US 3803037 A
Description (OCR text may contain errors)
United States Patent [191 Wygant Apr. 9, 1974 [54} LUBRICANTS HAVING IMPROVED 3,440,894 4/l969 Hammann et al. 74 200 LOADBEARING PROPERTIES 3.442.804 5/1969 LeSuer ct al 252/32.7 E
James C. Wygant, Creve Cocur, Mo.
Assignee: Monsanto Company, St. Louis, Mo.
Filed: Mar. 20, 1972 Appl. No: 236,437
, Related US. Application Data Continuation-impart of Ser. No. 26,446, April 7, 1970, abandoned.
US. Cl. 252/32.7 E, 252/59, 252/75 Int. Cl Cl0m 1/48 Field of Search 252/32.7 E, 73, 75, 52 R,
References Cited UNITED STATES PATENTS 11/1968 Hammann et al. 74/200 Primary ExaminerPatrick P. Garvin Assistant Examiner-Andrew H. Metz Attorney, Agent, or Firm-William H. Duffey 5 7 ABSTRACT 8 Claims, N0 Drawings LUBRICANTS HAVING IMPROVED LOAD-BEARING PROPERTIES CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 26,446, filed Apr. 7, 1970, and now abandoned.
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to functional fluid compositions particularly adapted for use as lubricants in tractive drives, and more specifically, to additives for increasing the load-carrying capability of these compositions.
2. Description of Prior Art A tractive drive is a device in which torque is transmitted from an input element to an output element through nominal point or line contact, typically with a rolling action, by virtue of the traction between the contacting elements. While tractive elements are commonly spoken of as being in contact, it is generally accepted that a fluid film is provided therebetween. Almost all tractive drives require fluids to remove heat, to prevent wear at the contact surfaces, and to lubricate the contacting elements, internal bearings and other moving parts associated with the drive. The lubricating fluid between the contacting elements is subjected to extremely high stress and it is essential that the composition have a high load-carrying capability in order to assure long life for the contacting elements.
Fluid compositions used in tractive drives are also useful as general lubricants for roller and ball bearings and other mechanical devices having elements in rolling contact. Like tractive devices, the load-carrying capability of the lubricant is an important consideration for many high stress applications. One particularly important application is found in lubricating jet engine bearings where such compositions are effective to reduce bearing wear by reducing the propensity of the bearings to skid.
It is accordingly an object of the present invention to provide lubricating compositions having improved load-carrying capability and antiwear characteristics. It is a further object of this invention to provide a class of additives to improve the load-carrying capability of certain compositions useful as tractive fluids without adversely affecting the tractive coefficient or the high temperature oxidation stability of the fluid. These and other objects of this invention will be apparent from the ensuing description of the invention.
SUMMARY The load-carrying capability of certain lubricating base stocks comprising compounds having from to about 70 carbon atoms and including at least two cyclohexyl groups is improved by incorporating into the base stock a minor amount of zinc di(neo-alkyl)phosphorodithioate wherein the neo-alkyl groups have from 5 to about 13 carbon atoms and may be the same or different. The addition of this material to the lubricant base stock composition significantly increases the loadcarrying capability of the composition as measured by standard wear tests without significantly diminishing the high temperature oxidation stability as indicated by change in viscosity and corrosivity. Preferred additives are zinc di(neo-hexyl)phosphorodithioate, zinc di(neo-pentyl)phosphorodithioate and mixtures thereof.
DESCRIPTION OF PREFERRED EMBODIMENTS The compositions of the present invention which are generally useful as lubricants and particularly useful as lubricants for tractive devices are comprised of a major amount of a base stock as hereinafter defined and a minor amount of a zinc di(neo-alkyl)phosphorodithioate inhibitor.
The base stocks of the instant invention are comprised of a major amount of one or more cyclohexyl compounds having two or more cyclohexyl rings which are fused, concatenated, or linked by a C to C alkylene, a carboxy, or an ether linkage, and having a total of from 10 to about carbon atoms. Preferred compounds are those having from 2 to about 6 cyclohexyl rings, and more preferably from 2 to 4 such rings. A compound having 3 or more cyclohexyl rings may have a structure which includes combinations of fused and/or concatenated and/or linked cyclohexyl rings.
The cyclohexyl compounds are known to have good lubricating properties and relatively high coefficients of traction as disclosed in US. Pat. No. 3,440,894. In addition to such cyclohexyl compounds, the base stocks of the present lubricating compositions may contain minor amounts of other lubricating compositions including, for example, paraffinic and naphthenic petroleum oils, C -C polyolefins and synthetic lubricants such as monoand dicarboxylic acid esters. The utility and operability of the instant invention is in no way negated by the inclusion of minor amounts of such noncritical base stock constituents in combination with the cyclohexyl compound which is the essential component.
As used herein the term major amount is defined to mean amounts greater than 50 percent by weight and the term minor amount" means amounts less than 50 percent by weight. While the compositions of this invention must contain at least a major amount of a cyclohexyl compound as hereinbefore defined, it is generally preferred that the cyclohexyl compound be present in amounts of at least about 65 percent by weight and more preferably at least about percent by weight of the total composition.
Examples of representative concatenated and linked cyclohexyl compounds include dicyclohexyl, 4-(1- methylethyl )-dicyclohexyl, 4,4"bis( l-methylethyl dicyclohexyl, x-isohexyl-4'-isopropyldicyclohexyl, x-cyclopentyldicyclohexyl, dicyclohexylmethane, (xethylcyclohexyl)cyclohexylmethane, [x-cyclohexyl( lmethylethyl cyclohexylmethane, bis( 2 ,4 ,6-trimethylcyclohexyl )methane, l l -dicyclohexylethane, l ,1 ,3-tricyclohexylpropane, l ,2,3-tricyclohexylpropane, trimethylolpropane tricyclohexanecarboxylate, l ,2-tercyclohexyl, 1 ,3-tercyclohexyl, x'( l ,1- dimethylbutyl)-l ,3-tercyclohexyl, x-( l ,1- dimethylbutyl)-l ,Z-tercyclohexyl, 1 ,2-isopropyltercyclohexyl, l,3-isopropyltercyclohexyl, bis( 1 ,3- cyclohexyloxy)cyclohexane, l,x-bis(methylcyclohexyl)cyclohexane, dicyclohexyl cyclohexane-l ,3- dicarboxylate, x,x'-quatercyclohexyl, tricylohexylmethane, bis-, cisand trans-1,2-cyclohexyl cyclohexanedicarboxylate, l l -dicyclohexyl-2-methylpropane, 1 l-dicyclohexyl-2-methylbutane, l l-dicyclohexyl- 2 ,S-dimethylhexane, l l -dicyclohexylpentane 1 ,2-dicyclohexylpropane, l,2-di( x-ethylcyclohexyl)- 3 propane, 2,2-dicyclohexylpropane, 2,3-dicyclohexyl- 2,3-dimethylbutane, l,3-dicyclohexyl-2-methylbutane, l ,B-dicyclohexylbutane and 2,4-dicyclohexyl-2- methylpentanc. A particularlypreferred class of such compounds are those selected from the group consisting of dicyclohexyl, alkyl dicyclohexyl, tercyclohexyl, alkyl tercyclohexyl, quatercyclohexyl, quinquicyclohexyl, 2,3-dicyclohexyl-2,3-dimethylbutane, and mixtures thereof, wherein the alkyl contains from 1 to about 18 carbon atoms.
Examples of fused ring cyclohexyl compounds and compounds having structures including combinations of fused, concatenated, and/or linked cyclohexyl groups include cisdecalin, trans-decalin, 2,3- dimethyldecalin, isopropyldecalin, t-butyldecalin, perhyclrofluorene, perhydrophenanthrene, perhydromethylcyclopentadiene (trimer), perhydrocyclopentadiene trimer, perhydrofluoranthene, 1- cyclohexyl-l ,3,3-trimethylhydrindane, x-hexylperhydrofluoranthene, x-cyclohexylperhydrofluoranthene, poly(ethyll -methyl)perhydrolfluoranthene, xisopropylperhydrofluoranthene, perhydrofluorene-xcyclohexyl, perhydrofluorene-x-isododccyl, lcyclohexyldecalin, Z-(cyclohexyl-x-methyl)bicyclo(2,2,l)heptane, perhydropyrene, ethylperhydrofluorene, perhydroanthracene, bis-Z-decalin, lcyclohexyldecalin, 2-cyclohexyldecalin, dimethyl cyclohexyldecalin, 4,5-methyleneperhydrophenanthrene, l,3-dicyclohexyloxycyclohexane, and cyclohexyl decahydronaphthyl ether. A particularly preferred class of such compounds are those selected from the group consisting of decalin, cyclohexyldecalin, alkyl substituted decalin, alkyl substituted cyclohexyldecalin, and mixtures thereof, wherein the alkyl contains from 1 to about 18 carbon atoms.
In addition to the base stock materials and the zinc di(neo-alkyl)phosphorodithioate inhibitor, the compositions of this invention may contain other additive materials including for example viscosity index improvers, antioxidants, antiwear agents, corrosion inhibitors, dispersants, dyes, antifoam agents and the like.
Viscosity index improvers useful in the lubricating compositions of the present invention may be any of the polymeric materials commonly employed in the art. Particularly preferred are the polymers of alkylesters of afi-unsaturated monocarboxylic acids, including for example, poly(butylmethacrylate), poly(hexylmethacrylate), poly(octylacrylates), and poly(dodecylacrylates). Also useful are polymers such as polyisobutylene, alkylated polystyrene, polyvinyl ethers, and copolymers of alkyl esters of monocarboxylic acids and other monomers copolymerizable therewith as for example, the copolymer of an alkyl mcthacrylate and vinyl pyrrolidone.
In a preferred embodiment of the present invention, the load-carrying and antiwear properties of the lubricating fluid are improved by incorporating into the fluid one or more zinc di-(neo-alkyl)phosphorodithioate compounds wherein the neo-alkyl groups contain from 5 to about 13 carbon atoms and may be the same or different, as for example zinc di(neo-pentyl)phos phorodithioate, zinc di(neo-hexyl)phosphorodithioate, or zinc (neo-pentyl)(neo-hexyl)phosphorodithioate. Although zinc dialkylphosphorodithioates generally are known to be antiwear agents, these compounds as a class have been found to be unsuitable for use in the base stocks of this invention because of an adverse effeet on oxidation resistance of the fluid. Examples of such known zinc dialkylphosphorodithioate antiwear agents which were evaluated and found to be unsuitable include those having as alkyl groups di( 1 ,3- dimethylbutyl), Z-ethylhexyl-isopropyl, Z-ethylhexylisobutyl, isobutyl-Z-ethylhexyl and di(n-hexyl).
In view of the consistently negative results obtained with many of the zinc dialkylphosphorodithioates on oxidation resistance of base stock material, it was most surprising and unexpected to find that one class of compounds, the zinc di(neo-alkyl)phosphorodithioates of this invention, and particularly zinc di(neohexyl)phosphorodithioate, significantly improved the load-carrying capability of the fluid without decreasing the oxidation resistance. The effectiveness of the additive was especially surprising since many of the unsatisfactory compounds were recognized antiwear agents generally useful in functional fluids. The n-alkyl equiv alent of the preferred additive of this invention, zinc di- (n-hexyl)phosphorodithioate, for example, reduced the oxidation resistance of the base stock as evidenced by a large increase in viscosity during a standard oxidation test. Likewise the l,2-dimethylbutyl compound caused a major increase in viscosity of the fluid in the oxidation test, and the isobutyl Z-ethylhexyl and Z-ethylhexyl isopropyl compounds each caused substantial increases in corrosivity of the fluid. On the basis of the unfavorable results obtained with these compositions, the excellent results obtained with the di(neo-alkyl)additives of this invention were not to be predicted.
In accordance with this invention, zinc di(ne0alkyl)- phosphorodithioate is added to the base stock at a concentration of at least about 0.1 percent by weight of the base stock, and preferably at a concentration of from about 0.5 to about 2 percent by weight. Higher concentrations can of course be used, but no substantial improvement in results is generally obtained thereby.
The nature and advantages to be gained by means of the present invention are illustrated in the examples which follow. These examples are presented for purposes of illustration only, and the invention is not intended to be limited to the specific embodiments presented therein.
In the following examples, the coefficients of traction was determined on the Thrust Bearing Test Machine described in Effect of Lubricant Composition on Friction as Measured With Thrust Ball Bearings by F. G. Rounds [1. Chem. and Eng. Data, Vol. 5, No. 4, pp. 499 (l960)]. This machine measures the torque transmitted from a central drive shaft to a torque arm through two thrust ball bearings which are submerged in the test fluid. The bearings are shaft-mounted and can be rotated while being subjected to an axial thrust load. Thrust loads are applied hydraulically or by compressing calibrated Belleville springs. A tachometer geared to the drive shaft measures the rotational speed. Thermocouples located within fix-inch of the balls of the test bearings measure the test fluid temperature which is held constant at various predetermined temperatures by heating or cooling the jacket fluid in the housing surrounding the test chamber.
The individual balls tend to spin on an axis parallel to the principal bearing axis as well as roll around the raceway. As a result, both rolling and sliding actions contribute to the traction. The output torque is measured with the torque arm which is fitted between the two bearings. This measured torque is then interpreted in terms of coefficient of traction for the tractant being evaluated. The coefficients obtained from this test machine are relatable to those measured in actual tractive drives. Hence, the machine is effective for screening candidate fluids. In determining the coefficients of 5 The data in Table II below illustrate the effectiveness traction reported in Tables I and Il below, tractant tem of the preferred zinc di(neo-hexyl)phosphorodithioate perature was maintained at 200 F., the Hertz stress additive in reducing the wear scar diameter when preswas 500,000 psi, and the linear ball velocity was 800 ent in the base stock over a concentration range of feet per minute. from 0.1 to 1.0 percent by weight of the base stock.
The Oxidation and Corrosion test (0 & C) was con- The composition of the base stock was essentially the ducted according to Federal Test Method No. same as that described for the tests shown in Table I. 791-5 308.4 under the following special conditions:
Temperature 350F. TABLE II Time 72 hours Air 5 litcrs l5 Metals M8. Cu, Fe Concentration of Wear Scar Example Zinc di(nco-hcxyh- Diameter, Improvement The Wear Scar Test Data was obtained according to phmphmdmmm the standard Shell 4-ball test, operated with 52100 steel 9 0 03/6 balls at 200 F. and 1260 rpm. under a 40 kgm. load. I
The data in Table l below illustrates the advantages 0 of zinc di(neo-alkyl)phosphorodithioates over related 11 0.25 .49 35 compounds in a typical tractant composition consistl2 ing of a mixture of dicyclohexyl, tercyclohexyl and 2,3- dicyclohexyl-2,3-dimethylbutane containing 1.5 per- 13 1.0 .44 42 :S g i i ii i m pi'b i if pyrrohdone copoly mprovement 0.76 Wear Scar Diameter/0.76
TABLE 1 Example Additive Coefficient O & C Test of Traction Viscosity Copper Corrosion"'" Wear Scar Test l None (Control) 0.0618 6 --0.04 0.62 2 1% di(neo-hexyl) 0.0638 13 +0.40 0.43 3 1% di(neo-pcntyl) 5 l.3 0.44 4 1% di(n-hexyl) 0.0629 2050 1.03 5 1.2% 1,3-dimethylbutyl 180 0.7 0.46 6 1% Z-ethylhexyl isopropyl 2344 3.5 7 1% isobutyl2-ethylhexyl 1800 7.7 0.49 8 2% 2ethylhexyl isopropyl 0.0623 24 -5.4
( l) Zinc (alkyl alkyl) phosphorodithioate, by weight of base fluid (2) Viscosity increase at I00F. Specification: less than (3) Mg. metal lost/sq. cm. surface area Specification: less than O.6
(4) Scar diameter Specification: less than 0.45 mm.
The data of Table I clearly illustrate the advantages It is apparent from the above data that substantial imto be gained by using the zinc di(neo-alkyl)phosporodiprovement in the load-carrying capability of the fluid thioate additives of this invention. In Example 2, a preis obtained by the addition of as little as 0.1 percent of ferred embodiment of this invention, the addition of zinc di(neo-hexyl)phosphorodithioate. zinc di(neo-hexyl)phosphorodithioate to the base fluid Although the preceding description and examples of Example 1 decreased the wear scar diameter from have been directed primarily toward the use of zinc 0.62 mm. to 0.43 mm. The small increase in viscosity di(ne0-pentyl)- and di(neo-hexyl)phosphorodithioate of 13 percent during the O & C test was well within the as the additives of this invention, the neo-alkyl grounds specification set for this property. The small weight may be different and may contain up to about 13 cargain in the copper corrosion during the O & C test is bon atoms. Included, therefore, within the scope of the indicative of a protective deposit being formed on the Present invention are, for p Zinc metal surface. Test results and visual observations indialky )p p t at ein the nee-alkyl group cate that this deposit does not interfere with the func- S neo-heptyl, neo-octyl, neo-decyl, neo-undecyl, neoi of h l b i dodecyl, neo-tridecyl, and mixtures thereof.
A similar improvement i the wear Scar test d was The embodiments of this invention in which an excluobtained by adding 1 percent zinc di(neo-pentyl)phos- Sive P p y Privilege is Claimed are defined as phorodithioate to the composition of Example 1 as IOWSI shown by the data in Example 3. In this case, however, A IUbTiCatIFIE Composition Consisting essentially of a small increase in the copper corrosion rate during the a base Stock Selected from group Consisting of O & C test accompanied the addition of the additive. dicyclohexyl, alkyl dicyclohexyli tercyclohexyl In certain applications where a corrosion rate of this alkyl tercyclohexyl, quatercyclohexyl, quinquicymagnitude is not acceptable, it is contemplated that a clohexyl, 2,3-dicyclohexyl-2,3-dimethylbutane and copper metal deactivator can be included in the tractmixtures thereof, wherein the alkyl contains from ant formulation.
The additives of Examples 4 and 5 were unsatisfactory because of the large viscosity increases occurring during the O & C test. Examples 6, 7 and 8 show the effect of other known zinc alkylalkylphosphorodithioate load-carrying additives on the oxidation stability of the defined base stocks and further illustrate that zinc phosphorodithioate compounds as a class are not suitable additives for use in these compositions.
l to about 18 carbon atoms, and
B. an amount of at least about 0.] percent by weight of the base stock and sufficient to improve the load-carrying capability of the base stock of a zinc di(neo-alkyl) phosphorodithioate wherein the neoalkyl groups contain from about to 13 carbon atoms and may be the same or different.
2. A lubricating composition consisting essentially of -A. a base stock selected from the group consisting of decalin, cyclohexyldecalin, alkyl substituted decalin, alkyl substituted cyclohexyldecalin, and mixtures thereof, wherein the alkyl contains from 1 to about 18 carbon atoms, and
B an amount of at least about 0.1 percent by weight of the base stock and sufficient to improve the load-carrying capability of the base stock of a zinc di(neo-alkyl) phosphorodithioate wherein the neoalkyl groups contain from about 5 to 13 carbon atoms and may be the same or different.
3. A composition of claim 1 wherein the zinc di( neoalkyl)phosphorodithioate is selected from the group consisting of zinc di(neo-pentyl)phosphorodithioate, zinc di(neo-hexyl)-phosphorodithioate and mixtures thereof.
4. A composition of claim 1 wherein the amount of the zinc di(neo-alkyl)phosphorodithioate is from about 0.5 to 2 percent by weight of the base stock.
5. A composition of claim 1 wherein the base stock comprises a mixture of dicyclohexyl, tercyclohexyl and 2,3-dicyclohexyl-2,3-dimethylbutanev 6. A composition of claim 5 wherein the zinc di-(neoalkyl)phosphorodithioate is zinc di( neo-hexyl)phosphorodithioate.
7. A composition of claim 2 wherein the zinc di-(neoalkyl)phosphorodithioate is selected from the group consisting of zinc di(neo-pentyl)phosphorodithioate, zinc di(neo-hexyl)phosphorodithioate and mixtures thereof.
8. A composition of claim 2 wherein the amount of zinc di( neo-alkyl)phosphorodithioate is from about 0.5 to 2 percent by weight of the base stock.