Thickener component and lubricating grease containing an aluminium complex

Abstract

This invention relates to a thickener component based on an aluminium carboxylate compound and to an aluminium complex grease made therefrom with addition of a base liquid.

Description

[0001] This invention relates to a thickener component based on an aluminium carboxylate compound and to an aluminium complex grease made therefrom with addition of a base liquid.

[0002] Aluminium complex greases have been known. They essentially comprise a mineral-oil base liquid and a thickener system containing one or more aluminium carboxylate compounds. The aluminium carboxylate compound is obtained by reacting a fatty acid and/or an aromatic carboxylic acid with an aluminium alcoholate derivative. The industrially used aluminium alcoholates comprise aluminium isopropoxylate and tri-oxy-aluminium-triisopropoxide. In theory, the reaction proceeds as shown hereinbelow: 1

[0003] When using aluminium isopropoxylate, partial hydrolysis is performed with water before, during, or after reaction of the acids with aluminium alcoholate to produce the usually required free —OH group on the aluminium. Aluminium complex greases are distinguished by a high dropping point, good conveyance and water resistance, and low separation of oil.

[0004] It is an object of this invention to provide more effective aluminium complex greases, in particular more suitable thickener components for manufacturing thickeners for aluminium complex greases. The term ‘more effective’ shall mean that the grease exhibits better lubricating properties than conventional aluminium complex greases. Furthermore, it is desired that the thickener component employed for making said aluminium complex greases be storable and marketable as such, thus enabling the grease manufacturer to produce the thickener-containing grease himself.

[0005] According to this invention, the problem has been resolved by providing a thickener component comprising

[0006] (A) from 99.99 to 94 weight percent, preferably 99.9 to 97 weight percent of an aluminium compound which can be prepared by reacting a hydrolysable aluminium compound with one or more aliphatic monocarboxylic acid(s) or aliphatic derivatives thereof, optionally in the presence of water and/or a C1- to C40-alcohol, thereby forming one or more aluminium compound(s) having at least one aluminium carboxylate bond per aluminium atom and, in addition, one or more aluminium-, hydroxy-, aluminium alcoholate-, or/or aluminium-oxygen-aluminium bond(s) and

[0007] (B) from 0.01 to 6 weight percent, preferably 0.1 to 3 weight percent of an ester compound having from 6 to 60 carbon atoms,

[0008] each referring to the total of components (A) and (B).

[0009] The term ‘hydrolysable aluminium compounds’ as used herein refers to aluminium compounds that are capable of forming aluminium-oxygen bonds by the action of proton-donating compounds, such as water or organic acids. Preferably, such hydrolysable aluminium compounds are aluminium alcoholate- or aluminium-oxo-alcoholate compounds with the alcoholate group preferably being a C2- to C4-alcohol, particularly isopropanolate. The carboxylic acids can be branched or unbranched aliphatic monocarboxylic acids of the type R1—COOH, wherein R1 represents a C10- to C40-radical, preferably a C14- to C24-radical, or a C16- to C24-radical.

[0010] Carboxylic acid derivatives as used herein are defined as compounds which are capable of forming in combination with said aluminium compounds the aluminium-carboxylate bonds that would likewise be obtained when using the corresponding acids. Examples thereof include the anhydrides, acid chlorides, or amides of the aforesaid carboxylic acids.

[0011] Ester compounds as used herein particularly refer to compounds which may be formed by reaction of the alcohols/alcoholates present in the reaction mixture with the carboxylic acids/carboxylate residues.

[0012] The thickener component is prepared by reaction, preferably about equimolar reaction, i.e. about 1 mole of monocarboxylic acid per mole of aluminium atoms in the compound, of a hydrolysable aluminium compound with one or more of the abovementioned carboxylic acid(s) or carboxylic acid derivative(s) at a temperature not exceeding 145° C., most preferably 135° C., with a temperature profile most preferably increasing gradually by at least 20° C. during a period of at least 90 minutes being ensured. It is preferred that the hydrolysable aluminium compound be placed in the vessel first.

[0013] Moreover, it is preferred that the reaction be carried out in a base liquid and the volatile compound released during the reaction, e.g. alcohol, be withdrawn from the equilibrium.

[0014] The term ‘thickener’ as used herein is defined as a compound or mixture of compounds prepared from the thickener component, which thickener can be produced by reacting the thickener component with aromatic or cyclic monocarboxylic acids of the type R2—COOH, wherein R2 represents a C6- to C16-radical, or with the derivatives thereof. Said (aromatic or cyclic) carboxylic acid derivatives are defined as described hereinabove.

[0015] The resultant aluminium compound preferably has more than 40 mole % of aliphatic monocarboxylic acid radicals, referring to the amount of carboxylate groups (100 mole %=all the carboxylate groups). The remainder is comprised of aromatic or cyclic monocarboxylic acid radicals.

[0016] As used herein, the term ‘aromatic monocarboxylic acid’ is defined as a carboxylic acid which has at least one benzene ring or condensed benzene ring and, in addition, may comprise aliphatic hydrocarbn radicals as well. Hence, compounds such as C6H5—CH2—CH2—COOH or CH3—CH2—C6H4—COOH are explicitly included herein.

[0017] The thickener as a constituent of the aluminium complex grease is produced by compounding the thickener component, optionally taken up in additional base liquid, with the aromatic or cyclic monocarboxylic acid.

[0018] The production process of the invention yields a raw material (thickener component) with a low ester content for making the real thickener that keeps its low ester content even upon storage.

[0019] Besides the thickeners of the invention the aluminium complex greases of the invention also comprise a base liquid which is a hydrocarbon compound and/or a synthetic oil added to the overall composition in quantities of from 30 to 98 weight percent, preferably 60 to 95 weight percent.

[0020] The hydrocarbon compound can be a paraffin-base or naphthenic mineral oil, a polyalphaolefin, or a white oil. Further synthetic oils which are suitable as base liquid include fatty acid esters based on mono- or multifunctional fatty acids having a chain length of from 8 to 24 carbon atoms and mono- or polyhydric alcohols. Additional constituents of the aluminium complex greases of the invention may be typical additives. Table 1 presents examples of suitable additives.

[0021] The thickener components of the invention are useful as raw materials for producing thickeners included in aluminium complex greases exhibiting improved lubricating properties. They are preferably employed in high-temperature applications for which high dropping points are especially desirable, in central lubricators, and/or for lubricating machinery used for example for producing or processing foodstuffs.

[0022] The prior art thickeners based on aluminium carboxylate compounds or the aluminium complex greases made therefrom have significantly higher ester concentrations. Surprisingly, compositions with lower ester concentrations, preferably less than 6% in the thickener component, and improved lubricating properties have now become accessible by the process.

[0023] It is preferred that the thickener components as well contain 20 to 80 weight percent, most preferably 30 to 70 weight percent of the base liquid described hereinabove.

EXAMPLES OF TESTS

[0024] Table 2 shows the rheometric values (Physica UDS 200, oscillating measurement, deformation=0.2%, frequency=0.1 Hz, temperature=20° C., plate/plate distance=1 mm) of aluminium complex greases of the invention. Example 4 presents a high ester concentration, whereas the ester concentration in Example 5 (comparative example) is too high. The measurements were made on a thickener component having an aluminium content of 4.1 weight percent. The solvent in the aluminium-containing thickener component is identical with the base oil. The starting material is aluminium isopropanolate. The aliphatic monocarboxylic acid employed herein is a technical-grade stearic acid mixture.

[0025] Exemplary Synthesis

[0026] Into a 5-litre agitated vessel equipped with a nitrogen supply line, a 30-cm column (metalized, packed with Raschig rings), and a reflux condenser there are placed 1.466 moles (299.5 g) of DOROX® D 10 (aluminium triisopropylate, liquid) and 500.0 g of Sera® 100 mineral oil (approx. 50 wt. % paraffin-base oil). The educts are heated to 97° C. (bottom temperature) while stirring. The stearic acid is heated to 75-80° C. to keep the product liquid upon feeding. 1.466 moles (393.5 g) of the liquid stearic acid (acid number=209 mg of KOH/g) and the mixture of water (1.372 moles=24.7 g) and 2-propanol (123.6 g) are charged steadily and simultaneously through separate submerged pipes during a period of 2.5 hours.

[0027] The released 2-propanol is removed overhead (head temperature max. 85° C.). The bottom temperature is gradually increased to 127° C. during this period. Once the bottom temperature reaches 127° C., the pressure is reduced to 200 hPa during 20 minutes and the remainder of the low-boiling 2-propanol is drawn off. During the reaction a distillate comprised of 3.623 moles (217.7 g) of 2-propanol is removed from the reaction and the mixture (123.6 g). The product, oxo-aluminium-stearate, is obtained after purification and filtration. The total residence time of the product at 127° C. is 30 minutes (until end of vacuum phase). Filtration is performed at approx. 120° C. using a 60-μm sieve.

[0028] The material parameters of the thickener component have been compiled in Table 3.

	TABLE 1
	Concentration
	Range, wt. %
Extreme-pressure	2-10	dibenzyldisulfide with chlorinated
additives		paraffins; sulphurized fatty
		oils or terpenes
Additives for	0.1-5	diisopropyl- or dilauryl
enhancing		hydrogen phosphite
film resistance
Rust-inhibiting	0.5-5	sodium petroleum sulfonates or
additives		barium dinonyl naphthalene sulfonate
Copper	0.05-1	2-mercaptobenzthiazol
deactivators
Viscosity index	0.1-1	polymethacrylates
improvers
Desludgers	0.001	silicone oils
Additives for	0.5-2	polymers
producing
ropiness
Antiwear	0.1-2	tricresylic phosphate, zinc
additives		dialkyl dithio-phosphate
Additives for	0.1-2	oil- or other vegetable fatty acids
producing
water resistance
Deodorants	0.05-0.5	perfumes
Anticorrosion	0.5-3	nonylphenoxy vinegar,
additives		ethylenediamine sulfonate, lead
		dinonylnaphthyl sulfonate,
		barium sulfonates,
		lead- and zinc naphthenates
Oxidation		diphenylamine, phenyl-
inhibitors		α-naphthylamine,
		dioctyldiphenylamine,
		phenothiazine, polymeric
		trimethyldihydroquinoline, 2,6-di-
		tert-butyl-4-methylphenol, lead
		diamyl-dithiocarbamate,
		dilaurylthiodipropionate-1/
		citric acid, ascorbic acid

[0029]

TABLE 2
					Base Liquid
				Ester Con-	Concentra-	Thickener	Benzoic
		Base Liquid	Base Liquid	centration in	tion in	Component	Acid Con-
		Viscosity	Concentration	Thickener	Thickener	Concentration	centration in	Modulus of	Modulus of
		at 40° C.	in Grease	Component	Component	in Grease	Grease	Elasticity	Viscosity
No.	Base Liquid	mm2/s	wt. %	wt. %	wt. %	wt. %	wt. %	Pa	Pa
1	Paraffin-based	100	91.3	1.4	60	7.3	1.4	860	330
	mineral oil
2	Paraffin-based	100	87.1	1.4	60	10.9	2.0	5,720	1,030
	mineral oil
3	Paraffin-based	100	82.8	1.4	60	14.5	2.7	35,100	5,400
	mineral oil
4	Paraffin-based	100	87.1	3.9	60	10.9	2.0	1,100	270
	mineral oil
5	Paraffin-based	100	87.1	8.7	60	10.9	2.0	800	170
	mineral oil
6	Naphthene-based	100	87.1	1.2	50	10.9	2.0	5,820	1,000
	mineral oil
7	Naphthene-based	40	87.1	1.2	50	10.9	2.0	2,680	450
	mineral oil
8	Polyalpha-olefin	30	91.3	2.4	60	7.3	1.4	290	60
9	Polyalpha-olefin	30	87.1	2.4	60	10.9	2.0	2,100	290
10	Polyalpha-olefin	30	82.8	2.4	60	14.5	2.7	13,300	1,100

[0030]

TABLE 3
			Method
Al content	4.1	%	M 635
Turbidity	20	FNU	DIN 38404 T2
Viscosity (25° C.)	1,500	mPa · s	DIN 53015
Viscosity (100° C.)	100	mPa · s	Rotation (200 s−1)
Pour point	16	° C.	DIN ISO 3016
2-Propanol concentration	3.5	%
Density (20° C.)	0.94	g/cm3	DIN 51757
Density (40° C.)	0.93	g/cm3	DIN 51757
Density (50° C.)	0.93	g/cm3	DIN 51757
Flash point	190	° C.	DIN 51758
Colour number	10		DIN 6162

Claims

1. A thickener component comprising (A) from 99.99 to 94 weight percent of an aluminium compound which can be prepared by reacting a hydrolysable aluminium compound with one or more aliphatic monocarboxylic acid(s) or derivatives thereof, optionally in the presence of water and/or a C1- to C40-alcohol, thereby forming one or more aluminium compound(s) having at least one aluminium carboxylate bond per aluminium atom and, in addition, one or more aluminium-, hydroxy-, aluminium alcoholate-, or/or aluminium-oxygen-aluminium bond(s) and (B) from 0.01 to 6 weight percent of an ester compound having from 6 to 60 carbon atoms, each referring to the total of components (A) and (B).

2. The thickener component of claim 1, characterised in that the hydrolysable aluminium compound is an aluminium alcoholate- or aluminium-oxo-alcoholate compound.

3. A thickener component according to any one of the preceding claims, characterised in that the aliphatic monocarboxylic acid is a branched or unbranched aliphatic monocarboxylic acid of the type R1—COOH, wherein R1 is a C10- to C40-radical, preferably a C14- to C24-radical, or a derivative of this monocarboxylic acid.

4. A thickener component according to any one of the preceding claims, characterised in that a temperature of 145° C., preferably 135° C., is not exceeded during the production of the aluminium compound by reacting a hydrolysable aluminium compound with one or more carboxylic acid(s) or carboxylic acid derivative(s).

5. The thickener component of claim 4, characterised in that an increasing temperature profile presenting a temperature difference of at least 20° C. is maintained at a time interval of at least 90 minutes during the reaction.

6. An aluminium complex grease comprising the composition according to any one of the preceding claims and, in addition, a base liquid which is a hydrocarbon compound and/or a synthetic oil and which is added to the total composition in quantities of from 30 to 98 weight percent, preferably 60 to 95 weight percent.

7. The aluminium complex grease of claim 6, characterised in that the base liquid has a viscosity of from 20 to 200 mm2/s at 40° C. measured in accordance with DIN 51562.

8. The aluminium complex grease of claim 6, characterised in that the base liquid is a mineral oil with a boiling point of greater than 250° C.