Patent Application
20230138681
The present invention relates to the provision of a novel lithium complex hybrid grease based on a lithium complex grease in combination with a PFPE grease which may be employed at high temperature, does not undergo varnishing as a result and exhibits a low hardening tendency. The invention further relates to the use of the novel lithium complex hybrid greases in components in the vehicle sector.
Hybrid greases are mixtures consisting of at least two base oils that are immiscible with one another. Hybrid greases which contain urea or urea/PTFE mixtures and ester/PFPE as immiscible base oil components represent an important group of these greases. These greases make it possible to close a temperature gap between about 180° C., such as are achieved in fluorine-free greases, and 270° C., which are possible with pure PTPE/PFPE greases. These products are also easier to adapt to particular requirements than is possible with pure PFPE/PTFE greases. This is because only very few oil additives are known for PFPE oils, so that for example the anticorrosion properties of PFPE oils can be improved only to a limited extent. Solid substances such as sodium nitrite or magnesium oxide are therefore employed as anticorrosion additives in PFPE/PTFE greases. However, the uniform distribution of a solid on the surface of the component is much more difficult to ensure than the wetting of the surface of the component with an oil containing a dissolved anticorrosion additive. The additives of a hybrid grease present in the non-fluorine-containing liquid phase are therefore better able to ensure properties such as anticorrosion than is possible in a pure PFPE/PTFE grease. The reduction of the content of PFPE oils in the hybrid grease and the lower density of the hybrid grease additionally result in significant cost advantages. The ester/PFPE/PTFE/urea greases described for example in EP0902828 B1 or the ester/PTFE/urea greases as described for example in U.S. Pat. No. 6,063,743 have the disadvantage that these greases have a tendency for post-hardening at high temperatures and have very low oil separations. They may also in some cases be critical when used with particular elastomers, so that they cannot be employed in a broad spectrum, such as for example roller bearings and corrugated board lines. The fluorinated greases are moreover very costly and there is therefore also a need for hybrid greases which are cost-effective to produce and have identical or even better properties than the fluorinated greases.
Lithium complex greases have a high oil separation and a lower hardening tendency at high temperatures compared to ester/urea greases. However, the upper usage temperature is markedly lower than for urea hybrid greases which is often related to an excessively high oil separation or else is attributable to the use of baseballs such as polyalphaolefins or mineral oils which have a lower thermal resistance.
It is therefore an object of the present invention to provide a lithium complex hybrid grease which overcomes the abovementioned disadvantages and which correspondingly exhibits a sufficient oil separation and a low hardening even at high temperatures.
This object was surprisingly achieved by combining lithium complex greases containing polyisobutylene and esters with PFPE oils or PFPE greases, in particular PFPE/PTFE greases, and so making it possible to achieve a high temperature performance matching that of the ester/urea/PFPE hybrid greases but without exhibiting the disadvantages thereof. Through selection of the mass fractions of the two greases the oil separation can surprisingly be adjusted such that the oil separation is lower than for the two greases used for the mixture.
The invention further provides a method for lubricating or greasing components, in particular in anti-friction bearings, plain bearings and transport and timing chains in vehicle technology which comprises applying the lubricant composition according to the invention.
The invention also provides a method for lubricating or for greasing track roller bearings in continuous casting lines, transport roller bearings in conveyor furnaces, of open ring gears in rotary furnaces, tube mills, drums and mixers, of bearings in corrugated board lines or film orienting lines or of bearings in lines for production and transport of foodstuffs which comprises applying the lubricant composition according to the invention.
The lubricant composition according to the invention comprises
A preferred lubricant composition according to the invention comprises a ring gear
A particularly preferred lubricant composition according to the invention comprises
An especially preferred lubricant composition according to the invention comprises
A further preferred lubricant composition according to the invention comprises
The lubricants according to the invention may contain as further components (G) additives and (H) solid lubricants.
Component (A)
Component (A) is present in the lubricant composition according to the invention in an amount from 70% to 7% by weight, preferably 60% to 15% by weight.
Component (A) is an ester or a mixture of esters, wherein the ester is selected from the group consisting of trimellitic acid esters comprising as alkoxy groups linear or branched alkyl groups containing 6 to 18 carbon atoms, preferably 8 to 14 carbon atoms, wherein the alkoxy groups may be identical or different, pyromellitic acid esters, preferably tetrakis(2-ethylhexyl)pyromellitate, hydrogenated or unhydrogenated dimeric acid esters, preferably bis(2-ethylhexyl)dimerate, estolides.
Estolides are to be understood as meaning esters containing oligomeric units constructed from homopolymers of hydroxycarboxylic acids, for example of 12-hydroxystearic acid or unsaturated carboxylic acids, for example such as oleic acid. Suitable estolides are described for example in U.S. Pat. Nos. 6,018,063, 6,316,649, WO 2018/177588 A1 and US 2013/0261325 A1.
Component (B)
Component (B) is a polyisobutylene or polybutene and present in the composition according to the invention in an amount of 0.5% to 20% by weight; preferably 1.5% to 15% by weight are employed.
Component (B) is a polymer such as described for example in Synthetics, Mineral Oils and Bio Based Lubricants Chemistry and Technology, Second Edition, Editor Leslie R. Rudnik, Authors M. Casserino, J. Corthouts, CRC Press 2013, Pages 273-300, (ISBN 978-1-4398-5537-9).
Suitable selection of the polyisobutylene, in particular with regard to the degree of hydrogenation and molecular weight, allows the properties of the grease according to the invention, for example the kinematic viscosity thereof, to be influenced in a desired manner. The polyisobutylene may be employed in non-hydrogenated, hydrogenated or fully hydrogenated form and a mixture of non-hydrogenated, hydrogenated and fully hydrogenated polyisobutylene may likewise be used. It is preferable to employ fully hydrogenated polyisobutylenes. The non-hydrogenated polyisobutylenes contain an unsaturated end group as a consequence of their production. Hydrogenated/partially hydrogenated polyisobutylenes are to be understood as meaning polymers whose bromine number is at least 20% lower compared to unhydrogenated polyisobutylene. Accordingly the bromine number for a non-hydrogenated polyisobutylene having an Mn of 1300 g/mol is 14 g of bromine per 100 g of polyisobutylene. The bromine number for fully hydrogenated polyisobutylenes is below 7 g of bromine per 100 g of polyisobutylene. The bromine number is determined according to ASTM D2170-09 (reapproved 2018).
In a further preferred embodiment the polyisobutylene has a number-average molecular weight of 115 to 10 000 g/mol, preferably from 500 to 5000 g/mol. The number-average molecular weight is determined by gel permeation chromatography according to ISO 16014-1, 2019-05 edition.
Component (C)
Component (C) is present in the lubricant composition according to the invention in an amount from 1% to 18% by weight, preferably 4% to 14% by weight.
Component (C) is a lithium complex soap. Lithium complex soaps are to be understood as meaning mixtures of lithium salts of monofunctional carboxylic acids, preferably carboxylic acids having 8 to 22 carbon atoms, especially preferably carboxylic acids having 14 to 20 carbon atoms, especially preferably 12-hydroxystearic acid and/or stearic acid with the lithium salts of higher-functional carboxylic acids, preferably dicarboxylic acids having 6 to 14 carbon atoms, especially preferably azelaic acid, sebacic acid and dodecanedioic acid. Lithium complex soaps may additionally contain short-chain carboxylic acids such as acetic acid and lactic acid and/or phosphonic acids and/or boric acid as further acid components.
Component (D)
Component (D) is a perfluoropolyether (PFPE) according to formula (I):
R1—(O—CF2)v—(O—C2F)w—(O—C3F6)x—(O—CFCF3)y—(O—CF2CF(CF3))z—O—R2 (I)
Wherein R1 and R2 identical or different and selected from —CF3, —C2F5 or C3F7 and v, w, x, y and z are integers from 0 to 500.
PFPE oils are marketed for example under the brand names Aflunox®, Krytox®, Fomblin® and Demnum®.
The PFPE oils are present in the lubricant composition according to the invention in amounts of 5% to 70% by weight, preferably 15% to 50% by weight.
Component (E)
The lithium complex hybrid grease according to the invention may comprise further thickeners (E) in addition to the lithium complex thickener.
The further thickeners (E) are present in the lubricant composition according to the invention in amounts of 1% to 30% by weight, preferably 3% to 20% by weight.
The further thickeners (E) in the hybrid grease according to the invention are selected from the group consisting of Al complex soaps, metal monosoaps of elements of the first and second main group of the periodic table without lithium, metal complex soaps of elements of the first and second main group of the periodic table without lithium, bentonites, sulfonates, silicates, aerosil, polyimides or PTFE or a mixture of the abovementioned thickeners. A particularly preferred further thickeners PTFE. The preferred PTFE is employed as a micropowder produced from high molecular weight PTFE thermally or by irradiation to achieve molecular weight degradation.
Component (F)
The hybrid greases according to the invention may contain further oils (F) present in the lubricant composition according to the invention in amounts of 0% to 20% by weight, preferably 2% to 20% by weight.
Component (F) is selected from the group consisting of mineral oil, alkylated benzenes, alkylated naphthalenes, aliphatic carboxylic acid and dicarboxylic acid esters, fatty acid triglycerides, alkylated diphenyl ethers, phloroglucinol esters, estolides and/or polyalphaolefins, alpha-olefin copolymers, metallocene-catalyzed polyalphaolefins. Preferred further oils are alkylated diphenyl ether oils. Alkylated diphenyl ether oils are marketed for example under the trade name Hilube® from Moresco. The alkyl groups contain between 10 and 20 carbon atoms. An average of between one and three alkyl groups are bonded to the diphenyl ether base unit.
Component (G)
The lubricant composition according to the invention further comprises from 0% to 10% by weight, preferably from 0.1% to 10% by weight, of additives (G) employed individually or in combination.
Component (G) is selected from the group consisting of anticorrosion additives, antioxidants, antiwear additives, UV stabilizers. It is also possible to employ additives that are soluble in component (A), that are soluble in the PFPE oils of component (D) or that are in soluble in both oil phases.
Examples of antioxidants are styrenized diphenylamines, diaromatic amines, phenol resins, thiophenol resins, phosphites, butylated hydroxytoluene, butylated hydroxyanisole, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, octylated/butylated diphenylamine, di-alpha-tocopherol, di-tert-butylphenol or di-tert-butyl methylphenol, benzenepropanoic acid, sulfur-containing phenol compounds, phenol compounds and mixtures of these components.
Examples of suitable anticorrosion additives include metal deactivators or ion complex formers. These include triazoles, imidazolines, N-methylglycine (sarcosine), benzotriazole derivatives, N,N-bis(2-ethylhexyl)-ar-methyl-1H-benzotrizole-1-methanamine; n-methyl-N(1-oxo-9-octadecenyl)glycine, mixtures of phosphoric acid and mono- and diisooctyl esters reacted with (C11-14)-alkylamines, mixture of phosphoric acid and mono- and diisooctyl esters reacted with tert-alkylamine and primary (C12-14)-amines, dodecanoic acid, triphenyl phosphorothionate and amine phosphates. Commercially available additives are the following: IRGAMET® 39, IRGACOR® DSS G, Amin O; SARKOSYL® O (Ciba), COBRATEC® 122, CUVAN® 303, VANLUBE® 9123, CI-426, CI-426EP, CI-429 and CI-498.
Further antiwear additives are amines, amine phosphates, phosphates, thiophosphates and mixtures of these components. The recited compounds generally comprise organic groups. The commercially available antiwear additives include IRGALUBE® TPPT, IRGALUBE® 232, IRGALUBE® 349, IRGALUBE® 211 and ADDITIN® RC3760 Liq 3960, FIRC-SHUN® FG 1505 and FG 1506, NA-LUBE® KR-015FG, LUBEBOND®, FLUORO® FG, SYNALOX® 40-D, ACHESON® FGA 1820 and ACHESON® FGA 1810.
Further additives that may be present include PFPE derivatives. For example PFPE carboxylic acids, metal and ammonium salts thereof, ester and amide derivatives thereof. Further suitable substances are described for example in WO01/72759A1, WO 01/27916A1, EP1070074B1, EP1659165B1 and US2015011446A1.
Component (H)
The lubricant compositions according to the invention may further contain solid lubricants (H) selected from the group consisting of BN, pyrophosphate, Zn oxide, Mg oxide, pyrophosphates, thiosulfates, Mg carbonate, Ca carbonate, Ca stearate, Zn sulfide, Mo sulfide, W sulfide, Sn sulfide, graphites, graphene, nanotubes, SiO2 modifications or a mixture thereof. The solid lubricants (H) are present in the lubricant composition according to the invention in amounts of 0% to 10% by weight, preferably 2% to 5% by weight.
The lubricant composition according to the invention is employed in the field of components, in particular in the field of anti-friction bearings, plain bearings, transport and timing chains in vehicle technology, in rail vehicles, in conveying technology, in film orienting lines, in corrugated board lines, of track roller bearings, fan bearings, bearings of traction engines, for lubricating bevel gear and spur gear transmissions, springs, screws and compressors, pneumatic components, valves and of machine components and in plants where occasional unintentional contact with foodstuffs occurs.
The accompanying figures show the and it is of the lithium hybrid companies greases according to the invention:
The invention will now be more particularly elucidated with reference to the following examples.
Production of the Inventive Lubricant Compositions
Production of the lubricant compositions according to the invention is not restricted and may be performed by any suitable methods.
Production of the lubricant composition according to the invention may be carried out for example by producing a base oil mixture with the components (A) and/or (B) and/or (F). The acids required for the lithium complex thickener (C) are melted into this base oil mixture which is entirely or only partly initially charged in a suitable reaction vessel containing heating, cooling and stirring means, and an aqueous lithium hydroxide solution is added. This forms a liquor containing the lithium soaps of the carboxylic acids. The acids may be added and neutralized individually or else the monocarboxylic acid is added and neutralized first and the higher-functional carboxylic acid is added and neutralized in a second step. The liquor is heated to 130° C. to expel water. The swelling of the thickener (lithium complex soap) is performed by thermal treatment at 150° C. to 210° C. The thermally treated liquor is then cooled and a portion of the base oil mixture may also be used. The components (D), (E), (G), (H) and the components (A), (B) and (F) which are optionally not used for the base oil mixture are added at a suitable temperature and pre-homogenized by stirring.
Solid lubricant additives soluble in the base oil mixture are for example added at temperatures above their melting point. Liquid additives or non-melting additives/solid lubricants/thickener components are added at temperatures below 80° C. The resulting lithium complex hybrid grease may be homogenized by suitable apparatuses such as three-roll mills, colloid mills or a Gaulin homogenizer.
The above-described method produces the inventive lubricant composition in one process. Alternatively, the addition of the PFPE oil (D) and the optional thickener component (E) may be omitted in the above-described method to form a lithium complex grease. The components (D) and (E) may be combined to afford a PFPE grease by stirring, homogenizing as described above. The lithium complex grease and the PFPE grease may be combined in a second method step to produce the inventive lubricant composition therefrom by stirring and homogenizing.
Production may also be effected by continuous methods, wherein ready-made Li complex soap in powder form may also be used.
Production of several inventive lubricant compositions, comparison with the lithium complex grease and PFPE/PTFE grease used for production, comparison with urea hybrid greases
Production
Lithium complex soap grease (grease A) and a PFPE/PTFE grease (grease B) are produced separately and the two greases A and B are mixed in different ratios, stirred and homogenized by rollers.
Grease A
A lithium complex grease consisting of 77% of a mixture of an alkyl diphenyl ether (100 mm2/sec/40° C.) and trimellitic acid ester and fully hydrogenated polyisobutylene (fully hydrogenated, Mn about 1300 g/mol) is produced as a base oil, wherein a viscosity at 40° C. of 100 mm2/sec is established, before 15% of a lithium complex of azelaic acid and 12-hydroxystearic acid and 8% of an additive package consisting of aminic antioxidants, phosphates, thiadiazoles, triazoles and amine phosphates are added. The worked penetration is 270 1/10 mm (see table 1).
Grease B
A PFPE/PTFE grease containing 70% of a mixture of linear and branched PFPE, kinematic viscosity 200 mm2/sec at 40° C., 26% PTFE micropowder, average particle size d50 (laser diffraction, DIN ISO 9277) about 5 μm, specific surface area (DIN ISO 9277) about 5 m2/g, and 4% disodium sebacate as anticorrosion additive is produced. The worked penetration is 286 1/10 mm (see table 1).
Mixture of grease A and grease B in the ratio 10% by weight to 90% by weight.
Mixture of grease A and grease B in the ratio 30% by weight to 70% by weight.
Mixture of grease A and grease B in the ratio 50% by weight to 50% by weight.
Mixture of grease A and grease B in the ratio 70% by weight to 30% by weight.
Mixture of grease A and grease B in the ratio 90% by weight to 10% by weight.
A urea hybrid grease consisting of 50% by weight of grease B and 50% by weight of a urea grease is produced. The urea grease consists of a mixture of trimellitic acid ester and a reaction product of octylamine and oleylamine with an MDI/TDI mixture as the urea thickener and additives. The base oil viscosity is about 80 mm2/sec. The worked penetration is 265 mm2/sec (see table 2).
A urea hybrid grease consisting of a complex ester based on a dimeric acid, V 40 about 400 mm2/sec at 40° C., and branched PFPE oil having a kinematic viscosity of about 400 mm2/sec in a mass ratio of 2:1 is produced. The urea thickener is present in a proportion of 10% and is a reaction product of octylamine and oleylamine with an MDI/TDI mixture. Also present are 8% by weight of PTFE powder (as in grease B) and 5% by weight of soluble additives (antioxidants, amine phosphates). The worked penetration is 290 mm2/sec (see table 2).
Table 1 shows the general characteristics of the inventive lithium complex hydrogen greases of examples B1 to B5 and of greases A and B.
Table 2 shows the data for comparative examples VG1 to 2.
As is apparent in
As is apparent in
The data also show that a desired oil separation behavior can be established through selection of the amount of greases A and B.
Determination of Evaporation Loss
The inventive lubricant compositions were tested for their thermal stability and the results compared especially with those of the urea hybrid greases. To this end investigations in respect of evaporation and viscosity under thermal stress of a 5 g initial weight of grease weighed into a stainless steel dish at 200° C. were performed. The results are shown in tables 3 and 4.
Evaporation loss is determined according to DIN standard 58397. For each grease sample three evaporation loss dishes made of stainless steel were required. The geometry of the dishes is described in the standard for determining evaporation loss (DIN 58397). Initially the respective empty weight of the dishes was determined. Subsequently the three evaporation loss dishes were filled with the grease sample. It must be ensured that the grease is applied so as to avoid air bubbles. A scraper is used to smooth the surface and excess grease that has entered the edge depression of the dish is removed. The dishes are subsequently stored in a customary laboratory drying cabinet with convection with the door closed at the appropriate test temperature (here 200° C.). After the duration specified in each case (48 h, 96 h, 144 h and 168 h) the dishes are removed from the drying cabinet and allowed to cool. The dishes are then weighed. The evaporation loss is determined from the difference between the initial weight and the measured weight. Three individual values are used to determine an average value (VM). Together with the average value of the three initial weights (AM) the evaporation loss may be calculated. V=(VM/AM)*100 [%]. After weighing, the dishes are replaced in the drying cabinet until the next time point. This is repeated until 168 h have elapsed.
Determination of Shear Viscosity
Shear viscosity is determined according to DIN standard 53019 part 1 and 3. The grease samples are in each case transferred into three evaporation loss dishes made of stainless steel. The geometry of the dishes is described in the standard for determining evaporation loss (DIN 58397). The dishes are subsequently dried in a customary laboratory drying cabinet with convection recirculation at the appropriate test temperature (here 200° C.). After the duration specified in each case (48 h, 96 h, 144 h and 168 h) the dishes are removed from the drying cabinet and allowed to cool. The starting value for the shear viscosity is determined for each grease before subjection to thermal stress.
Measurement of shear viscosity is carried out with a standard instrument for determining rheological parameters of lubricating greases (for example Anton Paar MCR 302 rheometer).
A cone and plate system is employed (DIN EN ISO 3219 and DIN 53019), preferably with a measuring cone having a diameter of 25 mm. The required amount of grease sample is based on typical amounts required for rheological measurements. The measurement duration is 120 seconds, of which 60 seconds are heating/holding time. Measurement is performed at a constant shear rate of 300 1/s and a temperature of 25° C. The value that may be read off after 90 seconds represents the shear viscosity for the respective grease sample. The three individual values determined are used to form an average value and finally reported.
The greases of examples 1 to 5 were then compared with the greases of comparative examples 1 and 2 and the two individual greases (A) and (B) in respect of their thermal stability. The results are shown in tables 5 and 6.
The above results show that for the inventive lithium complex hybrid greases the increase in shear viscosity is markedly lower than for the comparative products VG1 and VG2. VG2 shows a shear viscosity of 100 000 mPas and is no longer capable of lubrication after only 96 h. After a test time of 168 h VG1 shows a shear viscosity which is twice as high as all inventive compositions B1 to B5, see table 4.
The PFPE/PTFE grease (grease B) shows the lowest evaporation losses in the test as expected. Surprisingly, the shear viscosity of the inventive examples B1, B2 and B4 is lower than for grease B after a test time of 168 h and therefore exhibits hardening behavior that is more advantageous.
It is altogether apparent that the hardening behavior of the inventive greases at high temperatures is more advantageous than for urea hybrid greases. It has surprisingly even been found that some of the inventive compositions even exhibit a lower hardening than a PFPE/PTFE grease. It has surprisingly also been found that the oil separation behavior of the inventive lubricants can be adjusted and thus adapted to different requirements through selection of particular mixing ratios of the greases A (lithium complex grease) and B (PTFE/PFPE grease).
Production of an Inventive Grease with Different Production Methods
As previously described the inventive greases may be produced in different ways. In the “vessel-mixed” variant a lithium complex grease (grease C) and a PFPE/PTFE grease (grease D) are produced separately and then mixed by stirring in a vessel in a ratio of 40% to 60% by weight. The resulting lithium complex hybrid grease B6 is subsequently homogenized using a three-roll mill.
In the “in situ” production the lithium complex grease is produced identically to grease C but, in a departure, the constituents of grease D are then also added, thus producing the inventive lubricant composition in one operation. The inventive grease composition B6 is also subsequently rolled.
Grease C
A lithium complex grease consisting of 80% by weight of a mixture of an alkyl diphenyl ether (100 mm2/sec at 40° C.) and a trimellitic acid ester and fully hydrogenated polyisobutylene (fully hydrogenated, Mn about 1300 g/mol) is produced as a base oil, resulting in a viscosity at 40° C. of 100 mm2/sec. 15% by weight of a lithium complex of azelaic acid and 12-hydroxystearic acid and 5% by weight of an additive package consisting of aminic antioxidants and phosphates are provided. The worked penetration is 327 1/10 mm.
Grease D
A PFPE/PTFE grease containing 65% by weight of a mixture of linear and branched PFPE having a kinematic viscosity of 145 mm2/sec at 40° C., 33% by weight of PTFE micropowder, average particle size d50 (laser diffraction, DIN ISO 9277) about 5 μm, specific surface area (DIN ISO 9277) about 5 m2/g, and 2% by weight of disodium sebacate as anticorrosion additive is produced. The worked penetration is 286 1/10 mm.
Both production variants provide identical values within the experiment error.
The present data show that B6 according to production example 1 and production example 2 may be employed as a lubricant with both production variants.
It has therefore been demonstrated that the inventive lubricant compositions may be produced by different methods.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 112 993.9 | May 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/052523 | 2/3/2021 | WO |
