JP2011208802A - Sliding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding member having excellent mechanical strength such as a low coefficient of friction and impact resistance which are desirable for the sliding member, and also having more improved abrasion resistance.SOLUTION: This sliding member includes: a surface layer composed of a crosslinked fluororesin, preferably, polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; and a radiator made of material having higher thermal conductivity than that of the fluororesin, and being in close contact with the surface layer. The thickness of the surface layer is 0.1-100 μm.

Description

  The present invention relates to a sliding member that uses a fluororesin for the sliding portion and has excellent wear resistance and is suitably used for a non-lubricated bearing or the like.

  Fluororesin is chemically very stable and has excellent low adhesion and low friction (low friction coefficient). Due to its properties, industrial products such as seals and packing, and consumer products such as cooking utensils. Widely used in various applications. A sliding member such as a non-lubricated bearing is desired to have a low coefficient of friction, and heat resistance and chemical stability are often desired. Therefore, a sliding member made of a fluororesin is also expected. However, the sliding member is required to have excellent wear resistance, and on the other hand, since there is a problem that fluororesin is easily worn, it is difficult to use as a sliding member unless the wear resistance is improved. .

  As a method for improving the abrasion resistance of a fluororesin, a method of adding a filler to the fluororesin is known. However, this method has a problem that excellent properties inherent to the fluororesin, such as low friction, are easily impaired by the filler. Therefore, Patent Document 1 proposes a method for improving wear resistance by irradiating ionizing radiation to a fluororesin, and discloses a sliding member made of a fluororesin irradiated with ionizing radiation.

  In the past, fluororesins were thought to have reduced mechanical properties upon irradiation. However, the mechanical properties can be improved by irradiating under specific conditions. For example, in Patent Document 2, with respect to polytetrafluoroethylene (PTFE), in the absence of oxygen, a dose of about 1 kGy to 10 MGy of ionizing radiation such as an electron beam at a temperature above the crystal melting point, preferably around 340 ° C. , It is disclosed that the elongation at break and the deterioration of the breaking strength due to irradiation are suppressed, and that the rubber elasticity is developed with low crystallinity and the yield strength is improved.

Japanese Patent No. 3666805 Japanese Patent No. 3317452

  In patent document 1, it is a sliding member obtained by shape | molding PTFE, FEP, or PFA, Comprising: Ionizing radiation in the state heated within crystal | crystallization melting | fusing point within the range of irradiation dose 10kGy-1500kGy in the absence of oxygen The irradiated one is said to have excellent wear resistance with a low coefficient of friction. However, in recent years, more excellent wear resistance is desired for the sliding member. Therefore, the sliding member described in Patent Document 1 cannot sufficiently satisfy this requirement, and a sliding member having improved wear resistance has been desired.

  An object of the present invention is to provide a sliding member having excellent mechanical strength such as a low coefficient of friction and impact resistance desired as a sliding member, and having improved wear resistance.

  As a result of the study, the present inventors have made a structure in which a sliding member made of a fluororesin has a structure in which, when the temperature of the member surface rises due to heat generated during sliding, it becomes more easily worn and the temperature of the member surface is less likely to rise. It was found that the wear can be suppressed. And while providing a heat sink on the opposite side to the sliding surface of the sliding part (the surface in contact with the object to be slid), and making the thickness of the sliding part within a specific range, it is desired as a sliding member The inventors have found that, together with impact resistance and low friction properties, the temperature rise on the surface of the member is suppressed, and wear resistance further improved as compared with conventional fluororesin-based sliding members can be obtained, and the present invention has been completed.

  The present invention has a surface layer composed of a cross-linked fluororesin and a radiator that is in close contact with the surface layer, the radiator is made of a material having a higher thermal conductivity than the fluororesin, and the thickness of the surface layer is 0.1 to It is a sliding member (Claim 1) characterized by being 100 micrometers.

  As described above, the sliding member of the present invention is characterized by having a surface layer made of a fluororesin and a radiator that is in close contact with the surface layer, and that the thickness of the fluororesin layer is 0.1 μm or more and 100 μm or less. Due to this feature, heat generated on the sliding surface of the surface during sliding can be effectively conducted from the surface layer to the radiator as compared with the case where the sliding member is made of a fluororesin molded product as in Patent Document 1. Therefore, the temperature rise of the member surface can be suppressed, and as a result, the wear resistance can be improved.

  In recent years, in order to confirm the wear resistance of sliding members, a thrust wear test (ring-on-disk wear evaluation) has been carried out in which a cylinder is placed on a sample and rotated while measuring pressure to measure the degree of wear. There are also many. In particular, in this test method, wear resistance is often evaluated by a multiplier (limit PV value) of pressure (P) and rotational speed (V) at which rapid wear occurs. The sliding member of the present invention has a very high limit PV value, and has excellent wear resistance.

  When the thickness of the fluororesin layer is too thin, particularly when it is less than 0.1 μm, it is not preferable because the fluororesin layer is easily broken during sliding. On the other hand, when the thickness exceeds 100 μm, heat generated on the surface of the member during sliding becomes difficult to conduct to the radiator, and it becomes difficult to prevent a temperature rise on the surface of the member, and wear resistance tends to be insufficient. Preferably, the thickness is in the range of 3-50 μm.

  The radiator is made of a material having a higher thermal conductivity than that of the fluororesin, and has a volume larger than that of the surface layer made of the fluororesin. Moreover, in order to endure the heat by the heat_generation | fever etc. at the time of sliding, the thing excellent in heat resistance is used. When the thermal conductivity of the material constituting the radiator is low, the heat generated on the surface of the member during sliding is difficult to dissipate, and it is difficult to prevent the temperature of the member surface from rising. Further, when the volume of the heat radiating body is small, the heat capacity of the heat radiating body is small, so that similarly generated heat is difficult to radiate and it is difficult to prevent the temperature of the member surface from rising.

  The surface layer made of a fluororesin is provided in close contact with the radiator. If the adhesion between the surface layer and the radiator is insufficient, for example, if there is a cavity or insufficient contact between the surface layer and the radiator, the generated heat is prevented from being released, and the temperature of the member surface It becomes difficult to prevent the rise.

  The fluororesin constituting the surface layer is crosslinked by irradiation with ionizing radiation. When the crosslinking is not performed or when the crosslinking is insufficient, the wear resistance is low, and the mechanical strength of the fluororesin is lowered, so that it cannot be used as a sliding member. Irradiation is usually performed at a dose of about 1 kGy to 1500 kGy.

  The invention according to claim 2 is the sliding member according to claim 1, wherein the fluororesin is PTFE, PFA or FEP. As the fluororesin forming the surface layer, PTFE, PFA or FEP excellent in mechanical strength and chemical resistance is preferable, and among them, PTFE particularly excellent in mechanical strength, chemical resistance and heat resistance is preferable. Further, other components may be included in the polymer as long as the gist of the present invention is not impaired. For example, PTFE may contain a trace amount of polymerized units based on a copolymerizable monomer such as perfluoro (alkyl vinyl ether), hexafluoropropylene, (perfluoroalkyl) ethylene, or chlorotrifluoroethylene. Moreover, the mixture of 2 or more types of fluororesins may be sufficient.

  The invention according to claim 3 is the sliding member according to claim 1 or 2, wherein the surface layer made of the fluororesin includes a heat conductive filler. In order to more smoothly dissipate heat generated on the surface of the sliding portion during sliding, it is preferable that the thermal conductivity of the surface layer made of a fluororesin is high. Therefore, a method of improving the thermal conductivity of the surface layer by adding a thermally conductive filler to the fluororesin constituting the surface layer is preferably employed.

  The invention according to claim 4 is characterized in that the surface layer and the heat radiating body have an adhesive force that becomes 99/100 or more even when repeated 10 times or more by a cross-cut test. 4. The sliding member according to any one of items 3. Here, the cross cut test is a test method described in JIS-K-5400 (1998 version), and specifically, 100 cross cuts are made on the surface layer, and a tape is formed thereon. It is a test method that repeats the test of peeling off after pasting, and counts the number of grids remaining without being peeled off. 99/100 or more refers to 99 or more in 100 grids. It means that it remains without being peeled off.

  If the adhesion between the surface layer and the radiator is low, the contact (adhesion) between the surface layer and the radiator tends to be insufficient, and problems such as the occurrence of voids during sliding are likely to occur. If the contact becomes insufficient and voids or the like are generated, the heat generated on the surface layer is difficult to conduct to the radiator and it is difficult to prevent the temperature of the member surface from rising. As a result, the wear resistance tends to be insufficient. Therefore, it is preferable that the surface layer and the radiator have an adhesive strength of 99/100 or more after 10 or more repetitions by a cross-cut test. Is a case where the adhesive force is 99/100 or more by repeating 100 times or more.

  The excellent adhesion can be improved by selecting a method for forming the fluororesin layer on the radiator, adding a filler to the fluororesin layer, selecting a material for the fluororesin layer and the radiator, and the like. Also, the adhesion between the fluororesin layer and the heat radiating body may be improved by irradiating the fluororesin layer with ionizing radiation.

  In the sliding member of the present invention, it is preferable that the radiator is made of a material having a thermal conductivity of 0.001 Cal / ° C. · cm · second or more.

  As described above, the heat radiator is made of a material having a thermal conductivity better than that of the fluororesin, but the thermal conductivity of the fluororesin to which no filler is added is about 0.0005 Cal / ° C. · cm · sec ( Since PTFE is 0.0005 Cal / ° C. · cm · sec), a material having a thermal conductivity of 0.001 Cal / ° C. · cm · sec or more is preferable as the material constituting the heat radiator. More preferably, the material has a thermal conductivity of 0.01 Cal / ° C. · cm · second or more, and still more preferably 0.1 Cal / ° C. · cm · second or more.

  In addition, as above-mentioned, a heat radiator is a thing with a larger volume than the surface layer which consists of a fluororesin, and a larger volume is preferable for heat dissipation. Specifically, the value of the thermal conductivity of the radiator when expressed in Cal / ° C. · cm · second is X, and the value of (volume of the radiator) / (volume of the surface layer made of fluororesin) is Y. In this case, X · Y is preferably 0.005 or more, more preferably 0.05 or more, and still more preferably 0.5 or more.

  In the sliding member of the present invention, after preparing a radiator having a predetermined shape, the surface of the radiator is covered with a fluororesin to form a fluororesin layer, and then the surface of the fluororesin layer is irradiated with ionizing radiation. Thus, it can be produced by a method of crosslinking the fluororesin. As the shape of the sliding member of the present invention, a flat plate shape, a convex shape, a hollow shape, a cylindrical shape or a tubular shape having a sliding portion on the outer surface of the cylindrical shape, a circular tubular shape on the inner surface thereof Various shapes such as those having a sliding portion can be mentioned. Therefore, the above-mentioned various shapes can also be mentioned as the shape of the radiator.

  The sliding member of the present invention has a low coefficient of friction similar to that of a conventional sliding member made of a fluororesin, and further has wear resistance superior to that of the conventional sliding member. It is suitably used for non-lubricated bearings used in products such as those requiring high wear resistance.

  The sliding member of the present invention has a low coefficient of friction, is excellent in impact resistance, etc., is excellent in wear resistance, and has a high limit PV value.

It is sectional drawing of an example of the fluororesin coating | covering material of this invention. It is a side view of another example of the fluororesin coating | covering material of this invention. It is a perspective view which shows notionally the thrust abrasion test (ring-on-disk type abrasion evaluation) performed by the Example and the comparative example. 6 is a graph showing a relationship between a load and a temperature rise in a thrust wear test performed in Example 5.

  Next, the form for implementing this invention is demonstrated. In addition, this invention is not limited to this form and an Example, As long as the meaning of this invention is not impaired, it can change into another form.

  FIG. 1 is a cross-sectional view of an example of a sliding member of the present invention, which has a flat plate shape. In the figure, 2 is a fluororesin layer, and 1 is a radiator. FIG. 2 is a side view of another example of the sliding member of the present invention, which has a convex shape. In the figure, 2 is a fluororesin layer, 1 is a radiator, and the tip of the radiator 1 is covered with the fluororesin layer 2.

  The radiator is composed of a material having high thermal conductivity and high heat resistance. Examples of such a material include iron (thermal conductivity: 0.18 Cal / ° C. · cm · second), SUS, aluminum. (Thermal conductivity: 0.53 Cal / ° C. · cm · second) can be cited as a preferable material. Further, ceramic (brick) having a thermal conductivity of 0.07 Cal / ° C. · cm · sec can also be used. Furthermore, a filler for improving thermal conductivity is added to heat-resistant plastics such as polyimide, polyether ether ketone, and polyether sulfone having heat resistance that can withstand baking of a fluororesin (380 ° C., several tens of minutes). The one with higher thermal conductivity can also be used.

  Examples of the filler added to the fluororesin to improve the thermal conductivity of the surface layer include alumina, silica, alumina, boron nitride, graphite, carbon fiber, carbon nanotube, metal silicon, silicon carbide and the like. Carbon nanotubes are made of carbon crystals (graphite, etc.), have a short axis diameter (fiber diameter) of submicron size or less, have a shape in which a graphite layer is formed into a cylindrical shape, and the like. It is a filler that is known to improve thermal conductivity by blending it with the like. Carbon nanotubes are preferably used because they can improve thermal conductivity with a small addition amount, and have less problems such as inhibition of low friction due to the addition of filler. Two or more of these fillers may be added in combination.

  Next, the manufacturing process of the sliding member of the present invention will be described.

  First, a heat radiating body having a predetermined shape is formed, and a fluororesin layer is formed by coating a fluororesin on the surface, that is, a portion that becomes a sliding portion. As a method of coating the fluororesin, a method of covering a fluororesin film, a method of powder coating, for example, a method of electrostatic coating of fluororesin powder, a method of spraying fluororesin powder, a fluororesin dispersion ( And a method in which the dispersion medium is dried and removed by applying a liquid in which a fluororesin powder is uniformly dispersed in a dispersion medium.

  Among them, the method of applying a fluororesin dispersion is a preferable method in that a fluororesin layer having a uniform thickness can be easily formed. In the case of a fluororesin that is soluble in a solvent, a method in which a fluororesin solution is applied and the solvent is dried and removed may be employed, but this is not applicable to a resin that is insoluble in a solvent such as PTFE.

  In the case of applying the fluororesin dispersion, water and an emulsifier, water and alcohol, water and acetone, or a mixed solvent of water, alcohol, and acetone can be used as the dispersion medium. After applying the fluororesin dispersion, the dispersion medium is dried and removed by air drying or hot air drying. A film made of fluororesin powder is formed by drying and removing the dispersion medium.

  After a fluororesin coating film is formed by powder coating, electrostatic coating, fluororesin dispersion coating, etc., firing is performed to a temperature higher than the melting point of the fluororesin, the fluororesin powder is fused, and fluorine A resin layer is formed. Firing is preferably performed in a temperature range of 350 to 400 ° C. It is also possible to remove the dispersion medium in the baking step without providing a drying step.

  Subsequently, the surface of the fluororesin layer thus formed is irradiated with ionizing radiation to crosslink the fluororesin. When an appropriate combination of the fluororesin and the heat dissipating material is selected, the adhesion between the fluororesin layer and the heat dissipating material is also improved during this crosslinking.

  When crosslinking is performed, it is placed in an oxygen-free atmosphere, specifically in an atmosphere having an oxygen concentration of 100 ppm or less, preferably 5 ppm or less, and a temperature range of the fluororesin crystal melting point to about 400 ° C., preferably 0 to 0 from the crystal melting point. Irradiating the surface of the fluororesin film with ionizing radiation while maintaining a temperature range higher by 30 ° C. The range of irradiation dose is generally 1 kGy to 1500 kGy, preferably 100 kGy to 1000 kGy.

  At this time, the above baking and ionizing radiation irradiation may be performed simultaneously. If the temperature of the atmosphere is too low, the crosslinking reaction of the fluororesin is unlikely to occur, and if the atmosphere temperature is too high, especially when the temperature exceeds 400 ° C., thermal decomposition of the fluororesin is promoted and the material properties are deteriorated. Further, if the irradiation dose is less than 1 kGy, the crosslinking reaction is insufficient and improvement in characteristics cannot be expected, and if it exceeds 1500 kGy, decomposition of the fluororesin tends to occur, which is not preferable.

  Examples of ionizing radiation used for crosslinking of fluororesins include electron beam, charged particle beam such as high energy ion beam, high energy electromagnetic wave such as gamma ray and X-ray, neutron beam, etc. An electron beam is preferably used because it is inexpensive and can provide a high-power electron beam and can easily control the degree of crosslinking.

Example 1
A fluororesin dispersion (Daikin Co., Ltd .: D10-FE) is applied onto a 1.7 mm thick aluminum plate (JIS-regulated material type: 3003), dried, and then fired at 380 ° C. for 10 minutes. An aluminum plate coated with a 15 μm fluororesin film is obtained. Thereafter, the sample was heated to 330 ° C. in a nitrogen atmosphere (oxygen concentration: 5 PPM), and irradiated with 300 kGy with an irradiation apparatus (Sagatron: acceleration voltage 1.13 MeV) manufactured by Nissin Electric Co., Ltd., to prepare a test sample.

Example 2
A test sample was produced under the same conditions as in Example 1 except that a 2.0 mm thick SUS plate (JIS-specified material type: SUS430) was used instead of the 1.7 mm thick aluminum plate.

Example 3
A test sample was produced under the same conditions as in Example 1 except that a ceramic plate (commercially available tile manufactured by INAX) having a thickness of 5.0 mm was used instead of the aluminum plate having a thickness of 1.7 mm.

Comparative Example 1
Without using a heat radiating plate (aluminum plate), the same fluororesin dispersion as in Example 1 was used, and a sample that would be a fluorine plate was produced under the same conditions such as firing.

Comparative Example 2
After producing a sample under the same conditions as in Example 2, annealing was performed at 360 ° C. for 20 minutes to produce a test sample with reduced adhesion.

[Abrasion resistance measurement]
The abrasion resistance of the fluororesin coating was evaluated by a thrust wear test (ring-on-disk wear evaluation). Specifically, as shown in FIG. 3, with a metal cylinder (mating shaft) placed on the test sample and a predetermined load (surface pressure: P) applied, the test sample is moved to a predetermined speed (rotational speed). : V) and measure the wear state of the test sample. In Examples 1 to 4 and Comparative Examples 1 and 2, an S45C cylinder having an outer diameter / inner diameter = 11.5 / 7.4 was used as the mating shaft, and the wear was measured under dry (greaseless) lubrication conditions. By changing the pressure (P) and the rotational speed (V), the limit PV value (P · V value at which rapid wear occurs) was obtained. Table 1 shows the case where the limit PV value is 1500 MPa · m / min or more as “◯” and the case where it is less than 1500 MPa · m / min.

[Adhesion measurement]
The peel resistance of the fluororesin coating was measured by a cross cut test. Specifically, 100 samples of a grid-like scratch were made on the fluororesin coating of the sample, and a test for peeling after applying a tape was repeated, and the number of grids remaining without being peeled was counted. . Table 10 shows the case where 2 or more of 100 grids are peeled off in 10 repetition tests, and x is the case where 1 or less of 100 grids are peeled off. It was.

  From the results shown in Table 1, in Comparative Example 1 in which the sliding member is formed only with a fluororesin without providing a radiator, and in Comparative Example 2 in which the fluororesin layer and the radiator are not in close contact, the wear resistance is inferior, and the limit PV value On the other hand, in Examples 1 to 3, which are examples of the present invention, it is shown that a high limit PV value is obtained and wear resistance is excellent.

Example 5
PTFE dispersion (manufactured by Daikin) on a polyether ether ketone plate (hereinafter referred to as “PEEK plate”) having a thickness of 5 mm and an aluminum plate (3003, hereinafter referred to as “AL plate”) having a thickness of 1.7 mm. : EK-3700), followed by baking at 350 ° C. for 10 minutes to form a PTFE film having a thickness of 15 μm. The sample was heated to a temperature of 330 ° C. in a nitrogen atmosphere (oxygen concentration 5 PPM), irradiated with an electron beam of 300 kGy with an irradiation apparatus (Sagatron: acceleration voltage 1.13 MeV) manufactured by Nissin Electric Co., Ltd., and a crosslinked PTFE having a thickness of 15 μm. A test sample having a film formed thereon and having a heat radiating plate (PEEK plate or AL plate) and a surface layer (crosslinked PTFE film) adhered thereto was produced. Three test samples are prepared for the PEEK plate and three for the AL plate, which are designated as PEEK1, PEEK2, PEEK3, AL1, AL2, and AL3, respectively.

  Furthermore, a commercially available PTFE sheet having a thickness of 1 mm was heated to a temperature of 330 ° C. in a nitrogen atmosphere (oxygen concentration: 5 PPM), and irradiated with an electron beam of 300 kGy with an irradiation apparatus (Sagatron: acceleration voltage 1.13 MeV) manufactured by Nissin Electric. A test sample was obtained. This test sample is hereinafter referred to as “PTFE sheet”.

[Measurement of temperature rise by thrust wear test]
As shown in FIG. 3, on a test sample (PEEK1, PEEK2, PEEK3, AL1, AL2, AL3 or PTFE sheet), a cylinder made of carbon steel (S45C) with an inner diameter / outer diameter = 11.6 / 7.6 ( The sample is rotated at 1800 rpm for 10 minutes while applying the specified load (5 kgf) from the upper part of the device, and the temperature is set by a thermocouple (installed 3 mm above the contact surface with the sample). The rise was measured. If no problems such as destruction occur in the cross-linked fluorine film, after sufficiently cooling the sample, increase the load (as shown in Table 2) and repeat the same test to cross-link the PTFE film or PTFE sheet. Was carried out until the load reached the evaluation device limit (95 kgf). The results are shown in Table 2. (If the crosslinked PTFE membrane is broken, record the temperature at that time)

  FIG. 4 is a graph showing the results shown in Table 2, that is, the relationship between the load and the temperature rise in the thrust wear test performed in Example 5. The vertical axis shows the temperature rise (end temperature-start temperature), and the horizontal axis shows the load.

  As is clear from Table 2 and FIG. 4, the heat sink is a sample (PEEK1 to 3) made of PEEK (thermal conductivity: 0.0006 Cal / ° C. · cm · second) having a low thermal conductivity, and a crosslinked fluororesin. In the case of a sheet (PTFE sheet) with (thermal conductivity: 0.0005 Cal / ° C. · cm · second), the temperature rises rapidly with an increase in load. And with the load of 20-60 kgf, the temperature rise for 10 minutes exceeded 140 degreeC, and the PTFE membrane or the PTFE sheet destroyed.

  On the other hand, in the case of samples (AL1 to 3) consisting of AL (heat conductivity of 0.53 Cal / ° C · cm · sec) with good heat conductivity, the heat sink has a small increase in temperature due to an increase in load. Even when the temperature reached the device limit (95 kgf), the temperature rise was suppressed to about 100 ° C., and the PTFE membrane was not broken.

1. 1. Heat radiator Fluorine resin layer

Claims (4)

  It has a surface layer composed of a cross-linked fluororesin and a radiator that is in close contact with the surface layer, the radiator is made of a material having a higher thermal conductivity than the fluororesin, and the thickness of the surface layer is 0.1 to 100 μm. A sliding member characterized by the above.   The sliding member according to claim 1, wherein the fluororesin is polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.   The sliding member according to claim 1, wherein the surface layer made of the fluororesin includes a thermally conductive filler.   4. The adhesive according to claim 1, wherein the surface layer and the heat radiating body have an adhesion force of 99/100 or more even after 10 or more repetitions by a cross-cut test. The sliding member.

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