US2782166A - Ester base lubricating greases - Google Patents

Description

ESTER BASE LUBRICATING GREASES John J. Kolfenbach, Somerville, Arnold J. Morway, Rahway, and Paul V. Smith, Jr., Westfield, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application May 7, 1949, Serial No. 92,076

1 Claim. (Cl. 252-421) The present invention relates to ester base lubricating greases and particularly to lithium soap base greases employing synthetic esters as the oily lubricating medium.

In the prior art, various suggestions have been made for'the use of synthetic esters as lubricants and as ingredients of lubricating greases because of their superior low temperature properties, low volatility, and high viscosi'ty indexes. For certain purposes, such as the lubrication of aeroplane instruments for use at extremely low temperatures, such lubricants have found considerable success. In general, however, the oily esters used have been of low viscosity and their utility has been limited for that reason.

There is a demand for lubricating greases of higher viscosity base oils for numerous applications, for example gyroscope gears and other comparable mechanisms where low temperature properties are still desirable, but where superior performance characteristics at higher operating temperatures are also necessary. Also, the greases containing synthetic esters of dibasic acids have a marked deleterious effect on rubber seals in hydraulic systems. By the incorporation of large amounts of glycol esters in the greases in contrast to dibasic esters this undesirable swelling is greatly reduced. This is one feature of the present invention. The present inventionmakes possible the blending of synthetic oils to permit a wider choice 2,782,166 Patented Feb. 19, 1957 eral kinds may be prepared from polyhydroxy alcohols with superior high temperature properties.

In particular the complex esters applicable to this invention are of three main types, shown generically as follows:

aliiornoilaaiiom These are prepared by reacting one mole of a dibasic acid with one mole of a glycol under esterification con ditions until one molecular proportion of water is proin the base oil viscosity of low temperature lubricating greases. This in turn affords opportunity to use a wider selection of base lubricants to fit a wider variety of applications which is a major feature of the present invention. The desired wider range in viscosity may be of utility in securing either a better low temperature performance or better high temperature performance or both. The range over which the lubricant may be useful may be varied and adjusted to meet lubricating requirements.

-As suggested above prior art lubricating greases, consisting for example of di-2-ethylhexyl sebacate, thickened to a grease consistency with a suitable soap such as lithium stearate, for example, have proved very satisfactory for certain restricted applications. These branched chain esters are excellent dispersants for soaps, especially lithium soaps. The greases formed. have a high dropping point and are water insoluble. These may be modified in various ways. For example, other branched chain alcohols such as 0x0 alcohols may be used to esterify the dibasic acid. The prior art suggests the substitution of various dibasic acids such as adipic, pimelic, azelaic, and the like, in lieu of sebacic acid in such compositions. The normal alcohols, as distinguished from the branched chain alcohols, may also be used to esterify the dibasic acids. These non-branched alcohol esters also have good soap dispersant properties and greases may be prepared from them which have excellent texture and good structure stability. Such esters however, have relatively high freezing points which make them undesirable for service at particularly low temperatures It has now been found that complex esters of sev duced, and then stepwise esterifying the unreacted acid and alcohol groups with a monohydric alcohol and a monobasic acid respectively. Preparation is fully described in a copending application for Patent Serial No.

52,428, now Patent No. 2,575,195.

As set forth in the application of Smith, Serial No. 52,428, esters of this type have the general formula COOR where R is an aliphatic hydrocarbon group of 0 to 26 carbon atoms, preferably a saturated hydrocarbon (paraffinic) group of 6 to 10 carbon atoms; R is a saturated aliphatic hydrocarbon group of 2 to 18 carbon atoms, preferably a radical of ethylene, propylene, butylene or related glycol; R" is the saturated or unsaturated hydrocarbon radical of a monohydric alcohol, straight or branched chain, of 1 to 20 and preferably of 6 to 10 carbon atoms, with or without oxygen or sulphur substituents; R is an aliphatic hydrocarbon radical, straight or branched, saturated or unsaturated, of 1 to 22 carbon atoms, with or without interlinking oxygen or sulfur, preferably being an ordinary fatty acid of 2 to 10 carbon atoms.

The specific reaction conditions are set forth in said application Serial No. 52,428 and need not be repeated in detail here. It may be stated briefly that 1 mol of the dibasic acid, 1 mol of glycol, 4.5 g. of ptoluenesulfonic acid monohydrate and ml. of toluene were placed in a flask and refluxed until one mol of water was collected in a trap. After cooling, one mol of monohydric alcohol was added and the reaction continued until no more water collected in the trap and finally one mol of the monobasic acid was similarly reacted.

Examples of acids, glycols and alcohols actually used are described in detail in said Smith application Serial No. 52,428, and they include the following combinations:

(a) Adipic acid, thiodiglycol, n-caproic acid, 2-ethyl hexanol.

(b) (0) Same as (a) with triethylene glycol and trimethylene glycol, respectively, replacing the thiodiglycol.

(d) Sebacic acid, tetraethylene glycol, n-caproic acid, C10 0x0 alcohol.

(e) Cm-Cm alkenylsuccinic acid, pentamethylene glycol, n-caprylic acid, methyl alcohoL.

(f) Chi-C18 alkenylsuccinic acid, triethylene glycol, n-caprylic acid, methyl alcohol. r

(g) Clo-C12 alkenylsuccinic acid, polyethylene glycol (300 mol. Wt.), n-butyric acid, methyl alcohol.

(h) Sebacic acid, tetraethylene glycol, n-caprylic acid, C15-C19 oxo alcohol.

( o o o RiOi jRzi loRsoi lR /oRs These are prepared by reacting one mol of a monohydric alcohol with one mole of a dibasic acid under esterification conditions until no more H2O was pro- 3 duced. Then the mixture is further reacted with 0.5 mole of glycol to complete the esterification. Preparation is fully described in copending application for Patent Serial No. 52,429, now Patent No. 2,703,811.

As suggested in the application of Smith, Serial No. 52,429, these products may have the general formula COOR:

ooo

COORz Examples of the dibasic acids are oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, brassylic, pentadecanedicarboxylic, tetracosanedicarboxylic, C4 to C24 alkenylsuccinic, diglycolic and thiodiglycolic acids. Specific examples are prepared by combining:

(a) Adipic acid, n-butyl alcohol, trimethylene glycol, or the n-butyl alcohol may be replaced by C8 0x0, C10 oxo or Z-ethyl hexanol, the glycol being replaced with triethylene glycol, tetraethylene glycol, thiodiglycol. Other dibasic acids such as sebacic, thiodipropionic, Chi-C18 alkenyl-succinic acids are listed as alternates for adipic acid. These are reacted in the same general manner as those mentioned above under (1).

O O O O II ll II II RJCORZOCRQCORIOCRS These are prepared by reacting one mole of a monobasic acid with one mole of a glycol under esterifying conditions until no more H2O is produced. Then the mixture is further reacted with 0.5 mole of dibasic acid to complete the esterification. This preparation is fully described in copending application for Patent Serial No. 52,430, now Patent No. 2,575,196.

In general, these esters have the formula OOCR an obvious reversal of that set forth under (2) above. The radicals R, R1, etc., are defined in full in said Smith application, Serial No. 52,430. In general, the monobasic acids are the simple fatty acids, such as acetic, propionic, caproic, lauric, stearic, oleic, etc, and mercapto and oxy derivatives thereof, such as B-methoxypropionic acid, B-ethyl mercaptopropionic acid, etc. The glycols are as indicated above and the same dibasic acids as listed under (2) above may be used. The same general reactions set forth above are applicable, as explained in detail in said application Serial No. 52,430.

Specific examples are esters prepared from:

(a) Valeric acid, adipic acid, tetraethylene glycol.

(b) Same as (a), substituting triethylene glycol.

(c) Caproic acid or (d) caprylic acid, and adipic acid, tetraethylene glycol or (e) triethylene glycol.

(f) Acetic acid (g) propionic, (h) butyric, (i) valeric, sebacic acid, tetraethylene glycol, etc.

In the foregoing, the terms oxo" alcohol refer to alcohols prepared by the well-known oxo process, treating olefins with carbon monoxide and hydrogen in liquid phase under pressure, using a suitable catalyst.

The esters of dibasic acids and polyhydric alcohols have lower volatility than the branched chain dibasic acid-monohydric alcohol esters. These compositions also have low temperature properties that are almost as good as those of the conventional dibasic acid esters such as di-Z-ethylhexyl sebacate. Such esters would appear to be almost ideal lubricating bases for greases of the aeroplane instrument type. They have the very important deficiency, however, that they are poor dispersants for soap. When attempts have been made to prepare greases from these materials, the oil separates from the soap and no grease structure results.

For example, 20% by Weight of lithium stearate was mechanically dispersed in 80% of the ester of butyl alcohol, triethylene glycol, and adipic acid. The soap was dispersed in the cold ester as a slurry while stirring vigorously and the temperature was then raised to 420 F. When the resulting composition was cooled in thin layers, the soap separated completely from the ester. There was no grease structure produced.

According to the present invention, esters of the character just mentioned may be mixed with esters of the conventional branched chain type, such as di-Z-ethylhexyl sebacate and greases of smooth homogeneous structure and excellent structural stability may be produced.

In general, lubricating grease compositions made according to the present invention consist of about 5 to 30% by Weight of an alkali metal soap of substantially saturated fatty oils or acids of 12 to 22 carbon atoms in an oily vehicle comprising a complex ester mixed with a simple oil which is preferably a monohydric alcohol ester of dibasic aliphatic acid but may be a light mineral oil, e. g., one of about 35 to 200 S. U. S. at F.

The preferred composition is 5 to 30% by weight of a lithium soap of C12 to C22 fatty acids in about 20 to 60% of complex ester and 10 to 60% of the simple ester or oil. The complex ester is prepared from a C2 to C24 dibasic aliphatic acid, preferably C4 to C12. This acid is partially esterified with a polyhydric aliphatic alcohol, preferably a glycol, having 2 to 12 carbon atoms, or polyalkylene glycols having 2 to 4 carbon atoms in each group. Esterification is completed by using a C2 to C18, preferably a C2 to Ca monohydric alcohol. Where the use of polyhydric alcohol leaves unesteriiied hydroxyl groups, an aliphatic acid of 2 to 20 carbon atoms, preferably a C2 to C8 monobasic carboxylic acid such as acetic, propionic or butyric acid may be used.

The simple ester is preferably a monohydric alcohol ester of dibasic acid, e. g., di-Z-ethylhexyl sebacate, succinate, adipate, or the like. As previously noted, the simple ester may be replaced with a light mineral base oil or it may be mixed therewith. Numerous variations in the ingredients may be made and mixtures of simple and/or complex esters may be used.

The invention may be understood more clearly by reference to the following specific examples:

Example I The following ingredients were combined by mixing in the proportions indicated:

20% by weight lithium stearate 40% ester of 2 mols butyl alcohol, 1 mol triethylene glycol and 2 mols adipic acid 40% di-2-ethylhexyl sebacatc The soap was dispersed in the mixture of cold esters as a slurry while stirring vigorously, and the temperature was raised to about 420 F. Thereafter, the composition was permitted to cool in thin layers and was homogenized after cooling. The resulting grease was smooth and homogeneous in texture and showed no tendency toward oil separation. It had a worked penetration of 270 mm./l0 and a penetration of 361 after working 100,000 strokes in the standard A. S. T. M. fine hole worker plate.

Example II A composition was prepared exactly like Example I except that conventional oxidation inhibitors were added as follows: i

1% by weight, based on the total composition, of phenyl alpha naphthylamine and 1.25% of the condensation product of diisobutyl phenol and formaldehyde in the presence of ammonia. This composition was subjected to the copper corrosion test under standard conditions (24 hours at 210 F.). The copper strip showed no stain whatever at the close of the test period. The composition was also subjected to the Norma-Hoifman bomb test and went 500 hours to a 5 p. s. i. drop. It was also subjected to the Torque test at -67- F. This test is conducted by determining the time in seconds re quired to turn a standard 204 bearing under 10,000 grams-centimeter torque. The time required was 7.5 seconds, which is considered very satisfactory at this extremely low temperature.

Further examples are as follows:

Example 111 Percent by weight Lithium stearate Low cold-test mineral oil, S. U. S. vis. 210 F 20 Complex ester, prepared from 2 mols Ca oxo alcohol,

2 mols sebacic acid, 1 mol tetraethylene glycol 60 This example was prepared by the same method as Example I. pared in situ by using LiOH-HzO and stearic acid, added to the mineral oil and dried out before adding the ester complex.

This product had a dropping point of 378 F. Its

worked penetration at 77 F., in the standard fine hole A. S. T. M. grease worker was 285 mm./ 10. After working for 100,000 strokes in the same A. S. T. M. grease worker the penetration was 360 mm./ 10 which is quite soft but not liquid by any means.

Example IV An all ester base grease was prepared of the following composition Percent by weight Percent by weight Lithium stearate 20 Complex ester of 1 mol adipic acid, 1 mol triethylene glycol, 1 mol secondary butyl alcohol, 1 mol However, the lithium stearate can be prepropionic acid 40 Phenyl alpha naphthylamine 1 Y Inhibitor (condensation product of formaldehyde and diisobutyl phenol in presence of NH3) 0.5 Di-Z-ethylhexyl sebacate 38.5

This product had substantially the same characteristics as those of Example IV.

If desired, greases of the character described in Examples I to V may be prepared by using preformed soaps or the soap may be formed in situ in a small amount of mineral lubricating oil which may then be added to the esters. Thus, lithium hydroxide and stearic acid, for example, may be combined in a few percent by weight of mineral oil and after soap formation is complete the esters may be added in major proportions and cooked to the desired temperature. In this way, hydrolysis of the esters and the possible formation of the alkali metal soap of the di-basic acid, which would usually result if .alkali were added directly to the esters, is prevented.

The temperature of cooking may be varied considerably,

but for the greases of materials described above, it should normally be from about 380 to about 550 F.

Conventional additives may be combined with lubrieating greases of this invention, and structure modifiers, such as zinc naphthenate, may also be employed to advantage. The oils may be mixed with mineral oil or with other synthetic oils, such as silicones, polyglycols, and the like. Conventional anti-oxidants, viscosity index improvers, thickeners, tackiness agents, extreme pressure compounds, and the like, may be added for particular uses, as will be obvious to those skilled in the art.

In summary, the invention may be defined as the use of a mixture of lubricating materials of which one is a conventional ester of dibasic acid or a light mineral oil and the other is a complex ester, with alkali metal soap to florm a grease. The complex ester has the general formu a where R1 is a monofunctional radical, either monobasic acid or monohydric alcohol, R2 is a difunctional mate rial, either dibasic acid or dihydric alcohol (glycol), R3 is a difunctional material, either dihydric alcohol (glycol) or dibasic acid, and R4 is one of the following: (1) a monofunctional material, either monohydric alcohol or monobasic acid radical, or (2) a difunctional material, i. e., dibasic acid or dihydric alcohol half esterifie'd by a monofunctional radical like R1. In the latter case, the diagrammatic formula would be where R1 is monofunctional, R2 and R4 are preferably identical and are at least similar in being difunctional, i. e., either dihydric alcohol or dibasic acid,'and R3 is the converse of R2 or R4, i. e., a dibasic acid radical or a. dihydric alcohol. The chain alternates from acid to alcohol radical and all members except the end members, which are monofunctional, are difunctional.

The chain lengths of the members R1, R2, R3, R4 are as given above. Where R1 is monobasic acid, it has from 2 to 18 or 20 carbon atoms. If it is alcohol, its chain length is 2 to 10 carbon atoms. The dibasic acids and the dihydric alcohols have 2 to 12 carbon atoms in the chain.

It will be understood that the complex ester is composed of alternate aliphatic radicals of alcohol and acid, the end members of the chain being monofunctional (i. e., either monohydric alcohol or monobasic acid), and the intermediate members being difunctional (i. e., either dicarboxylic acids or dihydric alcohols). There are at least two intermediate members, preferably three. Hence, the complex ester always comprises at least one dihydric alcohol (glycol), at least one dibasic acid, and at least two monofunctional aliphatic radicals. The latter may be alike, acid or alcohol, or may be one monohydric C2 to C12 alcohol and one C2 to C20 fatty acid when there are only two intermediate members. As pointed out more fully in the copending applications, Serial Nos. 52,428, 52,429 and 52,430, complete esterification is preferred.

What is claimed is:

A lubricating grease consisting essentially of lubricating oil thickened to a grease consistency with 5-30% by weight, based ontotal composition, of alkali metal soap of a Cm-Cn-substantially saturated fatty acid, said lubricating oil comprising about 10-60% by weight, based on total composition, of a lubricating oil base selected from the group consisting of lubricating grade di-esters of ali- 5 phatic mono'hydric alcohols with aliphatic dibasic acids having 4-12 carbon atoms and lubricating grade light mineral oil, and about 20-60% by weight, based on total composition, of a lubricating oil grade complex ester formed of 1.0 11101 of butyl alcohol, 0.5 rnol of triethyl- 10 ene glycol, and 1 mol adipic acid.

References Cited in the file of this patent UN TED STA ES PATENTS Young Nov. '11, Young Feb. 10, Ashburn a- Sept. 28, Morway Apr. 12, Beavers Mar. 7, Beavers Mar. 7, Smith Nov. 13, Smith NOV. 13, Sanderson Feb. 17,