LUBRICATING GREASE COMPOSITION

Abstract

The present invention aims to improve the extreme-pressure properties and compatibility with seals of lubricating grease compositions used at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required in various kinds of machinery. To this end the present invention provides a lubricating grease composition wherein from 0.1 to 3% by weight of a molybdenum dialkyl dithiocarbamate, from 0.1 to 3% by weight of benzothiazole compounds and from 0.1 to 3% by weight of calcium sulphonates are incorporated in a grease in which a thickening agent is blended in the base oil.

Description

This invention provides a lubricating grease composition, and in particular a lubricating grease composition to be used at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required, such as in the bearings, gears, suspensions, joints and steering gear of domestic electrical appliances, construction machinery, transportation machinery, agricultural machinery, steel-making plant and machinery, and so on.

Hitherto, extreme-pressure greases containing molybdenum disulphide, sulphur-type, phosphorus-type or sulphur/phosphorus-type additives, or organomolybdenum compounds have been employed for greases to be used, for example, in coupling components or ball joints of suspensions and steering gear where oscillating and rotating motions or reciprocating motion occur.

Known examples of such extreme-pressure greases include urea greases containing as their essential constituents sulphurised molybdenum dialkyl dithiocarbamates and sulphur/phosphorus-type extreme-pressure additives comprised of one or a blend of two or more selected from a group comprised of sulphurised oils and fats, sulphurised olefins, tricresyl phosphate, trialkyl dithiophosphates or zinc dialkyl dithiophosphates. See for example Japanese Patent 4-34590.

When greases are used in the aforementioned applications, a sealing material such as a boot or a dust cover is used in order to create a tight seal so that the grease is reliably supplied to the lubrication points and to prevent ingress of muddy water or dust from outside. For this sealing material, chloroprene rubbers, nitrile rubbers, silicone rubbers, polyester-type elastomers, polyolefin-type rubbers and so on are used, but chloroprene rubbers, which have excellent mechanical strength, flexibility, heat resistance and oil resistance and which are low in cost, are used in particular.

However, under the more severe lubricating conditions the values for properties such as elongation and tensile strength are considerably downgraded because of swelling or contraction of the sealing material under effects due to heat, and it no longer performs its function as a seal.

For this reason, not only are the greases required to have a long life and a lubricating action which is capable of improving the extreme-pressure properties and load-bearing characteristics in respect of the lubrication points, an important factor also is that they have excellent compatibility with the sealing material by not damaging the sealing material which is in contact with the grease.

Among the various types of additives added to greases, molybdenum dialkyl dithiocarbamates are thermally stable and compatibility with seals is relatively good, but additives such as the aforementioned sulphurised oils and fats, sulphurised olefins and zinc dialkyl (aryl) dithiophosphates which are used therewith in order to enhance further the lubricating performance of the molybdenum dialkyl dithiocarbamates have a tendency to be detrimental to the seal-resistance properties.

Therefore, this invention is intended to provide excellent grease compositions which have high extreme-pressure properties and which also do not damage sealing material and are superior in regard to compatibility therewith.

By dint of repeated investigations and experiments to improve further the extreme-pressure properties of greases and also to obtain greases with superior compatibility with the chloroprene rubbers that are widely used as sealing material, the inventors have found that blends of specific additives which have a significant effect as regards the aforementioned extreme-pressure properties and compatibility with seals can be obtained.

The present invention provides a lubricating grease composition comprising a base oil, the composition further comprising: (A) from 0.1 to 3% by weight of a molybdenum dialkyl dithiocarbamate; (B) from 0.1 to 3% by weight of one or more benzothiazole compounds; and (C) from 0.1 to 3% by weight of one or more calcium sulphonates.

In particular this invention provides a lubricating grease composition wherein from 0.1 to 3% by weight of a molybdenum dialkyl dithiocarbamate as shown in the undermentioned Formula 1

(where R denotes an alkyl group of from 1 to 24 carbons), from 0.1 to 3% by weight, as a benzothiazole compound, of at least one of 2-mercapto-benzothiazole or a 2-mercapto-benzothiazole derivative as shown in the undermentioned Formula 2

(where R1 denotes an alkyl group having from 1 to 10 carbons or an alkylmercapto group) or N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio)benzothiazole and from 0.1 to 3% by weight of calcium sulphonates are incorporated in a grease in which a thickening agent is blended in the base oil.

The aforementioned molybdenum dialkyl dithiocarbamates used in this invention are known to improve extreme-pressure properties and wear-resistance in greases, but recent years have seen PRTR controlled substances (PRTR Law; Pollutant Release Transfer Register) and a desire to use molybdenum compounds as little as possible, or to use replacement compounds for molybdenum compounds, in view of concerns about the environment and so on.

This invention, as mentioned above, reduces to the utmost the amount of molybdenum dialkyl dithiocarbamates used and, by incorporating with these the aforementioned benzothiazole compounds and calcium sulphonates, is not only capable of improving the extreme-pressure properties but is also capable of improving compatibility between the chloroprene rubber in sealing materials and the grease.

For the base oil of the greases of this invention it is possible to use mineral oils, vegetable oils and synthetic oils such as ester oils, ether oils and hydrocarbon oils, or mixtures thereof.

For the thickening agent optionally but preferably incorporated in the aforementioned base oil it is possible to use lithium soaps, lithium complex soaps and diurea, triurea, tetraurea, polyurea and other urea compounds.

In the aforementioned molybdenum dialkyl dithiocarbamates used in this invention, alkyl groups having from 1 to 24 carbons are preferably used for the alkyl groups, but alkyl groups having from 3 to 18 carbons are preferred.

As specific examples of such molybdenum dialkyl dithiocarbamates mention be made of sulphurised molybdenum diethyl dithiocarbamate, sulphurised molybdenum dipropyl dithiocarbamate, sulphurised molybdenum dibutyl dithiocarbamate, sulphurised molybdenum dipentyl dithiocarbamate, sulphurised molybdenum dihexyl dithiocarbamate, sulphurised molybdenum dioctyl dithiocarbamate, sulphurised molybdenum didecyl dithiocarbamate, sulphurised molybdenum didodecyl dithiocarbamate, sulphurised molybdenum (butylphenyl)dithiocarbamate, sulphurised molybdenum (nonylphenyl)dithiocarbamate, sulphurised oxymolybdenum diethyl dithiocarbamate, sulphurised oxymolybdenum dipropyl dithiocarbamate, sulphurised oxymolybdenum dibutyl dithiocarbamate, sulphurised oxymolybdenum dipentyl dithiocarbamate, sulphurised oxymolybdenum dihexyl dithiocarbamate, sulphurised oxymolybdenum dioctyl dithiocarbamate, sulphurised oxymolybdenum didecyl dithiocarbamate, sulphurised oxymolybdenum didodecyl dithiocarbamate, sulphurised oxymolybdenum (butylphenyl)dithiocarbamate, sulphurised oxymolybdenum (nonylphenyl)dithiocarbamate and mixtures thereof.

For the aforementioned benzothiazole compounds, 2-mercaptobenzothiazole, N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide and 2-(4-morpholinyldithio)benzothiazole exist, for example, and these may be used singly or in mixtures.

The aforementioned 2-mercaptobenzothiazole has previously been proposed as a constituent in metalworking fluids and as a constituent in cutting and grinding process fluids, and 2-(4-morpholinyldithio)benzothiazole has been disclosed as a constituent in aqueous lubricants for use in plastic working of metals.

The aforementioned calcium sulphonates used in this invention may be ordinary calcium sulphonates, and as examples mention may be made of calcium salts of petroleum sulphonic acid, calcium salts of alkyl aromatic sulphonic acids, overbased calcium salts of petroleum sulphonic acid and overbased calcium salts of alkyl aromatic sulphonic acids. Further, these may be used singly or in suitable mixtures.

The amount of the aforementioned molybdenum dialkyl dithiocarbamates to be incorporated in the grease is from 0.1 to 3% by weight, and in respect of the aforementioned 2-mercaptobenzothiazole, N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio) benzothiazole, at least one is preferably incorporated in the order of from 0.1 to 3% by weight and calcium sulphonates in the order of from 0.1 to 31 by weight.

If more than 3% by weight of the aforementioned molybdenum dialkyl dithiocarbamates is incorporated, there may either be no change in effect or the effect may even reverse. The amount to be incorporated is preferably of the order of from 0.5 to 1% by weight.

Also in the case of the aforementioned 2-mercapto benzothiazole, N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio) benzothiazole, if the amount included in the grease is greater than 3% by weight the effect is either the same or even the reverse. Normally, it is preferable to use of the order of from 0.5 to 1% by weight.

For the aforementioned calcium sulphonates, too, the effect is the same, or the reverse, if more than the aforementioned 3% by weight is used. For preference it is appropriate to incorporate of the order of from 0.5 to 1% by weight.

It is possible in the lubricating grease composition of this invention to use also, as appropriate, in addition to the aforementioned blend constituents, additives such as anti-oxidants, rust preventatives, extreme-pressure additives and anti-wear agents.

This invention, as mentioned above, reduces to the utmost the amount used of molybdenum dialkyl dithiocarbamates, which are PRTR controlled substances, and, by incorporating with these the aforementioned benzothiazole compounds, such as 2-mercapto benzothiazole, N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide and 2-(4-morpholinyldithio) benzothiazole, and the aforementioned calcium sulphonates, not only is it capable of improving the extreme-pressure properties but it also improves compatibility between the chloroprene rubber in sealing materials and the grease.

Further, physical changes in sealing material in contact with grease are considered to be due chiefly to two factors. One is that the base oil of the grease and additives penetrate the sealing material and give rise to swelling, thus softening the material. The other is that plasticisers in the sealing material leach into the grease, causing compression and hardening. It is believed that these actions occur when affinity between the thickening agent and base oil and the additives collapses, but in the present lubricating grease compositions which include the aforementioned additives in a good balance it can be conjectured that this will perform the function of inhibiting the swelling and contraction of the sealing material.

EXAMPLES

The invention is explained below by means of examples of embodiment, but the invention is not in any way limited to these.

The lubricating grease compositions of Examples 1 to 5 and Comparative Examples 1 to 11 used to contrast therewith were obtained by proportionately incorporating the base groups and additives shown below and, after adding the various additives to the base greases, by kneading with a three-roll mill and finishing to a uniform consistency.

1. Base Greases

(1) Urea Grease

Diphenylmethane-4,4′-diisocyante (295.2 g) and octylamine (304.8 g) were reacted in a refined mineral oil with a kinetic viscosity of approximately 15 mm²/s at 100° C. (5400 g), until the diurea compound produced was uniformly dispersed and a grease obtained. The amount of the urea compound included was 10% by weight. This urea based grease had a penetration of 283 and dropping point of 263° C. as defined in JIS-K2220 (25° C., 60 W).

(2) Lithium Soap Grease

Lithium-12-hydroxystearate (630 g) was dissolved in a refined mineral oil with a kinetic viscosity of approximately 15 mm²/s at 100° C. (6370 g), until it was uniformly dispersed and a grease obtained. The amount of the lithium soap included was 9% by weight. This lithium soap based grease had a penetration of 268 and dropping point of 198° C. as defined in JIS-K2220 (25° C., 60 W).

2. Molybdenum dialkyl dithiocarbamate (MoDTC): The commercial product called “Molyvan A” of Vanderbilt Ltd. was used.
3. 2-mercaptobenzothiazole
4. 2-(4-morpholinyldithio)benzothiazole
5. Calcium sulphonate: Calcium salt of petroleum sulphonic acid
6. Zinc dialkyl dithiocarbamate (ZnDTC): The commercial product called “Lubrizol 1395” of Lubrizol Ltd. was used.
7. Sulphurised olefin: The commercial product called “Anglamol 33” of Lubrizol Ltd. was used.
8. Calcium salicylate: The commercial product called “M7121” of Infineum Ltd. was used.

The following tests were carried out in respect of the extreme-pressure properties and seal compatibility of the lubricating grease compositions of Examples 1 to 5 and Comparative Examples 1 to 11 shown in Tables 1 to 3, and evaluations were made.

Extreme-Pressure Tests

Test method: Four-ball tests were carried out in accordance with ASTM D2596.

	Test conditions:	Speed	1770 ± 60 rpm
		Duration	10 seconds
		Temperature	Room temperature

Test objective: The weld load (N) was obtained.

Seal Compatibility Tests

Test method: A chloroprene rubber immersion test was carried out in accordance with JIS K6258.
Test conditions: (1) Immersion for 120 hours at 140° C. was carried out in respect of the lubricating grease compositions using a urea based grease.

• • (2) Immersion for 120 hours at 120° C. was carried out in respect of the lubricating grease compositions using a lithium soap.
    Test objective: Elongation change (%) and change in tensile strength (%) were obtained. (JIS K6251)
    Evaluation criteria: If both elongation change (%) and change in tensile strength (%) were within 25% (0˜−25%), an evaluation as satisfactory could be given.

Results of Tests

The test results for the examples and comparative examples are shown in Tables 1 to 3.

Evaluation; discussion

As shown by the results in Table 1, all the Examples 1 to 5 show large values of 3089 N for weld load under extreme-pressure properties, so that it can be seen that the extreme-pressure properties are high. Also, with an elongation change of from −13.8% to −24.9% and a tensile strength change of from −18.5% to −24.2%, all cases are under −25%, so that it can be seen that they have good compatibility with sealing material.

In contrast, as shown by the results in Tables 2 and 3, in the case of Comparative Examples 1, 6, 7 and 11, elongation change was from −12.2% to −16.5% and tensile strength change from −13.8% to −18.6%, in all cases under −25% and so having good compatibility with sealing material, but the weld load was from 1236 N to 1570 N and so extreme-pressure properties were low, so that evidently these would not be suitable as lubricating grease compositions. Also, Comparative Example 9 exhibited a low weld load value of 1961 N and so extreme-pressure properties were low, while elongation change was −35.1% and tensile strength change −37.2%, both under −25%, so that compatibility with sealing material was poor.

Comparative Examples 2, 3, 4, 5, 8 and 10 all exhibited a large value for weld load at 3089 N and so extreme-pressure properties were high, but elongation change was from −36.6% to −62.4% and tensile strength change from −37.2% to −64.3%, in all cases above −25%, so that compatibility with sealing material was evidently poor.

Also, in the cases of Comparative Examples 1 and 7 with base greases alone, as mentioned above there was small elongation change and tensile change strength of the rubber, so that compatibility with sealing material was good, but extreme-pressure properties were low. In the case, too, of an example of the prior art as shown in Comparative Example 2, the extreme-pressure properties were high but elongation change and tensile strength change were large, so that compatibility with sealing material was inferior.

Furthermore, from a comparison of Example 1 and Comparative Example 3, it can be seen that the effect of improving seal compatibility is small with dispersants other than the calcium sulphonates of this invention.

	TABLE 1
	Examples
	1	2	3	4	5
Composition	I Urea grease	97	97
	II Lithium soap grease			97	97	97
	Mo-DTC	1	1	1	1	1
	2-mercaptobenzothiazole	1	0.5	1		0.5
	2-(4-morpholinyldothio)benzothiazole		0.5		1	0.5
	Calcium sulphonate	1	1	1	1	1
	Total, % by weight	100	100	100	100	100
Test	Extreme-pressure	Weld load (N)	3089	3089	3089	3089	3089
results	properties
	Seal compatibility	Elongation change (%)	−13.8	−24.9	−19.7	−19.7	−22.3
		Change in tensile	−21.7	−18.5	−24.2	−22.9	−20.2
		strength (%)

	TABLE 2
	Comparative Examples
	1	2	3	4	5	6
Composition	I Urea grease	100	97	97	97	97	97
	II Lithium soap grease
	Mo-DTC		1	1
	2-mercaptobenzothiazole			1	3
	2-(4-morpholinyldothio)benzothiazole					3
	Calcium sulphonate						3
	Zn-DTP		1
	Sulphurised olefin		1
	Calcium salicylate			1
	Total, % by weight	100	100	100		100	100
Test	Extreme-pressure	Weld load (N)	1236	3089	3089	3089	3089	1570
results	properties
	Seal compatibility	Elongation change	−13.7	−52.6	−36.6	−62.4	−56.7	−12.2
		(%)
		Change in tensile	−15.9	−57.2	−38.9	−64.3	−63.8	−13.8
		strength (%)

	TABLE 3
	Comparative Examples
	7	8	9	10	11
Composition	I Urea grease
	II Lithium soap grease	100	97	99	97	97
	Mo-DTC		1
	2-mercaptobenzothiazole			1
	2-(4-morpholinyldothio)benzothiazole		1		3
	Calcium sulphonate					3
	Zn-DTP
	Sulphurised olefin
	Calcium salicylate		1
	Total, % by weight	100	100	100	100	100
Test	Extreme-pressure	Weld load (N)	1236	3089	1961	3089	1570
results	properties
	Seal compatibility	Elongation change (%)	−16.5	−35.1	−38.2	−58.7	−14.8
		Change in tensile	−18.6	−37.2	−40.5	−62.5	−17.3
		strength (%)

Claims

1. A lubricating grease composition comprising a base oil, the composition further comprising: (A) from 0.1 to 3% by weight of a molybdenum dialkyl dithiocarbamate; (B) from 0.1 to 3% by weight of one or more benzothiazole compounds; and (C) from 0.1 to 3% by weight of one or more calcium sulphonates.

2. A lubricating grease composition according to claim 1 wherein the molybdenum dialkyl dithiocarbamate has the Formula 1 below, wherein R is an alkyl group having from 1 to 24 carbon atoms.

3. A lubricating grease composition according to claim 1 wherein the one or more benzothiazole compounds include at least one of 2-mercaptobenzothiazole, or a derivative thereof having the Formula 2, wherein R1 denotes an alkyl group having from 1 to 10 carbons or an alkyl mercapto group.

4. A lubricating grease composition according to claim 1 wherein the one or more benzothiazole compounds include N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio)benzothiazole.

5. A lubricating grease composition according to claim 1 further comprising a thickening agent.

6. Use of the lubricating grease composition according to claim 1 at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required.

7. Method for improving the lubrication at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required, by using the lubricating grease composition according to claim 1.

8. A lubricating grease composition according to claim 2 wherein the one or more benzothiazole compounds include at least one of 2-mercaptobenzothiazole, or a derivative thereof having the Formula 2, wherein R1 denotes an alkyl group having from 1 to 10 carbons or an alkyl mercapto group.

9. A lubricating grease composition according to claim 2, wherein the one or more benzothiazole compounds include N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio)benzothiazole.

10. A lubricating grease composition according to claim 3, wherein the one or more benzothiazole compounds include N-tert-butyl-2-benzothiazolylsulphenamide, N-cyclohexyl-2-benzothiazolylsulphenamide, N-oxydiethylene-2-benzothiazolylsulphenamide or 2-(4-morpholinyldithio)benzothiazole.

11. A lubricating grease composition according to claim 2 further comprising a thickening agent.

12. A lubricating grease composition according to claim 3 further comprising a thickening agent.

13. A lubricating grease composition according to claim 4 further comprising a thickening agent.

14. Use of the lubricating grease composition according to claim 2 at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required.

15. Use of the lubricating grease composition according to claim 3 at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required.

16. Use of the lubricating grease composition according to claim 4 at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required.

17. Use of the lubricating grease composition according to claim 5 at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required.

18. Method for improving the lubrication at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required, by using the lubricating grease composition according to claim 2.

19. Method for improving the lubrication at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required, by using the lubricating grease composition according to claim 3.

20. Method for improving the lubrication at lubrication points where extreme-pressure properties and seal-resistance properties at high loads are required, by using the lubricating grease composition according to claim 4.