Patent Application
20060111250
The present invention relates to stabilizing additives for lubricating oils and greases towards Lewis acids.
More specifically the invention relates to the use of fluorinated additives as stabilizing agents of fluorinated oils and greases, preferably having a perfluoropolyether structure, for their use in the presence of Lewis acids at high temperature, for example higher than 200° C. up to 280° C. The present invention also refers to the process for preparing said additives and to compositions of oils and greases, preferably having a perfluoropolyether structure, comprising said additives.
It is known in the prior art that perfluoropolyethers have high chemical and thermal stability and are therefore used in many applications as lubricating oils and greases, or hydraulic fluids. However in some extremely severe operating conditions, perfluoropolyethers show the drawback to have an insufficient thermal stability and they tend therefore to decompose.
Particularly critical applications are also those wherein lubricants having a perfluoropolyether structure are in the presence of Lewis acids. It is indeed known that Lewis acids, in particular aluminum, iron, titanium, vanadium and other fluorides, catalyze perfluoropolyether degradation. The applications wherein lubricants are in contact with Lewis acids are for example lubrication of magnetic discs. In this case the Lewis acid is generated by reading head of the hard disk. This process of degradation leads to the breaking and fragmentation of the perfluoropolyether chains. In some cases it is also possible to arrive to the total decomposition of the perfluoropolyether fluid. Under these conditions volatile fractions are produced which evaporate under the lubricant use conditions, so that the lubricant can be completely lost. Furthermore, the fluid decomposition is generally associated to a progressive metal corrosion, when in contact with the fluid.
It is known in the prior art that the stability to Lewis acids of oils and greases having a perfluoropolyether structure, when used at high temperatures, can be impoved by using specific stabilizing additives. European patent application No. 04011149.4 (publication No. EP 1 479 753) describes stabilizing additives having a (per)fluoropolyether structure for lubricating oils and greases towards Lewis acids ended with pyridine groups, optionally substituted.
Other stabilizing additives towards Lewis acids are known in the prior art, see U.S. Pat. No. 6,083,600. The additives of this patent have a (per)fluoropolyether structure and are ended at both ends with substituted amine groups. In the Examples it is shown that said compounds are stable in the presence of Lewis acids at the temperature of 200° C. for a time not higher than 4 hours (see the Example 7 and FIG. 3). The stability of these compounds at temperatures higher than 200° C., up to 280° C., is not reported.
The need was felt to have available compounds to be used as additives for fluorinated lubricating fluids, preferably having a perfluoropolyether structure, said compounds having the following combination of properties:
The Applicant has surprisingly and unexpectedly found compounds to be used as additives to stabilize fluorinated oils and greases in the presence of Lewis acids, having the above combination of properties.
An object of the present invention are compounds usable as stabilizing additives of fluorinated, preferably perfluoropolyether, fluids, working at high temperatures, higher than 200° C., up to 280° C. in the presence of Lewis acids, optionally even in the presence of metals, said compounds being formed of (per)fluoropolyether chains and end groups having a heteroaromatic structure, having the following general formula:
T1-CFW1—O—Rf—CFW2-T2 (I)
wherein
Preferably in formula (I—B) of Y when Q is CH═N, N is linked to the aromatic ring and the compound belongs to the quinoxaline class.
The repeating unit (C3F6O) of the (per)fluoropolyoxyalkylene chain represents units of formula:
—(CF2CF(CF3)O)— or —(CF(CF3)CF2O)—.
The preferred perfluoropolyether chain Rf is selected from the following structures:
—(CF2CF(CF3)O)a(CFXO)b—CF2(R′f)CF2—O—(CF2CF(CF3)O)a(CFXO)b— (A)
Particularly preferred (per)fluoropolyoxyalkylene structures are (A) and (B), preferably (B).
The above described (per)fluoropolyoxyalkylene structures can be obtained by using the synthesis methods described in GB 1,104,482, U.S. Pat. No. 3,715,378, U.S. Pat. No. 3,242,218, U.S. Pat. No. 4,647,413, EP 148,482, U.S. Pat. No. 4,523,039, EP 340,740, WO 90/03357, U.S. Pat. No. 3,810,874, EP 239,123, U.S. Pat. No. 5,149,842, U.S. Pat. No. 5,258,110.
The compounds of the present invention are transparent and odourless viscous liquids.
A further object of the present invention are lubricating formulations comprising:
The perfluoropolyethers usable as oils or as components for preparing greases are selected from the following classes:
E-O—[CF(CF3)CF2O]m′(CFXO)n′-E′ (1)
These compounds can be obtained by perfluoropropene photooxidation as described in GB 1,104,432, and by subsequent conversion of the end groups as described in GB 1,226,566.
C3F7O—[CF(CF3)CF2O]o′-D
These products are obtained by photooxidation of C2F4 as reported in U.S. Pat. No. 3,715,378 and subsequent treatment with fluorine as described in U.S. Pat. No. 3,665,041.
E-O—(CF2CF2CF2O)v′-E′ (6)
The perfluoropolyethers of the above classes from (1) to (7) are liquids having a very low vapour pressure and having a kinematic viscosity measured at 20° C. generally from 10 to 10,000 cSt, preferably from 300 to 2,000 cSt.
The preferred perfluoropolyether oils are those of the classes (1), (4), (5) and are available on the market with the trademark FOMBLIN® marketed by Solvay Solexis.
The formulations of the invention can contain other additives commonly used in fluorinated lubricant formulations, preferably having a perfluoropolyether structure. For example anti-wear, anti-rust additives and Lewis anti-acid additives can be mentioned. Anti-wear additives are for example those having a perfluoropolyether structure linked to phosphazene rings. For example those described in EP 1,336,614 in the name of the Applicant can be used.
Furthermore, in case of lubricating greases, the formulations contain as essential components, besides one or more perfluoropolyether oils belonging to one or more of the above classes and to the additive of formula (I), also thickening additives as for example PTFE, optionally sodium terephthalate, calcium or lithium soaps, polyurea. As thickening agent, PTFE (polytetrafluoroethylene) is preferably used.
Other components, generally contained in the greases, are the following: dispersing agents as for example surfactants, in particular nonionic surfactants and preferably with a perfluoropolyether or perfluoroalkyl structure; besides talc or inorganic fillers. The lubricating greases having a perfluoropolyether polyether structure can also contain other additives commonly used in grease formulations.
A further object of the present invention is a process for obtaining the compounds of formula (I), comprising the following steps:
In step a) the compounds of formula II) can be obtained as described in U.S. Pat. No. 3,810,874.
The organic solvent used in the process of the present invention is preferably selected from hydrogenated solvents, as for example terbutyl alcohol, acetonitrile, diglyme, DMF, toluene, xylene, or fluorinated or hydrofluorinated solvents, having a boiling point in the range 20° C.-150° C., preferably. 40° C.-100° C.
In step a) the ratio by weight solvent/(per)fluorinated alchol or thiol, preferably ranges from 0.5 to 10, more preferably from 2 to 5.
The base used in step a) can be an organic or inorganic base, for example it can be selected from potassium terbutylate, KOH, NaH.
In step a) the ratio in equivalents between the base and compound (II) ranges from 1.1 to 2, preferably from 1.2 to 1.5.
In step a) the reaction is very rapid.
The reaction times in step b) depend on the reaction temperature and are generally between 4 hours and 24 hours. For example when the reaction temperature is 80° C., the reaction time is about 6 hours.
In step b) the ratio [equivalents of the alcoholate or thiolate function of the (per)fluoropolyether]/moles of the compound (III) ranges from 1 to 0.5, preferably from 0.8.to 0.6.
In step c) the product is isolated by using the known methods of the prior art.
The yields obtained with the process of the present invention are high, anyway higher than 80%, preferably higher than 90%.
As said, the compounds of formulae (I) can be used as additives for fluorinated oils and greases and preferably for lubricating fluids having a perfluoropolyether structure.
Tests carried out by the Applicant have shown that the compounds of the invention can also be used as anti-wear additives for perfluoropolyether oils.
Furthermore tests carried out by the Applicant have shown that the compounds of the present invention can also be used as additives capable to confer thermooxidative stability to fluorinated oils when the temperatures are particularly high, for example higher than 200° C., up to 330° C.
Some Examples are reported hereinafter for illustrative and not limitative purposes of the present invention.
Methods
The tests used for evaluating the effectiveness of the additives described in the present invention are briefly reported hereinafter.
Stability Test to Lewis Acids for Oils
The determination of the stability of the oils to be tested to Lewis acids in the presence of the additives of the present invention was carried out as follows.
5 grams of the fluid to be tested, containing the additive excluding the comparative Examples carried out with the non additived fluid, and 0.1 g of AlF3 are fed into a glass test tube (about 10 cc). The test tube is weighed and closed with a screw plug having a hole in the middle on which a 30 cm PTFE little pipe is fixed which conveys possible decomposition products in a NaOH solution (0,1 N), contained in a collecting cylinder. The test tube is then brought to the temperature from 200° C. to 280° C. for 24 hours. At the end the test tube is cooled and weighed. The weight difference before and after heating, referred to the sample weight before the test, gives the loss determined in per cent by weight of the tested fluid.
Stability Test to Lewis Acids for Greases
A 50 g grease sample to be tested, containing the additive except the comparative Examples carried out with the non additived fluid, is additioned with 5% by weight of AlF3 and deposited, by means of a stratifying knife, in a glass capsule (plate) having a 95 mm diameter, so as to cover the whole exposed surface. The capsule is put in a drier for 30 minutes, then weighed and put in a stove at a temperature from 200° C. to 280° C. After 4 hours the capsule is taken from the stove and cooled in a drier. The capsule is then weighed again and the per cent weight loss with respect to the starting weight is evaluated. The test result is therefore expressed in per cent weight loss with respect to the starting weight.
Anti-wear Test
The ASTM D 4172 method has been used as application test allowing to determine the wear as described hereinafter.
Three AISI N. E-52100 steel spheres, having a 12.7 mm diameter, 25 EP degree (Extra Polish), previously cleaned by washing by dipping in n-hexane (15 minutes) and then in Galden® HT55 (15 minutes) followed by drying, are placed in a container equipped with a suitable hollow so as to have three points in contact and, then, are covered with the lubricant to be tested. A fourth sphere of the same kind, connected to an electric motor which allows its rotation, is placed over the three mentioned spheres with a load of 40±0.2 kgf (392 N). The whole is assembled, closed and heated to 75°±2° C. When said temperature has been reached, the fourth sphere, placed on the three of reference, is rotated at the rate of 1200±60 rpm for 60±1 minutes. At the end of the test the container is disassembled, the lubricant is removed and the wear of the three spheres contained therein is evaluated by an optical microscope having a 0.01 mm precision.
The wear value, expressed in mm, is obtained as an arithmetic average of six determinations, by measuring for each sphere, without removing it from the hollow, the wear diameter in the rotation direction and the diameter perpendicular thereto.
Determination of the Molecular Weight
The number average molecular weight is determined by 19F NMR analysis according to S. Turri et al. Macromolecules, 1995, 28, 7271-7275 and S. Turri et al. Macromol. Chem. Phys. 198 3215-3228 (1997).
Preparation of the Derivative of Formula (1) Having Number Average MW 4,116
30 g of terbutyl alcohol and 2.3 g (0.02 moles) of potassium terbutylate are introduced into a 250 ml glass reactor equipped with mechanical stirrer, thermometer and condenser. Then 30 g (0.0156 eq) of HOCH2CF2O(CF2CF2O)c(CF2O)dCF2CH2OH (equivalent weight EW=1923) wherein c/d=0.97, are fed under stirring at room temperature. The reaction mixture is left under stirring for about 30 minutes, then 3.2 g (0.02 moles) of 2-chlorobenzo thiazole are fed into the reactor. The so obtained mixture is heated to 80° C. and kept under stirring for about 6 hours. After cooling 100 g of demineralized water are added and then the mixture is neutralized with a HCl aqueous solution at 5% by weight. Then the phases are let separate, the heavy organic phase is separated and washed twice with 100 g of demineralized water. The organic phase is anhydrified at 120° C. at a residual pressure of 10−2 mbar for about 4 hours, and then filtered on 0.2 μm PTFE filter. 25.7 g of product are thus obtained having a conversion of alcoholic groups into ether groups equal to 98%. The IR and NMR (1H, 19F and 13C) analyses confirm the structure of the above product.
The thermogravimetric analysis has given the following results:
Preparation of the Derivative of Formula (2) Having Number Average MW 2,210
40 g of terbutyl alcohol and 3 g (0.027 moles) of potassium terbutylate are introduced into a 250 ml glass reactor equipped with mechanical stirrer, thermometer and condenser.
Then 20 g (0.02 eq) of HOCH2CF2O(CF2CF2O)c(CF2O)dCF2CH2OH (EW=970) wherein c/d=1.0, are fed under stirring at room temperature. The reaction mixture is left under stirring for about 30 minutes, then 4 g (0.023 moles) of 2-chlorobenzothiazole are fed into the reactor. The so obtained mixture is heated to 80° C. and kept under stirring for about 6 hours. After cooling 100 g of demineralized water are added and then the mixture is neutralized with a HCl aqueous solution at 5% by weight. Then the phases are let separate and the heavy organic phase is separated and washed twice with 100 g of demineralized water. The organic phase is anhydrified at 120° C. at a residual pressure of 10−2 mbar for about 4 hours, and then filtered on 0.2 μm PTFE filter. 17.9 g of product are thus obtained having a conversion of alcoholic groups into ether groups equal to 96%. The IR and NMR (1H, 19F and 13C) analyses confirm the structure of the above product.
The thermogravimetric analysis has given the following results:
Preparation of the Derivative of Formula (3) Having Number Average MW 4,106
20 g of terbutyl alcohol and 1.3 g (0.012 moles) of potassium terbutylate are introduced into a 250 ml glass reactor equipped with mechanical stirrer, thermometer and condenser.
Then 20 g (0.01 eq) of HOCH2CF2O(CF2CF2O)c(CF2O)dCF2CH2OH (EW=1923) wherein c/d=0.97, are fed under stirring at room temperature. The reaction mixture is left under stirring for about 30 minutes, then 2 g (0.012 moles) of 2-chloro quinoxaline are fed into the reactor. The so obtained mixture is heated to 80° C. and kept under stirring for about 6 hours. After cooling 100 g of demineralized water are added and then the mixture is neutralized with a HCl aqueous solution at 5% by weight. Then the phases are let separate and the heavy organic phase is separated and washed twice with 100 g of demineralized water. After separation the organic phase is anhydrified at 120° C. at a residual pressure of 10−2 mbar for about 4 hours, and then filtered on 0.2 μm PTFE filter. 17.6 g of product are thus obtained having a conversion of alcoholic groups into ether groups equal to 99%. The IR and NMR (1H, 19F and 13C) analyses confirm the structure of the above product.
A thermooxidation test is carried out by using 50 g of Fomblin® Z25, having number average molecular weight 10,000, additived with 0.5 g of the above synthesized product of formula (3).
The termooxidation test was carried out by using the equipment described by Carl E. Snyder, Jr. and Ronald E. Dolle, Jr., in ASLE Transactions, 13(3), 171-180 (1975). The operating conditions used were the following:
A sample of the fluid to be tested, containing the additive is introduced in the glass test tube of the equipment (see for example FIG. 1 of the reference). It is weighed and heated at the above indicated temperature. The required time elapsed (24 h), the glass test tube is cooled to room temperature and weighed again. The difference of weight before and after heating, referred to the weight of the sample before the test, gives the per cent weight loss of the tested fluid. At the end of the test also the state of the metals dipped into the fluid is visually evaluated.
After 24 hours a weight loss of the fluid equal to 0.22% is determined. The metals dipped into the fluid during the test (satinless steel and Ti, Al, V alloy) did not show oxidation/attack signs; at the end of the test their aspect was comparable with that of the specimens of the same metals not subjected to the treatment.
The previous test was repeated by increasing the exposure time of the mixture to 192 hours. At the end of the test the fluid showed a loss of 1.3% by weight. The metals dipped into the fluid during the test (stainless steel and Ti, Al, V alloy) did not show oxidation/attack signs, and at the visual inspection they were comparable with those not subjected to the treatment.
The thermooxidation test is repeated in the absence of the additive. After 24 hours under the indicated operating conditions the fluid was completely decomposed (weight loss=100%). The metals, dipped into the fluid during the test, show at the end signs of marked corrosion.
Preparation of the Derivative of Formula (4) Having Number Average MW 2,200
30 g of terbutyl alcohol and 2.7 g (0.024 moles) of potassium terbutylate are introduced into a 250 ml glass reactor equipped with mechanical stirrer, thermometer and condenser.
Then 20 g (0.02 eq) of HOCH2CF2O(CF2CF2O)c(CF2O)dCF2CH2OH (EW=970) wherein c/d=1.0, are fed under stirring at room temperature. The reaction mixture is left under stirring for about 30 minutes, then 4 g (0.024 moles) of 2-chloro quinoxaline are fed into the reactor. The so obtained mixture is heated to 80° C. and kept under stirring for about 6 hours. After cooling 100 g of demineralized water are added and then the mixture is neutralized with a HCl aqueous solution at 5% by weight. Then the phases are let separate and the heavy organic phase is separated and washed twice with 100 g of demineralized water. After separation the organic phase is anhydrified at 120° C. at a residual pressure of 10−2 mbar for about 4 hours, and then filtered on 0.2 μm PTFE filter. 18.3 g of product are thus obtained having a conversion of alcoholic groups into ether groups equal to 97%. The IR and NMR (1H, 19F and 13C) analyses confirm the structure of the above product.
The stability test to Lewis acids for oils is carried out by using 5 g of Fomblin® Z25 oil, having number average molecular weight 10,000, additived with 0.05 g of the product of formula (1) of the Example 1. After 24 hours at 250° C. a weight loss of the fluid equal to 0.17% is determined.
The stability test to Lewis acids for oils is carried out by using 5 g of Fomblin® Z25 oil, having number average molecular weight 10,000, additived with 0.05 g of the product of formula (2) of the Example 2. After 24 hours at 250° C. a weight loss of the fluid equal to 0.18% is determined.
The Example 5 is repeated, but in the absence of the additive of the invention.
The fluid results completely decomposed after 5 hours from the beginning of the test.
The stability test to Lewis acids for oils is carried out by using 5 g of Fomblin® Z25 oil, having number average molecular weight 10,000, additived with 0.05 g of the product of formula (3) of the Example 3. After 24 hours at 250° C. a weight loss of the fluid equal to 0.18% is determined.
A grease is prepared by mixing 70% by weight of Fomblin® M30 having molecular weight 9,800, with 30% by weight of PTFE. The grease is additived with 1% by weight of the additive prepared according to the Example 1 and then subjected to the stability test to Lewis acids for greases. At the end of the test, carried out at 250° C. for 4 h, a weight loss of 0.21% is determined.
The stability test to Lewis acids for oils is carried out by using 5 g of Fomblin® Z25 oil, having number average molecular weight 10,000, additived with 0.05 g of the product (I) of the Example 1 described in EP 1,354,932. This additive contains arylsubstituted end groups.
After 24 hours at 250° C. a weight loss of the fluid equal to 0.42% is determined. Said weight loss is about 2.5 times higher than that observed by using the additives of the present invention.
The stability test to Lewis acids for oils is carried out by using 5 g of Fomblin® Z25 oil, having number average molecular weight 10,000, additived with 0.05 g of the product of the Example 1 described in EP 1,336,614. This additive contains phosphazene groups.
After 24 hours at 250° C a weight loss of the fluid equal to about 5.0% is determined. Said weight loss is more than one order of magnitude higher than that observed by using the additives of the present invention.
A sample of Fomblin® M30 oil was subjected to the previously described anti-wear test ASTM D 4172. The wear value obtained as an average of 6 determinations is of 1.40 mm.
A mixture formed in % by weight of 99% of Fomblin® M30 oil and 1% of additive having structure (1) of the Example 1 of the present invention was subjected to the previously described ASTM D 4172 test. The wear value obtained as an average of 6 determinations is of 1.05 mm-equal to a 25% reduction with respect to the value obtained without additive (Example 12 comparative).
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2004 A 002239 | Nov 2004 | IT | national |
