DE102009005021B4 - Lubricant and its use - Google Patents

Abstract

Lubricant containing organic compounds and nanometer particles, characterized in that the organic compounds are at least one mesogenic compound selected from compounds of the general formula Iaworin A, a 1,4-cyclohexylene group in which one or two CH groups can be replaced by -O-, a mono- or di-substituted by a halogen or alkyl radical-substituted 1,4-phenylene group, a 1,4-bicyclo [2.2.2] octylene group, pure alkyl Group of 1 to 20 carbon atoms, in which also one or up to seven non-adjacent -CH groups are replaced by -O-, one or two non-adjacent -CH groups by -CO-, -COO-, -OOC- may be or H, and is a pure alkyl group having 1 to 17 C atoms, and is 1- (4-methyl-phenyl) -decane-1,3-dione, 1- (3,4-dimethyl-phenyl) -heptane 1,3-dione, 1- (4-octadecyl-phenyl) -pentane-1,3-dione, 1- (4-ethylphenyl) -eicosane-1,3-dione, 1- (4-butylphenyl) - tetradecane-1,3-dione, 1- (4-nonyl-phenyl) -4-cyclohexyl-butane 1,3-dione, 1- (4-ethyl-phenyl) -nonane-1,3-dione, and that the nanometer particles are oxides of silicon, titanium, zirconium, or aluminum, and sulfides of molybdenum or aluminum Tungsten is, wherein the proportion of mesogenic organic compounds 20 to 99.9 percent by mass and the proportion of nanometer particles 0.1 to 10 percent by mass.

Description

It is known that sliding bearings lubricated with isotropic oils containing mesogenic compounds which have a liquid-crystalline phase below the operating temperature experience a considerably lower friction loss compared with plain bearings operated with conventional oils ( R. Eidenschink et al., Mol. Cryst. Liq. Cryst. 330, 327 (1999) ; A. Kailer et al. in friction, wear and wear protection . A. Fischer, K. Bobzin Eds., Wiley-VCH, 2008). This so-called "hydrodynamic effect" with coefficients of friction μ <0.005 is observed after having formed by an initial abrasion of the bearing material in the regime of mixed friction with the usual coefficients of friction of 0.2 to 0.02 friction surfaces, which then in further operation under otherwise the same load and relative speed of the bearing parts not worth mentioning Show abrasion. This behavior is unknown in conventional, non-mesogenic lubricants.

It is well known that nanometer particles can be used to reduce the coefficients of friction in conventional non-mesogenic lubricants. A similar behavior of such lubricants described above hydrodynamic effect is also not known.

The object of the present invention was to improve the general technical applicability of the isotropic lubricants containing mesogenic compounds so that the unusually low coefficients of friction show less abrasion until such an ideal friction pairing within a plain bearing or even such a running-in phase is required. The latter would allow the production of machines with plain bearings operated with coefficients of friction <0.005, where under the same operating conditions with conventional lubricants friction coefficients must be accepted which are up to two orders of magnitude higher.

The present invention surprisingly achieves the object by adding nanometer particles to isotropic oils containing mesogenic compounds. It is achieved a significant reduction in abrasion in a sliding bearing until the achievement of the hydrodynamic effect. It can also be shown that some mesogenic lubricants only provide this effect by the addition of nanometer particles. Furthermore, it has been found that the lubricant according to the invention also tolerates fractions of non-mesogenic compounds which are essential in tribology, which considerably increases its technical applicability.

In this invention, a compound is considered to be mesogenic if it can form enantiotropic or monotropic liquid crystalline phases as a pure substance. These phases, which unlike isotropic liquids have directional physical properties, are well known (See Handbook of Liquid Crystals, Vol. 1, Eds. D. Demus, J. Goodby, GW Gray, H. -W. Spiess, V. Vill, Wiley-VCH, Weinheim 1998) , The so-called kalamitic phases formed by compounds with elongated molecules are known as nematic, smectic or cholesteric. Compounds with discus molecules can form discoid phases. The phase membership is determined by the temperature and the pressure. Moreover, within the invention, compounds are considered to be mesogenic, although they have none of these phases in the pure substance, but their mixtures with liquid-crystalline compounds show liquid-crystalline phases in wide concentration ranges. Compounds of the general formula I below are considered to be mesogenic within the invention because their molecules are shortened by a 1,4-phenylene or 1,4-cyclohexylene group compared to those of known liquid-crystalline compounds. Within the invention, compounds of the formula II below are also regarded as mesogenic, which, although they do not exhibit a discoid phase in pure substance, give discoid phases in mixtures with the known discoidic representatives of the sixfold-substituted benzenes, cyclohexanes or triphenylenes. These include representatives with triply, quadruply and six-fold substituted benzene, cyclohexane and triphenylene rings.

The use of lubricants used in their liquid-crystalline phase has long been described ( FR 2 525 626 A1 ). In contrast, the oils of the invention containing mesogenic compounds are isotropic liquids. The hydrodynamic effect achieved with them may be due to a shearing-induced transition from the isotropic to a liquid-crystalline phase or to a molecular arrangement which approximates that in such a phase (see R. Eidenschink, Mol. Cryst Cryst., 461, 71 (2007)). Due to the known law of thermodynamics existing dependence of the transition temperatures on the pressure (depending on the transition enthalpy between 0.2 and 0.5 ° C per N / mm ² ), which prevails in plain bearings, the behavior is not explainable. The mesogenic oils of the invention exhibit at atmospheric pressure a liquid crystalline phase below 20 ° C, preferably below -15 ° C.

DE 196 11 466 A1 relates to the use of sulfur-containing aromatic compounds as lubricants to reduce friction losses in gearboxes and machine bearings.

DE 195 43 185 A1 relates to liquid-crystalline lubricating greases for plain bearings containing 2-40% by mass of nanoparticles as non-molecular disperse substances in 60-98% by mass of liquid-crystalline medium from compounds having 1,4-cyclohexylene or 1,4-phenylene groups.

US 2008/0194441 A1 relates to a lubricant composition comprising at least one mesogenic structure polymer in the main or side chain and at least one thickener component.

worin

ein Cyclohexan- oder Benzol-Kern, R₃ jeweils unabhängig voneinander eine Alkyl-Gruppe mit 1 bis 20 C-Atomen, deren H-Atome ganz oder teilweise durch F-Atome ersetzt sein können und in der eine oder bis zu sieben -CH₂-Gruppen durch -O- ersetzt sein können, und eine, zwei oder drei -Y-R₃ auch H bedeuten können, und Y -COO- oder -S bedeuten.To achieve the object, mesogenic organic compounds of the general formulas I and II proved to be fundamentally suitable: R ₁ -A ₁ -Z- (A ₂ ) n R ₂ wherein A ₁ , A _{2 are} each independently a 1,4-cyclohexylene group in which also one or two -CH ₂ groups may be replaced by -O-, a one or two times with a halogen or alkyl radical Substituted 1,4-phenylene group, a 1,4-bicyclo [2.2.2] octylene group, R ₁ , R ₂ each independently represent an alkyl group having 1 to 20 carbon atoms, in which also one or bis to seven non-adjacent -CH ₂ groups may be replaced by -O-, one or two non-adjacent - CH ₂ groups by -CO-, -COO-, -OOC-, H, Z -CH ₂ CH ₂ -, -COO -, -OCO- or the single bond, n means zero, one or two, and

wherein

a cyclohexane or benzene nucleus, R _{3 are} each independently an alkyl group having 1 to 20 carbon atoms, whose H atoms may be wholly or partially replaced by F atoms and in which one or up to seven -CH ₂ Groups can be replaced by -O-, and one, two or three -YR _{3 can} also be H, and Y is -COO- or -S.

wobei R₁ und A₁ die obengenannte Bedeutung haben und R₄ eine Alkyl-Gruppe mit 1 bis 17 C-Atomen ist, in der auch eine bis zu sechs nichtbenachbarte -CH₂-Gruppen durch -O- ersetzt sein können, und wobei 6 C-Atome auch einer Cyclohexyl-Gruppe angehören können.For the invention, however, only those compounds of the formula I which are compounds of the formula Ia are claimed here

wherein R ₁ and A _{1 have} the abovementioned meaning and R _{4 is} an alkyl group having 1 to 17 carbon atoms, in which also one to six non-adjacent -CH ₂ groups may be replaced by -O-, and wherein 6 C atoms may also belong to a cyclohexyl group.

wobei R₁, R₂, A₂, n und Z die obengenannte Bedeutung haben.In addition, compounds of the general formula Ib which are not subject to the invention are described here,

wherein R ₁ , R ₂ , A ₂ , n and Z have the abovementioned meaning.

In the compounds of general formula I, R ₁ and R ₂ each independently of one another preferably represent an alkyl group having 1 to 20 C atoms. Preferably, they are unbranched and are preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, hexadecyl, octadecyl and eicosyl. In formula Ia, the alkyl groups included by methyl bis heptadecyl are also preferably unbranched.

The compounds of the formula Ia are known to be in equilibrium with their preferred keto-enol form. The compounds of the general formula Ia can be prepared by a well-known Claisen condensation of a substituted acetophenone and a carboxylic acid ester in the presence of strong bases, exemplified in the 1- (4-methyl-phenyl) -decane-1,3-dione leading synthesis scheme 1:

worin die Bedeutung von R₁ als H besonders hervorzuheben ist und R₄ die obengenannte Bedeutung hat.Other exemplary compounds prepared according to Synthetic Scheme 1 are 1- (3,4-dimethylphenyl) -heptane-1,3-dione, 1- (4-octadecyl-phenyl) -pentane-1,3-dione, 1- (4-ethyl -phenyl) -eicosane-1,3-dione, 1- (4-butyl-phenyl) -tetradecane-1,3-dione, 1- (4-nonyl-phenyl) -4-cyclohexyl-butane-1,3- dion. The compounds of the formula Ia, owing to their tautomeric equilibrium, can form salts and complexes which are counted within the scope of the invention as mesogenic compounds. Suitable representatives of the formula Ia can also be prepared by generally known condensation reactions of 4-alkylcyclohexyl-methyl-ketones with alkyl carboxylates to give 1- (4-alkylcyclohexyl) alkane-1,3-diones. Further 1,3-diketones of the general formula I are the known, not encompassed by the invention liquid-crystalline cyclohexyl derivatives

in which the meaning of R _{1 is to} be particularly emphasized as H and R _{4 has} the abovementioned meaning.

Compounds of formula Ib are well known. These include the connection classes

The di-substituted cyclohexylene groups of the compounds of formula I preferably have the trans configuration.

A not included in the invention, already used for mesogenic lubricant compound class of the formula II ( DE 196 11 466 ) is represented by the general formula IIa:

Not encompassed by the invention are hexakis [thioalkyl] benzenes in which R _{3 are} each, independently of one another, unbranched alkyl groups having 4 to 12 C atoms.

Further compounds of the general formula II not encompassed by the invention are the esters of trimesic acid IIb and cyclohexane-hexacarboxylic acid IIc, which are obtainable by generally known esterification methods, starting from the commercially available acids.

oberhalb von 40°C eine diskoid-flüssigkristalline Phase hat.Mixtures containing a minor proportion of the compounds referred to herein as mesogen and a major portion of known liquid crystalline compounds can form liquid crystalline phases. Thus, mixtures of 20% of a compound of the formula Ia with 80% of the known representative of the formula Ic with R ₁ pentyl and R ₄ ethyl have transition temperatures from the nematic to the isotropic phase between 40 and 60 ° C. Compounds of the general formula II are considered to be mesogenic if a mixture of 20 parts by mass of this substance with 80 parts by mass of 11- [pentakis (4-propylphenylethynyl) phenoxy] undecan-1-ol (compound III)

above 40 ° C has a discoid-liquid crystalline phase.

The nanometer particles contained in the lubricant according to the invention can have very different forms and diverse chemical compositions (compare D. Vollath, Nanomaterials: An Introduction to Synthesis, Properties and Application, Wiley-VCH Verlag, 2008, Weinheim). Within the present invention, nanometer particles are particles consisting of devices whose size is less than 100 nm in at least one dimension. For example, zero-dimensional nanometer particles consist of titanium (IV) oxide, aluminum oxide or zirconium (IV) oxide, one-dimensional molybdenum (IV) sulfide or tungsten (IV) sulfide and two-dimensional nanometer particles of thin layers of z. As silicates, such as nanoscale bentonites. All of these are suitable as components of the inventive lubricant. In addition, so-called. Aggregated nanometer particles are suitable, which are composed of spherical primary particles with diameters of less than 100 nm. Examples are the fumed silicic acids or the precipitated silicas, aggregated particles of titanium dioxide. The particles of fumed silicas and o. G. Metal oxides can also be modified on their surfaces in known manner by organic radicals.

The non-mesogenic organic compounds which may be present in the lubricant of the invention are preferably components of conventional lubricants, such as petroleum-derived mineral oils and synthetic oils, such as ester oils, or polyethylene glycol derivatives (see review in Ullmans Enzykl Ed., Vol. 20). The non-mesogenic organic compounds also include conventional additives, such as oxidation inhibitors, detergents, high pressure additives, friction reducers, anti-foaming agents and corrosion inhibitors. The lubrication with greases is widespread. The thickening agents, such as gelling agents or particles of polymers, added to the lubricant to produce a grease-like consistency, are counted among the non-mesogenic organic compounds within the invention. The invented lubricant may be accompanied by inorganic compounds which, like the conventional molybdenum (IV) sulfide, do not belong to the nanometer particles in order to improve the shrinkage properties of the machine bearings.

To prepare the lubricant according to the invention, its components are intimately stirred at room temperature, heated to 80 ° C. with stirring and then cooled to room temperature. To eliminate agglomerates between the nanometer particles, as they occur in particular in fumed silicas, an intensive treatment of the lubricant with ultrasound has proven.

The proportion of mesogenic compounds in the lubricant according to the invention is between 20 and 99.9%. It is preferably between 40 and 99.8%, more preferably between 50 and 99.8%. The proportion of nanometer particles is between 0.1 and 10%. Preferably, the proportion is 0.2 to 5%, more preferably, the proportion of nanometer particles is between 0.2 and 2%. The proportion of non-mesogenic organic compounds can be between 0 and 79.9%. Preferably, a proportion of 1 to 59.8% and particularly preferably from 2 to 49.8%.

The test device (drawing 1a) makes it possible to check the influence of the components of the lubricant according to the invention on the abrasion of the bearing material and the occurrence of the hydrodynamic effect. Based on the so-called Brugger test for testing lubricants in mixed friction area (DIN 51347) at room temperature as ambient temperature, a steel cylinder connected to a pivot bearing (St37 to DIN, diameter 12 mm, total length 200 mm, variable partial lengths I ₁ and I ₂ ) with a weight applied from a mass of 2 kg to a rotating at 3 revolutions per second Steel roller (9S28K to DIN, diameter 25 mm) pressed. The force measured at the point of contact with the roller is 45 N. For a measurement, a few drops of lubricant are sufficient, which are placed in the contact point. In contrast to the Brugger test, the initial surface pressure is lower, but the pattern of abrasion on the steel cylinder is tracked over a much longer time. By stopping the drive of the roller and swinging the cylinder, the abrasion surface can be measured and then tracked by repositioning and renewal of the lubricant, the time course of the expansion of the pattern. The surface A of the abrasion on the cylinder is approximated as a plane ellipse with the axes a and b, which are measured with a measuring magnifier (drawing 1b).

Drawing 2 shows in the form of a diagram the course of the abrasion surface A in mm ² with the time t in h (hours) for some lubricants. The hydrodynamic effect is manifested by the fact that with increasing time no increase of A results. A _h means the limit of the abrasion surface for this case.

The following examples are intended to show that the area A _{h is} reduced when using the lubricant according to the invention in comparison with a lubricant which contains the same mesogenic compounds but without the addition of nanometer particles. Conventional lubricants, even with the addition of nanometer particles, show no hydrodynamic effect under the selected conditions. It also turns out that some lubricants which contain mesogenic organic compounds but behave like conventional lubricants under the above-mentioned conditions only show a hydrodynamic effect by the addition of nanometer particles.

The following examples are intended to illustrate the invention without limiting it. Above and below are percentages by mass. All temperatures are given in ° C.

Example 1 (according to the invention)

A mixture of 20% 1- (4-ethyl-phenyl) -nonane-1,3-dione and 80% 1- [4- (4-trans-pentyl-cyclohexyl) -phenyl] -pentane-1,3-dione has a phase transition at 52 ° C. A few drops of a lubricant consisting of 99.8% of 1- (4-ethyl-phenyl) -nonane-1,3-dione and 0.2% of the oxidation inhibitor 2,6-di-tert-butyl-p-cresol (BHT ) are placed in the contact point between the test cylinder and roller of the test device described above (drawing 1). At intervals of between 5 and 12 h, the wear surfaces A are determined (drawing 2, curve a). The lubricant shows a hydrodynamic effect. The limit value for the abrasion surface A _h is 6.0 mm ² . A lubricant consisting of 98.8% of the same diketone, 0.2% BHT and 1.0% of the fumed silica Aerosil 380 (Evonik Degussa GmbH) with a mean diameter of the primary particles of 7 nm as nanometer particles is one above zero ° C isotropic cloudy liquid which, when allowed to stand for 48 h, does not show any sedimentation of the fumed silica particles with the naked eye. The resulting under the conditions described above Abriebflächen A can be seen from drawing 2, curve b. A _h results in 2.2 mm ² , which means a significant reduction compared to the nanometer particle-free lubricant.

Example 2 (not according to the invention)

A 20% solution of hexakis [thiooctyl] benzene in Compound III has a (monotropic) transition between the isotropic and a discotic phase above 40 ° C. in the above-described test device lubricated with this pure compound, a hydrodynamic effect results for an area A _h of 11.2 mm ² . A lubricant consisting of 99.8% hexa-kis [thiooctyl] benzene and 0.2% Aerosil 380 is a supercooling liquid which can be supercooled down to -15 ° C. and gives a limit of the area A _h at 7.1 mm ² in the test apparatus ,

Example 3 (not according to the invention)

A lubricant consisting of 99.8% of the compound 4- (trans-4-heptyl-cylohexyl) -pentylbenzene (transition from the smectic B phase to the isotropic phase at 18 ° C) and 0.2% BHT shows in the aforementioned Testing device no hydrodynamic effect, because the abrasion surface increases even after 65 h (Figure 2, curve c). A lubricant consisting of 97.8% of the same hydrocarbon, 0.2% BH% and 2.0% of the carbon black special black 4 (Evonik Degussa GmbH) with a mean diameter of the primary particles of 25 nm as nanometer particles, however, shows a limit A. _h of 12.6 mm ² (Figure 2, curve d), which is synonymous with the occurrence of the hydrodynamic effect.

Example 4 (not according to the invention)

The non-mesogenic mineral oil Nujol (Plow, Inc.), which can be used as a lubricant, shows markedly increasing wear surfaces A even after 65 hours under the conditions described above. The same applies to a lubricant consisting of 98% Nujol, 1% Aerosil 380 and 1% special black 4.

Example 5 (not according to the invention)

4,0% trans-1,4-Dipentyl-cyclohexan

4,0% (4-trans-Propyl-cyclohexyl)-4-trans-pentyl-cyclohexylcarboxylat

4,0% trans,trans-4-Ethoxy-4'-propyl-bicyclohexyl

30,0% 1-[4-Methylphenyl]-decan-1,3-dion

3,0% -[4-(4-trans-Pentyl-cyclohexyl)-phenyl]-pentan-1,3-dion 50% Paraffinöl, kinematische Viskosität bei 40°C 52 mm²/s (Sigma-Aldrich, Art. Nr. 18512) 5,0% Multiwall-Kohlenstoff Nanoröhrchen (Außendurchmesser 20-30 nm, Wandstärke 1-2 nm, Länge 0,5-2 µm, Sigma-Aldrich, Art.-Nr. 636495) zeigt bei Abkühlung auf -60°C keine flüssigkristalline Phase. Die unter den obenstehenden Bedingungen in Zeitabständen zwischen 5 und 12 h gemessenen Abriebflächen ergeben einen Grenzwert A_h von 4,1 mm². Ein Schmieröl, das außer den Nanometer-Partikeln dieselben Komponenten in denselben Masseverhältnissen enthält, ergibt ebenfalls einen hydrodynamischen Effekt mit einem Wert für A_h von 6,2 mm².A lubricant consisting of

4.0% trans-1,4-dipentylcyclohexane

4.0% (4-trans-propylcyclohexyl) -4-trans-pentylcyclohexylcarboxylate

4.0% trans, trans-4-ethoxy-4'-propylbicyclohexyl

30.0% of 1- [4-methylphenyl] -decane-1,3-dione

3.0% - [4- (4-trans-pentyl-cyclohexyl) -phenyl] -pentane-1,3-dione 50% paraffin oil, kinematic viscosity at 40 ° C 52 mm ² / s (Sigma-Aldrich, Art. No. 18512) 5.0% multiwall carbon nanotube (outer diameter 20-30 nm, wall thickness 1-2 nm, length 0.5-2 μm, Sigma-Aldrich, Item No. 636495) shows when cooled to -60 ° C no liquid crystalline phase. The abrasion surfaces measured under the above conditions at intervals between 5 and 12 h give a limit value A _h of 4.1 mm ² . A lubricating oil containing the same components in the same proportions in weight apart from the nanometer particles also gives a hydrodynamic effect with an A _h value of 6.2 mm ² .

Claims (7)

Lubricant containing organic compounds and nanometer particles, characterized in that it is at least a mesogenic compound in the organic compounds, which is selected from compounds of general formula Ia

wherein A _{1 is} a 1,4-cyclohexylene group in which also one or two -CH ₂ groups may be replaced by -O-, a mono- or di-substituted by a halogen or alkyl radical 1,4-phenylene Group, a 1,4-bicyclo [2.2.2] octylene group, R _{1 is} an alkyl group having 1 to 20 C atoms, in which also one or up to seven non-adjacent -CH ₂ groups are represented by -O- , one or two non-adjacent -CH ₂ groups can be replaced by -CO-, -COO-, -OOC- or denote H, and R _{4 is} an alkyl group having 1 to 17 C atoms, and 1- (4- Methyl-phenyl) -decane-1,3-dione, 1- (3,4-dimethyl-phenyl) -heptane-1,3-dione, 1- (4-octadecyl-phenyl) -pentane-1,3-dione , 1- (4-ethyl-phenyl) -eicosane-1,3-dione, 1- (4-butylphenyl) -tetradecane-1,3-dione, 1- (4-nonyl-phenyl) -4-cyclohexyl-butane 1,3-dione, 1- (4-ethylphenyl) nonane-1,3-dione. and in that the nanometer particles are oxides of silicon, titanium, zirconium or aluminum and sulfides of molybdenum or tungsten, the proportion of mesogenic organic compounds being 20 to 99.9% by mass and the proportion of nanometer particles being 0 , 1 to 10% by mass. Lubricant after Claim 1 , characterized in that the non-mesogenic organic compounds are components of a mineral oil. Lubricant according to one of the preceding claims, characterized in that its proportion of mesogenic organic compounds is 50 to 99.8% by mass and the proportion of nanometer particles is 0.2 to 2% by mass. Lubricant according to one of the preceding claims, characterized in that it contains 50 to 99.8 percent by weight of one or more mesogenic compounds of the general formula Ia, 0.2 to 2 percent by mass of a fumed silica or of a precipitated silica each having primary particle diameters of 3 to 20 nm contains. Lubricant according to one of the preceding claims, characterized in that it has no liquid crystalline phase at normal pressure above 20 ° C. Lubricant according to one of the preceding claims, characterized in that it has no liquid-crystalline phase at normal pressure above -15 ° C. Use of the lubricant according to one of the preceding claims in slide bearings.

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