US2754268A - Lubricating grease containing a metal salt of algin - Google Patents

Description

LUBRICATING GREASE CONTAINING SALT on ALGIN No Drawing. Application July 15, '1953, Serial No. 368,222

18 Claims. (Cl. 252-41) A METAL The present invention relates to improved lubricating greases. More specifically, the invention is concerned with lubricating greases having high dropping points and high structural stability to mechanical working over long periods of time at relatively low thickener concentrations. In its broadest aspect, the invention pertains to greases thickened with a soap-type grease thickener which contains a substantial proportion of a metal soap of algin, preferably in the form of a complex with the metal salt of a low molecular weight carboxylic acid.

Prior to the present invention, greases having desirably high dropping points and high mechanical stability to working have been prepared by using the alkali or alkaline earth metal soaps of combinations of high and low molecular weight carboxylic acids. It is also known that these greases require soap contents of at least to exhibit the desired structural stability and freedom from oil separation. As the soap thickeners are diluted with lubricating oil, i. e. as the soap concentration of the grease decreases, the dropping point is materially lowered and semi-fluid products of poor structural stability result.

It has now been found that greases having excellent hi h dropping points and highly desirable structure and stability characteristics at much reduced soap requirements may be obtained by incorporating into the grease thickener at least a substantial proportion of a metal soap, particularly an alkali metal soap, of alginic acid.

Preferably, the alginic acid soap forms all or part of" the high molecular weight fatty acid soap constituent of a thickener of the high molecular weight-low molecular weight complex soap type discussed above.

Alginic acid, more commonly called algin, is a seaweed colloid usually extracted by alkalis from brown algae (Phaeophyta) especially from members of the kelp order (Laminariales). The alginic acids are generally regarded as being hydrophilic colloidal polymers of anhydro-B-D-mannuronic acid units having the structural formula which is generally accepted to be:

COOH H It is not known whether the units have the pyranose or furanose structure, but the former is indicated in view of the excellent stability of alginic acid with respect to hydrolysis and the large negative rotation of the acid.

Natural algin in kelp is probably a combination of calcium alginate and aliphatic acid; it is insoluble in water and easily converted to a water solution of the sodium salt. In commercial preparation procedures the kelp is easily digested with sodium carbonate or hydroxide, the resulting viscous liquor is separated from the residue, and alginic acid is precipitated by the addi- 2,754,268 Patented July 10, 1956 tion of strong mineral acids. Since alginic acid is rather heat unstable whereas its salts or soaps are quite stable, it is generally marketed as sodium alginate. Various methods of producing algins are known to the art. Representative procedures are discussed in Colloid Chemistry Reinhold, New York, 1946, volume VI, pages 629-734. A preferred procedure is disclosed in U. S. Patent 2,036,922 to Clark et al. In general, polymers of anhydro-mannuronic acid and the stereo isomers thereof are suitable in the practice of the present invention.

Some of the advantages of the invention may be realized by using metal soaps, particularly alkali metal soaps of an alginic acid as the sole or essentially sole thickener. Soap concentrations of about 2-15 should be used in this case. However, in accordance with the preferred embodiment of this invention, the alginic acid soap is present in the grease in the form of a complex with a salt, preferably an alkali metal salt of a low molecular weight carboxylic acid. In many cases, it may be desirable to incorporate into the complex a soap of a high molecular weight fatty acid other than alginic acid. Thickeners of this type may contain about 10-75 Wt. percent, preferably about 2550 wt. percent, of algin soap. The low molecular weight acid salts and total high molecular weight acid soaps may be present in equi-molecular proportions. However, the low molecular weight acid may be present in smaller or larger proportions, mol ratios of 1:1 to 3:1 of low to total high molecular weight acids being preferred.

The total complex thickener content may vary within the wide range of about 2-40 wt. percent of the finished grease. It is however a particular advantage of the present invention that excellent greases having high dropping points and high structural stability to mechanical working may be obtained by using substantially less than 10 wt. percent and even as little as 2.5 wt. percent of an alginic acid soap containing-thickener. Complex soap concentrations of about 5-10 wt. percent are, therefore, preferred for most purposes.

The low molecular weight acids to be combined with the alginic acid to form the complex soap thickener of the invention may be any aliphatic carboxylic acid having 1-5 carbon atoms per molecule, such as formic, acetic, propionic, butyric, valeric, furoic, acrylic acids, etc. The preferred low molecular weight acids are formic and acetic acids. High molecular weight fatty acids which may be used together with alginic acid and the low molecular weight acids here specified include saturated or unsaturated fatty acids having 10-30 carbon atoms per molecule, such as hydrogenated fish oil acids, stearic acid, oleic acid, behenic acids, etc., saturated acids having 1822 carbon atoms per molecule being preferred.

Branched chain Oxo" acids, prepared by the Oxo synthesis, are also useful as a component of the high molecular weight acids. In general, these acids may be prepared by any one of several well-known processes, such as by the catalytic reaction of an olefin with carbon monoxide and hydrogen at temperatures in the order of 300 to 400 F., and at pressures above about 1000 p. s. i., using cobalt carbonyl or other suitable catalyst. The resulting branched chain aldehydes or alcohols may then be oxidized or otherwise converted to the Oxo" acids. In general, Oxo acids should be employed along with other high molecular Weight acids in concentrations below about 50% by weight based on the total non-alginic high molecular weight acid constituent.

Metal bases suitable for the formation of complex soaps in accordance with the invention include the hydroxides and carbonates of alkali, alkaline earth and certain other metals, for example, lithium, sodium, potassium, calcium, barium, and aluminum. However, alkali metal bases, particularly the hydroxides of sodium and lithium, which form complex soaps of satisfactory water irisolubility and temperature characteristics, are preferred.

Regarding lubricating oil bases suitable for the greases of the invention, all types of mineral lubricating oils as well as synthetic oils including diesters, complex esters, formals and hydrocarbon polymers having lubricating oil characteristics may be used.

Greases in accordance with the invention may be prepared by preforming the alginic acid soap or soap corn plex with other acids and incorporating the same in the lubricating oil by mechanical mixing. The preformed soap or soap complex may be prepared by neutralizing the alg in'ic acid or mixtures thereof with the other acids to be used by means of substantially stoichiometric amounts of the desired metal base preferably in aqueous solution, recovering the complex soap formed and compounding the same with the lubricating oil at grease-making conditions.

However, the preferred method of the invention involves formation of the soap or soap complex in situ in the lubricating oil in the course of the grease-making process. For this purpose the alginic acid and other high molecular weight fatty acids, if any, may be chargedto a reaction zone and heated together with a portion ofthe molecular Weight acid may be added and the mixture neutralized, preferably with a slight stoichiometrie excess of an aqueous solution or the metal base of about 30-50% concentration. Sufiicient metal base should be used to give the grease a free alkalinity of about 0.1l% as NaOI-I. V p 7 The mixture may then be dehydrated at temperatures of about 250-350 F. When dehydration is substantially complete, further lubricating oil may be added and heating :ontinued to about 450550 F. Thereafter, the grease may be cooled. When temperatures below 300 F. are reached other conventional additives, such as antioxidants, particularly amino compounds, extreme pressure agents containing sulfur, halogen and/ or phosphorus, etc., maybe added in any conventional manner. p

The invention will be further illustrated by the following specific examples.

EXAMPLE I Ingredients Weight percent Alg'inic acid 10.00 Hydrofol Acids 54 2 10.00

Acetic acid (glacial) 4.00 Sodium hydroxide 6.50 Phenyl alpha-naphthylamine 1.00

Blend of naphthenic-type mineral oil distillates having a viscosity of 50 S. S. U. at 210 F. 68.50 floinniercial alginic acid which was a free-ilo'wing fibrous powder. Y

flydrogenated {ishpilacids corresponding in degree of saturation to commercial stearic acid.

Preparation The alginic acid, Hydrofol acid and about' /z of the mineral oil were charged to a grease kettle and warmed to 150 160 F. At this temperature the acetic acid charged followed immediately a 40% aqueous "solution of sodium hydroxide. Heating was continued and at 300 -F'., when the soap mass in the kettle was fairly dry, the balance of the mineral oil'was added. The mix:

ture wa's further heated to about 500 F. At thistemlubricating oil to about l3 l70" F. Thereafter the low 4 Properties Percent free alkalinity as NaOH 0.72. Penetrations, 77 F. mm./ 10:

Unworked 102. Worked, 60 strokes 114. Worked, 100,000 strokes (270 hole worker plate) Too harddid not run. Dropping point, F. 500+. Water Washing test, percent loss None. Norma Hoffmann oxidation test, hours to 5 p. s. i. drop in Oz pressure 210.

EXAMPLE II The grease of Example I was diluted with 100% additional mineral oil by mixing together at F. and then Gaulin homogenizing. The mineral oil employed was a solvent extracted parafiinic-type oil, having low volatility, high viscosity index, and good oxidation resistance with a viscosity of 45 S. S. U. at 210 F. It is not possible to employ this type of mineral oil exclusively as a grease base due to the poor solubility or colloidal dispersibility of the soap in this less polar mineral oil.

Ingredients Weight percent Algini'c acid grease base of Example I 50.00 Additional mineral oil 50.00

or v

V...; Hydrefol-Aeid 54 5.00 Acetic acid 2.00 NaOH 3.25 Naphthenic-t'ype original oil 34.25 Parafliiiic-type additional oil 50.00 Phenyl alpha-naphthylamine 0.50 Properties Appearance of grease Excellent, smooth,

homogeneous. Dropping point, F. 480. Penetrations, 77 F. min/10:

Unworked 233. Worked, 60 strokes 275. Worked, 17,000 strokes (27035 hole v'vo'rker plate) e 280 Water washing test, percent loss 10.

sure 145.

The invention is not limited to the specific figures of the regoing examples. The relative proportions of the -e constituents may be varied withinthe limits indiabove to obtain greases of different consistency and sh as 'is What is claimed is:

1. A lubricating grease comprising a major proportion of a lubricating oil and a minor grease-making proportion of a carboxylic acid metal salt complex grease thickener containing at least 10 wt. percent of a metal salt of algi'nic acidgsaid' metal being selected from the group consisting of alkali metals, alkaline earth metals and aluminum.

2. The grease'of claim 1 in which said complex thickener comprises a carboxylic acid metal salt complex of a metal salt of alginic acid and a metal salt of a low moleculaivqeight earboayli acid.

3. The grease of claim 2 in which said complex thickener cer'npi-is'es a high molecular weight fatty acid soap in addition to-said metal salt of alginic acid and said metal salt of ailo'w molecular weight carboxylic acid.

A bric in r a e m ri n a m PP QP fiQ offa lubricating oil and a minor grease-making proportion of a carboxylic' acid metal salt complex grease thickener c ntaining abgut 10-75 wt. percent of a'rnetal salt-0f alginic acid, said metal being selected from the group consisting of alkali metals, alkaline earth metals and aluminum.

5. A grease as claimed in claim 4 which contains about 2-40 wt. percent of said thickener.

6. A lubricating grease comprising a major proportion of a lubricating oil and about 2-40 wt. percent of a carboxylic acid metal salt complex grease thickener containing at least 10 wt. percent of a metal salt of alginic acid and a metal salt of a low molecular weight carboxylic acid, said metal being selected from the group consisting of alkali metals, alkaline earth metals and aluminum.

7. A grease as claimed in claim 6 in which said complex thickener contains high molecular weight fatty acid soap in addition to said metal salt of alginic acid and said metal salt of a low molecular weight carboxylic acid.

8. A grease as claimed in claim 6 in which said metal is an alkali metal.

9. A grease as claimed in claim 6 in which said low molecular weight acid has 1-5 carbon atoms.

10. A grease as claimed in claim 7 in which said high molecular weight fatty acid has 10-30 carbon atoms.

11. A lubricating grease comprising about 60-98 wt. percent lubricating oil and about 2-40 wt. percent of a carboxylic acid salt complex grease thickener containing about 10-75 wt. percent, based on thickener, of an alkali metal salt of alginic acid, the remainder of said thickener comprising an alkali metal soap of a high molecular weight fatty acid having 18-22 carbon atoms and an alkali metal salt of a low molecular weight carboxylic acid having 1-5 carbon atoms, the mol ratio of low molecular weight acid salt to high molecular weight fatty soap plus alginic acid salt being 1-3.

12. A grease as claimed in claim 11 which contains about -10 wt. percent of said thickener, the latter containing about 25-50 wt. percent of said alginic acid salt.

13. A grease as claimed in claim 11 in which said high molecular weight fatty acid soap is the sodium soap of hydrogenated fish oil acids and said low molecular Weight carboxylic acid salt is sodium acetate.

14. The method of preparing lubricating greases which comprises heating a lubricating oil containing a minor thickening proportion of alginic acid to about F., adding a minor proportion of a low molecular weight carboxylic acid, neutralizing the mixture with sutficient alkali metal hydroxide to give the mixture a free alkalinity of about 0.1-1% calculated as NaOH, dehydrating the mixture at temperatures of about 250- 350" E, further heating the mixture to about 450-550 F., and cooling the mixture.

15. The method of claim 14 in which said lubricating oil is a naphthentic oil and said cooled mixture is diluated with a paraflinic lubricating oil.

16. The method of claim 14 in which-said lubricating oil contains additionally a thickening proportion of a high molecular weight fatty acid having 18-22 carbon atoms.

17. The method of claim 14 in which said hydroxide is sodium hydroxide.

18. A lubricating grease comprising about 90-95 wt. percent of mineral lubricating oil, about 1 wt. percent of an oxidation inhibitor and about 4-9 wt. percent of a complex carboxylic acid salt grease thickener consisting of about 40-42 wt. percent of the sodium salt of alginic acid, about 40-42 wt. percent of the sodium soap of hydrogenated fish oil acids and about 16-20 wt. percent of sodium acetate.

References Cited in the file of this patent UNITED STATES PATENTS 341,072 Stanford May 4, 1886 1,970,902 Brunstrum et a1 Aug. 21, 1934 2,036,922 Clark et al Apr. 7, 1936 2,441,720 Roehner et al. May 18, 1948 2,487,379 Roehner et a1. Nov. 8, 1949

Claims (1)

1. 6. A LUBRICATING GREASE COMPRISING A MAJOR PROPORTION OF A LUBRICATING OIL AND ABOUT 2-40 WT. PERCENT OF A CARBOXYLIC ACID METAL SALT COMPLEX GREASE THICKENER CONTAINING AT LEAST 10 WT. PERCENT OF A METAL SALT OF ALGINIC ACID AND A METAL SALT OF A LOW MOLECULAR WEIGHT CARBOXYLIC ACID, SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS, ALKALINE EARTH METALS AND ALUMINUM.