Lubricating grease of polyurea/high base number calcium sulfonate composite

Abstract

The invention discloses a lubricating grease with thixotropy and a preparation method thereof. The lubricating grease comprises a polyurea/high base number calcium sulfonate composite thickener, colloidally dispersed calcium carbonate solid particles in the form of calcite, a calcium borate or calcium borate composite, and a calcium soap of fatty acid having 12 to 24 carbon atoms. The above components are uniformly dispersed in an oil phase medium. The content of high base number calcium sulfonate in the lubricating grease is less than 22 wt %, and the lubricating grease has a worked cone penetration of 295 or less.

Claims

1. A high performance, thixotropic polyurea/overbased calcium sulfonate complex hybrid grease with a worked cone penetration rating of 295 or less comprising: 70 to 85 wt % oleaginous medium in which there is homogeneously dispersed: 8 to 21 wt % overbased calcium sulfonate complex thickener comprising fine particles of calcium carbonate in calcite form; 0.5 to 6.5 wt % polyurea thickener; 0.05 to 3 wt % calcium borate or calcium borate complex; 0.5 to 3.5 wt % calcium soap of C.sub.12-24 aliphatic fatty acids; and 0 to 3 wt % lime or calcium hydroxide, wherein all percentages are weight % based on the total weight of the grease.

2. The grease as claimed in claim 1 comprising: 75 to 85 wt % oleaginous medium; 10 to 19 wt % overbased calcium sulfonate complex thickener comprising fine particles of calcium carbonate in calcite form; 0.8 to 5 wt % polyurea thickener; 0.1 to 3 wt % calcium borate or a calcium borate complex; 0.8 to 3.5 wt % calcium soap of C.sub.12-24 hydroxy aliphatic fatty acids; and 0 to 3 wt % lime or calcium hydroxide.

3. The grease as claimed in claim 1, wherein the calcium soap of a fatty acid of 12 to 24 carbon atoms comprises a calcium soap of a hydroxy fatty acid of 12 to 24 carbon atoms.

4. The grease as claimed in claim 3, wherein the calcium soap of hydroxy fatty acid of 12 to 24 carbon atoms comprises a calcium soap of hydroxystearic acid.

5. The grease as claimed in claim 1, wherein the calcium soap of C.sub.12-24 aliphatic fatty acids comprises a calcium soap of C.sub.12-24 hydroxy fatty acids.

6. The grease as claimed in claim 5, wherein the calcium soap of C.sub.12-24 hydroxy fatty acids comprises a calcium soap of hydroxystearic acid.

7. The grease as claimed in claim 1, wherein the polyurea thickener is obtained by reaction of a diisocyanate and one or more amine containing compounds.

8. The grease as claimed in claim 7, wherein the diisocyanate comprises 4,4′-diphenylmethane diisocyanate.

9. The grease as claimed in claim 8, wherein the one or more amine containing compounds comprises one or more of octylamine, stearylamine or cyclohexyl amine.

10. The grease as claimed in claim 1 further comprising phenyl alpha-naphthyl amine.

11. A process for preparing the polyurea/overbased calcium sulfonate complex grease of claim 1, the process comprising mixing an overbased calcium sulfonate, a base oil, a C.sub.12-24 fatty acid such as 12-hydroxylstearic acid, water, detergent dodecylbenzene sulfonic acid, boric acid and a carboxylic acids having from 1 to 7 carbon atoms, in a sealed reactor while heating under elevated pressure; venting the reactor and then heating to remove water and volatiles; then adding additional base oil, diisocyanate and one or more amines, heating to effect reaction to form a polyurea thickener and removal of volatiles; and then adjusting the final properties of the grease by adding additional base oil and/or additives, followed by any additional processing steps.

12. The process as claimed in claim 11, wherein after calcite formation and before addition of the polyurea forming components, additional hydroxy stearic acid and/or boric acid, water, and an appropriate amount of lime are optionally added and mixed at temperatures of about 280° F.

Description

DESCRIPTION OF THE INVENTION

(1) The high performance, thixotropic, polyurea/overbased calcium sulfonate complex hybrid greases of the invention comprise:

(2) 70 wt % or more, e.g., 70 to 90 wt % or 70 to 85 wt %, oleaginous medium in which there is homogeneously dispersed:

(3) less than 22 wt %, e.g., 8 to 21 wt %, overbased calcium sulfonate complex thickener comprising fine particles of calcium carbonate in calcite form;

(4) 0.5 to 6.5 wt % polyurea thickener;

(5) 0.05 to 3 wt %, calcium borate or a calcium borate complex;

(6) 0.05 to 5 wt %, e.g., 0.5 to 3.5 wt %, calcium soaps of C.sub.12-24 aliphatic fatty acids; and

(7) 0 to 3 wt % lime or calcium hydroxide from lime or calcium hydroxide not consumed in the reactions during preparation of the grease;

(8) wherein all percentages are weight % based on the total weight of the grease.

(9) In many embodiments, the grease of the invention comprises:

(10) 75 to 85 wt %, or 80 to 85 wt %, oleaginous medium;

(11) less than 21 wt %, e.g., 8 to 20 wt % or 10 to 19 wt %, overbased calcium sulfonate complex thickener comprising fine particles of calcium carbonate in calcite form;

(12) 0.8 to 4.8 or 5 wt % polyurea thickener;

(13) 0.1 to 3 wt % calcium borate or a calcium borate complex;

(14) 0.8 to 3.5 wt % calcium soap of C.sub.12-24 aliphatic fatty acids; and

(15) 0 to 3 wt % lime or calcium hydroxide from lime or calcium hydroxide not consumed in the reactions during preparation of the grease.

(16) At least a portion of the calcium soap of C.sub.12-24 aliphatic fatty acids is formed in situ during conversion of the calcium carbonate to calcite, and preferably all of the calcium soap of C.sub.12-24 aliphatic fatty acids are formed in situ during the processing of the overbased calcium sulfonate during preparation of the grease. More than one type of calcium soap may be present, i.e., calcium soaps of different fatty acids may be present. Preferably the calcium soaps of C.sub.12-24 aliphatic fatty acids comprise calcium soaps of hydroxy C.sub.12-C.sub.24 fatty acids, in particular 12-hydroxystearic acid. It is also more preferred that the calcium borate species is formed in situ during the processing of the overbased calcium sulfonate during preparation of the grease. In some embodiments, the grease may also comprise calcium salts of short chain organic acids having from one to seven carbon atoms.

(17) Various common supplemental ingredients, e.g., antioxidants phenyl alpha naphthylamine and other additives, are often incorporated into the greases of the invention at commonly used levels.

(18) The grease is prepared according to a general process wherein 1) an overbased calcium sulfonate comprising amorphous calcium carbonate starting material in an oleaginous medium, e.g., base oil, is heated in the presence of water, a conversion agent comprising a C.sub.12-24 fatty acid such as 12-hydroxylstearic acid and typically other compounds useful in converting amorphous calcium carbonate to calcite calcium carbonate, such as alcohols, lower aliphatic carboxylic acids, ketones, etc., to convert the calcium carbonate crystal form; 2) calcium salts of boric acid and C.sub.12-24 fatty acids are formed; and 3) an isocyanate compound and one or more amine containing compounds are converted into a polyurea. In preferred embodiments, all of the calcium borates and the calcium soap of C.sub.12-24 aliphatic fatty acids are formed in situ during preparation of the grease starting from an overbased calcium sulfonate starting material.

(19) Typically, the mixture heated during calcite formation also comprises mono- and/or di-alkyl benzene sulfonic acid in which the alkyl groups contain 12 to 40 carbon atoms, and often the mixture of also comprises boric acid.

(20) In some embodiments, additional C.sub.12-24 fatty acids are added, optionally with boric acid and water, after the calcite has been formed, in which case the resulting mixture is heated to effect conversion of the added materials to calcium salts of boric acid and calcium soaps of C.sub.12-24 fatty acids.

(21) It is often convenient to introduce all of the boric acid and/or C.sub.12-24 fatty acids used in the process to the mixture subjected to calcite formation. Where all the boric acid and C.sub.12-24 fatty acids are present during calcite formation step, there is no need for an additional step to prepare the calcium borate and calcium salts, and the product of 1) and 2) above are formed during a single procedure. Typically, the polyurea is formed after the formation of the products of 1) and 2). Additional components, e.g., additional base oil or additives, may be added and other process steps, e.g., kneading or milling the final grease, may be used.

(22) The overbased calcium sulfonates useful in the preparation of the grease of the invention can be prepared by any technique employed in the art. Typically, these materials can be prepared by heating neutral calcium sulfonate or sulfonic acid, oleaginous medium, i.e., a base oil often comprising a mineral oil, hydrated lime and a carbonation promoter, such as methanol, to the carbonation temperature, and adding sufficient carbon dioxide to produce an overbased sulfonate having the desired TBN as described in U.S. Pat. No. 4,560,489. A molar ratio of 0.55-0.6 CO.sub.2/Ca(OH).sub.2 produces an excellent starting material for the production of the greases of the present invention.

(23) The overbased calcium sulfonate can have a metal ratio of about 6 to 40, e.g., 10 to 36. The base oils are, generally speaking, oils obtained by well-known refining procedures from mineral oils or can be derived from mineral oils. The mineral base oils can be of natural or synthetic character, the proportions of calcium sulfonates in the mineral oil can be variable, e.g., 15 to 45%. A semi-crude, unfiltered mineral oil composition containing about 10 to 20% naphtha and varying proportions of mineral oil and neutral calcium sulfonate is readily usable as a charge stock.

(24) Suitable sulfonic acids useful in the production of the calcium sulfonates are oil-soluble and can be produced by sulfonating a linear or branched chain alkyl benzene, such as a mixture of mono-and di-alkyl benzenes in which the alkyl group contains largely from 12 to 40 carbon atoms, generally mixtures of such alkyl groups. The sulfonic acids are conventionally converted to calcium sulfonates by reaction with calcium hydroxide.

(25) The oleaginous medium content of the finished grease, e.g., non-volatile mineral oil or other non-volatile lubricating oil, includes the total amount of all non-volatile oil present, that is, the oil introduced as part of the original overbased calcium sulfonate composition plus any added non-volatile oil. Any base oil useful in the art may be used and more than one lubricating oil may be used. Examples of useful base oils include naphthenic oil, paraffinic oil, aromatic oil, or a synthetic oil such as a polyalphaolefin (PAO), silicon oils, a fluoronated or polyfluoronated derivative of any of these preceding fluids, or combinations thereof. Refined solvent-extracted hydrogenated dewaxed base oil and combinations of such base oils are often used. The viscosity of the base oil can range from 50 to 10,000 SUS at 100° F., e.g., 200 to 2,000 SUS or 300 to 1500 SUS at 100° F.

(26) The polyurea thickeners of the present invention include diureas and higher oligomeric ureas. Diurea thickeners are preferred. Diurea compounds include those obtained through a reaction of one or more monoamine with a diisocyanate compound or one or more diamine with a mono-isocyanate compound, generally diureas prepared from a diisocyanate are preferred.

(27) Representative examples of diisocyanates include phenylene diisocyanate, diphenyl diisocyanate, tolylenediisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. Representative examples of mono-isocyanates include hexylisocyanate, decylisocyanate, dodecylisocyante, tetradecylisocyanate, hexadecylisocyanate, phenyl isocyanate, cyclohexylisocyanate and xyleneisocyanate.

(28) Representative examples of monoamines include pentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, eicosylamine, dodecenylamine, hexadecenylamine, octadecenylamine, octadeccadienylamine, isomers thereof, aniline, substituted anilines, toluidine, naphthylamine, substituted naphthylamines, benzylamine and substituted benzylamines.

(29) Higher oligomeric urea compounds include those obtained through a reaction of a diamine or triamine with a polyisocyante, typically a diisocyanate compound.

(30) Representative examples of diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, dodecanediamine, octanediamine, hexadecanediamine, cyclohexanediamine, cyclooctanediamine, phenylenediamine, tolylenediamine, xylylenediamine, dianiline methane, and ditoluidinemethane; representative triamines include aminoethyl piperazine, diethylene triamine, dipropylene triamine and N-methyldiethylene triamine.

(31) Examples of preferred urea thickeners include those obtained through a reaction of aliphatic amine such as octylamine, stearylamine, cyclohexyl amine, and often a mixture thereof, with a diisocyanate, such as diphenylmethane diisocyanate.

(32) Calcium-soap-forming fatty acids of 12 to 24 carbon atoms useful in the invention include dodecanoic acid, palmitic acid, stearic acid, oleic acid, ricinoleic acid, 12-hydroxystearic acid. The hydroxy fatty acids, particularly hydroxystearic acid, are preferred since they provide greater thickening to the greases than the unsubstituted fatty acids.

(33) Conversion agents, in addition to the calcium-soap-forming C.sub.12-24 fatty acids and boric acid, useful in the formation of calcite include (among many others): water; alcohols, lower aliphatic carboxylic acids, ketones; aldehydes; amines; phosphorus acids; alkyl and aromatic amines; certain imidazoilines; alkanolamines; other boron acids including tetraboric acid; metaboric acid; and esters of such boron acids; and, also, carbon dioxide as such or in combination with water.

(34) Suitable salt-forming acids (complex forming acids) may also be used in preparation of the greases of the present invention, including inorganic acids, such as sulfonic acid, hydrochloric acid, orthophosphoric acids, pyrophosphoric acid, sulfurous acid, boric acid; and organic acids of 1 to 7 carbon atoms, such as formic acid, acetic acid, propionic acid, valeric acid, oxalic acid, malonic acid, succinic acid and benzene sulfonic acid. Boric acid and boric acid formers, however, are preferred since they provide the best grease properties.

(35) In one embodiment of the invention, a polyurea/overbased calcium sulfonate complex grease having a worked cone penetration rating of 295 or less is prepared according to a procedure comprising mixing an overbased calcium sulfonate, a base oil, a C.sub.12-24 fatty acid such as 12-hydroxylstearic acid, water, detergent dodecylbenzene sulfonic acid, boric acid and a carboxylic acid having from 1 to 7 carbon atoms, such as acetic acid in a sealed high pressure reactor while heating, e.g., at temperatures of above 250° F., e.g., between 270 and 300° F., and elevated pressures, e.g., 20-25 psi; venting the reactor with heating to remove water and volatiles; then adding additional base oil, diisocyanate and one or more amines, heating to effect reaction and removal of volatiles; and then adjusting the final properties of the grease by adding additional base oil and/or additives, followed by any additional processing steps.

(36) For example, a grade 2 grease comprising less than 22 wt % overbased calcium sulfonate can be formed by the following procedure:

(37) To a mixture of 34 parts by weight overbased calcium sulfonate (400TBN) comprising amorphous calcium carbonate and 66 parts non-volatile mineral oil is added 1 to 6 parts, e.g., 2 to 2.5 parts detergent dodecylbenzene sulfonic acid; 0.5 to 5 parts, e.g., 1 to 3.5 parts 12-hydroxy stearic acid; 1 to 7 parts, e.g., 2.5 to 5 parts water; and 0.05 to 3.5 parts, e.g., 0.1 to 3 parts, boric acid. After mixing in a pressure reactor, 0.1 to 1 part, e.g., 0.4 to 0.7 part, acetic acid is added and the resulting mixture is heated to temperatures of 250-270° F. developing a pressure of 20 to 25 psi to convert the amorphous calcium carbonate to calcite. Formation of calcite is monitored by the appearance of calcite peaks in the IR at 880 and 705 cm.sup.−1. When calcite formation is complete, additional mineral oil is generally added, e.g., in this case from about 35 to 45 parts mineral oil, to the now thickened reaction mixture, after which 8 to 15 parts, e.g., 9 to 12 parts, 4,4-diphenylmethane diisocyanate is added followed by 4 to 8 parts, e.g., 5.5 to 6.4 parts cyclohexanamine and 3.7 to 7, e.g., 4.4 to 5.4 parts, octodecylamine. Heating is performed to about 280° F. to remove water and volatiles, then cooling is performed to below 250° F. If desired, additional components, such as the antioxidant phenyl alpha naphthylamine, are added and the grease is adjusted to the desired grade by addition of additional mineral oil. In order to obtain a smooth homogeneous grease, the product may then be kneaded or milled. “Parts” refers to relative amounts by weight of a component.

(38) Adjusting the levels of the various components in the processes above to obtain a grease with various levels of the overbased calcium sulfonate, calcium borate, calcium fatty acid soaps and polyurea thickener is well within the skill of the average practitioner in the art.

(39) Alternatively, the grease of the present invention may be prepared by a process similar to the above process except that after calcite formation and before addition of the polyurea forming components, additional hydroxy stearic acid and optionally lime are added and mixed at temperatures of about 280° F. Additional boric acid and/or water may also be added during this alternative step. In a less preferred process, the conversion to calcite is run without boric acid and all the boric acid used in the grease is added during this alternative step.

(40) In certain cases, lime or Ca(OH).sub.2 may be added to the reaction mixture at any stage prior to polyurea formation, but in many cases this is not done. Often after carbonation of the starting overbased calcium sulfonate, or after the conversion of amorphous calcium carbonate to calcite, free dispersed lime or calcium hydroxide may be present.

(41) The foregoing percentages are in terms of wt. %, based on the total weight of the grease, reaction mixture or composition being referred to.

(42) As with many commercial calcium sulfonate greases, the greases of the invention are characterized by good extreme pressure and anti-wear properties, high dropping points, good mechanical stability, salt spray and water resistance, thermal stability at high temperature and other desirable properties, even without additives. Significantly, the greases of the present invention have much lower ash content, making them useful in a wider range of applications, than available calcium sulfonate greases, including high speed applications in automobile and other industries, where lower ash content grease products are desired.

(43) The greases of the present invention are well suited for general use as a lubricant between contacting metals and/or elastomeric plastics. They are multi-purpose greases which equal and, in many cases, outperform other high temperature greases such as polyurea greases and are especially effective in environments with high load situations. A limited selection of possible uses includes CV joints, front-wheel drive joints, universal joints and bearings which are subjected to heavy shock loads, fretting, and oscillating motions and high temperatures such as in steel mills. Furthermore, the greases are conveniently prepared from non-toxic and low-cost materials.

EXAMPLES

Example 1

(44) Three hundred eighty grams overbased calcium sulfonate (400TBN) in 720 grams 1100 SUS viscosity oil, 23.5 grams detergent dodecylbenzene sulfonic acid, 21.5 grams 12-hydroxystearic acid, 50 grams water and 2.6 grams boric acid were mixed in a pressure reactor. After addition of 5 grams acetic acid, the reactor was sealed and heated to 250-270° F., developing a pressure of 20 to 25 psi. After 1 hour, thickening and conversion of amorphous carbonate to calcite was complete as determined by infra-red, the reactor was vented and heated to 260° F. Next, after cooling the reaction mixture to 160° F., 430 grams 1100 SUS viscosity oil and 10.88 grams 4,4-diphenylmethane diisocyanate was added, followed by 6.2 grams cyclohexanamine and 5.5 grams octodecylamine. The resulting mixture was heated to form the diurea thickener, water was removed and the reactants were stripped at 280° F. after which the product was cooled to below 250° F., 13 grams phenyl alpha naphthylamine were added and about 230 grams of 500 SUS viscosity oil was added to adjust the product to yield 1850 grams of a grade 2 grease containing 20.5% starting overbased calcium sulfonate and having a penetration rating between 265-295.

Example 2

(45) The procedure of Example 1 was repeated except that the amount of 4,4-diphenylmethane diisocyanate, cyclohexanamine and octodecylamine added was increased 1.2 times respectively and additional oil was added to adjust the final grease thickness, yielding 2035 grams of a grade 2 grease thickness containing 18.67% starting overbased calcium sulfonate.

Comparison Example A

(46) Three hundred eighty grams overbased calcium sulfonate (400TBN) in 720 grams 1100 SUS viscosity oil, 23.5 grams detergent dodecylbenzene sulfonic acid, 21.5 grams 12-hydroxystearic acid, and 50 grams of water were mixed in a pressure reactor. After addition of 5 grams acetic acid, the reactor was sealed and heated to 250-270° F. developing a pressure of 20 to 25 psi. After 1 hour, thickening and conversion of amorphous carbonate to calcite was complete as determined by infra-red and the reactor was vented and cooled to 200° F. with the addition of 200 grams 1100 SUS viscosity oil. To this mixture, 18.4 grams of additional 12-hydroxylstearic acid was added, the resulting mixture was mixed for 15 minutes, after which 29 grams lime in 50 grams water and 23 grams boric acid in 50 grams water were added. The reaction mixture was then mixed at 280° F., the thickness adjusted to grade 2 with about 180 grams 500 SUS viscosity oil, cooled to below 200° F., and 8.3 grams phenyl alpha naphthylamine were added to yield 1670 grams of a grade 2 grease containing 23.6% starting overbased calcium sulfonate.

(47) The greases from the above Example were subjected to the following tests:

(48) Penetration and prolonged penetration (ASTM D217), Dropping Point (ASTMD2265), 4-ball EP (ASTM D2596); 4-Ball Wear (ASTM D2266); Oil separation (ASTMD6184), Water washout performance (ASTM D1264), Copper Corrosion (ASTM 4048), Salt Fog Corrosion (ASTM B117). The results are shown in the following table.

(49) TABLE-US-00001 Test Example Comparison Example Properties method 1 Example A 2 Appearance Visual Smooth Smooth Smooth Dropping Point ASTM >316 >316 >316 D2265 Worked Cone Penetration, ASTM 280 284 285 60 Strokes, mm/10 D217 Prolonged Penetration ASTM −8 −10 −13 Change, 100K Strokes with D217 20/80 Water, mm/10 Prolonged Penetration ASTM 16 15 18 Change, 100K Strokes, D217 mm/10 4-Ball Wear, mm ASTM 0.38 0.42 0.45 D2266 4-Ball EP, Weld Point, Kg ASTM 400 400 315 D2596 Water Washout at 79 C., ASTM 1.9 3.0 2.31 % loss D1264 Copper Corrosion, grade ASTM 1b 1b 1b D4048 Salt Fog Corrosion, 1 mil ASTM >300 >300 >300 d.f.t., (dry film thickness) B117 hours

(50) It can be seen from the above data, the polyurea/overbased calcium sulfonate grade 2 greases of Examples 1 and 2 of the present invention have similar performance properties to the grease of Comparative Example A; however, the greases of Examples 1 and 2 of the present invention were prepared in higher yield of grease and had lower concentrations of overbased calcium sulfonate, (and lower ash content) than the grease of Comparative Example A prepared using only an overbased calcium sulfate thickener.