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Publication numberUS3093586 A
Publication typeGrant
Publication dateJun 11, 1963
Filing dateAug 11, 1960
Priority dateAug 11, 1960
Publication numberUS 3093586 A, US 3093586A, US-A-3093586, US3093586 A, US3093586A
InventorsHenryk A Cyba
Original AssigneeUniversal Oil Prod Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Stabilization of lubricants
US 3093586 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,0935% STABILIZATION OF LUBRICANTS Henryk A. Cyba, Chicago, Ill., assignor to Universal Oil Products Company, Des Piaines, 11]., a corporation of Delaware N0 Drawing. Filed Aug. 11, 1960, Ser. No. 48,814

3 Claims. (Cl. 252-515) This is a continuation-in-part of my copending application Serial No. 826,408, filed July 13, 1959, and relates to the stabilization of lubricants and more particularly to a synergistic inhibitor composition and the use thereof in lubricants.

In recent years, stringent requirements for lubricants in certain applications have resulted in the availability of a new class of lubricants referred to in the art as synthetic lubricants. These lubricants do not necessarily replace petroleum oils in conventional usage, but are designed for special applications where the petroleum oils do not function to a satisfactory degree. These synthetic lubricants have found particular use in winter-grade crankcase oils, turbo-engine oils, aviation instruments, automatic Weapons, etc. For example, aircraft gas turbines require oils capable of providing satisfactory lubrication at temperatures ranging as low as 65 F. and as high as 275 -F. during use. Temperatures up to 500 F. are encountered for intervals of from one to two hours during shut-down. Petroleum lubricants are unsatisfactory at high altitudes or in the winter season for use in machine guns and automatic cannons which frequently could not be made to fire because of congealed lubricants. Because they are use under such stringent conditions, the synthetic lubricants may undergo undesirable deterioration including, for example, formation of deposits, discoloration, change of viscosity, etc. While the features of the present invention are particularly applicable to the stabilization of synthetic lubricants, it is understood that they also may be used for the stabilization of petroleum lubricants.

The synthetic lubricants are of varied types including aliphatic esters, polyalkylene oxides, silicones, esters of phosphoric and silicic acids, highly fluorinesubstituted hydrocarbons, etc. Of the aliphatic esters, di-(Z-ethylhexyl) sebacate is being used on a comparatively large commercial scale. Other aliphatic esters include dialkyl azelates, dialkyl suberates, dialkyl pimelates, dialkyl adipates, dialkyl glutarates, etc. Specific examples of these esters include dihexyl azelate, di-(Z-ethylhexyl) azelate, di-3,5,5-trimethylhexyl glutarate, di-3,5,5-trimethylpentyl glutarate, di-(Z-ethylhexyl) pimelate, di-(Z-ethylhexyl) adipate, triamyl tricarballylate, pentaerythritol tetracaproate, dipropylene glycol dipelargonate, 1,5-pentanedioldi-(Z-ethylhexanonate), etc. The polyalkylene oxides include polyisopropylene oxide, polyisopropylene oxide diether, polyisopropylene oxide diester, etc. The silicones include methyl silicone, methylphenyl silicone, etc., and the silicates include, for example, tetraisooctyl silicate, etc. The highly fluorinated hydrocarbons include fluorinated oil, perfiuorohydrocarbons, etc.

Additional synthetic lubricating oils include 1) neopentyl glycol esters, in which the ester group contains from 3 to 12 carbon atoms or more, and particularly neopentyl glycol p *opionates, neopentyl glycol butyrates, neopentyl glycol ca,.:oates, neopentyl glycol caprylates, neopentyl glycol pelargon-ates, etc., (2) trimethylol alkanes such as trimethylol ethane, trimethylol propane, trimethylol butane, trimethylol pentane, trimethylol hexane, trimethylol heptane, trimethylol octane, trimethyl decane, trimethylol, undecane, trimethylol dodecane, etc., as well as the esters thereof and particularly triesters in which the ester portions each contain from 3 to 10.

carbon atoms and may be selected from those hereinbetore specifically set forth in connection with the discussion of the neopentyl glycol esters, and (3) tricresylphosphate, trioctylphosphate, trinonylphosphate, tn'decylphosphate, as well as mixed aryl and alkyl phosphates, etc.

The lubricating oils of petroleum origin include those referred to as motorlubricating oil, railroad type lubricating oil, marine oil, transformer oil, turbine oil, transmission oil, differential oil, diesel lubricating oil, gear oil, cutting oil, rolling oil, cylinder oil, hydraulic oil, slushing oil, specialty products oil, etc.

The present invention also is applicable to the stabilization of greases made by compositing metallic soaps with the synthetic lubricating oils described above and are referred to herein as synthetic greases. These metal base synthetic greases may be further classified as lithium base synthetic grease, sodium base synthetic grease, calcium base synthetic grease, barium base synthetic grease, strontium base synthetic grease, aluminum base synthetic grease, etc. These greases are solid or semi-solid gels and, in general, are prepared by the addition to the synthetic lubricating oil of hydrocarbon-soluble metal soaps or salts of higher fatty acids as, for example, lithium stear-ate, calcium stearate, aluminum naphthenate, etc. The grease may contain thickening agents such as silica, carbon black, talc, organic modified bentonite, etc., polyacrylates, amides, polyarnides, aryl u-reas, methyl N-noctadecyl terephthalamate, etc. Another type of grease is prepared from oxidized petroleum wax, to which the saponifiable base is combined with the proper amount of the desired saponifying agent, and the resultant mixture processed to produce a grease. Other types of greases in which the features of the present invention are usable include petroleum grease, whale grease, wool grease, etc., and those made from inedible fats, tallow, butchers waste, etc.

It is general practice to incorporate an antioxidant in synthetic lubricants in order to improve the stability thereof. Research continues to search for even better inhibitors in order to further improve the synthetic lubricants and permit their use for longer periods of time in present applications, as Well as to permit their use under even more severe conditions as, for example, in the engines of the future which are being developed to operate at peak efficiency at high altitudes. It is important that the synthetic lubricant under these conditions is stable, retains its lubricity properties, does not develop deposit formation, retains its desirable viscosity, etc.

It now has been found that a synergistic composition of both an antioxidant and certain nitrogen-containing polymers impart to the synthetic lubricant a considerably improved stability, much greater than obtained through the use of the antioxidants alone. In fact, this synergistic effect is surprising because the polymers themselves do not improve the stability of the synthetic lubricant to any substantial extent. Normally it would be predicted that this mixture would not be any better than the antioxidant alone. Accordingly, it is surprising that these great improvements in the stability of the lubricant are obtained through the use of the novel inhibitor mixture of the present invention.

In one embodiment the present invention relates to a method of stabilizing a lubricant which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of an antioxidant selected from the group consisting of diaminodiphenyl ethers, diamino' diphenyl sulfides and diaminodiphenyl alkanes and a synergist comprising a polymer of two unsaturated compounds, at least one of which contains a basic nitrogen.

In a specific embodiment the present invention relates to a method of stabilizing di-(Z-ethylhexyl) sebacate which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of 4,4'-di-sec-butyldiaminodiphenyl methane and a polymeric condensation product of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

In another specific embodiment the present invention relates to a method of stabilizing lithium base grease which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of 2,4-di-secbutyl-diaminodiphenyl ether and a polymeric condensation product of n-octyl methacrylate and beta-diethylaminoethyl methacrylate.

In another embodiment the present invention relates to a lubricant containing a stabilizing concentration of the synergistic inhibitor composition herein defined.

As hereinbefore set forth, the antioxidant used in the novel stabilizing composition of the present invention is selected from the group consisting of diaminodiphenyl ethers, diaminodiphenyl sulfides and diaminodiphenyl alkanes.

In a preferred embodiment the diaminodiphenyl alkanes contain from 1 to 4 carbon atoms in the alkane group and thus include the corresponding methanes, ethanes, propanes and butanes. Of these the diaminodiphenyl methanes and diaminodiphenyl propanes are particularly preferred. The preferred diaminodiphenyl Inethanes include N,N'-diisopropyl diaminodiphenyl methane, N,N'-di-sec-butyl-diaminodiphenyl methane, N,N'-di-sec-amyl-diaminodiphenyl methane, N,N-di-sechexyl-diaminodiphenyl methane, N,N'-di-sec-heptyldiaminodiphenyl methane, N,N di-sec-octyl-diaminodiphenyl methane, N,N di-sec-nonyl-diaminodiphenyl methane, N,N-di-sec-decyl-diaminodiphenyl methane, N,N'-di-sec-undecyl-diaminodiphenyl methane, N,N-disec-dodecyl-diaminodiphenyl methane, N,N'-di-sec-tridecyl-diaminodiphenyl methane, N,N-di-sec-tetradecyldiaminodiphenyl methane, etc. Other antioxidants include N,N'-di-cyclohexyl diaminodiphenyl methane and alkylated derivatives thereof. The amino groups are preferably in the 4,4'- and/or 2,4'-positions. It is understood that other suitable diaminodiphenyl methanes may be used in some applications.

Of the diaminodiphenyl propanes, preferred antioxidants include N,N'-diisopropyl-diaminodiphenyl propane, N,N-di-sec-butyl-diaminodiphenyl propane, N,N-di-secamyl-diaminodiphenyl propane, N,N di sec hexyldiaminodiphenyl propane, N,N-di-sec-heptyl-diaminodiphenyl propane, N,N-di-sec-octyl-diaminodiphenyl propane, N,N'-di-sec-nonyl-diaminodiphenyl propane, N,N'- di-sec-decyl-diaminodiphenyl propane, N,N'-di-sec-undecyl-diaminodiphenyl propane, N,N' di sec dodecyldiaminodiphenyl propane, N,N'-di-sec-tridecyl-diaminodiphenyl propane, N,N'-di-sec-tetradecyl-diaminodiphenyl propane, etc. Other antioxidants include N,N'-dicyclohexyl diaminodiphenyl propane and alkylated derivatives thereof. The amino groups are preferably in the 4,4- and/or 2,4'-positions. It is understood that other suitable diaminodiphenyl propanes may be used in some applications.

Any suitable diaminodiphenyl ether may be used as the antioxidant component of the inhibitor composition. Preferred diaminodiphenyl ethers include N,N-diisopropyl-diaminodiphenyl ether, N,N-di-sec-butyl-diaminodiphenyl ether, N,N' di-sec-amyl-diaminodiphenyl ether, N,N'-di-sec-hexyl-diaminodiphenyl ether, N,N-di-secheptyl-diaminodiphenyl ether, N,N'-di-sec-octyl-diaminodiphenyl ether, N,N di sec nonyl diaminodiphenyl ether, N,N-di-sec-decyl-diaminodiphenyl ether, N,N-disec-undecyl-diaminodiphenyl ether, N,N'-di-sec-dodecyl diaminodiphenyl ether, N,N-di-sec-tridecyl-diaminodiphenyl ether, N,N' di-sec-tetradecyl-diaminodiphenyl ether, etc. Other antioxidants include N,N'-di-cyclohexyl diaminodiphenyl ether and alkylated derivatives thereof. The amino groups are preferably in the 4,4- and/or 2,4'-positions.

Any suitable diaminodiphenyl sulfide may be used as the antioxidant component of the inhibitor composition. Preferred diaminodiphenyl sulfides include N,N-diisopropyl-diaminodiphenyl sulfide, N,N' di sec-butyl-diaminodiphenyl sulfide, N,N'-di-sec-amyl-diaminodiphenyl sulfide, N,N-di-sec-hexyl-diaminodiphenyl sulfide, N,N'- di-sec-heptyl-diaminodiphenyl sulfide, N,N'-di-sec-octyldiaminodiphenyl sulfide, N,N-di-sec-nonyl-diaminodiphenyl sulfide, N,N'-di-sec-decyl-diaminodiphenyl sulfide, N,N-di-sec-undecyl-diaminodiphenyl sulfide N,N'-di-secdodecyl-diaminodiphenyl sulfide, N,N'-di-sec-tridecyl-diaminodiphenyl sulfide, N,N-di-sec-tetradecyl-diaminodiphenyl sulfide, etc. Other antioxidants include N,N'-dicyclohexyl diaminodiphenyl sulfide and alkylated derivatives thereof. The amino groups are preferably in the 4,4'- and/or 2,4'-positions.

It is understood that the dilferent antioxidants are not necessarily equivalent, but all will form a synergistic mixture with the polymer containing a basic nitrogen and will produce improved benefits over and above those expected from the use of either component separately.

The polymer containing a basic nitrogen for use in the synergistic mixture is produced by the polymeric condensation of an unsaturated compound having a polymerizable ethylenic linkage and an unsaturated compound having a polymerizable ethylenic linkage and a basic nitrogen. In a preferred embodiment the first-mentioned unsaturated compound is amine free and contains from 8 to 18 carbon atoms in an acyclic chain. Examples of such compounds include saturated and unsaturated long chain esters of unsaturated carboxylic acids such as 2- ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, etc., and particularly methacrylates including n-octyl methacrylate, nnonyl methacrylate, 3,5,5-trimethylhexyl methacrylate, n-decyl methacrylate, seccapryl methacrylate, lauryl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, 9-octadecenyl methacrylate, etc.; unsaturated esters of long-chain carboxylic acids such as vinyl laurate, vinyl stearate; long-chain esters of vinylene dicarboxylic acids such as methyl lauryl fumarate; long-chain monoolefins such as the alkyl or acyl substituted styrenes as, for example, dodecyl styrene, and the like. A particularly preferred compound is lauryl methacrylate and more particularly technical lauryl methacrylate which is obtained by esterification of a commercial mixture of long-chain alcohols in the C to C range derived from coconut oil. The technical lauryl methacrylate is available commercially at a lower price and, accordingly, is preferred. A typical technical lauryl methacrylate will contain in the ester portion carbon chain lengths of approximately 3% C 61% C 23% C C16, and C18.

Examples of the second mentioned unsaturated compounds (those containing a basic nitrogen) include p- (beta-diethylaminoethyl)-styrene; basic nitrogen-containing heterocycles carrying a polymerizable ethylenically unsaturated substituent such as the vinyl pyridines and the vinyl alkyl pyridines as, for example, 2-vinyl-5-ethyl pyridine; esters of basic amino alcohols with unsaturated carboxylic acids such as the alkyl and cycloalkyl substituted aminoalkyl and amino cycloalkyl esters of the acrylic and alkacrylic acids as, for example, beta-methaminoethyl acrylate, beta-diethylaminoethyl methacrylate, 4-diethylaminocyclohexyl methacrylate, beta-beta-didodecylaminoethyl acrylate, etc.; unsaturated ethers of basic amino alcohols such as the vinyl ethers of such alcohols as, for example, beta-aminoethyl vinyl ether, beta-diethylaminoethyl vinyl ether, etc.; amides of unsaturated carboxylic acids wherein a basic amino substituent is carried on the amide nitrogen such as N-(beta-dimethylaminoethyl) -acrylamide; polymerizable unsaturated basic amines such as diallylamine, and the like.

The above polymeric condensation product is prepared in any suitable manner and generally by heating the reactants at a temperature of from about 100 to about 175 F. for a period of time ranging from two to forty-eight hours or more, preferably in the presence of a catalyst or initiator such as benzoyl peroxide, tertiary butyl peroxide, azo compounds as alpha, alpha'-azo-diisobutyronitrile, etc. When desired, the polymerization may be effected in the presence of a solvent and particularly aromatic hydrocarbons, including, for example, benzene, toluene, xylene, cumene, decalin, naphtha, etc. In general the condensation is effected using the first mentioned and the second mentioned unsaturated compounds in proportions to produce a copolymer containing from about 50% to about 95% and preferably from about 70% to about 90% by weight of the first mentioned compound and from about 5% to about 50% and preferably from about to about 30% by weight of the second mentioned compound.

The proportions of antioxidant and synergist may vary over a Wide range and thus may range from 0.1 to 4 and preferably from 0.5 to 2 parts by weight of synergist per one part by weight of antioxidant, although in some cases lower or higher proportions may be used. These proportions are based upon the active ingredient exclusive of solvent. While the antioxidant and synergist may be added separately to the lubricant, it generally is preferred to form a suitable mixture of the antioxidant and synergist and add the mixture to the lubricant. When desired, the antioxidant and synergist may be prepared as a solution in a suitable solvent, particularly aromatic hydrocarbons and more particularly an aromatic hydrocarbon as hereinbefore set forth, and marketed or used as a single product. Conveniently, the same solvent is used in the final solution as used in the preparation of one or both of the antioxidant and synergist. The solution may comprise from about 10% to about 90% and preferably from about 25% to about 75% by weight of active ingredient.

The inhibitor composition will be used in the substrate in an amount sufficient to obtain the desired stabilization. This stabilizating concentration will be within the range of from about 0.001% to about 5% and preferably from about 0.1% to about 3% by weight of the lubricant. The inhibitor composition is added to the lubricant in any suitable manner and preferably with intimate mixing in order to obtain distribution of the inhibitor composition in the lubricant. In some cases the inhibitor composition may be added to the lubricant during the manufacture thereof. For example, when used in grease, the inhibitor composition may be added to one or more of the components before final compositing thereof.

It is understood that the inhibitor composition of the present invention may be used along with other additives incorporated in the lubricant. For example, a metal deactivator, dye, viscosity index improver, pour point depressant, antifoaming additive, lubricity and extreme pressure additive, antiscutfiing additive, etc. may be incorporated in the synthetic lubricant. When desired, the inhibitor composition of the present invention may be prepared as a mixture with one or more of these other additives and incorporated in this manner in the lubricant.

The following examples are introduced to illustrate furtlrer the novelty and utility of the present invention but not with the intention of unduly limiting the same.

EXAMPLE I This example illustrates the use of two diaminodiphenyl methanes and a copolymer of lauryl methacrylate and diethylaminoethyl methacrylate. The diaminodiphenyl methanes were prepared as follows: 4,4-di-sec-b-utyl-'diaminodiphenyl methane was prepared by the reductive alkylation of 4,4-diaminodiphenyl methane with ethyl methyl ketone at 320 F. in the presence of hydrogen and a platinum-containing catalyst. The 4,4-di-sec-butyl-diaminodiphenyl methane was recovered as a viscous oil, having a specific gravity at 60 F. of 0.995, a Universal viscosity at 100 F. of 511.2 second and at 210 F. of 49.1 seconds, and a refractive index at 20 C. of 1.575- 1.577. 4,4-di-cyclohexyl diaminodiphenyl methane was prepared by the reductive alkylation of 4,4-diamin'odiphenyl methane with cyclohexanone in substantially the same manner as described above. The product is recrystallized from hexane and recovered as crystals having a melting point of 245 F., a basic nitrogen content of 5.50 meq./ g. and a basic molecular weight of 363 (theoretical is 362).

The copolymer is prepared by copolymerizing lauryl methacrylate and diethylaminoethyl methacrylate in concentrations to yield a product having by weight of lauryl methacrylate and 20% by weight of diethylaminoethyl methacrylate. The polymerization is efiected by heating the reactants at about 140 F. for about eighteen hours, with vigorous stirring in the presence of benzyl peroxide catalyst. The product is recovered as a straw colored, heavy viscous oil of the general proper-ties set forth in Table I.

Table I Viscosity at 210 F., SSU -2200.

Density, pounds/ gallon 7.5

Color, N.P.A. 1.

Pour point, F 10 to +10. Flash point (C.O.C.), -F 380.

Fire point (C.O.C.), F 420.

Total acidity 0.0.

Total base number, mg. KOH/ g. 8.0 (0.14 meq./g.). Ash, weight percent 0.00.

The diaminodiphenyl methanes alone and a synergistic mixture of these with the polymeric condensation product were separately evaluated in diootyl sebacate, marketed under the trade name of Plexol 201. The evaluation was made in accordance with an Oxygen Stability Test, in which a cc. sample of the synthetic lubricating oil is placed in a bath maintained at 400 F. and air is blow therethrough at a rate of 5 liters of air per hour. The sample of synthetic lubricating oil is examined periodically and the time to reach an acid number of 5 is reported. It is apparent that the longer the time required to reach an acid number of 5 the more stable is the sample of synthetic lubricating oil. In other words, it takes longer for the more stable oil to deteriorate.

The results of these evaluations, along with an evaluation of a sample of the lubricating oil without additive, are reported in the following table:

Table II Sample Hours to No. acid number 01'5 Additive 1 None 9 1%b3ggvcight of 4,4-di-sec-butyl-diaminodiphenyl m anc.

1% by weight of 4,4-dl-see-butyl-diaminodiphenyl methane plus 1% by weight of the condensation product of Example I.

1% by weight of 4,4-di-cyclohexyl-diamlnodiphenyl methane.

1% by weight of 4,4-di-cyclohoxyl-diaminodiphenyl methane plus 0.5% by weight of the polymeric condensation product of Example I.

1% by weight of 4,4-di-cyclohexyl diaminodiphenyl methane plus 1% by weight of the polymerlc condensation product of Example I.

From the :data in the above table, it will be noted that the synergistic mixture served to increase the time to acid number of 5. In sample No. 5, 0.5% by weight of the synergist was used and this served to increase the time to acid number of 5 from 48 to 75 hours. Sample 6 reports the results when using 1% by weight of the synergist.

EXAMPLE II As hereinbefore set forth, the improved results obtained by using the mixture of the present invention is surprising because the polymeric condensation product itself is not an inhibitor. This is shown by the data in the following table, which were obtained in the same manner as described in Example I. For comparative purposes, sample No. 1 (control sample without additive) is repeated in the following table:

Table III Sample Hours to N Additive acid number of 5 1 None 9 7 1% by weight of the polymeric condensation 10 product of Example I.

From the above data, it will be seen that the polymeric condensation product itself was not effective to extend the time required to reach an acid number of 5.

EXAMPLE III than 50 hours.

EXAMPLE IV As hereinbefore set forth, a synthetic lubricant being considered for use at high temperature is pentaerythrit ol ester. The pen taerythritol ester used in this example is available commercially from Hercules Powder Company as Hercofiex 600 and is stated to be monomeric pentaerythritol ester having an acid number of 0.10 maximum, a saponification number of 410, a refractive index at 20 C. of 1.453 and a specific gravity at 25/25 C. of 0.997.

The evaluations in the pentaerythritol ester are made in substantially the same manner as described in Example I for dioctyl sebacate. The synergistic inhibitor mixture of this example is 1% by weight of 4,4'-di-sec-butyl-diaminodiphenyl propane and 1% by weight of the polymeric condensation product formed by reacting n-octyl methacrylate and diethylaminoethyl methacrylate. The polymeric condensation product is prepared in substantially the same manner as described in Example I.

A sample of the pentaerythritol ester, when evaluated in this manner, reaches an acid number of 5 witln'n 16 hours. The use of the synergistic mixture described above increases the time to reach an acid number of 5 in excess of that obtained when using the diaminodiphenyl propane alone, and thereby serves to improve the stability of the lubricant beyond that expected when using each of these components alone.

EXAMPLE V Another advantage of the synergistic mixture of the present invention is that it also considerably reduces sludge and varnish formation when used in lubricating oil as a result of inhibiting deterioration of the lubricating oil during use. The following data reports results in a Chevrolet L4 test. This test is run using an engine speed of 3150 r.-p.m., an engine load of 30 B.H.P., a jacket outlet temperature of 210 F., a jacket inlet temperature of 190 R, an oil temperature of 280 F. and an air fuel ratio of 14.5:1. Regular grade gasoline and Mid-Continent sol- 8 vent refined S.A.E. 20 type lubricating oil are used. Each run is continued for 36 hours.

The following table reports the results of three runs conducted in the above manner. In the first run (run A) no additive was incorporated in the lubricating oil. In the second run (run B) 0.5% by weight of 4,4'-di-secbutyl-diaminodiphenyl methane was incorporated in the lubricating oil. In the third run (run C) a synergistic mixture of 0.5 by weight of 4,4'-di-sec-butyl-diaminodiphenyl methane and 1% by weight of the polymeric condensation product of Example I were incorporated in the lubricating oil.

Pertinent data of these runs are reported in the following table:

1 Run was discontinued after 12 hours due to excessive noise.

From the above table it will be seen that, while the use of 4,4-di-scc-butyl-diaminodiphenyl methane considerably improved operation of the engine, the use of the synergistic mixture even further improved the operation of the engine. It is particularly noteworthy that the varnish and sludge were considerably reduced. This is further shown by the considerable reduction in the insoluble matter of the used oil. Also, it will be noted that the viscosity of the used oil containing the synergistic mixture was lower, thus further indicating inhibition of deterioration of the lubricating oil during use.

EXAMPLE VI The synergistic mixture of this example is 0.5 by weight of a mixture of 70% by Weight of 2,4-di-secbutyl-diaminodiphenyl ether and 30% by weight of 4,4- di-sec-butyl-diaminodiphenyl ether and 1% by weight of the polymeric condensation product of Example I.

The present runs were made in the Chevrolet L4 test in substantially the same manner as described in Example V. Pertinent results are reported in the following table:

Table V Run D Run E Run F Diamino- Synergistic No additive diphenyl mixture ether Total varnish and sludge, gravimetric, grams 7. 289 1. 767

At 8 hrs. At 36 hrs. At 36 hrs.

Used oil analyses:

Pentane insolubles, weight percent 0. 0449 0. 786 0. 376 Benzene insolubles, weight percent 0. 237 0. 541 0. 242 Insoluble resin, weight per- 0.212 0.245 0.134 Viscosity, S.S.U. at F. 608 358 354 1 Run was discontinued after 12 hours due to excessive noise.

Here again it will be noted that the synergistic mixture served to improve the operation of the engine as compared to the use of the diaminodiphenyl ether alone. This is illustrated by the considerably lower sludge "and varnish formation and the insoluble matter of the used oil, again showing inhibition of deterioration of the lubricating oil during use.

EXAMPLE VII The synergistic mixture of this example comprised 0.5% by weight of 2,4'-di-sec-butyl-diaminodiphenyl ether and 1% by weight of the polymeric condensation product of Example I.

The results of runs made in the same manner as described in Example V are reported in the following table:

1 Run was discontinued after 12 hours, due to excessive noise.

Here again it is seen that the synergistic mixture of the present invention considerably improved the operation of the engine and inhibited deterioration of the lubrieating oil during use.

EXAMPLE VIII The synergistic mixture of the present example comprises 1% by weight of 4,4'-di-sec-butyl-diaminodiphenyl propane and 1% by weight of the polymeric condensation product of Example I.

The synergistic mixture is incorporated in dioctyl sebacate in a concentration of 1% by weight based on the lubricant. The lubricant containing the synergistic mixture then is utilized at elevated temperature. The lubricant containing the synergistic mixture satisfactorily performs at the elevated temperature encountered in such use.

EXAMPLE IX The synergistic mixture of this example comprises 2% by weight oat 4,4-diisopropyl diaminodiphenyl propane and 1% by weight of the polymeric condensation product of n-octyl methacrylate and beta-methylaminoethyl acrylate. The latter condensation product is formed in substantially the same manner as described in Example I.

The synergistic mixture described above is used in a concentration of 1% by weight in a synthetic lubricant comprising mixed oaproic and caprylic acid esters of trimethylol propane. The lubricant containing the synthetic mixture is stable for use at elevated temperature and high altitudes.

I claim as my invention:

1. A synergistic inhibitor composition consisting essentially of one part by Weight of an antioxidant selected from the group consisting of N,N'-di-sec-alkyl-and N,N'- di-cyclohexyl-diaminodiphenyl methanes and from about 0.1 to about 4 parts by weight of the polymeric condensation product of an alkyl methacrylate and an alkylaminoalkyl acrylate.

2. A synergistic inhibitor composition consisting essentially of one part by weight of N,N'-di-sec-butyl-diarninodiphenyl methane and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about to about F., of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

3. A synergistic inhibitor composition consisting essentially of one part by weight of N,N'-diisopropyl-diaminodiphenyl methane and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100" to about 175 F., of l auryl methacrylate and beta-diethylaminoethyl methacrylate.

4. A synergistic inhibitor composition consisting essentially of one part by weight of N,N'-di-cyclohexyl-diaminodiphenyl methane and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 to about 175 F., of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

5. A lubricating composition comprising a major proportion of dioctyl sebacate and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 1.

6. A lubricating composition comprising a major proportion of dioctyl sebacate and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 2.

7. A lubricating composition comprising a major proportion of dioctyl sebacate and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 3.

8. A lubricating composition comprising a major proportion of dioctyl sebacate and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,045 Sloan May 7, 1935 2,290,860 Burk et al July 28, 1942 2,367,264 Burk et a1 Jan. 16, 1945 2,452,320 Kluge et a1. Oct. 26, 1948 2,666,044 Catlin Jan. 12, 1954 2,737,496 Catlin Mar. 6, 1956 2,889,282 Lorensen et al June 2, 1959 2,892,784 Harle et a1 June 30, 1959 2,944,974 Lorensen et a1 July 12, 1960 FOREIGN PATENTS 808,665 Great Britain Feb. 11, 1959

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