US2813829A - Grease compositions having improved yield, load bearing capacity, and low temperature properties - Google Patents

Description

2,813,829 GREASE COMPOSITIONS HAVING ROVED YIELD, LOAD BEARING CAPACITY, AND LOW TEMPERATURE PROPERTIES No Drawing. Application April 22, 1955, Serial No. 503,342

Claims. (Cl. 252-40) This invention is directed to grease compositions having improved properties. More specifically, it is concerned with greases gelled with lithium soaps of hydroxy fatty acids having improved viscosity-temperature relationships, load bearing capacity and increased yield values.

Greases have been prepared from mineral oils gelled with a wide variety of soaps. These soaps are normally either fatty acids or hydroxy fatty acids, while the lubricating oil gelled therewith may comprise mineral lubricants or synthetic fluids.

The soaps act as gelling agents by the formation of characteristic needle-shaped or rope-like crystals referred to as fibers tions capable of holding oil in somewhat the same manner as a sponge can absorb water. Investigations have shown in the past that the precise physical character of these soap fibers may determine the physical properties of the greases, especially with respect to the gelling power, i. e., yield of the grease. In most cases the desirable or ideal form of these soap fibers is such that the requirement of soap content is at a minimum for a given grease consistency (penetration). While lubricating oils of a wide variety have been employed in grease manufacture, it has been the normal practice to utilize oils of moderately low viscosity and of low viscosity index since it was found that the gelling power of the soap in such oils was greater than when oils of higher viscosity and viscosity index were employed. The grease yield, in fact, falls off sharply as the viscosity index of the oil is increased.

One disadvantageous property of many grease compo sitions is that of oil separation commonly known as bleeding. This has been corrected to a certain extent by the incorporation of metallic naphthenates in the compositions. The relationship between the presence of the naphthenate and the extent of bleeding is not clearly understood but it would appear that the naphthenate probably modifies the physical characteristics of the soap fibers such that they are more capable of retaining the oil content of the grease within the mesh of said fibers.

While the use of low viscosity index oils promotes the formation of greases having maximum grease yield, other properties of the greases are somewhat unsatisfactory and particularly the physical properties of the greases at relatively low temperatures. At about 32 F. or below, when the greases are prepared from low viscosity index oils, the compositions rapidly become stiff and are difiicult to eject from their containers or to pass readily from machinery components to the sites where lubrication is desirable. This can be an extremely important disadvantage as the temperatures approach those encountered in Arctic operation or in higher altitudes as in airplane operations and similar situations.

Also, when relatively medium or low viscosity lubricating oils are utilized, the grease composition are not capable of withstanding for more than relatively short periods the effect of high loads when they are used for the lubrication of bearings. When low viscosity oils are so employed, the application of a high load to the bearing results in bearing failure within a relatively short period.

It is an object of the present invention to improve the resulting in a mesh of microscopic proporphysical characteristics of grease compositions. It is another object of this invention to improve the viscosityternperature relationship of grease compositions. It is a further object of this invention to provide greases not only with improved viscosity-temperature relationships but at the same time to do so without detrimental effects to the gelling power of the soaps present in the greases. It is a still further object of this invention to provide the latter type of greases with increased load bearing capacity. Other objects will become apparent from the description of the invention.

Now, in accordance with the present invention, it has been found that improved grease compositions can be made by utilizing as the lubricating oil component a mineral oil having a minimum viscosity index of about and a viscosity between about 70 and about 150 SSU at 210 B, said oil being gelled to a grease consistency with a lithium soap of a hydroxy fatty acid. Furthermore, in order to overcome the decreased yield apparently due to the high viscosity-high viscosity index oil, the composition also should contain between about 0.25% and about 2.5% by weight of an alkaline metal naphthenate. Still in accordance with this invention, it has been found that greases containing these three essential components exhibit substantially improved service life in bearings subjected to high loads, have improved low temperature pumpability and require a minimum of lithium soap to reach a given grease consistency.

The primary object of the present invention was to pro vide greases having an improved bearing life, when said bearings are subjected to high loads. It was found that when oils having a high viscosity but a low viscosity index were employed for the purpose of improving high load service life that the latter property was obtained, but at the expense of low temperature physical characteristics of the grease. This, of course, was due to the fact that such a lubricating oil, namely, one having a low viscosity index, has a relatively poor temperature-viscosity relationship. Thus, while improving the grease with respect to its load bearing capacity, the corresponding decrease in low temperature physical properties resulted in an overall unsatisfactory product for general use.

To overcome this aspect, therefore, a high viscosity mineral lubricating oil was employed having a relatively high viscosity index, namely, one greater than about 70, and preferably within the range between about and about 95. The viscosity of the oil component of the subject grease compositions is preferably greater than about 70 Saybolt Seconds Universal at 210 F. and still more preferably within the range of between about 75 and about SSU at 210 F.

The mineral lubricating oil to be employed in the subject grease compositions may comprise an oil from a single source having the required properties, the limits of which are set out above, or may be a blend of oils obtained from more than one source, the combined blend having the viscosity and viscosity index limitations recited hereinbefore. Preferably the lubricating oil comprises a blend of a refined mineral oil lubricant obtained from a distillate lubricating oil traction combined with at least an equal proportion of a mineral oil bright stock. The term bright stock is one which is well recognized in the art of refined mineral oils. To obtain the desired fraction, crude oils are usually subjected to distillation under ordinary pressures in order to obtain a long residue comprising the fraction which does not distill under these conditions without substantial decomposition. The long residue then may be subjected to steam distillation, usually under a vacuum. Under these conditions, gas oil and waxy lubricant fractions distill over, leaving what is normally termed a short residue or a steam refined stock, also known as cylinder stock." The steam refined stock is then deasphalted (if an asphaltic crude is employed) and subjected to dewaxing operations to remove microcrystalline or macrocrystalline waxes. Following this, the raffinate is treated with a solvent for the purpose of reducing or removing the aromatic fractions. The dewaxing and extraction sequence may be reversed, if desired. Clay contact treatment or percolation may be employed to clean up the oil following any one or all of these separate operations. The oil raftinate which remains after deasphalting, dewaxing, extraction, and clay treatment is generally called bright stoc The bright stocks suitable for use in the present compositions should have the following ranges of properties:

TABLE I.PROPERTIES OF BRIGHT STOCKS The tables which follow give the properties of typical bright stocks which are useful in the compositions of this invention.

changes and the viscosity of the oils defines their suitability for their present purpose. Hence, the best definition with respect to essential characteristics of mineral oil suitable for the present compositions comprises those having an aromatic hydrocarbon content less than about 15% by weight and having a viscosity of between about 1250 and about 11,000 SSU at 100 F. Having defined these particular properties, the other properties such as flash, fire, aniline point, and viscosity index usually are largely determined thereby.

As the examples given hereinafter demonstrate, when mineral lubricating oils are gelled with lithium soaps of hydroxy fatty acids, and the lubricating oils is one having the high viscosity and high viscosity index limitations set out hereinbefore, the soap requirement of the resulting grease to reach a given consistency is relatively high compared with greases wherein the mineral oil component has a lower viscosity index. In spite of this, it will be found that greases containing the high viscosity index oils having the recited range of viscosity, not only provide a grease composition having improved service life in bearings operating under a high load, but also exhibit improved low temperature consistency characteristics. Thus, the unsatisfactory increase in consistency and low pumpability of greases wherein the oil component has a low viscosity index is corrected by the use of an oil having a flatter viscosity-temperature curve. Having improved the grease composition with respect to load bearing capacity and low temperature characteristics, it therefore remained to correct the adverse yield characteristics TABLE II.EXAMPLES OF TYPICAL BRIGHT STOCKS SUS Ring Analysis Ratio of Aver. Viscosity Paratdns Aver. Rings Index to Naph- M01 per 100 210 Aro- Naph- Parafthenes Weight Mol matics theues fins Mid-Continent Bright Stock- Conventional Extraction 3, 650 164 77 13 17 4.1 685 3. 7 Mid-Continent; Bright Stock.-

Mild Extraction 2, 569 141 9 19 72 3. 8 685 3. 4 Mid-Continent Bright Sto Heavy Extraction, 2, 049 131 93 3 21 76 3.62 675 2.9 Pennsylvania Bright Stock 2, 144 102 5 16 79 4. 95 730 3. 0 Gulf Coastal Bright Stock 1,251 85 63 4 35 61 1. 74 515 3.4

TABLE IILTSPEQIFICATIQNS FOR TYPICAL MID-CONTINENT BRIGHT STOCKS Unfiltered Filtered Gravity, API, minimum 25. 5 5 25. 5 Color, NPA 8+ Dark Green. 6. 7 Pour Point, -F., maximum..- 10 1 Flash F., minimum 540 Fire F., minimum 615 SSU 10 F -170 Viscosity Index, minimum 90 J0 It will be understood from the above analyses that the source or treatment of a particular mineral oil is not as important for the, present purpose as the final properties of the mineral oil constituent to bev used in these compositions. For example, it is possible. to. vary the extent of solvent extraction dependent. upon the, original aromatic content and the requirements of the specific use of the final product, as well as upon the necessity or desirability of deasphalting, clay treating, acid treating, and the like. Hence, it will be recognized that the present invention is predicated upon the use of a mineral oil fraction having the above defined ranges ofproperties and not upon the source or treatment of such oil.

The two most important properties of a mineral oil suitable for the present use comprise the aromaticity and the viscosity characteristics. The aromatic content 'has a large influence upon the sensitivity of the oil to thermal occasioned by the use of the particular type of mineral oil necessary to obtain the two properties just referred to.

In accordance with this feature of the invention, it was found that an oil-soluble alkaline metal naphthenate unexpectedly provided greases wherein the lithium soap constituting the principal gelling agent had substantially the same gelling power that it exhibits when used for gelling a low viscosity-low viscosity index mineral oil. This is especially apparent when the naphthenate is employed in concentrations between about 0.25% and about 2.5% by weight of the total grease composition. Preferably the naphthenate is present in amounts varying between about 0.5% and about 1.5%. The naphthenates are preferably derived from mineral oil sources and comprise petroleum naphthenic acids neutralized either with alkaline earth metals or alkali metals, especially those having atomic weights up to 40. Hence, the calcium, barium, magnesium, sodium, lithium or potassium petroleum naphthenates are preferred for the present purpose.

The naphthenates are prepared from principally cyclopentaneand cyclohexane-carboxylic acids containing attached to the naphthene ring saturated or unsaturated hydrocarbon radicals (acyclic, alicyclic or aryl), including especially the naphthenic acids present in and extractable from various petroleum oils and fractions thereof and the alicyclic hydrocarbon carboxylic acids present in and derivable from other natural sources, such as the resin acids of various vegetable matter, e. g., abietic acid from pine rosin, etc. Thus, the acid may be modified by a substituent group which includes aryl and/ or alkyl radicals, unsaturated straight and/or branched chain radicals; substituted alkyl, aryl, and/or alkene radicals; and in addition, the saturated cyclic carboxylic acids may also be modified by addition of side groups comprising saturated cyclic hydrocarbons or by condensation to form groups of two or more saturated cyclic hydrocarbons chemically fused.

The various naphthenic acid products usually obtained from petroleum oils are mixtures of the saturated cyclic hydrocarbon acids and are included herein within the term a saturated cyclic hydrocarbon carboxylic acid. Due to the cheapness and availability of such mixtures of naphthenic acids, the alkaline earth metal salt employed to stabilize the non-aqueous gel in accordance with the present invention is advantageously a mixture of the alkaline earth metal soaps of the saturated alicyclic acids present in the naphthenic acids, which mixture of soaps is referred to herein as an alkaline earth metal naphthenate. The actual composition of the naphthenic acids is unknown but they are believed to contain a mixture of the cyclic hydrocarbon carboxylic acids having from to 6 carbon atoms in the saturated ring, although there may be present acids with smaller or larger rings. Furthermore, the mixture usually contains modified saturated alicyclic hydrocarbon carboxylic acids of the type heretofore mentioned. Other constituents of petroleum from which the mixture of acids, known as naphthenic acids, are obtained may also be present. Such commercial grades of naphthenic acids as Advance Solvents Co.s Grade A, Harshaw Chemical Co.s Grade 215-225AN, Oronnite Chemicals N, Stancos Aruba Dark, and Colonial Beacon Oil Co.s (Esso) Everett Refinery and Rectified Grades function satisfactorily.

Typical soaps falling within the above category include calcium naphthenate, strontium naphthenate and magnesuim naphthenate, wherein the molecular weight of the naphthenic acids from which the soaps are derived are preferably between about 100 and 600, and preferably between 220 and 450.

The soaps utilized as thhe principal gelling agent for the subject grease compositions comprise the lithium soaps of hydroxy fatty acids.

The hydroxy fatty acids from which such soaps are prepared are especially those containing at least carbon atoms and preferably between 12 and 36 carbon atoms per molecule. From the standpoint of economy and availability, the most practical examples of such acids are those derived from hydrogenated castor oil or by the catalytic oxidation of hydrocarbon oils and Waxes which have been extracted and fractionated to the desired molecular weight range. Suitable species of acids therefore comprise 9-, 10-, 11-, or 12-hydroxy stearic acids or their homologs and analogs, such as corresponding hydroxy palrnitic acids, e. g. 10- and IS-hydroxy palmitic acids. Other suitable acids for use in the formation of the subject compositions comprise hydroxy myristic acids, hydroxy behenic acids, 5,6-dihydroxy stearic acid, and 2,1l-dihydroxy palmitic acid. Other polyhydroxy fatty acids which may be employed include 6,7-, 7,8-, 8,11-, 9,10- and 10,1l-dihydroxy stearic acids.

Normally these soaps will be present in amounts varying from about 5% to about 20% and preferably are utilized in proportions between about 6% and about 12%. The presence of the naphthenate reduces the lithium soap requirement in proportions of the order of about 30% of the soap needed to reach a given penetration of grease when the high viscosity index-high viscosity mineral lubricating oils are utilized as the principal lubricating component thereof.

The substantial efiect upon grease yield caused by the presence of the naphthenate is especially unexpected due to the fact that the same naphthenates when added to a grease comprising a lower viscosity index oil have substantially no effect upon the grease yield. Furthermore, when the naphthenates are added to greases gelled with soaps of ordinary fatty acids there is substantially no change in grease yield. Consequently, there appears to be a unique relationship occurring between the subject naphthenates when utilized in grease compositions comprising the high viscosity-high viscosity index oil, especially when the gelling agent is a lithium hydroxy fatty acid soap.

Further combinations of additives which may be employed in the subject grease compositions for providing an unexpected extension in bearing life (as well as improving the emulsification characteristics and corrosion protection properties of the grease compositions) comprise the use of 0.25-5% by weight of both an alkaline earth metal, hydrocarbylsulfonate and a mono-(aliphatic carboxylic acid) ester of a polyalkylene glycol. The improvement in bearing life is unexpectedly extended by the combination of these two types of additives as compared with the use of either of them alone. However, for situations in which a moderate increase in corrosion resistance only is desired, it is suflicient to add to the compositions hereinbefore described the polyalkylene glycol monoesters. These are preferably esters of glycols having from 2 to 6 carbon atoms in each oxyalkylene radical and preferably containing between about 5 and about 20 oxyalkylene radicals per molecule. The monoester group contains an alkyl radical having from 8 to 24 carbon atoms and preferably the polyoxyalkylene glycols from which the monoesters are formed have molecular weights between about 150 and about 2000. Polyethylene gly cols are especially desirable, but polypropylene glycols and higher glycols having up to about 6 carbon atoms per glycol unit may be employed. The fatty acids used for the formation of the monoesters comprise especially capric, lauric, oleic, and stearic acid as well as the corresponding hydroxy fatty acids.

The alkaline earth metal hydrocarbylsulfonates are preferably the oil-soluble petroleum sulfonates and more particularly the oil-soluble calcium petroleum sulfonates. Preferably the so-called basic sulfonates are utilized.

The examples which follow illustrate the present invention. However, it will be understood that the invention is not to be limited thereto.

Example I A. A grease was prepared comprising 7% lithium 12- hydroxy stearate and a mineral lubricating oil having a viscosity of 63 SSU at 210 F. and a viscosity index of 35. While satisfactory for many lubricating purposes, it had relatively short service life in wheel bearings under high loads, apparently due to the low viscosity of the oil.

B. To correct this, a higher viscosity oil of substantially the same viscosity index can be used, but at tem peratures below about 0 C. such greases become unduly stifi and therefore have poor pumpability characteristics.

C. In order to retain the improved high load bearing life imparted by utilizing the higher viscosity oil, and at the same time correct the adverse low temperature properties referred to, a lithium 12-hydroxy stearate grease was prepared from equal parts of a pale lubricating oil having a viscosity of 300 SSU at F., and a mineral oil bright stock having a viscosity of about 3600 SSU at 100 F., the mixture having a viscosity of 958 SSU at 100 F, a viscosity of 78.2 SSU at 210 F. and a viscosity index of 74. However, the change from a low viscositylow viscosity index oil to a high viscosity-high viscosity index oil depressed the gelling power of the soap, about 10% soap being required to obtain a grease having the same consistency as in grease A, above, wherein only 7% soap was needed.

D. Since the lithium soap is the most costly ingredient in the grease, efforts were made to overcome the poor yield of grease C. It was found that the addition of 1% by weight, based on the grease, of a calcium naphthenate soap, reduced the lithium soap requirement to about 7.25% to obtain a grease of the same consistency of grease A. The calcium naphthenate soap was from a petroleum naphthenic acid having an average molecular weight of about 220.

E. The corresponding lithium naphthenate was found to be twice as effective as the calcium soap, 0.5 of the former, when added to the same oil and soap as in grease C, improving the yield so that only 7.25% lithium 12- hydroxy stearate were needed to obtain a grease of the same consistency as grease A.

Example 11 In addition to improving the yield, low temperature properties and high load bearing lubrication, as can be done by using samples D and E in Example I, it is highly desirable to provide protection against corrosion, especially due to salt water. The addition of 1% by weight of poly(oxyethylene) glycol mono-oleate and 2.5% of calcium petroleum sulfonates to grease D, above, results in a composition providing resistance against salt water corrosion for a period of time about 4 times greater than when the mono-oleate and sulfonate are omitted.

Example 111 A still further improvement relative to the oxidation resistance of the subject grease composition can be made by adding a combination of 0.25% phenyl-a-naphthylamine and 0.25% of 1salicylol amino guanidine monooleate to the grease described in Example II.

We claim as our invention:

1. A grease composition comprising a major proportion of a mineral lubricating oil having a viscosity of about 78 SSU at 210 F. and a viscosity index of about 74, a gelling proportion of soap consisting essentially of lithium 12-hydroxy stearate and about 0.5% by weight of lithium naphthenate.

2. A grease composition comprising a major proportion of a mineral lubricating oil having a viscosity of about 78 SSU at 210 F. and a viscosity index of about 8 74, a gelling proportion of soap consisting essentially of lithium l2-hydroxy stearate and about 1% by weight of calcium naphthenate.

3. Agrease composition comprising a major proportion of a mineral lubricating oil having a viscosity between about 75 and about 150 SSU at 210 F. and a viscosity index greater than about 73, a gelling proportionof soap consisting essentially of a lithium soap of a hydroxy fatty acid having between about 16 and about 20 carbon atoms per molecule, and between about 0.5% and about 1.5% by weight of an alkali metal naphthenate.

4. A grease composition comprising a major proportion of a mineral lubricating oil having a viscosity between about 75 and about 150 SSU at 210 F. and a viscosity index greater than about 73, a gelling proportion of soap consisting essentially of a lithium soap of a hydroxy fatty acid having between about 16 and about 20 carbon atoms per molecule, and between about 0.5% and about 1.5% by weight of an alkaline earth metal naphthenate.

5. A grease composition comprising a gelling proportion of soap consisting essentially of a lithium soap of a hydroxy fatty acid having from 12 to 24 carbon atoms per molecule, between about 0.25% and about 2.5% by weight of an alkaline metal naphthenate of the group consisting of alkali metal naphthenates and alkaline earth metal naphthenates, and a major amount of a mineral lubricating oil having a viscosity between about 70 and about 150 SSU at 210 F. and a viscosity index greater than 70.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,173 Brunstrum et al. Apr. 9, 1946 2,409,950 Meyer Oct. 22, 1946 2,455,892 Fraser Dec. 7, 1948 2,610,946 Eckert Sept. 16, 1952 OTHER REFERENCES Manufacture and Applicating of Lubricating Greases, Boner, Reinhold Pub. Co., N. Y. (1954), p. 593.

Claims (1)

1. A GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL HAVING A VISCOSITY OF ABOUT 78 SSU AT 210*F. AND A VISCOSITY INDEX OF ABOUT 74, A GELLING PROPORTION OF SOAP CONSISTING ESSENTIALLY OF LITHIUM 12-HYROXY STEARATE AND ABOUT 0.5% BY WEIGHT OF LITHIUM NAPHTHENATE.