JP2011241308A - Modified polytetrafluoroethylene composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modified polytetrafluoroethylene composition having excellent abrasion characteristics while maintaining compression-resistant creep characteristics and suitably used for sliding members and sealing materials, and to provide a sliding member obtained by molding the composition.SOLUTION: The modified polytetrafluoroethylene composition is obtained by compounding particles of copolyparaphenylene 3,4'-oxydiphenylene terephthalamide having an average particle diameter of 20 to 50 μm into a tetrafluoroethylene copolymer copolymerized with a copolymerizable monomer in a proportion of at most 1.0 wt.%, preferably in a proportion of 1 to 40 wt.%. A sliding member is obtained by molding the composition.

Description

  The present invention provides an average particle size of at least one copolymer of tetrafluoroethylene and a copolymerizable monomer (hereinafter referred to as modified PTFE) in a proportion of 1.0% by weight or less based on tetrafluoroethylene. The present invention relates to a modified PTFE composition formed by blending 20 to 50 μm of copolyparaphenylene · 3,4′-oxydiphenylene · terephthalamide particles, and a sliding member using the composition. More specifically, the present invention relates to a modified PTFE composition suitable for applications such as a sliding member and a sealing material that have excellent wear characteristics while maintaining compression creep resistance, and a sliding member obtained from the composition.

  Polytetrafluoroethylene (hereinafter referred to as PTFE) has a low friction coefficient and is excellent in heat resistance and chemical resistance. Therefore, a sliding member containing a filler for the purpose of improving wear resistance and creep resistance is used. It is often used as a sealing material. The PTFE used here is a molding powder which is a powder for compression molding, while the filler is an inorganic filler such as glass fiber, carbon fiber, graphite, molybdenum disulfide, bronze powder, or aromatic polyester. Organic fillers such as polyimide and polyphenylene sulfide are known.

  However, in hydraulic equipment for vehicles such as automobiles and various sliding devices, in recent years, weight reduction, compactness, environmental measures, etc. have been promoted, and the opportunity to use a soft metal such as an aluminum alloy is used without lubrication. Opportunities are being increased. In particular, in a sliding device under a high temperature and high load, it is easy to be in a non-lubricated state in which no lubricating oil is supplied. In the case of a soft metal such as, there is a problem that the counterpart material is easily damaged by wear.

  In order to solve these phenomena, a PTFE powder composition composed of PTFE fine powder, PTFE molding powder, and talc powder has been proposed (see Patent Document 1). However, there is still a problem that the wear of the mating material, which is a soft metal, is still large in a non-lubricated state. Further, a polytetrafluoroethylene resin composition in which graphite and carbon fiber are blended with a polytetrafluoroethylene resin has been proposed (see Patent Document 2). However, in the sliding member made of this resin composition, the spatial change due to the difference in the thermal expansion coefficient between the rotating shaft material and the fixed part material is large and the sliding surface wear is small, but a large amount of graphite or carbon fiber is added. Then, the gap increases and the fluid permeates (vents) the sliding member, and the wear of the mating material, which is a soft metal, is small, but the sliding member itself increases its own wear, and sufficient wear characteristics are obtained. There was a problem that it was not possible.

  Furthermore, in the thermal dimensional stability formed by mixing aramid particles having an average diameter in the range of 1 to 150 μm in the thermoplastic resin so as to have a volume content of 3 to 35% with respect to the thermoplastic resin. An excellent thermoplastic resin composition has been proposed, and a fluororesin is described as a thermoplastic resin (see Patent Document 3). However, the aramid particles have high hygroscopicity, and when added to PTFE having strong non-adhesive properties as a filler, the adhesion between PTFE and the added aramid particles becomes poor. There was a problem that cracks occurred in the molded product (sliding member).

JP-A-9-157472 JP 2001-294720 A JP 2005-120213 A

  The present invention is excellent in wear characteristics while maintaining compression-resistant creep resistance, because soft metals such as aluminum alloy as a counterpart material are not easily damaged by wear even under high temperature and high load or in a non-lubricated state where no lubricating oil is supplied. It is providing the fluororesin composition suitable for uses, such as a sliding member and a sealing material, and the sliding member obtained from this composition.

The present inventor has intensively studied to solve the above problems. As a result, it was found that the above problems can be solved by blending specific polyfluoroethylene with copolyparaphenylene • 3,4′-oxydiphenylene • terephthalamide particles having an average particle diameter of 20 to 50 μm. It came to be completed.
That is, the present invention relates to at least one copolymer of tetrafluoroethylene and a copolymerizable monomer in a proportion of 1.0% by weight or less with respect to tetrafluoroethylene, and a copolyparaffin having an average particle diameter of 20 to 50 μm. A modified PTFE composition containing phenylene 3,4′-oxydiphenylene terephthalamide particles, and a sliding member obtained by molding the composition.

  In the modified PTFE composition, a modified PTFE composition comprising copolyparaphenylene 3,4′-oxydiphenylene terephthalamide particles having an average particle diameter of 20 to 50 μm of 1 to 40% by weight based on the weight of the copolymer. Is a preferred embodiment of the present invention.

  In the modified PTFE composition, the copolymerizable monomer in a proportion of 1.0% by weight or less based on tetrafluoroethylene contains an unsaturated fluorinated hydrocarbon, an unsaturated fluorinated chlorinated hydrocarbon, and an ether group. A modified PTFE composition that is at least one monomer selected from the group consisting of unsaturated fluorinated hydrocarbons is a preferred embodiment of the present invention.

In the modified PTFE composition, the copolymerizable monomer in a proportion of 1.0% by weight or less with respect to tetrafluoroethylene is hexafluoropropylene, perfluoro (alkyl vinyl ether), (perfluoroalkyl) ethylene, trifluoro. A modified PTFE composition which is at least one monomer selected from the group consisting of ethylene, chlorotrifluoroethylene, vinylidene fluoride and vinyl fluoride is a preferred embodiment of the present invention.
A sliding member obtained by molding the modified PTFE composition is a preferred embodiment of the present invention.

  According to the present invention, there are provided a modified PTFE composition excellent in wear characteristics while maintaining compression creep resistance and suitable for uses such as a sliding member and a sealing material, and a sliding member obtained by molding the composition. can do.

  The present invention relates to at least one copolymer of tetrafluoroethylene (TFE) and a copolymerizable monomer in a proportion of 1.0% by weight or less with respect to tetrafluoroethylene, and an average particle size of 20 to 50 μm. The modified PTFE composition containing the copolyparaphenylene / 3,4′-oxydiphenylene / terephthalamide particles and a sliding member obtained by molding the composition are provided.

The modified PTFE used in the present invention is a copolymer of tetrafluoroethylene and a copolymerizable monomer in a proportion of 1.0% by weight or less with respect to tetrafluoroethylene. The copolymerizable monomer is an ethylenically unsaturated monomer, and consists of an unsaturated fluorinated hydrocarbon, an unsaturated fluorinated chlorinated hydrocarbon, and an ether group-containing unsaturated fluorinated hydrocarbon. And at least one monomer selected from the group consisting of: Preferably, C _n F perfluoroolefins represented by _{2n + 1 CF = CF 2 (} n = 1~12), C n F 2n + 1 O [CF (CF 3) CF 2 O] m CF = CF ₂ (n = 1-5, M = 0-10), perfluorovinyl ethers, ClCF = CF ₂ chlorotrifluoroethylene, C _n F _{2n + 1} CH═CH ₂ (n = 1 To 10), and fluorine-containing monomers such as perfluoroalkylethylenes, vinylidene fluoride, and vinyl fluoride.

  Among the fluorine-containing monomers, hexafluoropropylene is preferable as the perfluoroolefin, and the perfluoroalkyl vinyl ether has an alkyl group of 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms. It is preferable that perfluoroethyl vinyl ether (PEVE) and perfluoropropyl vinyl ether (PPVE) are more preferable. Moreover, as perfluoroalkyl ethylene, it is preferable that the alkyl group of perfluoro alkyl ethylene is C1-C5, and perfluoro (butyl) ethylene is more preferable. Modified PTFE obtained by copolymerizing the above monomers with 1.0% by weight or less with respect to tetrafluoroethylene does not have melt processability like the TFE homopolymer.

  The modified PTFE used in the present invention is at least one copolymer (modified PTFE) obtained from tetrafluoroethylene and the above copolymerizable monomer in a proportion of 1.0% by weight or less based on tetrafluoroethylene. Yes, two or more may be blended.

The modified PTFE used in the present invention may be in the form of powder, granules or granulated granules, and known suspension polymerization methods such as those described in US Pat. No. 3,855,191 are used. Even if it is directly powdered by a polymerization method or an emulsion polymerization method, for example, an emulsion polymerization method described in US Pat. No. 2,559,752, a pulverized bulk polymer, for example, a known suspension polymerization method The modified PTFE powder obtained by the above may be granulated and then pulverized. (US Pat. No. 3,155,486, Japanese Patent Publication No. 34-10177, Japanese Patent Publication No. 47-28087, etc.)
The average particle diameter of such modified PTFE is preferably 5 to 100 μm, more preferably 10 to 50 μm. The modified PTFE thus finely divided is advantageous for uniform mixing with the copolyparaphenylene 3,4'-oxydiphenylene terephthalamide particles.

The copolyparaphenylene 3,4'-oxydiphenylene terephthalamide particles having an average particle diameter of 20 to 50 μm according to the present invention are softer than inorganic materials, and have high strength, high elastic modulus, fatigue resistance, One type of para-aramid that has excellent dimensional stability, heat resistance of 400 ° C. or higher, chemical resistance, etc. is formed into particles. The aramid is fiberized and isolated by solution spinning, and then pulverized. Powdered fine particles. In addition to the spherical shape, the shape includes pulp, flakes, needles, fibers, and the like.
Further, from the viewpoint of anchor effect (improvement of interfacial adhesion) and improved thermal dimensional stability due to the penetration of modified PTFE into the pores of the aramid particles, the above-mentioned copolyparaphenylene / 3,4′-oxydiphenylene / terephthalamide The particles are preferably porous.

The average particle size of the copolyparaphenylene • 3,4′-oxydiphenylene • terephthalamide particles used in the present invention is usually 5 to 100 μm, preferably 10 to 50 μm, more preferably 20 to 50 μm. Such aramid particles are described in JP-A-2005-120213 and JP-A-2008-106086, and examples of products include Technora (registered trademark) (manufactured by Teijin Products Limited). The copolyparaphenylene • 3,4′-oxydiphenylene • terephthalamide particles in the modified PTFE composition are 1 to
It is preferably 40% by weight. When the copolyparaphenylene 3,4'-oxydiphenylene terephthalamide particles exceed 40% by weight, cracks are likely to occur in the obtained molded product, which is not preferable.

  In the modified PTFE composition of the present invention, a small amount of a heat-meltable fluororesin, specifically, a tetrafluoroethylene / perfluoro (alkyl vinyl 40 ether) copolymer (hereinafter, PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / hexafluoropropylene / perfluoro (alkyl vinyl ether) copolymer (EPE), tetrafluoroethylene / ethylene copolymer (ETFE) Etc. can be blended.

  When the heat-meltable fluororesin is a copolymer of TFE and a fluorovinyl compound, a fluorovinyl compound having a copolymerization ratio of about 0.5 to 20 mol% can be used. A melt flow rate (MFR) at a load of 5000 g is preferably from 0.5 to 20 g / 10 minutes, particularly preferably from about 0.5 to 10 g / 10 minutes. Further, in the case of a copolymer of TFE and ethylene, it is preferable to use an ethylene copolymer having a copolymerization ratio of about 30 to 70 mol%, and an MFR at 297 ° C. under a load of 2160 g is 1 to 20 g / 10 min. The thing of about 10 g / 10 minutes is preferable.

  The average particle diameter of these heat-meltable fluororesins is preferably 100 μm or less, more preferably 10 to 50 μm. The heat-meltable fluororesin is preferably in the range of 0.1 to 20% by weight, particularly 1 to 10% by weight in the modified PTFE composition.

  In the modified PTFE composition of the present invention, an inorganic or organic powder or fiber having an average particle size of 200 μm or less, which is generally blended as a filler of a fluororesin powder, is added as necessary within a range not impairing the object of the present invention. Can be blended. For example, glass filler (eg glass fiber or glass sphere), hydrophilic filler such as alumina powder, calcium sulfate, calcium carbonate or bronze powder, potassium titanate fiber, talc, zinc oxide powder, carbon fiber, disulfide Semi-hydrophilic fillers such as molybdenum and graphite powder, organic fillers such as polyimide, polyamide, aromatic polyamide, polyphenylene sulfide and the like can be used.

  The modified PTFE composition of the present invention can be obtained by mixing modified PTFE and copolyparaphenylene • 3,4′-oxydiphenylene • terephthalamide particles by any method. For example, using a known mixer, a V-type blender, a tumbler, a dry blender, a Henschel mixer, or a high-speed rotary mixer having a blade or cutter knife that rotates at high speed, and the like, and uniformly mixing by a known method Thus, a modified PTFE composition can be obtained. Specifically, for example, a blending method using a Henschel mixer and rotating at about 200 to 1000 rpm for about 4 to 15 minutes is used. Furthermore, this modified PTFE composition may be granulated to improve fluidity.

  The method of molding the modified PTFE composition of the present invention into molded products of various shapes (sliding members, sealing materials, etc.) is not particularly limited. For example, compression molding, ram extrusion molding, paste extrusion molding Various desired molded articles can be formed by a known compression molding method of PTFE powder such as a method, an isostatic molding method, and a hot coining molding method. For example, the modified PTFE composition of the present invention is preformed by a compression molding method, fired at a temperature equal to or higher than the melting point of the tetrafluoroethylene polymer to form a primary molded product, and then cut according to the shape of the final molded product. Can be used to produce products. The molded product obtained in this manner can be advantageous in that it is difficult to stretch and break and is not easily deformed.

The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to these examples.
In the present invention, each physical property was measured by the following method.

A. Measurement of physical properties (1) Specific gravity 12.0 ± 0.1 g of a pre-weighed modified PTFE composition was placed in a mold having an inner diameter of 28.5 mm, and using a press machine (manufactured by NPA Corporation), room temperature (23 ° C.), A cylindrical preform was obtained by holding for 2 minutes at a load of 600 kg / cm ² . The obtained preform was heated from 290 ° C. to 380 ° C. at 2 ° C./min using a precision sinter furnace (manufactured by Fort System), and kept at 380 ° C. ± 3 ° C. for 30 minutes ± 10 seconds. The temperature was lowered from 380 ° C. to 294 ° C./minute, held at 294 ° C. for 1 minute and fired, then taken out and allowed to cool at room temperature (23 ° C.) for 2 hours, and the diameter was 28.5 mm and the thickness was 9.5 mm Two cylindrical molded articles (chips) were obtained. The weights of the obtained chips (2 pieces) were measured in air and 0.1 wt% Triton (registered trademark) X-100 aqueous solution, respectively, and the average value of specific gravity (n = 2) obtained by the following formula Asked.
Specific gravity = Chip weight in air / (Chip weight in air−Chip weight in aqueous solution)

(2) Tensile strength and elongation value In accordance with ASTM D-1457, 14.5 ± 0.1 g of a modified PTFE composition weighed in advance is placed in a 3-inch screw mold, and the modified PTFE composition is adjusted while adjusting the screw height. After leveling the object, a disk-shaped sheet was obtained by holding it at room temperature (23 ° C.) under a load of 600 kg / cm ² for 3 minutes using a press machine (manufactured by NP System). The obtained preform was heated from 290 ° C. to 380 ° C. at 2 ° C./min using a precision sinter furnace (manufactured by Fort System), and kept at 380 ° C. ± 3 ° C. for 30 minutes ± 10 seconds. The temperature is lowered from 380 ° C. to 294 ° C./min, calcined by holding at 294 ° C. for 1 minute, taken out, allowed to cool at room temperature (23 ° C.) for 2 hours, and a disk having a diameter of 76.2 mm and a thickness of 1.8 mm Two shaped molded articles (sheets) were obtained. Two dumbbell-shaped test pieces (standard No. ASTM D-2116) were punched per sheet, and a total of four dumbbell-shaped test pieces were punched out.
Strograph (trade name) tensile tester (Toyo Seiki Co., Ltd.) in which the tensile strength and elongation values of the obtained four dumbbell-shaped test pieces were adjusted to a crosshead speed of 51 ± 1 mm / min and a grip interval of 22.2 ± 0.5 mm The average value of tensile strength (n = 4) and the average value of elongation values (n = 4) were obtained.

(3) Friction and wear coefficient 400 ± 0.1 g of a modified PTFE composition weighed in advance is placed in a mold having an inner diameter of 50.0 mm, and using a press machine (manufactured by NP System), room temperature (23 ° C.), 600 kg / cm ^A cylindrical preform was obtained by holding at a load of ² for 3 minutes.
The obtained preform was heated from room temperature (23 ° C.) to 300 ° C. at 1 ° C./1 minute using a sinter furnace (manufactured by Tojo Thermal Engineering Co., Ltd.), and from 300 ° C. to 370 ° C. at 1 ° C./3 minutes. The temperature is raised to 370 ° C. for 3 hours, the temperature is lowered from 370 ° C. to 150 ° C. at 1 ° C./3 minutes, the temperature is lowered from 150 ° C. to room temperature (23 ° C.) at 1 ° C./minute, and then taken out. And cooled at room temperature (23 ° C.) for 2 hours to obtain a cylindrical molded product having a diameter of 50 mm and a height of 100 mm. A ring having an outer diameter of 25.7 mm, an inner diameter of 20 mm, and a height of 20 mm was cut from the obtained cylindrical molded product to obtain a test piece.
In accordance with JIS K7218 (Method A), the friction coefficient and the wear coefficient of the obtained test piece are based on SS-41 (general structural rolling) as a mating material using a dual friction and wear tester (Intesco product). Measurement was performed by sliding for 24 hours under conditions of steel, JIS G3101 (2004)), load 6.0 kg / cm ² , and sliding speed 0.5 m / s.

(4) Sliding temperature Using an EFM-3F type machine manufactured by Orientec, measurement was performed with the tip of the thermocouple set approximately 2 mm above the sliding surface of the counterpart material.

(5) Compressive creep A cylindrical molded product having a diameter of 50 mm and a height of 100 mm was obtained in the same manner as the measurement of the friction coefficient and the wear coefficient. From the obtained cylindrical molded product, cubes each having a length, width and height of 12.7 ± 0.5 mm were cut into test pieces.
The compression creep of the obtained test piece was measured using a 6-unit compression creep tester (Orientec Co., Ltd.) in accordance with ASTM D-621. 24Hr deformation was measured for compressive creep after being held for 24 hours at a temperature of 23 ° C. and a load of 140 kgf / cm ² , and permanent deformation was held for 24 hours at a measurement temperature of 23 ° C. and a load of 140 kgf / cm ² , and room temperature (23 ° C. ) Compressive creep after standing for 24 hours under no load was measured. MD represents the compression direction, and CD represents the vertical direction perpendicular to the compression direction.

B. Raw materials The raw materials used in Examples and Comparative Examples of the present invention are as follows.
(1) PTFE powder
PTFE powder (average particle size: 5 to 100 μm) obtained by suspension polymerization, manufactured by Mitsui DuPont Fluorochemicals.
(2) Modified PTFE powder The content of modified PTFE powder (perfluoro (propyl vinyl ether)) obtained by suspension polymerization described in US Pat. No. 3,855,191, manufactured by Mitsui DuPont Fluorochemicals, is 0.05. % By weight of tetrafluoroethylene / perfluoro (propyl vinyl ether) copolymer, average particle size: 5 to 100 μm).
(3) Copolyparaphenylene / 3,4′-oxydiphenylene / terephthalamide particles Teijin Techno Products Limited, Technora (registered trademark), (average particle size 25 μm)
(4) Graphite
Made by Kureha Chemical Industry Co., Ltd. (average fiber diameter 14.5 μm, average fiber length 120 μm)

(Examples 1-3 and Comparative Examples 1-3)
In the ratio shown in Table 1, modified PTFE powder, copolyparaphenylene 3,4'-oxydiphenylene terephthalamide particles and graphite were put into a Henschel mixer and mixed for 5 minutes at 1600 rpm, and modified PTFE fat. A composition was obtained. Specific gravity, tensile strength (MPa), elongation (%), compression creep (%), wear coefficient (cm ³ · sec · 10 ⁻⁶ / MPa · m · hr), friction coefficient, slip of the obtained modified PTFE composition The dynamic temperature was measured. The results are shown in Table 1.

The modified PTFE composition of the present invention contains para-type aramid particles (copolyparaphenylene, 3,4′-oxydiphenylene, terephthalamide particles), which are organic fillers whose hardness is softer than inorganic materials, and modified PTFE. Thus, a molded product obtained by molding the PTFE composition of the present invention becomes a molded product with improved wear characteristics while maintaining compression creep resistance. The sliding member, sealing material and the like obtained by molding the modified PTFE composition of the present invention are less likely to wear and damage the counterpart material made of a soft metal such as aluminum, and are less likely to self-wear (abnormal It does not cause wear) and has excellent characteristics.

Claims (5)

  At least one copolymer of tetrafluoroethylene and a copolymerizable monomer in a proportion of 1.0% by weight or less with respect to tetrafluoroethylene, and copolyparaphenylene 3,4 having an average particle size of 20 to 50 μm A modified polytetrafluoroethylene composition comprising '-oxydiphenylene terephthalamide particles.   2. The modified polytetrafluoroethylene composition according to claim 1, comprising 1 to 40% by weight of copolyparaphenylene • 3,4′-oxydiphenylene • terephthalamide particles having an average particle size of 20 to 50 μm based on the weight of the copolymer. object.   The copolymerizable monomer in a proportion of 1.0% by weight or less is selected from the group consisting of unsaturated fluorinated hydrocarbons, unsaturated fluorinated chlorinated hydrocarbons, and ether group-containing unsaturated fluorinated hydrocarbons. The modified polytetrafluoroethylene composition according to claim 1 or 2, which is at least one monomer.   1.0 weight percent or less of copolymerizable monomer is hexafluoropropylene, perfluoro (alkyl vinyl ether), (perfluoroalkyl) ethylene, trifluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, and The modified polytetrafluoroethylene composition according to any one of claims 1 to 3, which is at least one monomer selected from the group consisting of vinyl fluoride.   A sliding member obtained by molding the modified polytetrafluoroethylene composition according to claim 1.