Patent Application
20060030500
This application claims the benefit of Japanese Application No. 2004-187190, filed Jun. 25, 2004, the entirety of which is incorporated herein by reference.
The present invention relates to a fluororesin which has both low friction coefficient and excellent wear resistance, particularly to a fluororesin preferably for use under lubrication by a lubricating oil or an operating oil, and a sliding member and a sliding device comprising such a fluororesin.
Since fluororesins have low friction coefficients, they heretofore have been used in many sliding portions. However, since fluororesins have a band structure, they are generally inferior in wear resistance. As a measure for enhancing the wear resistance of the fluororesin, it is common to add fiber-based fillers such as glass fibers and carbon fibers or metal fillers such as bronze. However, when these fillers are added, the fillers promote wear on a sliding target material in cases where the material is a nonferrous metal such as an aluminum alloy. On the other hand, when the addition of the filler to the fluororesin is limited in order to reduce the wear on the target material, predetermined wear resistance is not obtained.
As a means for solving the above-described problem, there has been provided a reformed fluororesin which has been reformed by irradiating the fluororesin with electrolytic dissociative radiation while being heated under an inactive gas atmosphere at a temperature equal to its melting point or higher (see, Japanese Patent Application Laid-Open NO. 11-116624). The wear resistance of this reformed fluororesin can be largely enhanced without adding the fillers thereto. Therefore, a superior sliding characteristic is indicated under dry lubrication.
Additionally, since the reformed fluororesin exhibits low surface energy, and exhibits an oil-repellent property in the same manner as a usual fluororesin, generation of an oil film is inhibited in the presence of the lubricating oil or the operating oil, and an effect of sufficiently reducing the friction coefficient is not obtained.
Although the wear resistance of the fluororesin is improved in this manner, an oil film is inhibited from being formed in the presence of the lubricating oil and the operating oil, and a fluid lubricating effect by the lubricating oil and the operating oil cannot be easily developed, because the fluororesin has the low surface energy and exhibits the oil-repellent property.
To solve this problem, as methods of improving wettability with the lubricating oil and the operating oil, a corona treatment, an RF bombardment treatment, a DC bombardment treatment (see International Publication No. WO 98/44026), a method of introducing monomer other than monomer constituting the fluororesin as a functional group (see Japanese Patent Application Laid-Open 2001-208249), and a plasma treatment have been known.
However, since a special step for increasing surface energy is required in any of the above-described methods, there has been a problem that costs rise.
Moreover, when a method of reforming a fluororesin by the above-described electrolytic dissociative radiation treatment, and a method of improving wettability with a lubricating oil and operating oil are used together, it is theoretically possible to manufacture a fluororesin exhibiting a superior friction characteristic in the presence of the lubricating oil and operating oil. However, two types of manufacturing steps have to be added, a cost aspect raises a problem, and therefore this method has not been put into practical use in the present situations.
The present invention has been developed in view of the problems of the conventional techniques, and objects thereof are to provide a fluororesin which has both a low friction coefficient and a superior wear resistance and which exerts a superior friction characteristic in the presence of a lubricating oil and/or an operating oil, a method of reforming a fluororesin, a sliding member comprising a sliding portion comprising such a fluororesin, a sliding apparatus comprising such a sliding member and at least one oil material, and a sliding system comprising such a sliding apparatus and a target material comprising a sliding surface on which the sliding member slides.
As a result of intensive studies performed in order to address the above-described objects, the present inventors have found that the above-described objects can be achieved, when a predetermined oxygen-containing functional group is introduced by an appropriate unsaturated bond introduction process or the like, and they have completed the present invention.
That is, according to the present invention, there is provided a fluororesin comprising a substituted main frame resin on which at least one of the hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin are substituted with an oxygen-containing functional group and in which the visible light transmittance in a wavelength of 600 nm of the fluororesin is greater than that of the main frame resin.
Moreover, there is provided a method of reforming a fluororesin, comprising: extracting some of the hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin to introduce an unsaturated bond to produce a modified main frame resin; and applying dissociation energy of the unsaturated bond in the presence of oxygen.
Furthermore, according to the present invention, there is provided a sliding member comprising a fluororesin as described above in a sliding portion. Additionally, according to the present invention, there is provided a sliding apparatus comprising a sliding member as discussed above and at least one oil material selected from among lubricating oil and operating oil. In addition, according to the present invention, there is provided a sliding system comprising a sliding apparatus as discussed above and a target material which comprises a sliding surface on which the sliding member of the sliding apparatus slides.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description of a preferred mode of practicing the invention, read in connection with the accompanying drawings in which:
A fluororesin of the present invention will be described hereinafter in detail. It is to be noted that in the present specification, “%” indicates a percentage by mass unless otherwise specified.
As described above, the fluororesin of the present invention is a fluororesin comprising a substituted main frame resin having a structure in which some of hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin are substituted with an oxygen-containing functional group, and in which a visible light transmittance in a wavelength of 600 nm of the fluororesin is greater than that of the main frame resin.
Here, examples of the main frame resin include various fluororesins, but the fluororesin of the present invention is used for a sliding purpose. Therefore, a fluororesin superior in sliding characteristic is preferably used as the main frame resin among these fluororesins. Specifically, one or more of a tetrafluoroethylene resin, a perfluoroethylene polypropylene resin, a perfluoroalkoxy resin, and a vinylidene fluoride resin are preferable.
As the oxygen-containing functional group substituted for at least one of the hydrogen atoms and/or at least one of the fluorine atoms bonded to the carbon atoms of the main frame resin, any functional group containing an oxygen atom may be used, and preferred examples include a hydroxyl group, a carbonyl group, a carboxyl group, a ketone group, an ether group and the like.
One or more hydrogen atoms and/or one or more fluorine atoms may be substituted with the oxygen-containing functional group. All of the corresponding hydrogen atoms may be substituted, but at least one fluorine atom needs to remain, i.e., not all of the fluorine atoms bonded to the carbon atoms of the main frame resin are substituted.
It is to be noted that for the sake of convenience of description, “substitution” has been described, but it does not have any limiting meaning attributable to a substitution reaction, e.g., the expression that an atom is “substituted” with a functional group indicates that the substituted main frame resin differs from the main frame resin in that the functional group is present instead of the atom in at least one location in the molecule (i.e., the expression “substituted” does not require that a particular reaction or any reaction have taken place in which the atom is replaced with the functional group at any location). Even when the atoms are substituted by an additional reaction, this is included in the scope of the present invention. Similarly, the expression “extracted” as used herein, does not have any limiting meaning, e.g., the expression that an atom is “extracted” from a main frame resin indicates that the modified main frame resin differs from the main frame resin in that the atom is not present in the modified main frame resin (i.e., the expression “extracted” does not require that a particular reaction or any reaction have taken place in which the atom is removed). In other words, the substituted main frame resins and the modified main frame resins of the present invention are defined chemically, and are not in any way limited in regard to how they were produced.
By the introduction of the oxygen-containing functional group, the wettability of the lubricating oil or the operating oil on the obtained fluororesin is improved.
For example, when the oxygen-containing functional group is introduced, it is possible to obtain a surface energy of the obtained fluororesin within the range of from about 20 to about 40 dyne/cm, preferably about 25 to about 35 dyne/cm.
In general, the surface energy of the lubricating oil or the operating oil is in the range of from 25 to 35 dyne/cm. Therefore, when the surface energy of the fluororesin is within the range of from about 20 to about 40 dyne/cm, preferably from about 25 to about 35 dyne/cm, the wettability of the fluororesin with respect to the lubricating oil and/or the operating oil can be largely enhanced, and prohibition of production of an oil film because of the wettability can be avoided in the presence of the lubricating oil and/or the operating oil.
Moreover, in the fluororesin of the present invention, the visible light transmittance in the wavelength of 600 nm is greater than that of the main frame resin.
This increase of the visible light transmittance is a phenomenon caused by reduction of a crystal size of the fluororesin after irradiation with the electrolytic dissociative radiation.
When the sliding member using the fluororesin of the present invention slides, the crystal size is reduced. Therefore, a size of wear powder is smaller than with a conventional fluororesin. Moreover, fluidity of crystals increases, the crystals easily move/stick to a target material, production of a moved/stuck film is promoted, sliding between the fluororesins is caused, and therefore wear on the fluororesin itself decreases.
It is to be noted that the fluororesin of the present invention is usable as a solid lubricating material. In this case, the fluororesin is preferably added to another resin at a ratio in the range of from about 5 to about 70%.
When an addition amount is less than 5%, friction characteristic is reduced. On the other hand, even when the addition amount increases from 70%, a friction characteristic improving effect is saturated, and the effect is not improved any more.
Next, a method of reforming the fluororesin of the present invention will be described.
As described above, the method of reforming the fluororesin of the present invention is a method of manufacturing the fluororesin, comprising: extracting some hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin to introduce an unsaturated bond; and applying dissociation energy of the unsaturated bond in the presence of oxygen.
Here, the step of introducing the unsaturated bond is not especially limited, but irradiation with an electrolytic dissociative radiation in a range of from about 1 to about 10 kGy is preferable in a state in which the bond is heated in an inactive gas atmosphere having an oxygen concentration of about 10 Torr or less at not less than a melting point of the main frame resin, while a component (e.g., another polymer) other than a component containing the same monomer as that of the main frame resin is not allowed to be present.
In this case, when the oxygen concentration exceeds 10 Torr, or a heating temperature is less than the melting point of the main frame resin, the unsaturated bond is not formed, main chain cutting of the main frame resin selectively occurs, and the main frame resin itself is sometimes decomposed.
Moreover, when the intensity of the electrolytic dissociative radiation is less than 1 kGy, formation of the unsaturated bond is inhibited. On the other hand, when the intensity of the electrolytic dissociative radiation exceeds 10 kGy, decomposition of the main frame resin itself is sometimes promoted.
It is to be noted that the electrolytic dissociative radiation is not especially limited, but an α-ray, a proton ray, a heavy ion, a β-ray, an X-ray, a γ-ray, a neutron ray and the like are usable.
On the other hand, in the step of dissociating the unsaturated bond, the dissociation energy of the unsaturated bond is preferably applied as heat energy preferably under an oxygen partial pressure of about 13.3 kPa or more, but this is not especially limited.
In this step, the unsaturated bond introduced into the main frame resin is dissociated to react with the oxygen atoms, and changes into an oxygen-containing functional group such as a hydroxyl group, a carbonyl group, a carboxyl group, a ketone group, or an ether group, and the fluororesin of the present invention is produced.
When the oxygen partial pressure is less than 13.3 kPa, a chemical reaction between the unsaturated bond and the oxygen atom is inhibited, and a sufficient amount of the oxygen-containing functional group might not be formed in some cases. As a result, the wettability of the lubricating oil and/or the operating oil on the fluororesin is not improved very much in some such cases.
It is to be noted that in the present invention, the heat energy applied in the step of dissociating the unsaturated bond may be supplied during mixing with the main frame resin or resin forming.
That is, as described above, a precursor of the fluororesin of the present invention obtained by introducing the unsaturated bond into the main frame resin may be used as a raw material of the resin forming, and the heat energy may be applied to the material. Moreover, the material may be mixed with or formed into the main frame resin. Accordingly, the fluororesin of the present invention is manufactured, and simultaneously molded, and a resin molded article formed of the fluororesin of the present invention can be obtained.
A compound obtained by introducing the unsaturated bond into the main frame resin in this manner is a precursor of the fluororesin of the present invention. In a molding step involving heating, the precursor functions as a molding material as such.
It is to be noted that the molding method in which the fluororesin precursor of the present invention is usable simply as the molding material is not especially limited as long as the heating is performed. The examples include injection molding, ram molding, compression molding and the like.
According to the present invention, a predetermined oxygen-containing functional group is introduced by an appropriate unsaturated bond introducing process or the like. Therefore, there can be provided a fluororesin which has both a low friction coefficient and a superior wear resistance and which exhibits a superior friction characteristic in the presence of a lubricating oil and/or an operating oil, a method of reforming a fluororesin, a sliding member and a sliding device comprising such a fluororesin.
That is, by use of a fluororesin in a sliding member, a satisfactory friction characteristic can be realized in the presence of a lubricating oil and/or an operating oil. The fluororesin is constituted by substituting some of the hydrogen atoms and/or fluorine atoms bonded to carbon atoms of a main frame resin with an oxygen-containing functional group, so that a visible light transmittance in a wavelength of 600 nm is increased as compared with that of a main frame resin.
Furthermore, according to the present invention, substantially by only an irradiation step of an electrolytic dissociative radiation, it is possible to manufacture a fluororesin which exerts a satisfactory friction characteristic in the presence of a lubricating oil and/or an operating oil, and therefore there is an advantage that investment into improvement of a sliding characteristic of the fluororesin may be small.
In the present invention, the introduction of the unsaturated bond and the dissociation of the unsaturated bond can be confirmed from analysis results of a Fourier transform infrared spectrophotometer (FT-IR), shown in Table 1 below.
That is, when irradiated with the electrolytic dissociative radiation, a peak area of a peak assigned to the unsaturated bond increases. Furthermore, when the step of dissociating the unsaturated bond is performed, the increased peak area decreases. From this, it is confirmed that the unsaturated bond has been produced and dissociated.
When some of the hydrogen atoms or fluorine atoms bonded to the carbon atoms are substituted with the oxygen-containing functional group through the above-described steps, the surface energy of the obtained fluororesin can be set to within the range of from about 20 to about 40 dyne/cm, preferably from about 25 to about 35 dyne/cm.
In general, since the surface energy of the lubricating oil or operating oil is within the range of from about 25 to about 35 dyne/cm, the surface energy of the fluororesin is set to be within the range of from about 20 to about 40 dyne/cm, preferably from about 25 to about 35 dyne/cm. Consequently, the wettability of the fluororesin with respect to the lubricating oil and/or operating oil is largely enhanced, and the inhibition of the oil film production because of the wettability can be avoided even in the presence of the lubricating oil and/or the operating oil.
On the other hand, as described above, the main frame resin is irradiated with the electrolytic dissociative radiation in a range of from about 1 to about 10 kGy when heated at not less than the melting point in the inactive gas atmosphere having an oxygen concentration of about 10 Torr or less. Then, simultaneously with the production of the unsaturated bond, the crystal size is reduced.
Specifically, as shown in
When the crystal size is reduced, the size of wear powder decreases in a case where the fluororesin is slid. Moreover, crystal fluidity increases. Accordingly, the moving/sticking to a target material is facilitated, formation of a moved/stuck film is promoted, the fluororesins slide on each other, and therefore wear on the fluororesin itself decreases.
Additionally, by the irradiation with the electrolytic dissociative radiation, a bridging structure is formed in a molecule chain of the fluororesin. Even in this case, the wear resistance of the fluororesin is enhanced.
To sufficiently enhance the wear resistance by the above-described reduction of the crystal size, the visible light transmittance in a wavelength of 600 nm is set to preferably about 10% or more. When the visible light transmittance in the wavelength of 600 nm is less than 10%, the crystal size is not sufficiently reduced, and sufficient wear resistance is not obtained in some cases.
Next, a sliding member, a sliding apparatus and a sliding system of the present invention will be described.
In the sliding member of the present invention, the fluororesin of the present invention is applied to one or more sliding portions, and the sliding portion or portions preferably contain the fluororesin of the present invention at a ratio of from about 5 to about 70%.
When a content of the fluororesin is less than about 5%, a friction improving effect by the addition of the fluororesin is not sufficiently exerted. When the content exceeds about 70%, the forming sometimes becomes difficult.
Moreover, since the wettability of the fluororesin of the present invention with respect to the lubricating oil and/or operating oil is improved as described above, the sliding member of the present invention is also suitable for use in the presence of the lubricating oil and/or operating oil. However, in this case, surface roughness of a sliding surface of a sliding target material is set to Rz=about 10 μm or less, preferably Rz=about 5 μm or less.
When the surface roughness Rz of the sliding target material exceeds about 10 μm, the fluororesin of the present invention is inhibited from being moved/stuck to the target material sliding face, a friction coefficient reducing effect is not developed, and conversely wear is promoted.
It is to be noted that the sliding apparatus of the present invention comprises a sliding member of the present invention, and at least one oil material selected from lubricating oils and operating oils. A sliding system of the present invention comprises a sliding apparatus of the present invention and a target material which comprises a sliding surface on which the sliding member of the sliding apparatus slides.
A suitable surface roughness of the sliding target member is similar to that of the sliding member.
The present invention will be described hereinafter in more detail in accordance with examples and comparative examples, but the present invention is not limited to these examples.
Tetrafluoroethylene superior in low friction among fluororesins was used as the main frame resin, the molding powder (manufactured by Asahi Glass Co., Ltd., trade name G163) was irradiated with electron rays (pressurizing voltage of 2 MeV) in an atmosphere having an oxygen concentration of 1 Torr, nitrogen concentration of 800 Torr on heating conditions at 350° C. to introduce an unsaturated bond into the powder, and a targeted precursor of the fluororesin was obtained. Next, the precursor was crushed with a jet mill until an average particle diameter reached about 20 μm.
A fluororesin precursor obtained by subjecting 90% of a resin (G163) (which was the same as the main frame resin used in the above-described unsaturated bond introducing process) was added by 10%. A powder mixture was sufficiently mixed with a mixer. Thereafter, the mixture was treated at 300° C. for 12 hours, a high-temperature volatile component was removed, and a fluororesin mixture, that is, a mixture of one example of the fluororesin of the present invention and the main frame resin was obtained.
Next, the obtained fluororesin mixture was preliminarily molded into a cylindrical shape at a molding pressure of 50 MPa, and next fired in an electric furnace at 350 to 400° C. for three hours. The obtained fluororesin molded member was worked with a lathe, and a ring test piece 10 having a straight abutment joint 20 shown in
To 70% of the above-described main frame resin (G163), 30% of a precursor fluororesin into which an unsaturated bond was introduced in a method similar to that of Example 1 was added, and worked into a ring test piece in the same manner as in Example 1.
To 60% of the above-described main frame resin, 30% of a precursor fluororesin into which an unsaturated bond was introduced in the same manner as in Example 1, and 10% polyamide imide powder (manufactured by Amoco Co., trade name Tohron 4203L, average particle diameter of 15 μm) were added. Thereafter, the material was worked into a ring test piece in the same manner as in Example 1.
A fluororesin (G163) was preliminarily molded into a cylindrical shape at 50 MPa, and thereafter fired in an electric furnace at 350 to 400° C. for three hours. The obtained fluororesin molded member was worked into a ring test piece in the same manner as in Example 1.
A fluororesin was subjected to a corona treatment in the atmosphere on a condition of 200 W·min/m2, and a functional group was applied to the fluororesin. After performing the corona treatment, the fluororesin was preliminarily molded into a cylindrical shape at a molding pressure of 50 MPa, and thereafter fired in an electric furnace at 350 to 400° C. for three hours. The obtained fluororesin molded member was worked into a ring test piece in the same manner as in Example 1.
A fluororesin was subjected to a corona treatment in the atmosphere on a condition of 200 W·min/m2, and a functional group was applied to the fluororesin. To 70% of the fluororesin subjected to the corona treatment, 20% of graphite powder (manufactured by SEC Co., trade name SGL 3 μm), and 10% of carbon fibers (manufactured by Kureha Chemical Industry Co., Ltd., trade name Kureha Chop M-2007S, fiber diameter of 14.5 μm, fiber length of 90 μm) were added. The mixture was sufficiently mixed with a mixer.
Next, the mixture was preliminarily molded into a cylindrical shape at a molding pressure of 50 MPa, and thereafter fired in an electric furnace at 350 to 400° C. for three hours. The obtained fluororesin molded member was worked into a ring test piece in the same manner as in Example 1.
Performance Evaluation
Contact Angle Measurement and Surface Energy Calculation
With respect to test pieces of Examples 1 to 3 and Comparative Examples 1 to 3, a contact angle of pure water and methylene iodide was measured, and surface energy was calculated from a measured value. Obtained results are shown in Table 2.
As shown in Table 2, in test pieces of Examples 1 to 3, surface energy is remarkably greater than in Comparative Examples 1 to 3. It has been seen that some of the hydrogen atoms or fluorine atoms bonded to carbon atoms of the main frame resin are substituted with an oxygen-containing functional group by a combination of the unsaturated bond introducing process and the dissociation process of the unsaturated bond according to the present invention.
Sliding Characteristic Improving Effect
With respect to the test pieces of Examples 1 to 3 and Comparative Examples 1 to 3, a friction test was conducted in the following procedure using an automatic shift operating oil (manufactured by Idemitsu Kosan Co., Ltd., trade name Matic J).
An aluminum die cast material (ADC-12) was selected as a target material to be brought into sliding contact. To attach the material to a vertical type pin-on-disk type frictional wear tester shown in
Here, a frictional tester shown in
On the other hand, a disc holder 26 connected to a rotation shaft 27 is disposed in a lower part of the tester. When a disc 25 is fixed to the disc holder 26 via a bolt, the disc 25 is rotatable with respect to the ring test piece 10. Next, when the ring holder 21 is lowered, the ring test piece 10 is brought into sliding contact with the disc 25. Furthermore, when a pressure P is applied from an axial direction of the ring holder 21, the ring test piece 10 is brought into pressing contact with the disc 25. It is to be noted that in this case, a sliding contact portion between the ring test piece 10 and the disc 25 is immersed in an operating oil (Matic J) 28 for the automatic shift.
Results of a friction test performed using the tester on test conditions including pressing contact face pressure: 5 MPa, friction speed: 10 m/second, test time: 6 hours are shown in
It is seen from
Moreover, in comparison of Example 1 with Example 2, it is seen that when an addition amount of the main frame resin subjected to the combination of the unsaturated bond introducing process and the unsaturated bond dissociating process according to the present invention is increased, the friction coefficient tends to drop. It is to be noted that, as shown in Table 2, when the wettability with the lubricating oil and operating oil is improved by the increase of the surface energy, and an oil film forming capability is enhanced, a friction coefficient reducing effect is developed.
On the other hand, as to Example 3, PAI powder superior in wettability with the lubricating oil or operating oil is added to the fluororesin whose wettability has been improved as described above. Accordingly, the oil film formation is further promoted, and the friction coefficient drops.
Table 3 shows wear amount measurement results of the ring test piece and the disc test piece after ending the friction test. It is seen in Examples 1 to 3 that the wear amount of the ring test piece is remarkably reduced by the reduction of wear powder accompanying the construction of the bridging structure and the reduction of the crystal size.
On the other hand, as to Comparative Examples 1 to 3, since test conditions themselves exceed PV limits of a general fluororesin, abnormal wear is generated in a comparatively short time (typically about one hour) after test start.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-187190 | Jun 2004 | JP | national |
