US2831812A - Water-resistant alkali metal and alkaline earth metal-containing grease - Google Patents

Description

WATER-RESISTANT ALKALI METAL AND ALKALINE EARTH METAL-CGNTAWIING GREASE Harry J. Worth, Fullerton, Califi, assiguor to Union Oil Company of California, Los Angeles, 'Calii'l, a corporaion of California No Drawing. Application October 6, 1953 Serial No. 384,527

20 Claims. (Cl. 252-423.)

This invention relates to lubricating greases and particularly greases which are resistant to and retain their grease like structure in the presence of water. More particularly the invention relates to alkali metal-alkaline earth metal mixed base greases having a large excess of metal and being prepared in a certain manner.

Alkali metal soap greases and particularly sodium soap greases are relatively cheap to prepare because of the simplicity of compounding procedures and partic ularly because of the low cost of the metal and the saponifiable material used in preparing the soaps. However, these greases are not suitable in many applications due primarily to their lack of water resistance, especially at elevated temperatures. Although water-resistant greases have been prepared from various metals and combinations of metals, greases cause of the high cost of metal and/or saponifiable material employed, or the greases lack other properties which are desirable and which are normally possessed by sodium or other alkali metal soap greases.

Applicant has found that a grease havin exceptional water resistance and having other properties making it a desirable grease for many applications can be prepared by first preparing a magnesium stearate grease, or a concentrate of magnesium stearate in oil, either by dissolving magnesium stearate in lubricating oil or by preparing the magnesium stearate in oil, and adding to this grease, at a temperature of approximately 210 F. to 250 F., a concentrated aqueous solution of sodium hydroxide and/ or sodium carbonate. Apparently metathesis occurs forming the sodium stearate and releasing magnesium in the form of the hydroxide and/or carbonate which remains dispersed or complexed in, and becomes a part of the final grease composition.

Thus, it is an object of this invention to provide a water-resistant modified alkali metal soap grease and particularly a modified sodium soap grease, which grease has in addition to exceptional water resistance, the desirable characteristics of relatively high melting point, stability at high temperature, mechanical stability and reversibility and stability to oil separation.

A further object of this invention is to provide a method for the preparation of a modified alkali metal soap grease and particularly a sodium soap grease, which method results in the production of a grease having exceptional water resistance in addition to the usual characteristics of alkali metal soap greases.

In preparing greases of this invention, an alkaline earth metal soap grease, as for example, a magnesium stearate grease or concentrate of magnesium stearate in oil, such as one containing between about and about 50% by weight of magnesium stearate in an SAE 30 solvent-treated Western paratfinic mineral lubricating oil, is first produced by conventional procedures, i. e. either by dissolving magnesium stearate which has been separately prepared in the lubricating oil or by forming the magnesium stearate in the oil, as for example, by reacting so prepared are either costly berates atent iii 2,831,812 Patented Apr. 22 1958 stearic acid with magnesium hydroxide in a small amount of oil and subsequently adding additional oil to provide the concentration desired. The grease or concentrate so prepared is heated to a temperature of approximately 215 F., i. e., within the range of about 210 F. to 250 F. and to the heated grease, with agitation, is added a concentrated aqueous solution of at least one equivalent of sodium carbonate and/or sodium hydroxide per equivalent of magnesium stearate present in the grease. Preferably, the amount of alkali metal compound added will be between about one and about two equivalents per equivalent of magnesium stearate or other alkaline earth metal soap. Following the addition of the aqueous hydroxide and/or carbonate, additional oil may be added to produce a finished grease of the desired soap content at a temperature of approximately 265 F. while the mix ture is being agitated and the resulting product then heated to a maximum of 325 F. Following this heat ing the mixture is cooled with agitation to room temperature. As is well known in the art, antioxidants and/or dispersing agents may be employed. Thus, oil-soluble organic amines, such as phenyl alpha-naphthylamine, phenyl betanaphthylamine and diphenylamine may be added as oxidation inhibitors. Compounds, such as fatty acid and related esters of polyethylene glycols, N-substituted fatty acid amides, the substituents being polyethylene glycol groups, glycerine and similar materials may be used as dispersing agents.

The properties and characteristics of greases prepared according to the procedure described hereinabove have been determined using usual test methods applicable to greases and the water resistance has been determined using various test methods. One method is to place a small lump of the grease, approximately 3 grams, in boiling water and determine the time required to break down or dissolve the grease. Another method of testing consists in placing the grease in a ballbearing assembly and operating the hearing at 600 R. P. M. while directing a stream of water maintained at F. and/or 180 F. against the bearing for a period of 1 hour. In the first test, which will be referred to as the boiling water test, an ordinary sodium base grease containing 20% by weight of sodium stearate completely disintegrated in 2 minutes. In the second test, which will be referred to as the bearing test, the same soda base grease was completely washed from the bearing at 140 F. A commercial sodium base grease prepared from a mixture of tallow and tallow fatty acids was completely washed out of the bearing even at room temperature. On the other hand, greases prepared following the teachings of this invention have been found to be capable of withstanding 1015 minutes or more without appreciable solution or decomposition in the boiling water test and show losses of as low as only a few percent in the bearing test run at 180 F.

Although the greatest advantages are gained by the use of sodium hydroxide and/or carbonate and reacting these compounds with magnesium base greases to produce sodium base greases containing magnesium hydroxide and/ or carbonate in that the greases produced in this manner are relatively cheap and have all of the characteristics desired, including exceptional water resistance, other alkaline earth metal soaps, as for vexample, calcium, strontium and barium soaps, may be substituted for the magnesium soaps. Moreover, potassium hydroxide and/or carbonate may be substituted for the corresponding sodium compounds and the resulting modified potassium greases show improved water resistance over typical potassium base greases and have physical characteristics similar to those obtained with sodium.

3 Lithium hydroxide and/ or carbonate may, of course, be substituted for the corresponding sodium compounds and the resulting modified lithium base greases have all of the desirable characteristics of the sodium greases of this invention. v

It is to be noted that some variation occurs in the resulting greases where the various alkaline earth metal soaps are employed. Thus, it is to be noted'that the greases prepared by reacting sodium or other alkali metal carbonate and/or hydroxide with calcium, barium or strontium soap greases, are in some instances not as water resistant as those prepared using magnesium soap greases although the water resistance of these greases is far superior to the water resistance of the corresponding alkali metal grease and thus such compositions form a part of this invention.

The preferred composition is a grease prepared by reacting a magnesium base grease with sodium hydroxide and/or carbonate. Moreover, greases which are substantially equivalent to grease prepared in this manner are prepared by reacting alkali metal hydroxide and/or carbonates with a mixed grease in which the soap constituent contains at least about 20% by weight of magnesium soap in combination with calcium, tium soap, preferably at least about 50% by weight of the magnesium soap should be employed. Furthermore, where calcium, barium and strontium base greases are employed alone or in combination with magnesium, it is preferable to employ the alkali metal carbonate rather than the hydroxide since usually greater water resistance is obtained in the resulting grease.

Although stearic acid is shown as the saponifiable material to be employed, other fatty acid materials may be substituted for stearic acid, provided the fatty acid materials contain at least about 90 to 95% by weight of saturated high molecular weight fatty acids. Other acids and acid mixtures which may be employed, therefore, include hydrogenated fatty acid mixtures, such as hydrogenated tallow fatty acids, hydrogenated fish oil acids and the like. It is to be noted that greases prepared using oleic acid, which is an unsaturated acid, do not possess the water resistance desired. However, a grease prepared using 90% stearic acid and oleic acid does have a water resistance substantially equal to that obtained using stearic acid alone. Where the percentage of oleic acid is permitted to rise above about 10% the resulting greases show inferior water resistance.

barium or stron- Fatty acids having hydroxyl substituents may also be employed. Thus, 12-hydroxy stearic acid is a satisfac tory soap stock although there does not appear to be any appreciable advantage in employing such hydroxy fatty acid materials over the corresponding non-hydroxy fatty acid.

The following examples illustrate various aspects of the invention but it is to be understood that the invention is not to be limited to the particular combinations of metals indicated in these examples nor to the specific conditions set forth. In many of the compositions shown in the examples the dispersing agents are referred to as Ethofats or Ethomids. These compounds are made by Armour Chemical Division, Armour and Company, Chicago, Illinois. The Ethofats are mono-fatty or resinacid esters of polyethylene glycols. Ethofat 242/25 is a rosin fatty acid ester of polyethylene glycol having ap proximately 15 ethylene glycol units per molecule.

the-fat 60/ i5 is a stearic acid ester of polyethylene glycol having approximately 5 ethylene glycol units per molecule. .Ethomid C/25 is an N-substituted coco fatty acid amide, the substituents being polyethylene glycol having approximately 15 ethylene glycol units per molecule.

Example I A grease was prepared using the following materials: Grams Magnesium stearate 282 Sodium hydroxide (97%) 41.5 Ethofat 242/25 1S grams of water was added dropwise while mixing. A

heavy dough formed as the sodium hydroxide was being added. The product was mixed and heated while adding the remainder of the mineral oil and then heated to a temperature of 325 F. At this point, the phenyl alphanaphthylamine was added and the grease cooled to room temperature while mixing. The finished grease had an A. S. T. M. worked penetration of 335 at 77 F. and contained 18.5% by weight of soap calculated as sodium stearate. A small lump of this grease broke down after 15 minutes in the boiling water test. In the bearing test the loss was 2.5% at F. and 42.1% at 180 F.

Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1050 The magnesium oxide was slurried with 300 grams of mineral oil, stearic acid was added and the mixture heated to 285 F. At this point Ethcfat was added together with an additional 100 grams of mineral oil and the mixture cooled to 240 F. The sodium carbonate, dissolved in grams of hot water, was then added slowly while mixing and when a heavy dough formed, heating was resumed. At 265 F. an additional 400 grams of mineral oil was added as rapidly as the mixture would absorb it smoothly and following the completion of the oil addition, the temperature was raised to 325 F. The grease was then cooled while adding the phenyl alpha-naphthylamine and the remaining oil, and mixingwas continued until the grease reached room temperature. The grease prepared in this manner had an A. S. T. M. penetration of 298 at 77 F. and contained 20.6% by weight of soap calculated as sodium stearate. A small lump of this grease did not entirely break down after 1 hour in the boiling water test and in the bearing test the loss at 180 F. was 4.8%. The dropping point of the grease determined by the rapid dropping point method was 330 F.

Example 111 A grease was prepared from the following materials using a procedure similar to that described in Example ll.

The resulting grease had a worked A. S. T. M. penetra tion at 77 F. of 292, a rapid dropping point of 360 F. and contained approximately 19.5% soap calculated as sodium stearate. The loss in the bearing test was 23% at 180 F.

Example IV Example III was repeated with the exception that Ethofat 60/ and the phenyl alpha-naphthylamine were eliminated from the composition. The resulting grease was very similar to that produced in Example III. In the bearing test at 180 F. the loss amounted to 24%.

Example V A grease was prepared from the following materials using the procedure set forth in Example II.

Grams Stearic acid 270 Magnesium oxide 40 Sodium carbonate (anhydrous) 55 Sodium hydroxide (97%) 12 Ethofat 60/15 15 Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1700 The sodium hydroxide was added as an aqueous solution immediately after the addition of sodium carbonate. The resulting grease had a worked A. S. T. M. penetration at 77 F. of 286, a rapid dropping point of 380 F., and contained 14.1% by weight of soap calculated as sodium stearate. A small lump of this grease did not completely dissolve in boiling water in 1 hour. The loss in the bearing test at 180 F. was 23.8%.

Example VI For purposes of comparison with the grease made using steaiic acid, a grease similar to that prepared in Example V was made using olcic acid in place of the stearic acid. The resulting grease was typical of those which have been prepared with unsaturated fatty acids as the only acids present in the composition. The grease was prepared with the following materials following the procedure out- 1 A Western solvent-treated paratfinic mineral lubricating oil.

The resulting product had a worked A. S. T. M. penetration of 275 and a soap content calculated as sodium oleate of 18.5%. This grease showed losses of 92% and 81%, respectively, in the hearing test at 180 F.

Example VII A grease was prepared from the following materials using the procedure outlined in Example III.

Grams Stearic acid 270 Calcium hydroxide (90%) 22 Magnesium oxide 22 Sodium carbonate (anhydrous) 55 Sodium hydroxide (97%) H 12 Ethofat C/ 15 15 Phenyl alpha-naphthylamine 6 SAE lubricating oil 1300 This grease had an unworked A. S. 'l. M. penetration of 274, a rapid dropping point of 330 F. and contained 17.6% by weight of soap calculated as sodium stearate. The loss in the hearing test at 180 F. was 0.74%.

Example VIII A grease was prepared using the following materials Grams Stearic acid 270 Calcium hydroxide 42 Sodium carbonate (anhydrous) 55 Ethofat 60/15 l5 Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1400 This grease had a worked A. S. T..M. penetration of 290 and contained 16.7% by weight of soap calculated as sodium stearate. The loss in the bearing test at F. was 2%. This grease sample showed some oil separation on standing.

Example IX A grease was prepared from the following ingredients:

Grams Hydrogenated fish oil acids 310 Calcium hydroxide (90%) 33 Sodium carbonate (anhydrous) 55 Sodium hydroxide (97%) 16 Ethomid C/25 15 Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1300 Theresulting grease had a Worked A. S. T. M. penetration at 77 F. of 290 and contained 19.3% by weight of soap calculated as sodium soap. the loss amounted to 36% at 180 F.

Example X A grease prepared as described in Example Iii using an equivalent amount of potassium carbonate in place of the sodium carbonate was a water resistant grease.

Example XI A grease prepared as described in Example III substituting an equivalent amount of lithium hydroxide for the sodium carbonate showed a loss of less than 10% in the bearing test at 180 F.-

Example XII For purposes of comparison with the greases of this invention, a grease was prepared in which a sodium soap grease was first formed and to the sodium grease was added approximately one equivalent per equivalent of sodium soap of magnesium hydroxide. The following materials were employed:

In the hearing test Grams Stearic acid 270 Sodium hydroxide (97%) 42 Magnesium hydroxide 30 Ethofat 60/ 15 15 Phenyl alpha-naphtylamine 6 SAE 20 lubricating oil 900 A mixture of stearic acid, Ethofat and 400 grams of oil was heated to 210-220 F. and to this solution was added a solution of the sodium hydroxide in approximately 55 grams of water. Heating and mixing was continued to effect saponification and then the magnesium hydroxide slurried in 38 grams of water was added slowly while agitating the grease mixture. The heating and mixing was continued while the temperature was increased to 265 F. and at this time the remainder of the oil was added. The resulting product was heated to 332 F,

e phenyl alpha-napthylamine added and the batch cooled to room temperature while continuing the mixing.

The resulting grease contained approximately 23% by weight of soap calculated as sodium soap, had a rapid dropping point of 365 F. and an A. S. T. M. penetration at 77 F. of 300. In the bearing test the grease was completely washed out of the hearing at 180 F It will be seen from the above that a soda base grease containing magnesium hydroxide prepared by adding the magnesium compound to the sodium grease is not water resistant and requires a higher soap content to give -a grease of the same physical characteristics as those prepared by metathesizing magnesium base greases with sodium hydroxide or carbonate.

In the above description and in the above examples it is shown that the aqueous solution of alkali metal hydroxide or carbonate is added to the alkaline earth metal grease at a temperature within about 210 F. and 250 F. It is to be pointed out, however, that this temperature range is not critical and that the addition may be made at lower or higher temperatures. The indicated range, however, is the preferable range, in that at tempera tures below about 210 F. the alkaline earth metal grease is too stiff to work readily in a kettle and thus it is difiicult to obtain the desired dispersion of the aqueous solution in the grease. Moreover, at temperatures above about 250 F. it is sometimes more difiicult to control foaming.

Following the addition of aqueous hydroxide or carbonate, the final grading with oil is shown to be accomplished at a temperature of about 265 F. Again this temperature is not critical since the final quantities of oil may be added at temperatures higher or lower than the indicated temperature without alfccting the characteristics of the finished grease. This particular temperature is merely a convenient temperature at which to carry out this operation. At about this temperature or at higher temperatures the grease seems to absorb oil more readily than at lower temperatures.

It is to be noted also that the maximum temperature to which any of the greases shown were heated has been indicated to be about 325 F. The object of heating to about this temperature is to remove water since it is desired that the finished grease be substantially anhydrous, i. e., that it contain less than about 1-2'% by weight of water and preferably less than 0.5% water. Greases prepared following the principles of this invention, which have been heated to as high as 400 F. and then cooled while mixing, have been found to have the same characteristics, including high water resistance, as corresponding compositions heated to only 325 F. Moreover, it is not necessary to heat to a temperature as high as 325 F. to effect dehydration, providing the heating period is extended to insure reasonably complete removal of water. Thus, entirely satisfactory greases have been finished at temperatures as low as 300 F.

The percentage of soap, calculated as the alkali metal soap, in the final grease compositions of this invention will generally be between about 10% and about 30 or 40% by weight of the total composition although lower soap contents, such as about have been found to be satisfactory in some cases. The amount of antioxidant to be employed may vary between 0.1% and about 1% by weight and the amount of dispersing agent may vary between about 0.1% and about 1.5% by weight, however, as indicated above-the use of these auxiliary agents is not an essential feature of the invention. These auxiliary agents may be added at any point in the procedure, however, generally the antioxidant will be added along with, or following, the addition of the final quantities of oil.

I claim:

1. A water-resistant grease prepared by reacting a mixture of mineral lubricating oil and alkaline earth metal soap of fatty acids containing at least about 90% by weight of saturated high molecular weight fatty acids with an aqueous solution of between about 1 and about 2 equivalents, per equivalent of alkaline earth metal soap, of a compound selected from the class consisting of alkali metal hydroxides and carbonates and heating the resulting mixture to remove water.

2. A water-resistant grease consisting of mineral lubricating oil containing between about 5% and about 40% by weight of soap prepared by reacting an alkaline earth metal soap grease with between about 1 and about 2 equivalents, per equivalent of alkaline earth metal soap, of an alkali metal compound selected from the class consisting of alkali metal hydroxides and carbonates in the presence of a small amount of water and heating the resultant product to eflect dehydration, said alkaline earth meal soap being a fatty acid soap in which said fatty acid is at least about saturated high molecular weight fatty acid.

3. A grease according to claim 2 in which said alkaline earth meal soap grease is a magnesium soap grease.

4. A grease according to claim 2 in which said alkali metal compound is a sodium compound.

5. A grease according to claim 4 in which said sodium compound is sodium hydroxide.

6. A grease according to claim 2 in which said alkali metal compound is a potassium compound.

7. A grease according to claim 2 in which said alkaline earth metal soap contains at least about 20% by weight of magnesium soap.

8. A grease according to claim 2 containing also between about 0.1% and about 1.5% by weight of a dispersing agent of the class consisting of esters of polyethylene glycols, polyethylene glycol-N-substituted fatty acid amides and glycerine.

9. A grease according to claim 2 containing also between about 0.1% and about 1% by weight of an oilsoluble organic amine as an antioxidant.

10. A water-resistant, modified sodium base grease consisting of mineral lubricating oil containing between about 5% and about 40% by weight of a soap prepared by reacting a mixture of oil and magnesium soap of substantially saturated high molecular weight fatty acids with between about 1 and about 2 equivalents of sodium hydroxide per equivalent of magnesium soap in the presence of a small amount of water and heating the resulting product to efiect dehydration.

11. A method of preparing a water-resistant grease which comprises reacting a mixture of mineral lubricating oil and alkaline earth metal soap of fatty acids containing at least about 90% by weight of saturated high molecular weight fatty acids with an aqueous solution of between about 1 and about 2 equivalents, per equivalent of alkaline earth metal soap, of a compound selected from the class consisting of alkali metal hydroxides and carbonates and heating the resulting mixture to remove water.

12. A method of preparing a water-resistant grease which comprises reacting an alkaline earth metal soap grease, consisting of mineral lubricating oil containing between about 5% and about 40% of alkaline earth metal soap, withbetween about 1 and about 2 equivalents, per equivalent of alkaline earth metal soap, of an alkali metal compound selected from the class consisting of alkali metal hydroxides and carbonates in the presence of a small amount of water and heating the resultant product to effect dehydration, said alkaline earth metal soap being a fatty acid soap in which said fatty acid is at least about 90% saturated high molecular weight fatty acid.

13. A method according to claim 12 in which said alkaline earth metal soap grease is a magnesium soap grease.

14. A method according to claim 12 in which said alkali metal compound is a sodium compound.

15. A method according to claim 14 in which said sodium compound is sodium hydroxide.

16. A method according to claim 14 in which said sodium compound is sodium carbonate.

17. A method according to claim 12 in which said alkali metal compound is a lithium compound.

18. A method according to claim 12 in which said fatty acid comprises hydroxy stearic acid.

19. A method according to claim 12 in which about 0.1% to about 1.5% by weight of a dispersing agent of 9 the class consisting of esters of polyethylene glycols, polyethylene glycol-N-substituted fatty acid amides and glycerine is added at some point in the preparation.

20. A method according to claim 12 in which about 0.1% to about 1% by weight of an oil-soluble organic amine is added at some point in the preparation.

10 References Cited in the file of this patent UNITED STATES PATENTS Clarke Nov. 26, 1940 Morway et a1. July 4, 1950 Peterson May 5, 1953 OHalloran June 9, 1953 OHalloran July 21, 1953

Claims (1)

1. A WATER-RESISTANT GREASE PREPARED BY REACTING A MIXTURE OF MINERAL LUBRICATING OIL AND ALKALINE EARTH METAL SOAP OF FATTY ACIDS CONTAINING AT LEAST ABOUT 90% BY WEIGHT OF SATURAATED HIGH MOLECULAR WEIGHT FATTY ACID WITH AN AQUEOUS SOLUTION OF BETWEEN ABOUT 1 AND ABOUT 2 EQUIVALENTS, PER EQUIVALENT OF ALKALINE EARTH METAL SOAP, OF A COMPOUND SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL HYDROXIDES AND CARBONATES AND HEATING THE RESULTING MIXTURE TO REMOVE WATER.