LUBRICANT

Abstract

A lubricant containing one or more compounds selected from the keto compounds of general formula 1 in which R1, R2 and X have the indicated significance.

Description

BACKGROUND OF THE INVENTION

This invention relates to lubricants containing mesogenic compounds.

Lubricants which contain mesogenic compounds have long been known (EP 0 330 068). It is assumed that a mesophase, that is to say a nematic, smectic or discotic liquid-crystalline phase, can be induced therein by increasing the pressure or by a lubricating action in machine bearings. Such phases which are formed by compounds with elongated bar-shaped or discoid molecules are generally known (H Kelker, R Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim 1980). Such phase transitions make it possible to avoid in particular in the lubrication gap of plain bearings contacts between the solid bodies which are moving relative to each other. In comparison with conventional lubricants it is possible therewith to achieve an enormous reduction in frictional losses. Thus, under conditions at which coefficients of friction of between 0.2 and 0.1 (typical of mixed friction) were found, coefficients of friction of <0.005 were measured, which are typical for plain bearings operated in the hydrodynamic range (R Eidenschink, Mol. Cryst. Liq. Cryst. 461, 71-81 (2007) and literature quoted therein).

The lubricants which have been known hitherto and which contain substances with liquid-crystalline properties must be produced in an expensive and complicated procedure and with high losses in respect of materials used. Hitherto therefore they could only be used for the lubrication of highly problematical bearings.

BRIEF SUMMARY OF THE INVENTION

The invention concerns a lubricant containing between 20 and 99.9% by mass of one or more compounds of the general formula 1

wherein

X denotes H, F, Cl, —CH₃, —C₂H₅, —OCH₃, R₁ respectively denote independently of each other H, an alkyl residue having a total of between 1 and 18 C-atoms, in which also one or two non-adjacent CH₂ groups can be replaced by —O—, —S— or —CO— and two adjacent CH₂ groups can be replaced by —COO— or —OOC—,

R₂ respectively denote independently of each other an alkyl residue having a total of between 1 and 18 C-atoms, in which also one or two non-adjacent CH₂ groups can be replaced by —O—, —S— and two non-adjacent CH₂ groups can be replaced by —COO— or —OOC—, or the residue

with the above-specified significances for X and R₁ and wherein n is a number between zero and 12 and q is zero or 1,

and machine bearings lubricated therewith.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention was to find the lubricant which can be economically produced from inexpensive starting materials and which nonetheless permits particularly low coefficients of friction in comparison with conventional lubricants, in particular in plain bearings. The compounds of formula 1 above have admittedly been recorded by a Markus formula of an earlier invention (DE 38 10 626) but because of the low ratio of length and diameter of their molecules no liquid-crystalline properties can be assumed by the man skilled in the art, and also a liquid-crystalline phase was never observed in such compounds.

Surprisingly however particularly low coefficients of friction can be achieved in machine bearings by the lubricant according to the invention. An above-indicated phase transition which is induced by shearing actions in the lubrication gap of a bearing is responsible for that surprising effect, in spite of the disadvantageous geometry of the molecules of the compounds of formula 1. It is however also possible that there is an unknown cause in that respect.

The compounds of the general formula 1 can advantageously be produced by a single synthesis step from inexpensive compounds. For that purpose an acetophenone which is dissolved in a carboxylic acid ester can be condensed under the effect of sodium (see DE 29 18 775, synthesis diagram 1).

With the same reaction implementation, starting from an acetophenone and a dicarboxylic acid ester, compounds of formula 1 are also obtained (synthesis diagram 2).

The β-benzoyl carboxylic acid esters also embraced by the invention (see K Matsuki et al, Chem. Pharm. Bull 41, 643 (1993), synthesis diagram 3) can be produced in the same fashion.

R₁ in general formula 1 preferably denotes an alkyl or an alkoxy group with between 1 and 7 C-atoms. They are preferably unbranched.

R₂ in general formula 1 preferably denotes an alkyl or alkoxy group with between 1 and 12 C-atoms, wherein the chains are preferably unbranched.

X in general formula 1 preferably denotes H or —CH₃, of which H is particularly preferred.

The compounds of general formula 1 include the following preferred sub-formulae 1a, 1b and 1c, wherein in the formulae 1b and 1c the significances of X and R₁ are respectively independent of each other.

Thereof compounds of the formulae 1a and 1c are preferred.

Besides compounds of formula 1 the lubricant according to the invention can contain up to 80% of one or more additives. Such additives can be known lubricating oils such as mineral oils produced from crude oil or synthetic oils (see Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition, Vol A15, page 423 ff) and the additives known in tribology such as anti-wear substances, anti-oxidants or anti-seizure substances.

Within the invention those additives which as is known involve a grease-like consistency such as metal soaps or polymers also apply as additives. The latter can act as gel-forming agents or can be present in the form of finely distributed particles such as for example PTFE (polytetrafluoroethylene). Besides lubricating oils therefore the lubricants according to the invention also include lubricating greases.

It is generally known that aryl-substituted 1,3-diketones are predominantly present in the tautomeric keto-enol form 1 in accordance with the diagram:

Within the present invention all tautomeric forms which are present in equilibrium are attributed to the keto compounds of the general formula 1. In the databanks such compounds are referred to in a simplifying fashion as 1,3-diketones and thus also in Example 1 hereinafter. As is known metal compounds (metal complexes) are derived from a keto-enol form. Those compounds are embraced by the present invention. Their general formula can be reproduced as follows:

wherein M^m is a m-valent metal atom and m is a number between 1 and 4.

Thus the structural formula

can be specified for the zinc complex which can be produced from the keto compound from synthesis diagram 1.

Preferred metal compounds are those of lithium, magnesium, titanium, zirconium, chromium, molybdenum, manganese, iron, nickel, copper, zinc and tin, of which those of lithium, magnesium and zinc are particularly preferred. Those compounds are preferably produced by the acetate, the acetyl acetonate complex or an alcoholate of the metal in question being heated with one or more compounds of formula 1 and by the acetic acid which is liberated in that respect or the acetyl acetone or the alcohol being evaporated. Those metal compounds produced from compounds of the general formula 1 can be present in a dissolved form but also in the form of a solid body if the lubricant according to the invention is a lubricating grease. If there are more than one compound of formula 1 there can be metal compounds with different ligands. A proportion of those metal compounds deemed to be within the present invention is that which is obtained when the compounds of formula 1 and possibly also volatile additives are removed from the lubricant by distillation at 180° C. sump temperature under an adequate reduced pressure. The residue comprises the metal compounds according to the invention which are most stable at the sump temperature, and possibly further non-volatile additives. The distinction which is possibly necessary between the metal compounds from the compounds of formula 1 and further non-volatile additives is effected in accordance with generally known analytical methods. A distinction which is possibly necessary between compounds of formula 1 and other volatile additives is also effected in the distillate.

The compounds of general formula 1 can be mixed with other components which are usual in the lubrication art, by simple stirring at ambient temperature.

The lubricant according to the invention contains between 20 and 99.9, preferably between 50 and 99.9 and quite preferably between 70 and 99.9% of compounds of general formula 1 and/or metal compounds produced from those compounds.

The lubricant according to the invention can advantageously be used in the generally known machine bearings which as is known are divided into plain bearings or rolling bearings. Particular advantages are achieved in the lubrication of plain bearings, more specifically those in machines in the textile industry, for example in regard to the needle guides of sewing machines, but also for lubricating pistons of high-speed internal combustion engines.

The following Examples are intended to describe the invention without limiting it. Temperatures are specified in degrees Celsius hereinbefore and hereinafter. Percentages denote percent by mass. Hz denotes the oscillation frequency in 1/s. Within the invention a coefficient of friction is deemed to be particularly low if a coefficient of friction of ≦0.05 can be achieved therewith in the test arrangement described in Example 1, with the specified parameters.

Example 1

The compound produced in accordance with synthesis diagram 1, 1-(4-ethylphenyl)-3-hexyl-1,3-propandion, has a melting point of −1° C. and above that temperature is an isotropic fluid with a kinematic viscosity of 11.7 mm/s² at 23° C. 0.2% of the anti-oxidant 2,6-di-tert.-butyl-p-kresol was dissolved therein.

To demonstrate the attainability of particularly favorable coefficients of friction in plain bearings that lubricant was investigated in a reversing sliding wear contact (Tribometer SRV III, Optimol Instruments Prüftechnik GmbH, Munich). A drop of the lubricant was put on to a flat disk of a diameter of 24 mm and a thickness of 7.9 mm. A cylinder of a diameter of 15 mm and a length of 22 mm was moved thereon (both components involved in the frictional relationship were of steel 100Cr6, corresponding to the Deutsche Industrie Norm DIN 51834) at 90° C. under a load of 50 N at 50 Hz and a stroke of 1 mm at an angle of 10° in parallel relationship with the axis of rotation of the cylinder. After 6 hours of test duration the coefficient of friction had fallen from initially 0.20 to below 0.005. That value was not exceeded up to the time that measurement was broken off after 20 hours. For comparison: commercially available lubricants, with the same parameters in respect of measurement, have coefficients of friction of between 0.2 and 0.1.

Example 2

A lubricant (lubricating grease) produced from:

30% PTFE powder, 5 μm (Dr Tillwich GmbH, Horb) presents particularly low coefficients of friction in plain bearings.

Example 3

A lubricant comprising

80% paraffin oil, with a dynamic viscosity at 20° C. 100-145 mPa·s, CAS 8012-95-1 presents particularly low coefficients of friction in plain bearings.

Example 4

A lubricant comprising

25% paraffin oil, with a dynamic viscosity at 20° C. 100-145 mPa·s, CAS 8012-95-1 presents particularly low coefficients of friction in plain bearings.

Example 5

are brought together and heated for 2 hours with agitation in a vacuum of 10 mbar at 120° C. The lubricant freed of ethanol (a lubricating grease) is of the composition

It presents particularly low coefficients of friction in plain bearings.

Claims

1-5. (canceled)

6. A lubricant containing between 20 and 99.9% by mass of one or more compounds of the general formula 1 wherein with the above-specified significances for X and R1 and wherein n is a number between zero and 12 and q is zero or 1.

X denotes H, F, Cl, —CH3, —C2H5, —OCH3,

R1 respectively denote independently of each other H, an alkyl residue having a total of between 1 and 18 C-atoms, in which also one or two non-adjacent CH2 groups can be replaced by —O—, —S— or —CO— and two adjacent CH2 groups can be replaced by —COO— or —OOC—,

R2 respectively denote independently of each other an alkyl residue having a total of between 1 and 18 C-atoms, in which also one or two non-adjacent CH2 groups can be replaced by —O—, —S— and two non-adjacent CH2 groups can be replaced by —COO— or —OOC—, or the residue

7. A lubricant as set forth in claim 6 wherein it contains between 50 and 99.9% by mass of one or more compounds selected from the keto compounds of general formula 1.

8. A lubricant as set forth in claim 6 wherein it contains between 70 and 99.9% by mass of one or more compounds selected from the keto compounds of general formula 1.

9. A method for reducing frictional losses between mutually moved solid bodies comprising interposing a compound according to claim 6 between the solid bodies.

10. A method for reducing frictional losses between mutually moved solid bodies comprising interposing a compound according to claim 7 between the solid bodies.

11. A method for reducing frictional losses between mutually moved solid bodies comprising interposing a compound according to claim 8 between the solid bodies.

12. A bearing containing a lubricant according to claim 6.

13. A bearing containing a lubricant according to claim 7.

14. A bearing containing a lubricant according to claim 8.