EP2260091A1 - Lubricating grease composition on basis of ionic fluids - Google Patents

Abstract

The invention relates to the use of ionic fluids for the production of water-resistant lubricating grease compositions, which are employed in a temperature range of at least -30°C to at least 180°C and have good anti-corrosion properties.

Description

 Grease composition based on ionic liquids

description

The invention relates to a lubricating grease composition based on ionic liquids, for the protection treatment of components used in the automotive sector, in wind turbines, as well as in processing and working machines and which are exposed to continuous contact with water. In particular, the invention relates to a water resistant lubricating grease composition which is used in a temperature range of at least -30 ⁰ C to at least 180 ⁰ C in order to protect the components provided with this lubricant to oxidation and corrosion.

The development of new grease compositions must be accompanied by the general advancement of the art which places new and higher demands on grease compositions. These requirements, the known compositions are no longer equal. In particular, the

Requirements for use as operating fluids in process and

Working machines in view of the extreme operating conditions, such as high and low temperatures, high speeds enormous.

The use of ionic liquids in lubrication, hereinafter referred to as IL (= lonic liquid), has been intensively studied in recent years. Ionic liquids are defined as materials that consist of Cations and anions are composed and have melting points less than 100 ^C C. Some IL ^'s have considerably lower melting points so that they referred are present at room temperature as liquids, hereinafter referred to as RTIL (= Room Temperature Ionic Liquid). In the field of tribology especially RTIL are interesting as base oils, since salt-like compounds show a particularly low to nonexistent evaporation, as long as no chemical change by decomposition processes occurs. Ionic liquids have an extremely low vapor pressure, are nonflammable and often thermally stable up to more than 260 ⁰ G and, in addition, can be lubricated.

Chenggeng Ye, Weimin Liu, Yunxia Chen and Laigui Yu (Chem. Commun. 2001, 2244-2245) have presented friction and wear tests on ionic liquids. Tribological studies were carried out with 1-methyl-3-hexylimidazolium tetrafluoroborate and 1-ethyl-3-hexylimidazolium tetrafluoroborate. It was found that the tested compounds have a good reduction of friction, good anti-wear properties and a high load capacity.

Japanese Patent Application No. 2005-185718 describes a grease composition containing as a base grease a mixture of an ionic liquid, a thickener and other additives. This grease is used for rolling or ball bearings.

Japanese Patent Application No. 2005-112597 discloses a grease composition used in electronic devices containing an ionic liquid as a base oil and a thickener having a dropping point of 260 ^° C.

Japanese Patent Application No. 2003-376010 relates to a semi-solid grease composition containing as part of a base oil an ionic liquid and thickening agents. This grease composition is suitable for vacuum applications. Japanese Patent Application No. 2005-197958 relates to a lubricating grease composition for rolling bearing machines which contains an ionic liquid as a part of a base oil.

Japanese Patent Application No. 2005-294405 describes an electrically conductive bearing grease used in a printer or a copier and composed of a carbonaceous thickener and a base oil containing an ionic liquid.

In the publications mentioned above, so fats are proposed, which should be suitable for the dissipation of electric currents, for use at high temperatures and / or in a vacuum.

The known grease compositions described above have the following drawbacks from a tribological point of view. Due to the salt-like nature of the ionic liquids, lubricant additives such as antioxidants, antifriction agents, anticorrosion additives, antiwear agents, extreme pressure additives, and the like are, in most cases, insoluble in ionic liquids. However, many tribological applications require that ionic liquids be provided with such additives to improve the properties. However, the development of new additives represents a high technical complexity, so that it is desirable for cost reasons that standard additives can be used in ionic liquids.

Another disadvantage of using the known grease compositions is the tendency to absorb water and / or react with water through the ionic liquids. When anions such as sulfate, chloride, bromide or tetrafluoroborate are present in the ionic liquids, this usually results in water-soluble ionic liquids. In addition, tetrafluoroborate and hexafluorophosphate can form hydrofluoric acid under the influence of water, which can lead to a strong tendency to corrode. This also applies when chloride is present. Yet another disadvantage is that even the use of hydrophobic anions such as bis (trifluoromethylsulfonyl) imide is not sufficient to provide sufficiently water-stable fats from a tribological point of view.

In addition, the low-temperature properties of the ionic liquids used are insufficiently taken into account in the known grease compositions. There are mentioned, for example, in JP 2003- 376010 bis (trifluoromethylsulfonyl) imide-containing ionic liquids with N- Alkylpyridiniumkationen or N ₁ N ^{'Dialkylimidazoliumkationen,} which have a strong tendency to the formation of the supercooled melt. For example, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide is an ionic liquid of low viscosity and high tendency to hypothermia; However, the relevant melting point for tribological applications is -16 ° C (low temperature DSC measurements). For many tribological applications, however, it is necessary that up to -30 ⁰ C and less, a good flowability is vorhangen. Ionic liquids, such as 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, also have the disadvantage that they can spontaneously solidify at low temperatures, which can lead to failure of the lubricated component.

Ionic liquids, for example, the anion

Tris (perfluoroethyl) trifluorophosphate, usually show a lower water absorption capacity than ionic liquids with the bis (trifluoromethylsulfonyl) imide as the anion, but the melting points are higher. Therefore, these are tris (perfluoroethyl) trifluorophosphate containing ^IL's usually from the low-temperature behavior not suitable to be used as the sole base oil for lubricants with good low-temperature behavior.

The object of the present invention is to provide a water resistant, oxidation and corrosion inhibiting lubricating grease composition which can be used over a wide range of application temperatures.

This object is achieved by the use of a grease composition consisting of an ionic liquid as a base oil, - suitable. Standard additives and thickeners. By using ionic liquids in which the hydrophobic anions are combined with cations containing a high proportion of hydrocarbon groups, excellent corrosion protection and water resistance are achieved.

With this combination it is achieved that standard additives are soluble in the ionic liquid. The high proportion of hydrocarbon groups sets the

1 'I

Resistance to oxidation down. As a countermeasure you can use antioxidants. The use of standard antioxidants enhances the thermal / oxidative stability of the grease composition. In addition, it has surprisingly been found that the fats despite a strong oxidation of the ionic liquid in life tests remain in a good lubricious state. The ionic liquids used in this invention have at low temperature DSC experiments, no melting points or glass transitions or other phase transitions above a temperature of -30 ⁰ C, leading to a strong increase in the viscosity of the ionic liquid.

Among these ionic liquids used in the grease composition are the ionic liquids containing as cations a quaternary ammonium cation or a phosphonium cation containing an anion containing fluorine selected from the group consisting of bis (perfluoroalkylsulfonyl) imide, especially Bis (trifluoromethylsulfonyl) imide ,, Tris (perfluoroalkyl) methides, is combined. In the case of the abovementioned anions, individual fluorine atoms can be exchanged for hydrogen. The cations have a sufficiently long hydrophobic alkyl chain, aryl group or alkylaryl group of at least 8 to 25 carbon atoms, and the number of such hydrophobizing groups of the cation must be at least 15 to 60 carbon atoms. Comparable nonpolar groups such as aryl or alkylated aryl groups are also conceivable. In addition, the ionic liquids used in this invention have the viscosity changing phase transitions to below -40 ⁰ C. This is inter alia achieved by the fact that the cations have low symmetry, ie long and short substituents are combined.

Particularly preferred are ionic liquids with highly fluorinated anions, since these usually have high thermal stability. The ability to absorb water can be significantly reduced by such anions, for example, the bis (thfluoromethylsulfonyl) imidanion.

The grease compositions of the present invention may be a single ionic liquid or a mixture of two or more ionic liquids

Having liquids, wherein the second ionic liquid does not necessarily have to be water resistant. The amount distribution of the ionic liquids used is in the range of at least 75 to 95% of the first long-chain ionic liquid to 5 to 25% of the second ionic liquid. The second ionic liquid is advantageously selected from the group consisting of ionic liquids containing fluorinated anions, such as bis (fluoroalkylsulfonyl) imides, in particular

Bis (trifluoromethylsulfonyl) imides, bis (fluoroaryl) imides, tris (perfluoroalkyl) triphosphates, and fluorinated alkylsulfonates of any cation, or alternatively ionic liquids with any anions but with the long chain cations described above.

In addition, the grease compositions according to the invention contain conventional additives or additive mixtures, which are selected from corrosion inhibitors, such as oxalines, tiazoles, succinic acid, zinc carboxylates, sodium sulfonates, calcium, barium sulfonates, antioxidants, such as aromatic amines, aromatic phenols, phosphites, sulfur-containing compounds, such as dialkyldithiophosphates, Anti-wear agents and extreme pressure additives, such as phosphorus- and sulfur-containing compounds, eg zinc dialkyldithiophosphate, sulphurised fatty acids and fatty acid esters, dialkyl sulphide and dialkyloligo- and polysulphides, boric acid ester agents for reducing friction, such as glycerol mono- and di-esters, agents for protection against metal influences, as chelated compounds, radical scavengers ,. UV stabilizers, reaction layerers present are .... Viscosity improvers such as polyisobutylene, polymethacrylate, and inorganic or organic solid lubricants such as polyimide, polytetrafluoroethylene (PTFE), graphite, metal oxides, boron nitride, molybdenum disulfide, and phosphate.

Suitable thickeners are PTFE, bentonite, aerosols, water-insoluble carboxylic acid salts and mixtures thereof, water-insoluble sulfonic acid salts and mixtures thereof, ureas, carbon blacks, graphites, metal oxides such as titanium and zinc oxide and mixtures thereof.

In particular, additives in the form of phosphorus and sulfur compounds, e.g. Zinc dialkyldithiophosphate, dithiocarbamates sulphurised hydrocarbons and fatty acids, phosphorus and sulfur-free substances, such as boric acid esters used as wear protection agents and agents for reducing friction; Metal salts, esters, phenols, nitrogen-containing compounds such as aromatic amines, aromatic heterocyclic compounds, sulfonate salts, organic acid and salts are used as anti-corrosive agents, glycerol mono- or diesters as friction inhibitors, and polyisobutylene, polymethacrylate as viscosity improvers.

The water-resistant used in the invention

Contain lubricant compositions

(a) 40 to 95% by weight ionic liquid,

(b) 5 to 60% by weight of water-resistant thickener; and (c) 0.1 to 10% by weight of additives.

Preferably, the grease composition of the present invention contains 60 to 90% by weight of ionic liquid, 10 to 40% by weight of water-resistant thickener, and 0.1 to 10% by weight of additives.

The cation of the ionic liquid is selected from the group consisting of a quaternary ammonium cation or a phosphonium cation, and the anion is selected from the group consisting of a bis (perfluoroalkylsulfonyl) imide. in particular bis (trifluoromethylsulfonyl) imide, Bis (perfluoroaryl) imide, tris (perfluoroalkyl) triphosphate, wherein the cation of the ionic liquid comprises a long hydrophobic alkyl chain, aryl group or alkylaryl group having at least 8 to 25 carbon atoms and all hydrophobicizing alkylklyl aryl or alkylaryl groups of the cation comprise at least 15 to 60 carbon atoms and have a melting point of <-30 ° C. Preferred additives are aminic and phenolic antioxidants, anti-corrosion additives, such as amine phosphates, heterocyclic compounds, succinic acid half esters, zinc dialkyldithiophosphates and extreme pressure / anti-wear additives, such as phosphorus and / or sulfur carriers.

The use of ionic liquids, the lubricant compositions of the invention can be used at high temperatures of at least 180 ⁰ C, they can also be used by lowering the electrical resistance of the oils in areas where it by flowing current again and again by electrical breakdown, as in Railway wheel bearings, rolling bearings with passage of current, in the automotive sector or in electric motors to damage.

A particularly preferable ionic liquid is thhexyltetradecyphosphonium bis (trifluoromethylsulfonyl) imide, hereinafter referred to as HDPimide, represented by the following formula (I):

NΛΛΛΛΛΛΛΛΛΛ Formula (I)

The advantages of the grease composition according to the invention are illustrated by the following examples.

Examples

In the following, two ionic liquids and their fat formulations are compared.

The grease composition according to the present invention contains trihexyltetradecylphosphonium bis (trifluoromethylsulfonyl) imide as the ionic liquid.

In a comparative example, a grease composition contains an ionic liquid having the identical anion, referred to as butylmethylpyrrolidinium bis (trifluoromethylsulfonyl) imide, hereinafter referred to as MBPimide, represented by the following formula (II)

Formula (II)

Bis (trifluoromethylsulfonyl) imide is counted among the hydrophobic anions. MBPimid, in contrast to HDPimid, does not have long alkyl chains.

MBPimide can be up to temperatures from -40 ⁰ C to remain liquid with simple cooling which is after certain DSC melting point but at -6 ⁰ C. MBPimide therefore has a strong tendency to form a supercooled melt. Further, by way of another ionic liquid called methyltrioctylammonium bis (trifluoromethylsulfonyl) imide, hereinafter called moimide, having an ammonium cation and long hydrocarbon chains, it is further shown that the advantageous properties of the grease composition is not limited to the use of phosphonium cations, but also can be achieved with ammonium cations. The compound is represented by the following formula (III):

Formula (II!)

The physical data of these three compounds are shown in Table 1.

Table 1

* A first, minor oxidation starts slightly above 200 ⁰ C, but only from about 24O ⁰ C sets a clearer oxidation.

example 1

Water resistance according to DIN 51807 part 1 of fats based on MBPimid and HDPimid in comparison

The two IL ^'s are PTFE powder thickened to a grease consistency (stirring, rolling) and according to DIN 51807 Part 1 in 3 h / 90 ° C tested. The fat pattern with HDPimide shows no signs of breakup and is rated 0 (= very good). In the case of the fat pattern with MBPimid, separation of the strip occurs. After cooling the test medium water turbidity is observed, which is due to a partial dissolution of the MBPimid at high temperatures. The exam is therefore rated 3 (= bad).

Example 2

Solubility of standard additives in MBPimid and HDPimid

The following three anticorrosion additives were reviewed for their solubility in the mentioned IL ^'s: A Bernsteinsäurehalbester, an oxazoline and an acetic acid derivative. In HDPimid, all substances are 1% soluble at room temperature. In MBPimid only the oxazoline derivative dissolves after heating to about 150 ⁰ C, but separates on cooling again.

Example 3

Effectiveness of standard additives in HDPimid using the example of an antioxidant In HDPimid 1% of a p, p ^' dialkyl-diphenylamine is dissolved as an antioxidant. The mixture remains clear even after prolonged standing at room temperature. In a DSC run under oxygen under conditions as indicated in Table 1, the onset of oxidation is 223 ° C. This represents an increase of 55 ° C when compared to HDPimid without additive.

Example 4

Effectiveness of a grease composition based on HDPimide

In HDPimid conventional additives for improving corrosion protection properties and oxidation stability are solved. It is a zinc-containing corrosion protection additive and an amine antioxidant. In addition, an insoluble zinc-containing anticorrosive pigment is used. The mixture is thickened with PTFE powder by conventional methods to a fat consistency. The mixture gave the test results shown in Table 2:

Table 2

Emcor, dest. Water 0 DIN ISO 51802

Copper corrosion 24 h / 15O ⁰ C; 1 DIN 51811

VKA welding force, DIN 5500 N 51350 Part 4

Shell Roll Test 50 h / 80 ° C + 56 units Based on ASTM D 1831

FEG FE 9, 180 ^° C, 6000 rpm, L10 => 300 h 1500 N, installation A L50 ^; > 400 h DIN 51821

FEG FE 9, 200 ^° C, 6000 rpm, L 10 = 92 h 1500 N, installation AL 50 = 101 h DIN 51821

Water resistance DIN 0 51807 part 1, 3 h / 90 ° C

Water resistance DIN loss 2% 51807 part 2, 1 h / 80 ° C

Table 2 shows that the grease composition of the invention achieves good high and low temperature properties, good anticorrosion properties for steel and copper with resistance to water in both the static and dynamic experiment.

With the above-mentioned grease composition according to the present invention, a water resistance test according to DIN 51807 part 2 was carried out, with the result that the grease sticks very well in the bearing.

Example 5

Water-resistant fat formulation with an ammonium cation

Moimide is thickened with PTFE to a grease consistency by conventional methods, the test results are shown in Table 3.

Table 3

Table 3 shows that not only ionic liquids with phosphonium as cation, but also ammonium-water-resistant formulations allow.

Another advantage of the lubricating grease compositions according to the present invention with the ionic liquids used herein is the density lowered by the hydrocarbon groups, which results in a lower price per volume of lubricant and thus at a lower cost per component to be lubricated.

Example 6

Behavior of mixtures of ionic liquids with respect to water resistance

From HDPimide and MBPimide mixtures with different contents with respect to both IL ^'s can be produced. The mixtures are thickened with approx. 30% PTFE powder and homogenized by rolling, resulting in fats with penetration corresponding to a consistency level of 2. The fats are tested for their static water resistance and partly for dynamic water resistance. The results are shown in Table 4.

Table 4

In the case of water resistance according to DIN 51807 Part 2, mass losses of up to 10% are rated as 1 = very good. Results with losses greater than 30% are rated 3 (poor resistance).

Table 4 shows that a lubricating grease composition according to the invention using a combination of ionic liquids which, from a tribological point of view, such as MBPimide, exhibit inadequate water resistance, is possible. In the present example, at least 10% of the insufficiently hydrophobic IL MBPimide may be used relative to the base oil content while maintaining very good water resistance. Up to 25% base oil content is given a partial water resistance. A mixture of equal parts of the ionic liquids is no longer water resistant. The critical or acceptable mixing ratios depend on the ionic liquids used and therefore can not be generalized.

Example 7

In this formulation, 89% HDPimid is mixed with 10% lithium 12-hydroxystearate (soap thickener) and brought into the melt. After cooling, 1% of a conventional amine antioxidant is added. The mixture is homogenized by repeated intensive rolling over a roller mill.

Table 5

Example 8

In separate portions of HPDimid cyclohexylamine and bis (paraisocyantophenyl) methane (MDI) are dissolved in a molar ratio of 2: 1 and the solutions are reacted by combining. After heating to 180 ⁰ C and then cooling 1% of a typical aminic antioxidant is added and the fat is homogenized by rolling through a roller mill.

Table 6

Examples 7 and 8 show that by using an ionic liquid together with either a urea thickener or a soap thickener, water-resistant formulations are possible which can be applied as a protective film to a wide variety of corrosion and oxidation protection materials and give these materials consistent protection against water , This grease composition is particularly useful in automotive applications in water pump bearings, wheel bearings,

Cardan shafts, clutch release bearings, central bearings (centerbearing), thrust bearings in the strut, electromechanical brakes, fan bearings, miniature bearings exhaust gas recirculation systems, generator bearings, windscreen wiper bearings and the like necessary to ensure that during operation oxidation or corrosion of the coated surface is avoided. In addition, the water-resistant grease composition is used in wind turbines, main bearings, generator bearings, blade bearings, azimuth bearings, as well as in all components and surfaces that are exposed to constant water contact.

Claims

Greasing composition based on ionic liquids Patent claims Use of a water-resistant grease composition consisting of (A) 40 to 95 wt .-% of an ionic liquid whose cation is selected from the group consisting of a quaternary ammonium cation or a phosphonium cation and whose anion is selected from the group consisting of a Bis (perfluoroalkylsulfonyl) imide, especially bis (trifluoromethylsulfonyl) imide, bis (perfluoroaryl) imide, Ths (perfluoroalkyl) trifluorophosphate, wherein the cation of the ionic liquid has a long hydrophobic alkyl chain, aryl group or alkylaryl group of at least 8 to 25 carbon atoms and all hydrophobic alkyl, aryl or alkylaryl groups of the cation comprise at least 15 to 60 carbon atoms and have a melting point <-30 ⁰ C, (b) from 0.1 to 10% by weight of soluble lubricious additives and (c) 5 to 60% by weight of water-resistant thickener, for protection against corrosion and oxidation Temperatures of at least -30 ⁰ C to at least 180 ⁰ C. 2. Use of the grease composition according to claim 1, wherein the ionic liquid is a compound selected from among Group trihexyltetradecylphosphonium bis (trifluoromethylsulfonyimide (HDPimide), methyltrioctylarnmonium bis (trifluoromethylsulfonyl) imide (Moimide), trihexyltetradecylphosphonium trisperfluoroethyl). Use of the grease composition of any of claims 1 or 2, which contains a single ionic liquid or a mixture of two or more ionic liquids, wherein the second ionic liquid need not necessarily be water resistant. Use of the grease composition of any one of claims 1 to 3, wherein the mixture of the first long-chain ionic liquid to the second ionic liquid is in the range of 75 to 95% to 5 to 25%. 5. Use of the grease composition according to any one of claims 1 to 4, wherein the second ionic liquid is a fluorinated anion selected from the group consisting of bis (fluoroalkylsulfonyl) imides, especially bis (trifluoromethylsulfonyl) imides, bis (fluoroaryl) imides, Tris (perfluoroalkyl) tri-phosphate, or fluorinated alkyl sulfonates containing any cation or a long-chain cation selected from the Group consisting of a quaternary ammonium cation or a phosphonium cation and any anion. 6. Use of the grease composition according to any one of claims 1 to 5, wherein the additives are selected from the group consisting of corrosion inhibitors, antioxidants, Anti-wear agents, extreme pressure additives, friction reducing agents, metal impact inhibitors, UV stabilizers, inorganic or organic solid lubricants selected from polyimide, polytetrafluoroethylene (PTFE), graphite, Metal oxides, boron nitride, molybdenum disulfide and phosphate. Use of the grease composition according to any one of claims 1 to 5, wherein the antioxidants are selected from the group of aromatic amines, phenols or sulfur carriers. 8. Use of the grease composition according to any one of claims 1 to 5, wherein the corrosion inhibitors are selected from the group of aromatic heterocycles, sulfonate salts, organic acids and organic salts. Use of the grease composition of any one of claims 1 to 5, wherein the high pressure, antiwear / friction modifier (s) are selected from the group consisting of phosphates, sulfur carriers, phosphorus and sulfur containing compounds, boron containing compounds, and heterocyclic compounds. 10. Use of the grease composition according to any one of claims 1 to 9, wherein the thickener is selected from PTFE, bentonite, aerosils, water-insoluble carboxylic acid salts and / or mixtures thereof, water-insoluble sulfonic acid salts and mixtures thereof, ureas, carbon blacks, Graphites, metal oxides such as titanium and zinc oxide and / or mixtures thereof. 11. Use of the grease composition according to any one of claims 1 to 10, which contains as ionic liquid a compound of Trialkyltetradecylphosphoniumkationen and highly fluorinated anions, which are used in combination with water-insoluble thickeners and additives. 12. Use of the grease composition according to any one of claims 1 to 11 for the protective treatment of components in automotive parts, parts in wind turbines, in process and work machines, as well as in household articles from oxidation and corrosion, and to improve the water resistance of the protective film.