Patent Application
20080167208
The present invention relates to a lubricant, and more particularly to a lubricant comprising a lubricating oil or a grease for use in contact with graphite or molybdenum disulfide such as sintered, oil-impregnated bearings containing graphite or molybdenum disulfide or for use in contact with aluminum materials such as sliding members, etc., formed from aluminum materials.
Sintered, oil-impregnated bearings comprises porous bodies made compression of several kinds of solid powder obtained by adding solid lubricants such as graphite, molybdenum disulfide, carbon black, etc. to metal powders such as iron, copper, tin, zinc, etc. The sintered, oil-impregnated bearings can be used without any addition of oil owing to the self-lubrication action of a small amount of initially impregnated lubricant. Thus, it is important for the life of bearings that the a sufficient amount of lubricant can be retained in the bearings and can be stably used for a long time.
Cheaper sintered, oil-impregnated bearings than the ball-and-roller bearings have been increasingly used as automobile bearings, and consequently the lubricant for use in such sintered, oil-impregnated bearings have been inevitably exposed to such situations more strict where the high-temperature durability and low-temperature characteristics of lubricant are essentially required. Lubricating oil compositions comprising a perfluoropolyether oil as a base oil have been so far used in such situations, and have been inevitably brought into and kept with contact with some kinds of metals or solid lubricants having a very large surface area, so even the perfluoropolyether oils fail to maintain stable high-temperature characteristics, depending on their structures.
Patent Literature 1: JP-B-2,595,583
Aluminum has a high specific strength in spite of its low specific gravity, and can have a higher strength upon alloying or processing and further has a corrosion resistance. Thus, the aluminum has been used in various fields covering automobile parts, airplane and marine vessel parts, domestic electric appliances, electric tools, etc., of course, including sliding members, contributing to lighter weight of the machinery, higher working efficiency of high-speed revolution parts or sliding parts, or even to energy consumption saving. It is required that lubricants for use even in the parts of aluminum materials must be able to maintain their distinguished performance stably for a long time.
The present inventors have found that the high-temperature characteristics of perfluoropolyether oil are drastically deteriorated not only due to the structure of perfluoropolyether oil, but also due to contact with graphite or molybdenum disulfide used as one component of the sintered, oil-impregnated bearings, and further have found that the perfluoropolyether oil also undergoes drastic deterioration of the high-temperature characteristics even by contact of aluminum materials.
An object of the present invention is to provide a lubricant free from considerable deterioration of high-temperature characteristics (high-temperature durability), when used in contact with graphite or molybdenum disulfide such as sintered, oil-impregnated bearings, etc. containing graphite or molybdenum disulfide, or in contact with metallic parts such as ball bearings, etc. containing graphite or molybdenum disulfide, or even used in contact with aluminum materials including aluminum material as sliding members.
Such an object of the present invention can be attained by a lubricant for use in contact with graphite or molybdenum disulfide, or in contact with aluminum materials, which comprises a perfluoropolyether oil free from (CF2O)n groups as a repeat unit of polymer and having a kinematic viscosity at 40° C. of 50-1,500 mm2/sec., preferably 50-250 mm2/sec., more preferably 65-200 mm2/sec., as a base oil. The lubricant may be in any form of lubricating oil or grease, where perfluoropolyether oils represented by the following general formulae can be used as a base oil:
F(CF2CF2CF2O)mC2F5
RfO[CF(CF3)CF2O]p(CF2CF2O)qRf′
Perfluoropolyether oils undergo dramatically deterioration of the high-temperature characteristics (high-temperature durability) not only due to the structure of perfluoropolyether oils, but also due to contact with graphite or molybdenum disulfide used as one component in the sintered, oil-impregnated bearings. The present invention provides a lubricant free from considerable deterioration of high-temperature characteristics when used in contact with graphite or molybdenum disulfide such as the sintered, oil-impregnated bearings, etc. containing graphite or molybdenum disulfide, or in contact with metallic parts such as ball bearings, etc. containing graphite or molybdenum disulfide. Cases of the lubricant as used in contact with metallic parts include those used in atmospheres where the graphite or molybdenum disulfide prevails as scattered particles or as contaminants, for example, cases in contact with graphite or molybdenum disulfide coming from motor parts such as brushes, shafts, etc. The atmospheres where the graphite or molybdenum disulfide prevails as scattered particles or as contaminants are not to be restricted to the afore-mentioned cases.
The perfluoropolyether oils having a kinematic viscosity at 40° C. of 50-1,500 mm2/sec. can maintain the volatility and stability for a long time, even if used at higher temperature more than 150° C. in the presence of a solid lubricant such as graphite, molybdenum disulfide, etc., thereby attaining a longer life of parts to be used. Particularly, perfluoropolyether oils having a kinematic viscosity of 50-250 mm2/sec., preferably 65-200 mm2/sec., have distinguished low-temperature characteristics as well.
The present lubricant can be used in any mode of sliding including revolution, reciprocation, slipping, and oscillation, for example, as sintered, oil-impregnated bearing or bushes containing graphite or molybdenum disulfide in automobile uses fuel injectors including units for controlling rates of idle revolution, units for recycling an exhaust gas, units for electronic throttle controlling, etc., and uses such as those requiring a heat resistance, a low-temperature resistance and a load resistance, typically hub units, traction motors, alternators, etc. or in those requiring abrasion resistance or a low friction characteristics, typically power transmission units, power wind motors, wipers, etc.; in information system uses requiring a high speed, a low friction coefficient, a low outgassing capacity, etc., typically hard disc drives, flexible disc memory devices, compact disc drives, photomagnetic disc drives, etc.; business machine uses, typically LBP scanner motors, etc.; and motor uses such as domestic electric appliances, sound equipment, etc., used in the high-temperature circumstances, etc. The present lubricant can be also effectively used in atmospheres where graphite or molybdenum disulfide comes into contact with the lubricant directly or through the contaminant prevailing there.
The high-temperature characteristics (high-temperature durability) of perfluoropolyether oils are drastically lowered also when used in contact with aluminum materials including aluminum material as sliding members, but the present lubricant never undergoes considerable deterioration of high-temperature characteristics, even when used in such a case as above. That is, the present lubricant can maintain the volatility or stability for a long time and can show a lubricability in various sliding operations, even if used in the presence of aluminum materials at higher temperature more than 150° C. or 200° C., thereby attaining an extremely longer life of parts to be used.
Besides such various uses as mentioned above, the present lubricant can be used also in bearings or bushes of heated rolls used in plastics-processing machines, business machines, and copiers, and those of chains, etc. used in construction machines, machine tools, electrically driven tools, machines for printing, book-binding and paper processing, or their parts, and also can be used in lubrication of contacts between sliding members of ball-and-roller bearings, plain bearings, sintered bearings, gears, valves, cocks, oil seals, rolls, electric contacts, etc.
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Base oils for use in the present invention are those having a kinetic viscosity at 40° C. (according to JIS K2283, corresponding to ASTM D445) of 50-1,500 mm2/sec., preferably 50-250 mm2/sec., more particularly 65-200 mm2/sec., and free from (CF2O)n groups as a repeat unit of polymer. As shown in the following Example 1 and
As shown in the results of the following Example 2, percent weight loss of the present lubricant at such a high temperature as 250° C. even in the presence of aluminum materials is within an allowable range, and have the similar tendency even at a the kinetic viscosity at −40° C.
Perfluoropolyether oils (base oil) free from (CF2O)n groups as a repeat unit of polymer includes the following perfluoropolyether oils:
F(CF2CF2CF2O)mC2F5 (A)
RfO[CF(CF3)CF2O]p(CF2CF2O)qRf′ (B)
Perfluoropolyether oil (A): obtainable by anionic polymerization of 2,2,3,3-tetrafluorooxetane in the presence of a cesium fluoride catalyst, followed by a fluorine gas treatment of the resulting fluorine-containing polyether (CH2CF2CF2O)n under ultraviolet irradiation at 160°-300° C. The product oils having a kinetic viscosity at 40° C. of 5-2,000 mm2/sec. are available, which can satisfy conditions of m=2-100 in the general formula for perfluoropolyether oil (A).
Perfluoropolyether oil (B): obtainable by complete fluorination of a precursor formed by photooxidation polymerization of hexafluoropropylene or together with tetrafluoroethylene, or by anionic polymerization of hexafluoropropylene oxide or together with tetrafluoroethylene oxide in the presence of a cesium fluoride catalyst, followed by a fluorine gas treatment of the resulting acid fluoride compound having the terminal CF(CF3)COF groups. The product oils having a kinetic viscosity at 40° C. of 5-2,000 mm2/sec. are available, which can satisfy conditions of p+q=2-200 and q/p=0-2:1 in the general formula for perfluoropolyether oil (B).
When the kinetic viscosity is below 50 mm2/sec., the percent evaporation loss (percent weight loss) will be larger, and the oil film strength will be lowered, making the life shorter or causing attrition or seizure, whereas when the kinetic viscosity is above 1500 mm2/sec., the pour point will be much higher, resulting in not only a failure to obtain satisfactory low-temperature characteristics, but also the inconvenience of increasing a viscous resistance, thereby increasing a power consumption or a torque. So long as the base oil has a kinetic viscosity at 40° C. of 50-1,500 mm2/sec., a satisfactory stability to heat resistance can be obtained. Particularly when good low-temperature characteristics are required at a low temperature, for example, at −40° C., perfluoropolyether oil having a limited kinetic viscosity to 50-250 mm2/sec., preferably 65-200 mm2/sec., can be used. The perfluoropolyether oil having such a limited kinetic viscosity can not only satisfy the evaporation loss-resisting characteristics or low-temperature characteristics fully, but can be also used stably at high temperatures over 200° C. A mixture of two or more perfluoropolyether oils can be used, where the kinetic viscosity of such a mixture of base oils must be within such a range as mentioned above.
A thickener, preferably fluororesin, can be added to the base oil. The fluororesin for use herein includes, for example, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropene copolymer, perfluoroalkylene resin, etc. so far used as a lubricant. Polytetrafluoroethylene for use herein is such one as prepared by emulsion polymerization, suspension polymerization, solution polymerization, etc. of tetrafluoroethylene, thereby obtaining polytetrafluoroethylene having a number average molecular weight Mn of about 1,000 to about 1,000,000, followed by heat decomposition, electron beam-irradiated decomposition, physical pulverization, etc. thereof, thereby reducing the number average molecular weight Mn to about 1,000 to about 500,000. Copolymerization of tetrafluoroethylene and hexafluoropropene, and successive treatment to reduce the molecular weight to a lower one can be carried out in the same manner as in the case of polytetrafluoroethylene as mentioned above, and the resulting copolymer having a number average molecular weight Mn of about 1,000 to about 600,000 can be used. Molecular weight can be also controlled by using a chain transfer agent at the time of copolymerization reaction. Powdery fluororesins thus obtained have an average primary particle size of generally not more than about 500 μm, preferably about 0.1 to about 30 μm. Addition of powdery fluororesin can give the lubricant an oil film formability, anti-scattering and anti-leakage properties, and a rust inhibitiveness, thereby making the lubricability and durability much better.
Other thickeners for use herein than the fluororesins include, for example, metal soaps such as Li soap, etc., urea resin, minerals such as bentonite, etc., organic pigments, polyethylene, polypropylene, polyamide, etc., but from the viewpoint of heat resistance and lubricability it is preferable to use aliphatic dicarboxylic acid metal salts, monoamide mono-carboxylic acid metal salts, monoester carboxylic acid metal salts, diurea, triurea, tetraurea, etc.
The thickener such as the powdery fluororesins, etc., can be used as admixed in a proportion of 0.1-40% by weight, preferably 0.5-30% by weight, on the basis of total weight of composition comprising a perfluoropolyether base oil and a thickener. When the proportion is above 40% by weight, the composition will be too hard to seal bearings, etc., whereas when the proportion is below 0.1% by weight, the thickening capacity of fluororesin will not be displayed, resulting in lowering of apparent viscosity and deterioration of dispersibility into the base oil, and any satisfactory increase in the oil film formability, anti-scattering and anti-leakage property, and rust inhibitiveness cannot be expected. When the thickener is used in a proportion from a little less than about 10% by weight on the basis of total weight of the thickener and the base oil, the composition takes a grease form. When the thickener is used in a proportion of 5% by weight or less on the same basis as above, the composition shows a fluidity in a category of “liquid grease”, as will be shown in the following Examples and Comparative Examples, where the low-temperature characteristics are evaluated as a low-temperature viscosity of base oil mixtures, whereas in embodiments of using a thickener in a proportion of 30% by weight, the composition shows a semi-solid form in a category of grease, where the low-temperature characteristics are evaluated as a low-temperature torque.
Within such a range as not to injure the object of the invention, so far well known fluorine-based additives can be used, if required, such as perfluoropolyether oils having terminals substituted with alcohols, carboxylic acids or their esters, amines, amides, phosphoric acids or their esters, phosphonic acid or its ester, reaction products, formed from isocyanates and alcohols or amines, etc.
The lubricant base oil can further contain additives so far added to the conventional lubricants such as various non-fluorine-based additives so far having had no compatibility with perfluoropolyether oils, due to the addition of fluororesin, a viscosity index-improver, a pour point depressant, an ashless dispersant, a metal-based detergent, an antioxidant, a rust inhibitor, a corrosion inhibitor, an antifoaming agent, an extreme pressure agent, an oiliness agent, a friction-controlling agent, a solid lubricant, etc., if required.
The antioxidant for use herein includes, for example, a phenol-based antioxidant such as 2,6-di-t-butyl-4-methylphenol, 4,4-methylenebis (2,6-di-t-butylphenol), etc., and amine-based antioxidants such as alkyldiphenylamine having an alkyl group of 4-20 carbon atoms, triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylated α-naphthylamine, phenithiazine, alkylated phenithiazine, etc.
The rust inhibitor for use herein includes, for example, fatty acid, fatty acid amines, alkylsulfonic acid metal salts, alkylsulfonic acid amine salts, oxidized paraffin, polyoxyethylene alkyl ethers, etc., and the corrosion inhibitor includes, for example, benzotriazole, benzoimidazole, thiadiazole, etc.
The extreme pressure agent includes, for example, phosphorous-based compounds such as phosphoric acid esters, phosphorous acid esters, phosphoric acid ester amine salts, etc., sulfur-based compounds such as sulfides, disulfides, etc., dialkyldithiophosphoric acid metal salts, dialkyldithiocarbamic acid metal salts, etc.
The oiliness agent includes, for example, fatty acids or their esters, higher alcohols, polyhydric alcohols or their esters, aliphatic amines, fatty acid monoglycerides, etc.
The solid lubricant includes, for example, graphite, molybdenum disulfide, boron nitride, silane nitride, etc. In the case of using graphite or molybdenum disulfide as solid lubricant lowering of changes in heat resistance with time of perfluoropolyether base oil can effectively prevent.
A composition to be formed by adding a thickener to a perfluoropolyether base oil can be prepared, for example, by any of the following procedures:
(a) By mixing a perfluoropolyether base oil with a thickener in a predetermined amounts, respectively, followed by thorough kneading thereof through three rolls or a high pressure homogenizer, (b) by adding a perfluoropolyether oil and an aliphatic carboxylic acid to a heatable and stirrable reactor, melting the content with heating, and then adding thereto a metal hydroxide (and an amide compound or an alcohol compound) in predetermined amounts, to conduct metal salting reaction (and amidation reaction or esterification reaction), followed by cooling and thorough kneading thereof through three rolls or a high pressure homogenizer, and (c) by adding a perfluoropolyether oil and an isocyanate to a heatable and stirrable reactor, heating the content, adding a predetermined amount of an amine thereto, followed the resulting reaction product by cooling and thorough kneading thereof through three rolls or a high pressure homogenizer.
The present invention will be described in detail below, referring to Examples, but is not limited thereto.
The following three kinds of perfluoropolyether base oils were admixed with 10% by weight of graphite powder (flake graphite powder CB-150, a product of Japan Graphite Co.; fixed carbon content: 98.0% or more, and average particle size: 40 μm), or molybdenum disulfide (LM13-SM powder, a product of Daito Lubricant Manufacturing Co.; average particle size: 0.4 μm) on the basis of the sample, and 0.6 g each of the samples was sampled into individual glass dishes, 36 mm in diameter, smeared onto the dish surfaces in a uniform thin film state, and left standing in a thermostat tank at 200° C. to determine changes in percent oil weight loss with time.
The results are shown graphically in
It can be seen from the results that in the case of perfluoropolyether base oils free from (CH2O)n groups as a repeat unit of polymer, the percent oil weight loss at 200° C. is a substantially independent from the presence of graphite, whereas in the case of perfluoropolyether oil having (CH2O)n groups as a repeat unit of polymer, substantially all of the oil is evaporated and lost within a very short time by the presence of graphite or molybdenum disulfide, particularly graphite.
The following perfluoropolyether base oils (A) or (B) having various kinetic viscosities at 40° C. were admixed with 10% by weight of aluminum powder (a product of Wako Pure Chemical Co., purity: 99.5%, and particle sizes: 53-150 μm) on the basis of the sample, and 0.3 ml each of the samples was sampled into individual glass dishes, 37 mm in diameter, smeared onto the dish surfaces in a uniform thin film states and left standing in a thermostat tank at 250° C. to determine weights of entire glass dishes after 100 hours, thereby calculating percent oil weight losses.
Perfluoropolyether oil (A): F(CF2CF2CF2O)mC2F5
Perfluoropolyether oil (B): RfO[CF(CF3)CF2O)pRf′
Perfluoropolyether oil (C): RfO(CF2CF2O)m(CF2O)nRf′
Emulsion-polymerized polytetrafluoroethylene powder (Mn: about 50,000 to about 100,000; average primary particle size: 0.2 μm) was used as fluororesin powder.
The results are shown in the following Table 1, together with kinds and amounts (parts by weight) of base oils, amounts (parts by weight) of fluororesin and additive, where the kinetic viscosity at 40° C. and pour point (according to JIS K2269, corresponding to ASTM D97) of the base oil or base oil-fluororesin mixture, and percent weight loss and low-temperature viscosity (kinetic viscosity at −40° C. according to JIS K2283, corresponding to ASTM D445) are given as results of determination, where Nos. 1-12 relate to Examples, whereas Nos. 13-15 relate to Comparative Examples.
It can be seen from the results that the percent weight loss at 250° C. is considerably increased in the cases of using base oils having a kinetic viscosity at 40° C. of less than 50 mm2/sec. (Nos. 13 and 14), and the percent weight loss at 250° C. is considerably increased after 100 hours in the case of using a base oil having (CF2O)n groups as a repeat unit of polymer (No. 15), so the sample has been almost lost, whereas the percent weight loss at such a high temperature as 250° C. is within an acceptable range in the cases of using base oil having a kinetic viscosity at 40° C. in a range of 50-1,500 mm2/sec., and the base oils having a kinetic viscosity at 40° C. in a range of 50-250 mm2/sec. have the similar tendency even at a kinetic viscosity at −40° C. (Nos. 1-10).
Furthermore, in addition above items, grease consisting of 70 parts by weight of A-1 and 30 parts by weight of fluororesin (No. 21); 70 parts by weight of A-2 70 and 30 parts by weight of fluororesin (No. 22); 70 parts by weight of B-2 and 30 parts by weight of fluororesin (No. 23); and 70 parts by weight of B-3 and 30 parts by weight of fluororesin (No. 24) were subjected to a low-temperature torque test (according to JIS K2220.5.14, torques were measured at the start-up and in the stationary state; corresponding to ASTM D1478). The results are shown in the following Table 2. No. 24 relates to Comparative Example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-044949 | Feb 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/302801 | 2/17/2006 | WO | 00 | 8/22/2007 |
