US3329611A - Lubricating oil composition - Google Patents

Description

United States Patent 3,329,611 LUBRICATIWG OIL COMPOSITION Tai S. Chan, Homewood, lll., assignor to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 17, 1965, Ser. No. 440,634 12 Claims. (Cl. 252-33.6)

This application is a continuation-in-part of application S.N. 411,718, filed Nov. 17, 1964 and now abandoned.

This invention relates to an ester-based lubricant composition containing a novel combination of additive agents. More specifically, the invention is concerned with liquid lubricating oil compositions comprising a synthetic ester base oil of lubricating viscosity having incorporated therein a dimer acid extreme pressure agent, an anti-oxidant combination of an aromatic amine and a soluble alkali metal compound, and a halo-substituted carboxylic acid as a haze inhibiting agent. In addition, the composition may contain an alkyl ester of an alkylene diamine tetraalkanoic acid as an anti-corrosion agent.

The demand for synthetic lubricants is ever increasing in view of the need for lubricants of low pour point, high viscosity index and low volatility for a given viscosity. The demand is particularly great due to the present and increasing widespread use of turbojet engines for military and commercial aircraft. Even though most synthetic ester lubricants have high viscosity index, low volatility and low pour point, the latter affording good low temperature starting characteristics, these oils, including those desired from the standpoint of stability and cost, normally must have additives incorporated therein to provide the required load carrying capacity and high temperature oxidation stability.

Effective load carrying, anti-scuff and anti-fatigue agents for the synthetic lubricants are of the dimer acid type, i.e. dimer acids and their derivatives, for example, their amides. Superior oxidation inhibition of these oils can be obtained by adding a combination of an aromatic amine and soluble alkali metal in the form of a derivative of an organic compound. It has been found that synthetic ester lubricants containing this combination of additives may develop a haze upon standing, that is, the clear lubricants tend to become cloudy. Thus far, no adverse eifects on the properties of the lubricant have been found due to the haze, nevertheless, the haze is undesirable and may make the lubricant unacceptable because industry and military standards aften require a haze free lubricant. Thus an object of this invention is to provide a synthetic lubricant which has superior load-carrying ability, thermal and oxidation resistance and yet has little, if any, tendency to haze upon standing. Thus, the present invention provides an improved ester based lubricant composition which is a liquid of lubricating viscosity at normal temperatures and contains small, effective amounts of a dimer acid load-carrying additive, an aromatic amine, a soluble alkali metal compound and a halosubstituted carboxylic acid, the latter being a haze-reducing agent. All of these additives are soluble in the base ester oil.

The halo-substituted carboxylic acid haze-reducing agent may be added in either the acid or the alkali metal salt form. Generally, the alkali metal salt has been found to be the more convenient. A further advantage of using the alkali metal salt is that it can serve the dual function of haze-reducing and be the alkali metal co-antioxidant which cooperates with the aromatic amine. Suitable a1- kali metals are Li, Na, K, Rb and Cs, with lithium and sodium being preferred. The acids which may be used alone or in the alkali metal salt form include monocarboxylic acids containing from about 2 to 18, preferably 4 to 12, carbon atoms and are represented by the "ice formula RSOOH. R is a halo-substituted hydrocarbon radical which may be alkyl, including cycloalkyl, or aryl, including alkaryl, R may be unsaturated; however, it is preferably free of olefinic and acetylenic unsaturation, that is, all of the carbon-to-carbon linkages in the chain are not less than 1.40 A., the interatomic distance of carbon atoms in a benzene ring. In addition to the fluorine, chlorine, bromine or iodine halo substituents, the halo acids may also contain other non-interfering substituents such as ether, hydroxyl and ester groups. Examples of suitable halo-substituted fatty and benzoic carboxylic acids are w-H-polyfiuoro heptanoic acid, 3,5-bis-(trifluoromethyl) benzoic acid, trichloro acetic acid, perchloro benzoic acid, etc. The preferred halo-substituted carboxylic acids are the perfluoro fatty and benzoic acids such as perfluoroacetic acid, perfluoropropionic acid, perfluorobutyric acid, perfluorocaprylic acid, perfluoro benzoic acid, etc.

The load carrying additives which are added to the lubricant of this invention are dimer acid compounds including dimer acids and derivatives thereof. The commercial dimer acids which can be used in forming the additive of our invention are bimolecular addition prod: nets of conjugated or non-conjugated polyolefinic fatty acids having from about 16 to 22 or more carbon atoms before dimerization. Such dimerized fatty acids may be prepared by known methods, for example, the monomer of a polyolefinic fatty acid may be subjected to heat treatment above 300' C., under elevated pressure. The dimer acid is recovered from the reaction mixture by distillation. Another method of preparation involves heating the methyl ester of a polyolefinic fatty acid at about 300 C. for several hours in an inert atmosphere. The resulting dimerized ester can be used as such in the lubricant of this invention or separated by distillation, saponified and then acidified with a mineral acid.

In general, dimerized acids suitable for purposes of this invention are those prepared from polyolefinic alkanoic or monocarboxylic acids having the formula:

wherein n is an integer of from 15 to 21 and x is an integer from 2 to 7, preferably 3 to 5. The resulting dimerized acids will thus contain 32 to 44 carbon atoms.

Representative of the class of dimerized acids suitable for the purposes of this invention are dimers of dienoic acids such as palmitolic (hexadecadienoic), linoleic (octadecadienoic), humoceric (nonadecadienoic) and eicosinic (eicosadienoic) acids. Dimers of trienoic acids, for example, such as linolenic and eleostearic (octadecatrienoic) acids may also be used. The dienoic and trienoic acids containing 18 carbon atoms, and especially those having conjugated olefinic linkage are distinctly preferred. It is not necessary that both of the unsaturated fatty acid moles in the dimer be identical. Dimers of mixed compositions such as those obtained by dimerizing mixtures of dienoic, trienoic or dienoic and trienoic acids, for instance, obtained from naturally-occurring drying oils are satisfactory.

The dimerized acids disclosed above may be hydrogenated to reduce or substantially eliminate carbon-carbon unsaturation. It is preferred that unsaturation be reduced in order that a product highly resistant to degradation be obtained. The hydrogenated dimer acids can be formed by catalytic hydrogenation of commercial dimer acids, preferably, the hydrogenated dimer acid has less than /2 double bond per average molecule. An example of a suitable commercial hydrogenated dimer acid is Emery 3389R which is a mixture of C dimer acids containing an average of 36 carbon atoms and having an average of less than /3 double bond per molecule. It has an acid number of l210 and an iodine number of'2530.

The dimer acid may be used as such in the lubricants of this invention or as a derivative thereof, e.g., amine salt, metal salt, amide, ester, anhydride, partial salts, partial esters, partial amides, etc. Suitable metals for salt formation include the alkali and alkaline earth metals such as Li, Na, K, Rb, Mg, Ca and Sr. The amine salt, amide and ester-forming compounds may contain hydrocarbon radicals of up to about 20 or more, preferably up to about 12, carbon atoms, such as alkyl, including cycloalkyl, and aryl radicals, including mixed aryl-alkyl radicals. The amine salts may be formed from alkyl and aryl, including mixed alkyl-aryl, amines such as diethyl amine, methyl amine, propylamine, 2-ethylhexylamine, dibutylamine, n-octadecylamine, cocoamine, diphenylamine, di- (p-octylphenyl)amine, cyclohexylamine, tetrahydrofurfural amine, etc. The esters may be formed, for instance, from primary or other alcohols such as ethyl alcohol, dodecyl alcohol, octadecyl alcohol, phenol, t-butyl phenol, etc.

The preferred dimer acid derivatives are the amides which are soluble in the ester base oil, at least to the extent used and can be represented by the formula:

(COOH): A

wherein A is the hydrocarbon residue of a dimer acid and R and R can be hydrogen or a hydrocarbon radical usually of up to about 20 or even more, preferably up to about 12, carbon atoms such as alkyl, including cycloalkyl, and aryl radicals, including mixed aryl-alkyl radicals. The hydrocarbon radicals may be substituted with non-deleterious substituents or unsubstituted. The letter x is a small number up to about 1.7, usually at least 0.1 and preferably between 0.5 and 1.5. All or a portion of the non-amidified carboxyl groups may, if desired, be in the ester form, for instance, a lower alkyl ester. Hydrogenated dimer acids are preferred and can be derived from dimer acid by hydrogenation. Advantageously the dimer acid has a minimum of residual olefinic bonds, i.e., on the average of less than /2, and preferably less than olefinic bond in the A radical. Thus, the preferred dimer acid amides of this invention contain less than an average of /2 and preferably less than /3 carbon-carbon linkages per molecule which are less than 1.40 A., the interatomic distance of carbon atoms in a benzene ring. Essentially, all of the carbon-carbon linkages are not less than 1.34 A., the interatomic distance of carbon atoms in an olefinic double bond. The hydrogenated dimer is therefore more resistant to thermal and oxidative degradation than the unsaturated dimer acids. The hydrogenated dimer of linoleic acid is especially preferred.

The dimer acid amides can be prepared from the hydrogenated dimer acids by treating with a calculated amount of ammonia or amine and heating the acid salts thus formed to remove the desired amount of water. The reaction can be carried out in the presence or absence of a solvent or a diluent and can be conducted either under atmospheric pressure or in an autoclave, although a pressure reaction is preferred when ammonia or a low boiling amine is used as the reactant. The preferred nitrogen compounds are ammonia and alkyl amines. The amines may be primary or secondary amines and generally have up to about 20 or more carbon atoms. The amines disclosed for preparing amine salts are also suitable for preparation of the amides.

The aromatic amine anti-oxidant component of the lubricant is soluble in the ester fluid to the extent used and can be represented by the following general formula:

wherein Q is a monovalent hydrocarbon of 1 to 20 carbon atoms, preferably 6 to 12 carbon atoms, whose adjacent carbon atoms are no closer than 1.40 A. (i.e., a non-olefinic, non-acetylenic, monovalent hydrocarbon),

and Q is a non-olefinic, non-acetylenic aromatic hydrocarbon radical of 6 to 12 or 16 carbon atoms. Thus Q can be an alkyl group, including cycloalkyl, or an aromatic group. Preferably, both Q and Q are aromatic, and often at least one is a fused ring aromatic, e.g., naphthyl. Q and Q can be substituted with non-interfering substituents such as alkyl, aryl, hydroxyl groups and amine groups, preferably alkyl or aromatic amines, and Q and Q can be linked together by means of a non-interfering element such as carbon, sulfur and oxygen. Illustrative of suitable amines are phenothiazine, N-phenyl-a-naphthyl amine; di(e-naphthyl amine); N,N'-diphenyl para-phenylene diamine; N,N'-dioctyl para-phenylene diamine, N, N-diheptyl para-phenylene diamine; diphenyl amine, poctyl diphenyl amine, p-p'-dioctyl diphenylamine, etc.

The soluble alkali metal which serves as a co-antioxidant may be introduced into the lubricant as a base oil soluble alkali metal organic compound. If the anti-haze agent is introduced as an alkali metal organic acid salt no other source of alkali metal may be necessary. However, alkali metal may :be introduced as an alkali metal derivative of an organic compound other than the antihaze agent even when the latter is in the salt form. Thus, the alkali metal may be supplied as the derivative of any convenient organic compound and the useful alkali metals include Na, K, Li, Cs and Rb. Typical organic compounds which form alkali metal derivatives are carboxylic acids, phenols, alcohols, ketones, aldehydes, various chelating agents, etc., often of about 2 to 50 or more carbon atoms, preferably about 4 to 30 carbon atoms. Although the alkali metal is an essential active component, certain classes of alkali metal derivatives or salts of acidic organic compounds are especially effective in enhancing oxidation inhibition. Exemplary of these acidic organic compounds are unsubstituted and S, O, N and halogensubstituted carboxylic acids, phenols, including thiophenols, beta-diketones, substituted phenols and Schifis bases. However, the invention is not limited to the compounds disclosed because the oxidation inhibition obtained with an aromatic amine and soluble alkali metal is believed to be a general phenomenon applicable to the various alkali metal compounds which are soluble in the base ester fluid to the extent needed to impart an anti-oxidant effect. The carboxylic acids which may "be used to prepare the alkali metal salts include monoand polycarboxylic acids, for instance, those having straight, branched or cylic hydrocarbon structures, including alkylated benzoic acids. The carboxylic acids may be saturated or unsaturated and may often contain from about 4 to 22 or even up to 50 or more carbon atoms. Examples of suitable fatty acids are caprylic, isodecanoic, isostearic cerotic, myristic, cyclohexanoic acid, cyclooctanoic and ethylcycloootanoic acids. A group of monocarboxylic acids which can be used is represented by the formula RCOOH wherein R is an alkyl, aryl, aralkyl or alicyclic hydrocarbon radical of 3 to 21 carbon atoms.

Other suitable carboxylic acids for making the alkali metal derivative include those substituted with groups containing, for instance, S, O, N and halogen. The substituted carboxylic acids may be saturated or unsaturated and may preferably contain from about 2 to 36 carbon atoms. The base or parent carboxylic acid may be aromatic or aliphatic, for instance, alkanoic, including cycloalkanoic, benzoic or a mixed aliphatic-aromatic acid. The sulfur-containing carboxylic acids include mercaptans, thioether, thioacids and sulfones. Exemplary of the sulfur-containing compounds are 4-thiodecanoic acid, mercaptoacetic acid, thiosalicylic acid, 4-mercaptooctanoic acid, thiooctanoic acid, thiododecanoic acid, thioacetic acid and 2- (butyl sulfonyDacetic acid. A group of suitable sulfurcontaining monocarboxylic acids can be represented by the formula:

wherein R is an alkyl radical of 6 to 20 carbon atoms, R is an alkylene radical of 1 to 8 carbon atoms, e.g.

CH CH m is or 1, n is 0 or 1 and m=n. The acids include C H SCH COOH; C H S(CH COOH;

C H OCOCI-l CH SCH CH COOI-I wherein R is an alkylene radical of l to 8 carbon atoms, R' is an alkylene radical of 2 to 8 carbon atoms, R is an alkyl radical sufircient to impart ester base oil solubility to the additive, e.g. up to about 18 carbon atoms on the average, often at least about 4 carbon atoms, a, b,canddare0or1,eis0to2,whenbis1,ais1, When dis 1c is 1 and e is 2, and when d is 0 and c is l, e is 1. Also when b is 0 and a is l, c and d are 0. Exemplary compounds of this type include:

CHzC O O Butyl N-CHzC O O Butyl CHzCOOH (a=1, b=0, c=0, d=0, 0:0)

CHzCOO Octyl The halogen substituents may be fluorine, chlorine, bromine or iodine. Examples of halo-substituted carboxylic acids are perfluoro acetic acid, perfluoro butyric acid, (0- H-polyfluoro heptanoic acid, perfluoro benzoic acid, 3,5- difluoro methyl benzoic acid, trichloro acetic acid, bromo acetic acid, monochloro difiuoro acetic acid, pentachlorophenoxyacetic acid, etc. Acids having at least 50% of their hydrogen replaced by halogen are preferred, especially the perhalogen acids.

The alkali metal salts of halogen-substituted, lower alkanoic monocarboxylic acids, in addition to their outstanding antioxidation elfect in combination with amine antioxidants, have many other properties which qualify their use in synthetic lubricants. In the first place they are sufliciently soluble in ester type base fluids. For example, lithium perfluorobutyrate is soluble at more than 50% by weight in either Hercolube A or Hercolube F. Sodium perfluorob-utyrate, although less soluble than the lithium salt, is soluble at several times the necessary concentration even at 40 F. In the second place, these salts are derived from strong acids and strong bases and are therefore compatible with the weak acids present in synthetic lubricants which are either added as additives or are formed during the service life of the lubricant. In the third place they have no adverse effect on the seal materials used in aircraft jet engines, including Viton O-rings, carbon seals and H-rubber seals.

The phenols suitable for preparation of the alkali metal phenates may contain as substituents, for example, al'kyl, acyl or amido groups and often have from about 7 to 24 carbon atoms. Examples of suitable phenols are plauroylamino phenol, t-butyl phenol, t-octylphenol, dodecyl phenol, nonyl phenol, p-aminophenol, N-phenyl-paminophenol and condensation products of phenol, formaldehyde and primary or secondary amines such as The useful phenols include those of the formula:

wherein X is O or S, R is alkyl of 4 to 18 carbon atoms on the average, and n is 1 to 3.

The ketones which may be used to form the alkali metal derivatives include further substituted materials such as keto esters and keto amides. The ketones preferably contain from about 5 to 22 carbon atoms. The ketones may be aliphatic, aromatic or mixed aliphatic-aromatic and they may be saturated or unsaturated and substituted with non-deleterious substitutents. Examples of suitable compounds are acetyl acetone, ethyl aceto acetate, N,N- dimethyl aceto acetamide, 1,3-diphenyl-1,3-propanedione, ethyl formyl-acetate, and ethylbenzoyl acetate.

Schitfs bases which are condensation products of aldehydes or ketones with primary amines are also effective as the alkali metal derivative-forming compounds. Examples of suitable Schifl?s bases are bis(salicylidene) propylene diimine, bis (acetylacetone)-ethylenediim-ine, N- pheny1-N,N-'bis(salicylidene)ethylenediimine, etc.

A preferred group of alkali metal compounds are monoalkali metal salts of the trialkyl ester of alkylene diamine tetraacetic acid which may be represented by the following structural formula:

wherein M is the stoichiometric equivalent of an alkali metal such as Na, K, Li, Ca and Rh; Z is an alkylene radical, including cycloalkylene, of 1 to 20 carbon atoms,

preferably 2 to 12 carbon atoms, and can be interrupted with one or more non-interfering elements such as oxygen and nitrogen and substituted with non-interfering substituents such as lower alkyl groups; and R is a hydrocarbon radical having on the average about 3 to 18 carbon atoms, whose adjacent carbon atoms are no closer than 1.40 A. (ie a non-olefinic, non-acetylenic, monovalent hydrocarbon). Thus, R can be an alkyl radical (including cycloalkyl) straight or branched chain, preferably of about 4 to 8 carbons on the average, or an aryl radical and can be substituted with non-interfering groups such as hydroxy and alkyl groups. The R groups can be the same or different and are of sufiicient molecular weights to render the salt of the triester soluble in the base oil. Illustrative of alkylene radicals represented by Z are (-CH wherein x=1 to wherein R and M are as designated above.

The monoalkali metal salts can readily be prepared by partial saponification with an alkali metal base of the tetraesters of the alkylenediamine tetraacetic acid obtained, for instance, by the method described in US. Patent No. 2,428,353 to Frederick Bersworth, hereby incorporated by reference. Suitable bases include for example, the hydroxides, carbonates, etc. of the alkali metals. Alternatively, the salts can be obtained as by-products of the process of the aforementioned patent. Briefly, the esterification of the patent involves reacting a polycarboxylic amino acid with an alcohol in the presence of sufficiently strong mineral acid to form an amino acidmineral acid addition product, the reaction being carried out so that the water resulting from the esterification reaction is driven oiT. Alternatively, the amino-mineral acid addition product is first prepared and separated as a crystalline product and esterified by heating with alcohol. On completion of the esterification reaction in either method, excess alcohol is removed by distillation which leaves the ester usually in the form of an addition prodnet with the mineral acid. To neutralize and remove the mineral acid, the ester product is treated before or after the alcohol removal, with an alkaline solution and in so doing forms at least in part the alkaline metal salts of the present invention which can be separated from the ester, if desired, by any suitable means such as solvent extraction. Generally the reaction product includes on the basis of the tetraester about 0.005 to 0.4 or even more equivalent weights of the alkali metal, preferably about 0.0 2 to 0.1. The monoalkali metal salts per se can be employed in the composition of this invention but it is preferred to utilize the mixture of monoalkali metal salt, tetraester and other by-products, as such, formed by the neutralization step of the process described in the aforementioned patent. I have referred to the monoalkali metal salt herein on the basis that all of the alkali metal up to an equivalent weight based on one -COOH group, is present as the mono-salt, whereas in most instances, other salts, e.g. the di-metal salt of diester and the trimetal salt of monoester will also -be present. However, the mono-salt would be the predominant salt in the mixtures. Ordinarily, the resulting neutralized ester product mixture will contain anywhere from 3 to weight percent of monoalkali metal salt. Although it is preferred to use this mixture as such, should the monosalt by itself be desired, it can be separated from the ester mixture. Alternatively, a substantially pure tetraester is first prepared as described by the Bersworth patent and the substantially pure ester obtained saponified as with an equimolar amount of the alkali base in solution to give the monosalt on a calculated basis. If desired, the polyalkali metal salts of the partial ester may be used.

The lubricants of this invention may also have added thereto, for instance see Example I, a small corrosioninhibiting amount of an ester of the formula:

wherein R and Z are as given above with respect to the alkali metal salts of compounds of this general structure. Aside from the tetraester, partial esters may be used, and as noted above, the partial ester alkali metal salts afford a means whereby the anti-corrosion properties of the ester as well as the antioxidant characteristics of the alkali metal can be obtained. Also, even though the tetraester be added to the lubricant it may be converted to a partial alkali metal salt form in situ when the alkali metal is present as a different salt, for example, of a weaker acid.

The lubricant composition of this invention includes as the major compound a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester groupings such as complex esters, di or other polyesters, and polymer esters. These esters are usually made from monoand polyfunctional aliphatic alcohols or alkanols, and aliphatic mono and poly carbo-xylic or alkanoic acids. Frequently, the alcohols and acids have about 4 to 12 carbon atoms. The reaction product of a mono-functional alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a dicarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of a monohydric alcohol or of 1 mole of a glycol, for instance of 4 to 10 carbon atoms, with two moles of a monocarbxylic acid, e.g. of 4 to 10 carbon atoms. The diesters frequently contain from 16 to 40 carbon atoms.

A complex ester is usually considered to be of the type XYZYX in which X represents a monoalcohol residue. Y represents a dicarboxylic acid residue and Z represents a glycol residue and the linkages are ester linkages. Those esters, wherein X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have 30 to 50 carbon atoms.

Polymer esters or polyester bright stocks can be prepared by direct esterification of dicarboxylic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about 15 to 200 centistokes at 210 F., and preferably 40 to centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are particularly useful when added or blended with each other in synthetic lubricant compositions. These esters and blends have been found to be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures. In addition, many complex esters have shown good stability to shear. Natural esters, such as castor oil may be employed and also be included in the blends, as may be small amount of a foam inhibitor such as a methyl silicone polymer, or other additives of lubricant components to provide a particular characteristic.

The monohydric alcohols employed in these esters usually contain about 4 to 20 carbon atoms and are generally aliphatic. Preferably the alcohol contains up to about 12 carbon atoms. Useful alkanols include butyl, hexyl, n-octyl, iso-octyl and dodecyl alcohols, C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used to improve the low temperature viscosity of the finished lubricant composition. Alcohols such as n-decanol, 2-ethylhexanol, oxo alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products such as diisobutylene and C olefins, ether alcohols such as butyl Carbitol, tripropylene glycol monoisopropyl ether, dipropylene glycol mono-isopropyl ether, and products such as Tergitol 3A3 which has the formula C H O(CH CH O) H, are suitable alcohols for use to produce the desired lubricant. If the alcohol has no hydrogens on the beta carbon atoms, it is neo-structured; and esters of such alcohols are often preferred. In particular, the neo-C alcohol-2,2,4-trimethyl-pentanol-1--gives lubricating diesters or complex esters suitable for blending with diesters to produce lubricants which meet stringent viscosity requirements. Iso-octanol and iso-decanol are alcohol mixtures made by the oxo process from C -C copolymer heptenes. The out which makes up iso-octanol usually contains about 17% 3,4-dimethylhexanol; 29% 3,5-dimethylhexanol; 25% 4,5-dimethylhexanol; 1.4% 5,5- dimethylhexanol; 16% of a mixture of 3-methylheptanol and S-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% ot-alkyl alkanols and other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however, if desired they could contain a greater number. Among the specific glycols which can be employed are 2-ethy1-l,3-hexanediol, 2-propyl-3,3-heptanediol, 2-methyl-1,3-pentanediol, 2-butyl-l,3-butanediol, 2,4-diphenyl-1,3-butanediol, and 2,4-dimesityl-1,3-butanediol. In addition to these glycols, ether glycols may be used, for instance, where the alkylene radical contains 2 to 4 carbon atoms such as diethylene glycol, dipropylene glycol and ether glycols up to 1000 to 2000 molecular weight. The most popular glycols for the manufacture of ester lubricants appear to be polypropylene glycols having a molecular weight of about 100-300 and 2-ethyl hexanediol. The 2,2-dimethyl glycols, such as neopentyl glycol have been shown to impart heat stability to the final blends. Minor amounts of other glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously affected.

One group of useful monocarboxylic acids includes those of 8 to 18 or even 24 carbon atoms such as stearic, lauric, etc. The carboxylic acids employed in making ester lubricants will often contain from about 4 to 12 carbon atoms. Suitable acids are described in US. Patent No. 2,575,195, and include the aliphatic dibasic acids of branched or straight chain structures which are saturated or unsaturated. The preferred acids are the saturated aliphatic caboxylic acids containing not more than about 12 carbon atoms, and mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic and sebacic acids and isosebacic acid which is a mixture of a-ethyl suberic acid, a,a'-diethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other dicarboxylic acids, which natural oils and fats are frequently in short supply. The preferred dibasic acids are sebacic and azelaic or mixtures thereof. Minor amounts of adipic used with a major amount of sebacic may also be used with advantage.

The ester base oils to which incorporation of the additive combination of the invention is particularly advantageous are the oils commonly referred to as neopentyl polyol polyesters, i.e. having more than one ester group. These are the esters of aliphatic carboxylic acids, generally monoalkanoic acids, of about 4 to 12 carbon atoms, and a polyhydric alkanol free of beta hydrogen, i.e. containing no hydrogen on the beta carbon atoms, and including the di(polyhydric alcohol)ethers. The polyhydric alcohol generally contains about 2 to 6 hydroxy groups and about 5 to 20, preferably 5 to 12 carbon atoms. Illustrative of the alcohols are those having the general formula:

wherein n is 0 to 1 and R is a lower alkyl group, preferably of about 1 to 4 carbon atoms, which can be straight or branched chain, or a hydroxy methyl group. These esters can be made by reacting a mole of the alcohol with about 2 moles up to the stoichiometric equivalent of the carboxylic acid.

Illustrative of polyhydric alcohols free of beta hydrogen are neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, 2-butyl-2- ethyl-1,3-propanediol, etc. Suitable aliphatic carboxylic acids with which the polyhydric alcohols free of beta hydrogen may be esterified are n-butyric acid, isobutyric acid, valeric acid, isopentanoic acid, caproic acid, isohexanoic acid, n-heptanoic acid, isoheptanoic acid, neoheptanoic acid, n-octanoic acid, isooctanoic acid, pelargonic acid, n-decanoic acid, isodecanoic acid, neodecanoic acid, lauric acid, myristic acid, stearic acid, isostearic acid, etc.

The amine and alkali metal additives of the invention are incorporated in the base ester oil in small amounts sufficient to retard oxidation of the oil at temperatures in excess of 400 F., e.g. 450 F., and the concentrations employed for optimum results may be dependent on the particular base oil and other additive component selected. The amount of the additives is insufficient to destroy the fluidity of the base ester oil, i.e. the oil remains essentially liquid at normal conditions and the alkali metal and other components are not used in an amount which produces a grease or gel-like structure. Ordinarily about 0.005 to 5%, preferably about 0.01 to 2%, by weight of the alkali metal derivative provides satisfactory results, and often the alkali metal content of the lubricant is in the range of about 5 to 1000 p.p.m., preferably at least about 10 or even at least about 40 p.p.m. to p.p.m. or even to 500 p.p.m. The amine anti-oxidant additive component provides satisfactory results when present in amounts of about 0.05 to 5% and preferably about 0.1 to 2%. Normally the amount of dimer acid load-carrying agent is between about 0.01 to 1 weight percent with the preferred amount being between about 0.1 and 0.5 weight percent. The amount of halo-substituted carboxylic acid haze reducing agent is generally between about 0.01 and 1- weight percent with the preferred amount being between about 0.02 and 0.5 weight percent. Anti-corrosion agents such as the tetra ester of alkylene diamine tetra acetic acid when used are normally present in amounts between about 0.05 to 5 weight percent and preferably about 0.1 to 2 weight percent. Other additives can also be advantageously used in the lubricant of this invention, The viscosity of the lubricating oil containing the additives is preferably less than about 13,000 centistokes at -40 F.

The effectiveness of the haze-reducing agent of this invention is shown by the following examples which are not to be considered limiting.

EXAMPLE I A synthetic lubricant was prepared by blending the fol lowing ingredients at a temperature of 160-170 F.

Tetrabutyl ester of EDTA containing mono- Na salt of triester (percent Na=0.518) 1.50 Di- (p-octylphenyl) amine 1.00 Half amide of hydrogenated dimer acid 0.20

Dow Corning fluid (200-60,000) 0.001

1 An essentially complete pentaerythritol ester of fatty acids having an average of 6 carbon atoms and with the following approximate inspection data: Acid No. 0.01; saponrfication No. 420-428; viscosity at 210 F., 4.25-4.35 cs.; V15 cosity at 100 R. 20.5-21.5 cs.

An essentially complete ester of dipentaerythritol and a mixture of alkanoic acids containing an average of 5 to carbon atoms per molecule and characterized by an acid number of about 0.1, a saponification number of about 391-397 and a kinematic viscosity at 210 F. of 8.7-8.9 cs. and at 100 F. of 56-58 cs.

3 EDTA is ethylene diamine tetra acetic acid.

The hydrogenated dimer acid was Emery 389R and the half amide analyzes approximately: Acid No. 104.9 and percent N, 2.16.

A Dow Corning antifoam silicone having a viscosity of 200 cs. at 250 C. and a molecular weight of 60,000.

After intimate mixing the lubricant was filtered through paper coated with a layer of Hyflo Super-Cel (a diatomaceous silica) yielding .a clear oil of bright reddish purple color.

In spite of its superior oxidation resistance, the fluid developed a haze after standing for 3 months in the presence of light. In the absence of light, e.g. as in metal drums and cans, the development of haze was much slower. However, in accelerated oven storage tests the haze developed in a few days. After 7 days in a 221 F. oven, a noticeable amount of precipitate was found at the lower corners of the glass storage bottle.

EXAMPLE II Another synthetic lubricant was prepared from the following components:

Component Wt. percent Hercolube A 71.99 Hercolube F 24.25 Phenyl-a-naphthylamine 1.00 Dip-octylp'henyl) amine 1.00 Tetrabutyl ester of EDTA 1.50 Sodium perfiuorobutyrate 0.06

Half amide of hydrogenated dimer acid of Example I 0.20 Dow Corning fluid (200-60,000) 0.001 This formula is the same as that given in Example 1 except that the Na salts of partial esters of EDTA were eliminated and, in their place, sodium perfluorobutyrate was added. The resultant lubricant was much more stable toward haze and precipitate formation. No haze was observed during storage for months at room temperature. The oil was bright and clear after a 7 day 221 F. storage test and no precipitate was observed after 3 /2 months in a 130 F. oven. Table I shOWs the superior oxidation resistance, load carrying property, non-corrosiveness to metals, compatibility to seal materials, non-foaming and non-shearing characteristics and other superior properties of this lubricant.

TABLE I (1) O Absorption test, 450 F., 1 ft. O /hr., g.

samples 1 T min 1,145 T min 1,145 V "ml--- 2,500 (2) Type II bearing rig test Acid No., final 0.93 Viscosity rise, final (KV/), percent 50.0 WADD demerit rating 58 100 mesh filter deposit, gm. 1.24 (3) Ryder gear scuff test Scuff load:

A side, l b/in. 2590 B side, lb/in. 2860 Relative rating, percent 100 (4) Gear fatigue testmore than hours. (5) Corrosion-oxidation test (425 F., 48 hours) Wt. Change, mg./cm.

Cu --0.30 Ag +0.024 Steel +0.054 Al +0.007 Mg 0.77 Ti +0.038 Viscosity rise (KV/100), percent 22.2 Acid No. increase 1.27

(6) SOD Pb corrosion, 325 F. 1 hr., mg./in. +6.48,

+4.46. (7) Carbon seal wear, inches/min.0.017 l0* (8) Inspection tests KV/210 F., cs 5.104. KV/100 F., cs 27.63. KV/-40 F., cs. 9.824. Flash point, F. 495. Four point, F. Below -80. Acid No. (pH 11) 0.3.

Foam test 000. 0-0-0. Percent swell, H rubber 26.1. Percent swell, Viton 18.4. Durometer, Viton 65. Evaporation loss, 6.5 hrs.:

400 F., sea level 3.41%. 450 F., 5.5" Hg 18.62%. Percent sonic shear None.

450 F., 5.5" Hg. Clear and fluid.

1 TiTime in minutes elapsed before a sharp change in the rate of 0:: absorption occurs.

'I'tTotal time of test in minutes.

Vt-VO111D18 of O2 absorbed during the per-rod Tr in mi.

Table H shows a number of other high temperature synthetic lubricants which are haze-free and remained clear after a 7 day 221 F. oven test.

TAB LE IL-C OMPOSITION Component 1 Hercolube A Hercolube F Plienyl-a-naphthylarnine Di(p-0ctylphenyl) amine Tetrabutyl ester of EDTA Tetra-l-ethylhexyl ester of EDTA- C F COON CsF'z COOLi C3F7 COOK Half amide of hydrogenated dimer acid as in Example I NPG-bis-(dimeracid) Dow Corning Fluid (200-60,000).

and.

l NPG-bis (dimer acid) a condensation product of 1 mole neopentylglycol and 2 moles of hydrogenated linoleic dimer acid of Example I.

TABLE III polyfluoro carboxylic acid is a perfluoro lower alkanoic acid.

8. The lubricant composition of claim 7 in which the ester oil-soluble member which decreases the haze-form- 450" F., 48 hr. oxidation corrosion test showing effect of tetra-n-butyl ester of ethylenediarninetetraacetie acid (Bu4Y)] Run 1 2 3 4 Com osition:

ercolube A 73.01 72.50 72. 3 71.99 Hercolube F 24. 71 24. 22 24. 31 24. 25 Phenyl-Alpha-Naphthylarnine l. 1. 00 1. 00 1.00 Di(p-octylphenyl)amine... 1. 00 1. 00 1. 00 1. 00 Na perfiuorobutyrate 0.08 0.08 0. 06 0.06 Haglf arnlrlielof hydrogenated 0 0 2O 0 20 0 20 Xamp e Dow Corning Fluid (20060,000) +0.001 +0.001 +0. 001 +0.001 Bu Y None 1.00 None 1.50 Weigit Changes, mg. crnfl: 1 510 0 270 0 81 0 40 +0.007 0.054 +0. 046 -0. 046 +0. 015 +0. 015 -1. 23 0. 015 0. 0 -0. 031 Viscosity Rise, 0 (XV/100) 77. 28. 6 27. 9 23. 0 Acid N 0. Increase 5. 2.08 1. 65 1.02 MacConll Ryder Oxid Corro Wt. Change, mg %ig.g igfl SOD Lead Corrosion: Wt. Change, mg +0.86

It is claimed: ing tendency is sodium perfluorobutyrate.

1. A normally liquid lubricating oil composition consisting essentially of a major amount of a normally liquid, carboxylic acid ester base oil of lubricating viscosity having dissolved therein a small effective amount of an ester oil-soluble, aromatic amine anti-oxidant having the general formula:

wherein Q is a non-olefinic, non-acetylenic monovalent hydrocarbon radical of 1 to 20 carbon atoms and Q is a non-olefinic, non-acetylenic aromatic hydrocarbon radical of 6 to 16 carbon atoms, a small amount sufiicient to impart load-carrying properties of an ester oil-soluble dimer acid load-carrying agent, said dimer acid being of a polyolefinic fatty acid of about 16 to 22 carbon atoms and an ester oil-soluble member selected from the group consisting of a halo-substituted monocarboxylic acid of about 2 to 18 carbon atoms and the alkali metal salts thereof in an amount sufficient to decrease the haze-forming tendencies of the lubricant, said lubricant having dissolved therein sufi'icient ester base oil-soluble alkali metal organic compound to enhance the anti-oxidant characteristics of the lubricant.

2. The lubricant composition of claim 1 wherein the dimer acid load-carrying agent is an amide of a hydrogenated dimer acid.

3. The lubricant composition of claim 2 wherein the load-carrying agent is the half amide of a hydrogenated dimer of a polyolefinic fatty acid having on the average about 18 carbon atoms, said agent containing less than /3 of an olefinic bond per molecule on the average.

4. The composition of claim 1 wherein the aromatic amine is a combination of phenyl-a-n-aphthylamine and di(p-octylphenyl) amine.

5. The lubricant composition of claim 1 wherein said ester oil-soluble member which decreases the haze-forming tendency is a polyfluoro carb-oxylic acid.

6. The lubricant composition of claim 1 wherein said ester oil-soluble member which decreases the haze-forming tendency is a polyfluoro carboxylic acid in alkali salt form.

7. The lubricant composition of claim 6 wherein said 9. The lubricant of claim 5 which contains a corrosion preventing amount of an alkylene diamine tetraacetic acid ester having the formula:

wherein R is a lower alkyl radical.

10. The lubricant composition of claim 9 wherein the alkylene diamine tetraacetic acid ester is the tetrabutyl ester of ethylene diamine tetraacetic acid.

11. The lubricant composition of claim 1 wherein the load-carying agent is the half amide of a hydrogenated dimer of a polyolefinic fatty acid having on the average about 18 carbon atoms, said agent containing less than about /a of an olefinic bond per molecule on the average, the aromatic amine is a combination of phenyl-u-naphthylamine and di(p-octylphenyl)amine, and the ester oil-soluble member which decreases the haze-forming tendency is sodium perfluorobuty-rate.

12. The lubricant composition of claim 11 which contains a corrosion preventing amount of the tetrabutyl ester of ethylene diamine tetraacetic acid.

References Cited UNITED STATES PATENTS 2,197,836 4/1940 Reiif et al 252400 X 2,344,988 3/ 1944 Kavanagh et al. 25242.7 X 2,352,462 6/ 1944 Weiss et al 252400 X 2,421,631 6/1947 Lincoln et al. 252-33.6 2,680,094 6/1954 Bartlett et al. 25251.5 2,715,107 8/1955 Talley et al. 25242.7 X 2,805,203 9/1957 Knapp et al. 25234 3,021,281 2/1962 Matson 2525l.5 3,121,691 2/1964 Eickemeyer 2525l.5 3,256,196 6/ 1966 Eickemeyer et al. 25251.5

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner.

Claims (1)

1. A NORMALLY LIQUID LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A NORMALLY LIQUID, CARBOXYLIC ACID ESTER BASE OIL OF LUBRICATING VISCOSITY HAVING DISSOLVED THEREIN A SMALL EFFECTIVE AMOUNT OF AN ESTER OIL-SOLUBLE, AROMATIC AMINE ANTI-OXIDANT HAVING THE GENERAL FORMULA: