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  • C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
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  • C10M2207/10—Carboxylix acids; Neutral salts thereof
  • C10M2207/12—Carboxylix acids; Neutral salts thereof having carboxyl groups bound to acyclic or cycloaliphatic carbon atoms
  • C10M2207/121—Carboxylix acids; Neutral salts thereof having carboxyl groups bound to acyclic or cycloaliphatic carbon atoms having hydrocarbon chains of seven or less carbon atoms
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  • C10M2213/00—Organic macromolecular compounds containing halogen as ingredients in lubricant compositions
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  • C10M2213/06—Perfluoro polymers
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  • C10M2219/00—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions
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  • C10M2223/00—Organic non-macromolecular compounds containing phosphorus as ingredients in lubricant compositions
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  • C10N2020/00—Specified physical or chemical properties or characteristics, i.e. function, of component of lubricating compositions
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  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
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  • C10N2040/30—Refrigerators lubricants or compressors lubricants

Definitions

• the present invention relates to fluorinated greases having a low torque.
• the invention specifically relates to perfluoropolyether-based greases having lower torques at low temperatures, in particular at temperatures lower than -40°C.
• the invention more specifically relates to perfluoropolyether grease compositions having improved torques at -40°C, in particular at temperatures lower than -40°C, and to the use of said compositions in the lubrication in a wide temperature range, preferably between -100°C and +180°C.
• perfluoropolyether oils as lubricants in a wide temperature range, in particular at very low temperatures, for example in the aerospace and refrigeration industry.
• these lubricants those used for the low temperatures have a typically linear structure, as for example FOMBLIN® marketed by Solvay Solexis S.p.A..
• These oils are used alone or formulated with particular thickeners, for example polytetrafluoroethylene (PTFE), to obtain greases.
• PTFE polytetrafluoroethylene
• Fluorinated greases having a low torque at -40°C are known.
• USP 6,329,326 describes greases for ball-bearings for cars containing linear perfluoropolyether oils having a kinematic viscosity, measured at 40°C, between 40 and 160 cSt, and PTFE having an average diameter lower than 0.1 micron.
• These greases are characterized by a low torque at -40°C and a good durability at 180°C and can therefore be used in a temperature range from -40°C to 200°C.
• applications at temperatures lower than -40°C are not mentioned, the behaviour of the greases at temperatures lower than -40°C is described neither.
• USP 6,723,684 describes greases for bearings in the automotive field and planes, having the following composition: a perfluoro-polyether oil having a linear structure and viscosity, at 40°C, equal to or lower than 25 cSt; a perfluoropolyether oil having a linear structure and viscosity, at 40°C, equal to or higher than 250 cSt; PTFE as thickener.
• the two oils used to prepare the grease are mixed so as to have a total viscosity, measured at 40°C, from 40 to 150 cSt.
• These greases are used in a temperature range from -40°C to +180°C. Torques at -40°C are given, however values and/or applications at temperatures lower than -40°C are not reported.
• the Applicant has surprisingly and unexpectedly found fluorinated greases comprising particular linear perlfuoropolyethers usable in applications at temperatures lower than -40°C showing torques lower than those of the prior art greases.
• the thickener (A) can be selected from the known thickeners of the prior art, for example talc, silica, polytetrafluoroethylene (PTFE), or their mixtures.
• silica is used as thickener, the amounts range from 1 to 10% by weight with respect to the total weight of (A)+(B); when talc or PTFE are used, the amounts range from 5% to 40% by weight, more preferably from 5% to 35%, with respect to the total (A) + (B).
• PTFE is used, more preferably PTFE having an average particle size between 0.01 ⁇ m and 0.3 ⁇ m.
• PTFE, used as thickener can be obtained by the known polymerization techniques, in particular by microemulsion, emulsion or dispersion polymerization. Furthermore the PTFE can also be subjected to irradiation. Known processes for preparing PTFE are described in patents EP 1,520,906 , US 4,864,006 , US 6,297,334 , US 6,576,703 .
• Compounds (B1) of formula (I), wherein the chlorine atoms, determined by 19 F NMR, are substantially absent, are compounds wherein the chlorine atoms are lower than the sensititivy limit of the analytical 19 F NMR method.
• Component (B1) is liquid at 20°C, shows a low vapour pressure, a high viscosity index and therefore it can be considered a lubricating oil. Besides it shows pour point values preferably lower than -90°C.
• Component (B2) can be selected from the following classes: (1) E-O-(CF 2 CF(CF 3 )O) m , (CFXO) n ,-E' wherein:
• the classes (1), (4), (5), (8) or their mixtures are preferred, the classes (5) and (8) or their mixtures are more preferred.
• the mixture of oils (B1)+(B2) preferably has a kinematic viscosity lower than 40 cSt at 40°C.
• additives commonly used in the lubrication field f.i. anti-wear additives for high and low loads, anti-rust, antioxidant additives and/or stabilizers can be present in the lubricating composition of the present invention, in an amount not higher than 10% by weight with respect to the total composition.
• stabilizing additives the perfluoropolyether dinitro derivative compounds, described in patent application US 2003/0203,823 ; the pyridine derivatives obtained according to patent application US 2004/235,-685 , can be mentioned.
• anti-wear additives it can be mentioned molybdenum sulphide, molybdenum organic compounds, boron nitride, graphite, phosphazene derivatives, in particular phosphazene derivatives containing perfluoropolyether chains, for example as those described in patent application US 2003/176.738 .
• anti-rust additives the disodic sebacate, sodium carbonate, functionalized derivatives of carboxylic acids containing perfluoropolyether chains, for example as those described in USP 5, 000, 864 or in USP 6, 025, 307 , can be mentioned.
• Component (B1) can be prepared, for example, according to the following process comprising the following steps:
• the solvents are the following: perfluoropropane (C 3 F 8 ), hydropentafluoroethane (C 2 F 5 H) and 2-hydroheptafluoropropane (CF 3 CFHCF 3 ), C 4 F 9 H (for example CF 3 C-FHCF 2 CF 3 , (CF 3 ) 3 CH, HCF 2 CF 2 CF 2 CF 3 ).
• the solvent used in step a1) is liquid at the synthesis temperatures (-40° ⁇ -80°C) and solubilizes the peroxidic polymer even in high molecular weights forming a homogeneous solution. This represents a remarkable advantage since there is no separation of the peroxidic polymer. This makes possible the industrial use of said process as no cloggings of the industrial plant piping due to uncontrolled viscosity increase take place. Further the thermal exchanges are extremely effective and this avoids uncontrolled degradation of the peroxidic polymer.
• the solvents used in step a1) allow a high reaction kinetics, so to maintain high productivities combined with a low peroxidic content in the polymer, lower than 4-5 g of active oxygen/100 g of product, to avoid explosion risks.
• the fluorine used in step a1) must be diluted with a gas.
• a gas Generally an inert gas, as nitrogen or helium is used.
• Oxygen can also be used as diluent.
• the fluorine when undiluted fluorine is used, the fluorine produces uncontrolled local reactions and gaseous decomposition products. The latter cause stopping of the process due to fouling of the reactor and of the optical system (UV lamp) in case of polymerization in the presence of UV radiations.
• the fluorine acts in step a1) as chain transfer agent with a very high selectivity, of the order of 90%.
• the fluorine furthermore, in step a1), reduces and substantially eliminates the reaction induction times avoiding the use of reaction activators.
• the solvents can be those above mentioned, or chlorinated solvents.
• CF 2 Cl 2 optionally in admixture with COF 2 can be mentioned.
• step a2) the molar ratio TFE/chemical initiator ranges from 10 to 200, preferably from 40 to 120.
• step b) the use of chain transfer agent can be omitted when the control of the molecular weight is not necessary. This happens, for example, when the viscosity of the peroxidic product is lower than 5,000 cSt.
• step b) generally fluorine or hypofluorites of formula (III), when present, are used with a flow-rate from 1 ⁇ 10 -2 to 3, preferably from 2 ⁇ 10 -2 to 2 moles ⁇ h/Kg polymer.
• Step a) and step b) of the process of the present invention can be carried out in a discontinous, semicontinuous or continuous way.
• Step b) ends when the peroxidic content in the polymer is substantially absent.
• the P.O. value is equal to or lower than the sensitivity limit of the analytical method used (1 ppm), by titration with thiosulphate of the iodine developed by the reaction of the peroxidic polymer with sodium iodide.
• the thermal treatment times are from 10 to 30 hours, depending on the P.O. and the temperature used in this step.
• Step c) is usually carried out in a discontinuous way.
• the reaction ends when, at 19 F NMR analysis, the functional end groups (mainly -OCF 2 COF and -OCOF) have been transformed into perfluoroalkyl end groups (method sensitivity limit: 1 maq/Kg polymer).
• step c) the fluorine is fed in amounts so to have a concentration in the perfluoropolyether generally corresponding to the fluorine solubility limit.
• the temperature used in the step it is of the order of 10 -2 moles of fluorine/litre of polymer.
• the product can be distilled to obtain fractions having a given number average molecular weight and a determined distribution of the molecular weights.
• the fluorinated greases of the present invention can be obtained according to the mixing procedures described in the prior art, for example comprising the following steps:
• the consistency of the greases of the present invention depends on the total concentration of the thickener used in the composition; in particular by increasing the thickener content, the penentration value decreases.
• the amounts of thickener (A) reported above allow to obtain all the penetration NLGI classes defined by the ASTM D 217 method, from degree 000, corresponding to a penetration value of 475 mm/10', to degree 6, corresponding to 85 mm/10'. This allows to satisfy the various requirements in a wide application range.
• component B) is preferably formed of an oil mixture, wherein the oil (B1) is present up to at most 50% by weight with respect to (B2), preferably up to 30%, and the kinematic viscosity of the mixture is preferably lower than 40 cSt, more preferably lower than 35 cSt.
• component (B) is preferably formed of the oil (B1) alone.
• compositions of the present invention show furthermore the advantage to be usable in applications having wide temperature ranges, for example -100/+180°C. It has indeed been found that the compositions wherein the oil (B2) belongs to the class (8) show a high thermal stability at 180°C combined with a low torque value. Therefore said compositions can be used as lubricants in applications where wide temperature ranges are present.
• the torque measurements have been carried out at different temperatures (-40°C, -60°C and -70°C) by using a ball-bearing according to what described in the ASTM D 1478 method.
• the measured parameters are the "starting torque", representing the initial starting point of the bearing, and the "running torque", which represents the working stress after 1 test hour.
• the measure unit is the g ⁇ cm.
• the kinematic viscosity at a given temperature has been determined by using capillary Cannon-Fenske type viscometers according to the ASTM D 445 method.
• the penetration value has been evaluated according to the ASTM D 217 method. The higher the penetration value and the lower the grease consistency.
• the starting torque and running torque values were measured, at the temperature of -70°C, and resulted equal to 578 g ⁇ cm and 44 g ⁇ cm, respectively.
• the starting torque and running torque values were measured, at the temperature of -70°C, and resulted equal to 3,667 g ⁇ cm and 1,581 g ⁇ cm, respectively.
• the grease starting torque and running torque values were measured at the temperature of -60°C, and resulted equal to 358 g ⁇ cm and 34 g ⁇ cm, respectively.
• the starting torque and running torque values of the grease were measured at the temperature of -40°C, and resulted equal to 455 g ⁇ cm and 198 g ⁇ cm, respectively.
• the starting torque and running torque values of the grease were measured also at the temperature of -60°C, and resulted equal to 676 g ⁇ cm and 181 g ⁇ cm, respectively.
• a mixture B) of oils was prepared formed of:
• the kinematic viscosity of the so obtained mixture measured at 40°C, is lower than 40 cSt and is equal to 23.1 cSt.
• Example 4 was repeated but by replacing the oil of formula (I) with a perfluoropolyether oil of class (5) having a substantially equal kinematic viscosity and lower than 25 cSt.
• the mixture of basic oils B) was prepared so as to obtain a mixture having a kinematic viscosity substnatially equal to that of the Example 4, by mixing:
• the kinematic viscosity of the so obtained mixture, measured at 40°C, is 25.5 cSt.
• the starting torque and running torque values of the grease were measured at the temperatures of -40°C and -60°C, and the following results were obtained: T (°C) Starting torque (g ⁇ cm) Running torque (g ⁇ cm) -40 299 162 -60 819 153

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