Polytetrafluoroethylene composition

Abstract

Provided is a PTFE composition containing PTFE fine powder and a filler, which is inhibited from forming agglomerates and from adhering to the inner wall of a mixing device even when dry-blended by high-speed stirring. SOLUTION: A polytetrafluoroethylene composition containing a modified polytetrafluoroethylene fine powder having an extrusion pressure of less than 25 MPa at RR1600, and a filler.

Description

[Technical Field]

[0001] The present invention relates to a polytetrafluoroethylene composition in which modified polytetrafluoroethylene fine powder and a filler can be uniformly dispersed and mixed by dry blending (powder mixing) with high-speed stirring, and which also has excellent productivity. [Background technology]

[0002] Polytetrafluoroethylene (hereinafter also referred to as "PTFE") has a low coefficient of friction and excellent heat and chemical resistance, and these properties are utilized for a variety of purposes.

[0003] Two methods of polymerizing PTFE are generally used: emulsion polymerization in an aqueous medium of tetrafluoroethylene (hereinafter also referred to as "TFE") and suspension polymerization.

[0004] PTFE obtained by emulsion polymerization is called fine powder and is obtained by coagulating the aqueous dispersion, extracting it, and drying it. Fine powder has the characteristic of fiberizing when subjected to shearing force. This property can be exploited by mixing it with an extrusion aid such as naphtha, pre-compressing it, and then extruding the preform from a cylinder to form electrical wire coating (paste extrusion molding). Fillers such as conductive materials and foaming agents can be added to enhance performance. Furthermore, by stretching the paste extrusion, porous membranes can be formed. Furthermore, because a small amount of PTFE can entangle many particles, it is also used as an electrode material (binder) for fuel cells and capacitors.

[0005] On the other hand, PTFE produced by suspension polymerization is called molding powder, which is less likely to become fibrous than fine powder and is less expensive. Therefore, molding powder is used for various purposes, such as by cutting out cylindrical billets that are heat-treated after compression molding into various parts or by cutting them into thin, skived sheets.

[0006] In addition, filled molding powders, which contain various fillers to improve wear resistance and creep resistance, are commonly used in sliding and sealing components. However, molding powder particles are relatively large and hard, making them difficult to crush during compression molding, resulting in voids between the powder and the filler. This can lead to voids and fracture initiation points during stretching. Furthermore, poor adhesion between the resin and filler can lead to the filler detaching from the molded product, resulting in poor wear resistance.

[0007] Furthermore, filled molding powders are also used in automobile oil seal rings, and in this case, as soft metals such as aluminum are increasingly being used as materials to reduce the weight of automobiles, it is necessary for the filler to not only have sliding properties but also not damage the soft metal that it is sliding against. Metal oxides such as potassium titanate and zinc oxide are suitable fillers that satisfy these properties (e.g., Patent Documents 1 and 2). However, filled molding powders are often granulated using an aqueous medium (wet granulation), and in this case, a problem arises in that the metal oxide, which has a high affinity for water, is released into the aqueous phase.

[0008] For these reasons, the use of PTFE fine powder, which has excellent adhesion to fillers, is being considered instead of PTFE molding powder.

[0009] As a method for mixing PTFE and filler, there is a dry blend ( Powder mixing) is the simplest method, can be mixed in a short time, and has good productivity. However, in the case of fine powders, high-speed mixing can cause the formation of agglomerates or the fine powder can adhere to the inner walls of the mixing device, preventing uniform mixing. Furthermore, mixing at low speeds takes time to achieve uniform mixing, resulting in a decrease in productivity. For this reason, methods such as dispersing a filler in an aqueous dispersion after polymerization and coagulating it at the same time (co-coagulation / co-agglomeration) (Patent Document 3, Patent Document 4), and turbular mixers that mix by rolling the mixing container itself have been used, but these methods also have low productivity and are not a fundamental solution.

[0010] To address this issue, a method has been proposed in which PTFE fine powder and a filler are dry-blended at temperatures below 10°C (Patent Document 5). However, this method also suffers from problems such as reduced productivity and increased costs due to cooling, and is therefore not a satisfactory method.

[0011] Therefore, a more suitable method for dry blending PTFE fine powder and a filler is desired. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 4386633 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-164216 [Patent Document 3] Special Publication No. 48-12052 [Patent Document 4] Japanese Patent Application Publication No. 56-18624 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-151543 Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide a PTFE composition containing a PTFE fine powder and a filler, which is capable of suppressing the formation of agglomerates of the fine powder and adhesion to the inner wall of a mixing device even when the PTFE fine powder and a filler are dry blended by high-speed stirring. [Means for solving the problem]

[0014] The present inventors have found that the above object can be achieved by using, as the PTFE fine powder in the composition, a modified PTFE fine powder having an extrusion pressure of less than 25 MPa at an RR (Reduction Ratio, cylinder area / orifice area) of 1600, and have thus completed the present invention.

[0015] That is, the present invention is as follows. 1. A polytetrafluoroethylene composition comprising a modified polytetrafluoroethylene fine powder having an extrusion pressure of less than 25 MPa at RR1600, and a filler. 2. A molded article obtained by molding the polytetrafluoroethylene composition described in 1 above. 3. The molded article according to 2 above, which is a sliding material or a sealing material. 4. The molded article according to 2 above, which is a wire coating material or a porous membrane material. 5. A method for producing the polytetrafluoroethylene composition according to 1 above, which comprises dry-blending a modified polytetrafluoroethylene fine powder having an extrusion pressure of less than 25 MPa at RR1600 with a filler. [Effects of the Invention]

[0016] According to the present invention, a PTFE composition containing a PTFE fine powder and a filler can be provided in a short time by utilizing a simple dry blend and high-speed stirring. Furthermore, according to the present invention, fine powder having a small particle size and a filler can be mixed uniformly, Since defects caused by the aggregation of the filler are suppressed, the effect of the filler can be obtained even with a small amount of filler, and the amount of creep deformation can be reduced. Furthermore, the composition of the present invention using fine powder is generally softer than molding powder, resulting in a denser structure with fewer voids between the filler and the composition (higher adhesion). Therefore, molded articles made from the composition of the present invention have better tensile and compression properties, and also have excellent wear properties because the filler is less likely to fall off during sliding. Another advantage is that the pressure required for compression molding the composition is lower than that required for molding powder.

[0017] Specific applications of the PTFE composition of the present invention include materials for oil seal rings in automobile transmissions, shock absorbers, etc. Oil seal rings are required to follow minute movements, so that they are able to deform without cracking or breaking when a load is applied to the ring itself. Furthermore, if the seal ring is elastically deformable, it has the advantage of facilitating installation when it is fitted to a cylinder. To be used as a seal ring for a shock absorber, the PTFE composition must have a tensile elongation of 0.01 mm or more in a tensile test conforming to ASTM D-4894. It is preferably 100% or more, and more preferably 250% or more. The PTFE composition of the present invention is suitable for this application because the filler is finely dispersed and the composition is more flexible than molding powders. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a stereomicroscope photograph (300x magnification) of the 641-J / carbon fiber mixture (powder) obtained in Example 2. [Figure 2] 1 is a stereomicroscope photograph (300x magnification) of the 6-J / carbon fiber mixture (powder) obtained in Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below. The polytetrafluoroethylene (PTFE) composition of the present invention comprises a modified polytetrafluoroethylene (PTFE) fine powder having an extrusion pressure of less than 25 MPa at an RR (Reduction Ratio, cylinder area / orifice area) of 1600, and a filler.

[0020] In this invention, "modified polytetrafluoroethylene (PTFE) fine powder" refers to PTFE particles (powder) obtained by coagulating and drying latex (aqueous dispersion) obtained by emulsion polymerization. It is also a fine powder of tetrafluoroethylene (TFE) copolymer containing 1% by mass or less of a monomer (comonomer) copolymerizable with TFE. In modified PTFE, the presence of the comonomer prevents the molecular chains from sliding against each other, increasing the strength and elastic modulus of the resin and improving creep resistance. However, if the amount of comonomer exceeds 1% by mass, the sliding properties of PTFE decrease and the PTFE becomes fluid at temperatures above its melting point, making it unsuitable for use at high temperatures.

[0021] In the present invention, the monomer copolymerizable with TFE is not particularly limited as long as it contains an unsaturated bond and is radically polymerizable. However, in order to maintain the excellent performance of PTFE, such as heat resistance and chemical resistance, it is preferable to use a fluorine-containing monomer. Examples include fluoroalkenes having 3 or more carbon atoms, preferably 3 to 6 carbon atoms, such as perfluoropropene, perfluorobutene, perfluoropentene, and perfluorohexene, and fluoro(alkyl vinyl ethers) having 3 to 6 carbon atoms, such as perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), and chlorotrifluoroethylene. Preferably, fluoroalkenes having 3 to 6 carbon atoms and fluoro(alkenes) having 4 to 5 carbon atoms are used. vinyl ether).

[0022] The modified PTFE fine powder of the present invention can be prepared by a known method, but commercially available modified PTFE fine powders, such as Teflon (registered trademark) PTFE 641-J manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd., may also be used.

[0023] The average particle size of the modified PTFE fine powder of the present invention is preferably 350 μm to 650 μm. In this specification, the average particle size means the particle size at an integrated value of 50% (volume basis) in the particle size distribution obtained by a sieving method. The standard specific gravity (SSG) of the modified PTFE fine powder of the present invention is preferably 2.100 to 2.200, more preferably 2.120 to 2.180. The standard specific gravity (SSG) is measured in accordance with ASTM D-4895.

[0024] The modified PTFE fine powder of the present invention is characterized in that the extrusion pressure during paste molding is less than 25 MPa at a reduction ratio (RR: cylinder area / orifice area) of 1600. In the present invention, RR1600 is the value obtained by rounding off the value obtained by the above calculation formula to the nearest tenth.

[0025] The test sample for measuring the extrusion pressure is a mixture of modified PTFE fine powder and an extrusion aid in an amount of 16.2% by mass. A lubricant manufactured from raw materials with an initial boiling point of 110°C or higher and a dry point of 145°C or lower is used. An example of such an extrusion aid is an isoparaffin hydrocarbon, specifically, ISOPAR E (manufactured by ExxonMobil Corporation). TM E FLUID) and Idemitsu Supersol FP manufactured by Idemitsu Kosan Co., Ltd. The extrusion conditions are RR 1600, temperature 30±2°C, and extrusion speed 18 mm / min.

[0026] In the present invention, the term "filler" refers to a powdery substance used to improve various physical properties of molded articles, and various organic and inorganic fillers can be used. Examples of organic fillers include engineering plastics such as polyphenylene sulfide, polyether ether ketone, polyamide, polyimide, and wholly aromatic polyester resin. Examples of inorganic fillers include metal powder, metal oxides (aluminum oxide, zinc oxide, tin oxide, titanium oxide, etc.), metal titanates, glass, ceramics, silicon carbide, silicon oxide, boron nitride, calcium fluoride, carbon black, carbon fiber, graphite, coke, mica, talc, barium sulfate, and molybdenum disulfide. If necessary, a combination of these fillers can also be used.

[0027] The filler may be in various shapes such as particles, fibers, flakes, etc.

[0028] The composition ratio of the filler in the PTFE composition of the present invention is preferably in the range of 0.1 to 90.0 mass%, more preferably in the range of 5.0 to 70.0 mass%. If the ratio is below the lower limit, it is difficult to obtain the effect of adding the filler, and there is a problem that the PTFE is likely to adhere to the inner wall of the mixer during mixing. If the ratio is above the upper limit, there are problems such as difficulty in molding and deterioration in the physical properties (tensile strength, elongation, etc.) of the obtained molded product.

[0029] The PTFE composition of the present invention may contain one or more additives such as solid lubricants, oxidation stabilizers, heat stabilizers, weather stabilizers, flame retardants, pigments, etc., depending on the desired properties such as lubricity, conductivity, and foam prevention. For example, adding a few percent of a solid lubricant as an additional component is useful for improving self-lubrication, and examples of solid lubricants include graphite and molybdenum disulfide. Examples include silicon dioxide and boron nitride.

[0030] The "molded article" of the present invention is one obtained by molding the polytetrafluoroethylene composition of the present invention. The molding method is not particularly limited, but includes known molding methods such as ram extrusion molding, compression molding, isostatic molding, and hot coining molding. Furthermore, paste extrusion molding, which has conventionally been used for coating small-diameter electric wires with fine powder, can also be used.

[0031] The molded articles of the present invention have excellent heat resistance and chemical resistance, and the addition of various fillers improves their abrasion resistance and creep resistance, making them suitable for a variety of applications requiring these properties. For example, they can be used not only for wire coating materials and porous membrane materials, for which fine powders have traditionally been used, but also for sliding and sealing materials, for which molding powders have primarily been used. Examples of sliding applications include bearings, rolls, piston rings, and oil seal rings (piston rings and oil seal rings slide against a housing). Examples of sealing applications include packings such as oil seal rings, piston rings, mechanical seals, and belloframs, as well as gaskets classified as stationary seals such as O-rings. The molded articles of the present invention are particularly suitable for use as materials for automotive oil seal rings.

[0032] In producing the composition of the present invention, various known methods can be used to mix the modified PTFE fine powder and the filler, but dry blending (powder mixing) under dry conditions without using a liquid medium such as water or an organic solvent is the simplest and most preferable. According to the present invention, even when dry blending is performed with high-speed stirring, the formation of aggregates and adhesion to the side walls of the mixing device are suppressed, making it possible to achieve uniform mixing in a short time.

[0033] The apparatus used for dry blending in the present invention is not particularly limited, but examples include mechanical stirring apparatuses with stirring blades (various mixers such as a mill with stirring blades, a cutter mixer, a Henschel mixer, a Loedige mixer, a V-blender with a chopper, and a double cone mixer with a chopper), a rocking mixer, and a turbular mixer.

[0034] In the present invention, it is preferable that the rotation speed and peripheral speed of the stirring blades, etc. used to dry-blend the modified PTFE fine powder and the filler are high, as this enables uniform mixing in a short time. Specifically, the composition of the present invention can be mixed without any problems even at high stirring speeds of 15 m / s or more. [Example]

[0035] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. The following raw materials and methods were used in the present examples and comparative examples.

[0036] (PTFE fine powder) The following PTFE fine powders were used: Teflon (registered trademark) PTFE 641-J (manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd., SSG: 2.168, average particle size: approximately 500 μm) Teflon (registered trademark) PTFE 640-J (manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd., SSG: 2.162, average particle size: approximately 500 μm) Teflon (registered trademark) PTFE 6-J (manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd., SSG: 2.214, average particle size: approximately 450 μm) Polyflon (registered trademark) PTFE F-208 (manufactured by Daikin Industries, Ltd., SSG:2 .176, average particle size: approx. 590μm) Polyflon (registered trademark) PTFE F-201 (manufactured by Daikin Industries, Ltd., SSG: 2.181, average particle size: approximately 500 μm) Only 6-J is unmodified PTFE fine powder, the rest are modified PTFE fine powder.

[0037] (PTFE molding powder) Teflon (registered trademark) PTFE 7-J (manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd., SSG: 2.166, average particle size: approximately 50 μm)

[0038] (PTFE fine powder extrusion pressure) 150 g of PTFE fine powder was placed in a clean sample bottle and mixed with a hydrocarbon lubricant (ISOPAR manufactured by ExxonMobil). TM Add 29.1g of FLUID and then quickly close the lid. The mixture is mixed for 20 minutes using a windmill mixer, and the sample bottle is left to stand in a thermostatic water bath maintained at 30°C for 2 hours to mature. A rheometer (model: ESE-428-00) manufactured by Toyo Hydraulic Machinery Co., Ltd. was used as a device for measuring the paste extrusion pressure. The mixture was filled into a preforming cylinder with an inner diameter of 28 mm, and a load of 50 kg was applied to a piston inserted into the cylinder and maintained for 1 minute to obtain a cylindrical preform. The resulting preform was placed in a cylinder (inner diameter 31.7 mm) equipped with an extrusion die (orifice diameter: 0.79 mm) preheated to 30°C, and the mixture was extruded at a ram speed of approximately 18 mm / min to obtain a string-like material (bead). At this time, RR, which is the ratio of the cylinder area to the orifice area, was 1600. The extrusion pressure at the point where the pressure reached equilibrium in the latter half of the extrusion was divided by the cross-sectional area of ​​the cylinder to obtain the paste extrusion pressure (MPa). The results are shown in Table 1.

[0039] [Table 1]

[0040] (Evaluation of the composition) [Example 1] 40 g of modified PTFE fine powder, Teflon (registered trademark) PTFE 641-J, and 60 g of mica filler were added to a mill with a stirring blade (Osaka Chemical Co., Ltd. Wonder Crush Mill D3V-10, stirring blade diameter 142 mm). After stirring at 25,000 rpm for 10 seconds, the polymer adhering to the wall was scraped off with a spatula, and then the mixture was stirred for 30 seconds. The mixture was stirred at 25,000 rpm. The inside of the tank was observed to see if there was any polymer that had adhered or stuck to the inner wall and was unable to flow during stirring. The results are shown in Table 2.

[0041] [Comparative Example 1] Except for using Teflon (registered trademark) PTFE 640-J, which is a modified PTFE fine powder, the observation was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0042] Comparative Example 2 Except for using Teflon (registered trademark) PTFE 6-J, which is an unmodified PTFE fine powder, the observation was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0043] Comparative Example 3 Except for using modified PTFE fine powder, Polyflon (registered trademark) PTFE F-208, observation was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0044] Comparative Example 4 Except for using modified PTFE fine powder, Polyflon (registered trademark) PTFE F-201, observation was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0045] [Table 2]

[0046] [Example 2] 170 g of Teflon (registered trademark) PTFE 641-J, a modified PTFE fine powder, and 30 g of artificial graphite filler (AT-NO. 10E, manufactured by Oriental Sangyo Co., Ltd.) were placed in a mill with a stirring blade (Wonder Crush Mill D3V-10, manufactured by Osaka Chemical Co., Ltd., stirring blade diameter 142 mm) and stirred at 25,000 rpm for 40 seconds (PTFE / artificial graphite = 85 / 15 (weight ratio)). The resulting composition was placed in a mold with a diameter of 50 mm and subjected to a pressure of 400 kg / cm 2 By pressurizing with The mixture was molded and fired in an electric furnace at 370°C for 3 hours to obtain a cylindrical molded product having a height of about 40 mm. The resulting cylindrical molded product was used to evaluate dispersibility by the following method, and the results are shown in Table 3.

[0047] (Evaluation of dispersibility) From the obtained cylindrical molding, a sheet with a thickness of 0.3 mm was made by skiving, and the size and number of resin agglomerates observed as white spots by transmitted light observation were confirmed within an area of ​​approximately 40 mm wide and 3500 mm long. The size of the resin agglomerates was ranked as 1 mm or more, 0.5 to 1 mm, and 0.3 to 0.5 mm according to the value shown in the following formula, and the number of resin agglomerates in each rank was was counted. (Maximum vertical diameter [mm] + Maximum horizontal diameter [mm]) / 2

[0048] Comparative Example 5 Except for using modified PTFE fine powder Teflon (registered trademark) PTFE 640-J instead of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J, the treatment was the same as in Example 2, and dispersibility was evaluated in the same manner as in Example 2. The results are shown in Table 3.

[0049] Comparative Example 6 Except for using unmodified PTFE fine powder Teflon (registered trademark) PTFE 6-J instead of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J, the treatment was the same as in Example 2, and dispersibility was evaluated in the same manner as in Example 2. The results are shown in Table 3.

[0050] Comparative Example 7 Except for using PTFE molding powder Teflon (registered trademark) PTFE 7-J instead of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J, the treatment was the same as in Example 2, and dispersibility was evaluated in the same manner as in Example 2. The results are shown in Table 3.

[0051] [Table 3]

[0052] It can be seen that Example 2, which used modified polytetrafluoroethylene fine powder (Teflon (registered trademark) PTFE 641-J) with an extrusion pressure of less than 25 MPa at RR1600, exhibits high dispersibility equivalent to that of Comparative Example 7, which used molding powder that is easy to mix without fiber formation.

[0053] [Example 3] 160 g of Teflon (registered trademark) PTFE 641-J, a modified PTFE fine powder, and 40 g of carbon fiber (M2007S, manufactured by Kureha Corporation), a filler, were mixed in the same manner as in Example 1. The resulting mixture (powder) was observed under a stereomicroscope (VHX-900, manufactured by Keyence Corporation). It was confirmed that little fibrillation occurred, and that the PTFE and filler were uniformly mixed (Figure 1).

[0054] [Comparative Example 8] Mixing was carried out in the same manner as in Example 3, except that unmodified PTFE fine powder 6-J was used instead of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J, and the resulting mixture (powder) was observed. Compared to Example 3, the mixture of PTFE and filler had more fibrous formation, and it was confirmed that the mixture was not uniform due to the grown aggregates. Figure 2).

[0055] (Evaluation of molded products) [Example 4] As in Example 3, 160 g of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J was mixed with 40 g of carbon fiber (M2007S, manufactured by Kureha Corporation) as a filler. This mixing was repeated three times, and a little over 400 g of the resulting 600 g mixture (powder) (200 g x 3 times) was sieved in a 50 mm diameter mold at 400 kg / cm. 2 Pressurize with This was preformed by heating in an electric furnace at 370°C for 3 hours to obtain a cylindrical molded product with a height of about 100 mm. The obtained cylindrical molded articles were evaluated by the following methods.

[0056] (shrinkage rate) The shrinkage rate of the obtained cylindrical molded product was calculated using the following formula. Shrinkage rate = 100 - (periphery length of cylindrical molded product) x 100 / (inner circumference length of mold)

[0057] (Tensile properties) A disk having a thickness of 2 mm was cut out from the obtained cylindrical molded product, and the obtained disk was punched into a dumbbell shape in accordance with ASTM D-1708, and a tensile test was carried out.

[0058] (Compression creep measurement) A cube measuring 12.7±0.5 mm in length, width and height was cut out from the obtained cylindrical molded product to prepare a test piece. The obtained test pieces were measured in accordance with ASTM D-621 using a six-barrel compression creep tester (manufactured by Orientec Co., Ltd.). 60-minute deformation at a temperature of 23°C and a load of 140 kgf / cm 2 Compression creep after holding at 1 hour Measure the 24-hour deformation at a temperature of 23°C and a load of 140kgf / cm 2 Compression after 24 hours at Measure creep, Permanent deformation at 23°C and a load of 140kgf / cm 2 After keeping it at room temperature ( The compressive creep was measured after leaving the specimens at room temperature (23°C) without load for 24 hours. MD represents the creep deformation in the compression direction, and CD represents the creep deformation in the direction perpendicular to the compression direction.

[0059] The results of the shrinkage, tensile properties (tensile strength (at break), elongation), and compression creep measurements are shown in Table 4.

[0060] Comparative Example 9 The same mixing as in Comparative Example 8 was repeated three times, and a little over 400 g of the resulting 600 g (200 g x 3 times) mixture (powder) of Teflon (registered trademark) PTFE 6-J / carbon fiber, which was unmodified PTFE fine powder, was added to a mold with a diameter of 50 mm and compressed at 400 kg / cm. 2 Pressurize with This was preformed in an electric furnace at 370°C for 3 hours, to obtain a cylindrical molded product having a height of about 100 mm. The obtained cylindrical molded article was measured for shrinkage, tensile properties, and compression creep by the methods described above in Example 4. The results are shown in Table 4.

[0061] [Comparative Example 10] The same mixing as in Example 3 was repeated three times, except that PTFE molding powder Teflon (registered trademark) PTFE 7-J was used instead of modified PTFE fine powder Teflon (registered trademark) PTFE 641-J. Of the resulting 600 g (200 g x 3 times) of 7-J / carbon fiber mixture (powder), slightly more than 400 g was poured into a 50 mm diameter mold. / cm 2 The mixture is preformed by pressing at 370°C for 3 hours in an electric furnace. As a result, a cylindrical molding having a height of about 100 mm was obtained. The obtained cylindrical molded article was measured for shrinkage, tensile properties, and compression creep by the methods described above in Example 4. The results are shown in Table 4.

[0062] [Example 5] 170 g of Teflon (registered trademark) PTFE 641-J, a modified PTFE fine powder, and 30 g of artificial graphite (AT-NO. 10E, manufactured by Oriental Sangyo Co., Ltd.), a filler, were mixed in the same manner as in Example 1 (PTFE / artificial graphite = 85 / 15 (weight ratio)). This mixing was repeated three times, and a little over 400 g of the resulting 600 g composition (200 g x 3 times) was mixed in a 50 mm diameter mold at 400 kg / cm 2 The mixture is preformed by pressing at The mixture was fired in an electric furnace at 370°C for 3 hours to obtain a cylindrical molded product having a height of about 100 mm. The obtained cylindrical molded article was measured for shrinkage, tensile properties, and compression creep by the methods described above in Example 4. The results are shown in Table 5.

[0063] [Comparative Example 11] Using Teflon (registered trademark) PTFE 1123-J, a molding powder containing a filler manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd. (a composition of molding powder / artificial graphite = 85 / 15 (weight ratio) mixed by a Henschel mixer), a molding pressure of 500 kg / cm was applied to a mold with a diameter of 50 mm. 2 The mixture was preformed by pressing at 370°C for 3 After firing in an electric furnace for 1 hour, a cylindrical molded product having a height of about 100 mm was obtained. The obtained cylindrical molded article was measured for shrinkage, tensile properties, and compression creep in the same manner as in Example 4. The results are shown in Table 5.

[0064] [Table 4]

[0065] [Table 5]

[0066] The molded article of Example 4, which used a modified polytetrafluoroethylene fine powder (Teflon (registered trademark) PTFE 641-J) at an extrusion pressure of less than 25 MPa at RR1600, had a lower molding pressure and shrinkage rate, higher tensile strength and elongation, and less creep deformation than the molded article of Comparative Example 9, which used an unmodified PTFE fine powder (Teflon (registered trademark) PTFE 6-J). The high elongation rate prevents damage due to cracking when a load is applied to the molded article, and the small creep deformation means that there is little deformation during long-term use, even in environments where high pressure is continuously applied, allowing for stable use.

[0067] Furthermore, compared with the molded articles of Comparative Examples 10 and 11, which used PTFE molding powder, the molded articles of Examples 4 and 5, which used modified PTFE fine powder, exhibit a high elongation rate and a small amount of creep deformation.

Claims

1. A polytetrafluoroethylene composition for dry blending contains a modified polytetrafluoroethylene fine powder having an extrusion pressure of less than 25 MPa at RR1600, and a filler, the composition ratio of the filler being in the range of 15.0 to 60.0 mass %.

2. A molded article obtained by molding the polytetrafluoroethylene composition according to claim 1.

3. The molded article according to claim 2, which is a sliding material or a sealing material.

4. The molded article according to claim 2, which is a wire coating material or a porous membrane material.

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