Patent Application
20180245010
The present invention relates to lubricating grease compositions that are especially suitable as high-temperature lubricating greases and find use for lubrication in oven systems, driers, dishwashers, electric motors or ventilators.
Lubricating greases generally comprise a thickener dissolved or dispersed in a base oil, and dispersants are frequently employed for better and more stable distribution of the thickener. The thickener serves to establish the desired consistency, and a multitude of inorganic and organic compounds are used.
Base oils used are mineral oils and synthetic oils. Frequently, perfluorinated polyalkyl ethers (PFPEs) are used, i.e. fluorinated synthetic oils having good lubrication properties that are chemically unreactive and stable at high temperature and therefore nontoxic (see, for example, “Synthetics, Mineral Oils and Bio-Based Lubricants”, Leslie R. Rudnick ed., Taylor & Francis, CRC Press, 2006). For instance, WO 97/47710 describes lubricating grease compositions comprising, as base oil, a mixture of a hydrocarbon oil and a perfluorinated polyalkyl ether oil (PFPE) and a thickener based on a diurea compound. The composition may also comprise polytetrafluoroethylene (PTFE) and customary additives.
EP 657 524 describes lubricating grease compositions comprising a mineral oil and/or a synthetic oil on a hydrogenated basis, a perfluorinated polyalkyl ether oil and PTFE as thickener.
DE 10 2004 021 812 A1 describes a lubricating grease comprising a base oil, a thickener, especially a polyurea, and an inorganic material distributed in the lubricating grease, such as silicon dioxide.
WO 2008/154997 A1 describes a lubricating grease comprising a base oil, an ionic liquid, a thickener and an additive. The ionic liquid is said to bring about an increase in the lifetime and lubricity of the lubricant and to serve to adjust the viscosity and the electrical conductivity.
Within the higher temperature range (200° C. to more than 600° C.), many of the known lubricants, for example, polyfluorinated compounds, meet the limits of material durability and are therefore no longer usable in spite of excellent sliding and lubricating properties within the higher temperature range.
WO 2013/037456 therefore describes high-temperature greases comprising a fluorine-free base oil, a thickener that may be PTFE, additives and optionally a further fluorine-free oil component.
EP 1589291 A1 discloses an oven pullout guide having rolling bodies arranged in a rolling body cage. The rolling body cage and the rolling bodies here have a lubrication layer which comprises a solid lubricant, for example graphite, molybdenum sulfide, tungsten disulfide or boron nitride, and is applied and baked in the form of a paint.
WO 2010/046456 A1 describes a pullout guide for a baking oven in which the tracks of the pullout guide have been lubricated with boron nitride and/or a polysiloxane-containing lubricant.
EP 648 832 A1 describes lubricating grease compositions comprising a fluorinated polymer oil, boron nitride and optionally solid fluorinated polymers. The lubricating grease compositions are said to have good lubricating properties even under harsh operating conditions.
US 2008/0167208 describes lubricating grease compositions comprising a perfluoropolyether oil having a kinematic viscosity of 50-1500 mm2/s at 40° C., optionally a thickener and further customary additives. The lubricating grease compositions are said to be usable at higher temperatures in contact with graphite or molybdenum disulfide as well.
PTFE-containing lubricating greases form toxic vapors at relatively high temperatures and are additionally washed out relatively quickly in cleaning operations by water. PTFE-free lubricating greases in turn have the disadvantage that they are washed out even more quickly by water than PTFE-containing lubricating greases.
It is therefore an object of the present invention to provide lubricating grease compositions having improved ease of washout by water. Moreover, the lubricating grease compositions are to have improved thermal stability and bring about a longer lifetime of the lubrication at high temperatures.
This object is achieved by a lubricating grease composition comprising at least one high-viscosity, fluorinated oil, hexagonal boron nitride and a binder.
The present invention therefore relates to a lubricating grease composition comprising
The kinematic viscosity is measured with a SVM 300 viscometer, Anton Paar, at a temperature of 40° C.
In one embodiment, component (a) comprises fluorinated, especially perfluorinated, polyalkyl ether oils or fluorinated silicone oils, especially perfluorinated silicone oils, and mixtures thereof.
Suitable perfluorinated polyalkyl ether oils are described, for example, in WO 97/47710 or EP 657 524, which are fully incorporated by reference.
In one embodiment, the perfluorinated polyalkyl ether oils conform to the formula:
A1-[OCF2]a—[OC2F4]b—[OC3F6]c—[OC4F8]d—[OCF2CF(CF3)]e—[OCF(CF3)CF2]f-A2
in which
A1 is —CF3, —C2F5, or —C3F7;
A2 is —OCF3, —OC2F5, or —OC3F7;
a, b, c, d, e and f are randomly distributed and are 0 or an integer from 1 to 200, where not all of them can simultaneously be 0.
In a further embodiment, e/a and f/a are in the range from 20 to 50 and b/a is in the range from 0.5 to 2.
In a further embodiment, c and d are 0. More preferably, the perfluorinated polyalkyl ethers are formed from the following units:
—[OCF2CF(CF3)]e or
—[OCF2]a—[OC2F4]b or
—[OCF2]a—[OCF2CF(CF3)]e
where e/a is in the range from 20 to 50 and b/a in the range from 0.5 to 2.
In a further embodiment, the perfluorinated polyalkyl ether oils conform to the formula:
CF3—[OCF(CF3)CF2]f—[OCF2]a—[OCF2CF(CF3)]e—OCF3
In which a, e and f are randomly distributed and are 0 or an integer from 1 to 200, where not all of them can simultaneously be 0, and e/a and f/a are in the range from 20 to 50.
In a further embodiment, the perfluorinated polyalkyl ether oils conform to the formula:
T-O-[A-B]z-[A-B′]z′-A-T′ (I)
-A=-(X)a—O-A′-(X′)b—
in which A′ is a perfluoropolyether chain comprising one or more repeat units selected from (CF2O), (CF2CF2O), (CF2CF2CF2O) and (CF2CF2CF2CF2O) and optionally (CF(CF3)O)—, (CF(CF3)CF2O)—, (CF2CF(CF3)O)— units;
X and X′ are the same or different and are —CF2—, —CF2CF2— or optionally —CF(CF3)—;
a and b are the same or different and are integers having a value of 0 or 1, with the proviso that the index a in the A block bonded to the end group T-O— is 1 and the index b in the A block bonded to the end group T′ is 0;
—[(CR1R2—CR3R4)j(CR5R6—CR7R8)j′]— (Ia)
in which
j is an integer from 1 to 5,
j′ is an integer from 0 to 4, with the proviso that (j+j′) is greater than 2 and less than 5;
R1, R2, R3, R4, R5, R6, R7 and R8 are the same or different and are selected from halogen; H;
z is an integer of not less than 2;
z′ is 0 or an integer;
where z and z′ have such a value that the number-average molecular weight of the polymer of the formula (I) is in the range of 500-500 000;
B′ is a block which derives from one or more olefins of the formula (Ia), but at least one of the substituents R1 to R8 is different than in block B, where (j+j′) is not less than 2 and less than 5;
the end groups T and T′ are the same or different and are perfluoroalkyl groups having 1 to 3 carbon atoms, where a fluorine atom may be replaced by a chlorine or hydrogen atom; or nonfluorinated C1-C6-alkyl groups.
These polyethers oils are described in EP 2 089 443, and reference is made in full to the disclosure thereof, especially the embodiments disclosed in the claims.
In one embodiment, component (a) may additionally comprise a nonfluorinated oil, especially a mineral oil. The nonfluorinated oil is generally present in an amount of 0.1% to 40% by weight, especially 0.5% to 30% by weight, based on the amount of the fluorinated oil.
The lubricating grease composition further comprises boron nitride, especially hexagonal boron nitride. In one embodiment, the lubricating grease composition comprises hexagonal α-boron nitride. In a further embodiment, the boron nitride has a BET surface area in the range from 10 to 20 m2/g, determined according to ISO 9277:2010. In a further embodiment, the boron nitride has a median particle size D50 of 1 to 10 μm, especially 2 to 6 μm, determined by means of laser diffractometry (Malvern Mastersizer 3000). A suitable boron nitride is available, for example, under the Boronid® trade name from ESK Ceramics GmbH & Co. KG, Germany.
The lubricating grease composition further comprises a binder. The binder generally has a median particle size D50 in the range from 1 to 10 μm, preferably 2 to 8 μm, determined by means of laser diffractometry.
In one embodiment, the binder is selected from bentonite, alkali metal phosphates, aluminum phosphates, alkali metal silicates, alkaline earth metal silicates, aluminum silicates, alkaline earth metal carbonates, calcium borate, silicon dioxide, titanium dioxide, aluminum oxide and mixtures thereof. Preference is given to bentonite, alkali metal phosphates, aluminum phosphates and mixtures thereof. More preferably, the binder is organically modified bentonite or a mixture of organically modified bentonite with at least one further binder selected from alkali metal phosphates, aluminum phosphates, alkali metal silicates, alkaline earth metal silicates, aluminum silicates, alkaline earth metal carbonates, silicon dioxide, titanium dioxide, aluminum oxide and mixtures thereof. The further binder is generally present in an amount of 0.1% to 50% by weight, especially 0.5% to 40% by weight, based on the amount of the organically modified bentonite.
Preferred silicon dioxide is organically modified fumed silica, and preferred titanium dioxide is organically modified pyrogenic titanium dioxide. Modified fumed silica and modified pyrogenic titanium dioxide are products that have been surface-treated with an organosilane, especially with an alkylsilane. Corresponding products, such as Aerosil R 912, Aerosil R 812, Aerosil R 805, Aerosil R 202, Aeroxide® TiO2 T 805, Aeroxide® TiO2 NKT 90, VP NKT 65, are commercially available, for example from Evonik Industries AG, Germany or Wacker Chemie AG, Germany.
Bentonite is a mixture of various clay minerals with montmorillonite (60% to 80%) as the most important constituent. Further accompanying minerals are quartz, mica, feldspar, pyrite or else calcite. The expression “bentonite” encompasses all naturally occurring versions and modified bentonites. Bentonite is commercially available in the form of various commercial products. In the context of the present invention, preference is given to using organically modified, especially hydrophobically modified, bentonite, for example the commercial product BARAGEL® from Elementis Specialities Inc., USA.
Organically hydrophobically modified bentonite can be obtained, for example, by the reaction of natural or purified bentonite with quaternary ammonium compounds in the manner of a cation exchange reaction in which, for example, alkali metal cations are exchanged for quaternary ammonium compounds. Quaternary ammonium compounds suitable for this reaction are, for example, those of the general formula R1R2R3R4N+X− where X is an equivalent of an anion, for example sulfate, hydrogensulfate, alkylsulfate, arylsulfate, alkylsulfonate, arylsulfonate, halide, phosphate, carbonate, alkylphosphate, alkylcarbonate, nitride, alkoxide, hydroxide, tetrafluoroborate or perchlorate, especially halide, and R1, R2, R3 or R4 may be the same or different and may be C1-C20-alkyl. For example, R1 and R2 may be the same or different and may be C1-C4-alkyl, and R3 and R4 may be the same or different and may be C12-C20-alkyl. More particularly, it is possible to use quaternary ammonium salts in which X is halide, especially chloride, R′ and R2 are methyl and R3 and R4 are the same or different and are C16-C18-alkyl. The commercial product BARAGEL© is bentonite modified with Me2N(C16-C18-alkyl)2Cl.
When bentonite is used as binder, the lubricating grease composition, in a preferred embodiment, additionally comprises water in an amount of 0.01% to 1% by weight, especially 0.05% to 0.2% by weight, based on the total mass of the composition. Water serves here as an activating agent for bentonite, especially for activation of the dispersing and thickening properties of bentonite.
In a further embodiment, the lubricating grease composition of the invention may comprise at least one additive, especially an additive customary in the field of lubricating grease compositions. The additive is preferably selected from antioxidants, for example functionalized perfluoropolyalkyl ethers as described in EP 1 354 932 A1 and U.S. Pat. No. 5,550,277; antiwear additives, for example functionalized perfluoropolyalkyl ethers as described in WO 2016/020232; anticorrosives, for example sodium sebacate, functionalized perfluoropolyalkyl ethers as described in U.S. Pat. No. 5,550,277; dyes, for example azo dyes, and solid lubricants, for example molybdenum disulfide, tungsten disulfide, tin sulfide.
In a further embodiment, the lubricating grease composition of the invention comprises
(a) 50-96% by weight of the fluorinated oil;
(b) 0.9-20% by weight of boron nitride; and
(c) 3-25% by weight of the binder;
(d) 0-5% by weight, especially 0.01-5% by weight, of at least one additive;
based in each case on the total weight of the composition.
In a further embodiment, the lubricating grease composition of the invention comprises
(a) 50-96% by weight of at least one perfluorinated polyalkyl ether oil;
(b) 0.9-20% by weight of boron nitride; and
(c) 3-25% by weight of organically modified bentonite;
(d) 0-5% by weight, especially 0.1-5% by weight, of at least one additive;
based in each case on the total weight of the composition.
In one embodiment, the lubricant composition is essentially free of PTFE.
In a further embodiment, the lubricating grease composition is essentially free of an ionic liquid.
In a further embodiment, the lubricating grease composition is essentially free of graphite.
“Essentially free” means that the lubricating grease composition contains less than 0.5% by weight of PTFE, less than 0.5% by weight of ionic liquid or less than 0.5% by weight of graphite, especially 0% by weight of each of these components, based on the total mass of the composition.
The lubricating grease composition of the invention is generally produced by mixing the components under high shear force, for example using a rotor-stator mixer, optionally followed by a homogenization, for example using a roll mill.
It has been found that, surprisingly, the lubricating grease compositions of the invention have a number of advantageous properties compared to known lubricating greases:
The lubricating grease compositions of the invention are suitable for lubrication within the temperature range from −30° C. to 700° C., especially +20 to 300° C. They can therefore be used in many fields. For instance, they are usable for the lubrication of sliding guides and running wheels in oven systems or roller bearings and slide bearings in driers, electric motors or ventilators, for the lubrication of molds, especially molds for the injection molding of plastics, machines and installations, especially for the food and animal feed industry. Examples of applications are the lubrication of: roller bearings and slide bearings, sliding guides, valves, joints, slides, pillar guides, ejectors and other sliding surfaces as, for example, in circular conveyor systems, painting lines, calenders, kiln cars, ventilators, switches, film stretching systems, extraction systems, textile machinery, wood press systems, pumps, driers, motors, tire molds, construction machinery, electrical engineering and automobile technology, elastomer and plastics technology, and applications in the corrugated cardboard industry, paper industry and steel industry, and machinery and installations, for example, in the food and animal feed industry.
Preferably, the lubricating grease composition of the invention is used for the lubrication of sliding guides and running wheels in oven systems or roller bearings and slide bearings in driers, electric motors or ventilators. Especially preferred is the use of the lubricating grease compositions of the invention for the lubrication of oven pullout rails.
The lubricating grease composition is applied by application to the parts to be lubricated in an amount suitable for lubrication. Preference is given to applying the lubricating grease composition of the invention as a paste. This form of application enables very exact selection and coating of the application areas. The lubricating grease composition can be applied in a simple manner without the lubricating grease composition flowing away or dripping off, for example, at the ends of the tracks of oven pullout rails.
An optional aftertreatment by slide grinding after the application of the lubricating grease composition enables better distribution and adhesion of the lubricating grease on a metallic substrate, for example.
Preferably, the lubricant composition is thixotropic, meaning that the viscosity decreases under mechanical action and the original viscosity is re-established after the shear stress has ended. As a result, the pastes can be distributed relatively easily on the surface of oven pullout rails, for example, under pressure without dripping off.
The examples which follow elucidate the invention without restricting it.
Two perfluorinated polyether oils (68% by weight of PFPE oil 1, 500 cSt at 40° C. from DuPont, USA and 10% by weight of PFPE oil 2, 1005 cSt at 40° C. from DuPont, USA) were introduced into a mixing vessel and heated to 100° C. while stirring for 15 min. Thereafter, BARAGEL® (14.9% by weight, organically hydrophobically modified bentonite from Elementis Specialties Inc., USA) were introduced into the mixing vessel, the heating was switched off and the resulting mixture was stirred for five minutes. Then 0.1% by weight of water was added and the mixture was stirred for 30 min. After cooling to room temperature, boron nitride (5% by weight Boronid®, ESK Ceramics GmbH & Co. KG, Germany) and an anticorrosive (2% by weight, Irgacor®, BASF SE, Germany) were introduced into the mixing vessel and the resulting mixture was stirred for 30 min. The resulting lubricant grease was homogenized with a roll mill. The figures in % by weight are each based on the total weight of the lubricant grease.
Test Program and Results
The lubricating grease composition produced according to example 1 was first subjected to a VKA test (four-ball apparatus, ASTM D1831/DIN 51350-4). The VKA welding force was determined as 4800 N and the VKA wear as 0.9 mm under a load of 150 kg/1 min.
For the lubricating grease composition produced according to example 1, the thermal stability was also determined at 300° C. A measure employed for the thermal stability was the evaporation rate with time:
Hours: 0 24 72 140
Evaporation rate [%]: 0 14 26 41
In addition, the following were determined for the lubricating grease composition produced according to example 1:
Washout Tests
Washout tests were conducted for the lubricating grease composition produced according to example 1 and three comparative samples (comparative example 1, comparative example 2, comparative example 3). For this purpose, the various samples were applied to oven pullout rails and subjected to the following cycle: the oven pullout rails were subjected to a temperature of 250° C. in an oven for 4 h; thereafter, the rails were taken out of the oven and treated with a commercial dishwashing composition in a machine dishwasher at 70° C. for 2 h; after the wash cycle, the rails were taken out of the machine dishwasher and dried at 105° C. for 1 h. (3 cycles were conducted for each sample; the rails were thus in the oven for a total of 12 h and in the dishwasher for 6 h.) Composition of the comparative examples (% by weight, based on the total weight of the composition):
74.75% PFPE (perfluorinated polyether; 500 mm2/s)
25% PTFE (polytetrafluoroethylene)
0.25% anticorrosive
81% PFPE (500 mm2/s)
10% PFPE (1005 mm2/s)
5% PTFE
2% SiO2
2% anticorrosive
10% PFPE (1005 mm2/s)
83% PFPE (500 mm2/s)
5% boron nitride
1% graphite
1% WS2 (tungsten sulfide)
The following results were obtained:
Endurance Tests
Endurance tests were conducted for the lubricating grease composition produced according to example 1 and two comparative samples (comparative examples 4 and 5). For this purpose, the various samples were applied to oven pullout rails and the pullout rails were mounted on side grids. Subsequently, the grids were installed into a baking oven. A test load was positioned in the middle of a baking sheet in the oven. The weighted baking sheet was pulled in and out using a pneumatic cylinder. The rails were subjected to an endurance test with 24 000 cycles. After every 6000 cycles, movement force and lowering of the rails were tested and, likewise after every 6000 cycles, the rails were subjected to a machine dishwasher wash cycle. After a total of 24 000 cycles, the rails were deinstalled and examined. The testing was conducted with the following parameters and according to the following schematic procedure:
Composition of the comparative examples (% by weight, based on the total weight of the composition):
as comparative example 2, see above.
90.5% PFPE (500 mm2/s)
6% boron nitride
3.25% SiO2
0.25% anticorrosive
The following results were obtained:
| Number | Date | Country | Kind |
|---|---|---|---|
| 15181667.5 | Aug 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/069423 | 8/16/2016 | WO | 00 |
