. 2,416,503, or alternatively by u~ing various halogenated materials, e.g. V.S. 2,394,595, and U.S.
2,515,115, or di~persed metal complexes, or surfactants. However, because the compositions of the inventlon contain large quantlties of sillcone oil, their properties are inherently different from those of compositlons previou~ly known, and their foaming tendencies are not controlled by the addition of most conventional additives.
It is an additional feature of this invention that a csrtain species of fluorocarbons, in contrast to the behaviour of other known ty~es of antifoam a~ents, and in contrast to the behaviour of other well known foam controlling fluorocarbons, has been discovered to be an effective antifoam agent in compositions of the invention. ~ -Specifically, the lubricating compositions may contain a minor foam inhibiting amount of perfluoroalkylpolyether.
More specifically, the compositions as described above may contain from about 1 to 500 parts per million by weight and preferably 5 to 100 parts per million by weight, of a perfluoroalkylpolyether corresponding to the formula:
F _LT (CF3) CF2~ X C2F5 in whlch x ha~ a value providing an average molecular weight for the ~067~

perfluoroalkylpolyether rflnging from about 2,000 to 7,000. Thi~
molecular weight ranRe wlll corre~pond to value~ for x of about 10 to 41. The preferred perfluoroalkylpolyethers are tho~e in whlch the average molecular wel~ht r~nBea from about 2,000 to about 5,500 whlch molecular welghes corre~pond to values for x of about 11 to 32, re~pecelv~ly. Specific ~xample~ ~f effectlve perfluoroalkylpolyethers are described below.

A perfluoroalkylpolye~her havlng the formula:

F _ ~ (CF3)CF2~ x C2F5 and having an average molecular welght of 4,500 corresponding to a value for x of about 26. Thi~ ~erfluoroalkylpolyether has a vi8c08ity in centistokes at 100F of 85 and at 0F of 6,900, a~d an approximate boiling range at 0.8 mm. Hg of 440-485 F.

EXAMPL~ 45 A perfluoroalkylpolyether having the formula:

_ :.' ~( 3) 2 x 2 5 and having an average molecular weight of approximately 2,000 corre~
ponding to a value for x of about 11. Thi8 perfluoroalkylpolyehter has a viscoslty in centi~tokes at 100F of 18 and at 0F of 550 and an approximate boiling range at 0.8mm. Hg of 290-365 F.

EXAMPL~ 46 A perfluoroalkylpolyether having ~he formula: ; .

F~ ~(CF3)C~ x 2 5 ~;

and having an average molecular weight of about 7,000 corresponding to a value for x of about 41. This perfluoroalkylpolyether has a viscoslty in centistokes at 100F of 495 and at 210F of 43, and a vapor pre~ure at 700P of about 80 mm of Hg, ~0678~'7 ~
Commercial products corresponding to this description are Krytox fluids manufactured by E. I. duPont de Nemours & Company.
To illustrate the s~rprising effectiveness of the perfluoroal'~yl-polyethers of the invention, the antiform properties of a series of lubricant compo$itions, both with and without antifoams, were deter-mined in a modified ASTM Foam Test, D-892. According to this test, the foam volume is determined at the end of five (5) minutes blowing with air, and again after standing for an additional ten (10) minutes, ~he test being conducted at room temperature.

EXAMPL~S 47-52 The significance of the presence of dimethyl silicone oil in - compositions of the invention is demonstrated by comparing foaming properties of hydrocarbons before and after the addition of said silicone oil. The effectiveness of perfluoroalkylpolyethers of the invention is also unambiguously demonstrated. Results appear in Table I.

The promotion of foaming due to the presence of substantial ~i concentrations of poly (organosiloxanes) as a class is demonstrated ¦~ 20 by comparing the corresponding data in Table I with that of Examples 47-48. The foam controlling effectiveness of the perfluoroalkyl-i polyethers of the invention is again demonstrated.

As an illustration of the outstanding and unexpected performance of the antifoams of the invention, they may be compared (especially Example 47) with the performance of various conventional antifoams, and other fluorinated antifoams (shown in these examples). Results appear in Table I. It is understood .hat the antifoam agents described in Examples 55-60 are presented for comparative purposes, and thatsaid antifoams are not part of the invention.

'Krytox" is a trade mark ~ - 18 -~"
..... .....

~Q6~7887 T A B L E

~FO~M VO~UME ASTM D892 75 F
WITHOUT ANTIFOAM WITH ANTIF0~M
AFTER AFTER AFTER AFTER
5' 10' 5' . 10' EXAYPLE C0MPOSITIO~ ANTIFOAM AERATION SETTLING AERATION SETTLING

Ex. 47 10% 1009000 cs2.5 ppm Krytox AZ~ 400 ml20 ml 30 ml 0 ml dimethylsilicone analogous to that : : oil, 90% U~ivolt described in : 40, as described Example 45 in Example 13 Ex. 48 Univolt 40lO ppm Krytox AZ 95 ml0 ml 35 ml 0 ml Ex. 49 25~ poly(dimethyl10 ppm Krytox AZ ~450 ml 40 ml 25 ml 0 ml siloxane) (10,000 c~) 75% Uni~olt 4~ . .
Ex. 50 1~ 750,000 cs 1 ppm Krytox AD, 200 ml0 ml 140 ml 0 ml : dimethyl silicone analogous to that oil, 99% Univolt described in Example 46 ~ :
`Ex. 51 As described in 400 ppm Kry~ox AZ 400 ml 20 ml 0 ml . O ml I : Example 47 IFx. 52 As described in 400 ppm Rrytox AD 400 ml 20 ml 10 ml~ 0 ml I Example 47 ¦ Ex 53 50% alkylpolysilo- 10 ppm Krytox AZ 170 ml 5 ml 35 ml ~ ml i . xane, 50% Univolt Ex. 54 25X poly(phenyl- 10 ppm Krytox AZ 560 ml 260 ml 185 ml 0 ml ~' methysiloxane), - 75% Univolt 40 ~5Ex. ~5 As described in 142 ppm Pentel 52~ 400 ml 20 ml 250 ml 15 ml Example 47 (chromium metal ~.
complex) Ex. 56 As described in 112 ppm FC-43 ~400 ml 20 ~1 345 ml 0 ml ~'. Example 47 (heptacosafluoro-- - tributyl amine) x. 57 As described in 100 ppm 100,000 cs 400 ml 20 ml No No ' Example 47 silicone antifoam Change hange ~; L-45 ;,~iEx. 58 As described in 132 ppm FS-1265400 ml 20 ml 175 ml 0 ml .. Exampl.e 47 (300) ~rifluoro-propylpolvsiloxane) Ex. 59 As describ2d in 145 ppm FC-170 '~ 40n ml20 ml 365 ml 30 ml ExamDle 47 (fluorosurfactant), EY 60 As described in 93 ppm Monflor 71400 ml 20 ml 120 ml 30 ml '' (fluorosurfactant) "Krytox Ai~ rytox AD', "Pent~l 52","FC-43", "FS-1265", "FC-170" and . .~ S, "~on10r 71" d~ S trade ~(rdrl~ ~
, ', A ~:, .,, ~

~ ' gL06~781~7 ` ' ` `
The foregoin~ examples illustrate the exceptional foam resistant tendencies of compositions of the invention containing the perfluoroalkyl-polyether antifoam additive of the in~ention. This outstanding imp~ove-ment over other foam controlled compositions is essential to qualify compositions of the inve~tion for certain rigorous applications.
In the industry, it is common practice to disperse antifoam agents such as perfluoroalkylpolyethers in foaming fluids by first dissolving the said antifoam additives in solvents which are themselves soluble in the foaming fluids (e.g. U.S. 3,775,324). A useful, very fine dispersion of the antifoam is thus obtained. The only known hydrocarbon oil soluble solvents for the perfluoroalkylpolyethers of the invention are poly- or per halocarbons such as trichlorotri~luoroethane. However, it has bPen show~ by M~Z. Fainman ("Halogenated Solvents and Corrosion in Dynamic Systems ` Lubrication Engineering, pp. 556-558, November 1974.) that a parts per milllon concentration of such halocarbons can cause grave corrosion problems in certain applications such as hydraulic systems.
It is an additional aspect of this invention that we have discovered an alternative method of dispersing perfluoroalkylpOlyethers in compositions containing silicone and hydrocarbons, as previously described.
~ Specifically, a fine dispersion of a minor portion of said perfluoroalkyl-, - . polyethers can be achieved and maintained in poly(dimethylsiloxanes) having j .. a viscosity at 100F less than 500 cs, and greater than 5 cs. These silicone oil/antiioam compositions can then be added to the lubricating compositions of the invention in the minute quantities required to provide a ~ighly dispersed foam inhibiting perfluoroalkylpolyether concentration between 1 and 500 ppm. This is illustrated by the following example.

~XAMPLE 61 198 grams of poly(dimethylsiloxane) having a viscosity of 50 cs at 100F were agitated in a household type blender while 2 grams of Krytox 143 AZ, a pe~fluoroalkylpolyether as described in Example 44, were added dropwise. The resultant 1% emulsion was stable for more than 24 hours, and was added with stirring to compositions of the "Krytox 143 ~z" is a trade mark .

0678~3 7 ~`
?

invention, as in Examples 47 ,through 54 in quan,itites to give the concen~rations of perfluoroalkylpolyether indicated. As seen by the foam test results, the method of dispersion is effective.
The foregoing data and discussion serve to reveal the exceptional - properties and characteristics of functional fluid compositions containing high molecular weight silicone oil, and in some cases specific and surprisingly effective additives for the control of wear and foaming tendencies. For use in extreme and rigorous environments, functional fluids are required which possess properties such as those exhibited by compositions of the invention. As a final illustration of such a composition the follo~Jing example is presented. 5 ' , To a composition containing 10% by weight poly (dimethylsiloxane), ~,~ (100,000 cs) and 90% by weight Esso Univolt 40, was added: 2~ by 'I` ~eight of Elco 116, 7.9 ppm Krytox AZ, 1% by weight of an oxidation i inhibitor; and a minor concentration of coloring dye. The resulting ¦ composition was homogeneous at -65F, and had viscosities of 2,241 cs and ~¦ . ` lOol9 cs at -65F and 210F respectively. The formulation gave good wear ¦ properties on a Shell four-ball wear test, and performed outstandingly ~hen run in a Vickers type V-104-A hydraulic pump for 40 hours under ' il- high pressure conditions. ` -'~i ' The specific details of the compositlons described with reference i to the above examples are for the purpose of illustratlng the invention.
i Modification in the incidental features and details of the composition t including the addition of other additives for specific functions can ,, be made without departing from the spirit and scope of the applicants invention.
Van Lube is a trade mark of R. T. Vanderbilt Inc.

~ Elco is a trade mark of Elco Corporation.
! ~ Oloa is a trade mark of Chevron Corporation.

"Univolt 40" is a trade mark of Imperial Oil END OF SPECIFICATlON

"Krytox i~ a trade mark of du Pont de hemours ' ~ 20 , ' ..
!

Claims (19)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A lubricating oil composition comprising a homogeneous mixture of from 1% to 50% by weight of (A) poly(dimethylsiloxane) having the general formula:

When R is a methyl group in essentially all cases and n has a value such that the average viscosity of the poly(dimethylsiloxane) at 100°F is between 10,000 cs and 1,000,000 cs, and the remainder of said mixture consisting of (B) hydrocarbon oil having a viscosity of less than 40,000 cs at -65°F, and a flashpoint higher than 175°F, and said hydrocarbon oil being at least one selected from the group consisting of (a) alkenes, (b) isoparaffins, and (c) naphthenics having a single ring which has multiple alkyl substituents;in the case of (a) and (b), the longest carbon chain, and in the case of (c) any alkyl substituent in which the longest carbon chain exceeds five carbon atoms, has multiple substituent alkyl branches, and its methyl branched homolog has a solubility parameter of less than 7.84 and said substituent alkyl branches of four or more carbon atoms are themselves branched, and where at least 50% of said substituent alkyl branches are bonded to carbons of the longest carbon chain which are immediately adjacent, or separated by only one carbon atom.

2. A composition as claimed in Claim 1 comprising a minor amount of an antiwear additive (C) selected from the group consisting of (1) metal salts of thiophosphates corresponding to the formula:
in which each of R', R", R'" and R"" is one selected from the group consisting of an alkyl group and an aryl group and M is one selected from the group consisting of cadmium, lead, and zinc in a concentration such that the weight percent of M in the total composition is between 0.02 and 0.5; (2) metal salts of thiocarbamates corresponding to the formula:

in which each of R', R", R'" and R"" is one selected from the group consisting of an alkyl group and an aryl group and M is one selected from the group consisting of antimony and cadmium in a concentration such that the weight percent of M in the total composition is between 0.02 and 0.5; and (3) esters of 4-isopropyl benzoic acid, commonly known as cumic acid, corresponding to the formula:
where R'"" is an alkyl group in a concentration comprising between 0.1 weight percent and 2 weight percent of the total composition.

3. A composition as claimed in Claim 1 containing a minor amount of (D) perfluoroalkylpolyether corresponding to the formula:
F-[CF(CF3)CF2O] x C2F5 in which x has a value providing an average molecular weight for the perfluoroalkylpolyether ranging from about 2,000 to 7,000, wherein the amount of (D) in said composition is from 1 to about 500 ppm, by weight of the total composition.

4. A composition as claimed in Claim 1, 2 or 3 where the longest linear segments of the hydrocarbon oil have no substituent alkyl branches which exceed two carbons in length, and wherein n has values such that the viscosity of the poly(dimethylsiloxane) at 100°F is between 10,000 cs and 500,000 cs.

5. A composition as claimed in Claims 1, 2 or 3 wherein said hydrocarbon oil is iso-paraffin, and wherein the amount of component (A) in said mixture of components is from 5% to 30%
by weight.

6. A composition as claimed in Claims 1, 2 or 3 wherein said hydrocarbon oil is alkene and wherein the amount of component (A) in said mixture is from 5% to 30% by weight.

7. A composition as claimed in Claims 1, 2 or 3 wherein said hydrocarbon oil is naphthenic, and wherein the amount of component (A) in said mixture is from 5% to 30% by weight.

8. A composition as claimed in Claims 1, 2 or 3 wherein the hydrocarbon oils (B) are saturated or unsaturated copolymers of hydrocarbons selected from the group consisting of 2, 3 and 4 carbon alkenes.

9. A composition as claimed in Claims 1, 2 or 3 wherein the hydrocarbon oils (B) are saturated or unsaturated copolymers of propylene and iso-butylene.

10. A composition as claimed in Claims 1, 2 or 3 wherein the hydrocarbon oils (B) are saturated or unsaturated polymers of propylene.

11. A composition as claimed in Claim 2 where (C) is (1), a metal salt of thiophosphate wherein M is zinc and wherein R', R", R'", R"" are alkyl groups of no more than 18 carbons, and wherein the proportion of component (C) ranges from a concentration such that the weight percent of zinc in the total composition is between 0.06 and 0.3.

12. A composition as defined in Claim 2 where (C) is (2), a metal salt of thiocarbamate wherein R', R", R'", R""
are alkyl groups of no more than 18 carbons each, and wherein the proportion of component (C) ranges from a concentration such that the weight percent of M in the total composition is between 0.06 and 0.3.

13. A composition as defined in Claim 2 where (C) is (3), an ester of cumic acid, wherein R'"" is an alkyl group of no more than 10 carbons, and wherein the proportion of (C) ranges from about 0.5 weight percent to about 1.0 weight percent of the total composition.

14. A composition as defined in Claim 13 wherein R'""
is an isobutyl group.

15. A composition as defined in Claim 3 wherein x has a value which provides an average molecular weight for the perfluoroalkylpolyether ranging from about 2,000 to 5,500 and wherein the proportion of (D) ranges from about 5 to about 10 parts per million by weight of the total composition.

16. A composition as claimed in Claim 2 containing a minor amount of (D) perfluoroalkylpolyether corresponding to the formula:
F-[CF(CF3)CF2O] x C2F5 in which x has a value providing an average molecular weight for the perfluoroalkylpolyether ranging from about 2,000 to 7,000 and wherein the amount of (D) in said composition is from 1 to about 500 ppm by weight of the total composition.

17. A composition as claimed in Claim 16 wherein x has a value providing an average molecular weight for the perfluoroalkylpolyether ranging from about 2,000 to 5,500 and wherein the proportion amount of (D) in said composition is from about 5 to about 100 parts per million by weight of the total composition.

18. A process for effecting movement of a movable member within an enclosing member which comprises transmitting pressure to said movable member through a liquid medium consisting essentially of a lubricating oil composition as defined in Claims 1, 2 or 3.

19. A process for effecting movement of a movable member within an enclosing member which comprises transmitting pressure to said movable member through a liquid medium consisting essentially of a lubricating oil composition as defined in Claim 16.