Grease composition and bearing

Abstract

The invention provides a grease composition suitable for being packed in roll bearings to be lubricated at elevated temperatures and a bearing in which the above-mentioned grease composition is packed. In the grease composition containing a base oil, a urea-containing thickener and an additive, the additive includes an overbased metal sulfonate and the amount of the overbased metal sulfonate is 0.05 to 1.00 mass % with respect to the total amount of the grease composition. The bearing has the above-mentioned grease composition sealed therein.

Claims

1. A grease composition for bearing comprising a base oil, a urea-containing thickener and a seizing life extending additive, wherein the base oil is alkyldiphenyl ether, the urea-containing thickener is represented by the following formula (1):
R.sup.1NHCONHR.sup.3NHCONHR.sup.2(1) wherein R.sup.1 and R.sup.2, which may be the same or different, represent an aryl group having 6 or 7 carbon atoms, and R.sup.3 is C.sub.6H.sub.4CH.sub.2C.sub.6H.sub.4, C.sub.6H.sub.4, or C.sub.6H.sub.3(CH.sub.3), wherein the seizing life extending additive extends seizing life of the grease composition and comprises an overbased Ca or Na sulfonate, wherein an amount of the base oil is 79.6 mass % or more with respect to the total amount of the grease composition, wherein an amount of the urea-containing thickener is 19 to 20 mass % with respect to the total amount of the grease composition and wherein an amount of the overbased Ca or Na sulfonate is 0.1 to 0.4 mass % with respect to the total amount of the grease composition.

2. The grease composition for bearing of claim 1, wherein the overbased metal sulfonate has a total base number (TBN) of 50 to 500 mgKOH/g.

3. A bearing comprising the grease composition for bearing of claim 1 therein.

4. A bearing comprising the grease composition for bearing of claim 2 therein.

5. The grease composition for bearing of claim 1, further comprising antioxidants having at least one functional group selected from amine functional groups, phenol functional groups and quinolone functional groups.

Description

DESCRIPTION OF EMBODIMENTS

(1) Examples of the metal for overbased metal sulfonate that can be used in the invention include Ca, Na, Ba, Li, Zn, Pb, Mg and the like. Preferably, Ca, Na, Mg and the like can be used. In particular, overbased Ca sulfonates prepared by dispersing finely-divided particles of metal carbonates, metal hydroxides and the like, for example, CaCO.sub.3, Ca(OH).sub.2 in the base oil are preferably used.

(2) The overbased metal sulfonates for use in the invention are generally used as a detergent dispersant for engine oils or the like, and also commonly contained in the greases for the purpose of improvement of rust prevention, extreme pressure properties and anti-flaking properties. The amount of overbased metal sulfonate in the grease composition of the invention is extremely less than that used for the above-mentioned conventional purposes (for example, as in JP Kokai 2002-53884 and JP Kokai 2003-321694).

(3) Until now, there is neither report nor disclosure about extension of the life of grease as a result of the use of a trace amount of overbased metal sulfonate prepared by dispersing metal carbonates and metal hydroxides such as CaCO.sub.3, Ca(OH).sub.2 and the like or finely-divided particles thereof.

(4) The amount of the overbased metal sulfonate is 0.05 to 1.00 mass %, preferably 0.08 to 0.70 mass %, and more preferably 0.10 to 0.40 mass % in the grease composition of the invention.

(5) When the amount is less than 0.05 mass %, the effect will become insufficient. The addition of the overbased metal sulfonate in an amount of more than 1.00 mass % will accelerate the deterioration of base oil by oxidation, which will decrease the seizing life on the contrary.

(6) As the base oil of the grease composition according to the invention any base oils including mineral oils are usable. In addition, a variety of synthetic oils, for example, synthetic ester-based oils including diesters and polyol esters; synthetic hydrocarbon oils including poly -olefin and polybutene; synthetic ether-based oils including alkyldiphenyl ethers and polypropylene glycols; silicone oils; fluorine-containing oils and the like can be used. Those base oils can be used alone or in combination.

(7) The urea-containing thickener used in the invention includes all the urea-based thickeners including diurea. Particularly preferable diurea thickeners may be represented by the following formula (1):
R.sup.1NHCONHR.sup.3NHCONHR.sup.2(1)
wherein R.sup.1 and R.sup.2, which may be the same or different, represent an alkyl group having 6 to 30 carbon atoms, an aryl group having 6 or 7 carbon atoms, or cyclohexyl group; and R.sup.3 is a bivalent organic group, for example, C.sub.6H.sub.4CH.sub.2C.sub.6H.sub.4, C.sub.6H.sub.4, C.sub.6H.sub.3(CH.sub.3) or the like.

(8) The diurea thickener as mentioned above can be obtained by a reaction of an alkyl monoamine such as octylamine, stearylamine, dodecylamine, hexadecylamine or the like, an aryl monoamine such as aniline, p-toluidine or the like, a monoamine such as cyclohexylamine or the like with a diisocyanate such as diphenylmethane-4,4-diisocyanate, 2,4-tolylene-diisocyanate, 2,6-tolylene-diisocyanate or the like. The most preferable thickener is a diurea compound represented by formula (1) wherein R.sup.1 and R.sup.2, which may be the same or different, represent an alkyl group having 6 to 30 carbon atoms or cyclohexyl group; and R.sup.3 is C.sub.6H.sub.4CH.sub.2C.sub.6H.sub.4 or C.sub.6H.sub.3(CH.sub.3).

(9) In the grease composition of the invention the amount of the urea thickener may be preferably in the range of 3 to 20 mass %, more preferably 4 to 15 mass %, with respect to the total amount of the grease composition.

(10) The grease composition of the invention may further comprise general-purpose additives when necessary. Examples of those additives are as follows:

(11) Antioxidant

(12) Amines: phenyl -naphthylamine, alkylated phenyl -naphthylamine, alkylated diphenylamine and the like.

(13) Phenols: hindered phenols such as 2,6-di-tert-butyl-p-cresol, pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and the like.

(14) Quinolines: 2,2,4-trimethyl-1,2-dihydroquinoline polymer and the like.

(15) Rust Preventive

(16) Carboxylic acids and derivatives thereof; alkenylsuccinic anhydride, alkenylsuccinate, half ester of alkenylsuccinate.

(17) Carboxylates; metal (Ca, Ba, Mg, Al, Zn, Na or the like) salts of fatty acids, dibasic acids, naphthenic acid, lanolin fatty acids, alkenylsuccinic acids and the like, or amine salts thereof.

(18) Sulfonates; Ba salt, Ca salt, Zn salt, Na salt or the like of sulfonic acid.

(19) Passivators; sodium nitrite, sodium molybdate and the like.

(20) Esters; sorbitan trioleate, sorbitan monoleate and the like.

(21) Metal corrosion inhibitors; benzotriazole or derivatives thereof, zinc oxide and the like.

(22) Extreme Pressure Agent

(23) Phosphorus-containing compounds; tricresyl phosphate, tri-2-ethylhexyl phosphate and the like

(24) Sulfur-containing compounds; dibenzyl disulfide, a variety of polysulfides and the like.

(25) Sulfur-phosphorus containing compounds; triphenyl phosphorothionate

(26) Organic metal-based extreme pressure agents; Zn, Mo, Sb, Bi salt or the like of dialkyl dithiophosphate, Zn, Mo, Sb, Ni, Cu, Bi salt or the like of dialkyl dithiocarbamate, and the like.

(27) Others, e.g., ashless dithiocarbamate, ashless dithiophosphate carbamate and the like.

(28) Solid Lubricant: Molybdenum Disulfide, Graphite, PTFE, MCA and the Like.

(29) For the purpose of extension of the life, it is required to keep on charging a lubricant into a portion to be lubricated for an extended period of time. In the conventional urea-based grease compositions, however, the base oil tends to deteriorate by oxidation when exposed to severe conditions of high temperatures and high speeds over an extended period of time, and the product thus caused to deteriorate by oxidation mutually reacts with the urea-containing thickener to harden the grease composition. As a result, the grease cannot be satisfactorily charged into the lubricating portions, thereby leading to the problem of seizing.

(30) The grease of the invention comprises a trace amount of overbased metal sulfonate, which can scavenge the generated products inclined to inclined by oxidation of urea grease, to inhibit the grease from hardening. This makes it possible to keep on charging the grease into portions to be lubricated for a long time, thereby significantly extending the life of grease.

Examples and Comparative Examples

(31) The additive was added to a base grease as shown in Examples and Comparative Examples, and the mixture was thoroughly blended and kneaded using a three-roll mill.

(32) Base Grease A

(33) Thickener: aromatic diurea (i.e., a reaction product of tolylene diisocyanate with p-toluidine)

(34) Base oil: alkyl diphenyl ether oil (Moresco Hilube LB-100, made by Matsumura Oil Research Corporation) with a worked penetration of 300

(35) Base Grease B

(36) Thickener: aliphatic diurea (i.e., a reaction product of diphenylmethane-4,4-diisocyanate with octylamine)

(37) Base oil: alkyl diphenyl ether oil (Moresco Hilube LB-100, made by Matsumura Oil Research Corporation) with a worked penetration of 300

(38) Base Grease C

(39) Thickener: aromatic diurea (i.e., a reaction product of tolylene diisocyanate with p-toluidine)

(40) Base oil: poly -olefin oil (Mobil SHE-101, made by Exxon Mobil Corporation) with a worked penetration of 300

(41) Base Grease D

(42) Thickener: lithium stearate

(43) Base oil: poly -olefin oil (Mobil SHF-101, made by Exxon Mobil Corporation) with a worked penetration of 300

(44) To each of the above-mentioned base greases, dialkyl diphenylamine (Irganox L57, made by Ciba Specialty Chemicals) was added as an antioxidant in an amount of 3 mass % with respect to the total mass of the grease composition, and any of the following compounds was further added as the additive:

(45) Overbased Ca sulfonate (BRYTON C-400C, made by Crompton Corporation, with a TBN of 405)

(46) Overbased Mg sulfonate (BRYTON M-400TG, made by Crompton Corporation, with a TBN of 395)

(47) Overbased Na sulfonate (Lubrizol 5318, made by The Lubrizol Corporation, with a TBN of 448)

(48) Test Method for Seizing Life (ASTM D3336 mod.)

(49) The bearing 6204 was charged with 1.8 g of a test grease, and steel plates located on both sides of the bearing were pressed. With the outer ring of the bearing maintained at 180 C., the inner ring was continuously rotated at 10,000 rpm under a load Fa (=Fr) of 67 N. The duration of time was determined until the rotational torque of the bearing became excessive to cause overcurrent of the motor (4 A) or to elevate the bearing temperature by 15 C. or more, which duration was determined to be a seizing life.

(50) Test Results

(51) In addition to the compositions, the test results are shown in Tables 1 and 2.

(52) TABLE-US-00001 TABLE 1 Examples 1 2 3 4 5 6 Base grease A A A A B C Overbased Ca 0.10 0.20 0.20 0.20 sulfonate Overbased Mg 0.40 sulfonate Overbased Na 0.15 sulfonate Test results of 598 744 623 733 623 594 seizing life (hour)

(53) TABLE-US-00002 TABLE 2 Comparative Examples 1 2 3 4 5 6 Base grease A A A B C D Overbased Ca sulfonate 0.02 5.00 0.20 Test results of seizing 298 210 200 180 230 20 life (hour)

(54) The grease compositions according to the invention as shown in Examples 1 to 6, each comprising the urea compound as the thickener and a trace amount of overbased metal sulfonate can exhibit significantly longer seizing life when compared with the grease compositions (of Comparative Examples 1, 4 and 5) containing no overbased metal sulfonate.

(55) The effect by the addition of overbased metal sulfonate becomes conspicuous in the urea-based grease compositions. To be more specific, no effect of the additive was observed in Comparative Example 6 where the thickener employed in Example 2 was replaced by a lithium soap.

(56) It is also confirmed that the effect of extending the seizing life cannot be exhibited when the amount of overbased metal sulfonate is 0.02 mass % as in Comparative Example 2 and 5.00 mass % as in Comparative Example 3.