Method for producing polytetrafluoroethylene micropowder, and polytetrafluoroethylene powder

Abstract

To provide a method for producing polytetrafluoroethylene micropowder capable of achieving clean work environments, and polytetrafluoroethylene micropowder.SOLUTION: The present invention relates to a method for producing polytetrafluoroethylene micropowder having an average particle diameter of 20 μm or less via a step of irradiating polytetrafluoroethylene powder having an average particle diameter of 700 μm or more with ionizing radiation.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing polytetrafluoroethylene micropowder and to a polytetrafluoroethylene powder. [Background technology]

[0002] 2. Description of the Related Art A method is known in which a fluororesin such as polytetrafluoroethylene (PTFE) is irradiated with ionizing radiation and then pulverized to produce fine particles of the fluororesin (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-139204 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 only states that the fluororesin to be irradiated with ionizing radiation may be in any form, such as powder, granules, fibers, or preformed, and no sufficient consideration was given to the matter.

[0005] An object of the present disclosure is to provide a method for producing polytetrafluoroethylene micropowder that can realize a clean working environment, and a polytetrafluoroethylene powder. [Means for solving the problem]

[0006] The present disclosure (1) relates to a method for producing polytetrafluoroethylene micropowder having an average particle size of 20 μm or less, by irradiating polytetrafluoroethylene powder having an average particle size of 700 μm or more with ionizing radiation (hereinafter also referred to as the "production method of the present disclosure").

[0007] The present disclosure (2) relates to a polytetrafluoroethylene micropowder having a melt viscosity of 1×10 at 380° C. 1 ~7×10 5 This is a method for producing the polytetrafluoroethylene micropowder according to the present disclosure (1), whose Pa·s is:

[0008] The present disclosure (3) is a method for producing a polytetrafluoroethylene micropowder according to the present disclosure (1) or (2), wherein the polytetrafluoroethylene powder has an apparent density of 0.40 g / ml or less.

[0009] The present disclosure (4) is a method for producing a polytetrafluoroethylene micropowder according to any one of the present disclosures (1) to (3), wherein the polytetrafluoroethylene powder is obtained by sieving through a sieve having an opening of 700 μm to 2 mm.

[0010] The present disclosure (5) is a method for producing a polytetrafluoroethylene micropowder according to any one of the present disclosures (1) to (4), wherein the polytetrafluoroethylene powder has a fluttering sensitivity index of 2 or less in a fluttering sensitivity test performed under the following conditions: (Midashi Sensitivity Test) The amount of fluff generated when polytetrafluoroethylene powder scooped up with a stainless steel measuring scoop 133 mm wide, 205 mm long, and 70 mm deep is dropped from a height of 1.2 mm into an 18 L plastic container is compared. The comparison is visually performed by three people and indexed as follows (fluffiness sensitivity index). 1: There is clearly no dancing. (The condition in which, immediately after pouring all the polytetrafluoroethylene powder into an 18 L plastic container (32 cm high), no powdered polytetrafluoroethylene particles can be visually confirmed above the top surface (32 cm high) of the plastic container for 5 seconds.) 2: There is some fluttering, but it is very slight. (The state in which polytetrafluoroethylene powder particles can be visually confirmed from the top surface (32 cm high) of an 18 L plastic container (32 cm high) for 5 seconds immediately after the polytetrafluoroethylene powder is poured into the container, but after 5 seconds, the powder particles are so minute that they can no longer be visually confirmed.) 3: There is concern that the substance may fly up and stick to workers' clothes. (A condition in which, immediately after the polytetrafluoroethylene powder was poured into an 18L plastic container (32cm high), powdered polytetrafluoroethylene powder particles could be visually confirmed approximately 5cm above the top surface (32cm high) of the plastic container, and a small amount of fine polytetrafluoroethylene powder was observed to have accumulated on the floor where the plastic was placed. There is concern that polytetrafluoroethylene powder may adhere to workers' clothing and shoes. However, the amount of accumulation was so small that it was difficult to measure.) 4: The fluttering is clearly visible. (The condition in which polytetrafluoroethylene powder particles can be visually confirmed approximately 10 cm above the top surface (32 cm high) of an 18 L plastic container (32 cm high) within 5 seconds after the polytetrafluoroethylene powder is poured into the container.)

[0011] The present disclosure (6) is a polytetrafluoroethylene powder having an apparent density of 0.40 g / ml or less and an average particle size of 700 μm or more (hereinafter also referred to as the “first PTFE powder of the present disclosure”).

[0012] The present disclosure (7) is the polytetrafluoroethylene powder according to the present disclosure (6), which has a fluttering sensitivity index of 2 or less in a fluttering sensitivity test performed under the following conditions: (Midashi Sensitivity Test) The amount of fluff generated when polytetrafluoroethylene powder scooped up with a stainless steel measuring scoop 133 mm wide, 205 mm long, and 70 mm deep is dropped from a height of 1.2 mm into an 18 L plastic container is compared. The comparison is visually performed by three people and indexed as follows (fluffiness sensitivity index). 1: There is clearly no dancing. (The condition in which, immediately after pouring all the polytetrafluoroethylene powder into an 18 L plastic container (32 cm high), no powdered polytetrafluoroethylene particles can be visually confirmed above the top surface (32 cm high) of the plastic container for 5 seconds.) 2: There is some fluttering, but it is very slight. (The state in which polytetrafluoroethylene powder particles can be visually confirmed from the top surface (32 cm high) of an 18 L plastic container (32 cm high) for 5 seconds immediately after the polytetrafluoroethylene powder is poured into the container, but after 5 seconds, the powder particles are so minute that they can no longer be visually confirmed.) 3: There is concern that the substance may fly up and stick to workers' clothes. (A condition in which, immediately after the polytetrafluoroethylene powder was poured into an 18L plastic container (32cm high), powdered polytetrafluoroethylene powder particles could be visually confirmed approximately 5cm above the top surface (32cm high) of the plastic container, and a small amount of fine polytetrafluoroethylene powder was observed to have accumulated on the floor where the plastic was placed. There is concern that polytetrafluoroethylene powder may adhere to workers' clothing and shoes. However, the amount of accumulation was so small that it was difficult to measure.) 4: The fluttering is clearly visible. (The condition in which polytetrafluoroethylene powder particles can be visually confirmed approximately 10 cm above the top surface (32 cm high) of an 18 L plastic container (32 cm high) within 5 seconds after the polytetrafluoroethylene powder is poured into the container.)

[0013] The present disclosure (8) is a polytetrafluoroethylene powder having an average particle size of 700 μm or more and containing 3 wt % or less of fine powder of 42 mesh or less (hereinafter also referred to as "the second PTFE powder of the present disclosure").

[0014] The present disclosure (9) is the polytetrafluoroethylene powder according to the present disclosure (8), having an apparent density of 0.40 g / ml or less.

[0015] The present disclosure (10) is a polytetrafluoroethylene powder according to the present disclosure (8) or (9), which is a polytetrafluoroethylene fine powder.

[0016] The present disclosure (11) is a polytetrafluoroethylene powder (hereinafter also referred to as "the third PTFE powder of the present disclosure") used as a raw material for polytetrafluoroethylene micropowder and having an average particle size of 700 μm or more. Effect of the Invention

[0017] According to the present disclosure, it is possible to provide a method for producing polytetrafluoroethylene micropowder, and polytetrafluoroethylene powder, which can realize a clean working environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As used herein, "organic group" means a group containing one or more carbon atoms or a group formed by removing a hydrogen atom from an organic compound. Examples of the "organic group" are: an alkyl group which may have one or more substituents; an alkenyl group optionally having one or more substituents; an alkynyl group optionally having one or more substituents; a cycloalkyl group optionally having one or more substituents, a cycloalkenyl group optionally having one or more substituents, a cycloalkadienyl group optionally having one or more substituents, an aryl group which may have one or more substituents; an aralkyl group optionally having one or more substituents; a non-aromatic heterocyclic group optionally having one or more substituents, a heteroaryl group optionally having one or more substituents, Cyano group, Formyl group, RaO-, RaCO-, RaSO2-, RaCOO-, RaNRaCO-, RaCONRa-, RaOCO-, RaOSO2- and RaNRbSO2- (In these formulas, Ra is independently an alkyl group which may have one or more substituents; an alkenyl group optionally having one or more substituents; an alkynyl group optionally having one or more substituents; a cycloalkyl group optionally having one or more substituents, a cycloalkenyl group optionally having one or more substituents, a cycloalkadienyl group optionally having one or more substituents, an aryl group which may have one or more substituents; an aralkyl group optionally having one or more substituents; a non-aromatic heterocyclic group optionally having one or more substituents, or a heteroaryl group optionally having one or more substituents, Rb is independently H or an alkyl group which may have one or more substituents. Includes: The organic group is preferably an alkyl group which may have one or more substituents.

[0019] The present disclosure will now be described in detail.

[0020] <Production Method of the Present Disclosure> The manufacturing method of the present disclosure involves a step of irradiating PTFE powder having an average particle size of 700 μm or more with ionizing radiation to obtain PTFE micropowder having an average particle size of 20 μm or less.

[0021] When irradiating PTFE powder with ionizing radiation as in the method disclosed in Patent Document 1, it is necessary to fill the PTFE powder in a dedicated container for irradiating ionizing radiation. The PTFE powder used as the raw material for PTFE micropowder generally has an average particle size of 300 to 650 μm. If the average particle size is within this range, the PTFE powder may fly up when filling the container, resulting in a poor working environment. In contrast, in the manufacturing method disclosed herein, the average particle size of the PTFE powder to be irradiated with ionizing radiation is set to 700 μm or more, thereby reducing the flying of the PTFE powder and realizing a clean working environment.

[0022] In addition, when comparing the PTFE micropowder obtained by the manufacturing method of the present disclosure with the PTFE micropowder manufactured from the PTFE powder having an average particle size of 300 to 650 μm, there is no substantial difference in the characteristics, and therefore the PTFE micropowder can be applied to the same applications as the conventional PTFE micropowder.

[0023] In addition, PTFE powder is roughly divided into PTFE fine powder and PTFE molding powder, and PTFE fine powder is known as a raw material for high-performance products such as special porous membranes, tubes, and coating layers of electric wires. In such high-performance products, in order to suppress the occurrence of voids, it is common to use PTFE fine powder without coarse particles having an average particle size of 700 μm or more. In other words, PTFE fine powder having an average particle size of 700 μm or more has little commercial value. The manufacturing method of the present disclosure also has the advantage of being able to effectively utilize PTFE fine powder having an average particle size of 700 μm or more.

[0024] PTFE molding powder is also known as a raw material for special packings, as well as special rods, tubes, and sheets, and other high-performance products. In these high-performance products, it is common to use PTFE molding powder without coarse particles in order to suppress the generation of voids. However, the size of the coarse particles varies depending on the product form of the PTFE molding powder, so it is difficult to give a unique definition.

[0025] The average particle size of the PTFE powder may be 700 μm or more, preferably 850 μm or more, more preferably 900 μm or more, even more preferably 940 μm or more, and particularly preferably 1000 μm or more. There is no particular upper limit, but it is preferably 10000 μm or less. The PTFE powder may have an average particle size of 700 μm or more, and may contain fine powder having a particle size of less than 700 μm.

[0026] The average particle size of the PTFE powder can be measured by the following method. Standard sieves of 10, 20, 32, 48, 60 and 83 mesh (inch mesh) are stacked from top to bottom, the PTFE powder is placed on the 10 mesh sieve, and the sieves are vibrated to allow finer PTFE powder to fall downward in succession. The proportion of PTFE powder remaining on each sieve is calculated as a percentage, and then the cumulative percentage of the remaining proportion (vertical axis) is scaled against the mesh opening of each sieve (horizontal axis) on a logarithmic probability paper, these points are connected with a straight line, and the particle size on this line where the proportion is 50% is determined, and this value is the average particle size.

[0027] The PTFE powder can be obtained by sieving the mixture through a sieve having an opening size of 700 μm to 2 mm. Examples of such a sieve include sieves having an opening size of 8 to 24 mesh. From the viewpoint of yield, sieves having an opening size of 8 mesh or 10 mesh are preferable. In this specification, the sieve openings are nominal dimensions according to JIS Z8801-1:2019.

[0028] The PTFE powder preferably has a content of fine powder of 42 mesh or less (e.g., 48 mesh or less) of 3% by weight or less based on the total amount of the PTFE powder. When the content of fine powder of 42 mesh or less based on the total amount of the PTFE powder is in such a range, the effects of the present disclosure can be more effectively obtained. The content is preferably 2.5% by weight or less based on the total amount of the PTFE powder, more preferably 2.0% by weight or less, even more preferably 1.5% by weight or less, and particularly preferably 1.0% by weight or less. The content of the fine powder of 42 mesh or less can be measured, for example, by the method described in the Examples section below. In this specification, "fine powder of 42 mesh or less" refers to fine powder that passes through a mesh of 42 mesh or less when classified.

[0029] The apparent density of the PTFE powder is preferably 0.25 g / ml or more, more preferably 0.30 g / ml or more, further preferably 0.32 g / ml or more, and is preferably 0.40 g / ml or less. The apparent density of the PTFE powder is measured in accordance with JIS K 6892.

[0030] The standard specific gravity (SSG) of the PTFE powder is preferably 2.130 to 2.280. The standard specific gravity is measured by a water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D4895 89.

[0031] The PTFE powder preferably has a fluttering sensitivity index of 2 or less, and more preferably 1, in a fluttering sensitivity test carried out under the following conditions. When the fluttering sensitivity index in the fluttering sensitivity test carried out under the following conditions is in this range, fluttering of the PTFE powder is suppressed, making it possible to realize a clean working environment. (Midashi Sensitivity Test) The amount of fluff generated when polytetrafluoroethylene powder scooped up with a stainless steel measuring scoop 133 mm wide, 205 mm long, and 70 mm deep is dropped from a height of 1.2 mm into an 18 L plastic container is compared. The comparison is visually performed by three people and indexed as follows (fluffiness sensitivity index). 1: There is clearly no dancing. (The condition in which, immediately after pouring all the polytetrafluoroethylene powder into an 18 L plastic container (32 cm high), no powdered polytetrafluoroethylene particles can be visually confirmed above the top surface (32 cm high) of the plastic container for 5 seconds.) 2: There is some fluttering, but it is very slight. (The state in which polytetrafluoroethylene powder particles can be visually confirmed from the top surface (32 cm high) of an 18 L plastic container (32 cm high) for 5 seconds immediately after the polytetrafluoroethylene powder is poured into the container, but after 5 seconds, the powder particles are so minute that they can no longer be visually confirmed.) 3: There is concern that the substance may fly up and stick to workers' clothes. (A condition in which, immediately after the polytetrafluoroethylene powder was poured into an 18L plastic container (32cm high), powdered polytetrafluoroethylene powder particles could be visually confirmed approximately 5cm above the top surface (32cm high) of the plastic container, and a small amount of fine polytetrafluoroethylene powder was observed to have accumulated on the floor where the plastic was placed. There is concern that polytetrafluoroethylene powder may adhere to workers' clothing and shoes. However, the amount of accumulation was so small that it was difficult to measure.) 4: The fluttering is clearly visible. (The condition in which polytetrafluoroethylene powder particles can be visually confirmed approximately 10 cm above the top surface (32 cm high) of an 18 L plastic container (32 cm high) within 5 seconds after the polytetrafluoroethylene powder is poured into the container.)

[0032] The PTFE of the PTFE powder may be a homopolymer of tetrafluoroethylene (TFE), or may be a modified PTFE containing a polymerization unit based on TFE (TFE unit) and a polymerization unit based on a modified monomer (hereinafter also referred to as a "modified monomer unit"). The modified PTFE may contain 99.0 mass% or more of TFE units and 1.0 mass% or less of modified monomer units. The modified PTFE may be composed of only TFE units and modified monomer units.

[0033] The modified PTFE preferably has a modified monomer unit content in the range of 0.00001 to 1.0% by mass based on the total polymerized units. The lower limit of the modified monomer unit content is more preferably 0.0001% by mass, more preferably 0.001% by mass, even more preferably 0.005% by mass, and even more preferably 0.010% by mass. The upper limit of the modified monomer unit content is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, even more preferably 0.20% by mass, even more preferably 0.15% by mass, and especially preferably 0.10% by mass. In this specification, the modified monomer unit means a portion of the molecular structure of PTFE that is derived from a modified monomer.

[0034] The content of each of the above-mentioned polymer units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0035] The above-mentioned modified monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [HFP], hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF], perhaloolefins such as chlorotrifluoroethylene, perfluorovinyl ether, perfluoroallyl ether, (perfluoroalkyl)ethylene, ethylene, etc. The modified monomer used may be one type or multiple types.

[0036] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF2=CF-ORf (A) (wherein Rf represents a perfluoro organic group). In this specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group may have an ether oxygen.

[0037] An example of the perfluorovinyl ether is perfluoro(alkyl vinyl ether) [PAVE], where Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0038] Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0039] The perfluorovinyl ether further includes those in which Rf in the above general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf is the following formula:

[0040] [ka]

[0041] (wherein m represents 0 or an integer of 1 to 4), Rf is a group represented by the following formula:

[0042] [ka]

[0043] (wherein n represents an integer of 1 to 4).

[0044] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0045] The perfluoroallyl ether may, for example, be a compound represented by the general formula (B): CF2=CF-CF2-ORf 1 (B) (In the formula, Rf 1 represents a perfluoro organic group.

[0046] Above Rf 1 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and further preferably CF2=CF-CF2-O-CF2CF2CF3.

[0047] The modifying monomer is preferably at least one selected from the group consisting of PAVE and HFP, and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE) and HFP.

[0048] The above-mentioned PTFE preferably has one or more endothermic peaks in the range of 325 to 347°C in a heat of fusion curve when the temperature is increased at a rate of 10°C / min using a differential scanning calorimeter [DSC], and has a heat of fusion at 290 to 350°C calculated from the heat of fusion curve of 62 mJ / mg or more.

[0049] The PTFE can be produced, for example, by emulsion polymerization or suspension polymerization, while the PTFE fine powder can be produced, for example, by emulsion polymerization, and the PTFE molding powder can be produced, for example, by suspension polymerization.

[0050] The emulsion polymerization can be carried out by a known method. For example, in the presence of an anionic fluorine-containing surfactant and a polymerization initiator, the emulsion polymerization of the monomers required for forming the PTFE is carried out in an aqueous medium to obtain an aqueous dispersion containing the PTFE particles (primary particles). In the emulsion polymerization, a chain transfer agent, a buffer, a pH adjuster, a stabilizing assistant, a dispersion stabilizer, a radical scavenger, etc. may be used as necessary.

[0051] The suspension polymerization can be carried out by a known method. For example, the PTFE particles can be obtained by carrying out polymerization of monomers required for forming the PTFE in the presence of water and a polymerization initiator. In the suspension polymerization, a chain transfer agent, a buffer, a pH adjuster, a stabilizing agent, a dispersion stabilizer, a radical scavenger, etc. may be used as necessary.

[0052] The ionizing radiation to be irradiated to the PTFE powder is not particularly limited, and examples thereof include electron beams, ultraviolet rays, gamma rays, X-rays, neutron rays, and high-energy ions, with electron beams and gamma rays being preferred.

[0053] The exposure dose of the ionizing radiation is preferably 1 to 2500 kGy, more preferably 1000 kGy or less, and even more preferably 750 kGy or less, and more preferably 10 kGy or more, and even more preferably 100 kGy or more.

[0054] The irradiation temperature of the ionizing radiation is not particularly limited as long as it is 5° C. or higher and the melting point of PTFE or lower. It is also known that PTFE molecular chains crosslink near the melting point, and in order to obtain low molecular weight PTFE, the temperature is preferably 320° C. or lower, more preferably 300° C. or lower, and even more preferably 260° C. or lower. From an economical perspective, irradiation at room temperature is preferable.

[0055] The irradiation with ionizing radiation may be carried out in any atmosphere, for example, in air, in an inert gas, in vacuum, etc. From the viewpoint of low cost, irradiation in air is preferred.

[0056] In the manufacturing method of the present disclosure, a PTFE micropowder having an average particle size of 20 μm or less is obtained through a step of irradiating the above-mentioned PTFE powder with ionizing radiation. The PTFE micropowder can be obtained, for example, by irradiating the PTFE powder with ionizing radiation and then pulverizing the PTFE powder.

[0057] The pulverization method is not particularly limited, but may be a method of pulverization using a pulverizer, which may be an impact type such as a planetary mill, hammer mill, pin mill, or jet mill, or a friction type such as a cutter mill that pulverizes the material by shearing force caused by unevenness between a rotating blade and an outer stator.

[0058] The grinding temperature is preferably -200° C. or higher and lower than 50° C. Grinding may be performed at a temperature close to room temperature (10 to 30° C.), or frozen grinding at -200 to -100° C. may be performed.

[0059] After the above pulverization, fine particles and fibrous particles may be removed by air classification, and then coarse particles may be removed by further classification.

[0060] The average particle size of the PTFE micropowder may be 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less, and is preferably 1 μm or more.

[0061] The above average particle size is measured using a laser diffraction particle size distribution analyzer (HELOS&RODOS) manufactured by JEOL Ltd., and is equal to the particle size corresponding to 50% of the integrated particle size distribution.

[0062] The melt viscosity of the PTFE micropowder at 380° C. is preferably 1×10 1 Pa s or more, preferably 5×10 2 Pa s or more, and preferably 7×10 5 Pa s or less, preferably 2×10 5 Pa s or less, more preferably 1×10 5 It is less than Pa·s.

[0063] The melt viscosity was measured in accordance with ASTM D 1238 using an elevated flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2 g sample preheated at 380° C. for 5 minutes and maintained at the above temperature under a load of 0.7 MPa.

[0064] <First PTFE powder of the present disclosure> The first PTFE powder of the present disclosure has an apparent density of 0.40 g / ml or less and an average particle size of 700 μm or more.

[0065] The first PTFE powder of the present disclosure can be suitably used as the PTFE powder in the manufacturing method of the present disclosure. That is, it can be suitably used as a raw material for PTFE micropowder. The preferred form of the PTFE powder described in the manufacturing method of the present disclosure can also be applied to the first PTFE powder of the present disclosure.

[0066] <Second PTFE powder of the present disclosure> The second PTFE powder of the present disclosure has an average particle size of 700 μm or more and contains 3 wt % or less of fine powder of 42 mesh or less.

[0067] The second PTFE powder of the present disclosure can be suitably used as the PTFE powder in the manufacturing method of the present disclosure. That is, it can be suitably used as the raw material of PTFE micropowder. The preferred form of the PTFE powder described in the manufacturing method of the present disclosure can also be applied to the second PTFE powder of the present disclosure.

[0068] <Third PTFE powder of the present disclosure> The third PTFE powder of the present disclosure is used as a raw material for PTFE micropowder and has an average particle size of 700 μm or more.

[0069] The PTFE micropowder is similar to the PTFE micropowder in the production method of the present disclosure, and the preferred form is also similar.

[0070] The third PTFE powder of the present disclosure can be suitably used as the PTFE powder in the manufacturing method of the present disclosure. The preferred form of the PTFE powder described in the manufacturing method of the present disclosure can also be applied to the third PTFE powder of the present disclosure.

[0071] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. EXAMPLES

[0072] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0073] Various physical properties were measured by the following methods.

[0074] Apparent density of PTFE powder Measurements were performed in accordance with JIS K6892.

[0075] Average particle size of PTFE powder and PTFE micropowder Standard sieves of 10, 20, 32, 48, 60 and 83 mesh (inch mesh) were stacked from top to bottom, the PTFE powder was placed on the 10 mesh sieve, and the sieve was vibrated to allow finer PTFE powder to fall downward in succession. The proportion of PTFE powder remaining on each sieve was calculated as a percentage, and then the cumulative percentage of the remaining proportion (vertical axis) was scaled against the mesh opening of each sieve (horizontal axis) on a logarithmic probability paper, these points were connected with a straight line, and the particle size on this line where the proportion was 50% was determined, and this value was taken as the average particle size of the PTFE powder. The average particle size of the PTFE micropowder is measured using a laser diffraction particle size distribution measuring device (HELOS&RODOS) manufactured by JEOL Ltd., and is defined as being equal to the particle size corresponding to 50% of the integrated particle size distribution.

[0076] Percentage of fine particles in PTFE powder The PTFE powder was sieved through a 48 mesh (inch mesh) sieve, and the mesh under rate (the rate of the PTFE powder that passed through the sieve to the total amount of the PTFE powder) was measured (48 mesh pass).

[0077] PTFE fine powder fluttering sensitivity test The amount of fluttering generated when PTFE fine powder was scooped up with a stainless steel measuring scoop 133mm wide, 205mm long, and 70mm deep and dropped from a height of 1.2mm into an 18L plastic container was compared. The comparison was visually performed by three people and quantified (indexed) in the following manner (fluttering sensitivity index). 1: There is clearly no dancing. (The condition in which, within 5 seconds after the PTFE fine powder is poured into an 18L plastic container (32cm high), no powdered PTFE fine powder particles can be visually confirmed above the top surface (32cm high) of the plastic container.) 2: There is some fluttering, but it is very slight. (The state in which powdered PTFE fine powder particles can be visually confirmed from the top surface (32 cm high) of the plastic container to the upper part within 5 seconds after the PTFE fine powder is dropped into an 18 L plastic container (32 cm high), but after 5 seconds, it becomes impossible to visually confirm the powder particles as they are floating in the air in minute quantities.) 3: There is concern that the substance may fly up and stick to workers' clothes. (The condition in which, within 5 seconds after the PTFE fine powder was poured into an 18L plastic container (32cm high), powdered PTFE fine powder particles could be visually confirmed approximately 5cm above the top surface of the plastic container (32cm high part), and a small amount of PTFE fine powder was observed to have accumulated on the floor where the plastic was placed. There is concern that the PTFE fine powder may adhere to workers' clothing and shoes. However, the amount of accumulation was so small that it was difficult to measure.) 4: The fluttering is clearly visible. (The condition in which powdered PTFE fine powder particles can be visually confirmed approximately 10 cm above the top surface (32 cm high) of the plastic container within 5 seconds after the PTFE fine powder has been poured into the 18 L plastic container (32 cm high).)

[0078] Melt Viscosity of PTFE Micropowder In accordance with ASTM D 1238, an elevated flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die were used to measure the flow rate of a 2g sample that had been preheated to 380°C for 5 minutes under a load of 0.7 MPa while maintaining the sample at the above temperature.

[0079] Examples 1 to 11 (Table 1) Commercially available homogeneous PTFE fine powder (standard specific gravity: 2.175) was sieved through a 10 mesh (1.7 mm opening) sieve. The mesh-up rate (the ratio of the residue on the sieve to the total amount of PTFE fine powder) is shown in Table 1. In Examples 1 to 8, the mesh-up products (residue on the sieve) were irradiated with cobalt-60 gamma rays in air at room temperature under the conditions shown in Table 1 to obtain low molecular weight PTFE powders. In addition, in Examples 9 to 11, a suitable mixture of mesh-up material (material remaining on the sieve) and mesh-under material (material that passed through the sieve) was irradiated with cobalt-60 gamma rays in air at room temperature under the conditions shown in Table 1 to obtain a low molecular weight PTFE powder. The low molecular weight PTFE powder was pulverized in a room temperature dry state using a free pulverizer (Mill) manufactured by Nara Machinery Manufacturing Co., Ltd. to obtain PTFE micropowder.

[0080] Comparative Examples 1 to 8 (Table 2) A PTFE micropowder was obtained in the same manner as in Examples 1 to 8, except that a mesh-under product (passed through a sieve) was used instead of a mesh-up product. Before using the under-mesh product, it was sieved through a 10 mesh (1.7 mm opening) sieve, but no residue was found on the sieve (mesh-up rate was 0 wt%).

[0081] [Table 1]

[0082] [Table 2]

Claims

1. A method for producing polytetrafluoroethylene micropowder, comprising the steps of irradiating polytetrafluoroethylene powder having an average particle size of 700 μm or more and an apparent density of 0.40 g / ml or less with ionizing radiation to obtain polytetrafluoroethylene micropowder having an average particle size of 20 μm or less.

2. The polytetrafluoroethylene micropowder has a melt viscosity of 1×10 at 380° C. １ ~7×10 ５ The method for producing polytetrafluoroethylene micropowder according to claim 1, wherein the viscosity of the powder is Pa·s.

3. 3. The method for producing polytetrafluoroethylene micropowder according to claim 1, wherein the polytetrafluoroethylene powder is obtained by sieving through a sieve having an opening size of 700 μm to 2 mm.

4. 3. The method for producing polytetrafluoroethylene micropowder according to claim 1, wherein the polytetrafluoroethylene powder has a fluttering sensitivity index of 2 or less in a fluttering sensitivity test carried out under the following conditions: (Midashi Sensitivity Test) The amount of fluttering generated when polytetrafluoroethylene powder scooped with a stainless steel measuring scoop 133 mm wide, 205 mm long, and 70 mm deep was dropped from a height of 1.2 mm into an 18 L plastic container was compared. The comparison was visually performed by three people and indexed as follows (fluttering sensitivity index). 1: There is clearly no dancing. (The state in which, immediately after the polytetrafluoroethylene powder is poured into an 18 L plastic container (32 cm high), no powdered polytetrafluoroethylene powder particles can be visually confirmed above the top surface (32 cm high) of the plastic container for 5 seconds.) 2: There is some fluttering, but it is very slight. (The state in which, immediately after the polytetrafluoroethylene powder is poured into an 18 L plastic container (height 32 cm), powdered polytetrafluoroethylene powder particles can be visually confirmed from the top surface (height 32 cm) of the plastic container to the upper part within 5 seconds, but after 5 seconds, they are floating in such a small amount that they cannot be visually confirmed.) 3: There is concern that the dust may fly up and stick to workers' clothes. (A condition in which, immediately after the polytetrafluoroethylene powder was poured into an 18 L plastic container (32 cm high), powdered polytetrafluoroethylene powder particles could be visually confirmed approximately 5 cm above the top surface (32 cm high) of the plastic container, and a small amount of fine polytetrafluoroethylene powder was observed on the floor on which the plastic was placed. There is a concern that polytetrafluoroethylene powder may adhere to workers' clothing and shoes. However, the amount of accumulation was so small that it was difficult to measure.) 4: The fluttering is clearly visible. (The state in which powdered polytetrafluoroethylene powder particles can be visually confirmed about 10 cm above the top surface (32 cm high) of the plastic container within 5 seconds after the polytetrafluoroethylene powder is poured into the 18 L plastic container (32 cm high).)

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